Runoff–sediment dynamics and degradation patterns in an abandoned terraced landscape on the Loess Plateau

Abstract

Terracing is an important measure to conserve water and soil on the Loess Plateau. Previous studies have showed that due to extreme rainstorms and a lack of maintenance, loess terraces have experienced degradation predominantly as collapses and sinkholes. Investigating the hydrological processes associated with terrace degradation is vital to understand terrace degradation mechanisms and maintain terraced landscape sustainability. Using a high‐resolution digital elevation model (DEM) based on unmanned aerial vehicle (UAV)remote sensing, as well as SIMulated Water Erosion (SIMWE) model, we explored the runoff–sediment dynamics on the terraced slopes on the Loess Plateau under rainstorm conditions and the terrace degradation patterns. The results showed that the dominant longitudinal water flow between terrace steps and converging lateral water flow along terrace surfaces indicate terrace ridge collapses and terrace surface sinkholes, respectively. Damaged areas exhibit high sediment flux and erosion potential. The water dynamics and degradation pattern were influenced by the original slope topography and terrace morphology. Specifically, most damages are distributed on concave slopes with concentrated water flow. In narrow terraces, under scattered longitudinal water flow, the dominant damages are ordinary collapses and the overall terraced topography tends to degrade into natural slopes. In wide terraces, concentrated longitudinal and well‐developed transverse water flows form a basic degradation pattern dominated by sinkhole‐induced collapses. This study verified the feasibility of SIMWE‐based hydrological simulation in assessing the degradation pattern of terraces on the Loess Plateau and demonstrated its potential for spatial scales and complex scenarios through compared with the soil moisture content (SMC)‐based method. The study concluded that the dominant runoff paths under the constraints of slope microtopography control the terrace degradation patterns. Our findings can serve as a theoretical basis for predicting hydrological hazards on terraces on the Loess Plateau and conducting a scientific design of terraces.