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Accounting for uncertainty in DEMs from repeat topographic surveys: Improved sediment budgets
Abstract
Repeat topographic surveys are increasingly becoming more affordable, and possible at higher spatial resolutions and over greater spatial extents. Digital elevation models (DEMs) built from such surveys can be used to produce DEM of Difference (DoD) maps and estimate the net change in storage terms for morphological sediment budgets. While these products are extremely useful for monitoring and geomorphic interpretation, data and model uncertainties render them prone to misinterpretation. Two new methods are presented, which allow for more robust and spatially variable estimation of DEM uncertainties and propagate these forward to evaluate the consequences for estimates of geomorphic change. The first relies on a fuzzy inference system to estimate the spatial variability of elevation uncertainty in individual DEMs while the second approach modifies this estimate on the basis of the spatial coherence of erosion and deposition units. Both techniques allow for probabilistic representation of uncertainty on a cell-by-cell basis and thresholding of the sediment budget at a user-specified confidence interval. The application of these new techniques is illustrated with 5 years of high resolution survey data from a 1 km long braided reach of the River Feshie in the Highlands of Scotland. The reach was found to be consistently degradational, with between 570 and 1970 m3 of net erosion per annum, despite the fact that spatially, deposition covered more surface area than erosion. In the two wetter periods with extensive braid-plain inundation, the uncertainty analysis thresholded at a 95% confidence interval resulted in a larger percentage (57% for 2004–2005 and 59% for 2006–2007) of volumetric change being excluded from the budget than the drier years (24% for 2003–2004 and 31% for 2005–2006). For these data, the new uncertainty analysis is generally more conservative volumetrically than a standard spatially-uniform minimum level of detection analysis, but also produces more plausible and physically meaningful results. The tools are packaged in a wizard-driven Matlab software application available for download with this paper, and can be calibrated and extended for application to any topographic point cloud (x,y,z). Copyright © 2009 John Wiley & Sons, Ltd.
... With the availability of good quality multitemporal HRTDs acquired over a sufficient vegetation interval, there is an opportunity to investigate land surface changes for areas of interest. Several authors in recent years have studied the topographical changes of riverbeds (Wheaton et al. 2010, Westaway et al. 2003, observations and monitoring of glaciers (Dall' Asta et al. 2017), (Ryan et al. 2015), snow cover monitoring (Nolan et al. 2015), landslides and agriculture (Clapuyt et al. 2017), (Mauri et al. 2021), coastal erosion (Brunier et al. 2016), as well as change in forest structural and biomass (Zahawi et al. 2015), (Messinger et al. 2016), (Mlambo et al. 2017), (Gobbi et al. 2022). The application of the direct method for georeferencing UAV images in the research of topographic changes is discussed in the publications of (Turner et al. 2016, Gonzalo 2018, Tomaštík 2019, and Zhang et al. 2019. ...
... The two surfaces (DEM or DSM) are compared pixel by pixel, which is equivalent to a vertical distance measurement. This technique is very fast and now includes explicitly calculating the uncertainties associated with point cloud registration, data quality, and point cloud roughness (Wheaton et al. 2010). However, the DoD technique suffers from two significant drawbacks (Lague et al. 2013): A) It cannot work correctly in 3D environments with highly dissected terrain, as DEM cannot handle overhanging parts (cliffs and drop-offs of banks, large blocks ), B) The fixed resolution of DEM imposes a limitation on the level of detail retained by the raw data, which can be a substantial limitation for surfaces showing many different characteristic scales. ...
... The most commonly adopted procedure for managing DoD uncertainty involves setting a minimum detection threshold (minLoD) to distinguish real surface changes from intrinsic noise (Brasington et al. 2003, Wheaton et al. 2010. ...
The mapping and three-dimensional modeling of mountain areas and the study of land cover change dynamics are current tasks in preserving and maintaining protected natural parks and forests. In this context, recent developments in digital photogrammetry using the SfM-MVS method to process captured imagery and the development of unmanned aerial systems (UAS) allow for reducing the costs, time, and the use of human resources and obtaining and repeatable 3D topographic data for moun-tainous regions. We will call this acquired 3D high-resolution topographic data (HRTD) 4D data in the context of an additional temporal component. The main objective of this study is to evaluate the applicability of PPK (Post-Processing Kinematic) direct georeferencing of images captured by UAVs and processed through the SfM-MVS method to obtain HRTDs for 4D land cover analysis. We analyze a 3D HRTD with an acquisition interval of two years for a mountain test area in Plana Mountain near Sofia. The test area has a diverse vegetation cover, including coniferous forest, grassland, hay meadows, shrubs, and single deciduous trees. We conducted multiple surveys of the test area with a budget PPK-UAV configuration (DJI Phantom 4 Pro with a single-frequency PPK-GNSS kit installed) from March 2020 to October 2022. Two autumn surveys from September 2020 and October 2022 were se-lected, which possess the most-good performance on numerical data accuracy. We performed 3D data analysis on 1) Assessment of the accuracy of PPK-SfM-MVS photogrammetry generated topographic data (3D clouds and DSM); 2) Investigation of the errors in the individual specific surfaces (for the individual isolated sections) using the M3C2 tool for comparing and evaluating dense point clouds; 3) Determining land cover changes in the demarcated areas using a surface of differences (DoD).
Accuracy analysis showed that the PPK solution provides comparable accuracy (about RMSE3D = 0.067 m for the 2020 data, georeferencing (PPK+1GCP) and RMSE3D about 0.13 m for the 2022 data, georeferencing (PPK only)) like the GCP method.
The multi-temporal topographic reconstructions based on UAV- PPK-SfM allowed us to quantify and qualitatively determine the land cover changes that occurred. The UAV-PPK-SfM workflow in the context of 4D land surface monitoring and the results suggested that even low-cost UAV-PPK systems can provide data suitable for measuring geomorphic change at the scale of the acquired data. The multi-temporal topographic reconstructions based on UAV- PPK-SfM allowed us to quantify and qualitatively determine the land cover changes that occurred. The UAV-PPK-SfM workflow in the context of 4D land surface monitoring and the results suggested that even low-cost UAV-PPK systems can provide data suitable for measuring geomorphic change at the scale of the acquired data.
... In order to identify and detect the changes in time, the tool needs at least two raster-based surfaces. The volumetric change in storage is calculated from the difference in surface elevations from digital elevation models (DEMs) derived from repeated topographic surveys [13]. ...
... As each DEM has an uncertain surface representation, the detection of the changes between two surveys is highly dependent on the surface representation uncertainties inherent in the individual DEMs [13]. Therefore, the uncertainties are computed independently in each DEM and then propagated to the DEM of difference. ...
... To do so, in the following work the Fuzzy Inference Systems for modelling the errors [14] was used. Such technique captured the potential source of elevation uncertainty driven by different parameters such as point density, slope and roughness [13,15,16]. Thus, according to the topographic characteristics of the study area under assessment and the available data (i.e., LiDAR and UAV), a set of rules to compute the surface error were applied (more info in [12]). ...
Large infrequent disturbances (LIDs) increasingly affect mountain basins, but secondary impacts are often disregarded although their understanding would provide advice to river managers. The following work aims at investigating primary and secondary impacts of the Vaia storm on the channel morphology and large wood (LW) load of a reach of Malgonera Stream (6,025 m2). To achieve the objectives, remote sensing and field data were exploited. Remote sensing data were used to compute two DoDs: the first investigated the Vaia impact (2010–2019) while the second the subsequent evolution (2020–2021). LW field data, combined with remote sensing surveys, were collected to compute the LW load entailed by Vaia and the subsequent fluctuations (2020–2021). The net sediment volume after the event was −2,025 m3. The area of erosion was 2,659 m2, while the deposition covered 1,222 m2. The recent DoD (2020–2021) featured a net sediment volume of 15.79 m3, showing irrelevant geomorphic changes. After the Vaia storm, 96.3 m3ha−1 of LW was detected inside the study area. Around 83 logs per ha were classified as single elements while the remaining as jams’ components. Between 2020 and 2021, the LW load increased up to 102 m3ha−1, for a total of 485 elements per ha due to cantilever failures of unstable banks. This work (i) underlines the capability of LIDs to rearrange the morphology of mountain streams, (ii) providing first evidence on secondary processes of LW recruitment along unstable mountain streams and (iii) highlighting how changes in the LW load are detached from morphological changes.KeywordsVaia stormAlpine streamMorphological changesLW loadLW recruitment
... Bedrock incision could then continue until a climate-driven increase in sediment supply armors the bed, favoring lateral planation over vertical incision, with subsequent strath formation (e.g., Gilbert, 1877;Wegmann and Pazzaglia, 2002;Fuller et al., 2009). Today, technological advances in remote acquisition of high-resolution bare topography allows the quantification of change in sediment storage over large fluvial systems through differencing of sequential digital elevation models (DEMs) (Wheaton et al., 2010;Vericat et al., 2017), hence bridging an outstanding historical limitation, i.e., beyond extrapolations drawn from reference channel cross sections. ...
... The two DEMs were obtained from each point cloud after filtering for vegetation and noise. Uncertainty on each DEM is evaluated through the application of Fuzzy Inference Systems (FIS), then propagated to the relevant DoD (Wheaton et al., 2010). In particular, we applied a FIS model that considers vertical uncertainty to be a function of point density, slope, roughness, and wetted area. ...
... Evaluation of volumetric channel changes is affected by both the quality of the LiDARderived DEMs, as well as by the temporal resolution associated with the DoD analysis. Errors in topographic surveys propagate into uncertainties in the estimates of volumetric channel changes (e.g., Brasington et al., 2000;Wheaton et al., 2010), and therefore may affect the partitioning of volumetric changes into aggradation, degradation, and resulting net change. These uncertainties may be particularly relevant in environments, or over temporal scales, in which vertical topographic changes are relatively low compared to the errors associated with the sequential DEMs. ...
We evaluate decadal coarse sediment dynamics along the Marecchia River of the Northern Apennines, a fluvial system with a history of gravel mining that led to the incision of a 6-km-long canyon. To this purpose, we subdivided the river into 21 reaches, seen as sediment reservoirs, to examine (1) historical variations in active channel width (1955−2019) in conjunction with (2) change in alluvial sediment storage (2009−2019), by differencing two sequential LiDAR digital elevation models (DEMs) within the active channel footprint. Combined examination of lateral (widening or narrowing) and vertical (aggradation or degradation) channel changes allowed the identification of composite styles of reservoir adjustment, as well as the refinement of geomorphic inference solely based on changes in active channel width. In particular, we find that different styles of decadal adjustment (1) are compatible with supply- and transport-limited conditions, as constrained by degree of confinement, stream channel slope, and active channel width; and (2) indicate different stages of evolution at reservoirs located upstream and downstream of the canyon head (dynamic equilibrium vs. transient response). The persistence of this geomorphic divide is supported over historical time scales by distinctive trends in planform channel changes, suggesting that sedimentary signal propagation downstream becomes abruptly interrupted at the canyon head. Over this 10-year natural experiment, the spatial pattern of erosion along the canyon exemplifies a striking case of transient response to anthropogenic forcing, where decadal topographic change, modulated by varying styles of hillslope-channel coupling, declines nonlinearly downstream. Depth of incision along the canyon increases progressively upstream, suggesting that the canyon head has been evolving toward a more unstable configuration with no significant change in sediment supply. This tendency, which points to a possible runaway style of development as bedload wearing on weak pelitic side walls continues, may hold basic implications for our understanding of channel incision into bedrock and strath terrace formation.
... To minimize the 3D distance between a reference surface (21.09.2018) and the interest datasets, we manually selected 30 multi-temporal well-150 distributed 3D corresponding points ( , , ) located in stable, non-changeable areas using the true orthophotos and the corresponding DSMs, and solved Eq. (1) using the least-squares adjustment solution in python. Repetitive topographic surveys, in our case DSMs, allow the identification and quantification of geomorphic 170 changes such as erosion and deposition (James et al., 2012;Wheaton et al., 2010). We estimated the area and volume of change based on 2.5 data., i.e., rasterized topography following Eq. ...
... We used the non-interpolated DSMs to minimize the change to noise ratio (Wheaton et al., 2010;Anderson, 2019). ...
... This concept provides an effective basis for representing the key components of the sediment delivery system within a 230 catchment and for assembling the necessary data to elucidate, understand and predict catchment sediment delivery (Walling and Collins, 2008) and estimate related natural hazards. The geomorphic sediment budget (Wheaton et al., 2010) is calculated as the sum of the masked DoD values of erosion (negative change) and deposition (positive change). ...
Massive sediment pulses in catchments are a key alpine multi-risk component. Substantial sediment redistribution in alpine catchments frequently causes flooding, river erosion, and landsliding, and affects infrastructure such as dam reservoirs as well as aquatic ecosystems and water quality. While systematic rock slope failure inventories have been collected in several countries, the subsequent cascading sediment redistribution is virtually unaccessed. This contribution reports for the first time the massive sediment redistribution triggered by the multi-stage failure of more than 150,000 m3 from the Hochvogel dolomite peak during the summer of 2016. We applied change detection techniques on seven 3D-coregistered high-resolution true-orthophotos and digital surface models (DSM) obtained through digital aerial photogrammetry later optimized for precise volume calculation in steep terrain. The analysis of seismic information from surrounding stations revealed the temporal evolution of the cliff fall. We identified the proportional contribution of > 600 rockfall events (>1 m3) from 4 rock slope catchments with different aspects and their volume estimates. In a sediment cascade approach, we evaluated erosion, transport, and deposition from the rockface to the upper channelized erosive debris flow channel, then to the widened dispersive debris flow channel, and finally to the outlet into the braided sediment-supercharged Jochbach river. We observe the decadal flux of more than 400,000 m3 of sediment with massive sediment pulses that (i) respond with reaction times of 0–4 years and relaxation times beyond 10 years, (ii) with faster response times of 0–2 years in the upper catchment and more than 2 years response times in the lower catchments, (iii) the inversion of sedimentary (102–103 mm/a) to massive erosive regimes (102 mm/a) within single years and the (iv) dependency of redistribution to rainfall frequency and intensity. This study provides generic information on spatial and temporal patterns of massive sediment pulses in highly-charged alpine catchments.
... Quantification of error in a study allows both the investigator and the reader to assess the signal to noise ratios and the overall uncertainty of the surface change estimates [2]. The type and complexity of accuracy assessment should be driven by the research question pursued to guarantee that the signal of interest is larger than the observed noise [130,131]. Passalacqua et al. [2] identified three main sources of uncertainty for topographic point-cloud data that include (i) positional accuracies (e.g., sensor precision, registration), (ii) point-cloud classification (e.g., bare-earth extraction), and (iii) surface representation (e.g., resolution, interpolation). However, uncertainty analyses are often missing in change detection studies. ...
... Error propagation in multi-temporal datasets remains a pressing challenge in change detection [52,[130][131][132]. However, some studies propose novel approaches for quantifying error propagation. ...
... Error is often reported as a single value for the entire grid, ignoring the spatial variation of error that can lead to misleading interpretations of targeted phenomena. Wheaton et al. [131] proposed an inference system through fuzzy logic to estimate the spatial variability of elevation uncertainty based on a range of empirically determined values. Since these studies focus on gridded products, there is a large gap for developing tools for 3D datasets. ...
Over the past decade, advancements in collection platforms such as unoccupied aerial systems (UAS), survey-grade GNSS, sensor packages, processing software, and spatial analytical tools have facilitated change detection analyses at an unprecedented resolution over broader spatial and temporal extents and in environments where such investigations present challenges. These technological improvements, coupled with the accessibility and versatility of UAS technology, have pushed the boundaries of spatial and temporal scales in geomorphic change detection. As a result, the cm-scale analysis of topographic signatures can detect and quantify surface anomalies during geomorphic evolution. This review focuses on the use of UAS photogrammetry for fine spatial (cm) and temporal (hours to days) scale geomorphic analyses, and it highlights analytical approaches to detect and quantify surface processes that were previously elusive. The review provides insight into topographic change characterization with precise spatial validations applied to landscape processes in various fields, such as the cryosphere and geosphere, as well as anthropogenic earth processes and national security applications. This work sheds light on previously unexplored aspects of both natural and human-engineered environments, demonstrating the potential of UAS observations in change detection. Our discussion examines the emerging horizons of UAS-based change detection, including machine learning and LIDAR systems. In addition, our meta-analysis of spatial and temporal UAS-based observations highlights the new fine-scale niche of UAS-photogrammetry. This scale advancement sets a new frontier in change detection, offering exciting possibilities for the future of land surface analysis and environmental monitoring in the field of Earth Science.
... ALS-derived data are characterized by much higher resolution than satellite data (up to several pt/m 2 ) [28][29][30][31]. The highresolution digital elevation models (DEMs) developed from them provide a good base for differential comparative analyses (DEM of Difference), which results in quantitative estimates of geomorphic changes [32][33][34]. However, ALS has significant limitations, which are mainly related to the high cost of the flight. ...
... (GCD) plug-in for ArcGIS 10.8 software ( Figure 2). Following the guidelines of the author of the DoD method [33,55], an approach based on the uncertainty range based on the minimum level of detection (min-LoD) was used. In the case of TLS measurements, the measurement error is related to the accuracy of the rangefinder (for ScanStation C10, it is ...
... (GCD) plug-in for ArcGIS 10.8 software (Figure 2). Following the guidelines of the author of the DoD method [33,55], an approach based on the uncertainty range based on the minimum level of detection (min-LoD) was used. In the case of TLS measurements, the measurement error is related to the accuracy of the rangefinder (for ScanStation C10, it is~0.006 ...
A four-day glacier-melt flood (13–16 August 2013) caused abrupt geomorphic changes in the proglacial gravel-bed Scott River, which drains the small (10 km2) Scott Glacier catchment (SW Svalbard). This type of flood occurs on Svalbard increasingly during periods of abnormally warm or rainy weather in summer or early autumn, and the probability of occurrence grows in direct proportion to the increase in temperature and/or precipitation intensity. In the summer of 2013, during the measurement season, the highest daily precipitation (17 mm) occurred on 13 August. During the following four days, it constituted in total 47 mm, i.e., 50% of the precipitation total for the measurement period of 2013. The largest flood in 20 years was caused by high precipitation with a synchronous rise in temperature from about 1.0 to 8.6 °C. These values exceeded multi-year averages (32 mm and 5.0 °C, respectively) at an average discharge of 0.9 m3/s (melt season mean 1986–2011). These conditions caused a rapid and abrupt response of the river with the dominant (90%) glacier-fed. The increase in discharge to 4.6 m3/s, initiated by the glacial flood, mobilized significant amounts of sediment in the river bed and channel. Geomorphic changes within the alluvial fan as an area of 58,940 m2, located at the mouth of the Scott River, were detected by multi-sites terrestrial laser scanning using a Leica Scan Station C10 and then estimated using Geomorphic Change Detection (GCD) software. The changes found involved 39% of the alluvial fan area (23,231 m2). The flood-induced total area of lowering (erosion) covered 26% of the alluvial fan (6035 m2), resulting in the removal of 1183 ± 121 m3 of sediment volume. During the final phase of the flood, two times more sediment (1919 ± 344 m3) was re-deposited within the alluvial fan surface, causing significant aggradation on 74% of its area (17,196 m2). These geomorphic changes resulted in an average lowering (erosion) of the alluvial fan surface of 0.2 m and an average rising (deposition) of 0.1 m.
... Este trabajo trata de poner el foco en cómo las herramientas de código abierto pueden ayudar a la gestión del medio litoral, evitando la necesidad de licencias comerciales y empleando tan sólo datos de acceso abierto. Por un lado, en la definición de las tasas de variación de la línea de costa se lleva a cabo una comparación entre DSAS (Digital Shoreline Analysis System) (Himmelstoss et al., 2018) y ODSAS (Open Digital Shoreline Analysis System) (Gómez-Pazo et al., 2022); y por otro, para la estimación de las variaciones volumétricas se ha optado por seleccionar un sector sedimentario e información de dos fechas sobre la que se empleó el Geomorphic Change Detection (GCD) (Wheaton et al., 2010) y una aproximación propia generada en el lenguaje de programación R (R Core Team, 2020) y denominada como Volumetric Changes using R (VolCR). ...
... Para el análisis de las variaciones volumétricas la opción propietaria escogida ha sido el GCD cuya primera aproximación se recoge en Wheaton et al. (2010) y que actualmente está disponible en su versión 7. Al igual que en el caso de DSAS, la interfaz de uso de GCD está en el entorno de ArcGIS, programa que requiere una licencia comercial para el procesado. Esta herramienta calcula a partir de Modelos Digitales (MDs) de distintas fechas las variaciones que se han dado en un sector concreto. ...
... En el caso de los análisis volumétricos, los datos LiDAR (IGN, 2022) hacen referencia a los años 2010 y 2015, cuyas características técnicas son semejantes (Tabla 3), por lo que se ha optado por generar los MDs con la misma resolución para ambas fechas (0,5 m). En ambos se ha seleccionado como Limit of Detection (LoD) 0,2 m, entendiendo que las variaciones por debajo de este umbral pueden deberse a las incertidumbres asociadas a la obtención de la información, las limitaciones técnicas de los dispositivos de adquisición de datos y su procesado(Anderson, 2019;Muñoz Narciso et al., 2017;Wheaton et al., 2010). ...
Coastal studies have a great relevance historically. This increase in the last with the new technologies and the possible global change impact. In this context, open-source tools represent a key element in these investigations. The present project analyzes the advantages and problems of open-source tools for estimate coastal variations and volumetric changes. For this purpose, a small sector of the Galician coast was used as an example. The open-source approaches have produced similar results to those obtained with proprietary software (ratios ≥ 0.97). In some cases, these methods improve processing times and allowing to users better possibilities for customization and decision-making.
... Differencing multitemporal topographic data is a fundamental technique with many valuable applications requiring three-dimensional (3D) Earth surface changes as prerequisite information [1][2][3][4][5][6][7][8][9]. Various platforms with different sensors from space (e.g., synthetic aperture radar (SAR) [2,3]) to the ground (e.g., terrestrial light detection and ranging (lidar) [4,5]) have been used to collect precise topographic information during the last several decades. ...
... The proposed method's effectiveness was assessed using county-level multitemporal airborne lidar datasets of Indiana, USA, where artificial elevation changes were manifested in their differencing results, which were performed using original DTMs from USGS 3DEP. The contributions of this paper can be summarized as (1) proposing a new scalable solution against the erroneous displacements frequently observed in DoD results without raw observation and (2) providing improved DoD results of Indiana 3DEP lidar datasets where the problematic displacements were reported but unsolved [24] with more reasonable terrain change information. This paper is organized as follows: First, Indiana statewide lidar datasets are introduced in Section 2. ...
Differencing digital terrain models (DTMs) generated from multitemporal airborne light detection and ranging (lidar) data provide accurate and detailed information about three-dimensional (3D) changes on the Earth. However, noticeable spurious errors along flight paths are often included in the differencing results, hindering the accurate analysis of the topographic changes. This paper proposes a new scalable method to alleviate the problematic systematic errors with a high degree of automation in consideration of the practical limitations raised when processing the rapidly increasing amount of large-scale lidar datasets. The proposed method focused on estimating the displacements caused by vertical positioning errors, which are the most critical error source, and adjusting the DTMs already produced as basic lidar products without access to the point cloud and raw data from the laser scanner. The feasibility and effectiveness of the proposed method were evaluated with experiments with county-level multitemporal airborne lidar datasets in Indiana, USA. The experimental results demonstrated that the proposed method could estimate the vertical displacement reasonably along the flight paths and improve the county-level lidar differencing results by reducing the problematic errors and increasing consistency across the flight paths. The improved differencing results presented in this paper are expected to provide more consistent information about topographic changes in Indiana. In addition, the proposed method can be a feasible solution to upcoming problems induced by rapidly increasing large-scale multitemporal lidar given recent active government-driven lidar data acquisition programs, such as the U.S. Geological Survey (USGS) 3D Elevation Program (3DEP).
... DEMs produced from structure-from-motion and multi-view stereo usually contain uncertainties and errors in the coordinates and elevation owing to the ground-control point precision and image resolution. Therefore, the simple subtraction of DEMs without accounting for uncertainties and errors did not result in significant changes [63,64]. To estimate the probability that trail surface changes were predicted by DoD, a 95% confidence interval was used as the threshold in this study. ...
... To estimate the probability that trail surface changes were predicted by DoD, a 95% confidence interval was used as the threshold in this study. The DoD analysis employed Geomorphic Change Detection software [63], which is an add-on for the ESRI Arc Map 10.8.1. The geomorphic-change-detection method has been used in many studies to reveal land surface changes using DEMs [65]. ...
Many mountainous, protected areas, such as national parks worldwide, face trail erosion; stakeholders have made significant efforts to manage eroded trails. However, their effectiveness has not been evaluated. This study aimed to (1) create digital elevation models of an eroded trail using structure-from-motion and multi-view-stereo photogrammetry in Daisetsuzan National Park, northern Japan; (2) conduct a six-year monitoring of the trails repaired by volunteers to reveal trail surface changes; and (3) discuss the effectiveness of the repair works. Palm-fiber bags were used on the trail section to stop the movement of the eroded soil. The results of the three-dimensional analysis identified a certain effectiveness of the repair work during 2017–2022. However, the effectiveness lasted for only approximately three years and was not permanent. Therefore, regular maintenance is necessary to ensure trail sustainability. In addition, the soil erosion rate calculated using the maximum erosion depth has increased from 0.52 mm y−1 (1923–1990) to 44.4 mm y−1 (2013–2022), suggesting the need for frequent observations. Trail maintenance through a combination of monitoring and repair work is vital, and the role of hikers/trekkers is becoming increasingly important.
... A potentially valuable remote-sensing method for investigating geomorphically dynamic areas is the Digital Elevation Model (DEM) of Difference techniques (DoD), which quantifies the volumetric change between successive topographic surveys [18]. At first, applications of this method were attempted on fluvial landforms to quantify geomorphological change triggered on the alluvial plain by modifications in rivers' discharge. ...
... In detail, 1997, 2000, 2003, 2006, 2008, 2011, 2014, and 2020 aerial orthophotos were collected from the archive of the Autonomous Province of Bolzano Geoportal, with different spatial resolutions reported in Table 1. High-resolution digital elevation models are useful for geomorphic analysis [18]; for this reason, we collected 2005 and 2016 DEMs of the area with a spatial resolution of 2.5 m and 0.5 m, respectively, produced by LiDAR data from the Autonomous Province of Bolzano ( Figure S1). ...
Since the end of the Little Ice Age (LIA, ~1830), the accelerated glaciers’ shrinkage along mid-latitude high mountain areas promoted a quick readjustment of geomorphological processes with the onset of the paraglacial dynamic, making proglacial areas among the most sensitive Earth’s landscapes to ongoing climate change. A potentially useful remote-sensing method for investigating such dynamic areas is the DEM (Digital Elevation Model) of Difference (DoD) technique, which quantifies volumetric changes in a territory between successive topographic surveys. After a detailed geomorphological analysis and comparison with historical maps of the Martello Valley (central Italian Alps), we applied the DoD for reconstructing post-LIA deglaciation dynamics and reported on the surface effects of freshly-onset paraglacial processes. The head of the valley is still glacierized, with three main ice bodies resulting from the huge reduction of a single glacier present at the apogee of the LIA. Aftermath: the glaciers lose 60% of their initial surface area, largely modifying local landforms and expanding the surface of the proglacial areas. The DoD analysis of the 2006–2015 timeframe (based on registered DEM derived from LiDAR—Light Detection and Ranging—data) highlights deep surface elevation changes ranging from +38 ± 4.01 m along the foot of rock walls, where gravitative processes increased their intensity, to −47 ± 4.01 m where the melting of buried ice caused collapses of the proglacial surface. This approach permits estimating the volume of sediments mobilized and reworked by paraglacial processes. Here, in less than 10 years, −23,675 ± 1165 m3 of sediment were removed along the proglacial area and transported down valley, highlighting the dynamicity of proglacial areas.
... The uncertainty of the elevation change assessment included the propagation of the identified errors into the DoD and the assessment of the significance of the DoD uncertainty. We used the probabilistic method described in Wheaton et al. (2010) and proposed earlier by Brasington et al. (2003) and Lane et al. (2003). The method estimates the critical threshold error, U crit , (Eq. ...
... Thus, we calculated the propagated error, and the probability of the predicted elevation change to occur, by relating the t-statistic to its cumulative distribution function at a selected confidence interval (more details in Wheaton et al., 2010). Based on that, the uncertainty can be spatially distributed over the area. ...
The western Peruvian region is prone to erosion and geomorphic change. Extreme precipitation events lead to rapid change in river channel and floodplain morphology due to bank erosion and debris flows delivering detrital material to the fluvial system. Monitoring geomorphic events and their associated topographic changes at high spatial and temporal resolutions remains a challenge. Here, we used an Uncrewed Aerial Vehicle - Post-Processing Kinematic - Structure from Motion (UAV-PPK-SfM) approach that includes co-registration of point clouds by using relative Ground Control Points (GCPs). This workflow adjusts each
elevation model to a reference model using invariant features that did not change their position or form over time. We applied this technique to monitor landscape change (2019-2021) in an area of 0.3 km2 located in the Cañete River basin. Our results showed that a minimum observable elevation change of 0.56 m (95% confidence interval) can be achieved using this workflow, beyond which an actual elevation change can be separated from
systematic error. Using object-based classification techniques on the aerial images, we separated geomorphic dynamics from land cover changes. This allowed us to isolate the effect of geomorphic processes, and quantify rates related to gully erosion, river scouring, bank erosion, and sediment deposition. Within the study area, a hotspot of geomorphic change corresponded to an ephemeral tributary channel. The gully channel incising an alluvial fan is highly dynamic, showing bank erosion of 0.75 to 3.2 m and net export of 37 m3 of sediment in the 25-month study period. Given that the monitoring period did not include high intensity
rainfall events, the study illustrates how geomorphic activity in ungauged Andean river basins, such as the Cañete valley, may be considerably underestimated in literature.
... The measured points are used to create a digital elevation model (DEM) of the study area. DEMs are mainly used in fluvial geomorphology research to assess and quantify morphological changes and sediment budgets using repeated topographic surveys [14][15][16][17]. If other parameters are measured, then digital terrain models (DTMs) are created. ...
... The results support the findings of Heritage et al., 2009 [13] regarding the use of TINs as the best interpolator in fluvial environments. The TIN itself is particularly prone to misrepresenting surface topography when low point density and greater topographic complexity combine [17]. Figure 5 also shows that, for lower density and near banks, TINs did not display the bed very well, but the amount of over/underprediction was less than that of OK. ...
Bed irregularities of water bodies play a significant role in many hydraulic and river engineering experiments and models. Accurate measurement of river geomorphology requires great fieldwork effort. Optimizing the dataset size of measured points will reduce the time and costs involved. In this study, the geomorphology of a gravel bed river reach was measured using different spatial acquisition methods. Digital elevation models were created for each measurement method and the volumes of under/overestimation were calculated. The results show that the sampling methods had more effect on the accuracy of the interpolated geomorphology than the density of the measured points. By choosing an optimized sampling method, the measurement efforts decreased to less than 50%, with negligible errors of around 15 m3 and 10 m3 over and underestimation, respectively, in a water body area of around 2200 m2. These findings help to provide more accurate geomorphological data with less effort as inputs for experimental and numerical models to derive better results.
... This uncertainty can be used to characterize the potential error associated with DoD calculations of net area or volumetric changes across the island. A second, more straightforward metric for visualizing change that exceeds the noise and inaccuracies of the input DTMs is the Root of Sum in Quadrature (RSiQ) method [38,76,77]. The RSiQ value indicates the threshold for which the combined possible error in the differenced DTMs is visually quantified. ...
... However, this is a broader challenge for terrain change quantification, as some degree of disparity occurs between all elevation data sources [88] and should be robustly accounted for using DoD-based error metrics [76,77]. The general similarity between the 1955 and 2016 crest or ridges indicates that the island's sand dunes are relatively static, despite the liberation of sand by bluff and shoreline change, and the large bare sand expanses. ...
South Manitou Island, part of Sleeping Bear Dunes National Lakeshore in northern Lake Michigan, is a post-glacial lacustrine landscape with substantial geomorphic changes including landslides, shoreline and bluff retreat, and sand dune movement. These changes involve interrelated processes, and are influenced to different extents by lake level, climate change, and land use patterns, among other factors. The utility of DEM of Difference (DoD) and other terrain analyses were investigated as a means of understanding interrelated geomorphologic changes and processes across multiple decades and at multiple scales. A 1m DEM was developed from 1955 historical aerial imagery using Structure from Motion Multi-View Stereo (SfM-MVS) and compared to a 2016 lidar-based DEM to quantify change. Landslides, shoreline erosion, bluff retreat, and sand dune movement were investigated throughout South Manitou Island. While the DoD indicates net loss or gain, interpretation of change must take into consideration the SfM-MVS source of the historical DEM. In the case of landslides, where additional understanding may be gleaned through review of the timing of lake high- and lowstands together with DoD values. Landscape-scale findings quantified cumulative feedbacks between interrelated processes. These findings could be upscaled to assess changes across the entire park, informing future change investigations and land management decisions.
... The channel changes in the reach manifestly relating to the 2019-2020 flood events were examined by considering bank position changes between 2018 and 2020, supported by a geomorphic change analysis (Wheaton et al., 2009;Williams, 2012) using LiDAR surveys acquired in 2009 and 2020. As highlighted by Donovan et al. (2019) and Leonard et al. (2020), the digitisation of bank positions is subject to four sources of error; co-registration error related to the georeferencing of the aerial images; interpretation error; digitisation error associated with the delimitation process itself; and the application of a level of detection (Lod) threshold that excludes small but significant features (Donovan et al., 2019;Gurnell et al., 1994). ...
Application of an integrated spatial approach combining several sources of remote sensing data to include both channel and floodplain morphological and sedimentological impacts has identified the geomorphological effects of three extreme flood events during a single flood season (2019–2020) along a 16-km reach of the River Teme, UK. This combined approach allowed the assessment of in-channel pattern development, incision and aggradation; lateral bank migration; and overbank sedimentation and scour by out-of-channel flows. Rates of change during the event period were compared with those in the previous 10 years. The approach also allowed the role of vegetation and cultivation, both bankside and out on floodplains, to be assessed with variations in the extent of riparian wood and channel slope driving contrasts in the extent of the response. The spatial impacts from such extreme events are highly localised, varied in kind, and can be considered for both rivers and floodplains together. Erosional effects were distinctively distributed and not simply contributions to ongoing meander development; channel aggradation was localised, and overbank sedimentation explicably patchy. In reaches without woody vegetation, differences in channel and floodplain slope, local floodplain relief as created by prior events, and the impact of man-made structures were factors that drove variations in flood response. This study strongly underlines the role of continuous riparian vegetation in maintaining bank stability and constraining lateral channel migration, but also to the potential influence of floodplain vegetation and planting for ‘natural engineering’ in the context of floodplains as well as channels in comparable environments. Maintenance of riparian vegetation in the context of landowner and Natural England conflict and management of future flood risk is important, but also highlighted is the need to consider the role of hedgerows and wider planting for constraining soil and riverbank erosion during flood events.
... The channel changes in the reach manifestly relating to the 2019-2020 flood events were examined by considering bank position changes between 2018 and 2020, supported by a geomorphic change analysis (Wheaton et al., 2009;Williams, 2012) using LiDAR surveys acquired in 2009 and 2020. As highlighted by Donovan et al. (2019) and Leonard et al. (2020), the digitisation of bank positions is subject to four sources of error; co-registration error related to the georeferencing of the aerial images; interpretation error; digitisation error associated with the delimitation process itself; and the application of a level of detection (Lod) threshold that excludes small but significant features (Donovan et al., 2019;Gurnell et al., 1994). ...
Application of an integrated spatial approach combining several sources of remote sensing data to include both channel and floodplain morphological and sedimentological impacts has identified the geomorphological effects of three extreme flood events during a single flood season (2019-20) along a 16km reach of the River Teme, UK. This combined approach allowed the assessment of in-channel pattern development, incision, and aggradation; lateral bank migration; and overbank sedimentation and scour by out-of-channel flows. Rates of change during the event period were compared with those in the previous 10 years. The approach also allowed the role of vegetation and cultivation, both bankside and out on floodplains, to be assessed with variations in the extent of riparian wood and channel slope driving contrasts in the extent of the response. The spatial impacts from such extreme events are highly localized, varied in kind, and can be considered for both rivers and floodplains together. Erosional effects were distinctively distributed and not simply contributions to ongoing meander development; channel aggradation was localised, and overbank sedimentation explicably patchy. In reaches without woody vegetation, differences in channel and floodplain slope, local floodplain relief as created by prior events, and the impact of man-made structures were factors that drove variations in flood response. This study strongly underlines the role of continuous riparian vegetation in maintaining bank stability and constraining lateral channel migration, but also to the potential influence of floodplain vegetation and planting for 'natural engineering' in the context of floodplains as well as channels in comparable environments. Maintenance of riparian vegetation in the context of landowner and Natural England conflict and management of future flood risk is important, but also highlighted is the need to consider the role of hedgerows and wider planting for constraining soil and riverbank erosion during flood events.
... The most straightforward approach is the construction of Voronoi/Thiessen polygons in the vicinity of every point, and then comparing them: the larger the polygon area (the farther the point is located from other ones), the more significant the error weighting factor should be, as shown by Zhang et al. (2009). In more complex cases, various interpolation algorithms (Liu et al., 2015) and more specific techniques, such as those based on slope gradient and dense cloud point density (Wheaton et al., 2010), can be used to obtain intermediate (located between points) error values. This approach facilitates the use of an error field instead of a constant averaged error. ...
... The uncertainty of the DoD was computed, propagating the uncertainty of the input DEMs by applying the root of the sum of the square [83] and obtaining values of 11.18 cm for z and 15.62 cm for the planimetric component. Furthermore, we refined this result, multiplying the error values for a t-value of 1.96 [41,84] ...
... According to previous studies [26,27,67], the uncertainty of the DEMs is estimated to be two to three times the value of these errors, which amounts to approximately 0.10 m. Meanwhile, the vertical uncertainty of the DoDs, also known as the minimum level of detection (minLoD), is estimated as [23,26,46,[93][94][95][96]: ...
This case study focuses on the area of El Plateado near the city of Loja, Ecuador, where landslides with a high impact on infrastructures require monitoring and control. The main objectives of this work are the characterization of the landslide and the monitoring of its kinematics. Four flights were conducted using a remotely piloted aerial vehicle (RPAS) to capture aerial images that were processed with SfM techniques to generate digital elevation models (DEMs) and orthoimages of high resolution (0.05 m) and sufficient accuracy (below 0.05 m) for subsequent analyses. Thus, the DEM of differences (DoD) and profiles are obtained, but a morphometric analysis is conducted to quantitatively characterize the landslide’s elements and study its evolution. Parameters such as slope, aspect, topographic position index (TPI), terrain roughness index (TRI), and topographic wetness index (TWI) are analyzed. The results show a higher slope and roughness for scarps compared to stable areas and other elements. From TPI, slope break lines have been extracted, which allow the identification of landslide features such as scarps and toe tip. The landslide shows important changes in the landslide body surface, the retraction of the main scarp, and advances of the foot. A general decrease in average slope and TRI and an increase in TWI are also observed due to the landslide evolution and stabilization. The presence of fissures and the infiltration of rainfall water in the unsaturated soil layers, which consist of high-plasticity clays and silts, contribute to the instability. Thus, the study provides insights into the measurement accuracy, identification and characterization of landslide elements, morphometric analysis, landslide evolution, and the relationship with geotechnical factors that contribute to a better understanding of landslides. A higher frequency of the RPAS surveys and quality of geotechnical and meteorological data are required to improve the instability analysis together with a major automation of the GIS procedures.
... The high-resolution digital terrain models of the topographic difference (HRDoD) between pairs of HRDTM in all the SfM surveys performed, as well as between the TLS-generated HRDTM, were obtained using ArcGis 10.5© (ESRI) by subtraction of the final topography from the previous one in the same area [32]. In all these HRDoDs, the extraction mask for the water sheet (at different peak flows) in each RCR and PBSA was applied; this procedure enabled the precise evaluation of the morphological changes and sediment budgets associated with each flood event. ...
This work proposes a methodological approach applied to ephemeral gravel-bed streams to verify the change in the magnitude and frequency of hydrological events affecting the morphological dynamics and sediment budget in this type of channel. For the case study, the Azohía Rambla, located in southeastern Spain, was chosen, emphasizing the research on two reference riverbed sections (RCRs): an upper one, with a predominance of erosion, and a middle one, where processes of incision, transport, and deposition were involved. First, this approach focuses on relationships between peak discharges and sediment budgets during the period 2018–2022. For this purpose, water level measurements from pressure sensors, a One-Dimensional Hydrodynamic model, and findings from comparative analyses of high-resolution differential digital elevation models (HRDEM of Difference-HRDoD) based on SfM-MVS and LiDAR datasets were used. In a second phase, the GeoWEPP model was applied to the period 1996–2022 in order to simulate runoff and sediment yield at the event scale for the watersheds draining into both RCRs. During the calibration phase, a sensitivity analysis was carried out to detect the most influential parameters in the model and confirm its capacity to simulate peak flow and sediment delivery in the area described above. Values of NS (Nash–Sutcliffe efficiency) and PBIAS (percent bias) equal to 0.86 and 7.81%, respectively, were found in the calibration period, while these indices were 0.81 and −4.1% in the validation period. Finally, different event class patterns (ECPs) were established for the monitoring period (2018–2022), according to flow stage and morphological channel adjustments (overtopping, bankfull and sub-bankfull, and half-sub-bankfull), and then retrospectively extrapolated to stages of the prior simulated period (1996–2018) from their typical sequences (PECPs). The results revealed a significant increase in the number of events and PECPs leading to lower bed incision rates and higher vertical accretion, which denotes a progressive increase in bed armoring and bank erosion processes.
... Additionally, 3D point clouds can be compared and the pointto-point distance between subsequent 3D reconstructions computed [72][73][74] to evaluate 3D displacements. The accuracies and resolutions of the generated reconstructions need to be evaluated and implemented in monitoring studies as they define the detectable geometric changes and the significance of computed distances [75][76][77][78][79][80]. When dealing with the monitoring of slow-moving landslides and the investigation of their interaction with fluvial dynamics, the integration of different survey methodologies and the careful design of the field survey are mandatory to perform high-resolution analyses [24]. ...
The relationships between hillslope and fluvial processes were studied in a mountainous area of the Northern Apennines (Italy) where intermittent landslide activity has interacted for a long time with river morphodynamics. The aim of the study was to analyse such relationships in two study sites of the Scoltenna catchment. The sites were analysed in detail and monitored through time. A long-term analysis was carried out based on multitemporal photointerpretation of aerial
photos. Slope morphological changes and land use modifications since 1954 were detected and compared with the evolution of the channel morphology. A short-term analysis was also performed based on two monitoring campaigns accomplished in 2021 and 2022 in order to detect possible slope displacements and channel-bed-level changes. The techniques used are global navigation satellite systems and drone photogrammetry accompanied by geomorphological surveys and mapping. The multitemporal data collected allowed us to characterise slope surface deformations and quantify morphological changes. The combination of various techniques of remote and proximal sensing proved to be a useful tool for the analysis of the surface deformations and for the investigation of the interaction between slope and fluvial dynamics, showing the important role of fluvial processes in the remobilisation of the landslide toe causing the displacement of a significant volume of sediment into the stream.
... DEMs of differences (DoDs) between initial and final states were calculated to locate areas of accretion (positive values) and areas of erosion (negative values) (Carvalho et al., 2020;Delgado-Fernández et al., 2018;Hesp et al., 2021b). The DEMs and DoDs were processed and analysed using the Geomorphic Change Detection (GCD) software, including the calculation of raw and threshold errors (Wheaton et al., 2010b(Wheaton et al., , 2010a. DoD errors (%) from DEMs between 1987 and 2019 were: accumulation (15.45, 9.99, 11.07, 4.21) and erosion (18.22, ...
Beach users often use a range of strategies to shelter from the wind and blown sand. This involves building structures made of stacking stones. Different from other portable wind blockers, stone-made wind shelters can remain in the landscape for a long time. The process of stone removal from their original place and stone-stacking at another location has well-known effects on rock-dwelling wildlife. Less known are the impacts of stone wind shelters on biogeomorphological processes of beach-dune systems, especially those in arid coastlines, where foredunes formed by nebkhas are naturally discontinuous. This is the case of Playa del Inglés beach (Gran Canaria, Spain), the main sediment input to the Maspalomas dunefield, where the presence of stone wind shelters (goros) made by users has increased in recent decades following an increase of visitors.
This research aims to investigate the effects of stone wind shelters on the dynamics of an arid beach-dune system at various spatiotemporal scales. The methodology includes the use of aerial photography to study the appearance and evolution of stone shelters in Playa del Inglés and some of their long-term effects on the foredune. Field data was also collected to investigate the effects that stone shelters have over a representative foredune nebkha in detail, by monitoring the changes (topography, airflow, and vegetation) of an individual landform as we progressively remove pebbles from a previously built stone shelter.
Results show that stone stacking has an impact on airflow and sediment transport dynamics around landforms, limiting sediment accumulation inside nebkhas and therefore arid foredune growth. Stone stacking also constrict vegetation growth and its ability to retain sediment. The impacts of these artificial structures can be reverted following their removal but that the process of dismantling stones must be carefully planned. We elaborate some recommendations here to do it avoid damaging foredune vegetation.
... We perform the DoD analysis using Geomorphic Change Detection (GCD) in ArcGIS (GCD add-in, version 7.5.0.0, http://gcd.riverscapes.xyz/). We consider the geomorphic changes to be reliable if they are greater than the inherent uncertainties of the DEM (Wheaton et al., 2010;James and Robson, 2012). Therefore, we applied the minimum level of detection method, where the threshold can be estimated from the root mean square error (RMSE) between the component DEMs (Milan et al., 2007). ...
... A braided reach of the River Feshie, Scotland, was chosen to assess the LiDAR system in a natural vegetated fluvial environment ( Figure 1c). This reach is iconic as a site to assess geomatics technologies for the quantification of topography, including RTK-GNSS (Brasington, Rumsby, & McVey, 2000), aerial blimps (Vericat et al., 2008), TLS (Brasington, Vericat, & Rychkov, 2012), wearable LiDAR (Williams, Lamy, et al., 2020) and RTK-GNSS-positioned UAV imagery for SfM photogrammetry (Stott, Williams, & Hoey, 2020), as well as geomorphological application to quantify sediment budgets (Wheaton et al., 2010) and to shed light on the mechanisms of channel change (Wheaton et al., 2013). This history of innovation, and the low vertical amplitude of topographic variation, made this both an ideal and challenging site to test the use of the LiDAR in a natural environment. ...
Unoccupied aerial vehicles (UAVs) with passive optical sensors have become popular for reconstructing topography using Structure from Motion (SfM) photogrammetry. Advances in UAV payloads and the advent of solid‐state LiDAR have enabled consumer‐grade active remote sensing equipment to become more widely available, potentially providing opportunities to overcome some challenges associated with SfM photogrammetry, such as vegetation penetration and shadowing, that can occur when processing UAV‐acquired images. We evaluate the application of a DJI Zenmuse L1 solid‐state LiDAR sensor on a Matrice 300 RTK UAV to generate digital elevation models (DEMs). To assess flying height (60–80 m) and speed parameters (5–10 ms ⁻¹ ) on accuracy, four point clouds were acquired at a test site. These point clouds were used to develop a processing workflow to georeference, filter and classify the point clouds to produce a raster DEM product. A dense control network showed that there was no significant difference in georeferencing from differing flying height or speed. Building on the test results, a 3 km reach of the River Feshie was surveyed, collecting over 755 million UAV LiDAR points. The Multiscale Curvature Classification algorithm was found to be the most suitable classifier of ground topography. GNSS check points showed a mean vertical residual of −0.015 m on unvegetated gravel bars. Multiscale Model to Model Cloud Comparison (M3C2) residuals compared UAV LiDAR and Terrestrial Laser Scanner point clouds for seven sample sites demonstrating a close match with marginally zero residuals. Solid‐state LiDAR was effective at penetrating sparse canopy‐type vegetation but was less penetrable through dense ground‐hugging vegetation (e.g. heather, thick grass). Whilst UAV solid‐state LiDAR needs to be supplemented with bathymetric mapping to produce wet–dry DEMs, by itself, it offers advantages to comparable geomatics technologies for kilometre‐scale surveys. Ten best practice recommendations will assist users of UAV solid‐state LiDAR to produce bare earth DEMs.
... From a geomorphic perspective, these represent the change in storage terms (due to erosion and deposition) of a sediment budget. In Wheaton et al. (2010) methods are described for accounting for uncertainties in the individual DEMs, such that confidence can be developed in distinguishing changes due to geomorphic processes from changes due to noise. Geomorphic Change Detection Software has been developed to perform these analyses (http://gcd.riverscapes.xyz). ...
This report is the monitoring plan to evaluate responses of Kern Plateau meadows to Low-Tech Process-Based Restoration described in the Final Kern Meadows Restoration Design. The documented was prepared for and edited by Trout Unlimited, with funding from California Department of Fish and Wildlife.
... For this study, Digital Elevation Models of Difference (DoD) were calculated using a 95% confidence interval (t = 1.96). Raster differencing was undertaken using the standalone version of the Geomorphological Change Detection toolset (Wheaton et al., 2010;ver. 7.5.0). ...
Within Alpine catchments, glacial landforms are subject to post-depositional reworking during and following deglaciation. Ice-marginal moraines are thought to rapidly stabilise within ~200 years in this topographic context, although ice-proximal slopes are particularly prone to alteration by debris flows and solifluction. This study investigates landform transformation, documenting geomorphological change at the Bas Glacier d’Arolla, Switzerland. Gully development on a moraine slope was assessed using archive image sets obtained in 1977, 1988 and 2009 to derive historical elevation models. Raster differencing suggests that the mean rate of surface lowering on the upper moraine slope was 7.15 ± 1.83 m (± minimum level of detection) over the observation period (1977–2009), a rate of 0.22 m yr−1. The erosion of the landform resulted in an incontiguous moraine crestline. Whilst some landforms may undergo limited transformation upon deglaciation, selected sites are subject to rapid geomorphologic change, involving crestline retreat via the initial dissection by gullies, followed by the removal of inter-gully slopes.
... Bathymetric surveying plays a fundamental role in the analysis of geomorphologic features of water bodies, with extensive applications in fluvial geomorphology, hydrologic sciences, and oceanic sciences [10][11][12]. Examples of fluvial and hydrologic studies are, but are not limited to: the management of water resources [6,7,[13][14][15], lacustrine studies [15][16][17], river and hydrologic modeling [18][19][20][21][22], vegetation and aquatic ecosystems [23], the study of artic ocean environments and biological processes [24][25][26], and flood forecasting [19,27,28]. There is a diverse range of applications in coastal and ocean environments [29][30][31][32], such as dynamic ocean circulations [29,33], management and protection of coastal areas [30,34], and bio-geophysical and socioeconomic processes [30]. ...
A reliable yet economical unmanned surface vehicle (USV) has been developed for the bathymetric surveying of lakes. The system combines an autonomous navigation framework, environmental sensors, and a multibeam echosounder to collect submerged topography, temperature, and wind speed and monitor the vehicle’s status during prescribed path-planning missions. The main objective of this research is to provide a methodological framework to build an autonomous boat with independent decision-making, efficient control, and long-range navigation capabilities. Integration of sensors with navigation control enabled the automatization of position, orientation, and velocity. A solar power integration was also tested to control the duration of the autonomous missions. The results of the solar power compared favorably with those of the standard LiPO battery system. Extended and autonomous missions were achieved with the developed platform, which can also evaluate the danger level, weather circumstances, and energy consumption through real-time data analysis. With all the incorporated sensors and controls, this USV can make self-governing decisions and improve its safety. A technical evaluation of the proposed vehicle was conducted as a measurable metric of the reliability and robustness of the prototype. Overall, a reliable, economic, and self-powered autonomous system has been designed and built to retrieve bathymetric surveys as a first step to developing intelligent reconnaissance systems that combine field robotics with machine learning to make decisions and adapt to unknown environments.
... The method used here is based on the concept proposed by Wheaton et al. (2010) for the estimation of a spatially uniform minimum Level Of Detection (minLOD) using Eq. 4: ...
Torrential processes are among the main actors responsible for sediment production and mobility in mountain catchments. For this reason, the understanding of preferential pathways for sediment routing has become a priority in hazard assessment and mitigation. In this context, the sediment Connectivity Index (IC) enables to analyse the existing linkage between sediment sources and the selected target (channel network or catchment outlet). The IC is a grid-based index that allows fast computation of sediment connectivity based on landscape information derived from a single Digital Terrain Model (DTM). The index computation is based on the log-ratio between an upslope and a downslope component, including information about drainage area, slope, terrain roughness, and distance to the analysis target (e.g. outlet). The output is a map that highlights the degree of structural connectivity of sediment pathways over analysed catchments. Until now, these maps are however rarely used to help defining debris-flow hazard maps, notably due to a lack of guidelines to interpret the IC spatial distribution. This paper proposes an exploitation procedure along profiles to extract more information from the analysis of mapped IC values. The methodology relies on the analysis of the IC and its component variables along the main channel profile, integrated with information about sediment budgeting derived from Difference of DEMs (DoD). The study of connectivity was applied in the unmanaged sub-catchment (without torrent control works) of the Rio Soial (Autonomous Province of Trento-NE Italy) to understanding the geomorphic evolution of the area after five debris flows (in ten years) and the related changes of sediment connectivity. Using a recent DTM as validation, we demonstrated how an IC analysis over the older DTM can help predicting geomorphic changes and associated hazards. The results show an IC aptitude to capture geomorphic trajectories, anticipate debris flow deposits in a specific channel location, and depict preferential routing pathways..
... Laser scanning and photogrammetry offer vast improvements in sampling density over traditional ground-based survey or erosion pin methods . Monitoring of rivers and ephemeral field gullies has led the advances in terrain monitoring (Lane et al., 2003;Wells et al., 2017;Wheaton et al., 2010), but permanent gullies are also increasingly being monitoring using laser scanning and photogrammetry-based DEM of difference analysis . A researcher workshop on gully terrain measurement at the 8th ISGE concluded that the diversity in gully dimensions and monitoring scales means there is no one best method for collecting such data, but that methods should be selected to best suit the purpose or measurement problem being addressed, the area to be covered, and the resources available. ...
This is an introduction to a special issue arising from the 8th International Conference on Gully Erosion, held in Townsville, Australia in 2019. Research has improved understanding of gully erosion processes and increasingly emphasizes sophisticated near‐and‐remotely sensed methods to characterize and measure gullies. These data can then be analysed using equally sophisticated models and scenarios can be simulated. These advances improve the capacity to predict gully initiation and development over time and space. It is often assumed that better prediction translates into greater impact and uptake of research to solve real world gully erosion problems. Examples of impressive associations between research programmes and major gully management programmes are evident. However, there has been little assessment of the impact of gully research. We argue for a greater focus on achieving impact including interventions that better manage and prevent gully erosion. Opportunities to deliver research impact are assessed using three indicators of progression towards impact; the practical usability of research, whether it is in use by non‐researchers, and whether it is useful in guiding improvements in management. Like other natural hazards, gully erosion is a phenomenon of the social, economic and environmental context in which it occurs. Defining the contexts and consequences of gully erosion and using these to frame further research is therefore a means to increase research impact. Enhancing collaboration between research disciplines and with practitioners who act on the research, and a greater focus on the translation of results into practice, is another avenue. Expanding the monitoring and evaluation of gully management can better demonstrate the impact of past research and enable further useful investigations. We urge gully erosion researchers to consider the potential impact of their research, including how it can more effectively inform better and more cost‐effective management and political decisions.
... Some fraction of it may also be due to bedload particles missed by the SPG system, typically if they are smaller than the size detection threshold of 10-20 mm (Nicollier et al., 2022a(Nicollier et al., , 2022b, if saturation occurs at high bedload transport rates , or if particle hops are greater than the SPG streamwise length when turbulence rate is higher (Schneider et al., 2014). But errors in the volumetric erosion and deposition may also arise from residual error in the DEMs used in the morphological change analysis (Lindsay and Ashmore, 2002;Bater and Coops, 2009;Wheaton et al., 2010). ...
Despite a critical importance for current and future Alpine watershed management, bedload transport remains a difficult process to measure and to predict accurately. It is extremely complex to describe physically, and the lack of reliable and cost-effective field monitoring systems has limited progress in this field. Recent methodological advances in acoustic and seismic techniques have permitted major developments in the continuous monitoring of bedload transport in steep Alpine streams. The aim of this PhD thesis is to develop further and to apply those emerging techniques to gain a new understanding of coarse material mobilization, transfer and storage throughout Alpine watersheds.
The first objective of this thesis was to improve the calibration of the widely-used Swiss Plate Geophone (SPG) acoustic bedload monitoring system, because variability in calibration coefficients were observed within and between different SPG sites, which limits their universal transferability. An impact experiment was performed at four SPG stations and positively showed that individual plates within and across sites present in general comparable signal response, but signal propagation due to poor insulation was identified as an important reason for calibration coefficient variability. This aspect needs to be accounted so as to obtain transferable calibration coefficients for the SPG system, which will save substantial sensor-specific field calibration effort.
The second objective was to use five-years of SPG-acquired bedload transport time-series to understand how hydrological variability drove bedload transport in a nival-dominated Alpine watershed (Vallon de Nant), and to assess implications for how climate change might impact bedload transport in the future in such environments through its effect on Alpine hydrology. Results of the analysis emphasized the importance of combined rain and snow-melt events for yearly transported bedload volumes (77% on average), the non-negligible contribution of snowmelt-only events (14% on average), and the non-negligible but smaller contribution of late-summer and autumn rainfall events (9% on average). In terms of climate change, this implies that lower snowfall amounts and seasonal shift in both precipitation and melt periods may lead to enhanced bedload transport in winter and spring, and reduced bedload transport in summer and autumn, although the timing and magnitude of extreme rainfall events is likely to be key. Results of the study allow development of climate-sensitive Alpine watershed management strategies.
The third objective was to improve understanding of the spatial structure of bedload sediment supply and transport that lead to the kinds of temporal variations we observe at the watershed outlets. The difficulty of measuring distributed bedload transport reliably means that there are no data and very little understanding of this spatial structure. Environmental seismology has great potential in this context; sensors are cheap, easily deployable, and previous research has shown that reliable bedload transport time-series could be extracted from the seismic signal emitted by a stream. A network of 24 seismic sensors was deployed across the Vallon de Nant Alpine watershed during a high-magnitude bedload transport event, providing with a unique distributed dataset. Comparison of the seismic inversion procedure with the calibrated SPG time-series was encouraging. Results of the analysis emphasized the relative inefficiency of steep Alpine watersheds in conveying coarse material even during a high-magnitude event. Bedload moved slowly, and over short distances. Multiple periods of competent flow would be required to evacuate coarse material mobilized in the watershed during individual-sourcing events. This understanding has major implications for constraining the present and future of coarse material fluxes throughout steep Alpine watersheds. Seismic networks have the potential to capture the time-space variability in bedload transport; a necessary condition towards obtaining more accurate predictions of the process.
... As a result, the proportion of points located within a gully may be used to determine the areal "gully density". Such an unreliable but quick proxy may be utilized for insightful empirical studies, such as investigating relationships between gully density and watershed sediment outputs (Wheaton et al., 2010). Overall, thorough evaluations or random sample techniques benefit from making mapping efforts objective. ...
The problem of “gully erosion” is one of the severe “natural hazards” associated with large‐scale land degradation in various parts of the world. Therefore, accurate modelling is one of the crucial responsibilities in this study on gully erosion. But there are still a lot of gaps in our knowledge of gully erosion and its consequences. Particularly at the regional to continental scale, this is true. Gullying is hence often forgotten about in regulation and watershed management plans. The scientific community is becoming increasingly interested in gully erosion, yet many information gaps still need to be filled. In this research, we are trying to fill the mentioned gap with the help of the existing literature. Most gully erosion research has been done to estimate the susceptible zones and ultimately select the best model. In this research, a test application has been made by considering some important models. Then the “vulnerability assessment” was done with the help of “gully erosion, climate‐induced chemical weathering and socio‐economic variables” at the village level. The village‐level information has been used to determine the vulnerability in this region. This information is beneficial for future researchers to conduct gully erosion research in various parts of the world. To determine the extent of the weathering, taking all variables into account, we employed a variety of weathering indices. Extensive empirical inquiry for assessing chemical weathering, gully erosion and its related vulnerability assessment has been done in this work.
... Such an analysis was extended to the whole digital cliff model, and for each selected block an approximate detaching plane was rasterized to calculate the difference in terms of elevation between the plane and the protruding rock block, and to turn it into a volume value. The reliability of such an approach has already been proved in the literature, even for the estimation of topographic volume changes applied to slope morphological analysis, e.g., [54,55]. Once the most evident unstable blocks on the point cloud were located and their volumes estimated, a database was created, and a rock volume distribution map was provided for practical purposes. ...
The analysis of a digital rock cliff model, built by airborne photogrammetric data and infrared thermal images, is herein presented as an alternative tool for rock mass study in restricted and poorly accessible areas. Photogrammetric and infrared thermography techniques were combined for the geostructural and morphological characterization of an unstable cliff located in a nature reserve, where the rock mass extension and the environmental preservation rules required the use of minimally invasive surveying solutions. This methodological approach provided quantitative and qualitative data on both the spatial orientation of discontinuities and the location of major structural features, jutting blocks and past rockfall source areas. The digitally derived spatial data were used to carry out a rock mass kinematic analysis, highlighting the most recurring unstable failure patterns. Thermal images were overlapped to the photogrammetric cliff model to exploit the data combination and to analyze the presence of protruding rock mass volumes to be referred to as potential unstable volumes. Based on this activity, rock volumes were quantified on the digital model and the results were used to provide a zonation map of the potential magnitude of future rockfalls threatening the reserve. Digital data were validated by a field surveying campaign, which returned a satisfactory match, proving the usefulness and suitability of the approach, as well as allowing the quick and reliable rock mass characterization in the frame of practical use and risk management purposes.
... Geomorphic changes caused by subsequent flood events were afterwards quantified with DEMs of difference (DoDs). DoDs were generated using Geomorphic Change Detection software (version 7) [99]. Thresholds of change detection (i.e., levels of detection (LoD)) used to evaluate uncertainty were evaluated using standard Gaussian error propagation: LoD = ((δ(z) DEM t1 ) 2 + (δ(z) DEM t2 ) 2 ) 1/2 (13) where δ(z) DEM t1 is the vertical error at time step 1 and where δ(z) DEM t2 is the vertical error at time step 2, respectively. ...
Local scour holes are erosional bed structures that are related to different scientific disciplines in Earth science and hydraulic engineering. Local scouring at naturally placed boulders is ubiquitous, but many competing factors make it difficult to isolate the effects of a given variable. This is especially true for local scouring at natural instream obstacles that are exposed to unsteady flow conditions in the course of flood hydrograph experiments. Experimental investigations in laboratory flumes offer the advantage that boundary conditions can be systematically varied. We present novel experimental data on the impact of the submergence ratio, hydrograph skewness, and flow intensity on local scouring at boulder-like obstacles during unsteady flow and evaluate the effect of discharge chronologies. In total, 48 flume experiments on subcritical clear-water conditions and channel degradation were performed. The experimental results reveal that local scouring dominantly occurred at the rising limb when flow depth was comparable to the obstacle size, so the obstacle was unsubmerged. The steeper the rising limb, the quicker the local scour hole matured. The experimental results are relevant for the hydraulic interpretation of local scour holes found at boulders in the field. They may be utilized as a proxy for the minimum duration of the beginning stage of a flood.
... A critical challenge in the study of elevation change detection, including slow-moving landslides, is addressing signal-to-noise ratios (Wheaton et al. 2009;Schaffrath et al. 2015; James et al. 2017). Frequently monitored landslides often register changes so small that the elevation changes may not be greater than the survey errors, referred to as noise. ...
Slow-moving, chronically destructive landslides are projected to grow in number globally in response to precipitation increases from climate change, and land disturbances from wildfire, mining, and construction. In the Cincinnati and northern Kentucky metropolitan area, USA, landslides develop in colluvium that covers the steep slopes along the Ohio River and its tributaries. Here we quantify elevation changes in a slow-moving colluvial landslide over 14 years using county-wide lidar, uncrewed aerial vehicle (UAV) structure from motion (SfM) surveys, and a UAV lidar survey. Because the technology and quality differ among surveys, the challenge was to calculate a threshold of detectable change for each survey combination. We introduce two methods, the first uses propagated elevation difference errors, and the second back-calculates the individual survey errors. Thresholds of detection range from ± 0.05 to ± 0.20 m. Record rainfall in 2011 produced the largest vertical changes. Since then, the landslide toe has continued to deform, and the landslide has doubled its width by extending into a previously undisturbed slope. While this study presents a technique to utilize older datasets in combination with modern surveys to monitor slow-moving landslides, it is broadly applicable to other studies where topographic data of differing quality is available.
... ). Precision maps were created by interpolating the vertical standard deviation (H) determined from the precision estimate (1-mm grid size)(Taylor, 1997; Brasington, Langham and Rumsby, 2003; Lane,Westaway and Murray Hicks, 2003;and Wheaton et al., 2010).Mangrove canopy covering is the main issue in this study, since it conceals the riverbank topography structures underneath. Physical erosion monitoring in the canopy-covered area is challenging to detect because of harsh mangrove environments and ecosystems such as route accessibility, tidal influence, and difficulty setting up surveying instruments in muddy and root-complex conditions(Kuenzer et al., 2011; Azian and Mubarak, 2012). ...
Estimating surface elevation changes in mangrove forests is dynamic because it is barely visible physically and because of the canopy-covered factor that restricts aerial monitoring. It demands a technique that filters the mangrove canopy at the top of the vegetation and the complex understory structures. Hence, this study estimated surface elevation changes underneath the mangrove canopy through geospatial and geomorphological approaches. The first objective of this study was to discover vegetation filtering algorithms for estimating surface elevation underneath the mangrove canopy, followed by generating an unmanned aerial vehicle-digital elevation model (UAV-DEM) underneath the mangrove canopy with vertical accuracy comparable to physical topography measurement. The other objective was to evaluate the rates of surface elevation changes using the geomorphological change detection method. The last objective was to correlate the interactions between mangrove surface elevation changes and sea level rise. This study's data processing stages included photogrammetric data processing using Structure from Motion-Multiview Stereo (SfM-MVS), filtering using the surface estimation from Nearest Elevation and Repetitive Lowering (SNERL) algorithm, and geomorphological change detection (GCD) analysis. Two epochs of UAV data collection were carried out in 2016 and 2017 at low tide conditions. UAV data processing was performed using the SfM-MVS method. Next, the SNERL algorithm was employed to extract the surface from the mangrove canopy and generate the mangrove ground as a DEM. Subsequently, GCD analysis was utilized to quantify the elevation change rates at the ground surface, which comprise erosion, accretion, and sedimentation, using the differential DEM (DoD) technique. The finding illustrated that the generated UAV-DEM using SNERL algorithms reached vertical accuracy of 0.345 m (RMSE), 0.107 m (mean), and 0.503 m (standard deviation). The other finding indicated that region of interest 5 (ROI 5) experienced the highest volumetric accretion (surface raising) at 0.566 cm3/yr. The highest erosion (surface lowering) was identified at ROI 8 at -2.469 cm3/yr. In contrast, for vertical change average rates, ROI 6 experienced the highest vertical accretion (surface raising) at 1.281 m/yr, while the highest vertical erosion (surface lowering) was spotted at ROI 3 at -0.568 m/yr. In conclusion, a geospatial approach comprising SfM-MVS, vegetation index (VI) segregation, and the SNERL filtering algorithm are efficient in generating UAV-DEM underneath the mangrove canopy at the closest level to the terrain level. The GCD map and the rates of surface elevation changes at Kilim River enabled authorities like Langkawi Development Authority (LADA) and the Department of Drainage and Irrigation (DID) to fully understand the situation and prepare a mitigation plan to avoid unbalanced surface elevation changes that could lead to long-term devastation of the mangrove ecosystem in the future.
The integration of multiple data sources, including satellite imagery, aerial photography,
and ground-based measurements, represents an important development in the study of landslide
processes. The combination of different data sources can be very important in improving our
understanding of geological phenomena, especially in cases of inaccessible areas. In this context,
the study of coastal areas represents a real challenge for the research community, both for the
inaccessibility of coastal slopes and for the numerous drivers that can control coastal processes
(subaerial, marine, or endogenic). In this work, we present a case study of the Conero Regional Park
(Northern Adriatic Sea, Ancona, Italy) cliff-top retreat, characterized by Neogenic soft rocks (flysch,
molasse). In particular, the study is focused in the area between the beach of Portonovo and Trave
(south of Ancona), which has been studied using aerial orthophoto acquired between 1978 and 2021,
Unmanned Aerial Vehicle (UAV) photographs (and extracted photogrammetric model) surveyed in
September 2021 and 2012 LiDAR data. Aerial orthophotos were analyzed through the United States
Geological Survey’s (USGS) tool Digital Shoreline Analysis System (DSAS) to identify and estimate
the top-cliff erosion. The results were supported by the analysis of wave data and rainfall from the
correspondent period. It has been found that for the northernmost sector (Trave), in the examined
period of 40 years, an erosion up to 40 m occurred. Furthermore, a Digital Elevation Model (DEM)
of Difference (DoD) between a 2012 Digital Terrain Model (DTM) and a UAV Digital Surface Model
(DSM) was implemented to corroborate the DSAS results, revealing a good agreement between the
retreat areas, identified by DSAS, and the section of coast characterized by a high value of DoD.
This work proposes a methodological approach applied to ephemeral gravel-bed streams to verify the change in the magnitude and frequency of hydrological events affecting the morphological dynamics and sediment budget in this type of channel. For the case study the Azohía Rambla, located in southeastern Spain, was chosen, emphasizing the research on two reference riverbed sections (RCRs): an upper one, with a predominance of erosion, and a middle one, where processes of incision, transport, and deposition converge. First, this approach focuses on relationships between peak discharges and sediment budgets during the period 2018 to 2022. For this purpose, water level measurements from pressure sensors, a One-Dimensional Hydrodynamic model, and findings from comparative analyses of high-resolution differential digital elevation models (HRDEM of Difference - HRDoD) based on SfM-MVS and LiDAR datasets were used. In a second phase the GeoWEPP model was applied to the period 1996-2022 in order to simulate runoff and sediment yield at the event scale for the watersheds draining into both RCRs. During the calibration phase a sensitivity analysis was carried out to detect the most influential parameters in the model and to confirm its capacity to simulate peak flow and sediment delivery in the area described above. Values of NS (Nash-Sutcliffe efficiency) and PBIAS (percent bias) equal to 0.86 and 7.81%, respectively, were found in the calibration period, while these indices were 0.81 and -4.1% in the validation period. Finally, different event class patterns (ECPs) were established for the monitoring period (2018-2022), according to flow stage and morphological channel adjustments (overtopping, bankfull and sub-bankfull, and half-sub-bankfull), and then retrospectively extrapolated to stages of the prior simulated period (1996-2018) from their typical sequences (PECPs). The results revealed a significant increase in the number of events and PECPs leading to lower bed incision rates and higher vertical accretion, which denotes a progressive increase in bed armoring and bank erosion processes.
In this study, the aerial photogrammetry, combined with the powerful algorithms of the Structure from Motion technique, allowed generating a detailed rock mass model of a sub-vertical cliff affected by instability features threatening the safe fruition of a nature reserve. Quantitative and qualitative data on the spatial orientation of discontinuities and on location of major structural elements were achieved. The digitally derived spatial data were used to perform a kinematic analysis of the rock mass, highlighting the most recurrent unstable failure patterns, for which the stability and the probability of failure were numerically calculated in both static and dynamic conditions.
The difficulties of measuring bedload transport in gravel bed rivers have given rise to the morphological method wherein sediment transport is inferred from changes in riverbed elevation and estimates of the distance traveled by sediment, its path length. Because current methods for estimating path length are time and labor intensive, we present a method to estimate path length from repeat digital elevation models (DEMs of difference i.e., DoDs). We propose an automated method to extract the spacing between erosional and depositional sites on the DoD by the application of Variational Mode Decomposition (VMD), a signal processing method, to quantify the spacing as a proxy for path length. We developed this method using flume experiments where bed topography and sediment flux were measured and then applied it to published field data with tracer measurements for validation. Our path length estimates had an error lower than 30 % when compared to the measured mode of the tracer distances in the field and generated sediment transport estimates not significantly different than the measured sediment flux at lower discharges in the lab. However, we observed an underestimation of sediment flux at the higher discharges in the flume study. We explore explanations for the underestimation and how the time between survey acquisitions, the morphological active width relative to the channel width, and DoD thresholding techniques affect the proposed method and the potential issues they pose to the morphological method in general.
This study analyses the long‐term dynamics in the Chauvet glacial and periglacial system (southern French Alps) over seven decades (1948–2020), where several lake outburst floods have been documented since 1930. To accurately describe and explain the complex dynamics of this site, our multidisciplinary approach combines (1) photogrammetry of historical aerial photographs and modern high‐resolution satellite and UAV images, (2) geophysical surveys and (3) geomorphological mapping. We provide evidence for spatial and functional interactions between glacial and periglacial features, especially in the lower sector where different landforms with variable ice‐ and debris‐content and specific dynamics are interplayed. We found the highest thinning rates on ice‐rich terrain located in the central part of the valley bottom, which, together with bedrock morphology, most probably determine the location of the thermokarst. We also documented an overall acceleration of the creeping of the landforms after the 2000s, with a flow direction largely oriented towards the thermokarst depression. The outburst water flowed through a conduit whose successive opening and closure seem to mainly depend on the rate of lateral convergence of left‐ and right‐hand landforms and on the rate of ice melting (and roof collapse) along the conduit walls. Today, the site of Chauvet still represents a potential hazard for the region due to the large water storage capacity (up to 180 000 ± 450 m ³ ) and the development of a predominantly bucket shape in the thermokarst sector.
Unmanned Aerial Vehicle (UAV) monitoring surveys are used to assess a dune restoration project in the protected natural area of the Bevano River mouth in the Northern Adriatic coast (Ravenna, Italy). UAV is among the most utilized tools in coastal geomorphology studies as high-spatial and temporal resolution surveys can be carried out in an efficient and cost-effective manner. The impact of the installed fences to dune development are assessed in terms of sand volume and vegetation cover changes over time by using a systematic data processing workflow based on Structure from Motion (SfM) photogrammetry and Geomorphic Change Detection (GCD) toolset. Accuracy assessment is performed using statistical analysis between GPS profiles and the elevation models. Results show that the dune fence proves to be effective to prevent dune erosion since significant sand accumulation is observed along the dune foot and front. Progradation of around 3–5 m of the foredune, development of embryo dunes, decrease in stoss slope and blowout features due to increase in vegetation colonization were observed. Erosion is evident at the northern portion of the structure, which could be accounted for by the aerodynamic and morphodynamic conditions around the dune fence, the efficiency of the fence and its configuration to trap sediments. Dune fencing and limiting debris cleaning along the protected coast has been proven to be very effective against dune degradation. The GCD toolset can be a valuable tool if sources of uncertainties are well accounted for. The proposed workflow can also aid in creating transferable guidelines to stakeholders in ICZM implementation in the Mediterranean low-lying sandy coasts.
One of the most commonly used surveying techniques for landslide monitoring is a photogrammetric survey using an Unmanned Aerial System (UAS), where landslide displacements can be determined by comparing dense point clouds, digital terrain models, and digital orthomosaic maps resulting from different measurement epochs. A new data processing method for calculating landslide displacements based on UAS photogrammetric survey data is presented in this paper, whose main advantage is the fact that it does not require the production of the above-mentioned products, enabling faster and simpler displacement determination. The proposed method is based on matching features between the images from two different UAS photogrammetric surveys and calculating the displacements based only on the comparison of two reconstructed sparse point clouds. The accuracy of the method was analyzed on a test field with simulated displacements and on an active landslide in Croatia. Moreover, the results were compared with the results obtained with a commonly used method based on comparing manually tracked features on orthomosaics from different epochs. Analysis of the test field results using the presented method show the ability to determine displacements with a centimeter level accuracy in ideal conditions even with a flight height of 120 m, and on the Kostanjek landslide with a sub-decimeter level accuracy.
The development of retrogressive thaw slumps (RTS) is known to be strongly influenced by relief-related parameters, permafrost characteristics, and climatic triggers. To deepen the understanding of RTS, this study examines the subsurface characteristics in the vicinity of an active thaw slump, located in the Richardson Mountains (Western Canadian Arctic). The investigations aim to identify relationships between the spatiotemporal slump development and the influence of subsurface structures. Information on these were gained by means of electrical resistivity tomography (ERT) and ground-penetrating radar (GPR). The spatiotemporal development of the slump was revealed by high-resolution satellite imagery and unmanned aerial vehicle–based digital elevation models (DEMs). The analysis indicated an acceleration of slump expansion, especially since 2018. The comparison of the DEMs enabled the detailed balancing of erosion and accumulation within the slump area between August 2018 and August 2019. In addition, manual frost probing and GPR revealed a strong relationship between the active layer thickness, surface morphology, and hydrology. Detected furrows in permafrost table topography seem to affect the active layer hydrology and cause a canalization of runoff toward the slump. The three-dimensional ERT data revealed a partly unfrozen layer underlying a heterogeneous permafrost body. This may influence the local hydrology and affect the development of the RTS. The results highlight the complex relationships between slump development, subsurface structure, and hydrology and indicate a distinct research need for other RTSs.
The response of temperate glaciers to rapid climate warming is reflected in the geomorphology (landsystem) resulting from snout recession. This paper develops a locally diverse process‐form model of active temperate glaciers through mapping and quantification of historical landscape change on the Fjallsjökull‐Hrútárjökull foreland, SE Iceland. Quantification of volumetric and areal changes on the foreland are based on time‐series of archival aerial images for the period 1945‐1998, high‐resolution satellite imagery for 2014, and digital elevation models of differences derived from time series of UAV imagery for the years 2014, 2016, 2018, 2019 and 2022. Landscape change and glacier snout behaviour since 1945 highlights the importance of azonal and potentially intrazonal signatures in temperate glacial landsystems, particularly: 1) the development and collapse of partially supraglacial outwash fans to produce outwash heads fronting depositional overdeepenings; and 2) the emergence of ice‐cored eskers that record the evolution of englacial drainage networks operating over overdeepenings. Such landform assemblages are manifested as substantial ice‐cored/hummocky terrains, a characteristic of deglaciating forelands that is likely to be widely replicated wherever ice‐contact glacifluvial assemblages create outwash heads that act as depositional overdeepenings. Due to its significantly greater supraglacial debris cover, complete de‐icing of the Hrútárjökull snout in response to post‐1945 warming was delayed until around 2014. This constitutes a prime example of incremental stagnation, which in a rapidly warming climate has resulted in significant landscape change (land surface elevation collapse of 0.8 m a‐1) over the last 8 years.
Geomorphological processes that occur on the surface structure of the region are included in badland geomorphology. Rapid soil erosion and the production of various geomorphic characteristics are related to badland development. The expansion of their main channels is inextricably tied to the formation of gullies. The “degree of badland formation” inside that catchment and the characteristics of the substrate may both be learned from an analysis of the longitudinal shape of these channels. In this work the mechanism and trend of erosion has been done with help of cross section analysis and prominent geomorphic process. The very high resolution DEM has been prepared in this perspective. Finding out how large-scale erosion occurs and how it contributes to the deterioration of the land is the main objective of the research. According to this viewpoint, the nature of erosion may be measured using the connectivity index and gullies. In this region, the early “rills and minor gullies emerge over the high duricrust escarpment”, where it is discovered that the ambient lateritic hardpan has a substantial impact on the gully channel character, with the majority of them having steeper portions in the middle of their course. Apart from this there is an increasing tendency of erosion from the previous period to present time.
The combination of the graphic potential of 3D CAD with the construction project schedule is known as 4D CAD. Since 4D CAD technology links the time-related and physical aspects of a construction project it presents opportunities for use as a tool for construction management. Design and construction planning alternatives and decisions can be evaluated, optimised and justified within the context of space and time. The technology provides the means to integrate the functions, roles, responsibilities and relationships of, and between, all participants in the construction process. This process is examined. Problems that need to be overcome to make 4D CAD more attractive for construction management are also explored.
Introduction The digital elevation model (DEM) is a computer representation of the earth's surface; it provides a base dataset from which topographic parameters can be digitally generated. The routing of water over a surface is closely tied to surface form, and hydrologic features are often extracted from DEM data. DEMs are used to perform cost analyses and view-shed analyses for resource management as well as business applications. The DEM is a model of the elevation surface and, like other models, the data are subject to error. Error is the departure of a measurement from its true value. In geographic analyses that use spatial data, we often do not know or do not have access to the true value. Our lack of knowledge about the reliability of a measurement's representation of the true value is referred to as uncertainty. DEM errors are elusive and constitute uncertainty. DEMs have broad applications, are used in many domains, and are an important component of decision-making. Users of DEMs bear a professional responsibility to assess their contributions to such decision-making efforts. To make such assessments, users must first be aware of the impact of DEM errors. This survey was designed to identify users' awareness of DEM uncertainty and determine their willingness to address it. Specifically, the survey identifies DEM users, uses of DEMs, whether these users are aware of DEM uncertainty, and whether the users perceive that uncertainty affects their DEM applications.
Better understanding of channel change in low-sinuosity gravel-bed rivers requires attention to within-reach spatial patterns of non-uniform flow and bedload transport. Field techniques for measuring such patterns are discussed and results illustrated. Point sampling of bedload is the weakest link in this approach. Mean transport rates and streamwise variations in transport can alternatively be estimated from the measured channel change using wining-reach sediment budgeting.
Digital elevation models of Gepatschferner in Northern Tyrol, Austria were obtained with digital photogrammetry from high altitude stereo photo pairs and by digitizing an analogue topographic glacier map, for 1990 and 1971, respectively. A difference map was calculated to identify regions of glacier elevation increases and decreases corresponding to glacier mass gain and loss. While the glacier tongue below 2600 m showed mainly increases in glacier surface elevation as compared to 1971, the remaining glacier thickness experienced both increases and decreases. The accumulation zone above 3200 m contained several extreme cases of morphological features with altitude changes>+30 m. While the increased ice thickness of the glacier tongue can be traced to a well documented period of mass accumulation in the 1970s, changes in glacier surface elevation in the higher zones may be linked either to the morphology of the glacier bed or to differences in insolation on the glacier surface. Between 1971 and 1990 the glacier experienced a net loss of 26×10 6 m 3 corresponding to approximately 0.9% of the entire glacier volume.
If you even occasionally enjoy surfing the Web, there is a good chance that you have visited the Google Earth site (http://earth.google.com). There seems to be a certain universal appeal to viewing Earth from the edge of space, selecting a point of interest, and zooming in until objects as familiar as the flowerbeds in your own yard become visible. Imagine then how appealing it would be for Earth scientists, who devote their careers to studying the evolution of the planet's surface - by examining processes as diverse as erosion, uplift, tectonic-plate motion, seismicity, and volcanism - to have access to a similar resource, but one that offers accurate three-dimensional coordinates of closely spaced points covering any area of Earth's surface.
p>Repeat topographic surveys are often used to monitor geomorphological change in rivers. Such surveys can yield Digital elevation models (OEMs), which are differenced against each other to produce spatially distributed maps of elevation changes called OEMs of difference (000). Both areal and volumetric budgets of erosion and deposition can be calculated from DoDs. However, questions arise about the reliability of the analyses and what they mean. This thesis presents two new methodological advances to address these two uncertainties. The question of reliabilities (reliability uncertainty) was addressed through the development of a flexible technique for estimating the spatially variable surface representation uncertainties in individual DEMs. A fuzzy inference system is used to quantify uncertainty in DEMs and the individual error estimates are propagated into the DoD on a cell-by-cell basis. This is converted into a probabilistic estimate of DoD uncertainty. This estimate can be improved using Bayes theorem and an analysis of the spatial coherence of erosion and deposition units within the DoD. The resulting probabilistic estimate of DoD uncertainty reflects the spatial variability of uncertainty, and can be used to threshold the DoD at user-specified confidence intervals. This addresses reliability by allowing the distinction between real and undetectable changes. The question of what the thresholded DoDs mean, geomorphically, is a fundamental one and what originally motivated the development of morphological sediment budgeting techniques. Herein, a range of masking tools were developed, which allow the quantitative interrogation of these rich spatial datasets and their patterns based on various classification systems and/or the expert-judgment of a trained geomorphologist. The tools extend the traditional DoD interpretation of whether a reach is net aggradational or net degradational to a detailed quantitative segregation of the DoD budget into the mechanisms responsible for the changes at the bar-scale. The utility of both these methodological developments were tested on three different data sets representing event-based monitoring (Sulphur Creek, California), restoration monitoring (Mokelumne River, California), and annual-monitoring of a natural dynamic system (River Feshie, Scotland). One of the themes that emerges across the application of these tools in the three different settings is the sharp contrast between which geomorphological mechanisms of change are dominant in areal versus volumetric terms. The tools extend what can reliably be inferred about geomorphological change from repeat topographic surveys.</p
An indirect methodology for determining the distribution of mass balance at high spatial resolution using remote sensing and ice-flow modelling is presented. The method, based on the mass-continuity equation, requires two datasets collected over the desired monitoring interval: (i) the spatial pattern of glacier surface-elevation change, and (ii) the mass-flux divergence field. At Haut Glacier d'Arolla, Valais, Switzerland, the mass-balance distribution between September 1992 and September 1993 is calculated at 20 m resolution from the difference between the pattern of surface-elevation change derived from analytical photogrammetry and the mass-flux divergence field determined from three-dimensional, numerical flow modelling constrained by surface-velocity measurements. The resultant pattern of mass balance is almost totally negative, showing a strong dependence on elevation, but with large localized departures. The computed distribution of mass balance compares well (R2 =0.91) with mass-balance measurements made at stakes installed along the glacier centre line over the same period. Despite the highly optimized nature of the flow-modelling effort employed in this study, the good agreement indicates the potential this method has as a strategy for deriving high spatial and temporal-resolution estimates of mass balance.
Previous studies of channel morphological change have often relied upon sparse spatial and temporal data-sets, resulting in a degree of uncertainty in their conclusions. Furthermore, previous methodologies have been unable to quantify small-scale changes in channels composed of sand and fine gravel due to inadequate data density. This study reports the use of a high-resolution 3D laser scanner (LMS-Z210) in the assessment of erosion and deposition volumes in the proglacial zone of Glacier du Ferpècle and Mont Miné, Switzerland. High-resolution (>500 points/m2) data obtained across a 5881 m2 area of braid plain during the early part of the melt-water season permitted digital elevation models (DEMs) of bar surfaces and channels to be produced. The approach negates the need for complex surface interpolation algorithms required in surveys with lower point density, e.g. those obtained from global positioning systems or total stations. Furthermore, the technique has the advantage of being able to cover a large area over a comparatively short time period. Laser scanner returns revealed high vertical precision, ±0·02 m, for dry bar surfaces; however, submerged areas (<0·2 m depth) returned lower precision, with a range of −0·15 to +0·06 m. To account for this, different levels of detection (LoD) were applied to the dry and wet parts of the study reach during DEM subtraction. Subtraction of successive DEMs revealed two short depositional episodes over the ten-day study, with erosion dominating in between. Three episodes of avulsion were identified, two of which appeared to be triggered by constriction avulsion, whilst the other was initiated by bar-edge erosion. Transient lobes and sediment sheets could also be identified at the downstream end of the reach, as could lobe progradation. Relatively minor, but common, changes in channel morphology could also be detected, such as bar edge accretion, bank erosion and chute development. In an analysis of the effects of survey frequency upon volumes calculated following DEM subtraction, daily surveys were found to increase erosion volumes by 67 per cent and deposition volumes by 14 per cent when compared with an 8-day survey interval. Copyright © 2007 John Wiley & Sons, Ltd.
This paper compares two approaches used to derive measures of annual sediment transfers within a 1 km long piedmont reach of the gravel-bed River Coquet in Northumberland, northern England. The techniques utilize: (i) channel planform and cross-section surveys based on a theodolite/electronic distance measurement (EDM) survey of 21 monumented channel cross-sections and channel and gravel bar margins; and (ii) theodolite-EDM survey generating a series of x,y,z coordinates, from which digital elevation models (DEMs) of the reach were constructed. Calculating the difference between DEM surfaces provided a measure of volumetric change between surveys carried out during the spring of 1999 and 2000. The use of kriging in DEM generation and differencing permits computation of estimate variances and confidence intervals for sediment transfer. Error analysis, validating the DEMs using surveyed cross-sections, indicated a mean error between surveyed and DEM-generated cross-sections of around twice the value of the D50 of the surface sediment in the reach. Comparison of sediment volumes derived from the two approaches suggests that, compared with the DEM method, monumented cross-sections underestimate the magnitude of volumetric changes that occur within the reach. The cross-section approach relies on a simplistic integration of the volumes, whereas DEM differencing provides an estimate at a resolution under the control of the analyst. Furthermore, the cross-section approach does not permit a reliable estimate of the uncertainty of the volumes calculated. In addition, the DEM methodology based on the morphological unit scale provides an explicit identification of spatial patterns of erosion and deposition, a feature that cross-section-based approaches may fail to include. Copyright © 2003 John Wiley & Sons, Ltd.
Bed elevation, feature adjustments, and spawning use were monitored at three Chinook salmon (Oncorhynchus tschawytscha)
spawning habitat rehabilitation sites to measure project longevity in a regulated river. Sites enhanced with 649?1323 m3 of gravel
lost from 3?20% of remaining gravel volume annually during controlled flows of 8?70 m3/s and 2.6?4.6% of placed material
during a short-duration (19 days) release of 57 m3/s. The oldest site lost ~50% of enhancement volume over 4 years. Of the
mechanisms monitored, gravel deflation was the greatest contributor to volumetric reductions, followed by hydraulic scour.
Spawning, local scour around placed features, and oversteepened slopes contributed to volumetric changes. As sites matured,
volumetric reductions decreased. Sites captured as much large woody debris as was lost. While complexity is an extremely
important aspect of ecological function, artificial production of highly diverse and complex habitat features may lead to limited
longevity without natural rejuvenatio
Maps and photo sources have problems and restrict investigation to little more than a century. In this article the behaviour of the strongly braided River Feshie (Cairngorms, Scotland) is examined for periods from 1-200 yr. It is braided in three reaches - elsewhere the channel is restrained by rock or terraces. Changes over 50-100 yr are difficult to separate from the short-term effects of discharge. No satisfactory quantitative measure of braiding could be extracted from aerial photographs. Repeated surveys at one-year intervals show that most changes involve channel switching during overbank floods, with limited channel migration by erosion/deposition. -Keith Clayton
The potential for mapping in-channel morphology within shallow gravel-bed rivers using airborne multispectral imagery and aerial photography is illustrated using a case study from the River Tummel, Scotland. The technique described relies on a good correlation between observed light reflectance levels from a water body and water depth. Measured water depths are regressed against reflectance levels derived from airborne multispectral imagery and black-and-white aerial photographs, to obtain equations that can be used for mapping channel bathymetry. The technique has a great deal of potential for wideranging applications, including detailed morphological surveys, assessing in-channel changes and mapping riverine habitats.
The objective of this paper is to compare probabilistic models and fuzzy set models for design against uncertainty when there is limited information about the statistics of the uncertainty or modeling error. First, we compare the axioms of probabilistic and fuzzy set methods and the rules governing the arithmetic operations that these methods use. Then, we compare the two methods in designing for maximum safety under a given budget. In general, if there is sufficient information to build accurate probabilistic models of uncertainties, probabilistic methods are better than fuzzy set methods. On the other hand, fuzzy set methods can be better if little information is available. One reason is that it is easier to identify the most conservative fuzzy set model than the most conservative probabilistic model that is consistent with the available information.
The digital elevation model (DEM] quality that can be obtained from a digital photogrammetric survey of a reach of the clear water, shallow, gravel-bed North Ashburton River, New Zea-land is assessed. An automated correction procedure is used to deal with point errors associated with submerged topog-raphy, based on a correction for refraction at an air-water interface. The effects of collection parameter variation upon DEM quality are also considered. The accuracy and precision of DEMs of submerged topography are evaluated using an independent data set. Results show that digital photogram-metry, if used in conjunction with image analysis techniques, can successfully be used to extract high-resolution DEMs of gravel riverbeds, but that the quality of submerged topographic representation is heavily dependent upon the water depth at the time of image acquisition. It is suggested that differences between the digital photogrammetric surface and the "actual" riverbed surface (as determined by terrestrial ground survey] will, in part, reflect the problem of defining what is the true elevation of a gravel-covered surface. A digital photogram-metric survey will generally see the tops of gravel cobbles, while a hand-held survey staff will tend to record the elevation between stones. The nomenclature of errors is also discussed, and it is concluded that the measure of surface quality adopted should be consistent with the application for which the DEM is to be used.
3D surface representation has long been a source of information describing surface character and facilitating an understanding of system dynamics from micro-scale (e.g. sand transport) to macro-scale (e.g. drainage channel network evolution). Data collection has been achieved through field mapping techniques and the use of remotely sensed data. Advances in this latter field have been considerable in recent years with new rapid-acquisition methods being developed centered around laser based technology. The advent of airborne and field based laser scanning instruments has allowed researchers to collect high density accurate data sets and these are revealing a wealth of new information and generating important new ideas concerning terrain characterisation and landform dynamics. The proposed book collates a series of invited peer revieved papers presented at the a conference on geoinformatics and LIDAR to be held at the National Centre for Geocomputation based in the National University of Ireland, Maynooth. Current constraints in field survey and DEM construction are reviewed together with technical and applied issues around the new technology. The utility of the data in process modelling is also covered. The book will be of great value to researchers in the field of geomorphology, geostatistics, remote sensing and GIS and will prove extremely useful to students and practitioners concerned with terrain analysis. The proposed work will: Highlight major technological breakthrough in 3D data collection. Feature examples of application across a wide range of environmental areas. Critically evaluate the role of laser based techniques in the environment. Detail theory and application of laser techniques in the natural environment.
The difficulties in obtaining reliable sediment transfer data from direct field measurement or from sediment transport formulae are widely recognized by geomorphologists and river engineers. Quantifying morphological changes (erosion and deposition) in rivers by the analysis of archive data or by field survey, however, can overcome many of these difficulties and provide a mechanism by which sediment budgets can be calculated over a variety of spatial and temporal scales. This paper applies three sediment budgeting methods based on morphological changes in a hypothetical braided reach. These methods range from a simple two-dimensional planform budget to more sophisticated three-dimensional cross-profile and morphological budgets. The development of each budget technique is described and the limitations and applicability of each identified. The three methods are then used to calculated sediment transfer rates in a multi-thread reach on the River Severn in mid-Wales, UK. Results show that across four budget periods spanning 2.5 years the reach was a net exporter of sediment. Application of the planform budget to eight time periods since 1836 shows a similar pattern of net sediment export in the nineteenth century, but during the majority of the twentieth century the reach was a net sediment sink. Finally, the applicability of applying budgeting techniques to extended centennial and millennial timescales is discussed and an assessment made of the role they might play in advancing our understanding of Holocene river dynamics and informing sustainable river management practices.
Synopsis
Detailed mapping and accurate heighting reveal the extent of a well-preserved terrace system whose highest fragments lie c. 40 m above contemporary stream level. Kame terraces, pitted outwash terraces, terraces dissected by braided rivers and fan terraces are identified. The terrace fragments form a valley train whose uppermost levels were produced when glacier ice was still present in the glen. As successive streams readjusted to postglacial hydrological conditions, they excavated the valley fill of glacial deposits and carved out the terraces. It is inferred that subsequent stream discharges were generally smaller than those associated with deglaciation at the end of the period of ice sheet wastage. Areally extensive, heavily dissected, low level terraces are suggested to have been produced by meltwaters from a later deglaciation at the end of Zone III.
This paper outlines some computational and methodological issues arising from the application of a two-dimensional hydrodynamic model to the Blyth Estuary, Suffolk. The Blyth serves as a case study for a programme of research into the environmental dynamics of anthropogenically modified estuaries in south-east England. Central to this work is the implementation of hydrodynamic and sediment transport models to characterize the present process regime; support further studies of intertidal processes; and, ultimately, provide a basis for the investigation of joint management and environmental change scenarios.
Advances in topographic survey and terrain modelling have enabled a revolution in the study in the fluvial morphodynamics in the last decade. Prior to the advent of electronic tacheometry in the 1990s, the analysis of channel dynamics was typically inferred from a combination of cross-section surveys and planform mapping. Distributed surveys acquired with GPS or EDMs enabled this analysis to be dimensionally extended and the pattern and magnitude morphodynamics elucidated in 3D; in particular through DTM differencing. Continuing developments in survey technology are now posed to reset this field once again. Now no longer confined to the laboratory, ruggedized laser scanners are capable of acquiring between 4-50,000 observations per second, at ranges exceeding 100 m. This latest development creates the potential for typical reach-scale (1-10 km) topographic datasets to rise in size by 7 orders of magnitude (hundreds to billions of points) in the coming years. Terrestrial Laser Scanning (TLS) offers a wealth of opportunities to better monitor fluvial systems; improving models of cut-and-fill, roughness and enhancing the prospect for ever more detailed parameterizations for fluid models. While this technology enables the creation of 'virtual facsimiles' of landscapes, the demands of storing, processing and modelling geomorphological products from such data requires a wholesale reappraisal of our data management and modelling methods. Here we outline a field-to-product methodology for TLS of fluvial systems using data from two annual surveys of a 1 km reach of the River Feshie, Scotland. These surveys delivered D point cloud datasets, incorporating over 200 million xyz observations, with median spatial densities of over 1000 pts/m2. The surveys were fixed to a GPS-based control network, including over 200 coincident tie- points to register multiple setups to a global coordinate system (RMS errors 0.002-0.011 m). Modelling reach-scale geometries from such dense point clouds poses a non-trivial computational problem and required the development of a bespoke spatial filtering toolbox. This was designed to allow intelligent decimation of TLS data and extract multi-resolution and statistical data suitable for describing bar-scale morphologies over the entire reach, whilst retaining grain-scale information. We use this toolbox to explore the precision and reliability of a morphological sediment budget for the study reach, following a 10 year flood in November 2006. The results are benchmarked against a traditional survey/DTM methodology based on GPS data.
The use of conventional survey methods to monitor large, gravel river beds has traditionally led to a reliance on repeat measurements of cross-sections which, unless very closely spaced, may give unreliable information about three-dimensional channel morphology and morphological change. Provided certain technological limitations can be overcome, remote survey techniques, such as digital photogrammetry and airborne laser scanning, remove the spatial and temporal constraints typically associated with ground-based surveys, allowing high spatial resolution, distributed, elevation mapping of gravel river beds. This paper develops the use of digital photogrammetry for the survey of a 3.3 km reach of the braided Waimakariri River, New Zealand, which, when combined with image analysis of water colour to infer water depth, provides a Digital Elevation Model (DEM) of the entire river bed. Central to the successful application of this method is DEM post-processing. Errors take two forms: (i) individual point errors associated with incorrect stereo-matching during automated data collection; and (ii) spatially-variable systematic errors that are associated with uncertainties in sensor position and orientation as determined during the bundle adjustment. An automated post-processing procedure is developed to deal with individual point errors and this improves DEM surface quality in terms of accuracy, precision and internal reliability. Systematic errors in the final DEM surface were reduced by applying a simple correction based on surveyed photo-control point elevations.
This paper focuses on developments in topographic data acquisition, including airborne remote sensing, digital photogrammetry, differential GPS, and laser profiling (e.g. LiDAR) technologies that allow rapid acquisition of high resolution and high precision topographic data sets over a range of spatial scales. These developments have offered new opportunities for investigating spatial and temporal patterns of morphological change in gravel-bed rivers and have contributed to revitalization in three key areas: (1) morphometric estimates of sediment transport and sediment budgeting; (2) boundary conditions for numerical models, including computational fluid dynamics and cellular modelling; (3) three dimensional characterisation of morphology that is independent of flow stage. The potential is clear but there remain a number of significant challenges, including quality control and the effects of error on specific applications and morphologies. This paper presents results from two investigations, representing field and laboratory analyses of gravel-bed river morphology at different spatial scales and for different applications. Case study 1 is concerned with monitoring and modelling morphological change in a large, braided gravel-bed river, using ground-based GPS survey and digital photogrammetry derived from airborne imagery. Case study 2 is an investigation of the mechanisms for infiltration of fine sediment into gravel-bed rivers, which applies close range laser altimetry in flume experiments to derive very high resolution digital elevation models (DEMs) that are used to quantify and analyse changes in bed texture. These case studies highlight the strengths and weaknesses of specific technologies and approaches to analysis of channel and floodplain morphology and change, and suggest key areas that remain to be fully resolved. In particular, the critical need to define a specific threshold level of detection associated with each acquisition method, and for different fluvial settings (e.g. bar surface, sub-aqueous zone), is emphasised.
The potential for mapping in-channel morphology within shallow gravel-bed rivers using airborne multispectral imagery and aerial photography is illustrated using a case study from the River Tummel, Scotland. The technique described relies on a good correlation between observed light reflectance levels from a water body and water depth. Measured water depths are regressed against reflectance levels derived from airborne multispectral imagery and black-and-white aerial photographs, to obtain equations that can be used for mapping channel bathymetry. The technique has a great deal of potential for wide-ranging applications, including detailed morphological surveys, assessing in-channel changes and mapping riverine habitats.© 1997 John Wiley & Sons, Ltd.
1. The River Feshie, a wandering gravel-bed river, has a prominent alluvial fan at its confluence with the River Spey forming a site of high conservation importance. The River Feshie is the best example of a relatively natural highly active gravel-bed river in the UK and the fan also contains one of the few remnants of Scotland's original floodplain forest cover.2. Channel switching and changes in gravel-bar morphology are a characteristic feature of this river. In recent years the river occupied a central position within the alluvial fan, until a major shift in the position of the channel to the southern sector of the fan occurred in 1990. However, riparian owners restored the flow to the original channel. In 1996, following this study, the channel again shifted course. This time no restoration of flow to the original course of the channel occurred and the river now follows a more northerly course. The old course is thus currently devoid of flow and pioneer species are starting to colonize the gravels.3. The natural vegetation on the alluvial fan and islands along the River Spey are a mosaic of grassland, partially vegetated gravel bars and woodland, the mosaic reflecting both channel and fan morphology and dynamics. Highest species diversity was on the riverine islands, followed by the woodland and grassland respectively. In total 129 plant species were recorded and identified within the area.4. In recent years there have been proposals to alter the location of the River Feshie and confine it to a more stable channel. In association with these channel works, dredging of the River Spey at the Feshie confluence would also be undertaken. These proposals prompted the research presented within this paper, and the results illustrate that the implementation of river training would lead to a loss of the site's unique character and vegetation diversity. Copyright © 2000 John Wiley & Sons, Ltd.
Cultural heritage recording and engineering surveying are prime applications for terrestrial laser scanners (TLSs) because of the high spatial resolution, high accuracy, and fast data capture rates this technology offers. To date, insufficient attention has been given to the many error sources contributing to the uncertainty of scanner datasets. A full error budget for directly georeferenced terrestrial laser scanner networks that considers both relevant error sources fundamental to surveying and those unique to sampled laser scanner systems is derived. In the case of the latter, new probabilistic models are proposed for angular positional uncertainty due to laser beamwidth and centroid-based target pointing. Analysis of a cultural heritage-recording project in Ayutthaya, Thailand, highlights the disparity between "expected" precision and the more realistic precision indicated by the error budget and demonstrates that the beamwidth error can be a significant factor. The causes and effects of several systematic errors inherent to TLS datasets are also discussed.
The long-awaited new edition of this classic text with its well-known "train wreck" cover. With twice the number of problems in this second edition, it is a valuable text and reference work for any student or instructor in the sciences and engineering.