Watershed Management

What is a watershed

The watershed area for a small stream may be a few hectares, while for a large river the watershed may be many square kilometres. For proper planning and execution, the size of a watershed area should ideally be 1,000 to 2,500 hectares. If the area is within this range, it will be possible to prepare a well balanced plan and to implement it in a period of 2 to 3 years.

Objectives of watershed management

Watershed management is an attempt to halt land degradation and a holistic process for getting maximum production out of land. Watershed management implies rational utilisation of land and water resources for optimum and sustained production, with the minimum of hazard to natural resources. With a bit of acumen and proper judgement, the rain water can be made to move down the slopes slowly, ensuring optimum infiltration and percolation, automatically solving the problem of soil erosion. Reducing the impact of the rain on the soil, checking its speed at various intervals, taking up all operations on the contour and diverting the excess to prevent the, pressure, are some of the procedures one could adopt; a process that starts at the highest point of the watershed and ends right down in the lower parts.

Steps in Watershed planning

• Preparation of base maps for carrying out surveys.
• Reconnaissance survey of the watershed for overall development.
• Assessing rainfall characteristics.
• Preparation of soil maps and classification of lands for different uses according to capability classification for agriculture, forestry, pasture, horticulture, etc.
• Preparation of inventory of existing land uses and farm sizes.
• Appraisal of agricultural production patterns and potentials, present and potential markets and possible group action arrangements.
• Carrying out topographic and hydrologic surveys for engineering works.
• Geo-hydrological survey to delineate areas suitable for groundwater development.
• Formulation of an integrated time-bound plan for land and moisture conservation, ground water. recharge, development of productive afforestation, agriculture production, grasslands and horticulture.
• Assigning of priorities for implementation of the project.
• Assessing social costs and benefits.

Land capability classification

Watershed management must take into account land capability classification, since a typical watershed may include lands suitable for cropping, trees, pastures, etc. The land classification is as follows:

Class I:

This type of land is nearly level, with minimum erosion, the soils are deep, well drained, with adequate water holding capacity. These soils need ordinary management practices to maintain productivity. Such practices may include the use of one or more of the following fertilisers, lime cover and green manure crops, conservation of crop residues aAd crop rotation. They are fit for agriculture, pasture, forests, etc.

Class II:

These soils have some limitations. They are subject to slight erosion, as they are slightly sloping lands, with less soil depth, occasional drainage problems that can be easily corrected, and they are sometimes saline. They may need one or more of the following practices terracing, strip-cropping, contour cultivation, excess water drainage, crop rotation, use of green manure crops, stubble mulching, the use of fertilisers, manure and lime.

These soils may be used for growing cultivated crops, raising pastures, forests, etc.

Class III:

The factors that limit plant growth are more severe than in class II. These factors could be moderately sloping land, land susceptible to water or wind erosion, land more susceptible to drainage problems, land with water-logging, shallow soil depth, low moisture holding capacity and moderate salinity.

Class IV:

The limitations to plant growth is more severe here than in Class III soils. Very careful management is required and the conservation practices are more difficult to apply and maintain. Some of the factors affecting these lands are steep slopes, severe susceptibility to water and wind erosion, shallow soils, low moisture holding capacity, severe water-logging and severe salinity. These soils can be used for crops, pastures, forests and wildlife food, etc.

Class V:

Cultivation is not feasible because of one or more limitations, such as over flow, stoniness, wetness or severe climatic conditions. Examples of this class are soils of low lands subject to frequent over flows which prevent the normal production of cultivated crops, or rocky or stony terrain. These soils are suitable for raising cultivated crops but are not suitable for perennial vegetation.

Class VI:

These soils have very severe limitations that make them generally unsuitable for cultivation and limit their use largely to pastures or forests or wildlife food and cover. Some of the limitations which cannot be corrected are: steep slope, very severe erosion hazard, shallow rooting zone, excessive wetness, low moisture capacity and severe salinity.

Class VII:

The physical condition of the soil is such that it is not practical to adopt pasture improvements and water control practices.

Class VIII:

Bad lands, rocky out crops, sandy beaches, marshes, deserts, mine tailings and other nearly barren lands may be included in this class. It may be necessary to give protection and management for plant growth to soils and land forms in class VIII in order to protect other more valuable soils, to control water, or for wildlife or for aesthetic reasons.

Water Management Activities

The best opportunities for moisture conservation lie in the control of the portion of precipitation which is normal runoff. Retaining surface water on the land surface for a longer time, increases the amount of water entering the soil. Effective methods are the following:

• Contour bunding / graded bunding
• Check dams and gully control structures
• Land levelling / land smoothening
• Bench terracing
• Farm ponds
• Percolation ponds
• Waterways
• Diversion drains

Water conservation starts in the topmost rocky areas where the runoff water needs to be drained out by forming diversion drains. This protects the steep slopes below which are suited only for growing fodder. While prevention of grazing in these areas ensures optimum regeneration, luxuriant fodder cut and fed to the animals ensures better nutrition and health.

Source : CPR Environmental Education Centre, Chennai