Rainfall conditions and rainwater harvesting potential in the urban area of Khartoum

• Published in: Resources, conservation and recycling Vol. 91; pp. 89 - 99
• Main Authors: Mahmoud, Wifag Hassan, Elagib, Nadir Ahmed, Gaese, Hartmut, Heinrich, Jürgen
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.09.2014; Elsevier
• Subjects: Applied sciences; Conservation; Continental surface waters; Drainage systems; Droughts; Exact sciences and technology; Flooding; Global environmental pollution; Khartoum; Natural water pollution; Pollution; Rain; Rainfall; Rainfall concentration; Rainfall–runoff equation; Rainwater harvesting; Rainwaters, run off water and others; Runoff; Seasons; Urban drainage management; Urban runoff; Water treatment and pollution; United States; North America; America; Sudan, Khartoum; USA; Sudan; Rainfall–runoff equation; Khartoum; Rainwater harvesting; Rainfall concentration; Urban runoff; Urban drainage management; Heatwave; Rainfall-runoff equation; Urban area; Runoff water; Flooding; Sustainable development; Rain; Flood; Health and environment; Dust storm; Watershed; Rain water; Street; Storm water; Drought; Water resources; Public health; Environmental protection
• ISSN: 0921-3449; 1879-0658
• DOI: 10.1016/j.resconrec.2014.07.014

•Urban Khartoum has potential for rooftop rainwater harvesting and runoff management.•High rainfall variability, concentration and dependence on very strong raindays.•CN=94% is found, indicating dominance of imperviousness and high runoff potential.•Rainfall of 3.3mm is the threshold for runoff generation.•Rain ≥30mm has 1–2 year return period, producing runoff ∼4 folds the drainage capacity. Runoff water management is among the inherent challenges which face the sustainability of the development of arid urban centers. These areas are particularly at risk from flooding due to rainfall concentration in few heavy showers. On the other hand, they are susceptible to drought. The capital of Sudan (Khartoum) stands as exemplary for these issues. Hence, this research study aims at investigating the potential of applying rainwater harvesting (RWH) in Khartoum City Center as a potential urban runoff management tool. Rapid urbanization coupled with the extension of impervious surfaces has intensified the heat island in Khartoum. Consequently, increased frequency of heat waves and dust storms during the dry summer and streets flooding during the rainy season have led to environmental, economical, and health problems. The study starts with exposing the rainfall behavior in Khartoum by investigating rainfall variability, number of raindays, distribution of rain over the season, probability of daily rainfall, maximum daily rainfall and deficit/surplus of rain through time. The daily rainfall data show that very strong falls of >30mm occur almost once every wet season. Decreased intra- and inter-annual rainfall surpluses as well as increased rainfall concentration in the month of August have been taking place. The 30-year rainfall variability is calculated at decade interval since 1941. Increasing variability is revealed with 1981–2010 having coefficients of variation of 66.6% for the annual values and 108.8–118.0% for the wettest months (July–September). Under the aforementioned rainfall conditions, this paper then explores the potential of RWH in Khartoum City Center as an option for storm water management since the drainage system covers only 40% of the study area. The potential runoff from the 6.5km2 center area is computed using the United States Natural Resources Conservation Services method (US-NRCS), where a weighted Curve Number (CN) of 94% is found, confirming dominant imperviousness. Rainfall threshold for runoff generation is found to be 3.3mm. A 24,000m3 runoff generated from a 13.1mm rainfall (with 80% probability and one year return period) equals the drainage system capacity. An extreme rainfall of 30mm produces a runoff equivalent to fourfold the drainage capacity. It is suggested that the former and latter volumes mentioned above could be harvested by applying the rational method from 18% and 80% rooftops of the commercial and business district area, respectively. Based on the above results, six potential sites can be chosen for RWH with a total roof catchment area of 39,558m2 and potential rooftop RWH per unit area of 0.033m3. These results reflect the RWH potential for effective urban runoff management and better water resources utilization. RWH would provide an alternative source of water to tackle the drought phenomenon.