Abstract: The gully head of south branch gully on Weiliantan Terrance in Longyangxia Reservoir area was monitored by laser 3D scanner, Trimble 4700 differential GPS and submeter differential GPS. After surveying the gully head erosion for 4 years (2006-2010) in field work and analyzing the meteorological data, this paper estimated primarily the erosion amount, and discussed the erosion causes and the gully head development. The results show that the fragmented form of the bank at the gully head in 2006 provided a favorable terrain for erosion in the following years. After 3 years, the erosion area was enlarged significantly, especially in the tension crack zone of the south bank. The scanning data during the period from 2007 to 2010 revealed that the headward erosion was the most serious in 2009. The tension cracks were resulted in by the repeated alternation of freezingthawing and wettingdrying process, which not only strengthened soil erosion in rainy season, but also intensified the erosion of gully head through destroying soil structure and causing soil collapse. The obvious increase of gully headward erosion did not occur in the years when there was more frequency erosive rainfall, but it could be easily caused by flood disaster under heavy rainfall, and flood disaster was an important power for the gully head erosion.

Key words: gully erosion, reservoir sand, dynamic monitoring, heavy rainfall, weiliantan terrance, Longyangxia Reservoir area, Yellow River