To Establish the Sand Drift:
Most dunes are born of small accumulation of sand or debris. Blocked by this insignificant obstruction, the ocean winds that cross the beach lose much of their force and drop any sand they have picked up. A little mound forms, enlarges into a hillock and eventually into a dune. Some dunes grow to a height of more 50 metres.
In India sand dunes occur in two distinct habitats – Coastal and inland dunes. The coastal sand dunes are in Madras, Orissa, Andhra Pradesh, Bengal, Mysore and Kerala.
The inland dunes are in Rajasthan, Punjab, Gujarat, Haryana and Saurashtra. In Rajasthan sand dunes occur in Bikaner, Barmer, Jaisalmer, Churu, Dugargarh, Jhunjhunu, Nohar, Sikar, Sardar Shahar etc. These are the spectacular features of Great Indian desert and occupy 58% of area.
Principles of Sand Dune Stabilization:
The primary principles for stabilisation of sand dune are viz.,
1. Stop the blowing of sand at its source.
2. Reduction of threshold velocity of wind at the sand dune surface by providing obstruction of some kind-bunch of grasses and shrubs, wooden planks etc.
Technique for Stabilization of Inland Dunes:
A uniform method of sand dune stabilization for all drift areas cannot be suggested as conditions vary in degree of wind velocity, aridity, duration of wind storms, availability of material and direction of wind.
The main phyto-reclamation to reclamation techniques involved for stabilization process are following:
1. Year-mark the dune for stabilization work.
2. Protection of sand dune area against biotic interferences by – barbed wires fixed on angle iron posts, spaced at 5 metres apart or thorny bush wood (Zizyphus nuwnularia (Bordi) or Prosopis spicigera etc.) by cutting and placing. This should be completed before April.
In the latter case repairs by replacement or renovation will be necessary as the shrub material is either easily blown off or is buried in the sand during the hot summer months.
3. The barriers may be fixed in parallel strips or in chess board designs – on windward side of sand dunes (Fig. 17-1).
4. Planting of vegetation by direct seedling or cuttings or transplanting seedling of indigenous and exotic species in earthen bricks, or polythene bags.
5. Afforestation by sowing of grasses and castor on the leeward .sides of sand dunes will form micro-wind breaks.
6. Continuous and timely proper management of afforested dunes
Stabilization of Coastal Dune:
1. All the processes involved in inland sand dune stabilization are common in coastal dunes stabilization. In this case a new littoral dune is erected (Fig. 17-2).
2. Stabilization of coastal dune by beach grasses:
Beach grasses may look fragile but they are durable and tenacious. They have an ability to grow back to the surface if their leaves are buried and to survive drought, heat and cold. Beach grasses knit together to form a network of roots and stems, and a dune acquires a degree of permanence.
Beach grasses are pioneer plants in stabilization of coastal sand dunes. They create an environment more attractive to other species of plants and thus encourages colonization by animals. Slowly the dune changes character. As the plants become established, the dune becomes more stable.
Management of Sand Dunes:
For the better management of sand dunes the grasses may be harvested after 2 years by cutting preferably at post seeding stages.
The trees may be lopped for fodder and felled for fuel after 10 years of planting. Ones rehabilitated sand dunes can best be managed as cut fodder-cum-fuel reserve.
Recommendations for Inland Sand Dune – Stabilization in Hot Dry Indian Desert:
Recommended trees, shrubs and grass species in different rainfall zones are following:
(i) Rainfall zones of 15 cm to 30 cm.
Prosopis juliflora (Vilayathi babool), Acacia tortilis (Israeli babool), Acacia Senegal (Kumat).
Calligonum polygonoides (Phog) and Zizyphus sps. (Bordif Calotropis species.
Lasiurus sindicus (Sewan).
(ii) Ranfall zone of 30 cm to 40 cm.
Acacia tortilis, Acacia Senegal, Prosopis juliflora, P. cineraria (Khejri), Tecomelta undulata (Rohida), Dichrostachys glomerata and Casuarina equisetifolia.
Zizyphus sps., Calligonum polygonoides, Ricinus communis (Arandi) Cordia gharaf.
Lasiurus, sindicus, Cenchrus ciliaris (Dhaman), Cenchrus setigerus (Kala Dhaman), Saccharum rnunja (Moonj).
(iii) Rainfall zone of 40 cm and above:
Trees : Prosopis juliflora, Prosopis cineraria, Acacia tortilis, Acacia Senegal, Acacia nilotica sub-sps indica (Kikar). Tecomella undulata, Parkinsonia aculeata, Albizzia lebbek (Siris), Dalbergia sissoo (Shisham), Dichrostachys glomerata, Colophospermum mopane.
Ricinus communis, Zizyphus sps., Cassia auriculata etc.
Cenchrus ciliaris, Cenchrus setigerus, Panicum antidotale (Gramna), Saccharum munja etc. The success of sand dune stabilization depends on choosing the right species, planting sturdy stocks, planting in time and deep timely replacement of casualties and after care. No grazing should be allowed within the area. Cropping and other hiotic interferences should be stopped.