Hydroclimatic control on suspended sediment dynamics of a regulated Alpine catchment: a conceptual approach

Abstract

Abstract.We analyse the control of hydroclimatic factors on suspended sediment concentration (SSC) in Alpine catchments by differentiating among the potential contributions of erosion and suspended sediment transport driven by erosive rainfall, defined as liquid precipitation over snow free surfaces, icemelt from glacierized areas, and snowmelt on hillslopes. We account for the potential impact of hydropower by intercepting sediment fluxes originated in areas diverted to hydropower reservoirs, and by considering the contribution of hydropower releases to SSC. We obtain the hydroclimatic variables from 10 daily gridded datasets of precipitation and temperature, implementing a degree-day model to simulate spatially distributed snow accumulation and snow-ice melt. We estimate hydropower releases by a conceptual approach with a unique virtual reservoir regulated on the basis of a target-volume function, representing normal reservoir operating conditions throughout a hydrological year. An Iterative Input Selection algorithm is used to identify the variables with the highest predictive power for SSC, their explained variance, and characteristic time lags. On this basis, we develop a hydroclimatic multivariate rating 15 curve (HMRC) which accounts for the contributions of the most relevant hydroclimatic input variables mentioned above. We calibrate the HMRC with a gradient-based nonlinear optimization method and we compare its performance with a traditional discharge-based rating curve. We apply the approach in the upper Rhone Basin, a large Swiss Alpine catchment, heavily regulated by hydropower. Our results show that the three hydroclimatic processes -erosive rainfall, icemelt, and snowmeltare significant predictors of mean daily SSC, while hydropower release does not have a significant explanatory power for 20 SSC. The characteristic time lags of the hydroclimatic variables correspond to the typical flow concentration times of the basin. Despite not including discharge, the HMRC performs better than the traditional rating curve in reproducing SSC seasonality, especially during validation at the daily scale. While erosive rainfall determines the daily variability of SSC and extremes, icemelt generates the highest SSC per unit of runoff, and represents the largest contribution to total suspended sediment yield. Finally, we show that the HMRC is capable of simulating climate-driven changes in fine sediment dynamics 25 in Alpine catchments. In fact, HMRC can reproduce the changes in SSC in the past 40 years in the Rhone Basin connected to air temperature rise, even though the simulated changes are more gradual than those observed. The approach presented is this paper, based on the analysis of the hydroclimatic control on suspended sediment concentration, allows the exploration of climate-driven changes in fine sediment dynamics in Alpine catchments. The approach can be applied to any Alpine catchment with a pluvio-glacio-nival hydrological regime and adequate hydroclimatic datasets. 30Hydrol. Earth Syst. Sci. Discuss., ...

Open-Source, Low-Cost, In-Situ Turbidity Sensor for River Network Monitoring

“…But in general, for every watershed and sediment type, it is likely that both a and b will be different. For example, Costa 12 found a = 0.56 and b = 1.25 in their investigated alpine catchment whereas Felix 54 found a = 0.59 and b = 1 in their HPP storage tunnel. In our case, at larger SSCs the relationship diverges from linearity (Fig.…”

“…High resolution estimates of SSC can be used to quantify human effects on sediment production, for example the effects of dam construction and erosion control 8,9 , the natural erosion gradients over entire mountain ranges 10 , the role of sampling in global erosion rates 11 , and many others. Measurements of SSC at a basin outlet can give us a basin-integrated picture of possible hydroclimatically-driven sources of sediment, like rainfall erosion, snowmelt hillslope erosion, glacier ice melt erosion, even hydropower storage in dams 12 . These measurements of SSC are also important for understanding the impact of hydroclimatic forcing on activating sediment sources and transport dynamics, and physically-based modelling thereof [13][14][15][16] .…”

Continuous Seasonal and Large-Scale Periglacial Reservoir Sedimentation

“…The sediment dynamics will be different, however [56]. A study on the upper Rhône catchment demonstrated that the SSC-Q relationships were not capable of reproducing probability distribution functions of SSC because they neglect physical processes that govern seasonal patterns of SSC, especially in summer [17]. Instead, a non-linear multi-variate rating curve performed fairly well, although it does not use discharge at all, but includes the input variables mean daily rainfall, ice melt, snow melt over unregulated areas, and release from reservoirs, which are governing the changes in SSC.…”

“…[10] or Ref. [17], for example, taking variables and processes such as rainfall, coverage with erodible soils and vegetation, glacier length change or snow and ice melt into account. Once the sediment input into the reservoir has been estimated, the well-known relationship of Ref.…”

Rainfall, runoff, and suspended sediment dynamics at the flood event scale in a Loess Plateau watershed, China

“…Although most of these studies examined the annual changes, some studies employed event scale data to analyse suspended sediment dynamics and their responses to climate change and land surface changes (Gao, Fu, et al, 2018; Horowitz, 2003; López‐Tarazón et al, 2009). Event rainfall amount, rainfall intensity and antecedent rainfall variables have been widely used to provide insights into event characteristics and spatiotemporal variations in hydrological processes (Ahn et al, 2017; Costa et al, 2018; Fang, Shi, et al, 2011; Gao, Fu, et al, 2018; López‐Tarazón et al, 2009; Zhang et al, 2018; Zhang, Chen, et al, 2019; Zhang, Zhao, et al, 2019). Different regression models have been developed to quantify the relationship between suspended sediment concentration (SSC) and runoff (Q) (Costa et al, 2018; Zheng, 2018).…”