Concept of Watershed CP

 Concept of Watershed CP

Watershed is a part of the land, where rain water or melted ice is captured as a drainage area and let out from a single exit to major rivers or streams. (Fig: 1) Technically, a watershed is the divide separating one drainage area from another (Chow, 1964). 

Watershed or catchment area or drainage basin are terms used for part of the earth surface, where precipitation and stream or river water are collected and drained out to a bigger river, these terms are used depending on the size of the physiographic unit. For instance, India has 35 drainage basins, 112 catchment areas and 3237 watersheds (Watershed Atlas of India, AISLUS, 1990). 

Precipitation that falls in a watershed ultimately reaches river system. Basically, the extra water from the catchment area is drained into rivers. Watersheds are found in varied sizes on the surface of the earth from very small to very large. Large watersheds are also known as macro watersheds and the smaller in size watersheds are called micro watersheds. Watershed looks like branches of tree where small branches join the trunk of the tree. 

Smaller size watersheds combine to form larger watersheds. Earth’s landscape determines the size of the watershed to a large extent; for instance in areas of intensive agriculture or mountainous areas smaller watersheds are preferred whereas in plain areas bigger watersheds are easily maintained. Also, at times smaller or sub watersheds supply water to the tributaries of the main river and nests within
the larger watersheds. 

Watersheds act as bowls, which collect excess runoff and rain water at the bottom. Uneven land in any region forms watershed areas, which collect water and drains out the same from single outlet. All valleys, mountainous regions, jungles etc. those enfolds precipitation and channelize it into rivers and streams, forms watersheds. All rivers, their tributaries and smaller streams have related watersheds. A watershed apart from maintaining hydrological unit and storing water supports life on the earth by providing source of food; drinking water and habitat for aquatic organisms. These are also conducive sites for many bio chemical reactions.

Demarcation of Watershed Area

Watershed management can be done accurately only when the area is demarcated. Watershed demarcation is done on toposheet with drainage and contour lines, as watershed boundary runs perpendicular to the elevation contours. Once the watershed is demarcated on a toposheet, the same is overlaid on other maps such as cadastral map, soil map etc. 

Digitally also the watershed area can be delineated on the basis of satellite images. The Digital Elevation Model can be attained from satellite images. The data about the topography is stored in grid cells of DEM. A ridge line, acts as a dividing line between two watersheds. Ridge is the higher elevation point of the watershed from where the slope starts. 

The entire stretch of the slope of a watershed from the ridge to the plain is called Ridge area. Within watersheds the streams or rivers are categorized in different orders such as small stream at the beginning of its journey is called first order streams or lower order stream, first order streams joins with second order streams and second order stream with third order or higher order stream or river and so on and so forth. 

Watershed development and management in India has a long history. Watershed management at community level has been practiced in the form of harvesting and storing rainwater and managing runoffs. Storing rainwater in tanks and small underground storages has been an effective traditional method of rainwater harvesting practiced in the country. 

Many such traditional methods have been adopted by The Government of India (GOI) with focus on micro watersheds planning, since the late 1980s. Land, water and human resources are major components of watershed development programs in India. These programs have multiple objectives from rainfall harvesting, building small dams and tanks, groundwater recharging and rehabilitation of the locals to conservation of water resources along with development of irrigation facilities for agriculture. 

Studies conducted by different government agencies to assess the impact of watershed management programs in India shows some positives in terms of reduction in soil erosion, controlling runoffs and marginal increase in groundwater levels. However, variations have been noted with states like Tamil Nadu and Gujarat faring well in water harvesting in comparison to other states. Also, most of the positive outcomes of watershed management have been noted in micro watershed areas.  

Dynamics of Watershed Management Watershed Management forms the base for water and land resource planning, thus degradation of watershed, in recent times has impacted both the quality and quantity of water as noticed in countries like Lesotho and Morocco. The reason behind watershed degradation varies from manmade to natural factors such as removal of top soil, excess extraction of water, felling of trees, over grazing, pollution and changes in agricultural pattern.

As discussed, watershed management is the combined usage of land, plants and water resources in a distinct catchment area for the benefit of the locals, with the purpose of conserving the natural resources and reducing the negative effect on groundwater and downstream water. In the 70’s and 80’s the watershed management approach focused on water and soil planning particularly in developing countries with emphasis on engineering works on specific sites and at the downstream, less importance were given to the population of the upstream area; the management cost was also high and not justifiable. 

As a result by the end of 80’s the engineering work approach was replaced by integrated and participatory approach accepted by international and national communities. The engineering approach was not completely written off but more emphasis was given on community participation and demand driven solution at the local level. Poverty reduction in rural areas was made part of the development programs. 

Focus was slowly shifted from planned investment to farming patterns. However, the challenge with the new approach of watershed management was to increase income of the local along with conservation and intensification of the natural resources with community participation. In many countries of the world, including India, China, Brazil and Turkey, success in integrated participatory based approaches led to formulation of national policies based on participatory watershed management approach.

 

However countries, like Indonesia and Morocco, due to uncertainties about the cost of community based approach and income; led to the interruption in its formulation of national policies. In the participatory approach all stakeholders are not only involved in implementation of the measures but are also associated in research process in every step starting from designing the plans, implementation, technological application and evaluation.

This approach needs organizations or institutes to coordinate with the research agencies at all levels. However, many countries of the world are now relying on integrated watershed management approach for conservation and restoration of nature. To conclude, it can be said that watershed management is an effective and sustainable method of utilizing land and water resources.