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A Review on Sand Dune Stabilization William M. Shehata and Mohammed H. Al-Rehaili.

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Presentation on theme: "A Review on Sand Dune Stabilization William M. Shehata and Mohammed H. Al-Rehaili."— Presentation transcript:

1 A Review on Sand Dune Stabilization William M. Shehata and Mohammed H. Al-Rehaili

2 Aeolian Sand Transport Creep Suspension Saltation

3 Sand movement by saltation

4 Modes of Sand Movements Natural sand drifting Dune migration

5 Types of Dunes Sand supply Wind velocity Presence of vegetation

6 Sinusoidal movement of a linear dune

7 Movement of a barchan dune by erosion of the windward face and deposition on the slip face

8 Sweeping action at high wind speed

9 Sand Dune Stabilization Temporary Sand Control Systems Sand Shielding Sand Fences Permanent Sand Control Systems Afforestation

10 Sand Shielding Stone Mulch Water or Brines Wetting Chemical Stabilizers Biological Crusting

11 Stone Mulch Gravel, stone or crushed rock blankets are used as mulches. Blankets formed of gravel smaller than ½ in. in diameter can withstand wind velocities up to 137 km/hr. A 1-in. layer of aggregate or gravel is normally adequate for areas not subject to traffic. Suggested grading: Passing 1 ½ in. sieve100% Passing 1 in. sieve60-90% Passing ¼ in. sieve0-20%

12 Water, Wastewater or Brine Wetting Increases cohesion between grains. Increases in the percentage of the fines (silt and clay) particles between the sand grains. Grow vegetations existing in the area. Reduce the harmful salt content in the soil. Brines rich in carbonates or sulfates precipitate salts that tend to cement the sand grains and resist wind erosion.

13 Chemical Stabilizers The nature of the bonding by chemical stabilizers in sand is adhesive. Some other chemicals form a film on the sand grains that increases its specific gravity and consequently decrease the rate of erosion.

14 Effectiveness of a Chemical as a Stabilizer Its solubility in water Optimum dilution ratio Optimum application rate Bonding strength Rate of surface erosion Effective life of the chemical under field conditions (heat, humidity, rain and ultraviolet rays). Effect of the chemical on seed germination and plant growth

15 A good bonding action of a chemical stabilizer between sand grains.

16 A weak but permeable bonding action of a chemical stabilizer between sand grains

17 Biological Crusting Dewfall is a process whereby moisture from the atmosphere condenses on the earths surface The frequent occurrence of dew can serve as an important source of moisture for biological crusts The crust is formed by biological activity of blue-algea. This idea is worth further investigations under the Saudi Arabian climatic conditions.

18 Sand Fences Checkerboard fences Fore dune fences Impounding sand fences Diversion sand fences

19 Checkerboard Fences Constructed of plant remains or plastic nets cm high forming 3 x 3 m rectangles Can withstand weather conditions for few years, which is long enough to implement the permanent solution

20 Impounding Sand Fences Fence heights should range between 0.5 m to 1.2 m Fences should be erected around 50 m down-wind the erosional area or times the fence height from the area to be protected Multiple rows of fences can trap more than 80% of wind- borne sand Gaps should be left between long fences to lessen the load caused by wind and accumulated sand The porosity of the fence should range between 30 and 40% A fence should extend times its height beyond the area to be protected

21 Impounding Sand Fences (continued) Since the fences will eventually be buried by trapped sand, new fences must be erected on the accumulating mound Fences should be located in areas where the creation of a large artificial dune will not pose any problems

22 Impounding Sand Fences (continued) Fences will require regular maintenance and renewal to avoid deterioration or constructed from better material

23 Diversion Sand Fences They are erected either as single fences slanted at about 45 o from the wind direction or in the form of a V-shaped fences pointing up-wind They not only trap the sand but also deflects it away from the area that needs to be protected The effectiveness and life span of the diversion fences depends on the material of construction, height and porosity

24 Permanent Sand Control System (Afforestation) Decrease the wind speed Protect the ground from scouring Change the microclimate in the area Enhance the soil condition for further plant growth Create recreational areas An appealing way to mitigate the dune migration hazard

25 Afforestation Application Water Plants Site maintenance

26 Water The presence of water is vital for plant growth Rain is scarce in desert areas Other sources of water should be envisaged Groundwater resources, rain and dew water harvesting and wastewater are posibilities Also water harvesting from sabkha should be considered

27 Plants Quantity and quality of the available water Soil moisture content Percentage of salts in the soil Speed and direction of wind Rate of sand movement Rate of plant growth Capability of the plant to multiply Capability of the plant to enhance the soil condition The root system of the plant

28 Site Maintenance The site should be protected against possible unlawful grazing activities The site should be protected against possible trespassing and firewood cutting

29 Stabilization Programs in Arid Countries (Case Histories) The stabilization programs used in China, Pakistan, Iran, UAE, Kenya, Libya, Palestine, USA and Saudi Arabia were reviewed The most effective and permanent mean of sand dune stabilization is the afforestation Tamarix, Acacia and Calligonum have been successfully used to stabilize dunes in many countries Prior to vegetation a temporary sand stabilization using ground shielding was always necessary

30 Suggested Sand Control Plan for the Eastern Region The plan is based on the previous knowledge of the geology and geomorphology of the region The region is mainly covered by sand dunes (barchans, shield or parabolic) and sand sheets The sand bodies are locally underlain by sabkha soil Limestone outcrops form the highlands in the area Several limestone quarries producing aggregates are present around Dhahran-Dammam area

31 Elements of the Suggested Sand Control Plan in a Test Plot Temporary stabilization using stone mulch Permanent stabilization using vegetation Water harvesting

32 Temporary Stabilization Using Stone Mulch Crushed limestone is suggested to be used as stone mulch to cover the windward face of several barchan dunes in a limited selected dune field The specification of the US Highway Research Board for stone mulching can be implemented in this test

33 Permanent Stabilization Using Vegetation Drought resistant plants such as Parkinsonia aculeate, Prosopis juliflora, Atriplex spp., Tamarix aphylla and/or Tamarix nitotica were recommended The experience of the Research Institute of King Fahd University of Petroleum and Minerals in this aspect should be considered

34 Freshwater Harvesting from Sabkha Brines Solar stills were used to harvest fresh water from the brines of Al- Lith sabkha Each solar still covered 10 m 2 of sabkha area

35 Freshwater Harvesting (continued) Freshwater was produced on the average of 1.2 to 1.8 lit/day/m 2 This amount can be improved by some modifications to the solar still


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