Title: Response of a soil-mantled experimental landscape to exogenic forcing Authors
|Gordon, Lee -|
|Bennett, Sean -|
Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 27, 2012
Publication Date: N/A
Interpretive Summary: This manuscript describes experiments conducted in a large indoor flume using simulated rainfall and downstream flume border manipulation to induce soil erosion. This type of experiment explores landscape evolution due to human and/or animal activities. Examples might include live stock overgrazing, forestry clear-cutting operations and river dredging activities. Experiments of this type are not unique; however, the data collection and interpretation techniques represent a substantial advancement in this area of research. Here, photographs (9 overlapping photos per rainfall event) were integrated to obtain high resolution surface maps. These maps were used to describe various aspects of the erosion process, including: evolution of the channel network (widths, depths and lengths of eroding channels), sediment loss from the landscape, and dominant mechanism of erosion (headcut migration). Approximately 80% of all erosion could be linked to headcut development and migration. Downstream border manipulation (lowering of outlet retaining wall) was required for significant erosion and headcuts and channel incision depths were strongly linked to the border adjustment height. Simple empirical relations, based on overland flow rates, were better predictors of headcut migration.
Technical Abstract: Experiments were conducted using a soil-mantled flume subjected to simulated rain and downstream baselevel lowering to quantify the growth, development, and spatiotemporal evolution of rills and 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 throughout 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; (4) flows were supply-limited and most of the sediment efflux was genetically linked to headcut development and migration; (5) hydraulic geometry relationships varied over time and between experimental runs but agreed well with previous findings; and (6) rates of headcut migration were well correlated to rates of overland flow. These findings have important implications for the prediction of soil loss, rill network development, and landscape evolution where headcut erosion can occur.