OPTIMUM USE OF PADDY FIELDS FOR FLOOD MITIGATION1

In Taiwan, the continuously increasing levels of rice imports are likely to result in surplus paddy fields. Hence, the surplus paddy fields may be developed into wetlands to increase ground water recharge, provide appropriate environments for wildlife, and most importantly, store flood water. This study developed a hydrological model incorporating the distributed rainfall‐runoff model based on the kinematics wave approach and the distributed tank model for simulation, respectively, in mountainous and flat areas. The hydrological model was found to simulate the rainfall‐runoff behavior well in the study area. Furthermore, a decision method based on the genetic algorithm concepts was proposed to give policy makers the optimal location and area size of paddy fields to construct wetlands for flood mitigation.     

SUBSURFACE RETURN FLOW AND GROUND WATER RECHARGE OF TERRACE FIELDS IN NORTHERN TAIWAN1

ABSTRACT: This study estimates subsurface return flow and effective ground water recharge in terraced fields in northern Taiwan. Specifically, a three dimensional model, FEMWATER, was applied to simulate percolation and lateral seepage in the terraced fields under various conditions. In the terraced paddy fields, percolation mainly moves vertically downward in the central area, while lateral seepage is mainly focused around the bund. Although the simulated lateral seepage rate through the bund exceeded the percolation rate in the central area of the paddy field, annual subsurface return flow at Pei‐Chi and Shin‐Men was 0.17 × 10⁶ m³ and 0.37 × 10⁶ m³, representing only 0.17 percent and 0.21 percent of the total irrigation water required for rice growth at Pei‐Chi and Shin‐Men, respectively. For upland fields, the effective ground water recharge rate during the second crop period (July to November) exceeded that during the first crop period (January to May) because of the wet season in the second crop period. Terraced paddy fields have the most efficient ground water recharge, with 21.2 to 23.4 percent of irrigation water recharging to ground water, whereas upland fields with a plow layer have the least efficient ground water recharge, with only 4.8 to 6.6 percent of irrigation water recharging to ground water. The simulation results clearly revealed that a substantial amount of irrigation water recharges to ground water in the terraced paddy, while only a small amount of subsurface return flow seeps from the upstream to the downstream terraced paddy. The amounts of subsurface flow and ground water recharge determined in the study are useful for the irrigation water planning and management and provide a scientific basis to reevaluate water resources management in the terrace region under irrigated rice.     

EFFECTS OF ARTIFICIAL RECHARGE ON GROUND WATER QUALITY AND AQUIFER STORAGE RECOVERY1

ABSTRACT: Ground water nitrate contamination and water level decline are common concern in Nebraska. Effects of artificial recharge on ground water quality and aquifer storage recovery (ASR) were studied with spreading basins constructed in the highly agricultural region of the Central Platte, Nebraska. A total of 1.10 million m³ of Platte River water recharged the aquifer through 5000 m² of the recharge basins during 1992, 1993, and 1994. This is equivalent to the quantity needed to completely displace the ground water beneath 34 ha of the local primary aquifer with 13 m thickness and 0.25 porosity. Successful NO₃-N remediation was documented beneath and downgradient of the recharge basins, where NO₃-N declined from 20 to 2 mg L^-1. Ground water atrazine concentrations at the site decreased from 2 to 0.2 mg L^-1 due to recharge. Both NO₃-N and atrazine contamination dramatically improved from concentrations exceeding the maximum contaminant levels to those of drinking water quality. The water table at the site rose rapidly in response to recharge during the early stage then leveled off as infiltration rates declined. At the end of the 1992 recharge season, the water table 12 m downgradient from the basins was elevated 1.36 m above the preproject level; however, at the end of the 1993 recharge season, any increase in the water table from artificial recharge was masked by extremely slow infiltration rates and heavy recharge from precipitation from the wettest growing season in over 100 years. The water table rose 1.37 m during the 1994 recharge season. Resultant ground water quality and ASR improvement from the artificial recharge were measured at 1000 m downgradient and 600 m upgradient from the recharge basins. Constant infiltration rates were not sustained in any of the three years, and rates always decreased with time presumably because of clogging. Scraping the basin floor increased infiltration rates. Using a pulsed recharge to create dry and wet cycles and maintaining low standing water heads in the basins appeared to reduce microbial growth, and therefore enhanced infiltration.     

Rainwater harvesting planning using geospatial techniques and multicriteria decision analysis

Growing water scarcity and global climate change call for more efficient alternatives of water conservation; rainwater harvesting (RWH) is the most promising alternative among others. However, the assessment of RWH potential and the selection of suitable sites for RWH structures are very challenging for the water managers, especially on larger scales. This study addresses this challenge by presenting a fairly robust methodology for evaluating RWH potential and identifying sites/zones for different RWH structures using geospatial and multicriteria decision analysis (MCDA) techniques. The proposed methodology is demonstrated using a case study. The remote sensing data and conventional field data were used to prepare desired thematic layers using ArcGIS© software. Distributed Curve Number method was used to calculate event-based runoffs, based on which annual runoff potential and runoff coefficient maps were generated in the GIS (geographic information system) environment. Thematic layers such as slope, drainage density, and runoff coefficient and their features were assigned suitable weights and then they were integrated in a GIS to generate a RWH potential map of the study area. Zones suitable for different RWH structures were also identified, together with suitable sites for constructing recharge structures (check dams and percolation tanks along the streams). It was found that the study area can be classified into three RWH potential zones: (a) ‘good’ (241 km²), (b) ‘moderate’ (476 km²), and (c) ‘poor’ (287 km²). About 3% of the study area (30 km²) is suitable for constructing farm ponds, while percolation tanks (on the ground) can be constructed in about 2.7% of the area (27 km²). Of the 83 sites identified for the recharge structures, 32 recharge sites are specially suited to the inhabitants because of their proximity. It is concluded that the integrated geospatial and MCDA techniques offer a useful and powerful tool for the planning of rainwater harvesting at a basin or sub-basin scale.     

CITY OF TUCSON WASTE WATER EFFLUENT DELIVERY FACILITY1

ABSTRACT: The Tucson area is totally dependent on ground water, which is in increasingly short supply due to excessive overdrafts. Tucson area waste water treatment plants discharge material quantities of secondary effluent downstream, which is lost to evapotranspiration and recharge of the ground water basin. The city and the four large mining companies who share the common Santa Cruz basin ground water, recognized the common water supply problem and agreed to fund a feasibility study for mining process use of the effluent to partly alleviate the overdraft of ground water. The study analyzed the projected waste water effluent resources, potential mining company demand for waste water effluent and possible interface of an effluent delivery facility with the proposed Central Arizona Project. The effluent resources were analyzed with respect to potential demand. An optimum alignment was selected. An optimum system was detailed through design schematics, amortized cost and finance requirements, and an implementation schedule. It was concluded that a waste water effluent delivery facility could be implemented which would utilize reclaimed effluent in quantities approximating 35 percent of basin overdraft and which would provide revenue for full cost recovery over a 20 year operation period. The mining companies are studying the internal economic impacts of the project.     

A REEVALUATION OF THE GROUND WATER BUDGET FOR LAS VEGAS VALLEY,NEVADA, WITH EMPHASIS ON GROUND WATER DISCHARGE1

ABSTRACT: An essential component to the ground water budget for the Las Vegas Valley (LVV) in southern Nevada is discharge from the ground water system. Discharge for the LW has been based on estimates made more than 50 years ago of 35,524,224 m3 per year as evapotranspiration (ET) and 0 m³ per year as subsurface outflow. Newly published values for recharge based on a more robust data set (70,308,360 m³) indicate a large imbalance associated with the earlier discharge estimates, providing the basis for the reevaluation conducted in this study. ET estimates in this study, as opposed to previous studies, were assigned a range in values that included an approach that assigned higher weight to the unique soil, plant, water, and climatic conditions that existed in predevelopment (1905) LW. The earlier discharge estimates also assumed that the basin was hydrologically closed; however, based on our evaluation, a range in yearly discharge by subsurface outflow from 1,480,176 m³ to 19,735,680 m³ could be assigned. Likewise, a range in yearly ET from 20,475,768 m³ to 78,819,372 m³ could be assigned. Based on newly published recharge values, closure can only occur if higher values are assigned to both the subsurface outflow and/or ET components of ground water discharge. We cannot provide a complete water balance closure with our ground water discharge estimate of 64,140,960 m³. However our reevaluation gives support to the higher recharge estimates and provides the rationale for future studies to be conducted based on a more rigorous scientific assessment.     

CORRELATION OF SELECTED WELL WATER QUALITY PARAMETERS WITH SOIL AND AQUIFER HYDROLOGIC PROPERTIES1

ABSTRACT: The geographical distribution of well water specific electrical conductivity and nitrate levels in a 932 km² ground water quality study area in the Fresno-Clovis, California, indicated that frequently areas of lower ground water salinity were also areas of relatively greater soil and aquifer permeability. From these observations and certain assumptions we hypothesized that the quality of the well water should be better in areas with permeable soils and geological formations. Correlation and multiple linear regression analysis supported this hypothesis for well water salinity. However, well water nitrate levels were significantly negatively correlated with only the estimated equivalent specific yield of the aquifer system. The multiple R² values of the most significant multiple linear regression models showed that only a fourth to a third of the variability in well water specific electric conductivity and nitrate levels could be ascribed to the effects of the hydrogeological parameters considered with more than 90 percent confidence. This indicates that three-fourths to two-thirds of the variability in ground water salinity and nitrate levels may be related to land use. Thus, there is considerable room for land use management techniques to improve ground water quality and reduce its variability.     

THE ECONOMIC VALUE OF GROUND WATER RECHARGE FOR IRRIGATION USE1

ABSTRACT: Artificial recharge as a means of augmenting water sup plies for irrigation is a management alternative which policy makers in ground water decline areas are beginning to consider seriously. A conceptual model is developed to evaluate the economic benefits from ground water recharge under conditions where the major water use is irrigation. The methodology presented separates recharge benefits into two components: pumping cost savings and aquifer extension benefits. This model is then applied to a Nebraska case to approximate the value of recharge benefits as a function of aquifer response. discount rate, and commodity prices. It was found that recharge benefits vary from less than $2 to over $6 an acre foot recharged.     

ANALYSIS OF NITROGEN MANAGEMENT STRATEGIES USING EPIC1

ABSTRACT: This paper illustrates a method of using a hydrologic/water quality model to analyze alternative management practices and recommend best management practices (BMPs) to reduce nitrate-nitrogen (NO₃^--N) leaching losses. The study area for this research is Tipton, an agriculturally intensive area in southwest Oklahoma. We used Erosion Productivity Impact Calculator (EPIC), a field-scale hydrologic/water quality model, to analyze alternative agricultural management practices. The model was first validated using observed data from a cotton demonstration experiment conducted in the Tipton area. Following that, EPIC was used to simulate fertilizer response curves for cotton and wheat crops under irrigated and dryland conditions. From the fertilizer response functions (N-uptake and N-leaching), we established an optimum fertilizer application rate for each crop. Individual crop performances were then simulated at optimum fertilizer application rates and crop rotations for the Tipton area, which were selected based on three criteria: (a) minimum amount of NO₃^--N leached, (b) minimum concentration of NO₃^--N leached, and (c) maximum utilization of NO₃^--M. Further we illustrate that by considering residual N from alfalfa as a credit to the following crop and crediting NO₃^--N present in the irrigation water, it is possible to reduce further NO₃^--N loss without affecting crop yield.     

IDENTIFYING DISCHARGE ZONES OF ARSENIC IN THE GOOSE RIVER BASIN,MAINE1

ABSTRACT: Water balance modeling and the analysis of stable water isotopes in ground water were conducted to aid the location of ground water discharge areas within the Goose River basin, in mid‐coastal Maine. Previous investigations of drinking water from wells in the fractured crystalline bedrock encountered persistent elevated total arsenic. Such contamination may be related to discharging ground water from fractured zones in the basin. Modeled discharge rates greater than +10 cm/yr and ¹⁸O values lighter than‐9.5 per mil VSMOW may indicate recent recharge is mixing with deeper ground water and is focused along some fractured zones in arsenic bearing crystalline rocks.     

GEOCHEMICAL CHARACTERIZATION OF SHALLOW GROUND WATER IN THE EUTAW AQUIFER,MONTGOMERY, ALABAMA1

ABSTRACT: Ground water samples were collected from 30 wells located in, or directly down gradient from, recharge areas of the Eutaw aquifer in Montgomery, Alabama. The major ion content of the water evolves from calcium‐sodium‐chloride‐dominated type in the recharge area to calcium‐bicarbonate‐dominated type in the confined portion of the aquifer. Ground water in the recharge area was under saturated with respect to aluminosilicate and carbonate minerals. Ground water in the confined portion of the aquifer was at equilibrium levels for calcite and potassium feldspar. Dissolved oxygen and nitrite‐plus‐nitrate concentrations decreased as ground water age increased; pH, iron, and sulfate concentrations increased as ground water age increased. Aluminum, copper, and zinc concentrations decreased as ground water age and pH increased. These relations indicate that nitrate, aluminum, copper, and zinc are removed from solution as water moves from recharge areas to the confined areas of the Eutaw aquifer. The natural evolution of ground water quality, which typically increases the pH and decreases the dissolved oxygen content, may be an important limiting factor to the migration of nitrogen based compounds and metals.     

Rainfall and Spring Discharge Patterns in Two Small Drainage Catchments in the Western Himalayan Mountains, India

Relationship between rainfall and spring discharge study is important to understand hydrological behaviour of springs and water resources management. In the Himalayan mountains springs are the freshwater sources for household consumption. We studied six springs of different recharge area characteristics in two micro-watersheds in western Himalayan mountains in India. Based on the recharge area geology these springs were divided into fracture/joint (FR/JT) and fracture/joint/colluvium (FR/JT/COLL). We found a strong positive relationship between rainfall and spring discharge. Peak spring discharge coincided with peak rainfall in two FR/JT/COLL springs, which was delayed by about one month in FR/JT springs. Mean annual discharge was about two times greater for FR/JT/COLL springs than the FR/JT springs (6.47 vs. 3.94 liter per minute). But spring discharge per 1000 L of rainfall in spring recharge area for FR/JT springs was about 2.3 times greater than the FR/JT/COLL springs (49 vs. 21 liter per minute). In the FR/JT springs, rainfall in spring recharge area and spring discharge were weakly related (r=0.174), while they were strongly related in FR/JT/COLL springs (r=0.595). In the former category of springs decline in discharge was gradual, while it was rapid in the latter category of springs. Therefore, with regard to sustained supply of water for household consumption FR/JT springs can be considered more suitable. Land use and land cover such as moderately grazed pasture, abandoned agricultural terraces and few trees but dense growth of bushes and oak forest in the spring recharge area were found conducive for spring discharge and may be promoted for long-term water resource conservation in this region.     

Effects of Rainfall and Ground‐Water Pumping on Streamflow in Mākaha,O’ahu,Hawai’i1

Abstract: Land‐use/land‐cover changes in Mākaha valley have included the development of agriculture, residential dwellings, golf courses, potable water supply facilities, and the introduction of alien species. The impact of these changes on surface water and ground water resources in the valley is of concern. In this study, streamflow, rainfall, and ground‐water pumping data for the upper part of the Mākaha valley watershed were evaluated to identify corresponding trends and relationships. The results of this study indicate that streamflow declined during the ground‐water pumping period. Mean and median annual streamflow have declined by 42% (135 mm) and 56% (175 mm), respectively, and the mean number of dry stream days per year has increased from 8 to 125. Rainfall across the study area appears to have also declined though it is not clear whether the reduction in rainfall is responsible for all or part of the observed streamflow decline. Mean annual rainfall at one location in the study area declined by 14% (179 mm) and increased by 2% (48 mm) at a second location. Further study is needed to assess the effect of ground‐water pumping and to characterize the hydrologic cycle with respect to rainfall, infiltration, ground‐water recharge and flow in the study area, and stream base flow and storm flow.     

POTENTIAL EFFECTS OF CLIMATE CHANGE ON GROUND WATER IN LANSING,MICHIGAN1

ABSTRACT: Computer simulations involving general circulation models, a hydrologic modeling system, and a ground water flow model indicate potential impacts of selected climate change projections on ground water levels in the Lansing, Michigan, area. General circulation models developed by the Canadian Climate Centre and the Hadley Centre generated meteorology estimates for 1961 through 1990 (as a reference condition) and for the 20 years centered on 2030 (as a changed climate condition). Using these meteorology estimates, the Great Lakes Environmental Research Laboratory's hydrologic modeling system produced corresponding period streamflow simulations. Ground water recharge was estimated from the streamflow simulations and from variables derived from the general circulation models. The U.S. Geological Survey developed a numerical ground water flow model of the Saginaw and glacial aquifers in the Tri‐County region surrounding Lansing, Michigan. Model simulations, using the ground water recharge estimates, indicate changes in ground water levels. Within the Lansing area, simulated ground water levels in the Saginaw aquifer declined under the Canadian predictions and increased under the Hadley.     

INFLUENCE OF WELL WATER QUALITY VARIABILITY ON SAMPLING DECISIONS AND MONITORING1

ABSTRACT: Local governmental agencies responsible for decisions in ground water quality management need not only data on ground water quality but they also must understand the relationship of accuracies and risks associated with this data as related to the number of wells to sample. In this report we address this problem by using the philosophical doctrines of probabilism and relativism with simple statistical procedures. This requires a reasonable estimate of the population variance in a quality parameter for a given management-unit area, and requires that the decisionmaker formulate constraints with an acceptable standard error of the sample mean and be willing to accept some level of probability of being Wrong. This technique is illustrated using a 21-year data base of well water chemical data in a 653 km² ground water quality study area in the San Joaquin Valley of California.     

Field-scale preferential transport of water and chloride tracer by depression-focused recharge

A tracer study was initiated in November 1993 to investigate depression-focused recharge and to monitor solute movement through the vadose zone into the shallow ground water in southeastern North Dakota. Granular potassium chloride (KCl) was surface-applied to two areas overlying subsurface drains and to one area instrumented with soil solution samplers, ground water monitoring wells, time domain reflectometry (TDR) probes, and temperature probes. One of the subsurface drain tracer plots was located on level ground while the other two sites were in small topographic depressions. Formation of ground water mounds beneath the depressions indicated that these areas are recharge sites. The applied Cl- tracer was found to move rapidly to the shallow ground water under the depressional areas after infiltration of spring snowmelt in 1994. Excessive rainfall events were also responsible for focused recharge and the rapid transport of the applied Cl- tracer. Water flow through partially frozen soil at the bottom of the depressions during thaw enhanced preferential movement of the tracer.     

HYDROLOGIC RESPONSE TO PUMPING AND CONTAMINANT ADVECTION IN A FRACTURED ROCK ENVIRONMENT1

ABSTRACT: Ground water flow and supply at the Whiteshell Research Area (WRA) in southeastern Manitoba and the advective movement of contaminants from a hypothetical nuclear fuel waste disposal vault to the adjacent biosphere and a nearby ground water supply well are simulated using finite-element modeling and numerical particle-tracking technique. The hypothetical vault is located at a depth of 500 m, below the water table, in low-permeability plutonic rock of the Canadian Shield. The rock mass is intersected by high-permeability fracture zones (aquifers), which also act as conduits for vault contaminants to migrate to the ground surface. The ground water resource is, therefore, limited in quantity and quality and should be explored with care. A 30 m deep well, which pumps water at a rate of 120 m³/yr from a low-dipping fracture zone, LD1, reduces natural discharge from the system to augment natural recharge. At this pumping rate, a 100 m or 200 m deep well neither reduces discharge nor induces recharge into the system. Thus, at the WRA, a 30 m deep domestic water supply well best meets the water requirements of a one-person household at the rate of 120 m³/yr. The 100 m and 200 m wells best meet the requirements of a family of six and a family of six with light irrigation, respectively, without capturing contaminants’pathways from the vault to the ground surface. By virtue of the proximity of the 200 m well intake to the hypothetical vault, this well performs best as a purge well at pumping rates of 0,000 m³/yr and greater. Finite-element modeling is useful in evaluating the water supply potential of a fractured rock environment in which a nuclear waste disposal vault is proposed to be sited.     

PREDICTIVE ASSESSMENT OF SEVERITY OF AGRICULTURAL DROUGHTS BASED ON AGRO-CLIMATIC FACTORS1

ABSTRACT: Past historical evidence indicates that droughts have had great impacts on human life. Drought (or scarcity of water) is assessed based on two key factors, namely, the estimated water demand, and the expected water supply. The formulation of these key factors for a region largely depends on the agro-climatic and economic conditions. Consideration of one such key factor is the relationship between the crop yield and water deficit in the assessment and prediction of agricultural droughts. The varying nature of this relationship from crop to crop adds to the complexity of agricultural drought analysis. To overcome this difficulty in analyzing agricultural droughts of a region, it is adequate to consider and place emphasis on a single crop (i.e., an index crop) grown homogeneously over the major area of the region. From one year to another year, the pattern of water requirement during the growing season of an index crop is rather stationary, and the water supply in arid and semi-arid area is mainly from seasonal random precipitation. In a region, grain yield of the index crop and, in turn, assessment of the severity of drought can reasonably be predicted as a function of the time of crop sowing and the distribution of rainfall, provided that temporal and spatial effects of other contributing factors (crop variety, soil fertility status, crop disease, pest control, cultivation practices etc.) on grain yield are considered to be uniformly distributed (i.e., stable). A predictive method of assessing agricultural droughts in an arid area of western India is presented. The major crop (Pearl Millet) of this region is grown from. July through September. The formulation of the proposed predictive method inherently implies that the grain yield of the main crop is a reliable indicator of agricultural drought. In the development of this predictive relationship (i.e., a regression type model) a number of potential yet simple variables affecting the grain yield in the region were investigated. The soil moisture index, although generally considered significant compared to the simple variables, has been found to account for insignificant variation in the grain yield. Results of our investigations suggest that it would be advisable to exclude the soil moisture index variable from the model. The proposed regression model can be used in the prediction of grain yield of the main crop several months ahead of crop harvesting operations and, in turn, the assessment of agricultural drought severity as mild, moderate, or severe. Such an assessment is expected to be helpful to planners for arranging appropriate measures to effectively combat agricultural drought situations.     

STABLE ISOTOPE CHARACTERIZATION OF THE IMPACTS OF ARTIFICIAL GROUND WATER RECHARGE1

ABSTRACT: Stable isotopes of deuterium and oxygen-18 of surface and ground water, together with anion concentrations and hydraulic gradients, were used to interpret mixing and flow in ground water impacted by artificial recharge. The surface water fraction (SWF), the percentage of surface water in the aquifer impacted via recharge, was estimated at different locations and depths using measured deuterium/hydrogen (DIH) ratios during the 1992, 1993, and 1994 recharge seasons. Recharged surface water completely displaced the ground water beneath the recharge basins from the regional water table at 7.60 m to 12.16 m below the land surface. Mixing occurred beneath the recharge structures in the lower portions of the aquifer (>12.16 m). Approximately 12 m down-gradient from the recharge basin, the deeper zone (19.15 m depth) of the primary aquifer was displaced completely by recharged surface water within 193, 45, and 55 days in 1992, 1993, and 1994, respectively. At the end of the third recharge season, recharged surface water represented ～50 percent of the water in the deeper zone of the primary aquifer ～1000 m downgradient from the recharge basin. A classic asymmetrical distribution of recharged surface water resulted from the recharge induced horizontal and vertical hydraulic gradients. The distribution and breakthrough times of recharged surface water obtained with stable isotopes concurred with those of major anions and bromide in a tracer test conducted during the 1995 recharge season. This stable isotope procedure effectively quantified mixing between surface and ground water.     

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

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 >30 mm 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 6.5 km² 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 3.3 mm. A 24,000 m³ runoff generated from a 13.1 mm rainfall (with 80% probability and one year return period) equals the drainage system capacity. An extreme rainfall of 30 mm 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 39,558 m² and potential rooftop RWH per unit area of 0.033 m³. 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.