for water conservation in the Sultanate of Oman. A land and ... the Arab world also Egypt relies on irrigation for crop yield, whereas Saudi Arabia has got a 39 ...
Water Conservation in Oman1 Hayder A.
Abdel-rahman2,
By and Isam Mohammed Abdel-magid3
Abstract Limited resources and growing needs for water has triggered a nationwide campaign for water conservation in the Sultanate of Oman. A land and soil survey study of Oman shows the availability of more arable land than present water resources could support. Groundwater is the main source for agricultural production. Over pumping at rates higher than the natural recharge has resulted in lowering of the ground water table, while seawater intrusion lead to an increase in soil salinity. A comprehensive water program is underway to (1) conserve water through efficient irrigation, use of soil additives, modern irrigation systems, agronomic management and institutionalization; and (2) augmentation of resources via introduction of more desalinization plants, more waste water treatment, use of brackish water, water fog collection, and water harvesting by building recharge dams.
Introduction Water, being a valuable natural resource, has been the focus of attention for many years. Nowadays, water is being considered as strategic commodity worldwide. With rising population sizes, introduction of more industrial sectors, and the increased share of agriculture in the Gross National Product water resources are being depleted at rates faster than their natural replenishment through the hydrologic cycle. About 97.5 % of the 1200 million Km3 world water reserves are in seas and oceans. Only about 2.5 % exists as fresh waters, 30 % of which is in the liquid form. Ninety-five percent of the fresh water is underground, while only 5 % forms the rivers and lakes. This renders five in a thousand part as easily and readily available to human beings. Worldwide, 70 % of the fresh waters are used for agriculture, 25 % for industry and 5 % for domestic use. In the case of Oman around 85 % of the fresh water is being utilized for agricultural purposes, 10 % for domestic consumption, and 5 % for industrial use (Figure 1) {1}.
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First published in Water International Journal,18 (1993) pp 95-102 Assistant Professor, Department of Soils & Water, College of Agriculture, Sultan Qaboos University 3 Assistant Professor, Department of Civil Engineering, College of Engineeringm Sultan Qaboos University 2
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With the drought cycles, increasing desertification, limiting water resources, and the growing needs and demands, water conservation seems to be the only feasible way out. The International Conference on Water and the Environment held in Dublin2 focused on the issue and considered the situation to have reached dangerous limits. Recommendations were made to take prompt actions. Collaboration was called for among all countries in taking measures for water conservation through re-use, better management and adoption of modern technologies in irrigation. The Sultanate of Oman is totally dependent on irrigation for crop production. Within the Arab world also Egypt relies on irrigation for crop yield, whereas Saudi Arabia has got a 39 % dependency, Sudan 13 % and Algiers only reaches 5 %. Worldwide the overall dependency of the Arab countries achieves 21 %, Asia attains 33 % and while Africa barely reaches 2.7 % reliance.
Inventory of Resources
Oman’s Land Resources Oman is dividsible into four main physiographic regions: the mountainous regions, coastal plains, the accumulation plains and the desert (Figure 2). The mountainous regions include the Hajar arid mountains of the north and monsoon-affected mountains and plateaus of the Southern Dhofar region (Jabal Al-Qara mountains). The accumulation plains include the Northern Batinah plain, Salalah plain and the Northern interior plains. The coastal alluvial plains are mainly the Batinah and Salalah plains, where the wadis originating in the nearby mountains deposit their load of sand and finer particles before reaching the sea. The desert sand dunes occur in the western part of the country in Al-Rub Al-Khali and the Wahiba sands.
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FAO classifies only about 791,651 hectares of Omani land (2.52 %) as highly to moderately suitable for agriculture {3}. Nevertheless, another 1,431,406 hectares (4.55 %) are categorized as being marginally suitable and could be put under production with increased inputs. The soils of Oman are young calcareous soils. Their low organic matter characterizes them and total nitrogen with an unbalanced sodium-calcium-magnesium contents, prominent potassium deficiency and localized zinc, ion and phosphorus deficiencies. The Batinah area accounts for about 50 % of the cultivated area (20,750 ha). On the other hand Salalah plain accounts for about 6 % (2417 ha). Table (1) gives the distribution of the Omani area by land utilization and region. Water Resources and Use: Rainfalls pattern and occurrence are diverse within the country. Regular rainy seasons in the country are only found in the Dhofar Mountains in the south and Hajar Mountains in the north. The Interior regions (which constitute around two-thirds of the country) receive less than 50 mm of the average rainfall. The rainfall in the costal areas reaches about 100 mm. The Hajar Mountains receive 100 - 300 mm and the monsoon affected Dhofar region receives about 200 - 300 mm annually.
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Table 1 Land area distribution by Utilization and Region (areas in ha.) {4} Region Unused but Usable Total Under Crop if Improved Batinah and Capital 46126 20750.18 24861.32 Massandam 1120.46 1030.04 90.42 Jahar &Al Gharbi 2623.72 1954.48 608.80 Hajar & Al Sharqi 1955.58 1235.30 568.92 Jow &Buraimi 1312.52 885.50 427.02 Al Zahira 7202.36 3303.08 3899.28 Oman Interior 14494.92 5166.70 7087.30 Sharqiya & Gaalan 5817.68 4284.94 1514.04 Dhofar 2706.66 2413.62 293.04 TOTAL 83359.98 41023.84 39410.14 The Batinah catch basin (12,183 km2) receives about 2089 million cubic meters of water. With an estimate of 83.33 % (five sixths of catchment runoff) for the evaporation at the area and a 16.67 % conversion to runoff, the total amount of surface and subsurface water is about 348.3 million m3 (=2089 x [100-83.33]/100). Some 75.5 million m3 are withdrawn up plain and the amount of surface and subsurface water that reaches the coastal plain is 272.8 million m3 (=348.3-75.5). With 48.3 million m3 flowing to the sea, the estimated groundwater recharge (1979) is about 224.5 million m3 (=272.8-48.3). The discharge that is actually required to irrigate the area (1986) is 226.3 million m3which depletes the groundwater reservoir at the rate of about 1.8 million m3 per year (226.3-224.5). Projected estimates, at the current 22 % rate of increase in water demand, give a 45 million-m3 deficit annually. (See table 2, and Figure 3). The catch in the Salalah region by the monsoon-affected basin (910 km2) is about 282 million m3 annually. With an evaporation of 90 % and a 10 % conversion, about 28 million m3 is precipitated as surface and subsurface water. Nine million m3 of which is in the form of surface springs and 19 million m3 goes as subsurface water. About 6 % of the rainfall is converted into surface runoff (17 million m3), 60 % of which runs into the sea and the rest (seven million m3) infiltrates into the ground bringing the total groundwater recharge to 26 million m3 per year. The water use in 1982 was estimated as 22 million m3, 17 million m3 of which is for agriculture, but the 1990 estimates put the requirement at 32 million m3 and with only about 20 million m3 of the recharge being available, 6 million m3 left as a safeguard against sea water intrusion, a deficit of 12 million m3 occurs, 9 million m3 of which is supplied by the springs, and the underground water reservoir is depleted at the rate of 3 million m3 per year.5 The water balance for the rest of the country is still on the positive side but with the current rate of development, problems could also be encountered elsewhere. Seawater intrusions into groundwater aquifers have been noticed to be more profound in the Batinah area where increasing soils have been salinized. (See table 2 and Figure 4).
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Table 2 Water Balance at Batinah and Salalah Basins (Units in million m3) Deficit - 1.8 Runoff component Batinah Evaporation 1740.7 Up plain use 75.5 Runoff to sea 48.3 Groundwater 224.5 Total basin runoff 2089 Irrigation requirements 226.3 Groundwater yield 224.5
- 12.8 Salalah -253.8 9 19.2 282 32 19.2
Crops and Climate Table (3) gives the total Omani area as being divided under different crops together with their average annual yields. Out of the 54901 hectares (only about 6.9 % of the suitable agricultural area) irrigated in the Sultanate, 5370 ha are under vegetable cultivation, 9747 ha under field crops and 33,133 ha under fruit trees. Tomatoes and watermelon account for about 46 % of the area under vegetable production, whereas 91% of the areas under field crops produce Alfa alfa. Date palms account for about 75% of the area under fruits, with a percentage of 45.5 % of the total area. In any water conservation plan it is very important to know the varieties and areas of crops grown. The water use of crops should be estimated through extensive research work under the prevailing climatic conditions. Hot and humid summer conditions prevail over the coastal areas of the Sultanate, with a comparatively cool winter. In the Interior the climate is hot and dry in the summer and somewhat cool in the winter. The average temperature in the Sultanate is around 17.8 28.9oC, the hottest months being June and July ranging between 30.7oC in Saiq and 46.1oC in Fahoud. The coldest month is January being 9.4oC in Saiq and 24.0oC in Fahoud. The lowest ever temperature recorded was - 3.6oC in Saiq.
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Table 3 Crop Productions by Areas and Yields – 1988 {4} Area (ha) Yield (Tons/ha) Crop Vegetables Tomato Pepper Onion Garlic Okra Water Melon Musk Melon Cabbage Potato Sub-Total
1212 610 560 150 53 1250 625 770 140 5370
22.19 9.02 13.75 8.00 13.21 19.04 13.12 23.25 25.00
Field Crops Alfa alfa Wheat Tobacco Sub-Total
8870 468 409 9747
38.00 1.50 4.89
Fruits Dates Lime Mango Banana Coconut Sub-Total Others TOTAL
25000 2400 3780 1625 328 33133 6651 54901
4.00 10.83 2.01 13.60 16.77
The 1990 estimates put the crop water requirements in the Batinah at 531 million m3 and 33 million m3 in the Salalah plain. The rest of the country requires 561 million m3 (table 4).6 With these values groundwater reservoirs will be depleted at rates higher than estimated, especially in the Batinah plains. As a result in the Batinah, soil salinity due to seawater intrusion is becoming a serious problem and a lot of date palm plantation can be seen withering away along this coastal plain. Table 4 Crop water requirements [million cm/year] {6} Region Fruit Fodder Total Vegetables Batinah 53.77 408.10 69.29 531.16 Oman Interior 15.55 72.68 42.46 130.69 Dhahira & Buraimi 11.18 59.60 26.63 97.41 Sharqiya & Gaalan 13.98 96.97 42.35 153.30 Masandam 1.89 14.62 6.46 22.97 Dhofar Total
4.10 100.47
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13.10 65.07
15.32 202.51
32.52 968.05
Water Conservation Measures Water conservation measures include using water when needed where needed with possible augmentation. Irrigation efficiencies are a measure of how effectively water is stored in the root zone for crop use. On farm irrigation efficiencies include application and storage efficiencies. Application efficiency is the percent of water stored in the root zone from that delivered to the field, whereas storage efficiency is the percent of water stored to that needed. In effect, the more water stored, by eliminating field losses of runoff and deep percolation, the higher are the efficiencies. This clearly outlines the significance of crop water use and consumptive use efficiencies. These efficiencies reflect measures of how beneficially water was used by the crop in terms of yield per unit amount of water delivered to the farm. Soil additives and water application methods greatly influence the ability of soils to store moisture. Soil additives: Omani soils are characterized by their low organic matter content and low-to-moderate moisture retention differences. Different forms of natural and processed organic matter in the forms of peat moss, cow dung, chicken manure, and hay straw are plowed into the soils to increase the fertility level and water movement and retention. Unfortunately, the biomass production in the country is not at the levels, which could effectively improve its soils. Field crop production, mainly Alfa alfa account for only about 16% of the area cultivated and is primarily utilized for animal production. In 1989 Oman had imported 17945 Tons of fertilizers 78 % of which (13744 Tons) were in the forms of
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organic manures.7 Even though organic matter could hold more moisture, yet it releases it quickly. This is one of the reasons that has triggered research for developing synthetic materials which would easily absorb moisture and slowly release it. These products are on commercial use now, and have proved to be effective. A seminar {8} organized by the private sector on "Water Conservation: A National Priority" held in Muscat on the 29th of February 1992, was meant to evaluate and introduce an absorbent- copolymer-water-management-medium which would increase the water holding capacity of the soil. Problems encountered in introduction and use of such additives has yet to be solved. Cost, technology and know-how needed to incorporate the material into the soil, farmer education and extension are but few problems. Agronomic management: Biomass production tends to be proportional to transpiration. However, there are significant opportunities for increasing production per unit of water (consumptive use efficiency), by crop selection, breeding and agronomic management. Drought and salt tolerant crop breeding is of great importance in this respect. Agronomic practices that can conserve water generally parallel those practices that give the maximum yield in the shortest time. Few efforts are being made to breed specifically for water use efficiency, but in the Sultanate research is being made to study the effect of quantity and frequency of irrigation on growth and yield of different crops to establish the best consumptive use efficiency. This should be the main concern since the Sultanate farmers are traditionally date and citrus growers, which account for almost 70 % of the total crop water requirements. The trees have already been established a condition which does not grant effective agronomic water management. Relatively salt sensitive citrus trees could be replaced with date palms, which are more tolerant. On the other hand the less water consuming fodder such as grasses could replace Alfalfa fodder. Modern Irrigation Systems: Traditionally, surface or gravity irrigation systems have been used in Oman. Water is pumped out of boreholes or led into the farm through the Aflaj (singular Falaj) systems. The Falaj is a sub-horizontal tunnel dug in the ground to tap an aquifer. Underground tunnels whose rate of descent is less than that of the ground surface, transport water collected from the aquifer. They eventually bring water to the surface continuously throughout the year. There are about 6000 active aflaj in the Sultanate providing 71 % of Oman's water supply and irrigate 55 % of the cropped land {9}. A sizeable amount of water is being lost in conveyance especially in places where the falaj spreads with no distinct channel. In surface irrigation systems only about 30 % of the water applied is stored in the root zone. The rest of the water is being lost to runoff and deep percolation beyond the root zone. This produces a condition that counts for the low efficiencies obtained. Generally, modern irrigation systems are adaptable to a wide range of crops and soils. They save water, but the initial cost incurred is very high especially when using an extensive pipe network or an advanced system such as center pivots. In adopting modern irrigation systems, a careful balance must be made between the crop water requirements and water needed to control salinity. Meeting only the evapotranspiration requirements would lead to salt build-up in the root zone. In this case, the crop water requirements should be met; a term which includes amounts, used for salt leaching, and that is needed to build plant tissues. Consumptive use is a term used to mean evapotranspiration and that amount stored within the plant system. Vast areas in the Sultanate, especially in the Batinah and Salalah are now being put under modern irrigation systems. The government is encouraging farmers to adopt these
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methods. The government bears 75 % of the overhead cost for areas less than 10 feddans (4.2 hectares), 50 % for areas greater than 10 but less than 50 feddans (21 ha) and 25 % for areas more than that. Nevertheless, modern irrigation farms still comprise less than 10 % of the cultivated area in the Sultanate. All new allocations of land for agriculture by the government are required to use modern irrigation systems. Extension services and all information media are employed to convince farmers to switch from their systems. Adoption of modern irrigation systems poses as the most significant method in water conservation practices and the savings could go up to 50 % over the traditional surface irrigation methods. Land fractionation and small farm holdings together with the high initial cost and farmer compliance are the challenges to be faced. In the Sultanate about 29 center pivot systems exist serving around 1300 ha. Augmentation: Possible techniques for increasing water supplies range from augmenting precipitation to transporting icebergs halfway around the world. Practical methods adopted in the Sultanate include desalinization, water harvesting (recharge dams), wastewater treatment and use, and trials of fog collection and use of brackish water. Desalinization: In the Sultanate, there are two desalinization plants, in the Capital area, using evaporators, the larger being in Ghobra. The 1989 account of the water production and consumption in the Capital area showed that desalinization plants supplied about 77 % of the water produced for domestic use with a yearly output of about 7026 million gallons. Total annual consumption was estimated as 9090 million gallons {7}. Problems associated with evaporators include formation of scales that limits the top temperature that can be used in distillation process. Other problems include: accelerated corrosion and sealing and high initial and operating costs. Plans are under their way to incorporate reverse osmosis techniques. In recent years the annual output of the desalinization plants were increased to about 8400 million gallons and a new plant with a capacity of 6 million gallons per day is being constructed at a cost of 57 million Omani Rials (US $ 147 million). Desalinized water is meant for domestic use but would save the water, which would otherwise be pumped out of the wells. Wastewater treatment: The Ministry of Health conducted a national seminar in collaboration with the WHO on wastewater reuse during 26-29 April 1992. The seminar discussed the state of water resources in Oman and reviewed the national, regional and world experience in effluent reuse. The economic aspects of wastewater reuse were discussed together with the health and environmental aspects. Recommendations were made to wastewater reuse for non-potable purposes and to be incorporated in a comprehensive water management program. The 1990 estimates of the Capital area [Muscat] inhabitants reached the value of 333,354 persons. With an average daily consumption of about 150 liters and assuming 70 % wastewater recovery, the total quantity of wastewater produced would be 35,000 cubic meters. This is enough to meet the daily requirements of only 437.5 hectares of a cropland using 8 mm per day. There are now a number of sewage treatment plants in operation in the Capital area. One in Darsait produces about 11,500 m3/day with input from the Greater Muttrah area. Another at Al-Ansab produces 5400 m3/day to be expanded in the future. This effluent is used for irrigating tree plantations in the Capital area from Darsait to Assahwah tower. A third treatment plant is at the University of Sultan Qaboos producing around 3000 m3/day and is used to irrigate the University tree
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plantation. Five other small treatment works exist in Maabaila, Al Khod, Murtafaa, Amrat and Diwan in Al Seeb. Table (5) gives an account of the existing sewage treatment works, their location, design capacity, actual flow rate of the effluent, and some of the averaged quality parameters, and the amount of wastewater utilized for irrigation purposes. Reuse is restricted to the irrigation of ornamental plants in the Capital area. The stringent regulations introduced for wastewater discharge and reuse are currently under revision in view of the existing experience. These regulations are established according to the Ministerial Decision number 5/86 addressing wastewater reuse and discharge. The reuse of wastewater was limited to irrigation of ornamental trees and shrubs, groundwater recharge in areas of no public exposure, and industrial closed circuit processes. Emphasis has been placed in the regulations towards physical quality parameters of total solids, suspended solids and turbidity. The bulk of the regulations addressed chemical parameters. The bacteriological quality was managed through the total coliforms and the viable pathogenic ova and cysts.10
Table 5 Sewage Treatment Plants (STP) at the Sultanate of Oman Description
Darsait
Design capacity
10800
Plant flow rate, m3/d 11500
BOD (mg/L)
SS
Ammonia (N)
Irrigation water,m3/d
10
10
1
800011500 2000-5000 800
AlAnsab 12000 5400 10 10 1 Shati 1350 800 10 10 1 AlQrum Mabella 1920 700 10 10 1 AlKoud 1200 700 20 30 Bowshar 400 400 10 10 1 AlAmerat 600 600 20 30 Jibroo 70 100 10 10 1 50 AlAynt 60 100 10 10 1 Total 28400 20300 17350 Saline waters: New knowledge in the plant and soil sciences and new irrigation techniques show that, with careful management, saline or brackish waters can be used to grow a variety of salt tolerant crops. With adequate leaching and drainage, water with concentrations of up to 6000 grams per cubic meter (0.6 %) will produce high yields from tolerant crops. Seawater contains up to 40,000 grams per cubic meter (4 %) whereas good quality irrigation waters contain up to 0.02 %. Successful trials have been made to produce salt tolerant crops in coastal sands with chemically treated waters containing up to 2 % salt. Extensive agriculture and over pumping has lead to seawater intrusions in the costal plains of the Batinah were more than 50 % of agriculture is practiced in the Sultanate. An inventory of the existing wells is being made and no new permits are issued in an effort to prevent or even reverse the water table decline. In the Sultanate research is underway to remove salinity stress from date plantations grown with brackish waters in the coastal areas of the Batinah by chemical treatments and modern trends of leaching. Atriplex, a grazeable saltbush, is being introduced as a
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first step towards establishing pasturelands for cattle through biosaline agricultural research programs. Water harvesting: Although rain falls infrequently in the Sultanate, it still comprises significant amounts of water; 10 mm of rain equals 100 cubic meters of water per hectare. Water harvesting captures and concentrates rainfall to irrigate crops, supply water for people and animals, or recharge groundwater. A water-spreading system controls water from ephemeral flows (infrequent or intermittent flow following heavy rains), a system of dams, dikes and ditches in the flood plain or wadi, then diverts and spreads the flood water. In the Sultanate, a total number of 58 recharge dams are projected with a total capacity of about 80 million m3. The total amount of rain lost to the sea and desert amounts to about 120 million m3 per year {11}. Table (6) gives the sites and specifications of the recharge dams, which has already been constructed. Other than those, there is a 1.63 Km long sea defense dam constructed at Khor Al Rusaq in Sur to prevent the intrusion of surface saline sea water and withhold part of the Wadi waters for recharge and leaching. Al- Khod recharge dam has the biggest storage capacity (11.55 million m3), followed by Wadi Al Maawil (10.00 million m3) which. Out of the 9062 meter length of the Wadi Hilti/Salahi dam 3250 meters is a diversion channel connecting the two dams to transfer water from W. Hilti dam (3040 m) to W. Salahi (2772 m) dam. A monitoring system is annexed to Wadi [valley] Al Khod dam for measuring the surface waters flowing in and to check the efficiency and maintenance works needed. Recharge dams are meant to connect part of the 120 Million cubic meters on rainwater lost yearly to the sea and desert. Lack of monitoring systems in most of the recharged dams made their assessment and evaluation rather difficult. Visual surveys, however, have indicated that on the average the dams have caught a sizable amount of runoff. With Wadi Tanoof occasionally filling up one disadvantage is that the dams have deprived the costal plains from the fertile silt and fine materials the streams used to carry down the valley. Fog collection: Weather modification was first sought of in 1946 and much has been learned since then. For example, cold fogs are routinely dissipated at a number of airports. Today seeding orographic clouds is an established practice. Fog consists of water droplets so small that their fall velocities are negligible. Fog particles, which contact vegetation may adhere, coalesce with other droplets and eventually form a drop large enough to fall to the ground. Condensation of the water vapor present in the air results in deposits of dew. The dew offers a source of water, which may be exploited locally. Rich, water-bearing fog and mist takes place in only few places of the world. In addition to parts of the coasts of certain Latin American countries, the same thing happens in Dhofar mountains of the Southern region of the Sultanate. Trials were to be made though the UNDP-World Bank water and sanitation program to collect fog using wire mesh. The solar chilled mesh sought would greatly enhance the process and increase yields. In studies conducted during the monsoon period at 865 meters a.s.l. the amount of water collected was 2.86 L/m2/hr at 4.2 meter height with a daily total of about 34.5 L/m2 of mesh13. Nevertheless, no matter how efficient the process is, fog collection would only constitute an insignificant amount to a localized area in the Sultanate for part of year and probably only to benefit grazing cattle by supplying pools of drinking water.
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Institutionalization The Ministry of Water Resources in the Sultanate has set a number of guides and rules to conserve water. Among those are: 1. Priority to water use is to humans, animals, agriculture and then industry. 2. A complete inventory of the wells, regardless of use, and contractors would be carried out all over the Sultanate. 3. No new wells would be dug except in areas where there is a good quality soil and excess water. 4. No new wells will be dug except licensed (after justification) and with the specifications set by the Ministry. 5. Wells should be deepened only for human use, animal use and irrigation of trees. 6. A phased water administration would be set to: • Install water meters on all wells • Collaborate with the Ministry of Agriculture to determine crops suited to different areas, crop value and water use. 7. All government-distributed lands should be irrigated from central wells through pipe networks. Modern irrigation systems should be installed in all those lands. 8. Construction of new recharge dams should continue following feasibility studies. 9. No wells should be dug in the vicinity (3.5 Km) of existing aflaj mother wells except for drinking water or to benefit existing wells. 10. There should be no exceptions to the rules set.
Conclusions 1. An integrated program is needed to conserve water in the country. This should start right from efficient water conveyance and through to the on-farm sound management schemes. 2. Government efforts should be coupled with an effective extension program of farmer education for collaboration and optimization of resources. 3. Attention should also be given to conserve water at home, in the growing industry, and other uses. 4. Available water resources are recommended to be used for the best soils. 5. Efforts for water harvesting need to be presented. Likewise, inventory making should continue together with investigations for new allocations using aerial and satellite images. 6. In adopting the modern irrigation systems, the know-how techniques should be locally available by training qualified personnel for operation and maintenance. Need not pointing the importance of surveillance, monitoring and better management measures. 7. Drought and salt-tolerant crop research should be shouldered and done. This would breed the most suitable crops with economic values, and that may turn the desert green.
References 1. Al Hayat Daily Newspaper, "Science and Technology", 15 February 1992 Issue #10600, 1992. 2. International Conference on "Water and the Environment", held in Dublin During 12
the Period 26-31 January 1992. 3. Ministry of Agriculture and Fisheries and Food and Agriculture Organization of the United Nations, " General Soil Map of the Sultanate of Oman ", 1990. 4. Ministry of Agriculture and Fisheries, Department of Agricultural Statistics, "Estimate of Cropped Area in the Sultanate", 1989. 5. Ministry of Agriculture and Fisheries, Directorate General of Water Resources and Irrigation, "Water Resources of the Sultanate of Oman", 1986. 6. Ministry of Water Resources, Sultanate of Oman,"National Water Resources, Master Plan 1990". 7. Development Council, Directorate General of the National Census, Sultanate of Oman,"National Census - Year Book, 1990". 8. Abdel-Rahman, H.A. "Water Conservation",( A Speech Delivered at the Seminar on "Water Conservation In Oman", Sponsored by the Al-Rawahy Co., held on Saturday 29 February 1992 at the Conference Hall, Oman Chamber of Commerce & Industry, CBD Area, Ruwi, Sultanate of Oman). 9. Al-Abri, B. S. H."An Explanation of Some of the Omani Afalj" Almatabi Aldhahabia, Ruwi, 1991. in Arabic "Albaian fi ba`ad Aflaj Oman". 10. Ministry of Environment and Water Resources (now Ministry of Environment and Regional Municipalities), Ministerial Decision 5/86 dated 17th May 1986, "Regulations for Wastewater Reuse and Discharge", Muscat, Sultanate of Oman. 11. Ministry of Agriculture and Fisheries, Directorate General of Water Resources and Irrigation, " Groundwater Recharge Schemes in the Sultanate of Oman ", 1986, 1991. 12. Schilfgaarde, J.V. and G.J. Hoffman. 1981. "Future Sources of Water", Proceedings of the ASAE Second National Irrigation Symposium, Lincoln, Nebraska, 20-23 October 1980. 13. Stanley Price, M.R., Al-Harthy, A.H., and Whitcombe, R.P., "Fog Moisture and its Ecological Effects in Oman", Ministry of Water Resources, Muscat, Oman, 1986.
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