In this article we will discuss about:- 1. Introduction to Water Resources Development Projects 2. Objects of Water Resources Development Projects 3. Classification 4. Compatibility of Multi-Purpose Uses 5. Stages 6. Augmentation.
Contents:
- Introduction to Water Resources Development Projects
- Objects of Water Resources Development Projects
- Classification of Water Resource Development Projects
- Compatibility of Multi-Purpose Uses of Water
- Stages of Water Resources Development Project
- Augmentation of Water Supplies
1. Introduction to Water Resources Development Projects:
Water Resource Development is a science which deals with conception, planning, design, construction and operation of facilities to control and utilize water. All these functions are basically functions of a civil engineer but services of specialists from other fields are also required.
Further each water resources development project comes across a unique set of physical conditions to which it must conform and hence standard designs leading to simple solutions are seldom available.
Planning is the orderly consideration of a project right from its conceptions to the final decision. It includes all the work associated with the design of a project except the detailed engineering of the structure. Planning is the most important aspect as decision to proceed with or abandon a proposed project depends on it. Since each water resources development project is unique in its physical and economic setting, it is rather impossible to describe a simple process which leads to the best decision.
Although nothing can take the position of engineering judgement during planning, each step towards the final decision should be supported by quantitative analysis rather than more judgement. This article deals with only some guideline for the planning of water resources development project.
2. Objects of Water Resources Development Projects
:
The water resources development projects are planned with the following objects in view:
1. Irrigation:
The sole purpose of irrigation is to grow crops successfully to augment agricultural production. Dams, reservoirs, wells, canals, pumps, weed control, desilting works, distribution systems drainage works are the usual works concerning irrigation.
2. Hydro-Electric Power:
The main objective in this case is generation of electrical power vitally necessary for the economic development of the region and also to achieve better living standard of the people of the region. Dams, reservoirs, penstocks, power channels power plants, transmission lines are the connected works with this objective.
3. Flood Control:
The various objectives to be achieved are the following:
I. Prevention or reduction of flood-damage.
II. Protection of economic development,
III. Conservation of storage.
IV. River training and regulation works.
The works are measured necessary to achieve the above objectives are dams, storage reservoirs, levees, flood watts, channel improvements, flood ways pumping stations, flood plain zoning and flood forecasting.
4. Navigation:
Its objective is transportation of goods and passengers through water ways. The works connected with this objective are dams, reservoirs, canals, locks channel and harbour improvements, harbour facilities etc.
5. Water Supply:
Provisions of water for domestic, municipal, commercial and industrial purposes are the main objectives. Dams, reservoirs, wells, pumping stations, water treatment plants, distribution of water are the works involved.
6. Recreational Use of Water:
Entertainment is the main objective in this case creation of reservoirs, development of recreational works, pollution control, selection and preservation of good scenes are the works involved for the purpose.
7. Water Shed Management:
Conservation and improvement of soil, sediment abatement, run-off retardation, forest and grass land improvement are the objective which comes under this heading.
8. Preservation or Fish and Wild Life:
Reduction of fish life losses and wild life losses, and provision for expansion of commercial fishing are the main objectives. The works connected with this objective are reservoir storage, regulation of flow, installation of fish ladders and screens, fish hatcheries, wild life refuges land management, pollution control,
9. Pollution Control:
The objective is protection or improvement of water supplies for Municipal, domestic industrial and agricultural use and for aquatic life. Treatment of water, reservoir storage, legal control measures etc. are the works involved in it.
10. Sediment Control:
The objective is to reduce the silt load in streams and projection of reservoirs. Soil conservation, desilting works, channel and revetment works, bank stabilization, special check dam construction and reservoir operation are the usual works involved.
11. Drainage:
Agricultural production, urban development projection of public health are the objectives to be achieved. Construction of drainage ditches, tile drains, levees, pumping stations are usual works connected with this.
3. Classification of Water Resource Development Projects
:
According to the purposes served the water resource development projects can be classified into following two categories:
1. Single purpose project
2. Multi-purpose project
The single purpose projects are designed and operated to serve only one purpose which may be irrigation, water supply, flood control or any other single purpose.
Multi-purpose projects are designed and operated to serve two or more than two objectives. Here it may be stated that a project which has been designed for single purpose but which is other benefits also for other purposes are not considered as multipurpose project.
Water resources are the most natural resources. They are available in abundance. However, since the world population is increasing at a very fast rate the food requirements are consequently increasing. It is imperative that food supplied can be increased only by making maximum use of available sources of water.
Moreover multiple use of water increases benefits without much increase in costs and thus increases economic justification for the project. Hence most of the major water resources development projects are planned as multipurpose projects.
4. Compatibility of Multi-Purpose Uses
of Water:
The water required for irrigation, water supply and navigation cannot be used jointly. Hence a project being designed for these three functions should be provided with separate allocations of storage for since power generation is not a consumptive use of water, any water released for the other purposes can be used for power.
If the power generation plant is operated as a base load plant is water requirement may fit in well with the relative uniform release of water for other purposes. However, if it is proposed to use the plant as peak load plant it may be necessary to construct an after bay or regulating dam D/S to smooth out the variations of the water released for power.
The after bay storage capacity needs to be sufficient only to regulate flows for a few days at a time. Its function is same as that of a distribution reservoir which smooth out the load on a pumping plant is a water supply system. At the regulating dam, a low head power plant may be established to produce a small amount of base load power. Since the seasonal variations in power demand may not coincide with the requirements of other uses, it is usually necessary to allocate curtain storage for power use.
Flood control requirement for empty storage space is the least compatible of all uses. The storage for flood control can be obtained either by permanent allocation of space exclusively for flood control or by seasonal allocation of space for flood, storage. Permanent allocated space is above the crest level of the spillway and is made available by closing the spillway crest gates.
Any additional space available for flood control is used but it is not dependable. In the second case, the space for flood control is made available by operating the reservoir in such a way that the required space is available for flood storage.
Recreational benefits, fish production etc. are taken into consideration as opportunity permits and some portion of space may be allocated for this purpose.
5. Stages of Water Resources Development Project
:
The various stages in the planning of a water resources development project are the following:
1. Purpose of the Project:
Before any project for planning is taken up, the planner must be clear about the objectives to be achieved. The objective of a water resources development project may be single in form of irrigation, water supply, flood control etc. or multiple. The objectives however depend upon the level of planning also.
For example the objective of planning a project by Central Govt. have a broad goal of achieving maximum economic and social benefits whereas objective of planning at state government level or district level may be single of reducing floods damage or irrigation or water supply.
The objectives of the project also depend on the availability of funds. Generally funds are never available in abundance. In such cases a comprehensive plan for the project including all the possible objectives may be prepared but it may be implemented, in stages depending upon the availability of funds.
2. Data Collection:
For this data is collected in respects of hydrology, geology, economic and social states of the area. Except hydrologic data, all other data are current and may be collected by survey at the start of the planning. The hydrologic data are always historical and the data collected for the past several years are required. Data in respect of agriculture, flood control, hydro-electric power, Municipal and industrial uses, drainage, recreational uses, navigation, fish and wild life are important.
3. Likely Future Need Projections:
All the projects are always planned keeping in view the present needs and also likely future needs. For this the projections of future needs are required. The historical and current data collected for or project planning are used to serve as the basis for projections of future needs.
The projections for planning should be worked out with utmost care and caution, because unrealistic higher values of water needs may lead to over design and wastage of resources. Similarly too lower values may furl to accomplish the purpose of the project. Thus all attempts should be directed to achieve rational planning.
4. Project Formulation:
Having obtained the data and future needs, the actual formulation of the project is started. First of all a very comprehensive list of alternatively is prepared and boundary conditions which restrict the project are defined. The restraints help eliminate sonic of the alternatives and thus simplify the process of project formulation.
Lastly the cataloging of the possible project units is done. In this all the possible project units along with the alternative plans for each project unit is indicated. Preliminary cost estimates for each catalogued unit are prepared. At this stage detailed estimates are not required since some of them are definitely to be discarded.
5. Project Evaluation:
Having considered various alternatives proposals, the next step is to select the most economically efficient proposal. The benefit cost ratio of the selected proposal should be more than one or any other specified minimum value.
If any unit is completely independent both physically and economically of all other units, it may be evaluated alone.
A physically independent unit is one which is not affected in respect of inflow by any other unit can contribute to the same.
An economical independent unit is one which is having no economic interconnection with any other unit. For example two power plants on two different streams are physically independent as far as flow is concerned but if they are serving the same power system they are not economically independent.
The devaluation of a single purpose independent project is done by benefit cost ratio and also by rate of return method.
Following three curves are plotted:
I. Benefit v/s cost
II. Benefit-cost ratio v/s costs
III. Benefits minus costs v/s costs
The three curves are shown in Fig. 28.1. From A to B, benefits exceed costs. The curve of benefits minus costs shows a maximum at point C. The maximum benefit-cost ratio occurs at point D and thus should be the limit of project size.
Figure 28.2 shows a net-benefit surface for a multipurpose project serving two purposes. With the increase in the number of purposes served by a project the number of net-benefit surfaces required to be prepared will all increase, because a large number of combinations of the various purposes will have to be considered.
6. Augmentation of Water Supplies
:
Augmentation of water supply means increasing the utility of available water by conservation or regulation. It also includes methods for providing an entirely new supply of fresh water. Providing completely new supplies of water include weather modification. Presently the main effort has been to increase local precipitation by cloud seeding.
Studies show that under favourable conditions on an average about 10% increase in precipitation can be expected by this technique. According to Mr. Lumb the increase is annual run-off AR resulting from a small increase is precipitation ΔP is given by-
where Ravg and Pavg are the mean annual runoff and precipitation respectively. The equation should be used only for preliminary estimates, where 0.1 < (Ravg / Pavg) < 0.5.
Another method of augmenting fresh water supplies is desalting of sea water.
Conservation of available water supplies can also be accomplished by following methods:
1. Sewage disposal by water transport needs vast amounts of pure water. Any technique which will use less water in homes and industry could substantially save water.
2. By reducing conveyance losses and other wasteful irrigation practices lot of useful water can be saved and used for other purposes.
3. By adopting measures which reduce evaporation of water from reservoirs.
4. Ground water is free from evapo-transpiration losses. Hence use of ground water storage together with surface storage will reduce large evaporation losses occurring from large reservoirs in arid regions.
5. Wild vegetation use large amounts of water by way of evapotranspiration. This water can be saved by eliminating wild vegetation. Measures adopted to reduce evapotranspiration by crops also help save useful water.
6. Reuse of water coining from industry and other uses also helps a great deal in saving precious water. If this water is to be used for higher uses it must be made safe both biologically and chemically.
7. Sending of soil surface using chemicals and other agent like asphalt greatly help augmentation of water yield in arid regions. Since, almost all the rain water falling oil the projected area is recovered the yield from the catchment stets increased. If this runoff water is lead to a covered tank evaporation loss is prevented.