In many arid and semi-arid regions, large amounts of water annually flood the desert during extreme rainfall events without harvesting. Intervention to harvest water through subsurface dam is important to improve water supply during dry season in Chad. This research aims to test effectiveness of the subsurface dam to guarantee and store water during wet season to be used during dry season. A subsurface dam has been built in the Wadi that crosses the village of Korlongo. Korlongo located in the Dangaleat East canton, Abtouyour department in Guera province, Republic of Chad. The subsurface dam was built of a trench crossing the wadi. A plastic sheet is placed in the trench and glued to the bottom to stop the subsurfaces lateral flow of water and thus delay the possible drying up of a well placed in upstream. Water levels were monitored using piezometers. The results confirmed that the subsurface dam provides significant volume of water upstream. The water levels at upstream, drops less quickly during the dry season compared with downstream. Despite the daily withdrawal of water from the well, the dam makes water available throughout the year at upstream. A t-test indicates significant difference (p = .002) between the water levels upstream and downstream. The findings show the effectiveness of the subsurface dam in providing sustainable water
in semi-arid and arid region.