TEMPORAL AND SPATIAL ANALYSIS OF RECHARGE IN THE INTER-ANDEAN CATCHMENT OF TARQUI (ECUADOR)

Recharge is a component of infiltration after accounting for water storage, losses by evapotranspiration and interflow in the percolation zone. Recharge varies widely in space and time, and rates are nearly impossible to measure directly. The time and spatial variations of recharge have been identified as nonlinear and it has been recognized as one of the least understood hydrological factors.

In the Andean region, studies of recharge processes are overlooked. The hydrological researches in Andean catchments have focused in retention capacity, storage characteristics, and average recharge characteristics. The range of altitudinal variation and distinct physical features present in Tarqui Andean catchment suppose considerable spatial and temporal variation of recharge. Andean catchments face an accelerated change of land cover from rural to urban.

The present study investigates the spatial and temporal distribution of recharge in the Andean catchment of Tarqui. We aim to quantifying differences in recharge among the most representative ecosystems. The study calibrates a fully distributed hydrological model (WETSPA). We compare recharge results of different land cover and elevation areas for dry and humid periods. Self-organizing maps (SOM) tool analyses relationships between recharge and the physiographic features of the catchment.

The results show a good performance of WETSPA model for calibration and validation periods, therefore the Nash Sutcliffe efficiency is 0.75 and 0.65 respectively. Notwithstanding differences for dry and humid conditions, the upper catchment acts as a permanent place of recharge. Higher rates and wider areas of recharge are in the páramos located southwest of the upper catchment. The area corresponding to the alluvial aquifer in the lower part of the catchment shows high values of average recharge close to páramo values, but only for humid periods. Beside páramo vegetation the afforested needle trees locations also show high recharge.

The distribution of precipitation and the elevation are the most determinant factors for recharge. Self-organizing maps (SOM) show also strong dependence of the recharge to slope in the areas located over 2650 m. a.s.l. of altitude and Below 2650 m a.s.l., the recharge is strongly influenced by the vegetation type.