Map Viewing Service (WMS) of the dataset: Isocotes of the flooding zone by hydrogeomorphological approach of the Sarsonne River, municipality of Ussel en Corrèze

L_ZI_SARSONNE_2001_ALEAS_L_019 The study determined the flooding areas of the Sarsonne at Ussel by hydrogeomorphological approach on the upstream and downstream areas of the urbanised part (maximum right-of-way only). The hydrogeomorphological approach is a naturalistic approach based on reading the morphology of the alluvial plain. It is supplemented here by extrapolation of the water line from a flood known to establish the reference flood water line. This reading of the morphology of the alluvial plain has been clarified on the urbanised area, thanks in particular to topographical works, allowing the definition of heights and flow rates in the crossing of the urbanised area. The flooding zone was determined by calculating the water line of a centennial flood (reference) determined by extrapolation of the 1994 flood water line, extrapolation based on topographical knowledge, the difference in flows between the 1994 event and a centennial event. Topographic knowledge has been used to determine water heights (between 0 and 1 m and > 1 m); flow velocities were defined qualitatively from valley morphology primarily. The crossing of these two parameters allowed to map the hazard (strength = H > 2 m or 1 m < H < 2 m and V > 0.5 m/s or 0 m < H < 1 m and V > 1 m/s; mean = 1 m < H < 2 m and V < 0.5 m/s or 0 m < H < 1 m and 0.5 m/s < V < 1 m/s; low hazard 0 m < H < 1 m and V < 0.5 m/s).L_ZI_SARSONNE_2001_ALEAS_L_019 本研究针对于塞勒境内的萨尔松讷河，采用水文地貌学方法（hydrogeomorphological approach），针对城市化河段上下游区域（仅以法定河道用地红线范围为准），划定了其洪水淹没范围。该水文地貌学方法是一种基于冲积平原（alluvial plain）形态解析的自然实证研究方法，本研究通过已知洪水的水位线外推得到基准洪水水位线，以此对该方法进行了补充完善。 针对城市化区域的冲积平原形态解析，本研究借助地形测绘工作进一步明确了细节，从而得以确定该河段穿越城市化区域区段的水位高度与流量。本次研究通过对1994年洪水水位线进行外推，结合地形测绘数据以及1994年洪水与百年一遇洪水的流量差值，计算得到基准百年一遇洪水的水位线，进而确定洪水淹没范围。研究借助地形数据确定了水位高度（分为0~1米与>1米两类）；流速则主要基于河谷地貌进行定性判定。结合水位高度与流速两类参数，可绘制洪水风险等级分布图：高风险（水位高度H>2米，或1<H<2米且流速V>0.5m/s，或0<H<1米且V>1m/s）；中风险（1<H<2米且V<0.5m/s，或0<H<1米且0.5m/s<V<1m/s）；低风险（0<H<1米且V<0.5m/s）。