Soil thickness effect on hydrological and erosion characteristics under sloping lands: A hydropedological perspective

Abstract

Soil thickness exerts a first-order control on the hydrological processes of the hillslopes. However, from a hydropedological perspective, the knowledge of soil thickness effect on hydrological and erosion characteristics under sloping lands is limited. Based on a comprehensive survey of an experimental watershed in the Three Gorges Area of China, five typical sloping land plots (2 m × 1 m) with different soil thickness were selected along a hillslope to investigate their hydrological processes and erosion response under three rainfall intensities (60, 90 and 120 mm h −1) using a portable rainfall simulator. The results can be summarized as follows: (1) The surface flow coefficient was increased with increasing soil thickness, especially under the event of 60 mm h −1. (2) The subsurface flow of the 23, 31 and 45 cm plots mainly took the form of preferential flow. Conversely, the 59 and 76 cm plots mainly took the form of matrix flow. (3) A prolonged low intensity rainfall is much more likely to facilitate deep percolation and subsurface flow than a short high intensity rainfall regardless of soil thickness. (4) Soil thickness and rock fragment cover were the most important factors than other soil properties in determining the hydrological and erosion behaviors. Thin soils showed higher infiltration capacity than thick soils due to their more distinct hydrological processes of subsurface flow and deep percolation. Rock fragment cover enhanced infiltration and served as a shield to protect the soil surface from detaching. Due to the synergies between thin soil thickness and high rock fragment cover, thin soils displayed significantly lower erosion rates than thick soils in all rainfall events, which increased from 211 g m −2 h −1 for the 23 cm plot with rainfall of 60 mm h −1 to 4220 g m −2 h −1 for the 76 cm plot with rainfall of 120 mm h −1. Our study suggested that the emerging interdisciplinary field of hydropedology promotes synergistic integration of pedology (e.g. watershed scale soil thickness investigation and soil profile description) and hydrology (e.g. rainfall simulation, subsurface flow and deep percolation) to enhance the holistic study of soil–water interactions in the sloping lands with different soil thickness.