Ephemeral gully is a common erosion process and represents one of the significant watershed sediment resources in the hilly region on the Loess Plateau of China.A watershed with closure measures implement in Wuqi County,Shaanxi Province was taken as case study to quantify the relationship between the lengths of ephemeral gullies and eroded volume and assess the erosion rate in six years period.A total of 60 ephemeral gullies were surveyed under field conditions,and lengths of 245 ephemeral gullies were identified by two QuickBird images with the same time phase in years of 2007 and 2013.Results revealed that ephemeral gully density was 36.21 km/km2 in 2013 and the total length of ephemeral gullies was changed from 13.74 km in 2007 to 14.12 km in 2013.Among 245 ephemeral gullies interpreted from images,the lengths of 46.94％ gullies were decreased owing to connecting with gully heads with larger erosion rate or measurement error.Assuming that the cross section of an ephemeral gully is quadrangular frustum pyramid,the volume of 60 investigated ephemeral gullies was ranged from 0.4 m3 to 15.43 m3,which was 4.06 m3 on average.Based on the built regression model,the volume change of 245 ephemeral gullies from 2007 to 2013 was 71.52 m3.For 53.06％ of ephemeral gullies with longer length than previous conditions,the average increasing rate was 0.2 m3 per year for each growing ephemeral gully and the total increased volume was 157.51 m3.The estimated erosion rate of ephemeral gullies was 67.31 m3/(km2·a) on the 12 slope units with area of 0.39 km2.The total eroded volume was about 100.97 t/(km2 ·a) if the average soil bulk density was taken as 1.5 g/cm3.Assuming that the average erosion rate of the other 46.94％ ephemeral gullies was similar to those with increased length,the average erosion rate on the slope covered by herbal could be 215 t/(km2 ·a).The results showed that ephemeral gully erosion rate could be estimated using very high resolution remote sensing such as QuickBird images,which could provide reference for the soil and water conservation on hilly Loess Plateau.%以陕西省吴起县黄土丘陵沟壑区封禁流域(合沟小流域)为研究对象,通过野外实地测量60条浅沟形态参数,建立浅沟长度与体积回归模型,使用2007年和2013年2期同时相QuickBird影像,提取245条浅沟的长度,计算浅沟侵蚀速率.结果表明:在2007-2013年的6a内,浅沟的数量基本不变,总长度从2007年的13.74 km增长到2013年的14.12 km,浅沟密度为36.21 km/km2.浅沟长度变化分为缩减与增长2类,缩减类浅沟占46.94％,沟口多数与切沟沟头相连,由于切沟溯源侵蚀速率高于浅沟的发育速率,导致浅沟长度缩减.依据构建的浅沟长度与体积回归模型,基于影像解译的245条浅沟在6a间总侵蚀量从1 889.97 m3增加到1 961.49 m3,若不考虑体积减小的浅沟,平均每条浅沟每年增长0.20 m3,草本覆盖的坡面浅沟平均侵蚀速率约为215∥(km2·a).
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