Response Of Runoff And Sediment To Rainfall In Changyan Small Watershed Of Enshi,Southwest Hubei

Due to heavy rainfall intensity,frequent and concentrated rainfall,high mountains and steep slopes and other factors,flood runoff and sediment are often produced in the southwest of Hubei Province,and the problem of soil erosion is becoming more and more serious,but there is little research and analysis in this area.Taking Enshi Changyan small watershed,a typical small watershed in Southwest Hubei,as the research object,and based on the artificially measured rainfall,runoff and sediment data,this paper analyzes the characteristics of rainfall,runoff and sediment in the small watershed and the response relationship between runoff and sediment yield and rainfall,and determines the empirical relationship through partial least squares regression analysis.This study draws the following conclusions:（1）The 30-year average rainfall of Enshi Changyan small watershed is 1408.4mm,and the rainfall erosivity is 7655.4mj·mm·hm-2·H-1·A-1.The occurrence times of normal water year are the most,and the occurrence times of partial abundant year are the least;The total rainfall in summer and autumn accounts for more than 60%of the annual rainfall;2018-2020 are the normal year,dry year and wet year respectively.In 2018,the number and proportion of heavy rain and rainfall are the largest,the number and proportion of heavy rain and rainfall are the smallest,the number and proportion of heavy rain and rainfall are the largest,the number and proportion of heavy rain and rainfall are the smallest,and the number and proportion of heavy rain and rainfall are the largest in2020,The number and proportion of heavy rainstorm rainfall are the smallest;In 2018,the rainfall duration of<2 hours accounted for the largest proportion,the rainfall duration of>24 hours accounted for the smallest proportion,the rainfall duration of 6～12 hours accounted for the largest proportion,the rainfall duration of<2 hours accounted for the smallest proportion,the rainfall duration of 12～24 hours accounted for the largest proportion in 2019,the rainfall duration of>24 hours accounted for the smallest proportion,and the rainfall duration of 12～24 hours accounted for the largest proportion,The rainfall of<2 hours is the smallest,the rainfall duration of<2 hours accounts for the largest proportion in 2020,the rainfall duration of>24 hours accounts for the smallest proportion,the rainfall duration of>24 hours accounts for the largest proportion,and the rainfall of<2 hours is the smallest;The rainfall types and processes are divided by K-means clustering.The proportion of type A,B,C and D rainfall sites is 71.1%,24.1%,3.7%and 1.0%respectively;1.The proportion of type II,III,IV and V rainfall sites is32.5%,15.9%,20.8%,15.9%and 14.9%respectively;From 2018 to 2020,there were 27rainstorm warnings,of which 16 Blue warnings were the main rainstorm warning form in small watersheds.（2）The peak value of runoff and sediment in small watershed appears or delays with the peak value of rainfall intensity;In 2018,the total runoff depth is 604.1mm,the runoff coefficient is 0.15,the sediment yield modulus is 6.78t/ha,the maximum peak discharge is 2.418m3/s,and the maximum sediment concentration is 0.630g/l,which occurs at the same time as the maximum peak discharge;In 2020,the total runoff depth is 828.4mm,the runoff coefficient is 0.46,the sediment yield modulus is 10.87t/ha,the maximum peak discharge is 16.693m3/s,and the maximum sediment concentration is 4.579g/l,which occurs in the same runoff with the maximum peak discharge;The rainfall in the small watershed is concentrated in the medium rainfall in the later stage,and the rainfall has a high contribution to the occurrence of flood runoff and sediment;The characteristics of typical runoff and sediment process show that there is a certain positive correlation among the overall changes of rainfall,runoff and sediment.（3）From the perspective of cluster a rainfall pattern,type B rainfall dominates the runoff and sediment yield of small watersheds at the same time.From the perspective of b-cluster rainfall pattern,type III rainfall dominates the runoff and sediment yield of small watersheds at the same time.The influence of rainfall type（process）on runoff and sediment yield in small watershed is similar.This also explains the correlation between runoff and sediment in small watersheds.（4）There is a good power function relationship between runoff,rainfall and rainfall erosivity in small watershed,and the expressions are y=13606.785x^0.915、y=693.251x^1.236,R²are 0.980;There is a good power function relationship between sediment and rainfall and rainfall erosivity,and the expressions are y=0.209x^1.114、y=0.001x^1.816,R²are 0.995and 0.982;There is a good power function relationship between sediment and runoff,and the expression is y=2.236E-07x^1.355,R²is 0.982.There is no significant correlation between runoff and sediment volume and early affected rainfall.（5）The total runoff QT of small watershed has a very significant correlation with rainfall P at the level of P<0.05,the total sediment se has a very significant correlation with rainfall P at the level of P<0.05,and the rainfall P has a very significant correlation with rainfall duration d at the level of P<0.05;There was a very significant correlation between peak discharge Qmax and rainfall erosivity at the level of P<0.05;The empirical relationship between total runoff and relevant variables is Q_T=-213483.533+2403.482 P+108.272 D+16861.259 I₃₀+5110.381SE,R²is 0.979;The empirical relationship between total sediment volume and relevant variables is SE=-5.900+0.161 P+0.007 D-0.311 I₃₀+1.927E-05 Q_T,R²is 0.959.