Quantification of tributaries contributions using a confluence-based sediment fingerprinting approach in the Canche river watershed (France)

Abstract

Since a few years, land use management aims to reduce and control water erosion processes in watersheds but there is a lack of quantitative information on the contribution of the sources of transported sediment. This is most important in agricultural areas where soils are sensitive to erosion. The geology of these areas is often characterized by large expanses of relatively homogeneous quaternary silts. The possibility of distinguishing the sources of erosion according to their geological substratum is thus very delicate. This information is important because its lack can lead to the mis-implementation of erosion control measures. To address this request, a confluencebased sediment fingerprinting approach was developed on the Canche river watershed (1274 km²; northern France), located in the European loess belt, an area that is affected by diffuse and concentrate erosion processes. Suspended particulate matter was collected during five seasonal sampling campaigns using sediment traps at the outlet of each tributary and confluence with the main stream of the Canche river. The final composite fingerprint was defined using physico-chemical and statistical analyses. The best tracer parameters for each tributary were selected using stepwise discriminant function analyses. These parameters were introduced into a mass balance mixing model incorporating Monte-Carlo simulations to represent the uncertainty. Estimates of the overall mean contributions from each tributary were quantified at different temporal scales. The annual sediment flux tributaries contributions range from 3 to 22% at the outlet of the Canche river, and annual sediment flux range from 0.87 to 40.7 kt yr -1 . The Planquette and the Créquoise tributaries appear to be those producing the largest sediment flux. In contrast, tributaries with the highest number of erosion control on their area exhibit the lowest values of sediment flux. Our results indicate a positive impact of recent land management policies in the Canche river watershed.

Magnetic Fingerprinting of Fluvial Suspended Particles in the Context of Soil Erosion: Example of the Canche River Watershed (Northern France)

“…This study aims to develop a straightforward magnetic proxy parameter to trace the erosion of topsoils at the scale of a catchment in order to quantitatively model spatiotemporal sediment flux. The presented results are akin to the studies of Patault (2018), Patault, Alary, Franke, & Abriak (2019), and Patault, Alary, Franke, Gauthier, & Abriak (2019) in which other, more routinely used sediment tracer parameters (such as grain size and geochemical elements) were used. We take advantage of the fact that soil particles have been found to carry a distinct magnetic mineral signature (e.g., Maher, 1998, 2007) compared to the average bedload of rivers.…”

“…Values were extrapolated from the closest monitoring station by multiplying the discharge of the gauged catchment ( Q gauged ) with the appropriate fraction related to the ratio between the closest catchment area ( A ungauged ) and the catchment area at the monitoring station ( A gauged ): where Q represents the discharge in m 3 s −1 and A the area of the catchment in km 2 . For more details on the calculation of the flow discharge, please see also Patault, Alary, Franke, and Abriak (2019).…”

Assessing temporal variability and controlling factors of the sediment budget of a small agricultural catchment in Northern France (the Pommeroye)

“…The observations on the Pommeroye catchment and the WATERSED modelling also should allow to upscale to larger areas (Canche watershed) which have the same erosion problems (e.g. Pataut et al., 2019) but not the same logistics in terms of monitoring.…”

Transfer Pathways and Fluxes of Water-Soluble Pesticides in Various Compartments of the Agricultural Catchment of the Canche River (Northern France)

“…The mean annual rainfall comprises 1000 ± 150 mm and the mean annual temperature is 11 • C. Altitudes ranges from 0 to 207 m and catchment slopes are in the range 2-3%. The catchment is mainly dominated by agricultural land use (80%) and affected by water erosion leading to highly variable specific sediment yield (29 to 185 kt year −1 between 1999 and 2016) at the outlet of the Canche River [13].…”

“…Several studies report consistent observations indicating slow contaminant transport in soil and shallow aquifers. For instance, [13] estimate the contamination for the Canche basin using a hydrodispersive modeling approach: a nonreactive solute that was applied on 1 km 2 of soil surface is spread on about 34-62 km 2 after 1.5 years following the considered models. Other studies indicate that groundwater travels in the order of cm per day [3].…”