WATERSHED DEVELOPMENT- A CONCEPTUAL CLARIFICATION
Rain falling on the mountains flows down in small rivulets. Many such rivulets, as they come down, join to form small streams. The small streams form bigger streams; and finally the bigger streams join the rivers. The entire area that supplies water to a stream or river, i.e. the drainage basin or catchment area, is called the watershed of that particular stream or river.
A watershed can be defined as the catchment area or a drainage basin that drains into a common outlet. Simply, watershed of a particular outlet is defined as an area, which collects the rainwater and drains through gullies, nallas to a single outlet.
Delineation of a watershed mean determining the boundary of the watershed i.e. ridgeline. A watershed consists of three types of lines – ridge line, drainage line and contour lines.
After knowing the concept of watershed, it becomes important to see how a watershed can be identified on the site. The watershed of any size can be delineated from the following:
1. Ridge Line
2. Outlet (Drainage Line)
Ridgeline is the line that joins comparatively the highest elevation points and that becomes the boundary of the watershed (in above figure, the ridgeline is shown in dark red colour). A ridgeline bifurcates the falling water on two opposite sides.
The most important aspect for defining and delineating a watershed is to fix the outlet of the drainage course. As the outlet goes downstream of the drainage course, the area of the watershed goes on increasing. Basically location (position) of the outlet defines the area of watershed.
1. Based on the area (size), watersheds are classified as follows:
a. Microwatershed (upto 10 ha)
b. Mini watershed (upto 200 ha)
c. Subwatershed (upto 4000 ha)
d. Watershed (upto 10000 ha)
e. River basin or River valley ( more than 10000 ha)
2. Based on the location of watershed, there are following types of watershed
a. Runoff watershed or ''A'' class watershed (Upper reach watershed): These watersheds are at the origin of river or at the upper catchment of river basin. Runoff is the main characteristic here.
b. Recharging watershed or ''B'' class watershed (Middle reach watershed): These are on the plateau area characterised by medium percolation and infiltration.
c. Storage watershed or ''C'' class watershed (Lower reach watershed): These watersheds are in the plains and characterised by good infiltration and recharging.
3. Based on the ground water exploitation, there are following types of watershed
a. Dark watershed: In theses watersheds annual ground water pumping is more than 85 % of annual recharging. These watersheds are also called fully “developed” (exploited) watersheds.
b. Grey watershed: In these watersheds annual ground water drafting is 65 - 85 % of annual recharging.
c. Yellow watershed: In theses watersheds annual ground water drafting less than 65 % of annual recharging. These are called as least developed or exploited watershed.
The dark watersheds need to be treated on the priority basis.
4. Based on the shape of watershed, it may be
a. Square
b. Rectangular
c. Triangular
d. Polygonal
The volume of water at the outlet of the watershed depends on the shape of the watershed and hence this needs to be taken into consideration while planning treatments for the watershed.
While planning for development of any watershed, one needs to look into various aspects in depth. These include:
· the size, shape, average slope of the watershed
· vegetation and land use
· soil texture, depth of soil, geology
· average annual rainfall, rainfall period and its distribution, rainfall intensity and frequency, infiltration rate
Watershed development refers to the conservation, regeneration and the judicious use of all the natural resources (like land, water, vegetation, animals and human- beings) - within a particular watershed.
Watershed development tries to bring an optimal equilibrium in the ecospace between natural resources, man and animals.
Man and environment are interdependent. It is basically the area of survival of the community living within it and drawing its sustenance from it. In resource fragile areas these demands and the claims on the environment are enormous. Any change in the surrounding environment directly affects the people living therein. A degraded environment results in a degraded quality of life of the people and environmental degradation does not recognize administrative and political boundaries (e.g. village, taluka or block etc.) Hence a watershed provides a natural environmental unit for planning the developmental initiatives. It is a scientifically proven method for insitu soil moisture and water conservation.
Since watershed development is an inter-sectoral activity, different components have to be taken into consideration and addressed while undertaking watershed development. These include:
Human Resource Development (Community Development)
Soil Conservation and Land management
Water Conservation and Management
Afforestation
Pasture / Fodder Development
Agricultural Development
Livestock Management
Rural Energy Management
Farm and non-farm value addition activities
All these components are interdependent and interactive.
Zfhcugneqoh ने कहा 11-Jan-2010 17:01:53
I an Jharkhand based Journalist cum Activist ....
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