Modeling the spatial and temporal distribution of coastal groundwater discharge for different water use scenarios under epistemic uncertainty: case study in South Portugal

Abstract

The following paper presents a discussion of spatial and temporal distribution of groundwater discharge estimates at a regional scale for two coastal aquifer systems in the Algarve region. A finite element distributed parameter groundwater flow model is applied to analyze the effect of uncertainties regarding definition of model boundary conditions and seasonality on estimated values. Finally, estimates of sustainable yields are provided based on predefined sustainability criteria and the importance of well location is analyzed. Steady-state simulations indicate a range of average annual coastal discharge between 6.5 9 10 6 and 15 9 10 6 m 3 /year from the AlbufeiraRibeira de Quarteira aquifer, and 4.5 9 10 6 and 11.3 9 10 6 m 3 /year from the Quarteira aquifer, as well as significant spatial variation. Transient simulations show that seasonal variability inherent to these systems can lead to inversions of hydraulic head gradient during short periods. Model results indicate that coastal discharge rates are between 1.5 and 2 times higher during the peak winter months than during the minimum in the summer, and as such seasonality has a larger impact on discharge rates than BC conceptualization. Up to 3.31 9 10 6 m 3 /year could be abstracted from existing well fields without causing seawater intrusion problems. Historical levels of abstraction are not within the selected sustainability criteria. However, by placing abstraction further from the coast sustainable yield increases. This work is part of ongoing research that aims to identify and characterize groundwater flow from the coastal strip towards the continental platform, taking into account structural geology, marine geology and the effects of the hydrological/hydrogeologic conditions on the associated ecosystems.

A Methodology to Analyse and Assess Pumping Management Strategies in Coastal Aquifers to Avoid Degradation Due to Seawater Intrusion Problems

“…Due to these computational advantages many application of these sharp interface solutions can be found to solve management optimization problems (AtaieAshtiani and Ketabchi, 2011;Sreekanth and Datta, 2011;Uddameri et al, 2014;). Although a direct use of finite difference groundwater flow models as MODFLOW code is not the most appropriate to modeling coastal aquifer processes, it is still a very employed approximation that can be useful to asses management alternatives in some cases (PulidoVelazquez et al, 2008;Rejani et al, 2009;Liu et al, 2010;Llopis-Albert and PulidoVelazquez, 2015;Hugman et al, 2015).…”

“…Over the last decade, the application of the EU Water Framework Directive (EU-WFD, 2000, Willaarts et al, 2014;Indset et al, 2015), has promoted the development of research work about sustainable use and management of groundwater in coastal aquifers (Ferreira da Silva and Haie, 2007;Hugman et al, 2015;Senent-Aparicio et al, 2015). To prevent progress of marine intrusion inland, the fresh groundwater flows to the sea must be maintained.…”

“…Though marine intrusion can be a hydrodynamically very complex process, it can be assumed that there is a direct relationship between the flow of fresh groundwater towards the sea and marine intrusion. As a consequence, the determination of the coastal groundwater discharges under different scenarios is important to analyze management alternatives (Zhou, 2014;Hugman et al, 2015). The classical sustainable and optimal yield concept has been extensively applied to analyze groundwater management problems (Peralta et al, 2011;Mays, 2013).…”

“…Again, its application has additional difficulties due to the higher complexity of the coastal aquifer processes and their modeling approximation. Some research works in coastal aquifers use the inversion of the hydraulic head gradient as the criteria to obtain the sustainable yield (Hugman et al, 2015;El-Kadi et al, 2014).…”

Integration of hydrogeophysics and remote sensing with coupled hydrological models

“…During year 1999 and for both aquifers ARQ and Quarteira (M7 in Figure 3.1), this value was 8.43×10 6 m 3 .y −1 , which corresponds to 30% of estimated average annual recharge of these two aquifers (Hugman et al, 2014b). After 1999, public water supply was mainly ensured by surface water, although groundwater was also episodically pumped in summer season to compensate dam surface water shortage.…”