Rivers solid discharge represents a substantial environmental issue, especially for the coastal marine environment. Unlike continental climate rivers, Mediterranean rivers show large discharge variability linked to rainfall, runoff and groundwater discharge, and can be temporary dry. Solid yields are difficult to predict due to variable source of floodwater. This paper assesses the suspended solid discharge of the Las River (SE France), a small stream in karst and urban environments, and its proportion due to flood events. Floods characteristics are analyzed to explore the variability of the solid yield and the influence of urban runoff and karst springs discharge, based on in situ data. The 35 floods events monitored during a 17 months survey largely contributed to the annual yield, with a proportion of 47% of the total water, and 69% of the total solid yielded in 11% of the time. The total rainfall and the total water discharge, related to the water levels in karst springs, drive the total solid yield, mostly composed of mud (90%). Urban runoff induces higher suspended solid concentration than karst flood, but generated a lower total solid yield. Karst springs, by expanding the catchment area of the stream, largely contribute to the total volume of water discharged to the sea and enhance the sand proportion due to their influence on the maximal water discharge. These results reveal the strong influence of the karst spring hydrodynamic functioning on the sediment yield to Mediterranean coastal environments. This study also highlights the efficiency of electric conductivity data to provide valuable insights about floodwater sources and sediment transport processes.

中文翻译：

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地中海沿岸河流岩溶和城市洪水引起的固体排放：拉斯河（法国东南部）的案例研究

河流固体排放是一个重大的环境问题，尤其是对沿海海洋环境而言。与大陆性气候河流不同，地中海河流表现出与降雨、径流和地下水排放相关的巨大流量变化，并且可能暂时干涸。由于洪水的来源可变，很难预测稳定的产量。本文评估了喀斯特和城市环境中的一条小溪拉斯河（法国东南部）的悬浮固体排放量及其因洪水事件造成的比例。分析洪水特征，以实地数据为基础，探讨固体产量的可变性以及城市径流和岩溶泉流量的影响。在 17 个月的调查中监测到的 35 次洪水事件对年产量有很大贡献，占总水量的 47%，在 11% 的时间内产生了总固体的 69%。与岩溶泉水位相关的总降雨量和总排水量推动了总固体产量，主要由泥浆（90%）组成。城市径流引起的悬浮固体浓度高于岩溶洪水，但产生的总固体产量较低。岩溶泉通过扩大溪流的汇水面积，对排海总水量有很大贡献，并由于影响最大水量而增加了沙子比例。这些结果揭示了喀斯特泉水动力功能对地中海沿岸环境的沉积物产量的强烈影响。这项研究还强调了电导率数据的效率，以提供有关洪水源和沉积物输送过程的宝贵见解。