Karstic aquifers present a complex heterogeneity in their conductive and capacitive characteristics that are evident in a great spatial and temporal variability. This fact is increased in the carbonate aquifer Pradoluengo-Anguiano (La Rioja, Spain) by the action of the tectonic structures that compartmentalize it. The Oja river crosses the aquifer draining it through some springs and indirectly through a quaternary deposit of alluvial materials. This defines two blocks of the carbonate formation on both banks of the river. In a natural regime, the blocks are hydrodynamically disconnected from each other.
The water supply provides the commonwealth (Oja – Tiron) composed of 46 urban areas. The water demand will be directly satisfied by the resources of the karstic aquifer due to the presence of threats in quantity and quality of water in relation with nitrate contaminants. This is an important touristic area which has a marked seasonal variation in the number of inhabitants. The fixed population is 31,000 and rises to 46,000 approx. in the summer months. The strong seasonality of demand is accentuated by the Mediterranean climate of the region where rainfall occurs in autumn and spring and by the current evolution of the climate. The main objective of the presented study was to quantify the resources of Pradoluengo-Anguiano carbonated aquifer between 1980 and 2017. The secondary objectives were: to analyze the temporal trend of recharge and to identify annual and seasonal water stress scenarios of the aquifer. All this trying to contribute to an improvement of the water management scheme oriented to the satisfaction of the urban demand.
A numerical study was carried out with the semi-aggregate model Visual BALAN (Samper et al., 2005) to quantify the water balance (WB). This code allows the representation of the different elements of the water cycle and, particularly in this case, the recharge from snow precipitation.
Numerical modeling reached all the established objectives and, possibly, has allowed the identification of some types of geological control over recharge that makes it not proportional to precipitation. The average annual recharge of the aquifer was evaluated at 5.25 hm3. In the block of the left margin (surf.= 18.12 Km2) it is 90.67% of the total recharge of the aquifer (surf.=19.97 Km2) and in the right margin (surf.= 1.85 Km2) it is 9.33%.