A variety of methods have been developed to process digital elevation models (DEMs) in order to extract morphological properties of land surfaces. Almost all rely on depression filling to facilitate drainage analysis. This study proposes an intuitive and relatively simple depression-filling algorithm, which is readily applicable to raster and irregular datasets. In this study, topographic data of two watershed areas were provided to test the capability of this new algorithm. The results show that the proposed algorithm can accurately identify the locations of depressions and efficiently assign pseudo flow directions across the filled depressions.

Considering that urban areas may suffer more substantial losses than riparian farmlands during floods, diverting floodwater into riparian areas for temporal detention is expected to mitigate flood damage in downstream urban areas. In this study, an assessment has been conducted to evaluate the effect of floodmitigation through riparian detention in response to a changing climate in the Tou-Chien River basin of Taiwan. An integrated 1D–2D flow model was used to simulate the movement of flood wave in the main stream and the overbank flow inundating into the nearby lowlands. Based on the numerical simulation results, the flooding extents in the basin corresponding to different return periods of flood using existing flood prevention infrastructures were investigated. A detention strategy by lowering the levee along the riparian farmlands was proposed to avoid severe flooding in the densely populated urban areas of the basin. Research findings showed that the proposed detention measure can completely protect thedownstream areas from overbank flooding when a flood having 20-yr period occurs, and can effectively alleviate the downstream flooding area from 27.4 to $\rm{7.6 km^{2}}$ for a flood possessing 200-yr period.