A Multi Resolution Valley Bottom Flatness Index for Mapping Valley Fill Storage Zones

Zones of deposition play an important role in hydrology because of their ability to absorb and store water. Mapping these areas automatically from digital elevation data has proven difficult, partly because these landscape features occur at a range of sizes from a few metres to hundreds of kilometres. The multi-resolution valley bottom flatness (MrVBF) index identifies relatively flat and low areas in the landscape at a range of scales. The algorithm operates on a grid digital elevation model (DEM) using slope to derive flatness and ranking of elevations within a circular context to derive local lowness. The DEM is smoothed and coarsened in several steps and the algorithm is applied at each resolution. The results at different resolutions are combined to produce a single multi-resolution index. The index separates upland terrain dominated by erosional processes from lowland depositional terrain and further divides the depositional areas into different classes based on slope and areal extent. Larger values correspond to broader and flatter valley bottoms. It is postulated that larger values also correspond to greater depths of sediment deposit and field testing of this hypothesis will be presented.