| As a first-level tributary on the right bank of Dadu River,Niri River is an important water source of Dadu River,flowing through important crop growing areas and densely populated areas in Liangshan Prefecture,Sichuan Province.In the basin,The distribution of water resources is in homogeneous in time-space,debris flow disaster and flood are prominent.Therefore,it is of great significance to analyze the hydrological characteristics,the annual runoff inversion and the abundance and depletion analysis of the trunk and tributaries of the Niri River.Quantitative analysis of the trunk and tributaries of the Niri River can effectively reduce the occurrence of geological disasters.Inversion and analysis of annual runoff can optimize the utilization and allocation of water resources and reduce the losses caused by flood disasters.In this paper,the hydrological characteristics of the main and tributary streams of Niri River were quantitatively studied based on the DEM data with a spatial resolution of 30 metres.Based on the spatial precipitation grid data in the basin,and combined with the measured runoff from Yanrun Hydrological Station during 1979-2018 and Shunhe Station during 1970-1988,the runoff coefficient was obtained.Using the relatively optimized runoff coefficient method to retrieve the annual runoff of the areas without data in the main and tributaries of the basin,compared with the inversion results of the traditional area analogy method,it is found that the inversion value of the runoff coefficient method is closer to the measured runoff with high accuracy,while the error of the area analogy method is larger,so the runoff retrieved by the runoff coefficient method is taken as the historical runoff value of the missing years in the main and tributaries of the Niri river.The annual runoff of the main and tributary streams at different frequencies was calculated by the method of suitable line and the abundance and drainness were analyzed.The results are as follows:(1)Through the quantitative study on the hydrological characteristics of the trunk and tributaries of the Niri River,it is found that the river system in the Niri River Basin is developed and the river network is dense.Among the six main primary tributaries,four are located on the left bank and the other two are located on the right bank,which indicates that the left bank is better developed than the right bank.The whole basin area of Niri River is 4084 km2,among the subbasins,Ganluo River Basin has the largest basin area of 909.6 km2,but Baisha River Basin has the largest river network density,reaching 0.297km/km2.The area and density of river network in the middle reaches of Shuanghe River Basin are the smallest.The basin area is only 94.5 km2,and the density of river network is 0.198km/km2.The shape coefficient of the Niri River Basin is 0.21 after calculation,and the whole basin is long and narrow,which is in line with the characteristics of mountain basin.The main river has a total length of 136 km,with an average gradient of 12.49‰,showing a slightly concave type.Yuexi River,its tributary,is the most concave,and its gradient has great internal differences.The vertical gradient of Baishahe River reaches 105.58‰,the depth of the channel cutting is shallow,and the water energy resources in the basin are rich.(2)Characteristics analysis of runoff coefficient in the main stream: the fluctuation range of runoff coefficient in the main stream of the Niri River Basin is 0.58 to 0.92,indicating that the overall water production capacity of the Niri River Basin is strong.Among them,the average runoff coefficient of Shunhe Station in the upper reaches during 1979-1988 was 0.79,lower than the average runoff coefficient of Yanrun Station in the middle reaches during the same period,which was 0.83.The average runoff coefficient of Yanrun Station during the different periods during 1979-2018 was 0.80,which was also higher than the runoff coefficient controlled by Shunhe Station,which fully reflected that the water production capacity of the lower reaches was stronger than that of the upper reaches.In order to better reflect the spatial difference of runoff among sub-basins,the runoff analysis among different hydrological units was carried out,and the results showed that the runoff depth from the upper basin to the lower basin showed a decreasing trend.(3)Based on the measured runoff data of hydrological stations,the optimized runoff coefficient method and area analogy method are used to carry out the annual runoff inversion and accuracy verification in the areas where the main and branch rivers are not measured.It is found that the inversion value of the runoff coefficient has higher accuracy,so it is used as the estimation value of the main and branch rivers.The total runoff of Niri River Basin from 1979 to 2018 is 155.596 billion cubic metres,and the average runoff in 40 years is 3.889 billion cubic metres.Among the sub basins,the total runoff of Ganluo river is 34.336 billion cubic meters,and the annual average runoff is 858 million cubic meters,accounting for 22% of the total runoff.However,the total runoff of Shuanghe river is 3.741 billion cubic meters,with an average runoff of 93 million cubic meters in 40 years,and its contribution rate to the runoff of the whole basin is only 2%.The main reason is that the grid precipitation data of runoff coefficient method is more accurate in this study.Secondly,the spatial difference of total precipitation is considered in the runoff inversion of tributaries.(4)Based on the fitting line method,the P-? distribution is selected as the overall line type,and the flood and dry flow of the main and tributaries under different probabilities of P = 1%,P =2%,P = 5%,P = 10% in hydrology are calculated.The results show that the annual high flow of the main stream of Niri river is 5.275 billion cubic meters,and the annual low flow is 2.372 billion cubic metres.The maximum annual flood flow of Ganluo river is 1120 million cubic metres in the tributary of the Nigerian river.The lowest low flow in tributaries is Shuanghe River,and the dry water flow rate of one hundred year return period is 66 million cubic metres.The comparison between the historical annual runoff and the predicted runoff shows that the year of the wet season in the Niri river basin is more than that in the dry season. |
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