岩溶管道结构影响泉流量变化的数值模拟研究

采用MODFLOW-CFP建立管道流数值模型，模拟岩溶含水系统在暴雨期的响应过程，以泉口流量峰值作为因变量，分别对控制管道结构的4个参数以及落水洞集中补给比例进行调整，研究管道结构如何控制泉流量变化过程。结果表明:管道直径、管壁渗透系数和落水洞补给比例对泉口流量峰值均表现为正相关，其中管壁渗透系数影响最大；管道弯曲度值较小时其增大促进出口流量峰值变大，当径流途径变长引起的流量减小幅度超过管壁面积变大引起的流量增大幅度时，流量峰值逐渐变小；管壁粗糙度在达到两个相对应的雷诺数临界值时水流状态发生突变，导致流量峰值也表现为两次突变。 

Numerical modeling of the influence of karst-conduit structure on variation of spring flow

The spring hydrograph, such as variation of flow, can be used to extract information on the structure of karst conduits, while the complexity of these conduits makes such study not very successful. To solve this problem, this work employs a numerical model of the known karst conduit structure to reveal the relationship between the spring hydrograph and the conduit structure, which will help address this issue for real cases. This conduit flow model is built with MODFLOW-CFP to study the karst aquifer response in a storm period. The basic features of the karst aquifer of this simplified model are taken from a deeply-cut valley of the Liuchong river in Guizhou Province. This karst aquifer consists of a single conduit and a fracture network which is treated as an equivalent continuous porous medium. The valley is regarded as the river boundary of the karst water system, and the water level of the river is higher than the location of the spring outlet, so the conduit can be saturated with water. In the modeling spring hydrograph, the peak flow value is chosen as the dependent variable in the analysis of the karst conduit, and 4 parameters of the conduit structure and the recharge ratio of sinkhole are studied, respectively. The results show that the pipe diameter, wall permeability and the concentrated recharge of the sinkhole are characterized by positive correlation with the spring flow peak, of which the wall permeability has the greatest effect on the flow peak. When pipe bending is smaller, the spring flow becomes bigger, while the growth of the flow peak is limited by the tortuous flow path. The water flow status experiences two abrupt changes at the two critical Reynolds number of conduit-wall roughness, leading to twice of sudden variations of flow peak.