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Changes in the equilibrium river profile due to interventions



Human interventions can result in changes in the equilibrium profile of rivers. It is difficult to identify the bed level changes that result from river interventions due to the various causes of bed level changes. Using wavelet filtering, we are able to isolate the effect of river interventions based on the length scale over which they occur. The method presented here can aid in verifying model results. In addition, it can be used to estimate bed level changes that occur over various spatial scales.
River interventions are carried out with various objectives such as increasing the discharge ca-
pacity of the river (e.g., van Denderen et al., 2019), increasing the ecological value of the river
(e.g., Riquier et al., 2015) and to mitigate the impact of human interventions on the river planform
(e.g., Formann et al., 2007). Such river interventions generally reduce the discharge conveyance
in the main channel and this reduces the sediment transport capacity of the channel. The reduced
sediment transport capacity is compensated locally by the river with an increase in the bed level,
i.e. a decrease in the water depth, and an increase of the local bed slope (de Vriend, 2015). These
morphological effects can have a negative impact on functions of the river, such as navigation
(van Vuren et al., 2015), and, at the same time, can have a positive effect on large-scale bed level
changes, such as large-scale bed degradation that results from engineering measures from the
past. The amount of aggradation that occurs due to the construction of the river intervention is a
function of the discharge that occurred. The objective of this paper is to identify the bed level
changes that occurred due to the construction of longitudinal dams in the river and show the var-
iation of this aggradation over time. Longitudinal dams replace groynes and create a secondary
channel within the main channel (Havinga et al., 2009, Collas et al., 2018, de Ruijsscher et al.,
2019). The secondary channel reduces the discharge conveyance of the main channel and thereby
the sediment transport capacity resulting in aggradation. The secondary channel does not attract
discharge during base flow conditions and in combination with a narrower main channel, the
effect on the water depth during base flow conditions should be minimal.
We focus on the bed level in the river Waal in the Netherlands. The river Waal is the largest of
the Dutch Rhine branches and, because of its important navigational function, the bed level is
measured every two weeks using multi-beam echosounders since 2005. As part for the Room for
the River project the groynes in the river were replaced with longitudinal dams in 2015. This
created a secondary channel and is expected to cause aggradation in the main channel. The bed
level changes in the river occur over various spatial and temporal scales, and can have various
causes. Using a wavelet transform we are able to differentiate between the spatial scales of the
bed level changes (Torrence and Compo, 1998, Gutierrez et al., 2013). We choose the spatial
Changes in the equilibrium river profile due to interventions
R.P. van Denderen
University of Twente, Enschede, The Netherlands
E. Kater & L.H. Jans
Ministry of Infrastructure and Water Management-Rijkswaterstaat, Arnhem, The Netherlands
R.M.J. Schielen
Ministry of Infrastructure and Water Management-Rijkswaterstaat, Lelystad, The Netherlands
Delft University of Technology, Delft, The Netherlands
ABSTRACT: Human interventions can result in changes in the equilibrium profile of rivers. It is
difficult to identify the bed level changes that result from river interventions due to the various
causes of bed level changes. Using wavelet filtering, we are able to isolate the effect of river
interventions based on the length scale over which they occur. The method presented here can aid
in verifying model results. In addition, it can be used to estimate bed level changes that occur over
various spatial scales.
range such that small scale changes such as bed forms and large-scale changes such as the large-
scale bed degradation are filtered out. Using the wavelet transform we can isolate the bed level
changes that are caused by the construction of river interventions and the bed level changes that
are caused by local variations of the river’s geometry.
Figure 1 shows the bed level in time in the main channel parallel to the longitudinal dams that
were construction in 2015. The second graph shows the filtered bed level variation around the
time-averaged bed level. Here we can see that large aggradation occurs at the upstream end of the
intervention (yellow areas in Figure 1). This corresponds with the sudden reduction of the sedi-
ment transport capacity in the main channel. At the downstream end, the geometry results in an
acceleration of the flow resulting in large scour (dark blue in Figure 1). The out and inflow of the
other secondary channels cause similar effects, but smaller because the largest gradient in sedi-
ment transport capacity occurs at the upstream and downstream end of the intervention. Figure 2
shows the bed level change averaged over the length of the intervention. The raw data clearly
shows the large-scale bed degradation that occurs in this part of the river. With the wavelet filter-
ing, we can ignore such large scale effects and focus on the bed level changes that are a direct
result of the intervention. It is clear that the average bed level continues to aggrade and that a new
equilibrium has not yet been reached.
Figure 1 Top: The bed level in the main channel as a function of time. Bottom: The bed level variation
around the time-averaged value filtered using the wavelet transform. The red vertical lines denote the
upstream and downstream end of the intervention. The white horizontal and vertical lines are caused by
missing data.
The equilibrium bed profile of a river changes due to river interventions. Such changes can have
secondary negative effects on other functions of the river. Using the wavelet filtering we are able
to identify the bed level changes that occur due to the interventions while ignoring both smaller
scale and larger scale bed level changes. The method presented here can aid in verifying model
results. In addition, it can be used to estimate bed level changes in rivers that occur over various
spatial scales.
This research is supported by TKI Deltatechnology (UTW01), the Ministry of Infrastructure and
Water Management-Rijkswaterstaat and by the Netherlands Organisation for Scientific Research
(NWO), which is partly funded by the Ministry of Economic affairs, under grant number P12-
P14 (RiverCare Perspective Programme) project number 13516. This research has benefited from
cooperation within the network of the Netherlands Centre for River studies.
Collas, F.P.L., Buijse, A.D., Van den Heuvel, L., Van Kessel, N., Schoor, M.M., Eerden, H. & Leuven,
R.S.E.W. 2018. Longitudinal training dams mitigate effects of shipping on environmental
conditions and fish density in the littoral zones of the river Rhine. Science of The Total
Environment, 619-620, 1183-1193.
De Ruijsscher, T.V., Hoitink, A.J.F., Naqshband, S. & Paarlberg, A.J. 2019. Bed morphodynamics at the
intake of a side channel controlled by sill geometry. Advances in Water Resources, 134.
De Vriend, H. 2015. The long-term response of rivers to engineering works and climate change.
Proceedings of the Institution of Civil Engineers - Civil Engineering, 168, 139-144.
Formann, E., Habersack, H.M. & Schober, S. 2007. Morphodynamic river processes and techniques for
assessment of channel evolution in Alpine gravel bed rivers. Geomorphology, 90, 340-355.
Gutierrez, R.R., Abad, J.D., Parsons, D.R. & Best, J.L. 2013. Discrimination of bed form scales using robust
spline filters and wavelet transforms: Methods and application to synthetic signals and bed forms
of the Río Paraná, Argentina. Journal of Geophysical Research: Earth Surface, 118, 1400-1418.
Havinga, H., Schielen, R.M.J. & Van Vuren, S. Tension between navigation, maintenance and safety calls
for an integrated planning of flood protection measures. Proceedings of River, Coastal, Estuarine
Morphodynamics - RCEM Conference, 2009 Santa Fe, Argentina.
Riquier, J., Piégay, H. & Michalková, M.S. 2015. Hydromorphological conditions in eighteen restored
floodplain channels of a large river: linking patterns to processes. Freshwater Biology, 60, 1085-
Figure 2 The bed level averaged over the length of the intervention with and without the wavelet filtering.
The dotted vertical lines denote peak flow events.
Torrence, C. & Compo, G. P. 1998. A practical guide to wavelet analysis. Bulletin of the American
Meteorological Society, 79, 61-78.
Van Denderen, R.P., Schielen, R.M.J., Westerhof, S.G., Quartel, S. & Hulscher, S.J.M.H. 2019. Explaining
artificial side channel dynamics using data analysis and model calculations. Geomorphology, 327,
Van Vuren, S., Paarlberg, A. & Havinga, H. 2015. The aftermath of “Room for the River” and restoration
works: Coping with excessive maintenance dredging. Journal of Hydro-environment Research, 9,
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
As part of a general trend towards river management solutions that provide more room for the river, longitudinal training dams (LTDs) have recently been constructed in the inner bend of the Dutch Waal River, replacing groynes. LTDs split the river in a main channel and a bank-connected side channel with a sill at the entrance. In the present study, a physical scale model with mobile bed was used to study morphological patterns and discharge division in the entrance region of such a side channel. Alternative geometric designs of the sill are tested to investigate the controls on the diversion of water and sediment into the side channel. After reaching a morphodynamic equilibrium, two bar features were observed in the side channel under low flow conditions. An inner-bend depositional bar emerged against the LTD, resembling depositional bars observed in sharp river bends. A second bar occurred in the most upstream part of the side channel, next to the sill, induced by divergence of the flow by widening of the channel and an increasing flow depth after the sill, hence defined as a divergence bar. The morphologically most active system in the side channel emerges for the configuration in which the sill height decreases in downstream direction. For such a geometry, the sediment that settles during low flow is largely eroded during high flow, reducing maintenance needs. A qualitative comparison based on a lab experiment mimicking field conditions demonstrates the realism of the experiments.
Conference Paper
Full-text available
Along the Dutch Rhine branches a vast flood protection scheme according to the Room for the River principle is planned. Execution of some 40 projects has to be completed in 2015, costing €2.1 billion, and taking into account increase of landscape quality (by constructing side channels and natural vegetation). The responsible Dutch Ministry of Public Works, Transport and Watermanagement has handed over the preparation of many projects to local authorities to obtain the necessary public support and to facilitate combinations with local developments. The preliminary designs of many flood level reduction plans show that the inland navigation interests and future maintenance (governmental interest) did get too little attention. To prevent a serious conflict of interests between flood protection, inland navigation and ecology the side effects of increased flood conveyance which may cause serious shoaling in the low water channel must be dealt with. Introduction of natural vegetation and alluvial elements in the floodplain (side channels) intensify maintenance efforts. A system of vegetation and morphological monitoring and regular intervention to set back vegetation succession and morphological developments is demanded to guarantee the targeted design flood levels. 2D morphological computations can adequately calculate effects of the flood protection plans to inland navigation. If proper morphological analyses will not be carried out from the very beginning sub-optimal designs in the final project phase may be the result.
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1. Over the past few decades, numerous floodplain restoration projects have attempted to re-establish complex and diverse river floodplains. They often aim to restore lateral connectivity (i.e. interactions between the main river channel and floodplain channels) and rejuvenate floodplain habitats which are no longer maintained or created by fluvial processes. Nonetheless, results of these experiences in terms of hydromorphological conditions and adjustments are rarely shared. 2. The Rhône River is a large, highly regulated system where lateral connectivity has been greatly reduced. We investigated habitat dynamics (using sedimentological indicators as proxies) in 18 floodplain channels that were restored between 1999 and 2006. Environmental data (bathymetry and grain size of surficial fine sediments) were acquired on 3–5 surveys for each channel covering 6–12 years after restoration. In addition, a pre-restoration survey was made in 12 of the 18 channels. 3. Using pressure sensors in the floodplain channels and rating curves in the main channel, we quantified the upstream overflow frequency and magnitude (i.e. maximum shear stress) in the channels and tested how these variables explain observed sedimentological patterns. 4. Between-channel diversity accounted for 81% of the sedimentological variability observed after restoration. Time-averaged sedimentological conditions were robust and well predicted from overflow frequency and magnitude. Similarly, an indirect index of lateral connectivity used by hydrobiologists was also predictable from overflow frequency and magnitude. 5. The remaining 19% of the sedimentological variability was attributed to temporal variation within channels and was mainly related to changes in longitudinal grain size gradient. This emphasises that grain size patterns are periodically reworked as a result of the flooding regime (backflow versus overflow) without significantly affecting average grain sizes. However, trajectories of grain size changes were stochastic and not always related to the hydrological regime. Accordingly, the partial pre-restoration data suggest that post-restoration sedimentological conditions were often similar to those observed before restoration, except in a few channels where major restoration works were performed. 6. Our results quantify how changes in upstream overflow frequency and magnitude can modify physical conditions in the floodplain channels. They can be used to design habitats that are infrequent or missing at the floodplain scale. These results also suggest that changes in upstream plug morphology are a primary habitat driver. Such changes could be more frequently implemented in the Rhône and elsewhere to maximise the diversity of physical conditions in floodplains.
Side channel construction is a common intervention to increase both flood safety and the ecological value of the river. Three side channels of Gameren in the river Waal (The Netherlands) show amounts of large aggradation. We use bed level measurements and grain size samples to characterize the development of the side channels. We relate the bed level changes and the deposited sediment in the side channels to the results of hydrodynamic computations. Two of the three side channels filled mainly with suspended bed-material load. In one of these channels, the bed level increased enough that vegetation has grown and fine suspended load has settled. In the third side channel, the bed shear stresses are much smaller and, in addition to the suspended bed-material load, fine sediment settles. Based on the side channel system at Gameren, we identify two types of side channels: one type fills predominantly with suspended bed-material load from the main channel and a second type fills predominantly with fine suspended load. This gives an indication of the main mechanisms that lead to the aggradation in artificial side channel systems.
The stability of habitat conditions in littoral zones of navigated rivers is strongly affected by shipping induced waves and water displacements. In particular, the increase of variability in flow conditions diminishes the suitability of these habitats for juvenile fishes. Recently, a novel ecosystem based river management strategy has resulted in the replacement of traditional river training structures (i.e., groynes) by longitudinal training dams (LTDs), and the creation of shore channels in the river Waal, the main, free-flowing and intensively navigated distributary of the river Rhine in the Netherlands. It was hypothesized that these innovative LTDs mitigated the effects of shipping on fishes by maintaining the natural variability of habitat conditions in the littoral zones during ship passages whereby shore channels served as refugia for juvenile fishes. Measurements of abiotic conditions showed a significantly lower water level fluctuation and significantly higher flow stability in shore channels compared to groyne fields. Flow velocity did not differ, nor did the variation in flow velocity fluctuation during ship passage between these habitats. Densities of fish were found to be significantly higher in the littoral zones of shore channels compared to nearby groyne fields. Moreover, electrofishing along the inner side of the newly constructed LTD showed a significant linear relationship between fish density and distance from highly dynamic in-and outflow sections and to lowered inflow sections in the LTD. Results of our field sampling clearly indicate successful ecological rehabilitation of littoral zones that coincides with a facilitation of navigation in the main river channel and increased flood safety.
Rivers respond to changes in their geometry or their controls in various ways and at a wide range of space and time scales. The response consists of changes in properties such as cross-sectional shape and area, slope, planform pattern, bed roughness and bed sediment composition. Usually, attention for the morphological impact of engineering works focuses on short-term effects. The usually much slower, but also much more persistent large-scale response is often ignored, or countermeasures are ineffective. In many cases this has led to extra maintenance costs, in some even to hazardous situations or disaster. This paper refreshes and extends long-existing but seemingly forgotten knowledge on large-scale river behaviour. It gives examples of impacts of engineering works, climate change and sea level rise, discusses potential countermeasures and gives a number of general conclusions on the large-scale morphological behaviour of lowland rivers.
In the 19th and early 20th centuries, the Rhine in the Netherlands has been heavily trained for the purpose of safe discharge of water, sediment and ice, and a better navigability. Currently a large number of new river intervention works are planned and built within the Room for the River Program (RfR) and the European Water Framework Directive (WFD). The measures increase the flood conveyance capacity as well as biodiversity. Popular measures are dike setback, lowering flood plains, reconnecting side channels and removal of bank defenses. Improving conditions for inland navigation has not been a design criterion in these RfR and WFD projects.
A practical step-by-step guide to wavelet analysis is given, with examples taken from time series of the El NiñoSouthem Oscillation (ENSO). The guide includes a comparison to the windowed Fourier transform, the choice of an appropriate wavelet basis function, edge effects due to finite-length time series, and the relationship between wavelet scale and Fourier frequency. New statistical significance tests for wavelet power spectra are developed by deriving theoretical wavelet spectra for white and red noise processes and using these to establish significance levels and confidence intervals. It is shown that smoothing in time or scale can be used to increase the confidence of the wavelet spectrum. Empirical formulas are given for the effect of smoothing on significance levels and confidence intervals. Extensions to wavelet analysis such as filtering, the power Hovmöller, cross-wavelet spectra, and coherence are described. The statistical significance tests are used to give a quantitative measure of changes in ENSO variance on interdecadal timescales. Using new datasets that extend back to 1871, the Niño3 sea surface temperature and the Southern Oscillation index show significantly higher power during 1880-1920 and 1960-90, and lower power during 1920-60, as well as a possible 15-yr modulation of variance. The power Hovmöller of sea level pressure shows significant variations in 2-8-yr wavelet power in both longitude and time.
[1] There is no standard nomenclature and procedure to systematically identify the scale and magnitude of bed forms such as bars, dunes, and ripples that are commonly present in many sedimentary environments. This paper proposes a standardization of the nomenclature and symbolic representation of bed forms and details the combined application of robust spline filters and continuous wavelet transforms to discriminate these morphodynamic features, allowing the quantitative recognition of bed form hierarchies. Herein the proposed methodology for bed form discrimination is first applied to synthetic bed form profiles, which are sampled at a Nyquist ratio interval of 2.5–50 and a signal-to-noise ratio interval of 1–20 and subsequently applied to a detailed 3-D bed topography from the Río Paraná, Argentina, which exhibits large-scale dunes with superimposed, smaller bed forms. After discriminating the synthetic bed form signals into three-bed form hierarchies that represent bars, dunes, and ripples, the accuracy of the methodology is quantified by estimating the reproducibility, the cross correlation, and the standard deviation ratio of the actual and retrieved signals. For the case of the field measurements, the proposed method is used to discriminate small and large dunes and subsequently obtain and statistically analyze the common morphological descriptors such as wavelength, slope, and amplitude of both stoss and lee sides of these different size bed forms. Analysis of the synthetic signals demonstrates that the Morlet wavelet function is the most efficient in retrieving smaller periodicities such as ripples and smaller dunes and that the proposed methodology effectively discriminates waves of different periods for Nyquist ratios higher than 25 and signal-to-noise ratios higher than 5. The analysis of bed forms in the Río Paraná reveals that, in most cases, a Gamma probability distribution, with a positive skewness, best describes the dimensionless wavelength and amplitude for both the lee and stoss sides of large dunes. For the case of smaller superimposed dunes, the dimensionless wavelength shows a discrete behavior that is governed by the sampling frequency of the data, and the dimensionless amplitude better fits the Gamma probability distribution, again with a positive skewness. This paper thus provides a robust methodology for systematically identifying the scales and magnitudes of bed forms in a range of environments.
Over the past 10 years many restoration projects have been undertaken in Austria, and river engineering measures such as spur dykes and longitudinal bank protection, which imposed fixed lateral boundaries on rivers, have been removed. The EU-Life Project “Auenverbund Obere Drau” has resulted in extensive restoration on the River Drau, aimed to improve the ecological integrity of the river ecosystem, to arrest riverbed degradation, and to ensure flood protection. An essential part of the restoration design involved the consideration of self-forming river processes, which led to new demands being imposed on river management.This paper illustrates how model complexity is adapted to the solution and evaluation of different aspects of river restoration problems in a specific case. Point-scale monitoring data were up-scaled to the whole investigation area by means of digital elevation models, and a scaling approach to the choice of model complexity was applied. Simple regime analysis methods and 1-D models are applicable to the evaluation of long-term and reach-scale restoration aims, and to the prediction of kilometre-scale processes (e.g. mean river bed aggradation or degradation, flood protection). 2-D models gave good results for the evaluation of hydraulic changes (e.g. transverse flow velocities, shear stresses, discharges at diffluences) for different morphological units at the local scale (100 m–10 m), and imposed an intermediate demand on calibration data and topographic survey. The study shows that complex 3-D numerical models combined with high resolution digital elevation models are necessary for detailed analysis of processes (1 m–0.01 m), but not for the evaluation of the restoration aims on the River Drau. In conclusion, model choice (complexity) will depend on both lower limits (determined by the complexity of processes to be analysed) and upper limits (field data quality and process understanding for numerical models).