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This simple guide lists out the most pertinent questions related to watersheds that will help understand this important topic a little better.
Please click on a topic to view more detailed information.
A watershed is the total land and water area, from where the rainfall runoff drains into any water body, be it a stream, river, lake or ocean. It may be a nearly flat area or include hills or mountains.
It is considered to be synonymous with a drainage basin and catchment area. Watersheds are separated from each other and the boundaries are known as watershed boundaries.
The size of a watershed varies as per the topography of the land. Smaller watersheds drain into streams and just as several streams form a river, several small watersheds group to form a larger watersheds or river basins with their own defined ridgeline.
For an irrigation-cum-hydel project, the size may be several thousands of square kilometers but for a farm pond it could be just a few hectares.
Every land area is a part of some watershed. We can identify our watershed by exploring the water body to which the water from our area drains to. And yes, each one of us lives in a watershed.
The main function of a watershed is to receive the incoming precipitation and then dispose it off. It’s five major functions come under the following two heads:
Hydrological functions:
Ecological Functions:
It is the categorisation of land in watershed management that specifies the land capability. It specifies the ability of the land and indicates the most intensive, profitable, and safe use, which can be made of any piece of land. The land is classified into different capability classes according to various parameters. The broad groups are:
Unfortunately, India does not have its own classification system, but uses the USDA system, that has many shortcomings in the Indian context.
Watershed deterioration takes place due to uncontrolled, unplanned, and unscientific land use, aided by human interventions. Some of the activities that cause this involve:
Some of the results of watershed detioration are:
Category | Number | Size Ranges (‘000 ha) |
| Regions | 6 | 25000-100000 |
| Basin | 35 | 3000-25000 |
| Catchments | 112 | 1000-3000 |
| Sub-Catchments | 500 | 200-1000 |
| Watersheds | 3237 | 50-200 |
| Sub-Watershed | 12000 | 10-50 |
| Milli-Watershed | 72000 | 1-10 |
| Micro-watershed | 400000 | 0.5-1 |
“Watershed Atlas of India” has been devised based on the drainage map on 1:1 million scale following stream hierarchy where the whole country has been divided into six River Resource Regions, 35 Basins, 112 Catchments, 550 Sub-catchments and 3257 Watersheds.
The codification has been made in a simplistic manner following alphanumeric system.
A watershed can be symbolized as 1A2B3 where:
Watershed management is simply watershed ‘protection’. It aims to utilize land and water resources wisely, to enable optimum & sustainable production, reduce floods with minimum hazards to natural resources. It essentially relates to the practice of soil and water conservation in the watershed.
The basic objectives are:
Boundary of states, districts, town, farms etc. are demarcated on different maps but watershed is demarcated only on toposheets because these are the only maps, which show the contour lines and the drainage lines. Initially the demarcation of watershed is done on toposheets and then this demarcation can be superimposed on other maps like cadastral maps, soil maps, geological maps etc. It’s demarcation depends on the selected point on the drainage line. Each selected point will have a different watershed boundary and size.
It is the line joining the points of higher elevation in a particular watershed. Ridgeline always divides different watersheds.
Wetlands are crucial in a watershed, they function as natural water filters and help control and improve the water quality of the water flowing downstream. They provide a conducive atmosphere for many biogeochemical reactions to take place, which help in the removal of nutrients like nitrogen and phosphorus, by converting them from inorganic forms to organic forms. The site of a wetland in a watershed is very important.
In India, a national level Watershed Atlas has been created. In this Atlas, the entire river systems of the country have been divided into 6 Water Resources Region, which have been further, divided into 35 basins and 112 catchments. These catchments have been further divided into 500 sub-catchments and 3237 watersheds. The atlas consists of 17 sheets on 1:1 million scales along with a compendium of watersheds giving details of other related information such as area within the basin, sharing states and stream names etc.
What we do affects the watershed we live in, both downstream and for future users. Whether it's doing the laundry, domestic, industrial or agricultural use of water, everyone impacts the watershed they live in. The soaps and detergents that you use, the medicines flushed out, all of these have the potential to affect the water quality in the watershed.
A TMDL (total maximum daily load) is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards.
In other words, it is the sum of the allowable loads of a single pollutant from all contributing point and non-point sources, and includes a margin of safety and consideration of seasonal variations. In addition, a TMDL contains the reductions needed to meet water quality standards and allocates those reductions among the sources in the watershed.
Yes there are and these new guidelines for watershed development projects broadly indicate a new framework for the next generation watershed programme. It was asserted that these guidelines coupled with the flexibilities inherent in them, would provide a helpful framework for the design, management and implementation of all watershed development projects in the country. The key features of this new unified approach can be broadly outlined as follows:
There are new guidelines to Integrated Watershed Management Programme (IWMP) proposed by the Mihir Shah Committee. It has been decided to make the IWMP a five-year programme with a renewed focus on professionalism, capacity building, institutional building and a greater role for civil society. Further, based on the experience of a lot of states, a new framework is proposed for the convergence of IWMP with allied programmes such as MGNREGA and National Rural Livelihood Mission.
Some of the organisations that hold training programmes and work in watershed management are:
IWP requests users to view the same as a starting point in collating information on watershed, and to add more suggestions, information as responses in this thread.
Access here: FAQ on watershed
Lead image source:
CSERC