Contents preface (VII) introduction 1—37

5.3.1. Preliminary Survey
To determine the feasibility of a proposal of extending canal irrigation to a new area, information on all such factors which influence irrigation development is collected during the preliminary (or reconnaissance) survey. During this survey all these factors are observed or enquired from the local people. Whenever necessary, some quick measurements are also made.
The information on the following features of the area are to be collected: (i) Type of soil,

(ii) Topography of the area, (iii) Crops of the area,

(iv) Rainfall in the area,
(v) Water table elevations in the area, (vi) Existing irrigation facilities, and

(vii) General outlook of the cultivators with respect to cultivation and irrigation.

The type of soil is judged by visual observations and by making enquiries from the local people. The influence of the soil properties on the fertility and waterholding capacity has already been discussed in Chapter 3.
For a good layout of the canal system, the command area should be free from too many undulations. This requirement arises from the fact that a canal system is essentially a gravity flow system. However, the land must have sufficient longitudinal and cross slopes for the channels to be silt-free. During the preliminary survey, the topography of the area is judged by visual inspection only.
Water demand after the completion of an irrigation project would depend upon the crops being grown in the area. The cropping pattern would certainly change due to the introduction of irrigation, and the possible cropping patterns should be discussed with the farmers of the area.
The existing records of rain gauge stations of the area would enable the estimation of the normal rainfall in the area as well as the probability of less than normal rainfall in the area. This information is, obviously, useful in determining the desirability of an irrigation project in the area.
Water table elevation can be determined by measuring the depth of water surface in a well from the ground with the help of a measuring tape. Water table elevation fluctuates considerably and information on this should be collected from the residents of the area and checked by measurements. Higher water table elevations in an area generally indicate good rainfall in the area as well as good soil moisture condition. Under such conditions, the demand for irrigation would be less and introduction of canal irrigation may cause the water table to rise up to the root zone of the crops. The land is then said to be waterlogged and the productivity of such land reduces considerably. Waterlogged land increases the incidence of malaria in the affected area. Thus, areas with higher water table elevation are not suitable for canal irrigation.
Because of limited financial and hydrological resources, an irrigation project should be considered only for such areas where maximum need arises. Areas with an extensive network

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of ponds and well systems for irrigation should be given low priority for the introduction of canal irrigation.

The success or failure of an otherwise good irrigation system would depend upon the attitudes of the farmers of the area. Enlightened and hard-working cultivators would quickly adapt themselves to irrigated cultivation to derive maximum benefits by making use of improved varieties of seeds and cultivation practices. On the other hand, conservative farmers will have to be educated so that they can appreciate and adopt new irrigated cultivation practices.
The information collected during preliminary survey should be carefully examined to determine the feasibility or otherwise of introducing canal irrigation system in the area. If the result of the preliminary survey is favourable, more detailed surveys would be carried out and additional data collected.