Groundwater resources in Maknassy basin (central Tunisia): hydrological data analysis and water budgeting

The Maknassy basin in central Tunisia receives only a small amount of precipitation (207 mm/year), and hydrological system retain very small quantities of water due to the steep topography and surface water resource partially mobilized which is evacuated toward the basin outlet. However, the Maknassy plain support agriculture based on ground water irrigation with increasing water demand for the last decades. These developments have boosted agricultural productivity in the region. While these problems are mainly due to poor surface water management strategies in the region, the groundwater resources in this basin should be properly assessed and suitable measures taken for uniform surface water mobilization. As a first step in this direction, groundwater resources have been assessed. Regional specific yield (0.017) and groundwater recharge have been estimated on the basis of water table fluctuation method. During the hydrological year 2004-2005, groundwater recharge amounting to 116*10(6) m(3) in a year takes place in the region through infiltration of rainwater (44.5* 10(6) m(3) for phreatic aquifer and 71.5*10(6) m(3) for the deep one), and recharge due to the infiltration in the Leben watercourse bed (1.57* 10(6) m(3)). Recharge from deeper aquifer to the shallow one has been estimated at 0.01*10(6) m(3). The outflow consists of (1) groundwater draft by wells (4.5*10(6) m(3) from phreatic aquifer and 5.78* 10(6) m(3) from the deep one), (2) spring discharges (0.15*10(6) m(3) only from shallow aquifer), and (3) groundwater evapotranspiration (92.52* 10(6) m(3)). Assuming that at least 40% (102.61*10(6) m(3)) of the total precipitation water (256.645* 10(6) m(3)) makes the runoff water, this important resource can be mobilized in order to increase groundwater recharge. Subject to an arid climate, such region requires an integrated water resource management. It permits to keep aquiferous system equilibrium and participate to the sustainable development which integrates natural resource management.