A sensitivity analysis of conduit flow model parameters and its application to the catch area of the Xujiagou spring

In the karst aquifer systems, the pipelines as the main drainage channels have a certain control effect on the spring flow dynamics, and the pipeline characteristic parameters also have an impact on the flow variation. In order to determine the influence of various parameters of the pipelines, the karst water systems developed by the pipelines were studied by predecessors, and the response of the spring discharge of short-time series was analyzed and discussed. However, the research on the karst water systems which were not very developed by the karst pipeline is relatively weak. For this reason, this study combines the development characteristics of karst water systems in North China, analyses the influence degree and sensitivity of various parameters of pipeline on the flow rate and flow pattern of karst systems by means of the CFP pipeline flow model, and constructs the MODFLOW-CFP model of the spring basin based on the karst hydrogeological characteristics of the Xujiagou spring basin in Hebi of Henan. The seepage of karst groundwater is simulated and the spring discharge under different rainfall guarantee rates is predicted. The results show that the pipe flow rate is positively correlated with the coefficient of permeability of the pipe wall, the slope and diameter of the pipe, while the pipe flow rate increases first and then decreases with the increasing bending and burial depth. The influence of the pipe wall roughness on flow rate is small and shows certain fluctuation, especially when the pipe wall roughness is small, the fluctuation is obvious. Sensitivity analyses show that the sensitivity of the coefficient of permeability and burial depth of pipe wall is the highest, followed by the curvature and slope of pipe, while the sensitivity of diameter and roughness of pipe wall is the lowest. Under the rainfall guarantee rate of 25%, the annual maximum spring discharge is 0.45 m3/s and the average spring discharge is 0.36 m3/s. Under the rainfall guarantee rate of 75%, the annual maximum spring discharge is 0.41 m3/s and the average spring discharge is 0.31 m3/s, which are consistent with those of the actual situation. This method can provide reference for water resources evaluation, development and protection in karst areas of northern China.