陕北子洲县“7·26”特大暴雨引发的小流域土壤侵蚀调查

目的]2017年7月25日20时到26日8时陕北榆林地区突降了一场特大暴雨,造成了严重的洪水灾害与经济损失。通过考察该次暴雨造成的土壤侵蚀危害,旨在为今后该区水土流失治理及暴雨灾害的防御提供依据。方法]于2017年8月2—6日赴暴雨受灾区子洲县,选取了清水沟、马家沟、蛇家沟3个典型小流域作为重点调查区域,对该次暴雨下流域内坡耕地、退耕林草地、梯田、填沟造地、淤地坝、道路等的土壤侵蚀特征进行了调查与分析。结果]在"7·26"特大暴雨洪水下,坡耕地细沟发育明显,甚至产生小切沟;而2000年退耕的林地和自然恢复草地以面蚀为主,无明显细沟产生;新修梯田连接两阶田面的道路及承接路面来水的田面冲毁严重,田埂部分区段被冲开,田坎发生塌落;在削坡填沟造地区域,不仅农作物和坝体遭到严重破坏,而且残蚀了田旁新修道路,切割裸露沟壁多处发生土体塌落;淤地坝或轻或重都存在损毁与隐患,但在该次暴雨中滞洪拦沙作用明显。同时,在调查中发现该区陡坡耕种现象依然存在,小流域蓄排水系统缺乏,部分水土保持工程管理与维护不到位,经济发展水平低,农民水土保持意识淡薄。结论]"7·26"特大暴雨洪水造成的土壤侵蚀依然很严重,而退耕林草地的土壤侵蚀轻微,证明水土保持工作在该区依然十分重要。在生态环境脆弱的陕北黄土高原地区,应该继续加强环境保护措施,加大水土保持治理力度,特别是陡坡退耕。同时,专业设计并实施小流域蓄水、引水、排水网络系统十分必要。

Investigation on Soil Erosion in Small Watersheds Under "7 · 26" Extreme Rainstorm in Zizhou County,Northern Shaanxi Province

Objective] An extreme rainstorm was occurred in Yulin Region of Shaanxi Province in 26 July, 2017, resulting in very serious flood hazards and economic losses. The aims of this paper were to figure out the hazards of soil erosion in the rainstorm and provide basis for soil and water conservation and rainstorm hazards defenses.Methods] Three small watersheds (Qingshuigou, Majiagou and Shejiagou) were selected as key investigation areas in Zizhou County (the devastated area in this rainstorm) in 2-6 August, 2017. Soil erosion of slope croplands, forest and grass lands after cropland abandoned, terraces, fields built by filling gullies, check dams and roads were investigated and analyzed.Results] Rills developed evidently in slope croplands, and even small gullies developed in down slopes. While in forest and grass lands after cropland abandoned in 2000, sheet erosion was dominant and no obvious rills developed. In the new built terraces, the roads connecting two terraces, the field surfaces taking over the runoff from the roads, and the ridge in some sections were washed out seriously, and collapse occurred in the field walls. In fields built by filling gullies, crops and dam bodies were destroyed severely, the roads beside was eclipsed and the cutting walls were collapsed. Check dams were damaged more or less, but block runoff and sediment obviously. The main existing problems were wide spread steep slope farming, lacking storage and drainage systems in small watershed, deficiency in maintenance mechanism of soil and water conservation engineering, lower level of economic development, weak awareness of farmers in soil and water conservation.Conclusion] Soil erosion under "7·26" extreme rainstorm was still severe, but it is slight in forest and grass lands after cropland abandoned. It suggested that soil and water conservation is still very important. Environmental protection measures should continue to be strengthened, and soil and water conservation, especially steep slope cropland abandonment should be increased in the fragile Loess Plateau of Northern Shaanxi Province. In the meanwhile, it is necessary to design and implement the storage, diversion and drainage network system in small watersheds.