EROSIONAL DEVELOPMENT OF SMALL SCALE DRAINAGE NETWORKS

Authors: HELMING, K - ZALF, GERMANY; Romkens, Mathias; PRASAD, S - UNIV OF MISSISSIPPI; SOMMER, H - TECH UNIV,MUENICH GERMANY

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 7/1/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Drainage networks are important from a hydrological and geomorphological standpoint in describing watershed and erosional processes. Geomorphologists have studied the principles of drainage network evolution of large river systems. They have introduced descriptive parameters of drainage networks and have developed a unified theory of network evolution based on the minimalization of energy dissipation in the drainage basin. Rills on field size areas show a remarkable resemblence with the drainage network of large river systems. This article reports observations made on small scale drainage network development of plot size areas for different initial conditions, subjected to a series of simulated rainstorms. The objective was to test the hypothesis of a similarlity between drainage networks of plot size upland areas and those of large river systems. The results confirm this similarity between these systems when expressed in terms of a commonly used parameter for describing stream order relatioships, the Horton ratio, and by fractal dimension.

Technical Abstract: Drainage networks are usually determined for large scale river systems. Small scale drainage networks of upland eroding areas have rarely been studied. In this scale, the development of runoff patterns substantially affect soil erosion. The objective of this study was to explore the similarities between drainage networks of eroding surfaces and those of river systems and to determine the interrelationships between drainage network development and soil erosion. In flume experiments sequences of simulated rainstorms and overland flow were subjected to soils of initially different surface configurations. Before and after each rainstorm and overland flow test, DEMs of the soil surface were generated using a laser scanner with 3 mm grid spacing. Drainage networks were determined from the DEMs and characterized with Horton's ratios, fractal characteristics, and with single stream properties like gradient, sinuosity, and orientation. Horton's ratios indicated convergence and organization for all determined networks. When expressed eith Horton's ratios and fractal characteristics, drainage networks of eroding surfaces were similar to those of river systems. Initially different network configurations yielded different erosion values but resulted in similar network characteristics at the end of the rainstorm and overland flow experiments. Raindrop detachment, clod destruction, and microrelief changes were identified as important mechanisms of network configuration and stream property changes during the rainstorm and erosion events. The network changes led to network structures that resulted in continuously decreasing soil erosion values. The results support the idea of optimization in drainage network development.