Investigating erosion processes involving surface morphological changes of coarse-textured soils under intermittent rainfall

Authors: NI, SHIMIN - Huazhong Agricultural University; ZHANG, DEQIAN - Huazhong Agricultural University; WEN, HUI - Huazhong Agricultural University; Wilson, Glenn; CAI, CHONGFA - Huazhong Agricultural University; WANG, JUNGWANG - Huazhong Agricultural University

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2021
Publication Date: 10/6/2021
Citation: Ni, S., Zhang, D., Wen, H., Wilson, G.V., Cai, C., Wang, J. 2021. Investigating erosion processes involving surface morphological changes of coarse-textured soils under intermittent rainfall. Catena. 208:105767. https://doi.org/10.1016/j.catena.2021.105767.
DOI: https://doi.org/10.1016/j.catena.2021.105767

Interpretive Summary: The relationships among the shape and properties of hillslopes to soil erosion and runoff provide tie changing feedbacks that form the basis for erosion models. Previous research rarely studied the interactions among erosion processes involved in surface shape and soil property changes of coarse-textured granite soil. This study used short-duration, intermittent rainfall conditions to investigate the interactions between erosion processes and surface changes of four coarse-textured soils. Observations included surface roughness, coarse grain coverage, soil loss, runoff, and sediment sorting. The results showed that the soil mechanical composition and the coarse grain coverage on the slope surface were the key to the rate of soil loss. The soil erosion rate of the four soils increased from 0.09 to 0.76 kg m-2 min-1 as the soil clay content in the original soil decreased from 24.2% to 13.6%, which was reflected in an increase in surface random roughness. The coarse grain coverage was shown to gradually increase with cumulative rainfall duration, reaching a maximum of 74.9%. This coarse grain enrichment of the surface corresponded with enrichment of clay- and silt-sized particles in the suspended sediment. This “armoring” cover could change the surface soil properties and provide a protective layer to reduce further soil loss. The gravel content of the original soil was related to the degree of armoring that developed with time and the reductions in the suspended sediment content in runoff. Additionally, runoff coefficient showed the opposite pattern compared with the soil erosion rate under the impacts of soil clay content and coarse grain coverage. Based on the importance of soil composition, an equation that combined soil clay content and stream power was shown to be suitable for soil erosion prediction of coarse-textured soils. This study enhanced the knowledge of erosion in coarse-textured granite soil and laid a foundation for establishing proper soil erosion prediction models in gully areas of southern China.

Technical Abstract: The interactions among slope morphology, soil erosion and runoff hydrodynamics is a dynamic feedback system that forms the basis for hydrologic and erosion models. Previous research rarely studied the interactions among erosion processes involved in surface morphological changes of coarse-textured granite soil. This study, under short-duration, intermittent rainfall conditions, aimed to investigate the interactive mechanisms between erosion processes and surface morphology changes of coarse-textured soils. Observations included surface roughness, coarse grain coverage, soil loss, runoff hydrodynamics, and sediment sorting. The results showed that the soil mechanical composition and the coarse grain coverage on the slope surface were the key to the loss of coarse-textured soil. The soil erosion rate of the four soils increased from 0.09 to 0.76 kg m-2 min-1 as the soil clay content in the original soil decreased from 24.19% to 13.60%, which can be reflected by the increase of surface random roughness. The coarse grain coverage was shown to gradually increase with cumulative rainfall duration, reaching a maximum of 74.89%, which corresponded with enrichment of clay- and silt-sized particles in the suspended sediment. This “armoring” cover could change the surface soil properties and provide a protective layer to reduce further soil loss. The higher the gravel content of the original soil was related to the coarse grain coverage, and the more significant the effect on suspended sediment reduction. Additionally, runoff coefficient showed the opposite pattern compared with the soil erosion rate under the impacts of soil clay content and coarse grain coverage. Based on the importance of soil mechanical composition, a power function that combined soil clay content and stream power was shown to be suitable for soil erosion prediction of coarse-textured soils (R2=0.93). This study enhanced the knowledge of erosion in coarse-textured granite soil and laid a theoretical foundation for establishing proper soil erosion prediction models in gully areas in southern China.