2.LITERATURE REVIEW2.1 Previous stu

2.LITERATURE REVIEW2.1 Previous studiesMany hydrologic and hydrogeologic investigations have been done in Dakhliya Region. Those done in the Nizwa area are pertinent to the evaluation of the Tanuf RechargeDam.* The first study in Dakhliya was done by Sir Alexander Gibb and Partners (1976). Water levels in several private dug wells were measured over a two –year period. Monitoring of some of these wells was continued by MAF or other agencies giving a 20- year period of record at these sites. Flow at several aflaj was also monitored by Gibb.* In 1986, a well inventory was undertaken for the public Authority for Water Resources (PAWR) by Sir M. MacDonald (1986) in the Manah, Izz, Nizwa, and Al Ghafat areas. W. S Atkins (1986) completed a water resources evaluation of the Greater Manah Area (which includes Nizwa). Consumptive use in the Grater Manah Area in 1968 was estimated to be between 16 x 10and 18 x 10m³/ yr, 95% of which is consumed by agricultural demands. Atkins (1986) concluded that further groundwater development was only possible in Wadi Yahlah, south of Manah.* MEW (Ministry of Electric and Water, now Ministry of Housing, Electricity and Waters) has drilled at least 50 boreholes in the region and directed several water supply studies in the Nizwa area. Sir M. MacDonald (1980) evaluated the potential for additional groundwater supplies for Nizwa in an investigation program, which included drilling and testing in the limestones at the base of Jabal Akhdar. In general, they found that the limestone did not produce high yields. A well field was recommended for the alluvium, which was later, built at the north end of Nizwa. Mott MacDonald in association with Watson Hawksley (1992) predicted thatwater demand in Nizwa would rise from 1.35 x 10m ³/yr in 1992-93 to 2.98 x 10m³ /yr by 1995.* Hydroconsult identified the Tanuf area in 1984 as a potential site for a recharge dam. Additional feasibility and detailed design studies were done on behalf of MAF (Hydroconsult 1986, 1987b, 1988). Hydroconsult (1987) evaluated the recharge that occurred in two wadi flow events in May and July of 1987. They presented hydrographs of these two events for three monitoring wells and then estimated the additional recharge that would have been achieved had the dam been built. As noted, the dam was built in 1989.* W.S. Atkins (1989, 1992) report on a detailed investigation of a proposed recharge dam on Wadi Al Abyad. The reports provide geologic descriptions of the bedrock and alluvium and summarize the rainfall records and wadi flow records for the area. Average rainfall and flood flows for the catchments were determined to be 20 mm/yr and 5.2-x10m³ (with a 10 year return period), respectively.* Data also include results of pump tests and infiltration tests in the alluvium. The aquifer shows rapid response to recharge events indicating low storage coefficient. Aquifer tests gave an average storage coefficient of 0.10 and transmissivity values ranging from 400 to 550 m²/d. Water budget analyses presented in the report consider agriculture in Nizwa (47% date palms, 17% alfalfa, 11% vegetables, and 4% limes) and notes that about 20% of the 550 ha is fallow due to lack of water.* Wells TF-3, TF-4, and TF-5 were drilled by the dams department in 1992. MWR drilled six boreholes (TN- series) in Wadi Tanuf (MWR, 1993) to monitor the effects of artificial recharge. General Agricultural Products Company (GAPCO) (1993) presents lithologic logs, geophysical logs and aquifer test data for the six wells (TN1 through TN6). Aquifer tests weredone to determine hydraulic conductivity. Other new and replacement wells were drilled by MWR-Nizwa during 1992 and 1993 to upgrade the regional groundwater-monitoring network. Nine wells (NTF-series) were drilled in 1992 up gradient and down gradient of Nizwa town. These wells showed that the aquifer thinned considerably downstream of Nizwa.* Also, a draft data compilation and review by NRAO (1995), which presents recent data for the Dakhliya Region, and a draft by report by Ali (1992) dealing specifically with the performance of the dam.* The most detailed study to date is done by Cansult Limited in association with Gartner Lee International Inc, Curry Consulting Services. They evaluated existing recharge Dams including Tanuf Dam.2.2 Previous Modeling studiesThere has been no detailed hydrogeologic modeling studies conducted for the study area except what was done by Cansult Limited. NRAO (1995) presented a detailed water budget analyses for wadi Tanuf and wadi Abyad. Atkins (1992) also presented a detailed water budget analysis for wadi Abyad . Ali (1992) and Hydroconsult (1987) provided information on precipitation and runoff in wadi Tanuf and discussed a variety of simple methods used to estimate recharge rates with and without the dam.