Abstract:Dynamic quantification of field ephemeral gully development and morphology on natural hillslope has great significance on ephemeral gully erosion control and ephemeral gully erosion modelling. Due to the difficulty of dynamically monitoring field ephemeral gully catchments and limitation of measurement method, quantification of ephemeral gully morphology and its dynamic evolvement process is still lacking. Thus, based on the long-term field ephemeral gully development investigation data, three-dimensional laser scanning and photogrammetry techniques were used to quantify the ephemeral gully morphology of three ephemeral gully catchments with different upslope drainage areas (1012m2, 995m2 and 424m2). The dynamic evolution processes of ephemeral gully were revealed, and the relationship between drop-sills distance of headcuts and slope gradient was also analyzed. The result showed that during the monitoring period from 2003 to 2015, when upslope drainage area was increased by 34.8% and 159.6%, ephemeral gully length was increased by 39.6% and 138.8%, average ephemeral gully width was increased by 19.7% and 75.3%, and average ephemeral gully depth was increased by 32.4% and 71.4%, respectively. Dynamic monitoring illustrated that ephemeral gully length was increased by 26.4%，12.1%，29.4% from 2003 to 2015 and the increasing rate was 0.82m/a，0.55m/a，0.5m/a;the crosssection areas of ephemeral gully in 2015 was increased by 22.5%，65.1%，45.9% compared with those in 2013, and the increasing rate was 5.0cm2/a，15.8cm2/a，4.1cm2/a. Tillage in spring brought the lateral topsoil into the ephemeral gully channel which induced 2cm decrement of soil layer around the channel. With the increase of slope length, ephemeral gully width and depth were increased first and then decreased, with maximum value in the location of about 20m to the slope bottom. Totally 70% of drop-sills distances of headcuts in ephemeral gully channel were distributed in 10~25cm, while slope gradients were distributed in the range of 15°~40°. A negative exponent relationship can be found between dropsills distance and slope gradient. The research results enhanced the understanding on ephemeral gully erosion processes, which could provide scientific bases for ephemeral gully erosion control.
