Impact of water harvesting techniques on soil and water conservation: a case study on a micro catchment in southeastern Tunisia

A commonly applied water harvesting technique (WHT) in Tunisia is the jessr, in which runoff from a micro catchment, called impluvium, is collected on a terrace in order to increase water availability for vegetation (crop and trees). In this study, infiltration and runoff measurements were carried out at the impluvium of the Amrich jessr (southeastern Tunisia) in order to predict runoff and sediment transport for different rainfall events. The simulation results indicated the importance of the jessr in retaining water and sediment. Furthermore, over a period of 3 years, rainfall and infiltration data were used to assess the water balance on the terrace of the jessr. The results showed that especially during dry years the impluvium of the jessr provides an important supplementary amount of water for the cultivation of olive trees (Olea europeae). Finally, it was estimated that the ratio “impluvium area/terrace area” (CCR) should be at least 7.4 in order to provide, on average, sufficient water for olive cultivation, taking into account an average annual precipitation of 235 mm.