Bulletin 19 - March 1983: Sand and Sand Dune Stabilization in the UAE


Sand and Sand Dune Stabilization in the UAE

by Mohamed I.R. Khan

Introduction

The overall climate of the Emirates may be described as subtropical, warm and arid. Air temperatures range between 35 and 50'C around midday from May to October and 20 and 35C during winter months. In the interior of the desert the highest temperatures on the ground during summer reach 70'C, but they may fall to freezing in winter. The average rainfall over the Emirates is less than 100 mm. per annum but this is very spasmodic and up to 50% of the annual total may fall in a single day. Some monsoonic showers are also received during summer months on the east coast and in the mountain belt which forms the watershed between the Arabian Gulf and the Gulf of Oman. Moisture also condenses in the form of fog and dew especially on coastal belts. Strong winds and sand storms are of common occurrence throughout the Emirates, being especially frequent and severe in summer months. Sand dunes are a dominant landscape feature.

Soils are generally coarse, sandy and undeveloped. They are deficient in organic matter, nitrogen, available phosphorus and trace elements such as zinc, iron and manganese. Non-calcareous soils may also be deficient in potassium. Soils in the 'subkha' coastal belt and low-lying depressions in the interior of the desert are highly saline.

Most of the country is extremely arid and sustained agriculture is not possible without artificial irrigation. Secondary salinization commonly occurs, however, as a result ot such irrigation and leaching. For agriculture to be successful, some protection against high velocity winds, sand invasion and extreme temperature is required. Dry and droughty years are not uncommon. Apart from the Empty Quarter itself, the UAE is perhaps the most difficult area in Arabia for practising sustained agriculture successfully.

Destruction and Degradation of Natural Vegetation

Both woody and non-woody species throughout the UAE have suffered a great deal from overexploitation and mismanagement. Much of the natural vegetation has been destroyed or considerably degraded in certain areas. The coastal mangrove belt has shrunk to a bare 3000 hectares and the inland wooded areas of 'Ghaf' (Prosopis spicigera) and 'Samar' (Acacia tortolis) have been greatly reduced; the surviving forest is badly depleted. Other rangeland areas including major plant types such as 'Haad' (Cornulaca spp.), 'Ghada' (Haloxylon persicum), 'Rims' (Hamada elegans), 'Arta' (Calligonum comosum) and 'Suaeda' (Suaeda spp.) have also been destroyed in large part.

The basic causes of extensive denudation, degradation and destruction of the natural vegetation in the UAE are intimately linked to the existence of a fragile ecological equilibrium and excessive pressure of population on the land resources. The mismanagement of these factors upsets the natural balance and leads to loss of surface soils through erosion. Under the harsh and variable climatic and environmental conditions prevailing in the country, it is a delicate matter to maintain equilibrium and not use rangelands beyond their carrying capacity.

Since the discovery and subsequent exploitation of oil since the mid-sixties, pressure on the Emirates' natural resources has increased dramatically. The human population in 1968 stood at about 180,000; now it is well over a million. Similarly, this same period has witnessed a vast increase in livestock numbers, as seen in the following table:

Animal 1972 1978 1979 1980
Goats 225,000 250,000 310,500 341,622
Sheep 85,000 95,000 120,000 132,237
Cattle 20,000 18,600 23,300 25,665
Camel 35,400 48,000 56,400 58,709
Total 365,400 411,600 510,200 558,233

In Abu Dhabi Emirate an annual subsidy of DH 50 for every head of sheep or goat and DH 200 for every head of camel raised by local inhabitants is paid by the Government. The increase in livestock further pressurises already depleted rangelands, and as a consequence wind erosion and sand dune movement have also increased.

Sand Dune Encroachment

This problem is most acute in the south western areas adjoining the Empty Quarter. The recent past has witnessed accelerated land degradation as roads, townships, farms and plantations have sprung up everywhere, and all are subject to encroachment by moving sand and dunes. Excessive removal of sand by winds may also expose foundations and other structures.

The sand has to be physically moved by using heavy earth-moving machinery. Then impediments such as cement asbestos sheets, galvanised iron sheets or date fronds are erected across the prevailing wind direction to check further encroachment. Sand piled against these barriers is periodically. removed. As a long-term measure live shelterbelts or wind breaks of arid zone species are raised to slow down wind velocity and keep sand from openly invading protected areas. Both live shelterbelts or windbreaks and block plantations are being raised to help cope with this problem, and in places where foundations or underground installations are liable to exposure by wind erosion sand and soil may have to be hauled in by heavy earth-moving machinery.

A variety of sand dunes are found in various parts of the Emirates, continually growing, moving and changing shape. Recent observations, made on the comparatively stable and mobile dunes in the Western Region indicate that there is an average annual rate of movement of one to three metres in the main direction of the prevailing wind.

In the UAE

In order to combat encroachment and to check dune movements various methods are used, such as the erection of barriers, protective afforestation, levelling followed by covering with 'kutch' (lime), and spraying with crude oil or other stabilizers.

a) Physical Impediments

Such barriers have been commonly used in the past, date frond barriers in particular to protect date gardens surrounded by dunes. Asbestos and iron sheets have been used especially around buildings, the accumulated sand being removed at intervals. These barriers provide only temporary relief, however, and never often a permanent solution.

b) Protective Afforestation

This is perhaps the most widely used method employed to combat wind erosion and its effects. Shelterbelts and windbreaks of trees and bushes have been raised to protect roads, and green belts and block plantations to protect habitations and townships. A traditional technique used in the Liwa is to plant rows of Leptadenia pyrotechnica along the dip sides of higher dunes; an extensive network of surface and deeper roots slows down the overall movement of a particular dune, but again its success is limited and the dune is never completely halted.

Besides arid zone afforestation attempts have been made to improve the depleted range lands. This involves fencing and treating fairly large areas. Even artificial rain with cloud seeding has been attempted to provide enough moisture for the rehabilitation of such areas. The artificial rain experiment conducted early in 1982 proved fairly successful, but it must be remembered that this time coincided with an exceptionally long and heavy rainy season throughout the country.

c) Levelling and Covering

Undulating sandy areas are levelled with heavy machinery and then covered with a layer of ground lime rock ('kutch') of varying thickness depending on the purpose for which the area is to be used. It may only be about a foot thick for a date garden or a farming lot, but it could be a few feet for an asphalt road. The consolidated hard surfaces do not accumulate sand, but must be protected from non-consolidated areas around by means of live shelterbelts. A layer of ground lime rock is also used to cover underground pipelines to help prevent their exposure by wind erosion. This has been the common practice wherever 'kutch' is readily available.

d) Spraying with Crude Oil

This has been very widely practised in the oilfields themselves to protect pipelines. Bases of transmission lines are also sprayed to help prevent wind erosion. Spraying is repeated at intervals; occasionally a fresh layer of sand is applied first. Stretches of dirt road may also be stabilized by having crude oil sprayed over them. However, this gives the track an ugly look and pollutes the immediate environment.

e) Sand Stabilizers

The following manufacturers' types have been tried out in the UAE:

(i) Wood Fibers Spray by Mis Sta-Soil Corp. of North Hollywood, California, USA. An experiment was carried out over an area of about six hectares in Al Babha Plantation, near Medina Zayed, in 1978. The stabilization was neither strong nor durable. The crust formed by the wood fiber spray was easily broken up under foot and by vehicle tracks. After about six months there was virtually no sign of the original crust.

(ii) Sandstill by Mis Energy Systems Assoc., Inc., Washington DC, USA. Sandstill is an adhesive resinous substance of light colour which is water soluble, non-toxic and nonflammable. It was tried out on an experimental basis by Mis Pakistan Forestry Consultants in Abu Dhabi in 1980-81. Results have not been too encouraging but the technique has yet to be tried on a large or commercial scale. The sand stability resulting is reported to be neither long-lasting nor strong. A gallon of the liquid costs about 4 US dollars.

(iii) Petroleum mulch. The use ot this material for dune stabilization was initiated in Iran in 1968, and since then has been used on a wide scale. It is followed by the planting of arid zone species such as Haloxylon spp., Tamarix stricta, Zizyphus spina-christi, Acacia and Calligonum spp. After visiting the work done in south western Iran, the Abu Dhabi Government decided to lease out an area of 3000 hectares of undulating sand dunes interspersed with higher dunes at Al Khatim and Bida Zayed areas. The area to be stabilized is first demarcated by fencing and laid out with automatic drip systems before being sprayed with the petroleum mulch during summer months. It is later planted with transplants of species such as Prosopis spicigera and Acacia, 7 x 7 metres apart. The project has been handled in Abu Dhabi by Iranian Government staff since 1979. Petroleum mulch seems to have given better results than the two previous stabilizers. The area sprayed does have a dirty appearance and may be locally polluting, however, and more time is required to evaluate its full worth.

5. Scope and Demand for Future Work

There would appear to be a continuous and growing demand for sand dune stabilization in the UAE, required not only for practising stable agriculture but for road construction and the development of urban and industrial areas too. In the field of agriculture national policy is to gradually become self-sufficient in food production, as seen in the following table of increase in agricultural holdings 1973-1980 (in donums [1 donum = 2,500 square metres]):

Land Use 1973 1975 1977 1978 1979 1980
Fruit trees 50,000 44,272 45,949 62,533 67,934 70,964
Vegetables 23,800 12,810 15,999 31,098 45,426 46,615
Field Crops 11,240 8,564 6,870 10,535 16,401 18,500
Other Cultivated Land 42,060 79,380 84,570 76,191 63,276 98,670
TOTAL 127,100 145,026 153,388 180,357 193,047 234,749

Thus it will be seen that the land developed into farms almost doubled from 12,710 hectares in 1973 to 23,475 hectares in 1980. After initial development agricultural land needs to be protected against dune encroachment, which can only be achieved permanently by a combination of stabilizers and live windbreaks. Protective aftorestation on the windward side of roads would appear to be necessary, as well as levelling and landscaping around new habitations.

So far, petroleum mulch seems to have given the best results, but it has its drawbacks from the aesthetic and environmental points of view. It would be worthwhile to try other sand stabilizers which don't produce the bad effects of petroleum mulch. More experimental work is required before introducing more stabilizers, which could be undertaken by the Agriculture and Forestry Departments, and the Central Agriculture Laboratories of the federal Ministry of Agriculture and Fisheries Resources near Al Ain.

 


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