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The following article will guide you about how to prepare watershed plan.
It is accomplished under following heads:
1. Watershed Description:
The description of watershed should be so explained that can represent a clear picture of the watershed’s condition. As for as possible, sufficient informations on physical features of watershed and problems encountered should be fully included in description of watershed.
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Mainly, the following contents are considered for watershed description:
i. Location:
To describe the location of watershed the informations such as name of river basin tributary, physiographic region, principal communication lines, latitude and longitude of watershed are included.
ii. Size and Shape:
The size of watershed either in the unit of sq. km or ha and shape of watershed either it is long, narrow or fan shape whatever they are, should be clearly mentioned.
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iii. Climate:
About climate of the watershed the following details are usually included:
1. Precipitation – forms, annual, seasonal and monthly distribution, storm pattern, rainfall intensity, duration and its areal distribution.
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2. Temperature – maximum and minimum, soil temperature etc.
3. Evaporation
4. Relative humidity
5. Wind velocity and its duration, and
6. Solar radiation.
iv. Geology:
The geological characteristics of watershed is also considered as an important input to describe the watershed undertaken for management. It includes the geological informations such as nature of parent rocks, fractures, weathering, ground water recharge and extent of outcrops.
v. Slope:
It includes the degree of slope, length of slope, mean slope of the land surface and areas of watershed falling under various slope groups.
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vi. Surface Drainage:
On drainage features of watershed the following informations are included for describing the physical features of watershed.
a. Nature of stream flow, i.e. whether it is perinneal, intermittent, ephemeral, spring fed or seasonal.
b. Drainage Network – stream orders, density, length of streams etc.
c. Morphological characteristics of streams.
vii. Soils:
The informations about major soil types existing in the watershed and their hydrologic grouping, physical and chemical properties of the soils etc., are cited.
viii. Physiography:
It includes the details of elevation of different parts of watershed, mountainous range etc., for describing the watershed.
ix. Watershed Needs:
Under this head, the contents such as sources of surface and sub-surface (ground water) water, water requirements for domestic, irrigation, power generation and recreation, and future needs of water exploration are included.
Land use and Cover Conditions:
It includes following details to describe the watershed:
(a) Existing land use and cover condition–
(i) Forest lands
(ii) Range lands
(iii) Cultivated lands
(iv) Waste lands
(v) Habitations; and
(vi) Miscellaneous uses.
(b) Forests –
(i) Types and area under each type of forest
(ii) Hydrologic conditions
(iii) Legal status
(iv) Present management
(v) Area under regeneration
(vi) Filling and logging practices
(vii) Rights and forest fires
(c) Range Lands –
(i) Extent and their major classification
(ii) Closure
(iii) Grazing practices
(iv) Grazing incidence
(v) Cattle population (number and types)
(vi) Important grass species, their distribution and hydrological conditions
(d) Agricultural Lands –
(i) Extent
(ii) Land use capability classification
(iii) Area under each class and sub-class
(iv) Major crops
(v) Rainfed areas with suitable crops grown
(vi) Orchards and their area.
x. Economics Data:
The economics and social data are needed to determine the cost-benefit ratio of the project formulated for watershed management.
Under this the following data are collected:
(i) Economic condition of the population
(ii) Profession and dependence on resources
(iii) Market and marketing practices, and
(iv) Return from various resources, e.g., from forests, range lands, agricultural lands including irrigated as well as rain fed etc.
2. Watershed Problems:
The problems such as flood, drought, erosion and sediment damage, and other problems related to the conservation, development, utilization, disposal of water originating from the watershed etc., are included under this section of watershed works plan.
The major problems are outlined as under:
(i) Flood Damage:
The following points are considered to evaluate the flood damage occurred in the watershed:
1. Amount of land and other properties affected due to the flood hazards in the watershed.
2. Frequency of flood occurrence.
3. Effects of small frequent floods or large infrequent floods.
4. Limitations.
5. Other pertinent problems.
(ii) Sediment Damage:
The problems raised by sediment deposition is considered in following cases:
1. Problem of reservoir sedimentation
2. Problem of channel silting
3. Drainage problem
4. Irrigation development, and
5. Loss of agricultural land.
(iii) Erosion Damage:
The problem of erosion damage is studied under following contents:
1. Extent of sheet erosion, gully and channel erosion.
2. Down-stream damage due to silt deposition.
3. Effects on agricultural production due to erosion.
4. General effects on watershed’s economy.
(iv) Water Management Problem:
It includes the details on irrigation needs, drainage, water supply required for agricultural and non-agricultural uses and other management needs.
(v) Special Problem:
The problems such as land slip, land slide, torrents, highway erosion, mines etc., are counted for preparation of watershed works plan.
3. Proposed Management Programmes:
Under this section, the management programmes to be used for removing the watershed problems encountered are described.
The different proposed management programmes are listed as under:
1. Management Programme for Agricultural Lands:
To control deterioration of agricultural lands, the various control measures for them are divided into following two groups:
(a) Agronomical Measures:
These are as under:
(i) Crop proposed
(ii) Crop rotation
(iii) Cultural operations
(iv) Introduction of improved seeds
(v) Use of manures and fertilizers
(vi) Plant protection measures
(vii) Expected yield obtained, and
(viii) Expected cost invested.
(b) Engineering Measures:
It includes:
(i) Proposed measures and their justifications.
(ii) Specification of individual measures with plan and design.
(iii) Cost estimation.
2. Management Programmes for Conservation Irrigation:
(i) Selection and design of irrigation methods for each part of land.
(ii) Irrigation duration
(iii) Conveyance system
(iv) Location and specification of system
(v) Levelling and smoothening operation
(vi) Plan for drainage, and
(vii) Agronomical measures.
3. Management Programmes for Drainage:
(i) Types of drainage system
(ii) Specification
(iii) Location of outlets and their design
(iv) Intercepting and relief drains along with their design
(v) Maintenance, and
(vi) Cost-estimation.
4. Management Programmes for Flood Protection:
For this work, the following proposal can be formulated:
(i) Channel improvements.
(ii) Flood retarding structures- their design and cost estimation.
5. Management Programmes for Forest Lands:
(i) Management practices for existing forests, degraded forests, scrubs and farm forestry.
(ii) Engineering measures for forests and range lands.
6. Management Programmes for Grazing Lands:
(a) Pastures –
(i) Selection of grass species
(ii) Raising methods
(iii) Mechanical practices, e.g., contour furrowing and water spreading.
(iv) Management practices
(v) Yields
(vi) Cost invested.
(b) Grass Lands –
(i) Use of improved practices, and
(ii) Grazing system.
7. Programmes for Special Problems:
Apart from above measures, used for control of different watershed problems the following more problems can also be encountered in watershed.
The control measures for them are as under:
(i) Land Slide – Retaining wall or other structures.
(ii) Stream Bank Erosion – Vegetative or structural methods.
(iii) Erosion along the Highway – Vegetation or revetment.
(vi) Gullies and Ravines – Vegetation and gully control structures.
4. Effects of Watershed Works:
Under this section the benefits likely to be occurred from various means under watershed management works are estimated and effects of different works on improvement are evaluated.
Normally, for prediction of benefits the following items are taken into consideration:
(i) Increased agricultural production.
(ii) Flood control achieved.
(iii) Reduction in sediment load.
(iv) Increased forest produce etc.
5. Comparison of Benefits & Costs:
The comparison of various benefits obtained and costs incurred, is done by computing the average annual benefit and average annual cost of the project. The ratio of benefit to cost (b/c ratio) is computed to show the comparison between them. Generally, the primary benefits are taken into account for comparison of benefits and cost of the project.