An Improved Method for Watershed Delineation and Computation of Surface Depression Storage

Surface microtopography plays an important role in overland flow generation and soil erosion processes. Characterization of surface depressions and delineation of the entire watershed are critical to watershed modeling and management. In most hydrologic models, however, surface depression storage is estimated indirectly and inputted as a known value. In addition, it is often assumed that overland flow initiates after all surface depressions are fully filled. In reality, surface microtopography may control overland flow generation, surface runoff, soil erosion, and other hydrologic processes in a dynamic manner. The role of depressions that have various spatial scales and distribution characteristics is far beyond the functions of storing and detaining/retaining surface runoff. In this study, an improved surface delineation method was proposed to identify surface depressions and their relationships, precisely quantify the surface microtopography, and compute the maximum depression storage based on high-resolution DEM data obtained by using an instantaneous-profile laser scanner. Furthermore, a user-friendly, Windows-based software package was developed to facilitate the associated computations and visualization. The delineation method and the related software were tested using various scale DEM data. It is demonstrated that the new delineation approach is effective and efficient.