ThesisPDF Available

Mapping of agricultural subsurface drainage systems using proximal and remote sensors

Authors:

Abstract and Figures

Soil as a three-phase system (solid particles, water and air) carries vital functions in the global ecosystems and is crucial for human societies as it acts as a medium for plant growth, purifies water for consumption by controlling the transport of contaminants, affects the earth’s atmosphere and is a habitat for many living organisms. For agricultural production, all three phases need to co-exist, hence the need for drainage of agricultural lands has long been realized, studied and practised by different civilizations over history. The widespread adoption of subsurface drainage practices started in the mid-19th century and since then they flourished concurrently with the intensification of agricultural activities to meet the growing population demand. Today, some of the most productive regions across the globe are a result of these artificial drainage systems that are mainly installed to remove the excess water in humid regions and prevent soil salinization in arid and semi-arid regions. Agricultural subsurface drainage systems provide many agronomic, economic, and environmental benefits. However, if improperly managed they have deleterious effects on the environment as they shorten pathways for the transport of solutes to the aquatic ecosystems. Thus, knowledge of these buried drainage pipes’ location is crucial to comprehend the hydrology and solute dynamics and plan effective mitigation strategies. This knowledge can also benefit drainage water management, a conservation practice that is increasingly being adopted to modulate the water table where a control structure can be retrofitted to the existing drainage system and on the contrary, for the drainage intensification, as it is a typical practice to install the new drainage system in between the existing one. Despite this, the location of the drainage systems is often poorly documented or entirely unknown. Conventional methods (tile probes and trenching equipment) for finding drainage pipes are invasive, tedious and causes pipe damage. Therefore, there is a growing need to find rapid, effective and non-destructive methods for drainage mapping purpose. Previous research showcases that proximal and remote soil and crop sensing methods may provide a potential alternative solution – amongst which maximum success was achieved by employing a ground penetrating radar (GPR) and aerial imagery captured using different cameras. Recent technological advances led to rapid developments in these techniques. While this constitutes the development of a 3D-GPR capable of scanning an ultra-wideband frequency with an antenna array of wide-area swathe, on another front, the unmanned aerial vehicle (UAV) and their associated cameras have become cheaper than ever making them flexible and feasible to capture aerial imagery. Hence, this dissertation aims at mapping subsurface drainage systems with state-of-the-art proximal and remote sensing methods (i.e. GPR and UAV imagery). A novel magnetic gradiometer (tMag) was also used but only to a limited extent and further research was discontinued owing to the lack of success. In relation to the stepped-frequency continuous wave 3D-GPR, firstly, at one study site in Denmark, the performance of the system was assessed for different survey configurations (i.e. ground-coupled vs air-coupled) and site conditions (i.e. dry vs wet soil) to discern optimal setup and timing for performing the drainage mapping surveys (Paper V). Out of the combinations tested, a clearer drainage pipe response (i.e. hyperbolic patterns in the vertical profiles) was observed in the survey carried on wet soil with snow cover, however, the ringing noise was substantial at places and prevented the detection of the shallow drainage pipes. The surveys performed on dry soil showed a similar drainage pipe response in both the survey configurations. Later, a thorough assessment of a 3D-GPR was made based on a study conducted at 12 sites in Denmark on a variety of soil types (Paper I). Here, algorithms were developed for calculating global and localized penetration depth (PD). Two different approaches were tested for determining the localized PD. While the first approach was qualitative and helpful to comprehend the attenuation characteristics of the subsurface, the second approach permitted quantification and allowed comparison between different study sites. In both approaches, efforts were made to comprehend the support extended by the electrical conductivity (EC) measured using electromagnetic induction (EMI) instrument to evaluate the performance of the 3D-GPR in finding the drainage pipes. Overall, a high success rate was observed at five amongst the 12 sites visited. At seven sites, the 3D-GPR demonstrated less success owing to a high soil EC (thus limiting the 3D-GPR PD) and the driving direction being parallel to the drainage pipe orientation. In relation to the UAV imagery, the studies conducted in Midwest U.S.A showcases the swiftly evolving UAV technology and associated cameras as a cost-effective and feasible tool for the drainage mapping purpose. More specifically, to determine the overall feasibility, a comprehensive set of UAV surveys were performed at 29 sites using visible-colour (VIS-C), multispectral (M.S) and thermal infrared (TIR) cameras covering a variety of soil types, surface and wetness conditions (Paper III). Amongst the three cameras employed, the imagery captured by the TIR camera (at 69% of the sites) was more successful in detecting the drainage signature (i.e. shaded linear features) in comparison to the M.S (59%) and VIS-C (48%) cameras. The key findings of this study were: (1) at some sites the M.S and VIS-C cameras were more effective than TIR camera, (2) prior rainfall events can sometimes have an important impact, hence the timing is crucial, and (3) under most circumstances, farm field operations (i.e. wheel tracks or crop residue) produced similar signature as the drain lines. For the latter, to avoid confusion, knowledge of the drainage installations and farm field operations could be employed to distinguish them. Moreover, as TIR imagery proved superior when compared to VIS-C, M.S cameras for the drainage pipe detection, the time of the day impact on capturing the TIR imagery was evaluated based on a set of sunrise to sunset surveys (Paper IV). The surveys performed during sunrise/sunset sometimes provided excellent results as it was easier to distinguish the drainage pipes’ signature (i.e. darker shaded linear features) from those caused due to farm field operations (i.e. lighter shaded linear features). However, occasionally problems were encountered in processing (i.e. stitching) the data. Less to no problems occurred for processing the data acquired from late morning through late afternoon surveys. Nevertheless, a similar drainage pipe response was observed as that of farm field operations, therefore impeding their discrimination. The combined ability of the GPR and UAV imagery was also tested as both the techniques differ in the mode of usage, applicability, and the properties they measure or respond to. Further, the techniques demonstrated their own advantages and drawbacks in relation to drainage mapping. This time, a time-domain GPR system was employed instead of the frequency-domain 3D-GPR discussed earlier. The study was conducted at four sites in the Midwest U.S.A, to compare and contrast both the methods (Paper II). While the UAV surveys covered the entire field area, the GPR data were acquired only on a limited spatial extent preferably in the direction perpendicular to the drain line orientation. In instances, where the UAV imagery partly/completely failed to capture the drainage pipes’ location, GPR proved useful to map them. In instances, where the UAV imagery was successful, GPR acted as a suitable validation technique (i.e. to discriminate the linear features). Furthermore, GPR provided depth information of the drainage pipes and insights on the soil drainage status (i.e. drained/undrained). Nonetheless, there was also a site where the GPR failed to locate the drainage pipes, whereas UAV imagery proved successful in mapping them. Therefore, both the techniques proved complementary in subsurface drainage mapping. Based on the above studies presented in this dissertation and previous research, it can be ascertained that there is “no silver bullet”, i.e. there is no single technique that can be used across all agricultural fields with different soil types and hydrological conditions, for mapping subsurface drainage systems. Hence, an attempt was made to develop guidelines for carrying out the drainage mapping surveys, especially concerning the sensors (i.e. GPR and UAV imagery) employed in this dissertation and suitable recommendations are provided for their individual and combined usage.
Content may be subject to copyright.
A preview of the PDF is not available
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
With the growing concerns of water quality related to tile drainage in agricultural lands, developing an efficient and cost-effective method of mapping tile drainage is essential. This research aimed to establish mapping of tile drainage systems in agricultural fields using optical and radiometric thermal sensors mounted on Unmanned Aerial System (UAS). The overarching hypothesis is that in a tile-drained land, spatial distribution of soil water content is affected by tile lines, therefore, contrasting soil temperature signals exist between areas along the tile lines and between the tile lines. Designated flights were conducted to assess the effectiveness of the UAS under various conditions such as rainfall, crop cover, crop maturity and time of the day. Image correction, mosaicking, image enhancements and map production were conducted using Agisoft and ENVI image analysis software. The results showed intermediate growth stage of soybean plants and rainfall helped delineating tile lines. In-situ soil temperature measurements revealed appropriate time of the day (14:00 to 18:00 h) for thermal image detection of the tile lines. The role of soil moisture and plant cover is not resolved, thus, further refinement of the approach considering these factors is necessary to develop efficient mapping techniques of tile drainage using UAS thermal and optical sensors.
Article
Full-text available
Subsurface drainage systems are commonly used to remove surplus water from the soil profile of a poorly drained farmland. Traditional methods for drainage mapping involve the use of tile probes and trenching equipment that are time-consuming, labor-intensive, and invasive, thereby entailing an inherent risk of damaging the drainpipes. Effective and efficient methods are needed in order to map the buried drain lines: (1) to comprehend the processes of leaching and offsite release of nutrients and pesticides and (2) for the installation of a new set of drain lines between the old ones to enhance the soil water removal. Non-invasive geophysical soil sensors provide a potential alternative solution. Previous research has mainly showcased the use of time-domain ground penetrating radar, with variable success, depending on local soil and hydrological conditions and the central frequency of the specific equipment used. The objectives of this study were: (1) to test the use of a stepped-frequency continuous wave three-dimensional ground penetrating radar (3D-GPR) with a wide antenna array for subsurface drainage mapping and (2) to evaluate its performance with the use of a single-frequency multi-receiver electromagnetic induction (EMI) sensor in-combination. This sensor combination was evaluated on twelve different study sites with various soil types with textures ranging from sand to clay till. While the 3D-GPR showed a high success rate in finding the drainpipes at five sites (sandy, sandy loam, loamy sand, and organic topsoils), the results at the other seven sites were less successful due to the limited penetration depth of the 3D-GPR signal. The results suggest that the electrical conductivity estimates produced by the inversion of apparent electrical conductivity data measured by the EMI sensor could be a useful proxy for explaining the success achieved by the 3D-GPR in finding the drain lines.
Article
Full-text available
Nutrient losses from agricultural fields have long been a matter of concern worldwide due to the ecological disturbance this can cause to surface waters downstream. In this paper a new design concept, which pairs a surface-flow constructed wetland (SFW) with a woodchip bioreactor (WB), was tested in relation to its capacity to reduce both nitrogen (N) and phosphorus (P) loads from agricultural tile drainage water. A nutrient mass balance and a comparative analysis were carried out together with statistical regressions in order to evaluate the performance of four SFW+WBs under different catchment conditions. We found marked variations between the systems in regard to hydraulic loading rate (0.0 to 5.0 m/day) and hydraulic retention time (1 to 87 days). The paired system worked as nutrient sinks throughout the study period. Total N and total P removal efficiencies varied from 8% to 51% and from 0% to 80%, respectively. The results support the use of the new design concept for nutrient removal from tile-drained agricultural catchments in Denmark as part of national management plans, with the added advantage that smaller areas are needed for construction (0.1% to 0.2% of the catchment area) in comparison to standalone and currently used SCWs (~1%).
Article
Full-text available
Agricultural drainage plays an important role worldwide in food production and conservation of soil resources, while safeguarding investments in agricultural production and irrigation projects. It can improve crop yields and land productivity, especially on poorly drained soils and in cases of prolonged waterlogging. Both the subsurface drainage materials and the installation techniques used have a long history dating to prehistoric times. Over time, new subsurface drainage materials, installation techniques and modernized equipment were being developed continuously to take advantage of technological advances provided through research and development, while the planning and organization of the implementation process were improved. Today’s new materials and improved installation methods can offer solutions to problems still unsolved, while sometimes creating new ones. This paper considers the evolution of basic subsurface drainage materials and their installation techniques as they developed and adapted over time as well as possible future trends in drainage system design and application.
Article
Full-text available
The aim of this study was to identify the tile drainage systems within the year (from spring to autumn) using the ground penetrating radar (GPR) geophysical method. The measurements were performed in the experimental locality Dehtáře in the Bohemo-Moravian Highland (Czech Republic) in the years 2016 and 2017. The profiles located in the drained area were repeatedly measured together with the drainage discharges, soil moisture and groundwater level. The best visibility of tile drains was observed during snowmelt (in March and April) when the drainage discharges usually reach their maximum. In other months, the visibility of the drains was variable, but mostly worse. For a reliable detection of individual drains, the measurements above the drainage must be performed in several profiles. Under the conditions of the Czech Republic, the best results were obtained by a 500 MHz frequency antenna.
Article
Full-text available
Effective and efficient methods are needed to map agricultural subsurface drainage systems. Visible-color (VIS-C), multispectral (MS), and thermal infrared (TIR) imagery obtained by unmanned aerial vehicles (UAVs) may provide a means for determining drainage pipe locations. Aerial surveys using a UAV with VIS-C, MS, and TIR cameras were conducted at 29 agricultural field sites in the Midwest U.S.A. to evaluate the potential of this technology for mapping buried drainage pipes. Overall results show VIS-C imagery detected at least some drain lines at 48 % of the sites (14 out of 29), MS imagery detected drain lines at 59 % of the sites (17 out of 29), and TIR imagery detected drain lines at 69 % of the sites (20 out of 29). Three key findings, listed as follows and emphasized in this article by site examples, were extracted from the overall results. (1) Although TIR generally worked best, there were sites where either VIS-C or MS proved more effective than TIR for mapping subsurface drainage systems. Consequently, to ensure the greatest chance for successfully determining drainage pipe patterns in a field, UAV surveys need to be carried out with all three types of cameras, VIS-C, MS, and TIR. (2) Timing of UAV surveys relative to recent rainfall can sometimes have an important impact on drainage pipe detection results. (3) Linear features representing drain lines and farm field operations can be confused with one another and are often both depicted on site aerial imagery. Knowledge of subsurface drainage system installation and farm field operations can be employed to distinguish linear features representing drain lines from those representing farm field operations. The overall results and extracted key findings from this study clearly indicate that VIS-C, MS, and TIR imagery obtained with UAVs have significant potential for use in mapping agricultural drainage pipe systems.
Article
Full-text available
Agricultural developments require changes in land surface and subsurface hydraulic functions as protection from floods, reclamation of flooded land, irrigation, and drainage. Drainage of agricultural land has a long history and apparently traces back to the earliest civilizations of Mesopotamia and Iran before 4000 BC. In the Eastern Mediterranean, the Minoan and Mycenaean civilizations developed techniques and strategies of drainage of agricultural lands from the middle of the 2nd millennium BC. After the collapse of the Aegean Bronze-age civilizations, society building and agricultural innovation in the archaic and Classical periods (ca. 800-300 BC) included successful attempts at controlling drainage and irrigation techniques. In addition, China, India, and Mesoamerica have extensive histories of drainage. The aim of this review paper is to trace the evolution of the main foundings on agricultural drainage technologies through the centuries until the present. This historical review reveals valuable insights into ancient hydraulic technologies as well as irrigation and drainage management that will help to find bright horizons for sustainable agriculture in future.
Conference Paper
Full-text available
Subsurface drainage systems are commonly installed in agricultural areas to remove the excess soil water. Knowledge of the position of the existing drainage network is often lacking. This complicates 1) the understanding of increased leaching and offsite release of nutrients and in turn the development of eutrophication mitigation strategies and 2) retrofitting the new drain lines within the existing drainage system to increase drainage efficiency. The conventional methods of drainage mapping include the use of tile probe and trenching equipment, which are invasive, laborious and often inefficient to apply at large spatial scales. Recent technological developments in non-destructive techniques (NDT) provide a potential alternative solution. In this study, we explore the suitability of unmanned aerial vehicle (UAV) imagery collected using three different cameras (visible-color, multispectral and thermal infrared) and a ground penetrating radar (GPR) for subsurface drainage mapping. Both these techniques are complementary in terms of their usage, applicability and the properties they measure. While UAV imagery is useful in measuring surface soil and plant properties and the flights can cover large areas in limited time, the GPR works the best to understand subsurface variation in soil electrical properties and is comparatively hard to employ across large areas. Both these techniques were applied at three different sites near Mount Gilead, OH; Clayton, MI and Palmyra, MI in the Midwest U.S. At the Mount Gilead site, it was possible to delineate the location of drainage pipes using both the UAV imagery and GPR, hence, providing a suitable validation technique and depth information. At the Clayton site, while UAV imagery was successful on the western part of the field, GPR proved to be useful in the eastern part where the UAV imagery failed to capture the drainage pipe locations. At the Palmyra site, less to no success was observed in finding the drain lines using UAV imagery, while good success was achieved using the GPR. Although UAV imagery seems to be an attractive solution for mapping subsurface drainage systems as it is cost-effective and can cover large field areas, the results suggest the usefulness of GPR to complement the UAV imagery as both a mapping and validation technique. Future research focuses on understanding the dependence of the UAV imagery and GPR on the soil type, crop residue, tillage practice, ground wetness level and rainfall event prior to the surveys with the aim of developing guidelines in relation to the choice of sensor for subsurface drainage mapping.
Article
Phosphorus (P) leaching from agricultural to tile drainage land contributes to nonpoint pollution of surface waters. Drainage filter technologies are potentially cost-effective technologies at the field scale for mitigating P losses. The objective of this study was to evaluate the removal efficiency for dissolved P (PRE) in a porous reactive filter constructed from crushed seashells, which was part of a full-scale filter system. The hydraulic properties (hydrodynamic and hydrodispersive) were estimated by performing salt (NaCl) tracer tests at two different flow rates representative for in situ discharge conditions in Denmark. The reactive properties of the filter material were determined in the laboratory by measuring P sorption in batch experiments. The hydraulic and reactive parameters were subsequently used as input parameters in a numerical model, which was calibrated based on flow data and dissolved P concentrations collected between May 2015 and 2017. Results show a homogeneous distribution of the tracer in drainage water outside the reactive P-filter and a uniform dissolved P load into the seashell material. The in situ saturated hydraulic conductivity was one order of magnitude lower than the estimation from previous column experiments. The model described accurately dissolved P concentrations at the filter outlet (Nash-Sutcliffe index = 0.79) and the P removal efficiency (PRE) of the reactive filter was equal to 62% during the monitored period. The model presented in this work can be integrated in a larger model addressing the complexity of P sorption processes for the evaluation of the removal efficiency in full-scale filter systems.
Article
The use of drainage pipe is documented as far back as 200 B. C. and continues to be used in poorly drained agricultural regions throughout the world. While good for crop production, the eco-hydrologic impacts of this modification have been shown to adversely affect natural drainage networks. Identifying the exact location of drainage pipe networks is essential to developing groundwater and surface water models. The geometry of drainage pipe networks installed decades ago has often been lost with time or was never well documented in the first place. Previous work has recognized that drainage pipes can be observed for certain soil types in visible spectrum (RGB) remote sensing data due to changes in soil albedo. In this work, small Unmanned Aerial Systems (sUAS) were used to collect high resolution RGB and thermal data to map subsurface drainage pipe. Within less than 96 h of a small (< 1.3 cm) rain event, a total of approximately 60 ha of sUAS thermal and RGB data were acquired at two different locations in the IML-CZO in Illinois. The thermal imagery showed limited evidence of thermal contrast related to the drainage pipe. If the data were acquired immediately after a rain event it is more likely a temperature contrast would have been detected due to lower soil moisture proximal to the drainage pipe network. The RGB data, however, elucidated the drainage pipe entirely at one site and elucidated traces of the drainage pipe at the other site. These results illustrate the importance of the timing of sUAS data collection with respect to the precipitation event. Ongoing related work focusing on laboratory and numerical experiments to better quantify feedbacks between albedo, soil moisture, and heat transfer will help predict the optimal timing of data collection for applications such as drainage pipe mapping.