Analysis of Water Table Fluctuations to Improve Understanding and Quantification of the Groundwater Recharge Process in the Shallow Aquifer of the Gulf of Urabá (Colombia)

The groundwater recharge is the main inflow to the hydrogeological system, its conditions and characteristics determine the groundwater resource being renewable. In the conceptual hydrogeological model, the spatial and temporal characterization of the recharge is fundamental for the integral and sustainable water resource management. The water table fluctuations are direct hydrogeological data of an aquifer system and represent a state variable of these, allowing the analysis of fluxes such as the groundwater recharge and interaction of groundwater with other hydroclimatological variables.

This paper presents the quantitative and qualitative analysis of water table fluctuations of shallow aquifer of Gulf of Urabá in Antioquia – Colombia, using the hourly water table records and daily aggregated records from December 2016 to May 2018 in 13 monitoring points spatially distributed in a 1206 km² area of the aquifer system. The obtained data are graphically and statistically related with other hydroclimatological variables such as precipitation, evaporation, atmospheric pressure and tides on the coast of Gulf of Urabá. Using the soils characterization, pedotransfer functions and a water balance approach, specific yield (Sy) scenarios are determined and together with daily water table fluctuations series, detailed estimates of groundwater recharge direct are obtained applying the WTF method (Water Table Fluctuation).

The most influential hydroclimatological variable in the water table fluctuations is the precipitation, showing high statistical correlations with a lag of less than 5 days on the daily scale. Evaporation and atmospheric pressure also influence fluctuations, but mainly in the diurnal cycle with small level variations compared to those caused by precipitation. The tides in the Gulf of Urabá show a strong influence on the water table fluctuations in the portion of the aquifer near the coastline. Recharge rates from precipitation in the area show spatial temporal variability, influenced by the cited hydroclimatological variables and soils properties (texture, permeability and specific yield), showing greater magnitudes in the southern zone of the aquifer and lower ones in the northern area and close to the coastline of the Gulf of Urabá in Turbo town.