Variation Of Runoff And Sediment In Kuye River Watershed

Kuye River is a tributary of middle reaches of the Yellow River. There are a large amount of factors impacting on runoff and sediment in Kuye river watershed, which is mainly caused by human activities and climatic conditions. This study aims to figure out some laws between runoff and sediment in this watershed. And it has great significance on rational development of water resources as well as soil and water conservation for the future research.This study takes Kuye basin as research area, and the hydrological and meteorological data is from 1956 to 2004. The annual changes and distributions of climatic factors of the watershed are analyzed systematically. The features of runoff and sediment narration under human activities and climatic conditions are figured out. The contribution rate of human activities and prediction on runoff and sediment variation is quantitatively analyzed. Then, trends of runoff and sediment are predicted though BP neural network and ARIMA model. The main conclusions are drawn from this paper are as follow:(1) The changing features of climate in Kuye river watershed(1)The annual average precipitation is 408.9mm, and annual precipitation is on an obvious decreasing trend. The mutation year happened at 1959 with the main periods of 9 or 3 years. The annul precipitation distribution is inhomogeneous, and it tend to be an obvious single peak curve. The maximum of precipitation in a year always happen in July or August.(2)The annual average temperature in watershed is 8.1℃, and annual temperature is on a significant increasing trend. The mutation year happened at 1996 with the main periods of 33 or 13 years. The annul temperature distribution is inhomogeneous. The maximum of temperature in a year oftenly happen in July.(3)The annual average evaporation is 1029 mm, and annual evaporation is on an obvious decreasing trend. The mutation year happened at 1978 with the main periods of 11 or 25 years. The annul evaporation distribution is inhomogeneous. The peak of evaporation happen in May to July, and the maximum oftenly appear in June.(4)Runoff in Wenjiachuan station where the section is located at outlet of the watershed is in a remarkable decreasing trend. The mutation year happened at 1979 and 1996 with the main periods of 9 or 16 years. The annul runoff distribution is inhomogeneous, it tend to be an obvious double peak curve. Continuous maximum of three months appears in July to September.(5)The annual sediment at Wenjiachuan station turned out a significant decreasing trend. The mutation year happened at 1979 with the main periods of 9 or 6 years. The annul sediment distribution is inhomogeneous, and it tend to be an obvious single peak curve. The maximum appears in July to September.(2) Temporal variation features of runoff and sediment in Kuye river watershedThere is an obvious positive correlation between runoff and sediment in Wenjiachuan station, Kuye river watershed. Both of them tend to be a significant decreasing trend, and the mutation year happened at 1979. Sediment inflow coefficient is also declining. For high sediment concentration in unit runoff, basic state is riverbed erosion.There is also a periodic law between runoff and sediment in Kuye river watershed, but the cycle characteristics of runoff and sediment are not entirely consistent. The annual runoff of Wenjiachuan station had 2-4 years, 6-12 years, 14-20 years and 22-34 years period of time scales, and the main period are 9 years and 16 years. Sediment discharge at Wenjiachuan station had 2-6 years, 6-12 years and 14-30 years period of time scales, the main period are 9 years and 6 years.(3) The influence of human activities and climate variation on runoff and sediment variation in Kuye river watershedThe study takes Wenjiachuan station as a representative station, and analyses influences of climatic factors on runoff and sediment variation. The results show that precipitation is the main factors. Runoff and sediment affected by human activities occurred significantly deviates at the year of 1979. It is the reasons that a large-scale water and soil conservation work happened in the late 1970 s in Kuye river watershed, which resulted the mutation occurred in nearly 1979. Taking 1956-1979 as the base period, the changing period were 1980-1996 and 1997-2004. The contribution rates of human activities on runoff reduction were 63.09% and 87.27%, and the contribution rates on sediment reduction were 80.1% and 92.9%. There is a significant increase in human activities of contribution rates on the reduction of runoff and sediment, and the contribution rates are greater than the contribution rates of precipitation. Human activities are the main reason for the reduction of runoff and sediment in Kuye river watershed.(4) Prediction for trend of runoff and sediment variationBP neural network and ARIMA model are used to predict trends of runoff and sediment variation in Wenjiachuan station, Kuye river watershed. The results indicate that prediction effect of BP neural network model on the annual runoff and annual sediment is better. On the other hand, prediction effect of ARIMA model is better on runoff and sediment during the non-rainy season.