This paper describes the problems relating to a mechanized wide site construction in Japan. While mechanized construction in this field has been more or less systematized, there remains the need to strive for optimum efficiency in construction through development of new machineries and new construction methods, as well as through refinement of construction planning.

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Investigation of two-dimensional backwater of obstacles, or of cross-sectional abrupt changes in a flow system including a large body of water, is often required in hydraulic engineering practice. The problem envisaged is modelled with the aid of the finite element Galerkin procedure, and the fully non-linear equations to be solved are adapted for the Newton-Raphson scheme. In view of the weak formulation of the continuity equation, the scheme can be operated from a cold start (zero initial guess) which produces acceptable linear solutions in the first iterative cycle. Convergence and accuracy explorations are made through model applications to a few channel-type basins, examining their sensitivities to four system parameters defined in advance. The model is also applied to the actual system of Kojima Lake: a man-made estuarine reservoir for irrigation water supply, aiming at investigating horizontal backwater establishment due to the flow expansion and contraction in the vicinity of an influent river mouth and outlet gate, and their implications. Reasonable agreement between computed and observed velocities shows the validity and applicability of the model.

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The area benefited by a new irrigation project is determined taking into account the present land use, topographical and soil conditions of the proposed area and its surround ings. In Southeast Asia countries, however, there are some difficulties in determining the benefited area due to social and administrative factors which are different from those of Japan.
In this paper, the difficulties and process of determining a project area in a feasibility study will be discussed and some approaches to delineating an irrigation project area will be presented.

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