Damming underground flow to enhance recharge of karst aquifers in the arid and semi-arid worlds.

Subsurface dams could be an optimal solution for storing floods or waters of temporary streams in countries with arid and semi-arid climatic conditions. Many such structures are already completed in the northern and eastern African countries and Middle East, but many other prosperous locations require feasibility assessment and construction if found appropriate. Two types of dams are common: one built in the karst (for direct recharge), and the other into the karst connected alluvial aquifer (for indirect recharge). The former is very rare due to its complicated construction and threat of water leakage. The latter has more often, but not always been applied with the aim to improve storage in karst, but as an indirect effect of damming of the flow in adjacent alluviums. This article discusses some positive experiences with dams built in northern Iraq, Algeria, Ethiopia and Somalia and advantages of the application of such subsurface structures in several potential locations in countries with a prevailing arid and semi-arid climate, but it also explores uncertainties which end-users may face if the engineering design is not prepared based on results of a proper research programme. [ABSTRACT FROM AUTHOR]