The Effects of Exchange Flow on the Karst Spring Hydrograph under the Different Flow Regimes: A Synthetic Modeling Approach

In this study, a synthetic modeling approach is proposed to quantify the effect of the amount and direction of the exchange flow on the karstic spring discharge fluctuations under different hydrologic conditions corresponding to high and low flow conditions. We hypothesis that the spring discharge fluctuations constitute a valuable proxy to understand the internal processes of the karst system. An ensemble of spring hydrographs was synthetically produced to highlight the effect of exchange flow by exploring the plausible range of variability of coefficients of exchange flow, conduit diameter, and matrix hydraulic conductivity. Moreover, the change of the rate of point recharge through the karst conduit allows for the quantifying of the sensibility of the spring hydrograph to the directions of exchange flow. We show that increasing the point recharge lies to a remarkable linear recession coefficient (β) as an indication of the conduit flow regime. However, a reduction in and/or lack of the point recharge caused the recession coefficient to change to exponential (α) due to the dominant effect of the matrix restrained flow regime and/or conduit-influenced flow regime. The simulations highlight that the exchange flow process from the conduit to the matrix occurred in a short period and over a restricted part of the conduit flow regime (CFR). Conversely, the exchange flow dumped from the matrix to the conduit occurs as a long-term process. A conceptual model is introduced to compare spring hydrographs’ characteristics (i.e., the peak discharge, the volume of baseflow, and the slope of the recession curve) under the various flow conditions with the directions of the exchange flow between the conduit and the matrix.

Modeling and Prefeasibility Management, and Conservation Strategies for Fuentetoba Springs, (Spain)

The efficacy of various catchment and management schemes in the regulation of the Fuentetoba karst spring (Spain) was evaluated by using its groundwater reserves. This regulation of the spring would simultaneously serve to increase the reliability of the drinking-water supply to Soria (Spain), develop the ecological flow of the river that has its source in that spring, and improve the environmental needs and requirements by managing the flow of a remarkable natural waterfall at its source. Speleological explorations have been essential in designing a pumping system in the drainage conduit of the spring located 400 m upstream of it and 45 m below the level of the aquifer drainage. For the evaluation of the viability of the interannual regulation, the hydraulic dynamics of the spring were analyzed by calculating the inputs and outputs of water to the system with the application of a precipitation–runoff model that was used to simulate the pumping effects in the spring hydrograph. The results indicated that the aquifer presented a high guarantee of having a flow for the supply for the environment. This study can be applied to other springs, and may be useful in sustainably managing any aquifer.