UNDERSTANDING THE CHARACTERISTICS OF RIVER VALLEY TOPOGRAPHY USING FLOOD MODEL

The surface topography of river valley influences hydraulic characteristics of flooding and the erosion and deposition process. Flooding may in turn influence river valley topography. The river valley in nature has been affected by human activities: farmers cultivate in river valleys because of the rich soil, and people build infrastructures within the floodplain. Previous studies have revealed how a valley can be shaped by flooding-induced erosion and deposition. However, the detailed hydraulic characteristics during different scale of floods have been poorly understood. This makes it difficult to assess how flooding interact with different ages of valleys and how human society responds to it. We develop a method that has enhanced our understanding of river valleys. We explore the relation between river valley cross-sectional geometry and flooding recurrence. We quantify the geometry of river valleys using hypsometric curve, which reveals the maturity of a valley segment. First, hypsometric curve needs the spatial coordinates of river valley cross-section lines. These are obtained from ArcGIS, specifically, the Hec-GeoRAS tool box. Second, we use a flood model, Nay2D Flood with iRIC to simulate the flooding events. The model is calibrated by comparing the simulated water level and the measured rating curve with different flood recurrence year. Third, we plot the simulated water level on the hypsometric curve to understand the relation between the given flood recurrence year and the river valley topography. Given a relative definition of terraces, (100yr flood as an example), we can approximately distinguish terraces within a certain river valley. Our method also shows that for younger valleys, floodplains are more easily submerged with lower flood recurrence.