Two pumping tests were performed in the unconfined Motril-Salobreña detrital aquifer in a 250 m-deep well 300 m from the coastline containing both freshwater and saltwater. It is an artesian well as it is in the discharge zone of this coastal aquifer. The two observation wells where the drawdowns are measured record the influence of tidal fluctuations, and the well lithological columns reveal high vertical heterogeneity in the aquifer. The Theis and Cooper-Jacob approaches give average transmissivity (T) and storage coefficient (S) values of 1460 m 2 /d and 0.027, respectively. Other analytical solutions, modified to be more accurate in the boundary conditions found in coastal aquifers, provide similar T values to those found with the Theis and Cooper-Jacob methods, but give very different S values or could not estimate them. Numerical modelling in a synthetic model was applied to analyse the sensitivity of the Theis and Cooper-Jacob approaches to the usual boundary conditions in coastal aquifers. The T and S values calculated from the numerical modelling drawdowns indicate that the regional flow, variable pumping flows, and tidal effect produce an error of under 10 % compared to results obtained with classic methods. Fluids of different density (freshwater and saltwater) cause an error of 20 % in estimating T and of over 100 % in calculating S. The factor most affecting T and S results in the pumping test interpretation is vertical heterogeneity in sediments, which can produce errors of over 100 % in both parameters.
Abstract:The geomorphological characteristics and hydrogeological functioning of a geologically heterogeneous evaporitic karst plateau in Southern Spain were studied. Land surface information (LiDAR data) was used to analyze the shape and distribution of closed depressions. An artificial tracer test and monitoring of the natural responses of the main spring have allowed to infer the karstic development of the studied system. Three dyes were injected in selected swallow holes to trace the main groundwater flowpaths and to estimate the dimension of the conduit network. Discharge, electrical conductivity and temperature were monitored in the groundwater that drains the evaporitic plateau during an individual and intense recharge pulse. Tracing techniques were adapted to high salinity environments by using specific calibration standards (NaCl + dye). The hydrological connection detected between two of the swallow holes and the outlet, and the deduced orientation pattern for closed areas, would suggest that the karst evolution (internal and external) is related to fault orientation. The rapid tracer detection (16-20 h) and high estimated maximum flow velocities (125-192 m/h), together with the fast impulsional response of the controlled physicalchemical parameters in spring waters (~15-16 h) demonstrate the existence of quick flows under recharge conditions with well-defined system drainage, indicating a high degree of internal karstification (estimated master conduit diameter ~1.5 m). However, flooding of the depressions feeding swallow holes and analysis of the spring response times from natural and artificial tracers point to a restriction of the system´s drainage, most likely due to the constrained morphology of the karst conduits. This results in sustained recharge periods and delayed spring responses of some parameters, highlighting the relevant role of concentrated recharge in the hydrogeological behavior of the studied evaporitic karst. Gil-Márquez J.M., Barberá J.A., Mudarra M., Andreo B., Prieto-Mera J., Sánchez D., RizoDecelis L.D., Argamasilla M., Nieto J.M. and de la Torre B., 2017. Karst development of an evaporitic system and its hydrogeological implications inferred from GIS-based analysis and tracing techniques.
ResultsQuick flow variations in response to the main recharge events (from 1.2 to 3 8.3 m /s); about 3 days between the center of gravity of precipitation and the discharge peaks.Falls of up to 200 µS/cm in EC during each recharge event. The magnitude depending on the quantity and intensity of rainfall.Water temperature falls (up to 0.7 ºC) following main rainfall episodes, within a general seasonal pattern influenced by air temperature.When rainfalls were intense, EC and water T decreases were preceded by more mineralized and slightly warmer groundwater.The turbidity values shows quick rises during all recharge events, proportionally to the intensity of precipitation episodes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.