Abstract

To improve water supply services in Port Sudan City (Sudan), a dam with storage capacity of 16 Mm3 was established at the upper gorge of the Khor Arbaat catchment area, which generates runoff that contributes to the sedimentation of the dam at an average rate of about 6% annually. At present (2021), the storage capacity of the dam is reduced by 69% of its original design capacity. Without interventions, the dam is expected to continue silting up reducing its capacity to 94% of the original design capacity by year 2044. Although the dam has reduced the amount of runoff that reaches the alluvium aquifer and has caused groundwater recession downstream, the continuous sedimentation and reduction of the dam’s storage capacity mean the amount of water that could flow out would gradually increase.  Despite its sedimentation, the dam has provided groundwater recharge 1 km upstream of the dam resulting in a rise of 2 m in groundwater level and enabled irrigation of 85% of the arable land. Comparatively, a drop of 1.8 m was observed in groundwater level at 5 km upstream of the dam, with irrigation of only 33% of the arable land. Also, the interception of the base-flow/underflow by the dam, has contributed to the recession of groundwater downstream. These observations can help optimize the use of this resource; by reducing evaporation losses and maximizing the benefit from the reservoir’s available storage through the intensification of pumping during the winter period (October-March) when evaporation is comparatively low and reservoir storage can be replenished by winter runoff. Beyond technical fixes (and in the long term), management of water resources in the Khor Arbaat should consider the catchment area as a whole and in an overall framework of Integrated Water Resources Management (IWRM).

Key words: Base-flow, groundwater, integrated water resources management, irrigated land, sedimentation, runoff.