Global Topographic Slope Enforcement to Ensure Connectivity and Drainage in an Urban Terrain

Sources of high-resolution topographic data, such as LiDAR, characterize urban terrains in great detail and can provide a resource for distributed hydrologic modeling. Incorporating these data in a distributed hydrologic modeling framework is complicated by the numerous real and artificial pits, barriers, and surface depressions contained in the urban landscape. These features create difficulties with simulating surface drainage that must be resolved to ensure model stability and convergence. This study presents a methodology to calculate distributed slope fields from LiDAR-based digital elevation models (DEM) that addresses this problem and preserves topographic details. This global slope enforcement approach ensures complete domain drainage, and the effects are demonstrated by performing a rainfall-recession test on an impervious domain using a distributed hydrologic model (ParFlow) of an urban watershed in Baltimore. This study shows that the fraction of rainfall input retained as surface storage in the model domain declined from 78 to 3.6%. Application to a high-resolution urban landscape demonstrates the capability of the method; the method can be applied to a variety of simulated topographies at coarser scales.