Hydrologic Modeling Of Karst Spring Using Storm Water Management Model

Karst aquifer is a multiple media system which is characterized by groundwater instead of surface water due to the high infiltration rates and the karst morphology developed comparing with non-karst system. Groundwater exists between diffuse flow and conduit; laminar flow and turbulent flow; linear and non-linear flow; continuous and non-continuous flow. Therefore, it is quite difficult to come to a precise description of flow movement in karst aquifer.The dynamic change of karst spring which is always the outlet of karst drainage system is considered as the reflection of the regional hydrogeologic characteristics. It is of great importance to probe into the relationship between regime of karst spring and the changes of physical environment and impacts from human beings, and to develop corresponding hydrologic model.This thesis took Shuifang spring which is located on the top of Jinfo Mt. as a case study. The catchment boundary and groundwater network were defined on the basis of field and cave survey, hydrologic observation and application of hydrochmecial analysis, infiltration and tracer tests. Main parameters for quantitative analysis were acquired from the DEM data and statistics in Arcgis. SWMM was taken as the tool to simulate time series processes in response to different type of storm. The preliminary study has come to several conclusions as followingSpecial technical methods must be applied to the study of karst aquifer due to its particular characteristics comparing with non-karst aquifers. With multi-tracer tests and quantitative analysis, the catchment boundary was defined. It also suggests conduit flow between swallow hole and the spring which provide the base of catchment conceptualization and hydrologic modeling.Soil infiltration tests in representative sites suggest that infiltration rates in karst systems largely exceed the normal reference value in non-karst area which could span a range of 40~360mm/h due to the heterogeneity of karst aquifer and spatial difference of soil thickness. However, the empirical SCS model could be well applied in karst area with some adjustment according to observation and evaluation.The karst aquifer could be considered as a conceptualizing equivalent porous media subsystem in order to reflect the heterogeneity and anisotropy.SWMM was proved to be applicable in simulation of karst hydrologic process. The error of simulation to storm (time series I and II) for calibration and validation were 1.7% and 6.9% respectively with the model efficiency coefficient of 0.99 and 0.91. And to the medium-low precipitation (time series III and IV), it comes to an error of 3.4% and 2.8%, and the efficiency coefficient of 0.88 and 0.99. Therein, comparison of simulated and observed hydrograph reflected impacts from human beings which cut and lag the flow peak, and consequently contributed to a relatively higher error and lower efficiency coefficient. For the simulated time series III, the lower model efficiency coefficient was mainly caused by the restriction of one Unit Hydrograph shared in one month.This study has come to a conclusion that Shuifang catchment is a matrix restrained flow recession system. Statistics of different simulated inflows suggested that groundwater inflow from small fissures, porous and seasonal and perennial epi-karst spring dominated the system. Rain dependent infiltration and inflow from sinkholes, big fissures and shafts took the second place of contribution to the spring discharge. And surface runoff which only or largely generated during storm events took the smallest proportion of the total outflow. This suggests that the spring has relatively good self-adjusting capability. In general, runoff and RDII took their highest proportion during rainfall period, and decreased with the recession process. In contrast, groundwater inflow and dry weather inflow (waste water from human beings) took their lowest proportion and increased as flow recessed. Still, in the low intensity and relatively long-time lasting rainfall, runoff took the lower proportion even none while groundwater took the higher comparing with that in storm events.This paper studied relations and effects between different flows in multiple media of karst systems by numerical modeling with the tool of SWMM which could be a reference to small karstsystem modeling.