Study On The Rainfall And Runoff Process Of Yaoxiang Small Watershed

Shandong province was located in the northern mountainous area of our country, the soil was thin,the rock was crushed and was badly weathered, the ecological environment was very fragile, soil fertility and retention capacity were low, hilly areas were drought and poor. The area of soil erosion area was larger and large and the soil erosion of Shandong province was three times of the national average. It was imminent to carry out the work to control the soil erosion of the hilly area in Shandong province. Through the study of rainfall and runoff in hilly areas would help to deeply understand on the process and mechanism of runoff response mechanism of rainfall, and it would provide theoretical basis for the corresponding soil and water conservation measures.This study was taken the Yaoxiang small watershed in Tai'an as the research object which was located in the hilly areas of Shandong province. On the basis of observation data of rainfall and runoff during 2012 to 2016, the quantitative and qualitative relationship between rainfall and runoff could be obtained through the analysis of rainfall and runoff.Different methods of base flow separation also be used to divide the components of runoff so as to obtain a more suitable method for the base flow separation in this small watershed then the hydrograph of flood water was also be divided. All what we do were to provide theoretical reference for the study of runoff production process in hilly areas of Shandong province. The main results were as follows:(1) The rainfall in Yaoxiang small watershed had obvious seasonal change and a unimodal distribution. It was mainly concentrated in May to September which was accounted for 85.6% of the rainfall in the year. The total amount of erosive rainfall accounted for 82.5%of the total rainfall, the proportion of July to September was the largest, which was accounting for about 18.7%-40.4% of all erosive rainfall. The maximum value of each rainfall characteristic appeared in July, the rainfall was mainly affected by the summer monsoon, and the rainfall was extremely unbalanced. Runoff had a certain lag effect compared with rainfall,but the time was generally the same as rainfall, which was distributed in May to November.The correlation between rainfall and runoff was got by Pearson correlation analysis and stepwise regression analysis. Rainfall, rainfall duration and maximum rainfall intensity of 30 min were the main controlling factor of runoff, and were positively correlated with the total amount of runoff. Rainfall and maximum rainfall intensity of 30 min had a greater impact on Runoff.(2) When the amount of rainfall and duration and other indicators of two rainfall was similar, whether there was a pre-rainfall had become the main factor to affect the runoff.When there was rainfall in the early stage, the runoff would generate at the beginning and it was very sensitive to the change of rainfall. The runoff reached the peak with the same time as the rainfall. When there was no rainfall in the early stage, runoff would lag behind the rainfall, and the length of the lag time depended on the soil moisture content.(3 ) According to rainfall, rainfall duration and rainfall erosivity, we divided 180 times of rainfall between 2013 to 2016 into three kinds of rain type by K-means clustering method in Yaoxiang small watershed. The type ? had the characteristic that the average rainfall was small, the rainfall duration was shorter and the rainfall erosivity was smaller. The type ? had the moderate rainfall, longer rainfall duration and moderate rainfall erosivity. The type ?had the characteristic that the rainfall duration was moderate, the rainfall and the rainfall erosivity were large. The difference between different runoff caused by three kinds of rainfall was very obvious, which was type ? >type?> type ? .Thus type ? was the main rain type to caused the runoff in Yaoxiang small watershed, which was about 50.3% of the total runoff.(4) Using digital filtering method and base flow index at the same time to do the base flow separation on runoff in Yaoxiang small watershed, we found that the most appropriate method for base flow separation was digital filtering method. And the most appropriate filter parameters were that a was0.525and ? was0.925. The beginning of the next flood was the turning point of this flood and the last of the flood, and the last time of the flood was from this point to the end. The second section of the withdrawal process of the flood was gentler than the first section.