[Quantitative monitoring of gully erosion in hilly-gully area of Loess Plateau based on aerial images].

Based on the aerial photographs in 1979 and 1993, and by using geographical information system (GIS) techniques, the digital elevation models (DEM) and digital orthophoto map (DOM) were constructed from the geomorphic changes in a chosen gully in the Loess hilly-gully area, and the spatial difference of the changes and their key affecting factors were analyzed. The results indicated that from 1979 to 1993, the gully head advanced actively (with a length of 8.5 meters and an erosion rate of 481.28 t x hm(-2) x a(-1)), and the slope tended to become steeper, exhibiting a high erosion risk. The middle part of the gully had the largest newly eroded area and the highest erosion rate, and the erosion process was quite active, with the highest erosion risk. The water outlet was primarily endowed with deposition formation, whose eroded area was smaller than its deposition area, and the gully depth and slope were becoming less, with a lower erosion risk.