Human Impact Intertwined with Glacial Legacy: Hydro-Geomorphologic Exploration using LiDAR data

Abstract:

Intensively managed landscapes (IMLs) in the Midwestern United States are heavily modified by agriculture, artificial drainage, deforestation, urbanization, and wetland destruction. These landscapes have been shaped by repeated glacial events over geologic time scales followed with rapid human modifications for agriculture and drainage that are overlaid on extremely low gradient stream networks.

In this study, using LiDAR data from the Upper Sangamon River Basin in Illinois, we attempt to understand how the long-term glacial legacy has shaped the landscape and what is the impact from short-term human activities, such as channel straightening and periodic dredging. Glacial and human legacy impact landscape dynamics simultaneously. Therefore, we evaluate the present-day dynamics of landscapes by attempting to address several questions. First, we explore whether the watershed is in equilibrium conditions or away from it due to human activities. Second, we study how this relates to the degree of maturity in the river valley. Moreover, we map the spatial distributions of terraces and floodplains to understand depositional and erosional history.

High-resolution LiDAR data is ideal for such a study as it reveals the impact of both glacial episodes and human activities. Methods used for extraction of useful information from LiDAR data include the TerEx tool, Stream Profiler, and Hec-GeoRas, among others. We analyze the terrace and floodplain geomorphic features, quantify stream sinuosity, and cross section geometries. An integral method is built based on stream power incision model to obtain sub-basin steady state condition. These features help to reveal local and global watershed properties. A bounded relationship between terraces/floodplains, sinuosity, cross section maturity, as well as sub-basin equilibrium condition is explored. In general, we find that the glacial legacy and present-day human activity have opposed each other in regards to the sub-basin equilibrium conditions of USRB. These studies of historic and recent floodplain dynamics from high-resolution topography will enhance our understanding of intensively managed landscapes, which will strengthen the understanding of watershed dynamics under human impact.