岷江上游干旱河谷区龙洞沟泥石流及其防治

Prevention and control of debris flow in dry valley of the upper Minjiang River:A case study of Longdong Gully

龙洞沟发育于岷江上游四川茂县境内,沟口地带属干旱河谷区。该沟流域面积14.52km2,沟长9.15km,相对高度2534m,沟床比降23.7%,沟内滑坡发育,形成泥石流的地形和松散固体物质条件充分;偶尔出现的高强度、短历时暴雨是泥石流形成的水源条件和激发因素。该沟主沟为低频率泥石流沟,以中-大规模和特大规模泥石流为主,中-大规模泥石流约30～50a一次,大-特大规模泥石流约50～100a一次;支沟泥石流活动频繁,但多为小规模。泥石流流体性质,支沟的几乎均为粘性,重度可达2.0～2.3t〗/m3,而主沟的则以稀性为主,重度一般为1.3～1.6t〗/m3。泥石流治理采用土木和生物工程相结合的综合措施,土木工程包括谷坊17座,拦砂坝5座,主沟排导槽1054m,支沟排导槽198m;生物工程按流域生态功能分区进行,在分出的5个生态区实施造林398hm2,退耕还林还草40hm2,林地封禁、抚育779hm2,果园改造、更新40hm2,生物谷坊10座。

Longdong Gully is located in the upper reaches of the Minjiang River, Maoxian County of Sichuan Province, where the climate is dry, the ecological environment is fragile and therefore the debris flow is active. Debris flow of Longdong Gully is the most representative, which has been long endangering the County. The gully is 14.52 km^(2) of basin area, 9.15 km of stream length, 2 534 m of relative elevation, and 23.7% of the channel-bed gradient. Loose solid material in the gully come from 10 landslides developing inside, which is extremely abundant for the formation of debris flow. Debris flow usually occurs for stir of heavy rainfall of short duration. Debris flows burst frequently and often in small scales in tributaries but seldom in the mainstream of the gully, with return period of 30～50 years for the moderate-scaled occurrence and 50～100 years for the large-scaled ones. Debris flows in tributaries are almost viscous, with density as high as 2.0～2.3 t/m^(3) and in the mainstream they are dominantly of non-viscosity, with density between 1.3 t/m^(3) and 1.6 t/m^(3). Control measures include civil engineering works and biological works. Civil engineering measures include 5 silt-trap dams, 17 check dams, 1 054m of headrace in the mainstream and 198 m in the tributary. Biological measures proceed in accordance with the five functional divisions in the basin, including forestation of 398 hm^(2), grassing 40 hm^(2) in cultivated land; sealing 779 hm^(2) of ban forest and nursing land; 10 check dams made up of trees and bushes.