Areal exploitation of groundwater in coastal dunes

Category Hydrogeology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Carretero, Silvina۱; Kruse, Eduardo۲
Holding Date 29 September 2008

In the study area, the groundwater of low salinity is restricted to the fringe of coastal dunes. This is the only drinking water source for a permanent population that is superior to 10.000 inhabitants. In summer, the region presents a tourist high which multiplies de population by 5.
In this paper the current groundwater exploitation is described and future management guidelines are evaluated in front of the necessary increase in water demand.
The coastal dunes has a morphological expression between 0.5 to 3.5 m.a.s.l. The fresh water lens is limited by sea water and brackish continental water. To avoid the salt water intrusion an areal exploitation is carried out. There is a pumping field, located outside of the urbanized area, composed by 7 horizontal wells, Ranney type, (flow 7 m3/h) and for 21 well point systems, each one connected to 10 wells (flow 13 m3/h).The extraction depth varies between 4 m & 6 m.
The system recharge only takes place from the precipitations (1000 mm/year), while the natural discharge is by the evapotranspiration (640 mm/year), with hydric excesses of 360 mm/year. In the current situation a direct relationship between the precipitations and the variations of the phreatic level is observed.
That is evidenced for a quick answer before the recharge from the excesses as a result of the rains. The extraction flows have a maximum value in January and February (1200 m3/day) which coincides with the tourist biggest affluence. In the minimum extraction period, between May and September (300 m3/day) a recovery of groundwater levels is manifested while they are significantly deepened in summer months with the increased demand. Given the methodology of exploitation the levels do not deepen below 0 m.a.s.l. oscillating between 0.7 and 3.1 m.a.s.l.
The extracted flows are in the range of the regulating reserves and therefore there is not a substantial modification of the natural water cycle. It is necessary to increase the drinking water supply to cover the needs of a bigger number of inhabitants. The management pattern should include the selection of new exploitation areas including a detailed water input and output quantification to the hydrological system. It is also recommended an areal exploitation to scarce depth, being fundamental that the use areas should be declared reservation areas to conserve the recharge areas and to avoid all possible contamination of the groundwater.