A complete methodology to assess hydraulic risk in small ungauged catchments based on HEC-RAS 2D Rain-On-Grid simulations

Abstract

This paper explores the use of the rain-on-grid (or direct rainfall) method for flood risk assessment at a basin scale. The method is particularly useful for rural catchments with small vertical variations and complex interactions with man-made obstacles and structures, which may be oversimplified by traditional hydrologically based estimations. The use of a hydrodynamic model solving mass and momentum conservation equations allows the simulation of runoff over the watershed at a basin scale. As a drawback, more detailed and spatially distributed data are needed, and the computational time is extended. On the other hand, a smaller number of parameters is needed compared to a hydrological model. Roughness and rainfall loss coefficients need to be calibrated only. The direct rainfall methodology was here implemented within the two-dimensional HEC-RAS model for the low-land rural, and ungauged, watershed of the Terdoppio River, Northern Italy. The resulting hydrographs at the closing section of the watershed were compared to synthetic design hydrographs evaluated through pure hydrological modelling, showing agreement on the peak discharge values for the low-probability scenarios, but not on the total volumes. The results in terms of water depth and flow velocity maps were used to create flood hazard maps using the Australian Institute for Disaster Resilience methodology. The Index of Proportional Risk model was then adopted to generate a basin-scale flood risk map, by combining flood hazard maps, damage functions for different building-use classes, and the value of reconstruction and content per unit area.

Assessment of the influence of DTM quality on dam rupture simulation processes

“…The process of simulation and prediction of mineral exploration dam failure is extensively covered by several authors, and even similar themes using HEC-RAS (Hydrologic Engineering Center -River Analysis System) are presented in several references around the world. [1][2][3][4][5][6][7][8][9][10][11][12] In the context of the application of this technology and the present work, it is worth highlighting that the input of primary data, that is, topographic and/or cartographic data, is extremely important, in order to collaborate in this process, as stated and the aforementioned subject covered. [11][12][13][14][15] Thus, with the DTM (digital terrain model) as one of the main elements, considered this as a primary data of Cartography, this research sought to carry out several simulations and tests, in order to assess which spatial resolution would be sufficient.…”