Effects of rainfall characteristics and contour tillage on ephemeral gully development in a field in Northeastern China

Abstract

Contour tillage can be an effective measure for increasing infiltration, reducing runoff volumes and velocities, and protecting against soil erosion. However, ephemeral gullies often occur when contours are overtopped because gradients of the contoured row slopes exceed critical values, causing the runoff to collect along furrows and be transported to low-lying areas, often in natural drainages. This study aims to determine the main factors that influence ephemeral gully development on a contour tilled slope in the black soil region of northeastern China by investigating development of ephemeral gullies after each heavy rainfall during the rainy season. Cross-sectional measurements were used to obtain estimates of volumetric soil loss from the ephemeral gullies. An Unmanned Aerial Vehicle (UAV) was used to collect photogrammetric data to create DEMs with a resolution of 0.08 m for monitoring morphologic changes of the ephemeral gullies. Data was collected six times during the season. After a 24 mm rainfall event at the beginning of the rainy season, three ephemeral gullies developed on the contoured slopes, with initial rapid length extension, followed by deepening during subsequent heavy rainfall events. Gully heads formed in positions with steep slopes and large drainage areas. The volumetric soil loss from the gullies under one heavy rainfall event accounted for an estimated 29–45% of the total erosion on the field. We found that the contour ridges changed drainage patterns in the field from their natural state, effectively reducing the size of the areas that contributed runoff to the gullies. Contours were overtopped and broken when the row slopes were greater than approximately 2°. The relationship between the volumetric gully erosion (ESL) and estimated surface runoff volume (VQ) was: ESL = 0.707 *VQ0.598 (R2 = 0.84). The critical relationship between gully runoff volume (VQ) and critical slope gradient (S) for ephemeral gully heads and deep gullies was SEG = 0.043 *VQ0.232 and SDG = 0.078 *VQ−0.050. This study provides a reference for the prediction and prevention of gully erosion on contoured tillage areas.