Hydrological Effects of Water and Soil Conservation Measures in Loess Plateau

Taking the two typical tributaries in the loess plateau as an example, the hydrological effects of water and soil conservation measures were studied with parallel comparative analysis method. The results show that water and soil conservation measures can reduce annual runoff and sediment module, cut down flood peak discharge and lower sediment concentration efficiently. And meanwhile, it also can delay the occurred time of flood peak; shorten the flood duration in small-scale watershed. Although the measures can change the relationships between runoff, sediment and rainfall, it has no significant effects on correlativity between these factors. 2 respectively. In order to study benefits of water and soil conservation measures, many measures were taken in Chacaizhu gully in 1954, and harnessing percentage of the gully was up to 78.3% in 1956, and meanwhile, Yangdao gully was still in natural state. Because the two gullies are adjacent and their area is very small, the rainfall condition in the basins can be taken as same to each other. According to the data from 1956—1970, statistical results showed that mean annual precipitation was about 544mm, and precipitation in flood period from June to September accounted for 72% of annual precipitation. Water and soil losses were caused by several high- intensity storms in the period, so runoff and sediment were concentrated in flood period. Precipitation in drought period was little and density was weak, there was less runoff and sediment yielded in the period. The mean annual runoff modules in the two gullies were 27,740 m 3 /km 2 and 14,115m 3 /km 2 , and mean value of annual sediment modules was 20,811t/km 2