Multi-scale assessment of overflow-driven lateral connectivity in floodplain and backwater channels using LiDAR imagery

Abstract

International audienceOverflow-driven lateral connectivity significantly influences the spatial distribution and diversity of floodplain habitats and biota. Proper understanding of lateral connectivity in floodplain and backwater channels is therefore critical for assessment of river quality and for targeting management or restoration actions. In this study, we present a methodological framework for spatial and temporal assessments of overflow-driven lateral connectivity at two spatial scales: bypass reach and backwater channel. Firstly, we compute the relative elevations, as well as overflow discharge, duration, and frequency using a simple, raster-based method that uses a LiDAR digital elevation model (DEM), rating curves, and streamflow time series. Subsequently, we analyse the accuracy of this approach with respect to the accuracy of a DEM and evaluate its further applications. Altogether, four 10-km-long bypass reaches and 11 backwater channels are analysed, located along the Rhone River corridor in France. The results proved the precision of the method to be affected by the LiDAR DEM accuracy, which was on average more precise in a typically homogeneous floodplain setting rather than for backwater channel plugs with pronounced topographic complexity and usually riparian forest canopy. Amongst the four studied reaches, Bregnier Cordon proved to have the greatest flooding dynamics, followed by Belley and Chautagne. The hydrological connectivity pattern of Pierre Benite differed significantly. Three longitudinal patterns of hydrological connectivity of backwater channels displayed stepwise advancement of the water. The presented results can be used to assess ecological potential of floodplain habitats and their historic and prospective evolution through time. Copyright (c) 2014 John Wiley & Sons, Ltd

Daily Monitoring of Shallow and Fine-Grained Water Patterns in Wet Grasslands Combining Aerial LiDAR Data and In Situ Piezometric Measurements

“…The comparison between the DGPS measurements and DTM pixels showed strong similarities in terms of the elevation values (a variation of 10 centimeters in the altimetry errors). Although some differences higher than 10 cm were observed in the dense herbaceous vegetation and shallow water bodies, this finding corroborates with previous studies [15,28]. To minimize the altimetric error of the LiDAR-based DTM, we tested the effect of applying a plant species-specific offset; this correction by plant height was shown to be efficient, although it may not have fully balanced the errors: the post-correction accuracy assessments reached a mean altimetric error of ~20cm in the salt marshes [39].…”

“…To model the flood extent at a daily step interval, the LiDAR-based DTM dataset was used and transformed into a binary raster (0 = unflooded; 1 = flooded) that was specific to each site, according to the daily water level measured by the piezometric probe. The model was iteratively performed using the R software [27] with the Raster package [28]. Since the accuracy of the LiDAR-based DTM altimetry values range between 5-30 cm in grasslands [29], a site-specific DTM calibration was necessary.…”

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Role of the geomorphic setting in controlling groundwater–surface water exchanges in riverine wetlands: A case study from two southern Québec rivers (Canada)

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Spillage sedimentation on large river floodplains

“…Major global rivers have been engineered for hundreds or thousands of years such that breach flows and minor channels are now artificially constrained in some form (Zhuang and Kidder, 2014). Elimination both of palaeochannel and active anabranches as detrimental to agricultural potential or river navigation, bank-breach sealing and bank stabilization (Hohensinner et al, 2014;Klasz et al, 2014;Džubáková et al, 2015), and new floodplain drainage works -all can create new styles of spillage sedimentation in constrained rivers. Levee growth may be increased with catchment settlement and soil erosion (Funabiki et al, 2012).…”