Identifying ephemeral gullies from high-resolution images and DEMs using flow-directional detection

Ephemeral gullies, which are widely developed worldwide and threaten farmlands, have aroused a growing concern. Identifying and mapping gullies are generally considered prerequisites of gully erosion assessment. However, ephemeral gully mapping remains a challenge. In this study, we proposed a flow-directional detection for identifying ephemeral gullies from high-resolution images and digital elevation models (DEMs). Ephemeral gullies exhibit clear linear features in high-resolution images. An edge detection operator was initially used to identify linear features from high-resolution images. Then, according to gully erosion mechanism, the flow-directional detection was designed. Edge images obtained from edge detection and flow directions obtained from DEMs were used to implement the flow-directional detection that detects ephemeral gullies along the flow direction. Results from ten study areas in the Loess Plateau of China showed that ranges of precision, recall, and F-measure are 60.66%-90.47%, 65.74%-94.98%, and 63.10%-91.93%, respectively. The proposed method is flexible and can be used with various images and DEMs. However, analysis of the effect of DEM resolution and accuracy showed that DEM resolution only demonstrates a minor effect on the detection results. Conversely, DEM accuracy influences the detection result and is more important than the DEM resolution. The worse the vertical accuracy of DEM, the lower the performance of the flow-directional detection will be. This work is beneficial to research related to monitoring gully erosion and assessing soil loss.