A Study On The Simulation Of Rainfall Runoff And Flood Process In Yunnan Reservoir Watershed

Rainfall runoff process is of great significance to the study on the water cycle in river basin,and the water balance of river basin is the prerequisite to scientific evaluation and appropriate allocation of water resources.Besides,the floods disasters in China are frequent,which caused enormous and catastrophic losses.Meanwhile,the simulation of the flood evolution process is an important reference for the development of the meticulous flood control plan.Therefore,it attaches great significance to water management in the watershed and flood prevention that characteristics of the runoff process and the water balance factors are accurately evaluated and the flood process and its impacts are precisely assessed.With regard to the issues above,this thesis simulates the rainfall runoff process in the upper reaches of Yudong Reservoir in Yunnan Province based on the NAM module and observation data of the MIKE 11 model and compares the influences that the different precipitation correction schemes and the evaporation estimation schemes to runoff simulation and basin water balance at the same time.Based on the MIKE11 HD module and the land use in the lower reaches of the reservoirs obtained by remote sensing,the thesis determines the spatial distribution of the surface roughness.Furthermore,the transmission characteristics of floods in three scenarios were simulated and analyzed by assuming three scenarios of water diversion and the burst in different river banks.The main conclusions are as follows:Firstly,the effects of Yang's,Chen's and Kang's precipitation schemes on the water balance in the upper reaches of Yudong Reservoir were compared respectively.It can be concluded that the average annual precipitation amount increased by 13.21%,7.94%and 8.75%,separately,and the average annual evaporation increased by 5.67%,2.53%and 3.59%,respectively.According to the Yang's scheme,the increase between annual precipitation and actual evaporation reaches the maximum after adjustment.The effect of precipitation correction on snowfall and mixed precipitation is larger,which indicates that the impact of solid precipitation influenced by the capture rate is the largest;in the extreme climate years,the corrected annual precipitation and the actual evaporation increased in high and low flow years,but the increase in low flow years was relatively large.Secondly,the effects of three kinds of evaporation schemes,including PM,ALLEN and 20 cm,on the runoff simulation and the water balance of the river basin were compared respectively.It was found that Nash efficiency coefficient is above 0.82 in regular and verification period,the correlation coefficient is above 0.95,the difference is relatively small,and the precision of the simulation is higher.PM and Allen have the applicability in a certain degree of this region,but the demand for data is large,the Allen fitting formula is relatively small for the amount of data.When the 20cm observation is used,the simulation results are the best,which indicates the importance of actual observation evaporation possesses for water balance simulation.P-M,ALLEN and 20cm evaporation schemes were calculated whose average actual evaporation was 560.4 mm,385.1 mm and 510 mm,respectively.Based on 20 cm observation evaporation,it is found that the evaporation of P-M is larger and ALLEN is smaller.Thirdly,the combination of different precipitation correction schemes and evaporation calculation scheme is adopted.The efficiency coefficient of regular and verification period is above 0.82,the correlation coefficient is above 0.92,and the difference of precipitation data is reduced.The results of the simulation are higher than those before the correction,indicating that the precipitation correction and evaporation may be considered to be closer to the true situation of the basin.Fourth,assuming the respective reservoir discharge flow is 150m3/s,200m3/s,and 250m3/s,in the case of river burst in its right bank of 3406m,the flow rate of the simulated initial flood is 3.34m/s,3.49m/s and 3.60m/s,respectively,which indicates that the continuous flow rate of the reservoir determines the transmission speed after the flood burst.The respective flow rate of the simulated floods is 3.61 m/s,2.75 m/s and 3.78 m/s,with continuous flow of 250 m3/s in the reservoirs and the river bank bursts the right bank of 3406m and the left bank of 8948m and 12363m respectively,which indicates that the flood flow is faster when the river burst under the circumstances that the bank-burst is closer to the reservoir.However,when a large tributary import into the mainstream during the river section,flood flow may be faster as well.Finally,with continuous flow of 250m 3/s in the reservoir,if the river burst in the right bank of 3406m,the flooding range will be 1.5km~2 and the flow rate will drop to 0.64m/s after floods transmitting for 96 h.Meanwhile,if the river burst at 8948m on the left bank of the river,the flooding range will be 0.87km~2 and the flow rate will drop to 0.57m/s after floods transmitting for 96h.Besides,if the river burst at 12363m on the left bank of the river,the flooding range will be 0.94km~2 and the flow rate will drop to 0.58m/s with the same time.When the flood transmission speed is less than 1m/s,its harm will be smaller.By and large,these results provide support for the development of flood control plans.