The characteristics of gully erosion over rolling hilly black soil areas of Northeast China

In this study, short-term gully retreat was monitored from the active gullies selected in representative black soil area, using differential global positioning system （GPS）. With the support of geographic information system （GIS）, multi-temporal digital elevation models （DEM） were constructed from the data collected by GPS and used for further analysis. Based on the analysis of multi-temporal DEM, we discussed the erosion-deposition characteristics within gully and a developing model for black soil gully area of Northeast China was proposed The results are： （1） The analysis of the monitored gully data in 2004 indicated that the retreat of gully head reached more than 10 m, gully area extended 170-400 m^2, net gully eroded volume 220-320 m^3, and gully erosion modulus 2200-4800 t.km^-2.a^-1. （2） Compared with the mature gully the initial gully grows rapidly, and its erosion parameters are relatively large. The erosion parameters have not only to do with flow energy, but also with the growth phase. （3） There are significant seasonal differences in gully erosion parameters. The extension of gully area and width dominates in winter and spring without marked net erosion while changes mainly occur in gully head and net erosion in rainy season. （4） It is remarkable for freeze-thaw erosion in the black soil area of NE China. The gully wall of SG2 extended 0.45 m under freeze-thaw effect in 2004, and the distance of gully head retreated maximally 6.4 m. （5） Due to freeze-thaw action and snowmelt, gully is primarily in the interior adjustment process in winter and early spring. There are much more depositions compared with that during rainy season, which can almost happen throughout the gully, while erosion mostly occurs near head, esp. for gullies having a relatively long history of development. On the other hand, the process of energy exchange with exterior dominates in rainy season. It is considered that this cyclic process is an important mechanism for gully growth in high latitude or/and high attitude regions.