Planning of an Irrigation Project

After reading this article you will learn about the process of planning of an irrigation project.

An irrigation project is an agricultural establishment which can supply con­trolled amounts of water to lands for growing crops. Irrigation projects mainly consist of hydraulic structures which collect (from a source), convey and deliver (to farm fields) water for irrigation. A small irrigation project may consist of a small diversion weir (or a pumping plant) with small channels and some minor control structures.

A large irrigation project includes a large storage reservoir created by a huge dam (or a long weir or barrage), hundreds of kilometres of canals, branches and distributaries, control structures and other works. Large irrigation projects are generally built as multipurpose projects which also serve to generate hydropower, control floods, and meet water supply and other demands.

Assuming other factors (such as enlightened farmer, availability of good infrastructure for supplying input material and marketing the agricultural production) reasonably favourable, the following are the essential conditions for the success of any irrigation project:

(i) Suitability of land (with respect to its soil, topography and drainage features) for the purpose of agriculture.

(ii) Favourable climatic conditions for proper growth and yield of the crops.

(iii) Adequate and economic supply of suitable quality of water.

(iv) Good site condition for the construction and operation of engineering works.

A small irrigation project can be developed in a relatively short time. For example, a farmer can develop his own tube well irrigation system by securing bank loan and, soon after, getting the engineering works constructed. How­ever, development of a large irrigation project is more complicated and time-consuming due to the associated organisational, financial, legal, ad­ministrative, environmental and engineering problems.

The main stages of a large irrigation project are:

(i) The promotional stage,

(ii) The planning stage,

(iii) The construction stage, and

(iv) The settlement stage.

The planning stage itself consists of three sub-stages:

(i) Preliminary planning, including feasibility studies,

(ii) Detailed planning of water and land use, and

(iii) The design of irrigation structures and canals.

The feasibility of an irrigation project is decided on the basis of prelimi­nary estimates of:

(i) Area of land suitable for irrigation,

(ii) Water requirements,

(iii) Available water supplies,

(iv) Productivity of irrigated land, and

(v) Required engineering works.

An irrigation project is considered feasible if the total estimated benefits of the project exceed its total estimated cost. Adequate planning of all aspects (organisational, technical, agricultural, legal, environmental and financial) is always essential for a feasible irrigation project.

The process of planning of an irrigation project is divided into the following two stages:

i) Preliminary planning, and

ii) Detailed planning.

Preliminary plans, usually based on available information, are generally approximate, but set the course for detailed planning. Based on preliminary planning, the accurate measurements are taken and, thus, more accurate detailed plans are prepared. The detailed plans may, however, have to be altered at different stages of the project.

The following are the main factors which must be determined accurately during the planning stage of an irriga­tion project:

i. Type of project and general plan of irrigation works.

ii. Location, extent and type of irrigable lands.

iii. Irrigation requirements for profitable crop production.

iv. Available water supplies for the project.

v. Culturable areas which can be economically supplied with water.

vi. Types and locations of necessary engineering works.

vii. Needs for immediate and future drainage.

viii.Feasibility of hydroelectric power development.

ix. Cost of storage, irrigation, power and drainage features.

x. Evaluation of probable power, income and indirect benefits.

xi. Method of financing the project construction.

xii. Desirable type of construction and development.

xiii. Probable annual cost of water to the farmers.

xiv. Cost of land preparations and farm distribution systems.

xv. Feasible crops, costs of crop production and probable crop returns.

The preliminary planning of an irrigation project consists of collecting and analysing all available data for the purpose, securing additional data needed by limited field surveys and determining the feasibility of the proposed development by making preliminary study of major features in sufficient detail.

For detailed planning, accurate data on all aspects of the proposed irrigation project are needed to prepare plans and designs of various com­ponents, and also to determine their most suitable site locations. There can be different feasible plans and designs possible for a particular project. Merits and demerits of all such possible alternatives must be looked into before arriving at a final plan for the project.