Emergence, persistence, and organization of rill networks on a soil-mantled experimental landscape

Soil erosion remains a critical concern worldwide, and predicting the occurrence, location, and evolution of rills on hillslopes and agricultural landscapes remains a fundamental challenge in resource management. To address these questions, a relatively large soil-mantled experimental landscape was subjected to continuous rainfall and episodes of base-level lowering to force the development of a rill network system, and high-resolution digital technologies were used to quantify its evolution over time and space. These results show that waves of degradation and landscape incision occurred in response to base-level lowering, where headcut development and its upstream migration produced a fourth-order rill network. Stream order indices derived for this incised rill network confirm that this pattern emerges relatively early in time, and it remains relatively unchanged despite continued application of rainfall and additional base-level lowering. Using the same digital technologies, a surface drainage system was defined and mapped on the landscape prior to any soil erosion and rill development, and similar network indices also were derived. These results show that network characteristics and organization of this surface drainage system, as well as its location in space, were in very close agreement with the subsequent incised rill network following base-level lowering. It is demonstrated here that rill networks formed in this experiment are strongly conditioned by surface drainage patterns prior to any significant soil erosion and that the location of rill networks can be accurately delineated through analysis of the high-resolution digital terrain.