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Essay on Watershed Management
Essay # 1. Meaning of Watershed Management:
Watershed means an area of land whose runoff drains to a common point i.e. in the river or water pool. Watershed may be defined as a natural unit of land whose runoff collects & flows out of the area through a single common outlet into a river or other water body. It is a drainage basin which is demarcated by ridges or gullies. Watershed, drainage area or catchment area are generally interchangeably used meaning for the same.
Ordinarily the catchment area (water collecting area) is larger but the area of watershed is comparatively smaller. Watershed area is the unit from the both angles i.e. land unit and water body unit, but there are separate units for both land and water in the catchment area.
Therefore catchment area comprises of all the areas from which water flows out into a common river or water pool. The different river’s tributaries having different water catchment areas flow out into a common larger river. The larger drainage area is called river basin.
The water catchment area of a tributary is called sub- catchment area and the different catchment areas may be identified in it for its certain parts. The catchment area of this certain part is called watershed area. There may be variations in the watershed area.
When these variations are more in number it means the area is hilly, undulating or rolling and we get smaller watershed area whereas in the plain we get larger. The watershed for the agricultural purpose may be several fields of farmers that contribute runoff water to the flow at the lower point. The runoff movement depends on the land topography. Runoff from the upper fields enters into the lower fields in a watershed causes soil and water erosion.
Soil conservation measures in an isolated manner are not sufficient to check the erosion. Therefore, it is necessary that soil conservation measures should be adopted on the watershed basis instead of personal individual field. In the dryland areas, soil and water erosion, flood etc. are the major problems.
Considering these points, the Govt., of India launched a Watershed Management Programme in the seventh five year plan to develop dryland areas on the basis of watershed. For soil and water conservation measures, watershed is demarcated into sub watersheds & micro- watersheds.
Micro-watersheds are the basis for planning and execution. In the beginning, there was a plan to develop 4000 watersheds in different agro-climatic regions. The Department of Agriculture provided the funds for this programme and the responsibility of evaluating 47 watersheds management programmes initiated in different states was given to ICAR. This programme was accelerated in 1983 when World Bank gave the assistance in the development of four watersheds.
Essay # 2. Features of Watershed Management:
Watershed management programme has following features:
(a) Soil & Water Conservation Measures:
Soil and water conservation measures on the watershed basis include all those measures which are effective in preventing or delaying the movement of soil and rock particles. In it the emphasis is given on soil surveying, contour and graded bunding, repairing of old bunds and dams, land reclamation, digging of farm ponds etc.
(b) Scientific Dry Fanning:
The agricultural activities like contour ploughing, pre-monsoon ploughing, deep ploughing, mulching, development of new varieties according to agro-climatic zones, weed control, integrated nutrient management and integrated pest management improve the production in dryland areas.
(c) Forestry and development of pasture; and
(d) Animal Husbandry and Development of Dairy:
Proper animal husbandry, artificial insemination, economic assistance to the milk producing cooperative societies etc. are to be adopted.
Essay # 3. Aims and Objectives of Watershed Management:
1. To protect, conserve & improve the land resources for efficient and sustained production;
2. To protect and enhance water resource, moderate floods & reduce silting up of tanks, increase irrigation and conserve rainwater for crops and thus mitigate droughts.
3. To utilise the natural local resources for improving agriculture and allied occupation or industries so as to improve socio-economic conditions of the local residents.
Thus, watershed management is the planned use of watershed lands in accordance with pre-determined objectives, such as the control of erosion, stream flow, sedimentation, and the improvement of vegetative cover and other related resources. Such watershed management integrate plans for soil conservation, soil improvement, irrigation drainage, flood prevention and development of water supplies for all purposes.
In case of agricultural micro-watersheds, important aspects are soil conservation measures, soil improvement, storage and utilisation of runoff water. In dry farming areas, watershed approach provides an ideal means for integrated development.
There is a need for multipronged approach to maximise crop production & also to ensure stability in rural income for integrated watershed management having following steps:
(i) Water harvesting
(ii) Location specific technology for crop production
(iii) Adoption of intercropping and crop substitution according to soil suitability
(iv) Afforestation on cultivable wastes and marginal lands
(v) Practice of dryland horticulture to minimise risk. Mango, guava, ber, pomegranate, sapota and tamarind have good potential on marginal land.
(vi) More efficient exploitation &use of ground water and irrigation
(vii) Development of dairying and pasture management
(viii) Stall fed goat and sheep farming needs to be popularized
(ix) Popularisation of sericulture and mulberry cultivation
(x) Processing of farm & horticultural produce
(xi) Sound extension and training programmes for the farmers
Water Harvesting/Runoff Concentration/Rainfall Precipitation:
In humid climates, runoff usually occurs only when rain falls on a saturated soil. Under semi-arid conditions, the total annual precipitation may or may not be sufficient, but most of the rain falls in a short period causing humid climate conditions and resulting into runoff. In both conditions, the excess rain water should be safely guided and collected in nearby ponds for recycling in drier period for life saving irrigation.
Water harvesting is defined as the collecting and storing water on the surface of soil for subsequent use. It is a method to induce, collect, store and conserve local surface runoff for agriculture in arid and semiarid regions. Water harvesting was developed to a fine art about 2000 years by the Nabateans. The term ‘water harvesting’ was first time used by Myors.
Normally water harvesting is more effective in areas situated near hill side or in the areas where large portion is bare soil and cultivation is done on small portions. The technology of water harvesting differs according to soil types, topography, annual rainfall and the crops to be grown.
Essay # 4. Techniques of Watershed Management:
In India three types of water harvesting techniques are generally practiced:
(i) Inter-Row Water Harvesting:
It is practiced in arid areas with light soil where annual rainfall does not exceed 400-450 mm. The crop is sown in narrow strips between wide intervals that are ridged as artificial miniature watersheds. Later on these are compacted to increase runoff to the crop rows. It is more practical since no land is sacrificed for harvesting water.
(ii) Inter- Plot or Microplot Water Harvesting:
In this case, water is harvested in the passages or furrows between the plots when rainfall is comparatively more. Runoff from the sloping area supplements rainfall for raising crop on level land.
(iii) Water Harvesting in Farm Ponds & Reservoirs:
Surface runoff from small watersheds is stored in farm ponds & reservoirs for utilization as supplemental or lifesaving irrigation. This harvested water can either be used as lifesaving irrigation to Kharif crops at the time of drought due to irregular monsoon or as supplemental irrigation to winter crops. Since the stored water is limited, steps should be taken to reduce losses from seepage and evaporation. Suitable lining materials for pond beds and anti- evaporants should be found out and used.
Runoff can be increased by either by land alteration or by chemical treatment. Impermeable catchments are prepared by spraying asphalt compounds. Thin plastic films or metal sheets can also be used to cover ground surface for water collection. Waterborne asphalt emulsions are much effective in controlling seepage loss. Bentonite has excellent sealing properties if kept continuously wet.
In the case of Broad Bed & Furrow system, excess water during rainy season is collected through the furrows and passed through grassed waterways into farm pond or reservoirs.
The stored water should be recycled most judiciously so as to get maximum return out of it. Only one or two irrigations are possible with the limited water stored. Therefore supplemental irrigation can be scheduled by two approaches viz. soil moisture depletion approach and critical stage approach. Irrespective of the crop stage, irrigation is scheduled when soil moisture approaches to permanent wilting point to save the crop. This supplemental irrigation is known as life-saving irrigation.
Jalshakti:
A chemical which when applied (mixed) in soil, improve the aeration, infiltration and water holding capacity of the soil.
Evapo-Transpiration (ET):
Soil moisture is the most limiting factor in dryland agriculture. About 60-75% of the rainfall is lost through evaporation. The evapo-transpiration is the evaporation from the soil surface and transpiration from the plant surface.
Such losses can be reduced by:
(i) Mulches
(ii) Antitranspirants
(iii) Wind breaks and
(iv) Weed control.
Antitranspirants:
Such materials are applied to transpiring plant surfaces to reduce water loss from the plant.
Antitranspirants are of four types:
(a) Stomata Closing Type:
Such antitranspirants reduce water loss through stomatal closing .e.g. phenyl mercuric acetate (PMA), herbicides like Atrazine in low concentrations, ABA and CO2.
(b) Film Forming Type:
Retard moisture loss due to formation of thin film as physical barrier e.g. Mobileaf, hexadecanol, silicone, oils, waxes.
(c) Reflecting Type:
Such materials reflect the radiation and thus reduce leaf temp and vapour pressure gradient from leaf to atmosphere and ultimately transpiration is reduced e.g. celite (a diatomaceous earth product) and Kaolin. Application of 5% Kaolin spray reduces transpiration loss.
(d) Growth Retardants:
Such chemicals reduce shoot growth and increase root growth and thus enable the plants to resist drought. It also induces stomatal closure e.g. cycocel (ccc).
Antitranspirants generally reduce photosynthesis. Therefore, their use is limited to save the crop from death under severe moisture stress. They have some practical use in nurseries and horticultural crops.
Windbreaks and Shelter Belts:
Windbreaks are such structures which break the wind – flow and reduce wind speed while shelterbelts are rows of trees or shrubs planted for protection of crop against wind. They provide a protective shelter against wind and suitable habitat for birds and honeybees as well as produce cattle feed and fuel wood. In the wind erosion areas, windbreaks & shelterbelts are to be planted. They prevent soil erosion, arrest the march of desert and protect the agricultural and residential lands from dust- storms.
A rows of trees & shrubs planted across the wind – direction is the most effective. It reduces the wind speed upto 60-80% on leewide side. The height of tall tree and length of windbreak determine the extent of protection provided to soil. Windbreak & shelterbelt provides the protective shelter against desiccating winds to the extent of 5-10 times the height of tall tree on windward side and upto 30 times on leeward side.
For example, a 10-11m tall windbreak when encountered by 45-50 km/hr. wind, it reduces on windward side to 20-30 km/hr and to 10 km per hour on just leeward side which is illustrated by the figure 5a.
The wind-break reduces the wind speed on the leeward side at 200m away upto 20% only and in the area as at 300m away, there is no effect at all. Therefore at an interval of 300m, such windbreaks should be repeated.
To control weed erosion, the capacity of shelterbelt depends upon the speed and direction of wind. In case of high wind speed, the protective area is reduced and in such areas, the interval between two shelterbelts is to be reduced.
To counter wind’s direction, it is necessary to be long length of windbreak so that wind blows across the wind break. Depending upon the porosity of shelterbelt, certain amount of wind passes through it and some deflects & crosses over it. Thus it does not produce turbulence of air.
Reduction in wind speed, reduces the evaporation losses and makes available more water to crops. According to planting pattern of trees & shrubs as shelterbelt, the grasses & shrubs are planted on the outer rows which train the wind to rise much above the ground surface. The inner rows are of small trees and the outer rows are planted by tall trees which further raise the wind level.
The beneficial effects of shelterbelts are more clearly seen in drought areas. In such areas windbreaks of 3-7 rows and 15-30m wide are more effective. It modifies the micro- climate favourable for crop production and shelters for birds, honey bees & pet animals.