Summary of previous studies carried out within the study area

4.5.1 Hydrologic studies

During the 1970's and in the course of various water resources studies, more than 13 rainfall stations were installed (MWR, 1997g). A further 6 rainfall stations were installed in the period 1982-84. Further 39 rainfall stations were installed in 1993-94 (MWR, 1997g). Figure 4.4 shows isohyets of the average annual rainfall for the 23-year period 1975-1997 and key gauging stations at Wadi al Batha Catchment. The hydrological analysis of the Wadi al Batha Basin was carried out by the Surface Water Department of the Ministry of Water Resources (MWR) in 1997 (MWR, 1997g). The main results are summarised in the following sub-sections.

4.5.1.1 Meteorological data

Sur Meteorological Station in the Ash Sharqiyah Region, which was installed in 1974 at the coast, is likely to be more representative of conditions in the study area. There, the monthly mean temperature ranges from 22°C in January to 34°C in June with the average annual temperature is 28.4°C. The range of mean monthly maximum daily temperatures is 26.2°C in January to 40.3°C in June (MWR, 1997a). These temperatures follow much the same pattern as other locations in northern Oman.

The monthly mean of average daily humidity range of 50% to 70%, the least humid months being April to July, and the annual average sunshine is 9.6 hours (MWR, 1997a).

The monthly mean wind speeds range from 2.1 m/s in November to 4.7 m/s in July with dominance northerly winds during winter (November to April) and southerly winds in summer (May to October), (MWR, 1997a).

The Sur annual potential evapotranspiration rate is 3.3m, which is higher rate compared to the other existing meteorological stations in Oman (MWR, 1997a). That is because of the higher wind speeds recorded at the coast. Therefore, the overall potential evapotranspiration rate for the study area is likely to be closer to the annual rate of 2.9 m for Seeb station, which is not effected by higher wind speeds as of Sur (MWR, 1997a).

Average annual rainfall in the 33-year period, 1975 to 2007 for Ash Sharqiyah varies from 80 mm to 190 mm. Isohyets constructed in Figure 4.4 show that annual rainfall in the northern part of the study area can be expected to exceed 125 mm and in much of the Ash Sharqiyah Sands is likely to be less than 75 mm (MWR, 1997g). The three wettest months are February to April which account for more than 60% of the total annual rainfall and less relatively wet period is July and August (MWR, 1997g).

4.5.1.2 Wadi flows

There are 13 usable Wadi gauging stations within Wadi al Batha. Eight of these gauges are located in the middle catchment within or close to the main study area. All of these gauging stations are transducer type within ± 5% accuracy. They used to be additional several peak discharge gauges to report Wadi peak flow at each particular Wadi flow (MWR, 1997g). The average annual recorded inflows amount to approximately 18.3x10⁶m³/year. The average annual flow from Wadi Bani Khalid accounts for the largest flows amounting to some 11.3x10⁶m³/year, representing more than 61% of the

total measured flows of Wadi al Batha (MWR, 1997g). The distribution of Wadi flow recharge input will be explained in Chapter 5.

4.5.1.3 Aflaj flows

Aflaj data, together with sample hydrographs have been collected in the study area of Wadi al Batha basin since 1982 (MWR, 1997g). Of the 74 Aflaj in Wadi al Batha basin, for which records exist, 31 fall within the main study area and on the edge of the Ash Sharqiyah sands. Average annual Flaj flow of the 31 Aflaj between 1982 and 1997 was approximately 33.4x10⁶m³/year. This decreased between 1998 and 2007 to 24.9x10⁶m³/year as presented in Table 4.5. The declining flows in some Aflaj are not only the results of drought and lack of maintains but the most likely explanation is that groundwater levels in these areas have been adversely affected by increased groundwater abstractions.

4.5.2 Remote sensing studies

The technology of remote sensing has been applied to assist a number of project studies within the study area. Three basic research activities were undertaken each focused on a major component of the regional water balance (MWR, 1997h);

 Regional vegetation analysis including differentiation of Aflaj- and non-Aflaj (wells) -fed agriculture.

 Evaluation of the extent and density of natural woodlands (prosopis cineraria) in the

study area. The results indicated that the prosopis forest is a significant consumer of water and covers about 13,000 hectares (approximately 85 km long and 20 km wide) and the total number of prosopis trees is about 555,000 trees.

 Estimation of the area covered by Sabka (salty water) in the lower catchment, south of

Jaalan Buni Bu Ali. It indicated 7.4 km² of "active" Sabka in the study area.

Difficulties in estimating the total area of Sabka were encountered because of the nature of the "inactive" Sabka, which are often covered by sand/gravel making them difficult to distinguish from their surroundings. Outflow to Sabka is estimated 8x10⁶m³/year.

4.5.3 Water use studies

4.5.3.1 Agriculture irrigated by Aflaj

The Remote Sensing Section in the Ministry of Water Resources (MWR) calculated the type of agriculture and agricultural areas irrigated by Aflaj in the study area during 1995 and 1996. The net water demands were calculated from the evapotranspiration requirements of different types of crops with allowances made for leaching and irrigation efficiency (MWR, 1997h). The results of these calculations showed that 28x10⁶m³/year was the net irrigation water demands in the area served by Aflaj. This estimate can be compared with that derived from average annual Aflaj flow in the area which is estimated at 33.4x10⁶m³/year between 1982 and 1997 and had decreased between 1998 and 2007 to 24.9x10⁶m³/year, as discussed above in Section 4.5.1.3. For modelling purposes, an average of 24x10⁶m³/year will be assumed in the current study because not all of the Aflaj flow is used for irrigation.

4.5.3.2 Agriculture irrigated by wells

The National Well Inventory undertook an inventory of all wells in the Sultanate, including the main study area. The information collected during 1995 for this inventory

included data on each well‟s location, physical dimensions, water-level, discharge, chemical quality and details of water use. The total net water demand for well-watered agriculture in the main study area is estimated at approximately 23.5x10⁶m³/year by using the Penman-Monteith Equation (MWR, 1997a). The main agriculture crops are Date Palms, limes, bananas, mangoes, alfalfa and grasses.

4.5.3.3 Water used by prosopis forests

The prosopis forests in the study area act as phreatophytic consumers of groundwater and are hydro-logically very significant when considering water balances. The prosopis receives groundwater flow from the Ash Sharqiyah Sands, from a west northwest direction. The annual net water demands for the prosopis were calculated from the evapotranspiration by the Remote Sensing Section in MWR. The total annual water consumption for 530,351 trees of prosopis in an area of 12,213.3 hectares north of Jaalan Bani Bu Ali was calculated to be approximately 47x10⁶m³/year and approximately 2x10⁶m³/year for the 24,614 trees of prosopis in an area of 673.6 hectares south of Jaalan Bani Bu Ali (MWR, 1997a).

4.5.3.4 Domestic, industrial, commercial and other municipal water demand

The National Well Inventory calculated the domestic, industrial, commercial, livestock and other municipal annual water demands. Household water demand was estimated by assuming as conservative per capita demand of 80 l/day. This per capital usage seems to be low because the water distribution network did not exist in 1995, hence the water supply was provided by tankers. However, it is more realistic to use 97 litre/capita/day in the management model than what was estimated in 1995 by the National Well Inventory because it is estimated base on several previous studies done in Oman (Parsons

International & Co LLC (2005). Industrial, commercial and other municipal demands were calculated by estimating the annual discharge from wells used for these sectors. The total water demand for the mentioned sectors was estimated to be in order of 6.7x10⁶m³/year (MWR, 1997a).