INTEGRATED ASSESSMENT AND ANALYSIS OF PHYSICAL LANDSCAPE PROCESSES THAT IMPACT THE QUALITY AND MANAGEMENT OF AGRICULTURAL WATERSHEDS
Location: Watershed Physical Processes Research Unit
Title: Evolution of rill networks on soil-mantled experimental landscapes driven by rainfall and baselevel adjustments
Submitted to: International Symposium on Gully Erosion
Publication Type: Proceedings
Publication Acceptance Date: January 15, 2010
Publication Date: April 19, 2010
Citation: Gordon, L.M., Bennett, S.J., Wells, R.R. 2010. Evolution of rill networks on soil-mantled experimental landscapes driven by rainfall and baselevel adjustments. Human Imipact on Gully Erosion, Proceedings of the V International Symposium on Gully Erosion. April 19-24, 2010, Lublin Poland, Wojciech Zglobicki (ed.). Maria Curie-Sklodowska University. pp 38-40.
Interpretive Summary: Soil loss due to rill and gully erosion remains a critical concern in agricultural regions, since these processes can lead to significant ecologic and landscape degradation. Experiments were conducted to examine the processes of soil erosion and rill network development in the presence of simulated rain and changes in the downstream baselevel control. These experiments showed that significant soil erosion, bed incision, and rill network growth occurred quickly and pervasively when the downstream baselevel was lowered, forming an actively migrating headcut. Following this wave of degradation, sediment leaving the landscape decreased markedly and further rill network development was halted. Nearly all soil loss could be attributed to migrating headcuts, and in particular those formed during baselevel adjustments. Thus by controlling such exogenic perturbations, soil-mantled landscapes can remain relatively stable for relatively long periods of time with very low rates of soil loss even in the presence of continuous, high-intensity rainfall.
Experiments were conducted using a soil-mantled flume subjected to simulated rain and downstream baselevel lowering to quantify the growth, development, and evolution of rill networks. Digital elevation models constructed using photogrammetric techniques greatly facilitated data acquisition and analysis. Results show that: (1) headcuts formed by baselevel lowering were the primary drivers of rill incision and network development, and the communication of this wave of degradation occurred very quickly and efficiently through the landscape, (2) rill networks extended upstream by headcut erosion, where channels bifurcated and filled the available space, (3) rill incision, channel development, and peaks in sediment efflux occurred episodically, linked directly to the downstream baselevel adjustments, and (4) sediment discharge and rill drainage density approached nearly constant or asymptotic values with time following baselevel adjustments despite continuous application of rainfall. These findings have important implications for the prediction of soil loss, rill network development, and landscape evolution where headcut erosion can occur.