In preparation of a sound and economical irrigation projects following steps are taken in order of sequence: 1. Investigations 2. Design of Works 3. Drawings 4. Estimates and Financial Analysis 5. Documentation of Project Report.
Step # 1. Investigations:
Following methodical investigations are generally carried out in preparation of an irrigation project:
(i) Reconnaissance:
Once it is decided to prepare an irrigation scheme for any region first question is which should be the site. There may be various localities where the scheme can be implemented.
By a very rough type of survey, which is also known as reconnaissance, it is actually possible to find out the number of sites where the project can be started. In reconnaissance the inspection of the region is done physically, without using any of the precise surveying instruments. Thus reconnaissance provides a number of alternatives where implementation of the scheme is possible.
(ii) Preliminary or Feasibility Investigations:
The next step is to study the merits and demerits of each alternative in the light of following considerations:
(a) Necessity for irrigation in the region.
(b) Availability of adequate water supply.
(c) Topography of the area.
(d) Cultural practice of the tract.
(e) Possibility of growing cash crops or other valuable crops after provision of irrigation water.
(g) Facilities regarding accessibility to the site and transportation of construction materials.
(h) Economical justification for implementing the irrigation scheme.
To gain sufficient information regarding above mentioned points it is generally necessary to collect history of the area. Also surveys are conducted which include Engineering survey, Geological and foundation survey, Hydrological survey, soil survey, economic survey etc. Then rough plans of various structures are prepared and the cost of the project is estimated roughly.
It should be remembered here that in no way these plans and estimates are exact, as they are prepared on the similar lines for all possible sites for the purpose of comparison. Soil survey is very important from the point of view of knowing suitability of the soil for particular crops under consideration.
Thus preliminary investigation gives complete and clear information of various alternatives in view. At this stage after comparison one of the alternatives may be adopted judiciously for implementing the project.
(iii) Detailed and Precise Investigations:
After selecting the alternative detailed surveys are conducted to decide following aspects:
(a) Selection of site for a reservoir and a dam.
(b) Selection of site for locating head-works.
(c) Alignment for canal system.
(d) Alignment for field channels and irrigation chaks.
In order to ensure preparation of sound and economical project the following types of surveys and investigations are considered to be minimum requirement:
1. Topographical Survey:
It includes river and reservoir survey; survey for dam, head-works, canal structures, bridges, tunnels, colony, power house, penstocks; surveys for canal and water conductor system; pre-irrigation soil survey; soil conservation survey; drainage survey etc.
2. Geological and Foundation Investigations:
It includes surface geological, geohydrological, geomorphological, geophysical, geotechnical and seismological investigations for the region in general and for reservoir area, dam site and other ancillary works area, head works, canal structures, canal system area etc. in particular.
3. Construction Material Survey:
The material survey has to be done to assess availability of adequate quantity of suitable materials including soil, sand, rock and aggregate, bricks, tiles, cement, lime stone, steel, etc.
4. Hydrological and Meteorological Investigations:
In this type of investigation long term data has to be collected for gauge, discharge, sediment, water quality, rainfall, storms, evaporation, temperature, humidity etc.
5. Communication Investigations:
Surveys to ensure rail, road, water transport facility, telephone and telegraph lines, transmission lines for making available power etc. are essential part of any project.
6. Investigations for Construction Planning:
These include surveys and data collection to plan river diversion arrangements like coffer dams, diversion tunnels, diversion channels etc.; construction of colony; store and workshop facilities; construction plant requirement like supply of water, power, compressed air etc.
7. Environmental Surveys:
Likely impact of a project on the environment has to be studied to ascertain that after construction of the project vegetation and animal life will not be destroyed completely. It will help in planning remedial measures.
8. Hydraulic Model Studies:
Future performance of the important structures envisaged in the project can be evaluated by constructing models and conducting tests on them.
Step # 2. Design of Works:
While conducting detailed surveys data should be collected which, will be useful in design of various structures.
Generally following works are to be designed completely:
(i) Storage dam,
(ii) Head-works,
(iii) Irrigation canal system,
(iv) Falls,
(v) Bridges,
(vi) Cross-drainage works,
(vii) Outlets, and
(viii) Other regulatory hydraulic structures (cross regulators, structures for silt control, etc.).
Step # 3. Drawings:
After designing the structures mentioned above their detailed working drawings are prepared to facilitate construction.
In addition to these drawings following plans are generally required:
(i) Index or Key Plan:
Scale used may be 1: 50,000.
(ii) General Plan of a Catchment Area:
Scale used may be 1: 50,000.
(iii) Contoured Plan of a Reservoir Basin:
Scale used may be 1: 10,000 to 1: 15,000.
(iv) Land Plan:
It shows the land to be acquired temporarily and permanently for construction of works. Scale used may be 1: 25,000.
(v) Plan of the Area to be Irrigated:
This plan shows the villages, roads, and other works together with the boundaries of culturable tracts.
(vi) Longitudinal Sections of Canal System:
(vii) Cross Sections of Canals:
Cross sections of canals at 100 m interval specially for maximum cutting and maximum filling sections.
Step # 4. Estimates and Financial Analysis:
An estimate is a statement which forecasts the expenditure likely to be done on the project. It consists measurement of works, specifications and rates of various items. The total cost of the project includes expenditure on various items from planning to completion of the project.
Various items considered are the following:
(i) Cost of preliminary and precise survey and investigations.
(ii) Cost of land acquisition, resettlement and environment protection measures.
(iii) Cost of various structures (dam, head-works, bridges, falls, outlets, buildings etc.).
(iv) Cost of earthwork and lining for canal system.
(v) Allowances made for foreseen and unforeseen contingencies. When allowance is made for foreseen expenditure the circumstances should be fully explained in the report.
(vi) Maintenance of facilities during construction.
(vii) Cost of communication system.
(viii) Cost of tools and plants.
(ix) Cost of establishment during construction.
(x) Proper allowances have also to be made for miscellaneous items. It includes leave and pensionary charges etc.
The estimates are prepared correctly. All calculations of quantities and costs are checked carefully to avoid calculational errors.
Total of the cost of all the items mentioned above gives project or capital cost of irrigation scheme.
To see whether any project is economically justifiable or not financial analysis is done. The test conducted to assess the financial feasibility is called benefit cost ratio (B-C ratio) criterion. According to this criterion a project is considered worthwhile only if the benefit cost ratio is not less than 1.5. In this method indirect or secondary benefits are not taken into account.
The benefit represents the difference between the value of the total annual agricultural production and the cost of cultivation before and after introduction of irrigation. The cost comprises annual interest on capital cost, annual depreciation and expenditure on operation and maintenance.
Thus information on following factors is collected for making benefit cost analysis:
i. Benefits:
(i) Agricultural production in the project area before taking up the project.
(ii) Agricultural production in the project area after irrigation.
(iii) Prices to be used to convert food production into monetary terms.
(iv) Cost of inputs viz., seeds, manure, hired labour, irrigation, hiring of machinery and implements etc. (i.e. cost of cultivation before and after introduction of irrigation).
ii. Costs:
(i) Capital cost of the project.
(ii) Interest on capital.
(iii) Depreciation.
(iv) Operation and maintenance cost of project.
> 1.5 for economically justifiable project.
Step # 5. Documentation of Project Report:
It is a comprehensive statement which discusses all the steps taken in planning and preparation of an irrigation project.
In general the report includes discussions of the following heads:
(i) Introduction:
It includes aim and history of the project, location of project area, accessability, population, interstate and international aspects, stages of development etc.
(ii) Physical Features.
(iii) Surveys and Investigations:
It includes surveys and investigations carried out for various alternatives to justify final choice of location and type of structures.
(iv) Hydrology:
It includes the details of data collected and various studies made.
(v) Design feature and drawings.
(vi) Irrigation planning.
(vii) Command area development.
(viii) Flood control and drainage.
(ix) Benefits expected from project.
(x) Construction programme and manpower and plant planning.
(xi) Schedule of rates.
(xii) Detailed estimate of various structures.
(xiii) Economic justification for taking up the project.
(xiv) Environmental and ecological aspects of the project.
After preparing complete project it is sent for government’s approval. On receipt of the approval work is started on the irrigation project.
Two important organisations are functioning at the centre to ensure speedy and successful implementation of all irrigation schemes in our country.
They are:
(i) Central Board of Irrigation and Power (C.B.I. & P.) and
(ii) Central Water Commission (C.W.C.).
The C.B.I. & P. does the work of co-ordinating research in the field of irrigation and power. It maintains contacts and liaison with irrigation and power research institutes in India and abroad. The C.W.C. is responsible for initiating, co-ordinating and furthering irrigation and power schemes in India.
C.W.C. is the highest expert body of irrigation engineers in the country. It works in consultation with the state irrigation departments for the success of planned irrigation schemes. Similarly for power projects Central Electricity Authority (C.E.A.) has been created at centre.