Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2003
Publication Date: 6/1/2003
Citation: Gomez, J.A., Darboux, F., Nearing, M.A. 2003. Development of rill networks under simulated rainfall: evolution towards a state of minimum rate of energy dissipation. Water Resources Research. 39(6):1148. Interpretive Summary: Rills are small, eroded channels that form on the surface of the land during a rainstorm. Rills act as the channels that carry the water and sediment from agricultural fields and other lands during the rain. The geometric pattern of the rill on the surface of the soil is generally branch-shaped, and we refer to its structure as a "network". Since rills are the primary mechanism for transporting water and sediment over the land, it is important to understand the rill network and how it forms if scientists are to understand how soil erosion occurs. The purpose of this study was to observe and measure the evolution of a rill network during rainfall, and to attempt to develop a theoretical basis for its ultimate structure. We found that the development of the network could best be described mathematically in terms of how the energy of the flowing water was expended as it moved down-slope. We also found that the micro-relief, or roughness, of the original soil surface played a key role in what the final network structure looked like. These results were corollary to other results found for larger stream and river networks. The results of this study help us to advance our basic understanding of how soil erosion happens so that scientists can develop better strategies for reducing soil erosion and developing soil conservation plans.
Technical Abstract: The evolution of drainage networks at large scales has been shown to follow a principal of minimization of energy dissipation. This study was undertaken to evaluate whether the same type of principal holds for rill networks at a much smaller scale. Simulated rainfall was applied to a 2m by 4m flume with varied initial slope (5% and 20%) and roughness (smooth, medium, and rough) conditions. The results indicated that the rill networks evolved according to a similar principal as that found for streams. The rate of energy dissipation was calculated from the network characteristics derived from digital elevation models acquired with a laser scanner. The exception to that minimization trend was the very rough surfaces at the lower (5%) slope, where the initial microrelief dominated the network evolution. These results justify the application of some models used to explain the evolution of river networks to the initiation and evolution of rill networks. Despite the convergence towards similar values of some of the networks characteristics, differences in the microrelief of the initial surfaces were translated into significant differences between the final microrrill networks.