Journal of Hydrology 403 (2011) 14–24
Contents lists available at ScienceDirect
Journal of Hydrology
journal homepage: www.elsevier.com/locate/jhydrol
Modern recharge to fossil aquifers: Geochemical, geophysical, and modeling constraints ⇑ M. Sultan a, , S. Metwally b, A. Milewski a, D. Becker a, M. Ahmed a, W. Sauck a, F. Soliman c, N. Sturchio d, E. Yan e , M. Rashed c, A. Wagdy f, R. Becker g, B. Welton a a Department of Geosciences, Western Michigan University, Kalamazoo, MI, USA b Desert Research Center, El Matariya, Cairo, Egypt c Suez Canal University, Department of Geology, Ismalia, Egypt d Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, IL, USA e Environmental Science Division, Argonne National Laboratory, Argonne, IL, USA f Irrigations & Hydraulics Engineering Department, Cairo University, Giza, Egypt g University of Toledo, Department of Environmental Sciences, Toledo, OH, USA article info abstract
Article history: The Nubian Sandstone (NSS) aquifer of northeast Africa is believed to have been recharged in previous Received 21 June 2010 wet climatic periods in the Quaternary Period. While this is largely true, we show using the Sinai Penin- Received in revised form 4 February 2011 sula as our test site that the aquifer is locally receiving modern recharge under the current dry climatic Accepted 22 March 2011 conditions. The validity of the advocated model was tested using geophysical (conventional electrical Available online 3 April 2011 resistivity [ER]) and isotopic (O, H) data, and estimates for modern recharge were obtained using contin- This manuscript was handled by L. Charlet, Editor-in-Chief, with the assistance of uous rainfall-runoff modeling over the period 1998–2007. Interpretations of ER profiles are consistent Philippe Négrel Associate Editor with the presence of unconfined NSS aquifers flooring recharge areas at the foothills of the crystalline basement in Sinai at Baraga (thickness: 20 to >188 m; resistivity: 16–130 X m) and Zalaga (thickness: 18 Keywords: 27 to >115 m; resistivity: 3–202 X m). The isotopic composition (dD: 22.7 to 32.8‰; d O: 4.47 Sinai Peninsula to 5.22‰) of groundwater samples from wells tapping the NSS aquifer underlying recharge areas is con- Recharge sistent with mixing between two endmembers: (1) fossil groundwater with isotopic compositions similar Stable Isotope to those of the Western Desert NSS aquifer (dD: 72 to 81‰; d18O: 10.6 to 11.9‰), and (2) average SWAT modern meteoric precipitation (dD: 9.84‰; d18O: 3.48‰) in Sinai, with the latter endmember being Nubian Aquifer the dominant component. A first-order estimate for the average annual modern recharge for the NSS Geophysics aquifer was assessed at 13.0 106 m3/yr using the SWAT (Soil Water Assessment Tool) model. Findings bear on the sustainable exploitation of the NSS aquifer, where the aquifer is being locally recharged, and on the exploitation of similar extensive aquifers that were largely recharged in previous wet climatic periods but are still receiving modest modern meteoric contributions. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction portions of eastern Libya, northeastern Chad, and northwestern Sudan (Fig. 1) lies an immense reservoir (>780,000 km3) of fresh- The deserts of Egypt, namely the Eastern Desert (ED), the water in the Nubian Sandstone (NSS) aquifer system (Thorweihe, Western Desert (WD), and the deserts of the Sinai Peninsula (SP) 1990). The aquifer consists mainly of continental sandstones with (Fig. 1), are among the most arid deserts in the world (WD receiv- intercalated shales of shallow marine and deltaic origin, uncon- ing <5 mm/yr; ED: 25 mm/yr; SP: 40 mm/yr); however, the geo- formably overlying Proterozoic basement, and reaching a thickness logic evidence indicates that climate alternated between arid and approaching 3 km in the center of the basin (Hesse et al., 1987). wet periods throughout the Quaternary Period, with the last of The NSS aquifer is believed to contain fossil groundwater that the major wet periods occurring in the Holocene (9500–4500 yr was recharged in previous wet climatic periods by intensification BP). Beneath the surface of the deserts of Egypt and adjacent of paleomonsoons (Sarnthein et al., 1981; Prell and Kutzbach, 1987; Yan and petit-Maire, 1994) or paleo-westerlies (Sultan et al., 1997; Sturchio et al., 2004). The progressive increase in Krypton-81 and Chlorine-36 ages ⇑ Corresponding author. Address: Department of Geosciences, Western Michigan University, 1903 W. Michigan Avenue, Kalamazoo, MI 49008, USA. Tel.: +1 269 387 for groundwater from the southwest to the northeast parts of the 5487 (office), +1 269 387 5451, +1 269 387 5446 (lab); fax: +1 269 387 5513. WD of Egypt was interpreted to indicate that local recharge E-mail address: [email protected] (M. Sultan). through intensified regional precipitation over the extensive NSS
0022-1694/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jhydrol.2011.03.036 M. Sultan et al. / Journal of Hydrology 403 (2011) 14–24 15
Fig. 1. (a) Location map showing the distribution of Neoproterozoic outcrops, the overlying Phanerozoic rock units, and the Upper Jurassic to Lower Cretaceous Malha Formation outcrops (primary recharge areas for the NSS aquifer) in the Sinai Peninsula (SP). Also shown are the locations of our groundwater samples (solid red triangles), and geoelectric cross sections in Wadi Baraga (Box a) and Wadi Zalaga (Box b). Inset shows the study area (Box c); the areal extent of the NSS aquifer in Egypt, Sudan, Libya, and Chad; and the distribution of deserts in Egypt, namely, the Western Desert (WD: west of the River Nile), the Eastern Desert (ED: east of the River Nile), and the Sinai Peninsula (SP: subtended by the Gulfs of Suez and Aqaba) Desert. (b) N–S trending cross section along line B–B0 plotted on Fig. 1a.
aquifer outcrops in southern Egypt and northern Sudan in the observations are at odds with earlier models that advocate that previous wet climatic periods must have played a major role in recharge was accomplished mainly by precipitation over more the recharge of the NSS aquifer (Sturchio et al., 2004). These distant mountains in Chad (e.g., Ball, 1927; Sanford, 1935). 16 M. Sultan et al. / Journal of Hydrology 403 (2011) 14–24
In this manuscript we advocate that in dry climatic periods sim- and structural information (e.g., layer thickness and composition, ilar to that of today, the NSS aquifer in the WD of Egypt (Fig. 1)is faults, folds) extracted from field observations and/or bore hole receiving no local recharge because there is negligible precipita- data (5 wells); (3) published resistivity values (e.g., Sultan et al., tion. That is apparently not the case in the ED and even less so in 2009) for lithologies reported from field and/or bore hole data; the SP. In both areas, precipitation over the mountains is channeled and (4) measured depth to water table (e.g., B.W.1: 65 m, Z.W.1: downstream over the NSS outcropping at the foothills of the Red 2 m, and Z.W.3: 14 m; Fig. 2). Fig. 3c shows two examples, one Sea Hills, providing ample opportunities for groundwater recharge. from Wadi Baraga (VES B4) and the other from Wadi Zalaga (VES In this manuscript we apply an integrated approach to test the Z4), for modeling layer depth, thickness, and apparent resistivity, validity of the advocated model in the SP. Specifically, we set out to and the RMS values for the model. accomplish the following: (1) examine the areal extent and distri- In the Wadi Baraga area, two geoelectrical cross sections were bution at depth of NSS groundwater in recharge areas at the foot- generated, one trending N–S and the other trending NW–SE hills of the basement complex, using geophysical investigations; (Fig. 2a). Along these two cross sections, six geoelectrical layers (2) investigate the origin of, and modern contributions to, the were recognized (Fig. 3a and b). These geoelectrical layers were groundwater in the NSS by comparing the isotopic compositions interpreted as representing three lithologic sub-units in these of groundwater from recharge areas to those of modern precipita- two geoelectrical cross sections. The uppermost unit was inter- tion and fossil precipitation; and (3) estimate to the first order the preted as a highly resistive layer representing dry wadi fill deposits magnitude of modern recharge, applying continuous rainfall runoff (q: 110–4896 X m) having thicknesses (h) ranging from 5 to 47 m. models. The upper highly resistive units are underlain by the water-bearing unit, the NSS. The saturated NSS unit has lower resistivity values (q: 16–130 X m) and ranges in thickness (h) from 20 to >188 m. 2. Site description The NSS is underlain by basement rocks of high-resistivity (q: 210–13432 X m) with varying depths ranging from 3 to Two main groups of rock units crop out in the SP: (1) Neoprote- 122 m below ground surface. rozoic (550–900 Ma) volcano-sedimentary basement rocks in In the Wadi Zalaga area (Fig. 2b), two geoelectrical cross sec- southern Sinai that are part of the Arabian–Nubian Shield Massif tions were generated, one trending N–S and the other NW–SE (Sultan et al., 1988; Stern and Kroner, 1993), and (2) overlying (Fig. 3d and e). Along these two cross sections, six geoelectrical lay- thick Phanerozoic cover (Fig. 1). The major stratigraphic units in ers were observed. These layers were interpreted as representing the SP and their distribution at depth along a N–S-trending cross three lithologic sub-units. The uppermost unit was interpreted as section (B–B0) are shown in Fig. 1b. The basement complex is highly resistive layers representing dry wadi fill deposits unconformably overlain by Upper Jurassic to Lower Cretaceous flu- (q: 384–2298 X m) having thicknesses (h) ranging from 10 to viatile sandstone and conglomerate that belongs to the Malha For- 100 m. The upper highly resistive units are underlain by the mation of the Nubian Sandstone Group. This formation crops out at water-bearing NSS with lower resistivity values (q: 3–202 X m) the foothills of the basement complex, providing ample opportuni- and variable thickness (h) from 27 to >115 m. The saturated NSS ties for groundwater recharge for the NSS aquifer. The Phanerozoic unit is underlain by high-resistivity (q: 246–1732 X m) fractured section is largely formed of Upper Cretaceous marine sandstone of basement rocks at depths ranging from 38 to 194 m below ground the Matulla Formation, overlain by thick Tertiary limestone surface. belonging to the Thebes Group. During the Oligocene, tectonic The reported ER investigations support the suggestion that movement led to the elevation of the Arabo-Nubian Massif; in groundwater accumulations are found within the NSS aquifer re- the Miocene the SP landscape was shaped during a period of in- charge areas at the foothills of the basement complex. Geochemical tense erosion, giving rise to numerous valley networks that were methods were then applied to address the question of whether the carved into the elevated Red Sea hills (Said, 1993). groundwater in question is receiving contributions from modern precipitation. 3. Modern recharge of the NA: geophysical constraints 4. Modern recharge of the NA: geochemical constraints Conventional Electrical Resistivity (ER) investigations were con- ducted to investigate whether groundwater accumulations are to Insights into the origin of the groundwater and the timing of its be found within the presumed NSS aquifer recharge areas at the recharge were gained from analysis of its isotopic composition. foothills of the basement complex in Central Sinai. Two areas were Groundwater samples were collected in high-density polyethylene selected: Wadi Baraga (Box a) and Wadi Zalaga (Box b) in Fig. 1.We bottles, which were then tightly capped. Stable H and O isotope ra- used vertical electrical soundings (VESs) with expanding electrode tios were measured by standard methods of equilibration with H spacing (Schlumberger, 4 Array) for horizontal profiling along tran- 2 and CO , respectively (Coplen, 1996; Nelson, 2000). Hydrogen and sects using maximum current electrode separations (AB) of 2 O isotope data are reported in terms of the conventional delta (d) 1400 m. ABEM SAS1000 was used for data collection during all of notation, in units of per mil (‰) deviation relative to a standard the field work. A total of 20 VESs were carried out in Wadi Baraga reference, whereby and its surroundings, and 14 VESs were carried out in Wadi Zalaga (Fig. 2). Topographic surveys were carried out with the purpose of 3 d; ‰ ¼½ðRsample=RstandardÞ 1 10 determining the location and ground elevation of the sounding sta- tions using a Magellan ProMark GPS unit. The RESIST (1988) and and R = 2H/1Hor18O/16O and the standard is Vienna Standard Mean RESIX-IP (1988) software packages were used for quantitative Ocean Water (Coplen, 1996). Precision of d2H values is ± 1.3‰ and inversion of the obtained VESs’ measurements and for the estima- that of d18O values is ±0.2‰. tion of apparent resistivity (rho: q) and thickness (h) values. The Fourteen groundwater samples were collected for isotopic anal- estimated root mean square (RMS) errors for the 34 VESs acquired yses of H and O in H2O(Table 1) from open and productive wells ranged from 2 to 6, indicating a good fit for the generated models. tapping three types of aquifers: (1) fractured basement (samples: The geoelectrical cross sections shown in Fig. 3 were generated Bir Haroun, Bir Zeituna, Bir Halwagy, Bir Sahab, Bir Al Gufa, Bir Al from, and/or constrained by the following: (1) the modeled layers Sidra, Bir Nadia); (2) NSS unconfined aquifer cropping out at the and their apparent resistivity and thickness values; (2) lithologic foothills of the basement outcrops (samples: Bir Zalaga 1, Bir M. Sultan et al. / Journal of Hydrology 403 (2011) 14–24 17
Fig. 2. False color Landsat TM image bands 2 (blue), 4 (green), and 7 (red) showing the distribution of VES locations (solid green triangles), well locations (open red circles) and geoelectric cross sections (blue and red lines). (a) Wadi Baraga area (Box a, Fig. 1). (b) Wadi Zalaga area (Box b, Fig. 1).
Zalaga 2, Bir Safra), areas that are considered here as potential months. One of the explanations for the observed variations in recharge areas for the NSS aquifer; and (3) alluvial aquifers (Bir isotopic compositions for our samples and those reported from 28, Bir Makateb, Bir 5 Makateb), all of which are believed to be the Gulf of Suez coastal plain is that they represent various degrees fed by fractured basement aquifer discharge into overlying alluvial of mixing between two endmembers, one being fossil waters sim- sediments. ilar to those reported from the WD, deposited by intensified paleo- The stable isotope ratios of H and O are given in Table 1 and are westerlies in previous cold and wet climatic regimes, and the other shown in Fig. 4, which includes data for samples from the present being modern precipitation deposited in dry and warm climatic study, as well as: (1) paleowaters from the NSS aquifers in the WD conditions (Sultan et al., 1997, 2011). If true, one might expect a of Egypt and the Gulf of Suez (Sturchio et al., 1996); (2) NSS aquifer progressive depletion in the isotopic composition and a progres- groundwater samples from the ED (Sultan et al., 2007); and (3) sive increase in the age of the groundwater with distance from data for modern precipitation from Al Arish and Rafah (Fig. 1) the recharge areas. That is apparently the case in the SP. The ana- (IAEA and WISER, 2008). lyzed NSS groundwater samples that were collected from locations Examination of Fig. 4 and Table 1 shows that the hydrogen (dD) proximal to recharge areas (e.g., SN1-3, SN1-4, SN1-5; Fig. 1) are and oxygen (d18O) isotopic compositions of the groundwater sam- less depleted than those reported from discharge areas in the Gulf ples collected from the unconfined NSS aquifers in the recharge of Suez coastal plain (Fig. 4). Similarly, analysis of the reported data areas cropping out at the foothills of the basement outcrops are indicates the radiocarbon ages increase with increasing distance somewhat depleted (dD: 22.7 to 32.8‰; d18O: 4.47 to from recharge areas in southern Sinai, and the oxygen and hydro- 5.22‰) compared to those collected from fractured basement gen isotopic compositions of groundwater of the NSS aquifer are outcrops (dD: 19.9 to 23.2‰; d18O: 3.77 to 5.05‰) and those progressively depleted with increasing distance from recharge from alluvial aquifers (dD: 22.7 to 23.4‰; d18O: 4.53 to areas (JICA, 1999). 5.01‰), but they are less depleted than those reported from the Additional support for the mixing hypothesis that we advocate Gulf of Suez (Sturchio et al., 1996). The Gulf of Suez samples from comes from examination of the variations in isotopic compositions Hammam Faraoun, Ayun Musa, Ain Sokhna, and Hammam of groundwater from the SP, ED, and WD in relation to the amount Musa (Fig. 1) are believed to represent groundwater in alluvial of modern precipitation in these areas (Fig. 5). The greater the aquifers fed by ascending NSS groundwater accessing the sub- amount of modern precipitation, the greater the contribution from vertical faults defining the Gulf of Suez and its coastal plain modern recharge, and the less depleted the isotopic compositions (Sturchio et al., 1996). become. The isotopic compositions of our Sinai samples are the The isotopic compositions of samples from the fractured base- least depleted (dD range from 19.9 to 32.8‰; d18O: 3.77 to ment and alluvial aquifers are similar to those of average modern 5.81‰) and the WD fossil groundwater samples are the most de- precipitation from Al Arish and Rafah (Fig. 1). These averages were pleted, whereas the ED samples have isotopic compositions that extracted from the reported isotopic compositions for cumulative are intermediate between those of the WD and the SP. Hydrogen samples acquired on a monthly basis and weighted in proportion and oxygen isotopic compositions of the WD water samples are to the amount of recorded precipitation for each of the investigated similar (dD: range from 72 to 81‰; d18O: 10.6 to 11.9‰) 18 M. Sultan et al. / Journal of Hydrology 403 (2011) 14–24
Fig. 3. Geoelectric cross sections showing VES and well locations, and apparent resistivity, thickness, and distribution of the saturated and unsaturated rock units in the Wadi Baraga (Box a, Fig. 1) and Wadi Zalaga (Box b, Fig. 1) areas. (a) S–N trending geoelectrical cross-section in the Wadi Baraga area. (b) SE–NW trending geoelectrical cross- section in the Wadi Baraga area. (c) Modeled layer depth, thickness, and apparent resistivity, and the RMS values for two locations (Wadi Baraga: VES B4; Wadi Zalaga: VES Z4). (d) S–N trending geoelectrical cross section along Wadi Zalaga. (e) SE–NW trending geoelectrical cross section along Wadi Zalaga. over large areas and throughout various depths in the aquifer; the range in hydrogen and oxygen isotope ratios (dD range from 73 ED fossil groundwater samples, on the other hand, have a wide to 19‰; d18O: 9.5 to 2.7‰). M. Sultan et al. / Journal of Hydrology 403 (2011) 14–24 19
Table 1 Isotopic data for the SP groundwater samples from fractured basement, and from open and productive wells.
ID Name Location Lat Long Altitude (m) Description DWT (m) dD ‰ d18O‰
SN1-2 Bir 28 Al Tur 28.37431 33.56984 90 Productive well (Alv)a 22.3 5.22 SN1-3 Bir Zalaga 1 W. Zelega 29.05652 34.40927 Open well (NSS)b 7 22.7 4.53 SN1-4 Bir Zalaga 2 W. Zelega 29.00975 34.38137 Open Well (NSS)b 5 31.0 5.44 SN1-5 Bir Safra Barga area 28.75737 34.34483 Open well (NSS)b 7 26.0 4.47 SN1-6 Bir W. Marra W. Marra 28.79905 34.24910 Production well (NSS)b 27 32.8 5.22 SN1-7 Bir Haroun W. El Sheik 28.56807 33.96538 1507 Open Well (FB)c 13 20.5 4.37 SN1-8 Bir Zeituna W.i El Sheik 28.59463 33.99162 1439 Open Well (FB)c 30 20.1 4.50 SN1-9 Bir Halwagy W. El Sheik 28.66773 33.99033 1299 Open Well (FB)c 55 19.9 3.77 SN1-10 Bir Sahab W. El Sheik 28.71512 33.77945 887 Open Well (FB)c 44 22.5 4.49 SN1-11 Bir Al Gufa W. El Sheikh 28.69378 33.69315 754 Open Well (FB)c 45 20.8 4.72 SN1-12 Bir Al Sidra W. El Sheikh 28.90050 33.47115 429 Open pit (FB)c 20 22.5 4.89 SN1-13 Bir Makateb W. Feiran 28.79910 33.46438 328 Open well (Alv)a 23.4 5.05 SN1-14 Bir Nedia W. El Sheikh 28.77593 33.52240 399 Productive well (FB)c 63 23.2 5.05 SN1-15 Bir 5 Makateb W. Feiran 28.78778 33.42263 268 Productive well (Alv)a 70/80 23.0 5.01
a Alluvial sediments. b Nubian sandstone. c Fractured basement.
Fig. 4. Comparison between stable isotope ratios [hydrogen (dD) vs. oxygen (d18O)] for groundwater samples from the SP with NSS aquifer paleowaters from the WD (Sturchio et al., 2004), the ED (Sultan et al., 2007), and the Gulf of Suez (Sturchio et al., 1996), and data for modern precipitation from El Arish and Rafah (IAEA and WISER, 2008). Also shown is the global meteoric water line (solid line): dD=d18O + 10 (Craig, 1961).
The progressive enrichment in the isotopic composition of the and potential recharge to the groundwater system. For this pur- NSS aquifer groundwater from the SP to the ED to the WD is here pose the Soil and Water Assessment Tool Model (SWAT) was interpreted to indicate variable degrees of mixing between fossil utilized. water that precipitated during wet climatic periods and meteoric precipitation deposited during the intervening dry climatic peri- 5.1. Model construction ods (e.g., present climate). This hypothesis is supported by the patterns of modern precipitation. Currently, rainfall over the The SWAT model provides a continuous simulation of the over- NSS outcrops (recharge areas) in southern Sinai is considerable land flow, channel flow, transmission losses, evaporation on bare ( 100 mm/yr) compared to that over their counterparts in the soils and evapotranspiration on vegetated canopy, and potential WD, which hardly receive any precipitation (0–5 mm/yr) (EMA, recharge to the shallow alluvial aquifers (Arnold and Fohrer, 1996; Legates and Wilmott, 1997; Nicholson, 1997). Precipitation 2005; Arnold et al., 1998). SWAT was selected because it is a con- in the ED is intermediate between that reported for the WD and tinuous model, allowing rainfall-runoff and groundwater-recharge that for the SP. estimates to be made over extended periods of time; it is also com- patible with GIS data formats, allowing us to import the existing 5. Modern recharge of the NA: modeling constraints GIS databases for the SP into the model.
We attempted to quantify modern recharge contributions to the 5.2. Database generation using GIS fossil water of the NSS aquifer of the SP. The adopted methodolo- gies were those of Milewski et al. (2009a,b) that compensate for The initial step in the development of our hydrologic model was uncertainties arising from scarcity of one or more of the following the generation of a database incorporating digital mosaics from data sets: temporal and spatial rainfall depths, stream flow data, various sources. Recently-released GIS-based SWAT modules and field data. A catchment-based, semi-distributed hydrologic (ArcSWAT: SWAT, 2007) can readily display and query geospatial model was developed for continuous simulation of surface runoff information in a GIS environment and use GIS databases as inputs 20 M. Sultan et al. / Journal of Hydrology 403 (2011) 14–24
Fig. 5. Average annual precipitation extracted from TRMM 3B42.v6 3-hourly data acquired (1998–2007) over Egypt showing the lowest precipitation in the WD, moderate precipitation in the ED, and the highest precipitation in the SP. Also shown are the distribution of the meteorological stations and TRMM stations in the SP and the ED.
to the SWAT model. We generated digital mosaics that were used latitude by 3° longitude (scale 1:500,000); (3) land-use maps as model inputs. These mosaics covered the entire SP and included extracted from the U.S. Geological Survey (USGS) 1 km global Land the following digital data sets: (1) temporal, calibrated rainfall data Use and Land Cover database generated from Advanced Very High (3-hourly precipitation data: 1998–2007) extracted from the Resolution Radiometer (AVHRR) data (acquisition date: April zsatellite-based Tropical Rainfall Measuring Mission (TRMM) data; 1992–March 1993); (4) a mosaic of three quadrants (each covering (2) a geologic mosaic from two geologic maps, each covering 2° 5° by 6°) from the NASA Landsat GeoCover Dataset 2000 (Landsat M. Sultan et al. / Journal of Hydrology 403 (2011) 14–24 21
GeoCover Orthorectified Thematic Mapper Dataset 2000; spatial storm events; and (3) alluvial deposits flooring the valleys have resolution: 15 m) (Tucker et al., 2004); (5) climatic parameters high hydraulic conductivities. including solar radiation, wind speed, air temperature, and relative Simulations were performed at daily time steps, the smallest humidity obtained from the Egyptian Meteorological Authority’s time steps allowed by SWAT, using cumulative 3-hourly TRMM Climatic Atlas (EMA, 1996); and (6) a digital elevation model mo- data over periods of 24 h and applying monthly average values saic from 37 Advanced Spaceborne Thermal Emission and Reflec- for temperature, wind speed, relative humidity, and solar radiation tion Radiometer (ASTER) scenes at 30 m resolution. The data sets as daily estimates. described above, originally in various projections, were co-regis- The adopted model parameters for this study were extracted tered to a reference map (NASA Landsat GeoCover Dataset 2000) from our previous investigations in the Wadi Girafi watershed, and re-projected to a common projection (UTM – Zone 36, an E–W trending, medium-sized (area: 3656 km2) watershed that WGS84). collects precipitation from the highlands of central Sinai and Average monthly climatic data (e.g., minimum temperature, flows eastwards towards Israel (Milewski et al., 2009a). Wadi maximum temperature, solar radiation, and wind speed) were ex- Girafi was selected for the following reasons: (1) in Sinai, the tracted from the Global Historical Climatology Network (GHCN) stream flow data needed for calibration purposes is only available global climatic dataset (EarthInfo, 1998–2005) and the Egyptian for the Wadi Girafi watershed, where the Israeli Hydrologic Ser- Meteorological Authority (EMA, 1996). vice collected (from 1998 to 2006) stream flow data at the outlet To alleviate problems arising from the paucity of rain gauges, (Bottleneck station) of the Wadi Girafi watershed; and (2) there and their general distribution in areas of low elevation, procedures are similarities in physical catchment descriptors (e.g., geography, were developed to extract precipitation data from satellite-based climate, catchment size, topography, geology, vegetation, etc.) of TRMM precipitation sensors as opposed to precipitation from rain Wadi Girafi and those of the investigated watersheds, and thus gauge data. We used the 3-hourly data from the TRMM datasets the key sensitive model parameters (e.g., SCS curve numbers, with a spatial resolution of 0.25° 0.25° that is available for the groundwater water delays, etc.) that were extracted for the Wadi study area from 1997 to present. Because TRMM can underesti- Girafi could be readily transferred to the similar proximal inves- mate precipitation in arid environments by 15–30% (Chiu et al., tigated watersheds. The procedures for calibrating (coefficient of 2006; Chokngamwong and Chiu, 2006), the TRMM-based precipi- determination, R2: 0.86; coefficient of efficiency: 0.85) the Wadi tation for the study area was calibrated against rain gauge data Girafi watershed were described in detail in Milewski et al. using procedures described in Milewski et al. (2009a). (2009a).
5.3. SWAT model setup and calibration 5.4. Model results
The hydrologic model of the SP was constructed within the Continuous rainfall-runoff models were simulated from 1998 to SWAT framework to simulate the hydrologic processes using its 2007 for 20 watersheds in the SP (Fig. 6) using model parameters physically-based formulations. Initial losses and direct overland extracted from the calibrated Wadi Girafi watershed (Milewski flows in the Hydrologic Response Units (HRUs) were estimated et al., 2009a). All of the selected watersheds are located at the foot- using the US Department of Agriculture, Soil Conservation Service, hills of the Precambrian mountains and encompass Nubian aquifer method (SCS, 1972), a method that was successfully applied to outcrops. Watersheds to the north that have NSS outcrops of lim- ephemeral watersheds in southwestern United States that bear ited areal extent were excluded; thus our average annual modern some resemblance in their climatic, hydrologic, topographic, land- recharge estimates for the NSS aquifer in the SP should be consid- scape, and soil and land-use types to watersheds in the SP (Gheith ered conservative estimates. and Sultan, 2002; Osterkamp et al., 1994). The bulk of the physical The SWAT model results for each of the investigated 20 water- properties of the HRUs in each sub-catchment was extracted from sheds, including the average annual amount of precipitation, ini- databases that we generated for soils, land cover, and land-use tial losses, surface runoff, total watershed transmission losses, types throughout our previous studies (Gheith and Sultan, 2001, and transmission losses over the Nubian outcrops throughout 2002; Milewski et al., 2009a). The soil types were extracted from the investigated period are summarized in Table 2. Nubian aquifer the 1:500,000 geologic map series (Klitzsch et al., 1987a–e), and recharge was assumed to be equal to the estimated transmission the land-use maps were derived from the USGS 1 km global Land losses, consistent with findings from similar arid environments Use and Land Cover database that was generated from AVHRR data that showed minimal recharge contributions from the initial (Anderson et al., 1976). Evaporation on bare soils and transpiration losses (Bazuhair and Wood, 1996; Dettinger, 1989; Flint et al., on vegetated canopy was calculated using the Penman–Monteith 2000). method (Monteith, 1981). A simplified top soil profile was em- Inspection of Table 2 shows that the total area of the modeled ployed in the model with soil properties dictated by the assigned watersheds in the SP is 14,209 km2, approximately 22.5% of the land-use and soil type. In our case, the ‘‘Southwestern US Arid area of the SP, whereas the Nubian outcrops covered approxi- Range’’ provided by the SWAT database was the selected land- mately 8% of the area of these watersheds. First-order estimates use type across the entire study area. for NSS recharge for each of the investigated watersheds were esti- Channel flows were estimated using the Muskingum routing mated by multiplying the watershed transmission losses by the method (McCarthy, 1938), whereby Manning’s coefficient for uni- proportion of NSS outcrops in the watershed. The average annual form flow in a channel was used to calculate the rate and velocity modern recharge for the NSS in the SP was estimated at of flow in a reach segment for a given time step. Channel flows 13.0 106 m3 from the sum of annual transmission losses for 20 were subject to transmission losses, a partitioning that depends watersheds for each of the investigated years (1998–2007) aver- on the channel geometry, upstream flow volume, duration of flow, aged by the number of years (10 years). bed material size, sediment load, and temperature (Neitsch et al., 2005). We assumed negligible losses from channel flows to tran- 6. Summary and conclusion spiration or evaporation for the following reasons: (1) vegetation is scarce or absent under the prevailing arid to hyper-arid We conducted an integrated study using geophysical, geochem- conditions; (2) flows are short-lived, typically not lasting for more ical, field, and remote sensing data sets, GIS technologies, and than a day, with cloudy conditions typically prevailing throughout continuous rainfall-runoff modeling to examine the validity of a 22 M. Sultan et al. / Journal of Hydrology 403 (2011) 14–24
Fig. 6. False-color Landsat TM image bands 2-4-7 for southern Sinai showing the 20 watersheds (red outlines) encompassing NSS outcrops (yellow outlines) that were modeled using SWAT continuous rainfall-runoff models.
Table 2 SWAT model results for the investigated watersheds from 1998–2007.
Watershed Area of watershed Area of Nubian Precipitation Initial losses Surface runoff Watershed Nubian transmission losses transmission losses km2 km2 106 m3 106 m3 (%) 106 m3 (%) 106 m3 (%) 106 m3 (%) Wardan 1161.23 14.53 97.89 86.78 0.89 3.66 3.74 7.46 7.62 0.09 0.10 Gharandal 882.39 76.99 83.65 79.23 0.95 0.97 1.16 3.45 4.12 0.30 0.36 Tayiba 356.22 132.33 32.77 27.65 0.84 4.59 14.00 0.54 1.64 0.20 0.61 El-Gart 728.84 55.35 91.62 83.05 0.91 3.80 4.15 4.76 5.19 0.36 0.39 Sidri 1074.61 40.23 111.44 76.40 0.69 6.52 5.85 28.51 25.58 1.07 0.96 Feiran 1806.47 23.65 64.49 29.16 0.45 6.65 10.31 28.69 44.48 0.38 0.58 Durba 124.47 7.79 2.96 2.63 0.89 0.04 1.39 0.30 10.00 0.02 0.63 ‘Araba 66.03 10.22 1.80 1.36 0.75 0.07 4.03 0.37 20.77 0.06 3.21 Awag 1943.14 0.81 73.65 46.42 0.63 6.86 9.31 20.36 27.65 0.01 0.01 Near Bir Taba 90.27 31.47 14.21 11.34 0.80 2.35 16.51 0.53 3.70 0.18 1.29 Bir Merakh 49.96 18.51 8.77 4.80 0.55 0.58 6.60 3.39 38.68 1.26 14.33 South of Bir Merakh 37.49 15.11 6.58 1.06 0.16 3.34 50.75 2.19 33.21 0.88 13.39 Near G. Ghazlani 46.06 8.41 8.09 3.80 0.47 1.62 19.98 2.67 33.04 0.49 6.03 North of Ain Quseiyib 30.93 9.92 2.72 1.54 0.56 0.66 24.28 0.52 19.26 0.17 6.18 Ain Quseiyib 54.30 4.45 3.19 2.19 0.69 0.83 25.92 0.17 5.34 0.01 0.44 El-Mahash 46.97 6.87 2.76 1.17 0.43 0.53 19.32 1.05 38.15 0.15 5.58 El-Malha 50.27 8.29 2.98 1.32 0.44 0.50 16.88 1.16 38.89 0.19 6.42 South of El-Malha 50.39 12.26 2.45 1.68 0.69 0.25 10.02 0.52 21.19 0.13 5.16 Watir 3531.35 338.00 208.35 187.09 0.90 2.12 1.02 19.14 9.19 1.83 0.88 Kid 2082.30 293.67 117.44 63.99 0.54 16.68 14.20 36.77 12.52 5.19 4.42
Total Nubian per year 1108.87 12.96 Total Nubian (1998–2007) 1108.87 129.65 M. Sultan et al. / Journal of Hydrology 403 (2011) 14–24 23 widely accepted notion that the NSS aquifer of northern Africa Arnold, J.G., Fohrer, N., 2005. Current capabilities and research opportunities in (Egypt, Sudan, Libya, Chad) was exclusively recharged by fossil applied watershed modeling. Hydrological Processes 19, 563–572. Arnold, J.G., Srinisvan, R., Muttiah, R.S., Williams, J.R., 1998. Large area hydrologic water in previous wet climatic periods in the Quaternary Period. modeling and assessment, Part I: model development. Journal of American Our working hypothesis is that while this is largely true for many Water Resource Association 34 (1), 73–89. of the areas occupied by the NSS aquifer, this might not be true in Ball, J., 1927. Problems of the Libyan Desert. Geography Journal 70, 221–224. Bazuhair, A.S., Wood, W.W., 1996. Chloride-mass balance method for estimating areas of relatively higher modern precipitation. One of these areas, groundwater recharge in arid areas: example from Western Saudi Arabia. our test area, is the SP. In dry climatic periods similar to that of to- Journal of Hydrology 186, 153–159. day, the precipitation over the mountains in Sinai is channeled Chiu, L., Liu, Z., Vongsaard, J., Morain, S., Budge, A., Neville, P., Bales, C., 2006. Comparison of TRMM and water district rain rates over New Mexico. Advances downstream over NSS Group exposures at the foothills of the crys- in Atmospheric Sciences 23 (1), 1–13. talline basement hills in southern Sinai, providing ample opportu- Chokngamwong, R., Chiu, L., 2006. TRMM and Thailand Daily Gauge Rainfall nities for groundwater recharge. In other words, the groundwater Comparison. American Meteorological Society, Atlanta, Georgia. p. 10. Coplen, T.B., 1996. New guidelines for the reporting of stable hydrogen, carbon, and in the NSS aquifer in areas of relatively higher precipitation repre- oxygen isotope ratio data. Geochimica et Cosmochimica Acta 60, 3369. sents a mixture of fossil water and modern precipitation. The advo- Craig, H., 1961. Isotopic variations in meteoric waters. Science 133, 1702–1703. cated model is supported by interpretations of our geophysical Dettinger, M.D., 1989. Reconnaissance estimates of natural recharge to desert (conventional electrical resistivity) investigations and geochemical basins in Nevada, USA, by using chloride-balance calculations. Journal of Hydrology 106, 55–78. data. The interpretation of our geophysical data is consistent with EarthInfo, 1998–2005. GHCN Global Climate. EarthInfo, Inc. the presence of unconfined NSS saturated aquifers flooring re- EMA, 1996, Climatic Atlas of Egypt: Cairo, Egypt, Egyptian Meteorological Authority, charge areas at the foothills of the crystalline basement in the SP Ministry of Transport and Communications, Cairo, Egypt. Flint, A.L., Flint, L.E., Hevesi, J.A., D’Agnese, F.A., Faunt, 2000. Estimation of regional at Baraga and Zalaga areas. The isotopic compositions (O, H) for recharge and travel time through the unsaturated zone in arid climates. In: our groundwater samples from wells tapping the NSS aquifer Faybishenko, B., Witherspoon, P.A., Benson, S.M. (Eds.), Dynamics of Fluids in underlying recharge areas could be accounted for as mixtures of Fractured Rock. American Geophysical Union Monograph Series, Washington DC, pp. 115–128. two endmembers: fossil groundwater with isotopic compositions Gheith, H., Sultan, M., 2001, Assessment of the Renewable Groundwater similar to that of the WD NSS aquifer, and modern meteoric precip- Resources of Wadi El-Arish, Sinai, Egypt: Modeling, Remote Sensing and itation, with the latter endmember being the dominant compo- GIS Applications. In: Owe M. (Ed.), Remote Sensing and Hydrology 2000. pp. 451–454. nent. This interpretation is supported by the observed increase in Gheith, H., Sultan, M., 2002. Construction of a hydrologic model for estimating wadi modern precipitation from west to east that could explain the pro- runoff and groundwater recharge in the Eastern Desert, Egypt. Journal of gressive west to east enrichment in the isotopic composition of the Hydrology 263 (1–4), 36–55. Hesse, K.H., Hissese, A., Kheir, O., Schnacker, E., Schneider, M., Thorweihe, U., 1987. NSS aquifer groundwater. Sinai receives the highest amount of pre- Hydrogeological investigations in the Nubian Aquifer system, Eastern Sahara. cipitation and its groundwater samples are the most enriched; the In: Kilitzsch, E., Schranck, E. (Eds.), Research in Egypt and Sudan: Berlin. Dietrich WD receives the least amount of precipitation and its samples are Reimer, Berlin, pp. 397–464. the most depleted, while the ED receives intermediate amounts of IAEA and WISER, 2008, Water Isotope System for data analysis, visualization, and Electronic Retrieval: The WISER Version 0.7. precipitation and the isotopic compositions of its samples are also JICA, 1999, South Sinai Groundwater Resources Study in the Arab Republic of Egypt intermediate. Report, In: Inc., P.C.I.A.S.C. (Ed.) Tokyo, Japan. Conservative estimates for the modern contributions to the NSS Klitzsch, E., List, F.K., Pohlmann, G., 1987a. Geological Map of Egypt, Asyut Sheet. Scale1:500,000. In: (Ed.), T.E.G.P. Corporation/Conoco, Cairo, Egypt. aquifer in southern Sinai were obtained using continuous rainfall- Klitzsch, E., List, F.K., Pohlmann, G., 1987b. Geological Map of Egypt, Beni Suef Sheet. runoff models for the watersheds that crosscut the NSS outcrops Scale 1:500,000. In: (Ed.), T.E.G.P. Corporation/Conoco, Cairo, Egypt. and act as potential recharge domains for the NSS aquifer. Adopt- Klitzsch, E., List, F.K., Pohlmann, G., 1987c. Geological Map of Egypt, Bernice Sheet. Scale 1:500,000. In: (Ed.), T.E.G.P. Corporation/Conoco, Cairo, Egypt. ing methodologies and calibration parameters from previous Klitzsch, E., List, F.K., Pohlmann, G., 1987d. Geological Map of Egypt, Gebel Hamata investigations (Milewski et al., 2009a), and using SWAT rainfall- Sheet. Scale 1:500,000. In: (Ed.), T.E.G.P. Corporation/Conoco, Cairo, Egypt. runoff simulations for the period 1998–2007, we estimated the Klitzsch, E., List, F.K., Pohlmann, G., 1987e. Geological Map of Egypt, Luxor Sheet. Scale 1:500,000. In: (Ed.), T.E.G.P. Corporation/Conoco, Cairo, Egypt. average annual modern recharge for the NSS aquifer at Legates, D.R., Wilmott, C.J., 1997. Legates Surface and Ship Observation of 6 3 13.0 10 m . Results highlight the importance of modern local Precipitation.Distributed Active Archive Center, Goddard Space Flight Center. recharge of the NSS aquifer and bear on its sustainable exploitation
Sanford, K.S., 1935. Sources of water in north-western Sudan. Geographical Journal Sultan, M., Arvidson, R.E., Duncan, I.J., Stern, R.J., El Kaliouby, B., 1988. Extension of 85, 412–431. the Najd shear system from Saudi Arabia to the central Eastern Desert of Egypt Sarnthein, M., Tetzlaff, G., Koopman, B., Wolter, K., Pflaumann, U., 1981. Glacial and based on integrated field and Landsat observations. Tectonics 7, 1291–1306. interglacial wind regimes over the eastern subtropical Atlantic and North-West Sultan, M., Sturchio, N., Hassan, F.A., Hamdan, M.A.R., Mahmood, A.M., ElAlfy, Z., Africa. Nature 293, 193–196. Stein, T., 1997. Precipitation source inferred from stable isotopic composition of SCS, 1972, Section 4: Hydrology, National Engineering Handbook. US Department of Pleistocene groundwater and carbonate deposits in the Western Desert of Agriculture, Soil Conservation Service, Engineering Division, Washington, DC, Egypt. Quaternary Research 48, 29–37. USA. Sultan, M., Yan, E., Sturchio, N., Wagdy, A., Abdel Gelil, K., Becker, R., Manocha, M., Stern, R.J., Kroner, A., 1993. Late Precambrian crustal evolution in NE Sudan: Milewski, A., 2007. Natural discharge: a key to sustainable utilization of fossil isotopic and geochronologic constraints. Journal of Geology 101, 555–574. groundwater. Journal of Hydrology 335, 25–36. Sturchio, N.C., Arehart, G.B., Sultan, M., Sano, Y., AboKamar, Y., Sayed, M., 1996. Sultan, S.A., Mekhemer, H.M., Santos, F.A.M., Abd Alla, M., 2009. Geophysical Composition and origin of thermal waters in the Gulf of Suez area, Egypt. measurements for subsurface mapping and Groundwater exploration at the Applied Geochemistry 11, 471–479. central part of the Sinai Peninsula, Egypt. The Arabian Journal for Science and Sturchio, N.C., Du, X., Purtschert, R., Lehmann, B.E., Sultan, M., Patterson, L.J., Lu, Z.T., Engineering 34 (1A), 103–119. Muller, P., Bigler, T., Bailey, K., O’Connor, T.P., Young, L., Lorenzo, R., Becker, R., El SWAT, 2007. Soil and Water Assessment Tool: ArcSWAT. Texas A&M University. Alfy, Z., El Kaliouby, B., Dawood, Y., Abdallah, A.M.A., 2004. One million year old Thorweihe, U., 1990, Nubian Aquifer System, In: Said, R. (Ed.), Geology of Egypt: groundwater in the Sahara revealed by krypton-81 and chlorine-36. Balkema, Rotterdam, Balkema. Geophysical Research Letters, 31. Tucker, C.J., Grant, D.M., Dykstra, J.D. 2004. NASA’s Global Orthorectified Landsat Sultan, M. et al., 2011. Red Sea rifting controls on aquifer distribution: Constraints Data Set, pp. 313–322. from geochemical, geophysical, and remote sensing data Geological Society of Yan, Z.W., Petit-Maire, N., 1994. The last 140 ka in the Afro-Asian climatic America Bulletin, B30146.1, doi:10.1130/B30146.1 transitional zone. Palaeogeog, Palaeoclimatol, Palaeoecology 110, 217–233.