在陕西省商州市市区西北七八公里的丹江河与水道河交汇处，有两座形似青龙的山峰倚河相峙，因有“二龙山”之名。两河汇为一流，每至汛期或遇山洪暴发，下游人民多受其害。1970年政府为兴利除弊，投资1700余万元，动用数万劳力，苦战3年锁二龙，建水库。在峡口筑起了一座长152 At the intersection of Danjiang River and Shuidou River, which is 78 kilometers northwest of downtown Shangzhou City, Shaanxi Province, there are two peaks shaped like blue dragon, which stand in the name of “Erlongshan”. The two rivers converge to the first class. Every flood season or flash flood occurs, the people on the lower reaches suffer much. In 1970, the government took advantage of the pros and cons to eliminate disadvantages and invested over 17 million yuan in tens of thousands of labors and locked up Erlong and built reservoirs for three years. In the gorge built a long 152