Restoration of Wadi Aquifers by Artificial Recharge with Treated Waste Water

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1 Issue Paper/ Restoration of Wadi Aquifers by Artificial Recharge with Treated Waste Water by Thomas M. Missimer 1,Jörg E. Drewes 2,3,GaryAmy 2, Robert G. Maliva 4, and Stephanie Keller 2 Abstract Fresh water resources within the Kingdom of Saudi Arabia are a rare and precious commodity that must be managed within a context of integrated water management. Wadi aquifers contain a high percentage of the naturally occurring fresh groundwater in the Kingdom. This resource is currently overused and has become depleted or contaminated at many locations. One resource that could be used to restore or enhance the fresh water resources within wadi aquifers is treated municipal waste water (reclaimed water). Each year about 80 percent of the country s treated municipal waste water is discharged to waste without any beneficial use. These discharges not only represent a lost water resource, but also create a number of adverse environmental impacts, such as damage to sensitive nearshore marine environments and creation of high-salinity interior surface water areas. An investigation of the hydrogeology of wadi aquifers in Saudi Arabia revealed that these aquifers can be used to develop aquifer recharge and recovery (ARR) systems that will be able to treat the impaired-quality water, store it until needed, and allow recovery of the water for transmittal to areas in demand. Full-engineered ARR systems can be designed at high capacities within wadi aquifer systems that can operate in concert with the natural role of wadis, while providing the required functions of additional treatment, storage and recovery of reclaimed water, while reducing the need to develop additional, energy-intensive desalination to meet new water supply demands. Introduction Wadis have been preferential locations for human habitation in the arid lands of the Middle East for thousands of years. These elongate, ephemeral streams are underlain by alluvial aquifers, commonly containing the only naturally occurring fresh water resources in vast 1 Corresponding author: Water Desalination and Reuse Center, King Abdullah University of Science and Technology (KAUST), Thuwal , Saudi Arabia; Thomas.Missimer@kaust.edu.sa 2 Water Desalination and Reuse Center, King Abdullah University of Science and Technology (KAUST), Thuwal , Saudi Arabia. 3 Advanced Water Technology Center (AQWTEC), Colorado School of Mines, Golden, CO Schlumberger Water Services, 1567 Hayley Lane, Suite 202, Fort Myers, FL Received October 2011, accepted March , The Author(s) Ground Water 2012, National Ground Water Association. doi: /j x arid regions (Figure 1). Wadi aquifers are rarely recharged and the fresh water resources within them are commonly, fully utilized leaving them dry or contaminated by human activities, particularly agricultural practices. It is estimated that 64, m 3 of fresh water are stored in wadi aquifers within the Kingdom of Saudi Arabia, and the annual natural recharge rate is only m 3 (Dabbagh and Abderrahman 1997). Populations of all the countries in the Middle East region, particularly Saudi Arabia, are growing with shifts in demographics and increased industrialization (Noory 1983; US Census 2011). While the region has resorted to desalination as the primary means of supplying water for human consumption, fresh water resources within both deep, confined aquifers (fossil water) and shallow, alluvial/fluvial aquifers (wadis) still constitute a significant part of the water resources being used, particularly for agricultural irrigation. The Kingdom of Saudi Arabia is the largest user of fresh groundwater in the region. With consideration of 514 Vol. 50, No. 4 GROUND WATER July-August 2012 (pages ) NGWA.org

2 Figure 1. Map of Saudi Arabia showing the locations of cities, studied wadis, and a few other major wadis. These ephemeral streams rarely have flow which commonly occurs as flash flood events. the growing demand on fresh water resources, there is a need to manage and augment groundwater supplies to provide an overall integrated water management system. The fresh water resources of the deep aquifers have been significantly depleted (Al-Saud 2010). Use of the shallow aquifers is limited to periods when there has been sufficient recharge to allow water use without fully depleting the resource or causing water quality changes, such as saline water intrusion (Al-Yamani 2000; Shammas 2008). Shallow groundwater is most commonly developed in ephemeral stream beds termed wadis. Saudi Arabia is a hyper-arid to semi-arid area with annual rainfall accumulations ranging from less than 50 to greater than 500 mm (Al-Jerash 1983, 1985; Sen 1983; Alehaideb 1985; Nouh 1987c; Abouammoh 1991; Subyani 1997, 2004b; Wheater et al. 1991a, 1991b). Rainfall accumulations across the country have an uneven spatial distribution. Rainfall events are temporally rare, but commonly intense when they do occur (Al-Qurashi 1981; Al- Yamani and Sen 1992; Subyani et al. 2010). When intense rainfall events occur, water runs off the land and gathers in wadis, where it drains downhill onto low-lying, coastal plain areas or discharges to tidal water. Commonly, intense flooding can occur from wadi discharges, particularly in areas where wadi flows are obstructed by development or catchment areas that are populated (Figure 2) (Deain 1985; Nouh 1987a, 1987b, 1988a, 1988b, 1990; Nouh and El-Laithy 1988; Sorman et al. 1990; Sorman and Abdulrazzak 1993b; Al-Wagdany and Al-Shahri 2000; Sen and Al-Suba I 2002; Khiyami et al. 2005; Sen 2005, 2007, 2008b; Sirdas and Sen 2007; Zahrani et al. 2007; Subyani 2011; Subyani and Al-Modayan 2010; Subyani et al. 2010; Subyani and Al-Ahmadi 2011). Recharge events within the wadis most commonly occur as a result of channel flows associated with flood events. Wadis, therefore, serve several functions within the natural hydrologic system, including the natural channelization of flood flows, the downhill transport of sediments generated in highlands areas, and the formation of shallow aquifers, which are locally important sources of fresh water. Indeed, in some areas of the Kingdom, wadi aquifers were the only sources of fresh water prior to development of desalination systems. Wadi aquifers have limited geographic extent and thickness, and thus storage volumes. Because rainfall events are so temporally rare, the wadi aquifers have a limited water capacity and can be depleted by overuse. Waste Water Production and Wadi Artificial Recharge Consummate with population and corresponding water demand growth in the Kingdom, municipal waste water production has increased, resulting in development of new and the retrofitting of existing treatment facilities. In 2010, of the 6.67 million m 3 /d of municipal waste water generated, 51% was discharged via septic tanks and cesspools, 16% was collected but not treated, and 33% was treated (Al-Saud, 2010). Most of the treated municipal waste water totaling over 2,200,000 m 3 /d is discharged to tidal water in coastal areas, into nearby wadis at interior locations or artificial lakes (Al-Aghar Group and Bushnak Academy, 2010). The discharge of waste water effluent to wadis is quite significant in many cities, such as Riyadh, where the Riyadh River discharge rate leaving the city is at least 60,000 m 3 /d and at Taif, where discharge of waste water combines with seasonal stormwater runoff to Wadi Wajj (Figure 3). The percentage of waste water effluent reuse in the Kingdom is about 10%, with a potential to grow this percentage to 70% considering the current efforts to build-out the country s waste water infrastructure (Al-Saud 2010). Municipal waste water has been recognized as a valuable resource that should be reused to the highest percentage possible and is considered a key element in the overall integrated water management plan for the Kingdom (Aborizaiza et al. 1989). Artificial recharge of wadi aquifers using treated waste water would increase the availability of water within these sensitive NGWA.org T.M. Missimer et al. GROUND WATER 50, no. 4:

3 Figure 2. The rapid urbanization of the City of Jeddah has cut off the channels of many natural wadis and buildings have been raised in wadi channels within the city. A heavy rainfall event in December, 2009, 90 mm of accumulation in 3.5 h, produced a flood that killed over 122 people and left 360 persons missing. periods of abundance and withdraw it during times of need (Maliva and Missimer 2010; Maliva et al. 2011). The purpose of this paper is to demonstrate the feasibility of using wadis for ARR with the explicit goals of treating and restoring water supplies within the aquifers and significantly increasing the utilization of reclaimed water within a scheme of integrated water management in the Kingdom of Saudi Arabia, thereby serving as an example for other arid regions. Some of the wadis are located near high population growth areas, close to areas producing waste water. Figure 3. Flow in Wadi Wajj originates from storm runoff (right) and treated waste water (left) both originating in the City of Taif. Runoff is quite seasonal while the waste water flow is perennial. systems and decrease the need to develop more capacity in desalination systems and accompanying conveyance infrastructure. The available storage capacity within wadis also makes them an excellent location in which to store and treat municipal waste water. Gravels, sands, and silts occurring within wadis gives this aquifer type both absorptive and adsorptive properties that can provide additional attenuation of pathogens, nutrients, organic matter, and trace organic chemicals that are not completely removed during conventional waste water treatment (Amy and Drewes 2007). The process of using a shallow aquifer to treat and store impaired-quality water is termed aquifer recharge and recovery (ARR). ARR differs from aquifer storage and recovery (ASR), which is a technology that serves primarily to store water in an aquifer during Review of Wadi Aquifer Hydrogeology Geomorphology and Geology Within arid and semi-arid regions, drainage of rainfall events occurs through a network of ephemeral stream channels. These features, occurring in the Middle East, northern Africa, and southwest Asia regions, are termed wadis. Wadi is an Arabic term used to define ephemeral streams that are used as sources of water in arid and semi-arid regions (Sen 2008a). The term wadi has been formally defined as a stream bed or channel, or a steepsided and boulder ravine, gully, or valley, or dry wash that is usually dry except during the rainy season, and often forms an oasis (American Geological Institute 1997). Wadis, like all types of ephemeral drainage features in arid and semi-arid regions, occur in topographically low areas formed by either structural deformation or erosion. They have a basic dendritic pattern controlled by the local topography and the hydraulic gradients, which in turn, control the potential for water erosion of the channels. The longitudinal profile of a typical wadi can be subdivided into at least three primary segments (Figure 4). The distal segment occurs in the highest altitude part 516 T.M. Missimer et al. GROUND WATER 50, no. 4: NGWA.org

4 Figure 4. Geomorphic parts of a wadi using Wadi Qidayd as an example. Even after extended dry periods some water flows into the distal segment of the wadi from fractured rock drainage while the middle and lower segments are dry. Note the active farming in the wadi channel. of the drainage basin and is characterized by narrow, steeply dipping channels that contain large boulders and a minimal quantity of sand and fine-grained sediment. Runoff entering the distal channels produces high-velocity flows and a high stream power gradient (Bull 1979) with flash floods occurring in major storm events that tend to erode the channel and move sediments down-gradient. The middle segment of a wadi system is characterized by a flatter hydraulic gradient with a tendency to contain a series of stepped changes in slope and variations in channel depth and width. Sediments occurring within the channel area are primarily a mix of boulders, cobbles, and coarse sand with some finer sand and silty-sand sediments occurring in flatter reaches. Flood-scouring to bedrock occurs in some channel segments during major flood events. Channel sediments are commonly reworked, mixed, and in part transported downstream in successive storm events. Old, preserved sediment sequences are not common, but do occur in channel segments where there are depressions in the bedrock allowing permanent deposits to be preserved and at locations where slopes lessen. The proximal segment of the wadi occurs near its terminus within either the coastal zone or a basin floor. The hydraulic slope of the channel is significantly lower, the channel incised relief is much lower, and there is a tendency for the channel width to increase. Channel fill deposits are thick and have a lower average grain size compared to those occurring in the middle segment of the wadi system. Commonly, there is a rather abrupt slope change of the channel at the boundary between the middle segment and the proximal segment. Some large cobbles, pebbles, and coarse sand deposits occur at the slope change and the nature of the sediment shows a significant reduction in grain size moving downstream to the point of discharge. The lowest part of the proximal wadi segment contains stratified deposits of cobbles, pebbles, coarse sand, medium to fine sand, and mud layers (mixture of sand, silt, and clay). Although some storm-event erosion occurs in the proximal segment, there is preservation of bedding and permanent accumulation of thick siliciclastic deposits. This description of geomorphology of wadis is based on personal observation and descriptions in Al- Shaibani (2008), Nouh (2006), Qari (2009), and Subyani (2004a, 2005b). Commonly, wadi channels are incised into the underlying bedrock. Many wadis in western Saudi Arabia occur within Precambrian shield rocks which are highly weathered and fractured (Figure 4). Therefore, groundwater flow is conducted down-gradient, not only within the channel-fill sediments, but also in the upper, fractured and weathered part of the bedrock. Fracture flow is significant in terms of recharge to wadis in the distal segments and in conducting down-gradient water movement in the middle segments. Once the wadi channels leave the fractured cratonic rocks and enter the coastal terrace province or the basin floor, fracture flow ceases to be a factor in groundwater flow. During dry periods, basal flow may occur solely within the fracture system within the wadi as water levels recede to the base of the wadi channel sediments. The largest number of wadis generally occurs in the western and southwestern parts of the country from the mountainous terrenes to the Red Sea (Nouh 2006). This region can receive over 500 mm of rainfall in an average year and there are a significant number of intense rainfall events. Examples are the Jeddah flood of 2009 during which greater than 90 mm of rainfall occurred in a 3.5- h period and the Wadi Dellah flash flood of 1982, when mm of rainfall occurred in a 12-h period (Vincent 2008). Because of the intense use of wadis in Saudi Arabia for water supply, the geology, hydrogeology, geomorphology, and the water quality within wadi aquifer systems have been investigated for many years (Al-Nujaidi 1978; Al-Hajeri 1974, 1977; Al-Saqaby 1974; Weir and Hadley 1975; Abdulrazzak 1976; Italoconsult 1976; Ghurm 1980; Zaidi 1983, 1984; Saleh 1984; Al-Kabir 1985; Red Sea Mining Company 1986; Sen 1986, 2008a; Dames and Moore 1988; Al-Suba l 1992; Hussein and Bazuhair 1992; Hussein et al. 1993; Al-Yamani et al. 1994; Subyani and Bayumi 2001; UNESCO 2002; Wheater 2002; Al-Sefry et al. 2004; Subyani, 2005a, 2005b, 2010; Nouh 2006; Hussein 2007; Sen and Wagdani 2008; Bastien 2009; Qari 2009; Subyani et al. 2012). Despite the generally large number of general hydrogeologic investigations on wadis in Saudi Arabia, the detailed analysis of aquifer hydraulics has not been carried out in many locations. The placement of instruments to measure flood flows and monitor groundwater levels has been the emphasis of the previous work. Most of the investigations of groundwater within wadis have utilized existing wells used for water supply and agricultural irrigation (Figure 5). Some groundwater quality investigations have been conducted to assess general water quality characteristics and man-induced changes, such as evaporative concentration and salinization caused by agricultural irrigation practices (Al-Yamani and Sen 1992; Subyani 2005a, 2005b, 2010; Al-Shaibani 2008; Subyani and Al-Ahmadi 2010). NGWA.org T.M. Missimer et al. GROUND WATER 50, no. 4:

5 Figure 5. Irrigation well in Wadi Qidayd dug by hand to a depth of 30 m below surface. Wells such as this have been used in Saudi Arabia for thousands of years. Wadi Aquifer Hydraulic Properties The hydraulic properties of wadi sediments have been measured or estimated at several sites in western Saudi Arabia with particularly important data sets collected at Wadi Wajj, located near Taif and within Wadi Yalamam, located south of Makkah (Sorman et al. 1997b; Bayumi 2001; Subyani 2005a; Al-Shaibani 2008). A summary of the wadi aquifer hydraulic properties is presented in Table 1. Some of the hydraulic conductivity estimates were made using grain size analyses and applying the Hazen method (Hazen 1892, 1911). These values ranged from 20 to 54 m/d. The authors conducted an additional 20 grain size analyses and applied the methods of Fair and Hatch (1933) and Barr (2001) to estimate the hydraulic conductivity and also measured the hydraulic conductivity using a permeameter. These values averaged 44 m/d with values ranging from 1.7 to 80.2 m/d. Wadi Aquifer Water Quality Water quality and hydrochemical investigations have been conducted within several of the wadi systems in Saudi Arabia. Research of particular note has been conducted in Wadi Wajj (Al-Shaibani 2008), Wadi Yalamam Table 1 Compiled Average Wadi Aquifer Hydraulic Parameters in Western Saudi Arabia Hydraulic Parameters Range of Values Average Value Hydraulic conductivity Horizontal m/d 38 m/d Vertical 1 15 m/d 8 m/d Specific yield Hydraulic slope Saturated thickness 0 38 m 10 m Depth to water table 0 33 m 10 m 1 Aquifer performance test data (pumping tests) yielded hydraulic conductivities ranging from 20 to 45 m/d. (Subyani 2005a; Subyani and Sen 2006), Wadi Tharad (Subyani 2004a), Wadi Khulays (Baisten Lemaire 2009), and Wadi Fatimah (Baisten Lemaire 2009). Water quality data collected from surface water and groundwater in Wadi Wajj, upstream and downstream of Taif (Al-Saibani 2008), are presented in Table 2 along with some recently collected upstream runoff data. These data are mean values and show that there is a marked increase in total dissolved solid (TDS) concentrations in the groundwater from upstream to downstream of Taif. The downstream runoff data show a seasonal increase in TDS concentration likely caused by evaporative concentration. The new upstream runoff data show that there are two water sources, one from urban runoff from Taif and the other from the local waste water treatment plant discharge (Figure 3). Groundwater in Wadi Wajj has a significantly lower concentration of TDS in its upper reach compared to that in Wadi Yalamam, but the downstream reach had a comparatively higher TDS concentration (Subyani 2005a; Al-Shaibani 2008). The TDS concentrations of samples collected in wells located in the upstream segment of Wadi Wajj had means of 531 and 837 mg/l in 1978 and 2003 respectively, and in the downstream area exhibited a mean of 3149 mg/l in In 2003, the wet and dry season means were 2685 and 2097 mg/l, respectively. The mean TDS concentration of 13 well samples collected from Wadi Yalamam was 1930 mg/l. Subyani (2005a) suggested that the wells containing the highest TDS concentrations in the channel were the result of mineralization caused by agricultural irrigation use. Wells located close to agricultural return flows had the highest salinities. It should be noted that the measured nitrate concentrations in Wadi Wajj were very high in the groundwater in the upstream reach with a mean of 78 mg-n/l and even higher in the downstream wells with wet and dry season mean concentrations being and 60.6 mg-n/l, respectively. The downstream runoff in the wadi had wet and dry season nitrate mean concentrations of 102 and 56.3 mg-n/l. Groundwater quality has been studied in Wadi Khulays and Wadi Fatimah by Lemaire (2009). The mean TDS concentration collected from wells in Wadi Khulays upstream of the Murwani Dam was 487 mg/l. The mean total TDS concentration of groundwater samples collected from Wadi Fatimah was 339 mg/l. The mean nitrate concentration in the Wadi Khulays wells was 19 mg-n/l vs. 31 mg-n/l in the Wadi Fatimah wells. The very high concentrations of TDS and nitrates found in wadi aquifers are the result of evaporative concentration caused by ponding and low rate of infiltration after flood events and from agricultural practices. Only 3% to 11% of storm water passing through wadis actually infiltrates as recharge to the underlying aquifer, depending on the geographic position in the wadi and the hydraulic characteristics. Some of the wadi flood water ponds in low-lying areas, where mud has accumulated at the surface in or adjacent to the channel. This water evaporates leaving a crust of residual salt at land 518 T.M. Missimer et al. GROUND WATER 50, no. 4: NGWA.org

6 Table 2 Water Quality Data Collected from Wadi Wajj over a 10-Year Period Downstream Groundwater Discharge WWTP Downstream Runoff Upstream Groundwater Wet Dry Wet Dry Wet (n = 2) (n = 2) Physical parameters Electrical conductivity (μs/cm) ph n.a. 6.5 n.a. 6.7 n.a T ( C) n.a n.a n.a Total dissolved solids (mg/l) n.a. n.a. Chemical parameters DOC (mg/l) n.a. n.a. n.a. n.a. n.a UV (1/m) n.a. n.a. n.a. n.a. n.a SUVA (l/mg/m) n.a. n.a. n.a. n.a. n.a Major ions (mg/l) Sodium Potassium Calcium Magnesium Sulfate Chloride Nitrate Nitrate N Ammonia N n.a. n.a. n.a. n.a. n.a Nitrite N n.a. n.a. n.a. n.a. n.a Bicarbonate n.a. n.a. Phosphate n.a. n.a. n.a. n.a. n.a Minor ions (mg/l) Aluminum Manganese n.d Iron n.d n.d. n.a. n.a. Barium Strontium Bromide Al-Thobaity and Al-Shaibani (2003), as referenced in Al-Shaibani 2008 (personal data). 2 Al-Shaibani (2008). 3 This study. surface, ultimately leaching into the underlying aquifer. Some urban storm water and treated waste water are discharged to wadis. The TDS of these anthropogenic flows is concentrated, thus adding to the salinity of water stored in the underlying aquifer. The addition of fertilizers in farming areas overlying wadi aquifers is the principal source of nitrate, although waste water discharges also add to the concentration. Natural Wadi Recharge Wadi recharge and groundwater recharge in general have been heavily investigated within Saudi Arabia (Abdulrazzak 1982, 1995; Abdulrazzak and Morel- Seytoux 1983; Abdulrazzak and Sorman 1988; Basmaci and Al-kabir 1988a, 1988b; Abdulrazzak et al. 1989a, 1992, 1994; Nouh 1989; Sorman and Abdulrazzak 1993a, 1997; Sorman et al. 1993, 1997a, 1997b; Scanlon 1994; Wood and Sanford 1995; Al-Yamani 2001; Subyani and Bayumi 2001; Subyani 2004a, 2005a, 2005b, 2010; Subyani and Sen 2006). Wadis are recharged directly by rainfall during high-intensity events and during flooding events. Quantification of recharge rates in wadis and other arid lands environments is problematical and has great uncertainty. During rainfall events in the arid lands of Saudi Arabia, there are only a few geologic environments that allow high rates of recharge. The Precambrian-aged rocks of the shield have high rates of runoff, and recharge can only occur in fractures and in the porous upper weathered part of the rock. Most of the volcanic rocks, particularly the flood basalts (harrats), share the same general characteristics of the igneous and metamorphic rocks of the Precambrian with recharge occurring primarily in fractures, but at greater rates. The coastal terrace deposits allow some infiltration during storm events, but those deposits are characterized by low vertical hydraulic conductivities caused by a significant percentage of mud contained within the sediments and the occurrence of NGWA.org T.M. Missimer et al. GROUND WATER 50, no. 4:

7 chemical precipitants, such as calcium carbonate (caliche). Only four geomorphic land forms in arid regions allow significant rates of recharge. These landscapes are alluvial fans, dunes or erg areas, karst terrenes, and wadis. Rainfall frequency is very low in the areas containing alluvial fans and in the hyper-arid erg basins of Saudi Arabia. Karst terrene is not a significant environment in most of Saudi Arabia, occurring only in the eastern part of the Kingdom. Therefore, the wadi areas have the highest potential for the recharge and storage of natural rainfall, particularly in the western part of the country. A number of methods have been developed to quantify recharge in the wadis of the Kingdom. These methods include direct observation using rainfall gages, staff gages and observation wells, tensiometers, chloride mass balance techniques, environmental isotopes, numerical modeling methods (calculation of the water balance using algorithms), and geophysical methods. Summaries of these and other methods used in arid land recharge estimation are given by Sen (2008a) and Scanlon et al. (2002). Recharge to wadi aquifers in western Saudi Arabia has been estimated by Bazuhair and Wood (1996), Subyani (2004a), Bazuhair et al. (2002), Subyani and Sen (2006), and Al-Shaibani (2008). Bazuhair and Wood (1996) constructed a regional estimate of groundwater recharge in western Saudi Arabia using the chloride mass balance technique. This investigation suggested that the recharge rate is between 3% and 4% of the effective annual rainfall. A specific basin recharge estimate was made by Subyani (2004a), who used the chloride mass balance technique and environmental isotopes to estimate the recharge rate in Wadi Tharad to be 6.2 mm/year, which is 11% of the effective average annual rainfall. Use of the chloride mass balance technique and a modification of this method were employed by Subyani and Sen (2006) to estimate the recharge in Wadi Yalamlam to be 1.8 mm/month for the classical method and 1.9 mm/month for the modified technique. The corresponding recharge percentage of effective annual rainfall was estimated to be 10 and 11%, respectively, using these techniques. Al-Shaibani (2008) estimated the recharge in Wadi Wajj using the chloride mass balance technique to be only 4.8% of average annual effective rainfall. Therefore, based on the investigations conducted to date, it can be concluded that the wadi basin recharge rates are controlled by the effective annual rainfall, infiltration rates, and locally by the availability of storage within the wadi channels. The available storage volume is controlled by the thickness of the alluvial deposits and the position of the water table. Lesser storage capacity occurs in wadis in the distal and upper middle segments. On the basis of all of the literature data reviewed, the groundwater recharge rates range between 3% and 11% of effective annual rainfall in western Saudi Arabia. The quantities of groundwater available for use from wadi aquifers are a function of rainfall and catchment rainfall-runoff relationships, the storage properties of both the sediments and fractured rock within or below the wadi channels, aquifer hydraulic characteristics (including infiltration rates), and local water use rates and patterns. There has been a historic increase in channel losses of water with increased water withdrawals from wadis (Sorman et al. 1997a). The increase in storage caused by pumping from the wadi sediments results in the creation of a lower water table position, allowing for more infiltration to occur during a flood event. Water Budgets and Evaporation in Wadis The water budget of a wadi aquifer is quite important in determining the amount of water available for use, the potential for evaporative increases in groundwater salinity (natural), and the available storage space for use as a storage zone in an artificial recharge scheme. Natural wadi hydrology is controlled predominantly by rain falling directly on the wadi sediments, runoff entering the wadi from the rocks and sediments lying outside of the channel (predominantly fracture flow), the evapotranspiration losses from the wadi aquifer system, and downstream water losses (discharges). The natural water balance or budget of a wadi aquifer for a given time period at any reach can be expressed as: S = P + R In (ET + G Out + SW Out ) where, S is the change in storage within the wadi aquifer (both saturated and unsaturated zones), P the precipitation, R In the runoff into the wadi channel from basin drainage, ET the evapotranspiration, G Out the downgradient groundwater movement through the wadi channel, and SW Out the down-gradient surface water discharge out of wadi (or segment of wadi). Lateral groundwater flow is included in the R In term. It is assumed that the surface flooding event that recharges the aquifer ends quickly and that any ponded water above the channel surface rapidly discharges down-gradient or is lost to surface evaporation. Some local groundwater flows into wadis occur via fractures, typically located in the distal parts of wadis located near basalt deposits (Figure 4, distal segment). Evapotranspiration losses from wadis occur as direct evaporation losses from ponded water at land surface in the channel, diffusive losses from the soils within the wadi, and from transpiration of plants (phreatophytes) that have root systems that penetrate the soils within the wadi. In most cases, plant transpiration is minor because of the low density of sustainable natural plant communities within most wadi systems. However, a significant density of woody plants does occur within some wadis in western Saudi Arabia with unknown water loss rates. The primary ET loss is from diffusive evaporation from the soils. Few data are available on the soil moisture profiles within wadis and the diffusive loss extinction depth or the depth to the water table at which water ceases to diffuse through the unsaturated zone and leave the aquifer system. The depth is dependent on the nature of the soil (Hellwig 1973a, 1973b), the corresponding nature of the capillarity within the unsaturated zone, 520 T.M. Missimer et al. GROUND WATER 50, no. 4: NGWA.org

8 and the thermal gradient within the unsaturated zone (Scanlon 1994; Scanlon and Milly 1994). Investigations of the aquifer grain size and the corresponding reduction in evaporative diffusion losses in an arid setting were performed by Hellwig (1973a). Within coarse sands, the loss rate declined rapidly from land surface to a depth of 0.6 m below surface. On the basis of the correspondence between the sands tested by Hellwig (1973a) and the grain size characteristics of wadi sediments in western Saudi Arabia, the diffusive evaporative loss from wadi aquifers in this region should be limited to about 1.5 m even with consideration of a high soil temperature gradient during the summer months. Evaporation loss rates have been estimated within Wadi Tabalah in southwestern Saudi Arabia by Sorman and Abdulrazzak (1997). Measured rates were 1.5 mm/d for the time immediately after a rainfall event and decreased to 0.42 mm/d thereafter. The minimum evaporation rate measured was 0.1 to 0.2 mm/d during the dry season. On the basis of seasonal temperature variations, the highest potential rates were 9.5 mm/d in June and July, the summer hot season, to 3.5 mm/d in December and January during the winter cool season. They concluded that direct evaporation from bare soil could take place to a depth of 1.5 m below surface based on the characteristics of the soil at the test location. The corresponding soil moisture ranged between 4% and 10% at one site and 7% and 15 % at another site. The soil was a fine and coarse sand with silt. Active evaporation loss from a depth of 1.5 m is greater than measured by Hellwig (1973a) for similar sediments in an arid condition. However, the wadi sediments in which Sorman and Abdulrazzak (1993c, 1997) measured diffusive evaporation losses may have a greater percentage of finer-grained sediment, thereby causing higher capillary fringe height with a corresponding lower extinction depth. The water balance of a wadi as a part of the general landscape is very important in assessing the amount of storage available for a given reach of a wadi aquifer (Al-Jerash 1988). A water balance was assessed for 13 storms that occurred within the Tabalah Basin in southwestern Saudi Arabia by Abdulrazzak et al. (1989a). They demonstrated that 63% of the precipitation is lost to evaporation from the water surface during flooding. Also, an additional 32% is stored as soil moisture in the vadose zone and may not reach the water table to cause recharge. Only about 3% of the total precipitation converts to surface runoff because of the low number of high-intensity events. Of the runoff from land surface, about 75% of this amount becomes discharge through wadi systems. Modeling of the water balance by Sorman et al. (1993) revealed that annual recharge ranges from 5% to 9% of annual rainfall, which is higher than some of the more recent estimates (up to 11%). This modeling effort concluded that 3% to 7.5% of rainfall became surface runoff, which is mostly wadi discharge. The largest element of the water balance was the evaporation loss rates, which ranged from 47% to 94.5% of rainfall depending upon event intensity. Storm water infiltration into wadi aquifers is very inefficient. The floods commonly occur as flash events with a short duration. Air is trapped within the vadose zone as flood water suddenly discharges in the wadi channel above the underlying aquifer. A combination of small ponding time periods, trapped air in the vadose zone, and the sediment load of the flood water collectively reduce the rate of aquifer recharge. Artificial Wadi Recharge Using ARR Artificial recharge of wadi aquifers in western Saudi Arabia has been considered in the past as part of an overall water management scheme (Abdulrazzak et al. 1989b; Sorman et al. 1990). Another means of storing water and creating artificial recharge in wadi systems has been the construction of dams (Sen and Al-Suba I 2002; Bastien Lemaire 2009). Also, the discharge of treated waste water into the distal or middle reaches of wadis could be considered to be artificial recharge of the system (i.e., discharge into the upper Wadi Wajj; Figure 3), especially where downstream farmers use the water for irrigation. As previously described, there is a vast volume of domestic waste water that is produced and discharged to waste within Saudi Arabia, which could be potentially used in a beneficial manner. Wadi aquifers are a potentially excellent place in which to artificially recharge the groundwater system with treated municipal waste water. Wadi sediments consist primarily of sands and gravels, ranging from coarse to fine in grain size. These sediments are biologically active and conducive to the removal of contaminants remaining in treated waste water. Typically, wadis contain a relativity thick unsaturated zone that could be used for temporary storage of the water within an ARR system. The average hydraulic gradient within a wadi aquifer allows gravity movement of impaired-quality water downstream without the necessity of pumping. A major advantage of using wadi aquifers for ARR is that the natural biological treatment processes occur with a very low expenditure of energy and a corresponding low carbon footprint (in aquifer natural processes and gravity flow). This low-energy, lowtechnology treatment solution is an alternative to advanced waste water (AWT) treatment processes, such as pressuredriven membranes and advanced oxidation processes, which are equally effective at removing pathogens, nitrogen, organic matter, and trace organic contaminants, but at great cost and energy expenditure (Drewes et al. 2003; Amy and Drewes 2007; Bellona et al. 2008). Another key element of a wadi ARR system is the ability to store water within the aquifer until it is needed. Periodic natural flood events do provide some recharge to wadi aquifers, but the percentage of flood water captured and recharged is small and would not effectively compromise the storage capacity of the aquifer when viewed over an extended timeframe. Development and design of an ARR system in a wadi aquifer within an arid or hyper-arid environment do have some challenges. The very high rate of evaporation requires that waste water being recharged cannot be NGWA.org T.M. Missimer et al. GROUND WATER 50, no. 4:

9 ponded for extensive time periods, because the high evaporative losses would result in the concentration of salts. Elevated TDS renders the water unacceptable for irrigation of crops or for indirect potable reuse. It is therefore desirable that the feed water to an ARR system be introduced into the wadi below the surface and not on the surface (percolation ponds). The high TDS (over 2000 mg/l) and nitrate concentrations (20 to 180 mg/l) found within some of the wadi aquifers are considerably above the drinking water standard of 1000 and 10 mg/l (World Health Organization 2006). The high TDS water may be unacceptable for irrigation if it exceeds the maximum allowable concentration of 2500 mg/l enforced by the Ministry of Water and Electricity for both restricted and unrestricted irrigation. The high nitrate water could be used for irrigation and may be beneficial as a source of nutrients thereby reducing the need to fertilize. However, if indirect potable reuse is a project objective, then the system would have to be designed and operated to minimize the introduction of native groundwater (altered to man s activities) into the stored system. On the contrary, if an objective is to avoid indirect potable reuse, then systems could be located in downstream parts of wadi aquifers, away from any potable supply wells. Large-capacity ARR systems will require that the treatment and storage capacity of the wadi aquifer is sufficient to accept the desired effluent flow capacity from the waste water treatment plant. This will require that the unsaturated zone must be thick and that the water will move downstream at a rate that will keep the water table below the evaporation extinction depth. Also, recovery of ARR-treated water is another issue that must be addressed in the development of any ARR system within a wadi aquifer. Thinning of the saturated thickness of the aquifer, caused by water spreading as it moves down-gradient, could make water recovery difficult using conventional vertical wells. Design of ARR Systems in Wadi Aquifers Design Considerations ARR systems require sufficient aquifer thickness and lateral distance to allow for natural treatment of infiltrated waste water. Where nitrification and denitrification are desired, percolation of the waste water through an unsaturated or aerobic zone before the water reaches the water table or zone of saturation can provide effective oxidation of ammonia with subsequent opportunities for denitrification. The water must then be able to move laterally through aquifer sediments to allow for additional treatment to provide additional residence time in the system. During this travel, additional attenuation of bulk organic carbon, trace organic chemicals, and pathogens can occur. After soil-aquifer treatment, the water is typically recovered using wells or galleries. Therefore, an ARR system constructed in a wadi will have a zone of recharge, a zone of treatment, and a capture zone (Figure 6). Figure 6. Wadi-ARR system showing the recharge, treatment, and recovery zones. The occurrence of high-salinity water in many wadi alluvial aquifers required that this water must be diverted around the primary facility. Wadi aquifers have generally good hydraulic characteristics for ARR system development and operation using either a natural setting or a fully engineered system. The key natural characteristics are: (1) sufficient hydraulic conductivity to allow for relatively high rates of infiltration and percolation, (2) relatively high lateral hydraulic gradients to allow for sufficient lateral or downslope water movement to enhance water treatment, (3) natural changes in slope to allow capture of the treated water at slope changes from high to lower slopes, (4) significant reduction in hydraulic conductivity between channel sediments and the channel boundaries to limit losses of water from the primary aquifer, and (5) a suitable water quality that provides a sustainable operation without compromising the hydraulic infiltration characteristics while supporting the biological function of an ARR system. There are some design challenges that require consideration in the placement of an ARR system in a wadi aquifer. It is unlikely that an ARR system can be developed in the distal (upstream) segment or perhaps in some middle segments of wadi systems because there is an insufficient thickness of stable sediment with adequate hydraulic properties to produce the desired degree of treatment. The sediments in the distal and upper middle wadi segments are thin, unstable, have a very coarse grain size, and are commonly transported during flood events. So an ARR system must be located in a segment of the wadi system that has a normally thick section of unsaturated sediment, perhaps a minimum of 10 m, which most commonly occurs in the lower middle or proximal (downstream) segments. The hydraulic conductivity of the wadi aquifer must be sufficient to allow rapid infiltration of the water and corresponding rapid percolation through the unsaturated and saturated zones. Use of percolation ponds or sites that expose the waste water to the atmosphere for significant time periods (ponding) is not desirable, because of the high rates of natural evaporative water loss that occur in 522 T.M. Missimer et al. GROUND WATER 50, no. 4: NGWA.org

10 Saudi Arabia and the high potential for extensive algal growth that can result in a reduction of infiltration rates. A high rate of evaporative loss would both reduce the volume of water available for reuse and significantly increase the salinity of the water, potentially rendering it unusable for drinking water or irrigation of most plants. Once the water is introduced into the wadi aquifer and is flowing down-gradient within the channel, it must be captured for use before it spreads out to a degree that it cannot be easily captured by wells or it mixes with water of an undesirable quality, such as highly saline water or water containing very high nitrate concentrations. These conditions can occur as a result of agricultural practices or high salinity water occurring adjacent to tidal water at the point of wadi discharge. In a natural setting, a good collection location for the use of wells to capture the water would be in thickened depositional areas of the aquifer on the downstream end of a slope reduction or in a depression of the bedrock in the wadi channel, where water will tend to fill the sediments. The system would also be designed so that there is sufficient retention time between recharge and recovery to allow for inactivation of pathogens, and attenuation of bulk carbon, trace organic chemicals, and nitrogen species commonly present in reclaimed water. The design of an ARR system must also be compatible with the natural function of wadi systems, which involves collection of water during flood events and the corresponding recharge that takes place within the wadi aquifer. Flood events should not destroy the infrastructure of the ARR system nor reduce the effectiveness of the treatment processes. Natural flood/recharge events should enhance the amount of water available to use within the ARR system. On the basis of the hydrogeology of wadi systems and the desired design characteristics of ARR systems within an arid region, it is likely that it will be difficult to find acceptable locations within natural wadi systems that will have all of the necessary characteristics to develop a managed natural ARR system. However, an ARR system can be engineered within wadi aquifers to meet the requirements for high-volume systems that would produce the desired goals of wadi-arr in many locations. Conceptual Wadi-ARR Design Although wadi aquifer systems share some common hydrogeologic characteristics, a final design of an ARR system within this type of aquifer would require the collection and analysis of considerable site-specific data. Analysis of the specific natural wadi system must include the desired rate of recharge and the treated waste water sources available to be used as well as the distance between the water source and the recharge site. Engineered wadi systems will require several interrelated components that will allow the treated waste water to enter the aquifer with minimal evaporative losses, will produce the necessary treatment processes, and will allow collection of the treated water in an effective manner. Engineering design solutions are available to overcome the specific issues within wadi aquifers. For example, the high evaporative loss rates can be mitigated by use of subsurface infiltration systems (wells or exfiltration galleries) or the wadi bed can be excavated to its full depth and the sediment replaced by high hydraulic conductivity gravel to enhance vertical rapid infiltration with passage of water horizontally into beds with the highest hydraulic conductivity. The rate of exfiltration would be designed to keep the water levels in the trenches below the evaporative diffusion extinction depth, which for wadi sediments would be greater than 1.5 m (Hellwig 1973a; Sorman and Abdulrazzak 1993c). For the subsurface infiltration solution, the depth of screen burial would also protect the exfiltration infrastructure from damage during flood events. The placement of the exfiltration process would be within a wadi aquifer with a minimum of 10 m of sediment thickness (Figure 7). In many potential wadi-arr systems, the groundwater in the aquifer is quite saline and, if allowed to mix with the recharged reclaimed water, would result in its water quality becoming unacceptable for irrigation and potential indirect potable water reuse. To minimize or eliminate (A) (B) (C) Figure 7. Conceptual design of a wadi-arr system using a series of exfiltration galleries (A and B) for recharge and wells (C) for recovery of the reclaimed water. (A) Sectional view of the ARR system showing the induced groundwater mound. (B) A plan view with a slurry wall used to exclude saline groundwater from entering the system. (C) The collection area, where a slurry wall dams the recharged and treated water and allows conventional vertical wells to be used for recovery. NGWA.org T.M. Missimer et al. GROUND WATER 50, no. 4:

11 the impact of impaired wadi groundwater, a slurry wall could be constructed from one wadi boundary partially across the aquifer to prevent downstream movement of groundwater into the recharge and treatment area. The slurry wall could be angled to cause the water to bypass the ARR system and move parallel to it (Figure 7B). The slurry wall could then be constructed parallel downstream the full length of the ARR system to prevent outflow of water from the system into the bypass area and to maintain water quality. The top of the slurry wall would likely be located about 1 to 2 m below the natural grade of the wadi. This would give protection to the slurry wall during floods and would also allow high-salinity groundwater passage to downstream reaches and would maintain the channel to pass water during extreme floods. In order to maximize the storage and recovery of the recharged water, a groundwater dam (slurry wall) could be constructed across the full channel width at the collection area (Figure 7C). The slurry wall and wadi aquifer boundary would fully contain the ARR system. If the wadi contains highly weathered and fractured bedrock, it may be required to pressure grout the base of the slurry wall near the collection area to prevent underflow losses of reclaimed water through the hydraulic conductivity contained within the underlying geologic unit. The concept of constructing slurry walls in wadi aquifers is not new. They have been proposed and designed for wadi aquifers in western Saudi Arabia as a means for the strategic storage of potable-quality water in the upstream reaches of wadis (Al-Ghamdi 2009; Khairy et al. 2010). An example is in Wadi Khulays, where both a surface dam and a subsurface slurry wall are used in concert with each other. On the basis of the geologic, hydrogeologic, and water quality characteristics of wadis, high-capacity, engineered wadi-arr systems can be designed and constructed for a reasonable cost. There are, however, many different approaches could be used to achieve the primary objectives of ARR, which are restoration and enhancement of wadi aquifers by storage, treatment, and recovery of treated waste water to be used for indirect potable and unrestricted irrigation uses. Conclusions Wadi aquifers within arid lands are commonly the only sources of naturally occurring fresh water, but are depleted by over-pumping. These aquifers can be restored by artificial recharge using treated effluent. Reuse of treated waste water is a critical component of integrated water management in the Kingdom of Saudi Arabia. The region has a climate ranging from semi-arid to hyper-arid with average annual rainfall ranging from a high of nearly 500 mm/year in the highlands of the southwestern part of the country to less than 50 mm/year over a large part of the country. Reuse of treated waste water, in general, requires that the final product is safe for the desired uses, ranging from irrigation of ornamental vegetation, nonfood crops, and food crops, and, perhaps in the future, for indirect potable reuse. To meet the water quality standards for either irrigation of food crops or indirect potable water reuse, the water must meet all standards adopted by the Ministry of Water and Electricity (MOWE) and the Saudi Arabia Standards Organization (SASO), along with a reduction in the presence of regulated trace organic chemicals that are associated with potential adverse human health effects. Typically, treatment of waste water to this degree would require AWT techniques, such as high-pressure membranes, advanced oxidation, and other processes, which are very costly, energy intensive, and have a large carbon footprint. Planned potable reuse is unlikely in the forseeable future because of great difficulty in obtaining social acceptance irrespective of the quality of the water. Development of large-scale wadi-arr systems could be a valuable tool for increasing the rate of waste water reuse, which would eliminate environmental impacts associated with disposal and provide additional water that could be used to meet water demands. Increased reuse would reduce demands on fresh groundwater resources and other alternative water supplies, such as expensive and energy-intensive seawater desalination systems. Maximization of reclaimed water reuse is necessary to meet present and future water demands in water scarce regions. There is growing recognition that managed aquifer recharge systems can be used to cost-effectively improve the quality of treated waste water and other impaired water. ARR using wadi aquifers can be used in Saudi Arabia, and other arid regions can achieve both reclaimed water treatment and storage goals. While the characteristics of wadi aquifers present some design challenges, the hydrogeology of wadi aquifers is favorable for development of fully engineered, large-scale waste water ARR systems. These systems can be designed in concert with the natural processes acting within the wadis to allow reuse of a valuable local resource that is currently being wasted. Acknowledgments The authors thank the reviewers Dr. H. Gao and Dr. P. Zhang as well as the editor Dr. Frank Schwartz for making helpful suggestions on improving the manuscript. Assistance on preparation of graphics was given by Samir Al-Mashharawi and Gina Lipor. References Abdulrazzak, M.J Losses of flood water from alluvial channels. Arid Soil Research and Rehabilitation 9, no. 1: Abdulrazzak, M.J Aquifer recharge from an ephemeral stream and the resulting evolution of the water table. Unpublished Ph.D. diss., Colorado State University, Fort Collins, Colorado. Abdulrazzak, M.J Ground water system evaluation for Wadi Nisah, Saudi Arabia. Unpublished M.S. thesis, University of Arizona, Tucson, Arizona. Adbulrazzak, M.J., and A.U. Sorman Transmission losses from ephemeral stream in arid region. Journal of Irrigation and Drainage Engineering, ASCE 120, no. 3: T.M. Missimer et al. GROUND WATER 50, no. 4: NGWA.org

12 Adbulrazzak, M.J., A.U. Sorman, and O.S. Aborizaiza Estimation of natural groundwater recharge. Final Report of Project No. ARP-6-170, vol. 1. King Abdulaziz City, Saudi Arabia: KACST. Abdulrazzak, M.J., A.U. Sorman, and A.S. Alhames. 1989a. Water balance approach under extreme arid conditions: a case study of Tabalah basin, Saudi Arabia. Hydrological Processes 3, Abdulrazzak, M.J., A.U. Sorman, and S.A. Alhames. 1989b. Techniques of artificial recharge from an ephemeral wadi channel under extreme arid conditions. In Proceedings of the International Symposium on the Artificial Recharge of Groundwater, ed. A.I. Johnson and D.J. Finlayson, New York: American Society of Civil Engineers. Abdulrazzak, M.J., and A.U. Sorman Water balance approach under arid conditions. Journal of Hydrological Processes 2: Abdulrazzak, M.J., and H.J. Morel-Seytoux Recharge from an ephemeral stream following wetting front arrival to water table. Water Resources Research 19: Aborizaiza, O.S., M.Z. Khan, Y. Basmaci, M.N. Allam, Bokhari, and M.J. Adbulrazzak Water resources potential, allocation and reuse in the western region. Final report of project No. ARP King Adbulaziz City, Saudi Arabia: KACST. Abouammoh, A.M The distribution on monthly rainfall intensity at some sites in Saudi Arabia. Environmental Monitoring Assessment 17: Al-Aghar Group and Bushnak Academy Executive summary of the initial study for the strategy of water and energy in the Kingdom of Saudi Arabia. Unpublished committee executive summary. Alehaideb, I Precipitation distribution in southwest of Saudi Arabia. Ph.D. diss., Arizona State University, Tempe, Arizona. Al-Ghamdi, A.S Development of strategic water reserve for the Holy City of Makkah, Saudi Arabia. Water Science & Technology: Water Supply 9 no. 5: Al-Hajeri, F.Y Groundwater Studies of Wadi Qudaid. Institute of Applied Geology, King Abdulaziz University Research Series, no. 2, Jeddah, Saudi Arabia. Al-Hajeri, F.Y The hydrology of Wadi Liyyah, Taif Region. Jeddah, Saudi Arabia: Institute of Applied Geology. Al-Jerash, M Climatic water balance in Saudi Arabia: an application of Thornthwaite-Mather model. Journal of the Faculty of Arts and Humanities, King Abdulaziz University, Jeddah, Saudi Arabia 5: Al-Jerash, M Climatic subdivisions in Saudi Arabia: an application of principal component analysis. Journal of Climatology 5: Al-Jerash, M Models of estimating average annual rainfall over the west of Saudi Arabia. Journal of the Faculty of Arts and Humanities: King Abdulaziz University, Jeddah, Saudi Arabia 3: Al-Kabir, M Recharge characteristics of groundwater aquifers in Jeddah-Makkah-Taif area. M.Sc. thesis, King Abdulaziz University, Jeddah, Saudi Arabia. Al-Nujaidi, H.A Hydrogeology of Wadi Murawani, Khulais. Unpublished M.S. thesis, IAG, King Abdulaziz University, Jeddah, Saudi Arabia. Al-Qurashi, M Synoptic climatology of the rainfall in the south-western region of Saudi Arabia. Unpublished M.Sc. thesis, Western Michigan University, Kalamazoo, Michigan. Al-Saqaby, A Geology and Hydrology of Wadi Wajj, Al-Taif Region. Jeddah, Saudi Arabia: Center for Applied Geology. Al-Saud, M Managing the Water Sector of Saudi Arabia. Deputy Minister, Ministry of Water and Electricity, Saudi Arabia. Keynote Lecture Water Desalination and Reuse Center, October 16, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia. Al-Sefry, S., S.A. Al-Ghamdi, W., Al-Ashi,and Al-Baradi Strategic ground water storage of Wadi Fatimah- Makkah region Saudi Arabia: Saudi Geological Survey, Hydrology Project Team, Final Report. Al-Shaibani, A.M Hydrogeology and hydrochemistry of a shallow alluvial aquifer, western Saudi Arabia. Hydrogeology 16, DOI: /s y Al-Suba I, K Erosion-sedimentation and seismic considerations for dam siting in the central Tihamat Asir region. Unpublished Ph.D. thesis, King Abdulaziz University, Faculty of Earth Sciences, Kingdom of Saudi Arabia, Jeddah, Saudi Arabia. Al-Yamani, M.S Isotopic composition of rainfall and groundwater recharge in the western province of Saudi Arabia. Journal of Arid Environments 49: Al-Yamani, M.S Salinity problem of groundwater in the Wadi Tharad basin, Saudi Arabia. GeoJournal 48: Al-Yamani, M.S., A.S. Bazuhair, and M.T. Hussein Interpretation of groundwater quality chemistry by factor analysis technique. Journal of King Abdulaziz University, Earth Sciences 7: Al-Yamani, M.S., and Z. Sen Regional variation in monthly rainfall amounts in the Kingdom of Saudi Arabia. Journal of King Abdulaziz University, Faculty of Earth Sciences 6: Al-Wagdany, A.S., M.A. Al-Shahri Rainfall-runoff relation for three mountainous arid basins. Journal of King Abdualaziz University, Earth Sciences 12: American Geological Institute Glossary of Geology, 4th ed., ed. J. Jackson. Alexandria, Virginia: American Geological Institute. Amy, G., and J.E. Drewes Soil-aquifer treatment (SAT) as a natural and sustainable wastewater reclamation/reuse technology: fate of wastewater effluent organic matter (EfOM) and trace organic compounds. Environmental Monitoring and Assessment 129, no. 1 3: Balkhair, K.S Outranking strategic groundwater basins in western Saudi Arabia using multi-criterion decision making techniques. In Groundwater Hydrology, ed. Sherif, Sing, and Al-Rashed, Lisse: Swets and Zeitlinger. Barr, D.W Coefficient of permeability determined by measurable parameters. Ground Water 39, no. 3: Basmaci, Y., and M.A. Al-kabir. 1988a. Recharge characteristics of aquifers of Jeddah-Makkak-Taif region. In Estimation of Natural Groundwater Recharge, ed. I. Simmers, NATO ASI Series C222Dordrecht, The Netherlands: Reidel. Basmaci, Y., and M.A. Al-kabir. 1988b. Groundwater recharge over western Saudi Arabia. In Estimation of Natural Groundwater Recharge, ed. I. Simmers Dorchecht, The Netherlands: Reidel. Baisten Lemaire Hydrogeological survey. Unpublished consulting report for the National Water Company, Jeddah City Business Unit. Bazuhair, A.S., M.O. Nassief, M.S. Al-Yamani, M.A. Sharaf, T.H. Batumi, and S. Ali Groundwater recharge estimation in some wadi aquifers of western Saudi Arabia: King Abdulaziz City for Science and Technology. Project No. AT-17-63, Riyadh, Saudi Arabia. Bazuhair, A.S., and W.W. Wood Chloride mass-balance for estimating ground water recharge in arid areas: example from western Saudi Arabia. Journal of Hydrology 186: Bellona, C., G. Oelker, J. Luna, G. Filteau, G. Amy, and J.E. Drewes Comparing nanofiltration and reverse osmosis for drinking water augmentation. Journal of the American Water Works Association 100, no. 9: NGWA.org T.M. Missimer et al. GROUND WATER 50, no. 4:

13 Bull, W.B Threshold of critical power in streams. Geological Society of America Bulletin 86: Dames, and Moore Representative basin study for wadis Yiba, Habawnah, Tabalah, Liyyah, and Lith. Unpublished consultant s report for the Ministry of Agriculture and Water, Riyadh, Saudi Arabia. Dabbagh, A.E., and W.A. Abderrahman Management of groundwater resources under various irrigation water use scenarios in Saudi Arabia. The Arabian Journal for Science and Engineering 22: Deain, M.A Estimation of floods and recharge volumes in wadis Fatimah, Naaman and Turabah. Unpublished M.Sc. thesis, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia, 127. Drewes, J.E., and M. Reinhard, P. Fox Comparing microfiltration-reverse osmosis and soil-aquifer treatment for indirect potable reuse of water. Water Research 37: Fair, G.M., and L.P. Hatch Fundamental factors governing the stream-line flow of water through sand. Journal of the American Water Works Association 25: Ghurm, A.A Hydrogeology of Wadi Wajj. M.Sc. thesis, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia, 169. Hazen, A Discussion of Dams on sand foundations by A. C. Koenig. Transactions of the American Society of Civil Engineers 73: Hazen, A Some physical properties of sands and gravels, with special reference to their use in filtration. 24th Annual Report, Massachusetts State Board of Health, Publication Document No. 34: Hellwig, D.H.R. 1973a. Evaporation of water from sand, 4: The influence of particle size on the depth of the water table and the particle size distribution of the sand. Journal of Hydrology 18: Hellwig, D.H.R. 1973b. Evaporation of water from sand: the loss of water into the atmosphere from a sandy river bed under arid conditions. Journal of Hydrology 18: Hussein, M.T Assessment of groundwater quality of Wadi Al Shamiyah for future development of water resources in western Saudi Arabia. Annuals of the Geological Survey of Egypt 39: Hussein, M.T., A. Bazhair, and M.S. Al-Yamani Groundwater availability in the Khulais Plain, western Saudi Arabia. SITH Bulletin 3: Hussein, M.T., and A.S. Bazuhair Groundwater in Haddat Al Sham-Al Bayada area, western Saudi Arabia. Arabian Gulf Journal of Scientific Research 10, no. 1: Italoconsult Detailed investigation of Wadi Khulays. Unpublished report, Ministry of Agriculture and Water, Riyadh, Saudi Arabia. Khairy, A.T., A.S. Al-Ghamdi, and S.A. Gutub Analysis and design of a deep subsurface dam. International Journal of Civil & Environmental Engineering IJCEE-IJENS 10, no. 3: Khiyami, H.A., Z. Sen, S.C. Al-Harthy, F.A. Al-Ammawi, A.B. Al-Balkhi, M.I. Al-Zahrani, and H.M. Al-Hawsawy Flood hazard evaluation in wadi Hali and wadi Yibah. Technical Report, Saudi Geological Survey, 138. Maliva, R.G., T.M. Missimer, F.P. Winslow, and R. Herrmann Aquifer storage and recovery of treated sewage effluent in the Middle East. Arabian Journal of Science and Engineering 36: DOI: /s y. Maliva, R.G., and T.M. Missimer Aquifer Storage and Recovery and Managed Aquifer Recharge Using Wells: Planning, Hydrogeology, Design, and Operation. Houston, Texas, USA: Schlumberger Water Services, Methods in Water Resources Evaluation Series No. 2. Noory, M Water and the Progress of Development in the Kingdom of Saudi Arabia. Jeddah, Saudi Arabia: Tihama Publisher (in Arabic). Nouh, M Wadi flow in the Arabian Gulf States. Hydrological Processes 20: Nouh, M Flood hydrograph estimation from arid catchment morphology. Hydrological Processes 4: Nouh, M Performance of geomorphologic rainfall-runoff models in extremely arid watersheds. In Proceedings of HYDROCOM 89, IAHR, Dubrovinik, Croatia, Nouh, M. 1988a. Estimate of floods in Saudi Arabia derived from regional equations. Journal of Engineering Science, King Saud University 14, no. 1: Nouh, M. 1988b. On the prediction of flood frequency in Saudi Arabia. Proceedings Institution of Civil Engineering 85, no. 2: Nouh, M. 1987a. Estimation of design flood in selected basins in Saudi Arabia. Arabian Journal for Science and Engineering 12, no. 4: Nouh, M. 1987b. Regional flood frequency analysis. Advances in Water Resources 10, 4: Nouh, M. 1987c. Analysis of rainfall in southwest region of Saudi Arabia. Proceedings of the Institution of Civil Engineers 83, no. 2: Nouh, M., and A. El-Laithy Construction damages due to floods in Wadi Ad-dilah. Final Technical Report, Riyadh, Saudi Arabia: KACST. Qari, M.H.T Geomorphology of Jeddah Governate, with emphasis on drainage systems. Journal of the King Abdulaziz University, Earth Sciences 20, no. 1: Red Sea Mining Company Hydrogeological investigations Makkah Project. Unpublished report, Wadi Ibrahim. Saleh, A.S Hydrogeology of Wadi Turabah, Saudi Arabia. Unpublished M.S. thesis, South Dakota School of Mines and Technology, Rapid City, South Dakota. Scanlon, B.R Water and heat flux in desert soils: 1. Field studies. Water Resources Research 30: Scanlon, B.R., and P.C.D. Milly Water and heat fluxes in desert soils: 2. Numerical simulations. Water Resources Research 30, no. 3: DOI: /93WR Scanlon, B.R., R.W. Healy, and P.G. Cook Choosing appropriate techniques for quantifying groundwater recharge. Hydrogeology Journal 10: DOI: / ss Sen, Z. 2008a. Wadi Hydrology Boca Raton, Florida: CRC Press, Taylor & Francis Group. Sen, Z. 2008b. Modified hydrograph method for arid regions. Hydrological Processes 22: Sen, Z Hydrograph and unit hydrograph derivation in arid regions. Hydrological Processes 21: Sen, Z The Saudi Geological Survey hydrograph method for use in arid regions. Technical Report, SGS-TR , Jeddah, Saudi Arabia: SGS. Sen, Z Determination of aquifer parameters by the slope matching method. Ground Water 24: Sen, Z Hydrology of Saudi Arabia: Symposium on water resources in Saudi Arabia, Riyadh, A68 A94. Sen, Z., and E. Wagdani Aquifer heterogeneity determination through the slope method. Hydrological Processes 22: Sen, Z., and K. Al-Suba I Hydrologic considerations for dam siting in arid regions: a Saudi Arabian study. Hydrological Science Journal 47, no. 1: Shammas, M. I The effectiveness of artificial recharge in combating sweater intrusion in Salalah Coastal Aquifer, Oman. Environmental Geology 55: Sirdas, S., and Z. Sen Determination of flash floods in western Arabian Peninsula. Journal of Hydrologic Engineering 12, no. 6: DOI: (ASCE) :6(676). 526 T.M. Missimer et al. GROUND WATER 50, no. 4: NGWA.org

14 Sorman, A.U., and M.J. Abdulrazzak Estimation of wadi recharge from channel losses in Tabalah Basin, Saudi Arabia. In Recharge of phreatic aquifers in (semi-) arid areas, ed. I. Simmers. International Association of Hydrogeologists vol. 19: Sorman, A.U., M.J. Abdulrazzak, and H.J. Morel-Seytoux. 1997a. Groundwater recharge estimation from ephemeral streams, case study: Wadi Tabalah, Saudi Arabia. Hydrological Processes 11: Sorman, A.U., M.J. Abdulrazzak, and M.A.S. Ugas. 1997b. Application of infiltration models to field data from Wadi Tabalah, Saudi Arabia. Proceedings of the International Conference, Application of Tracers in Arid Zone Hydrology 232: Sorman, A.U., and M.I. Abdulrazzak. 1993a. Infiltrationrecharge through wadi beds in arid regions. Hydrological Science Journal 38, no. 3: Sorman, A.U., and M.J. Abdulrazzak. 1993b. Flood hydrograph estimation of ungaged wadis in Saudi Arabia. Journal of Water Resources Planning and Management 119, no. 1 (19 pages). Sorman, A.U., and M.J. Abdulrazzak. 1993c. Estimation of actual evaporation using precipitation and soil moisture records in arid climates. Hydrological Processes 9, no. 7: Sorman, A.U., Y. Basmaci, and K. Eren Application of water balance model to western Saudi Arabia and use of GIS in future. Proceedings of HydroGIS93, Application of Geographic Information Systems in Hydrology and Water Resources, Vienna, April 1993, IAHS Publication no. 211, Sorman, A.U., M.J. Abdulrazzak, and A. Al-Hames A proposed artificial groundwater recharge scheme for wadi systems. Journal of the King Abdulaziz University 1: Subyani, A.M Identifying the hydrochemical processes of groundwater in Wadi Na man, western Saudi Arabia using factor analysis. Arabian Journal of Geosciences. DOI: /5/ Subyani, A.M Hydrologic behavior and flood probability for selected arid basins in Makkah area, western Saudi Arabia. Arabian Journal of Geosciences 4, no. 5 6: DOI: /s Subyani, A.M. 2005a. Hydrochemical identification and salinity problem of ground-water in Wadi Yalamlam basin, western Saudi Arabia. Journal of Arid Environments 60: Subyani, A.M. 2005b. Hydrogeological and hydrochemical features of Wadi Adam, Makkah Al-Mukarramah area. Journal of King Abdulaziz University, Earth Sciences 16: Subyani, A.M. 2004a. Use of chloride-mass balance and environmental isotopes for evaluation of groundwater recharge in the alluvial aquifer, Wadi Tharad, western Saudi Arabia. Environmental Geology 46: Subyani, A.M. 2004b. Geostatistical study of annual and mean rainfall patterns in southwest Saudi Arabia. Hydrological Sciences Journal 49, no. 5: Subyani, A. M Geostatistical analysis of rainfall in southwest Saudi Arabia. Unpublished Ph.D. thesis, Colorado State University, Fort Collins, Colorado, 182. Subyani, A.M., and M.E. Al-Ahmadi Rainfall-runoff modeling in Al-Madinah area of western Saudi Arabia. Journal of Environmental Hydrology 19 Paper 1. Subyani, A.M., and Al-Ahmadi M.E Multivariate statistical analysis of groundwater quality in Wadi Ranyah, in western Saudi Arabia. Journal of King Abdulaziz University, Earth Sciences 21, no. 2: Subyani, A.M., and A. A. Al-Modayan Flood analysis in Western Saudi Arabia. Journal of King Abduaziz University, Earth Sciences 220, no. 2. Subyani, A.M., A.A. Al-Modayan, and F.S. Al-Ahmadi Topographic, seasonal, and aridity influences on rainfall variability, Western Saudi Arabia. Journal of Environmental Hydrology 18. Paper 2. Subyani, A.M., and T. Bayumi Evaluation of groundwater resources in Wadi Yalamlam basin, Makkah area. Project no. 203/420, King Abdulaziz University, Jeddah, Saudi Arabia, 128 pp. Subyani, A.M., M.H. Qari, and M.I. Matsah DEM and multivariate statistical analysis of morphometric parameters of some wadis, western Saudi Arabia. Arabian Journal of Geosciences 5, no. 1: Subyani, A.M., and A.A. Al-Modayan Flood vulnerability assessment of Wadi Rabigh, western part of Saudi Arabia. Proceedings of the 2nd International Multidisciplinary Conference in Hydrology and Ecology, April 22 23, 2009, Vienna, Austria (poster). Subyani, A., and Z. Sen Refined chloride mass-balance method and its application in Saudi Arabia. Hydrological Processes 20: Subyani, A.M., and T. Bayumi Evaluation of groundwater resources in Wadi Yalamlam basin, Makkah area. Project No. 203/420, King Abdulaziz University, Jeddah, Saudi Arabia, 128. UNESCO Hydrology of wadi systems. IHP Regional Network on Wadi Hydrology in the Arab Region, IHP-V, Technical Documents in Hydrology, no. 55, Paris, France: UNESCO. 39. US Census International Data Base on Population Forecast. (accessed May 11, 2011). Vincent, P Saudi Arabia: A Environmental Overview. London, UK: Taylor & Francis. Weir, K.L., and D.G. Hadley Reconnaissance geology of the Wadi Sa diyah quadrangle [20/40A]. U. S. Geological Survey, Saudi Arabian Project Report PR-193, 27. Wheater, H.S Wadi hydrology: process response and management implications. In Proceedings of the UNESCO- NWRC-ACSAD Workshop on Wadi Hydrology and Groundwater Protection, ed. J.M. Lineke, M.A.S. Abdin, and S. Morad. Technical Document in Hydrology, No. 1, UNESCO Cairco. 143 pp. Wheater, H.S., A.P. Bulter, E.J. Stewart, and G.S.Hamilton. 1991a. A multi-variate spatial-temporal model of rainfall in Southwest Saudi Arabia, I. Data characteristics and model formulation. Journal of Hydrology 125: Wheater, H.S., C. Onof, A.P. Butler, and G.S. Hamilton. 1991b. A multi-variate spatial-temporal model of rainfall in Southwest Saudi Arabia, II. Regional analysis and longterm performance. Journal of Hydrology 125: Wood, W.W., and W.E. Sanford Chemical and isotopic methods for quantifying groundwater recharge in a regional, semiarid environment. Ground Water 33: World Health Organization Guidelines for Drinking Water Quality. Geneva, Switzerland: World Health Organization. Zahrani, M.I., G.H. Saad, H.W. Hawsawi, H.A. Khiyami, F.A. Al-Amawi, M. Theban, and Z. Sen Potential flood hazard in wadi Qanunah, Southwest Saudi Arabia. Saudi Geological Survey, Hydrogeology Team, Final Report. Zaidi, S Landforms and geomorphic evolution of Wadi Khulais area, western Saudi Arabia. Faculty of Earth Sciences Bulletin 5: Zaidi, S Geomorphology of Wadi Khulais area. Faculty of Earth Sciences Research Series 18: 98 pp. NGWA.org T.M. Missimer et al. GROUND WATER 50, no. 4: