Mechanics of Tillage and Traction

LESSON 13. APPROACH TO PLANNING, CONSTRUCTION AND MAINTENANCE OF ON FARM DEVELOPMENT WORKS

13.1   On Farm Development (OFD) Works:

The efficient management of irrigation water for maximizing productivity requires both, the efficient on farm water management and the optimization of the use of water and land, through appropriate methods of water application. The efficient on-farm water management is related to water delivery system and allied works in the command area of chak (Small irrigation block), which distributes the water to each farm. The items of works pertaining to on farm water management are termed as “On farm development works”.

The on farm development works comprise of following,

a) Field channels for conveyance of water

b) Control structures

c) Crossings

d) Surface drainage system

e) Farm roads

f) Field channel protection works and

g) Land forming (Smoothening / grading / leveling).

13.2  The General approach to design and execution of OFD works:

The general approach to design and execution of OFD works shall be in accordance with the Govt. technical circulars, the Govt. Resolution and other directives issued by the Govt. from time to time for this purpose. The participatory irrigation management and efficient water delivery system to provide timely as well as adequate water supply to each farm, shall be the main focus points in the design and implementation of OFD works.

The basic issues of general approach are,

a) Systems approach

b) Sequence of design and execution

c) Functional utility

d) Farmers’ Participation

e) Organizational coordination

13.2.1 Systems approach:

The conveyance system from the dam to the farm gate is one live system and it is necessary that the designs of the different components are matched properly. The water management proposed to be adopted on the canal system should always be kept in view as a reference frame. In Maharastra, canals and branches are designed for a 14 day rotation (irrigation interval) including a 12 day running period and a 2 day closure (except in unusual peaks when there is a 14 days running period); minors and distributaries are designed to complete the irrigation in half period. The chaks will be so laid out and designed that the entire irrigation thereon is completed in 6 days. The outlets are operated in sequence from tail to head of the minor. Outlets with a less than 6 day running period are alternated or rotated. Thus, basically a chak water delivery system will be designed to provide at the farm gates, (turnout or property head) within a 6–day running period, water requirements of 14 days irrigation interval.

13.2.2 Sequence of design and execution:

(a) The ideal sequence of finalization of design would be obviously from the tail to the head. First, according to the topography and soil conditions, the land forming of each farm would be decided, so as to ensure efficient irrigation. Next, the chak water delivery system and surface drains would be designed so as to ensure adequate water deliveries to the different farms and proper drainage. According to the number of outlets and period for which they would operate, the design capacity of the minor is decided and in turn, that of the distriburtory and of the main canal. Conditions do not always permit this ideal sequence of design and therefore the design may have to proceed from head to tail. Sometimes this may lead to designs with inadequate conveyance capacities in the distributaries and minors. One should keep these limitations in mind.

(b) The execution of OFD works shall be done only in places where canal water has actually reached. The OFD works get disturbed and deteriorated if these are not put to use immediately. As far as possible, the construction of OFD works may not be taken up till the formation of Water Users’ Association.

(c) After construction of OFD works, preparation of work-done drawings of OFD works (record drawings) form the basic record for planning irrigation management. The completion report shall include design report and work done cost estimates. The design report should explain the chak size, field channel alignments and gradients, network of surface drains and their design, details of OFD structures etc. The completion report shall explain for any deviations from the design and limitations, if any, arising out of these deviations for irrigation management.

13.2.3  Functional utility:

The purpose of the OFD works is to provide timely and adequate supplies of water to each holding and preserve environmental balance as well, by avoiding seepages, leakages and stagnations of water which trigger problems like water logging, causing adverse impact on environment. To achieve this functional utility, the planning and design of OFD works has to be hydraulically better and socially acceptable. The OFD works also need to be such that these are economical for the construction and maintenance. The functional utility of OFD works depends on levels of accuracies and quality of construction. In a water delivery system, accuracies are very important. Separate tolerances are, therefore, prescribed for different works of on-farm development. The quality of construction governs the cost of maintenance and overall life of OFD works. Thus the functional utility of OFD works is governed by following aspects

i) Hydraulic design

ii) Economy for construction and maintenance

iii) Social acceptance i.e. User friendliness to community of farmers who will be actually using OFD works and

iv)Levels of accuracies and quality of construction. These issues need to have a proper bearing in approach to design and execution of OFD works.

13.2.4  Farmers Participation:

Success of canal irrigation depends on the response of the farmer, both as an individual and as a member of the group benefited by the outlet. The irrigation facilities should be designed with a view to meet his requirements, particularly in respect of land forming. Active participation of the farmer at the stage of design should therefore be encouraged. This will also help in building up of an atmosphere of common purpose and thereby in the unification of the beneficiaries into a homogeneous group. The Irrigation Departments have taken a decision to promote and expedite the formation of WUA’s, so that all the created potential under various projects is taken over by Water Users’ Associations. The Govt. is also promulgating separate Act for farmers’ management in Irrigation system. Hence, it would be necessary to revamp the approach, if necessary, in accordance with the provisions and procedures laid down by the Govt. from time to time

13.2.5  Organizational Coordination:

The works from the canal head down to the distributory and from the distributory head to the outlet are carried out by the Construction Organization (C.O.) of the Irrigation Department. The outlet of a capacity of about 30 litre/second is the last Government structure on the canal system. Below outlet, OFD works are the community works. Design and construction proceed on the basis of the location of the outlet and its sill level. Experience has shown that when the work is done in isolation by construction Organization and Command Area Development wing, many a time errors creep in. To ensure a coordinated effort, it is necessary at the stage of design, that the design of a minor is treated as an overlapping function. Thus the PWD/WRO/AED/CADA should not consider the design and layout of a minor as a work unrelated to the work below the outlet. Instead, at least conceptually, the process of design of the works below the outlet, should continue upto the head of the minor. In near future, Water Users’ Associations may take up the work of design and construction.

13.3 Procedure for taking up OFD works:

The OFD works are part of CAD works. The cost estimates for OFD works are generally formulated in two parts.

a) Part I works.: Cost estimates for chak water delilvery system, field channel protection works and surface drainage works in a chak.

b) Part II: Cost estimate for land forming works for each holding.

The design and cost estimates for Part I works shall be done for “the chak system” i.e. a group of chaks under the command area of minor. This is essential because the design of a chak delivery system should not be done in isolation without consideration of the adjoining chaks. This helps to decide the efficient way of designing surface drains for the overall topography and so also the disposal of excess irrigation water. The overall average cost per ha for Part I works in “the chak system” may be compared with the prescribed cost norm.

The cost estimate for land forming works is prepared on individual holding basis after getting consent of concerned farmer and completing the financial formalities.  The design and cost estimate for field channel protection works may be done for each chak separately. The construction of OFD works may be taken up as per Govt.’s prevailing circulars and instructions in accordance with various provisions in Govt. Resolutions and Acts in vogue. As far as possible the OFD works may not be taken up till the formation of WUA.