River, pond, wetlands, lake or estuary is an ultimate destination of all water running downhill through an area of land, which is referred as watershed. A watershed is a catchment basin that is bound by topographic features, such as ridge tops and perform primary functions of the ecosystem (http://www.gdrc.org). It plays a critical role in the natural functioning of the ecosystem (Ahalya, N. and Ramachandra, T.V., 2002) such as:
- Hydrologically, watersheds integrate the surface water run-off of an entire drainage basin. It captures water from the atmosphere. Ideally, all moisture received from the atmosphere, whether in liquid or solid form, has the maximum opportunity to enter the ground where it falls. The water infiltrates the soil and percolates downward. Several factors affect the infiltration rate, including soil type, topography, climate, and vegetative cover. Percolation is also aided by the activity of burrowing animals, insects, and earthworms.
- It stores rainwater once it filters through the soil. Once the watershed's soils are saturated, water will either percolate deeper, or runoff the surface. This can result in freshwater aquifers and springs. The type and amount of vegetation, and the plant community structure, can greatly influence the storage capacity in anyone watershed. The root mass associated with healthy vegetative cover keeps soil more permeable and allows the moisture to percolate deep into the soil for storage. Vegetation in the riparian zone affects both the quantity and quality of water moving through the soil.
- Finally, water moves through the soil to seeps and springs, and is ultimately released into streams, rivers, and the ocean. Slow release rates are preferable to rapid release rates, which result in short and severe peak instream flow. Storm events which generate large amounts of run-off can lead to flooding, soil erosion and siltation of streams.
- Ultimately, the moisture will return to the atmosphere by way of evaporation. The hydrologic cycle (the capture, storage, release, and eventual evaporation of water) forms the basis of watershed function. Economically, they play a critical role as sources of water, food, hydropower, recreational amenities, and transportation routes.
- Ecologically, watersheds constitute a critical link between land and sea; they provide habitat - within wetlands, rivers, and lakes - for 40 percent of the world's fish species, some of which migrate between marine and freshwater systems.
- Watersheds also provide habitat within the terrestrial ecosystems such as forests and. grasslands for most terrestrial plant and animal species; and they provide a host of other ecosystem services - from water purification and retention to flood control to nutrient recycling and restoration of soil fertility - vital to human civilizations.
Hence, watershed should be managed as a single unit. Each small piece of the landscape has an important role in the overall health of the watershed. Paying attention primarily to the riparian zone, an area critical to a watershed's release function, will not make up for lack of attention to the watershed's uplands. They play an equally important role in the watershed, the capture and storage of moisture. It is seamless management of the entire watershed, and an understanding of the hydrologic process, that ensures watershed health.
Watershed-Based Approach to Resource Management
Each river system - from its headwaters to its mouth - is an integrated system and must be treated as such. The focus of water resource management is on wise and efficient use of water resources for such purposes as energy production, navigation, flood control, irrigation, and drinking water (Rajinikanth, R. and Ramachandra, T.V., 2001). It also places emphasis on improving ambient water quality. Watershed approach can provide benefits to individual citizens, the public sector, and the private sector. Individual citizens benefit when watershed protection improves the environment and the livability of an area. The watershed-wide participation of local citizens and organizations ensures that those who are most familiar with a watershed, its problems and possible solutions, playa major role in watershed stewardship. The private sector can benefit because the burden of water resource protection is distributed more equitably among pollution sources.
A comprehensive approach to water resource management is needed to address the myriad water quality problems that exist today from non-point and point sources as well as from habitat degradation. Watershed based planning and resource management is a strategy for more effective protection and restoration of aquatic ecosystems and for protection of human health. The watershed approach emphasizes all aspects of water quality, including chemical water quality (e.g., toxins and conventional pollutants), physical water quality (e.g., temperature, flow, and circulation), habitat quality (e.g., stream channel morphology, substrate composition, and riparian zone characteristics), and biological health and biodiversity (e.g., species abundance, diversity, and range).
To deal with non-point source pollution in an effective manner, a smaller and more comprehensive scale of analysis and management is required. While point source pollution control programmes encourage identifying isolated polluters, non-point source strategies recognize that small sources of pollution are widely dispersed on the landscape and that the cumulative impacts of these pollutants on water quality and habitat are great. A whole basin approach to protecting water quality has proved most effective because it recognizes connected sub-basins (Ahalya, N. and Ramachandra, T.V., 2002). This includes:
- Addressing issues of water quantity, protection of riparian areas, control of aquatic non-native species, and protection of water quality.
- Protecting the integrity of permanent and intermittent seeps, streams, rivers, wetlands, riparian areas, etc.
- Prioritising watersheds for protection and restoration and focus available resources on highest priorities. Also, identify subwatersheds in which to emphasize high water quality.
- Not implementing any.timber management in riparian areas without proof that these activities actually increase coarse woody debris above natural levels and the benefits outweigh the risks (sedimentation, oil and fuel runoff, etc).
- Conducting a comprehensive all seasons water quality monitoring.
- Eliminating commercial logging and unrestrained recreation in municipal watersheds.
Watershed Management Practices
Non-point source pollution poses a serious threat to the health of watersheds. It results from an accumulation of many small actions, and, although the individual impacts may seem minor, the combined cumulative effects are significant. Control measures and best management practices (BMPs) exist that can be utilized for improved watershed health (Kiran and Ramachandra, T.V., 1999). The effectiveness of the measures varies, depending on the specific pollutants addressed; the watershed hydrology and characteristics, such as soils, slopes, type of vegetative cover, and the nature and extent of area development; the waterbodies in the watershed; and the sources of the pollution. Effectiveness also depends on correct application of the control measure or practice. All types of land uses have the potential to create non-point source pollution. Most of this pollution results from changes and disturbances on the land. Some key sources include residential areas, agricultural activities and forest practices.
Residential problems stem from neighbourhoods containing typical single or multi-family dwelling units. The problems arise from impervious surfaces that increase the flow and volume of runoff causing stream channel erosion and flooding, and from sedimentation from eroded lawns and gardens. Runoff can become contaminated by household chemicals such as fertilizers, pesticides and herbicides, paints, solvents, and street/auto contaminants like oil. The most effective control measures to address residential non-point source pollution include:
- public education
- use of vegetated swales and wetlands for contaminate filtration before runoff enters receiving streams
- sediment traps in stormwater systems
- stormwater retention (e.g. detached downspouts)
- landscape design for erosion control
- recycling and proper disposal of household chemicals and wastes
- proper maintenance of on-site septic systems to reduce nutrient loading
- combined sewer overflow management
- vegetative planting and riparian enhancement of neighbourhood streams
- street sweeping to reduce suspended solid loading and decrease heavy metals and phosphorus contamination to receiving streams
- planned development on steep slopes
- limited amount of impervious surface
- increased use of cluster developments
- utilization of erosion control ordinances, especially on construction sites.
Agricultural activities include land uses such as orchards, nurseries, crop production, feedlots, and grazing. Most non-point source pollution from agricultural practices comes from erosion or chemical contamination of receiving waters. The most effective control measures to address agriculture related non-point source pollution include:
- riparian area protection and enhancement
- revised management practices for livestock grazing and manure handling.
Forestry practices generally lead to non-point source pollution problems of soil erosion and chemical contamination. The most effective control measures to address these problems include:
- technical assistance to landowners
- limits on road building and management
- use of erosion control standards
- chemical application controls (pesticides and herbicides)
- riparian area protection and enhancement.
This accentuates the need for healthier watersheds. Healthier watersheds would slow the runoff, increase percolation into underground aquifers, decrease siltation of waterways, and lengthen the flow period for the rivers.
Watershed management has worked for over a century in Tirunelvelli, where watershed recovered resulting in improved stream flow in less than five years when cattle grazing and fuelwood harvest were removed. The Palni Hills Conservation Council (PHCC) found that the watersheds of the Karavakurichi Reserve Forest improved in mere two years when fuelwood harvesters were given alternate employment in tree nurseries. Similar success stories are reported from dry arid districts like Ananthpur.