The Study On The Process Of Runoff In Tianlaochi Catchment In The Upper Reaches Of Heihe River Basin

The Qilian mountains are not only the water sources regions,but also the most critical zone where the interactions of ecological and hydrological processes occur in Hexi corridor region.The study area is selected in Tianlaochi catchment which is located in the upper reaches of Heihe River.We measure the underground water discharge,slop runoff,river runoff and analyze the correlation between them and the impact factors(i.e.,meteorological factors,soil moisture,and so on).We also analyze the relationship between underground runoff and river runoff.We hope to provide a scientific basis for water resources management.The results are as follows:(1)The groundwater discharge is affected by precipitation and temperature.Precipitation has hysteresis and the cumulative effect on the groundwater discharge,and temperature also has a hysteresis effect on the groundwater discharge.During winter times and from May to June,the change of the groundwater level is mainly controlled by temperature.From June to October,the groundwater dynamic is mainly affected by precipitation and rainfall pattern.From February to March,the underground water level reaches the lowest in a year,and it reaches the highest in July or August in a year.(2)There are five vegetation types(Qinghai Spruce forests,Sabina przewalskii forests,Grassland,Bushwood,Steppe).Only slope runoff is generated in steppe plots.This is mainly caused by soil bulk density and soil texture.In addition to the soil properties,slope and altitude also affect slope runoff.Within a certain range of slope,runoff increases with the increase of the slope.When the slope reaches a threshold,slope no longer affects the slope runoff.In the steppe plots,slope runoff increases with increase of elevation and altitude.The slope runoff has significant linear correlation with precipitation(P),rainfall intensity in 30 minute(I30)and rainfall intensity in one hour(I60).The correlation between the slope runoff and temperature,and the average rainfall intensity is not significant.The slope runoff is mainly affected by rainfall intensity and precipitation.(3)From April to May,river flow is mainly affected by temperature.The precipitation plays a main role in affecting the river flow after June.The current day runoff has a significant linear correlation with accumulating rainfall in 20 days.That is,the response of river flow to precipitation has a lag.After river runoff reaches the maximum,there is an exponential function relationship between runoff decline rate and time(d).(4)The correlation between river runoff and surface soil temperature and humidity is significant,expressed by a significant power function relationship between river runoff and soil moisture and a significant exponential function relationship between soil temperature and river runoff.(5)During the growing season,the base flow index(BFI)is 0.52.The groundwater runoff supplies for the river runoff.River runoff(Qr)increases with the increase of underground runoff(Qg),being an exponential function as: Qr=0.0028e112.17 Qg with R2 = 0.8104.The relationship between the base flow and water level difference is: Qb = 6 e + 0.8 e-2.843 ? h,R2 = 0.6213.Totally,the river flow is mainly supplied by the base flow and precipitation.