Turbulent and laminar flow in karst conduits under unsteady flow conditions – interpretation of pumping tests by discrete conduit-continuum modeling

<p>Due to the duality in terms of (1) the groundwater flow field and (2) the discharge conditions, flow patterns of karst aquifer systems are complex. Estimated aquifer parameters may differ by several orders of magnitude from local (borehole) to regional (catchment) scale because of the large aquifer heterogeneity and anisotropy. One approach to deal with this scale problem in karst aquifers is the application of large-scale experiments such as long-term high-abstraction conduit pumping tests, stimulating measurable groundwater drawdown in both, the karst conduit system as well as the fissured and fractured aquifer matrix. The numerical discrete conduit-continuum modeling approach MODFLOW-2005 Conduit Flow Process Mode1 (CFPM1) is employed to simulate laminar and non-laminar conduit flow, induced by large-scale experiments, in combination with Darcian matrix flow. Effects of large-scale experiments were simulated for idealized settings. Subsequently, diagnostic plots and analyses of different fluxes are applied to interpret differences in the simulated conduit drawdown and general flow patterns.</p> <p>The main focus is set on the question to which extent different conduit flow regimes will affect the conduit as well as the matrix drawdown depending on the hydraulic properties of the conduit system, i.e. conduit diameter and relative roughness In this context, CFPM1 is applied to investigate the significance of turbulent flow consideration for the simulation of karst conduit flow. This work quantifies the relative error that results from assuming laminar conduit flow for the interpretation of a synthetic large-scale pumping test in karst.</p> <p>https://doi.org/10.1002/2017WR020658</p> <p>&nbsp;</p>