As development pressures rise along the Barrage reach of the Vaal River so also do the costs of flood damage. By means of computer-operated flood plain management programs developed in the Hydrological Research Unit it has been possible to determine the heights to which floods of various recurrence intervals are likely to rise, and thus to delineate areas that would be affected. The computer is programmed to plot the water surface profiles for floods of various return periods as affected by bridges and other obstructions. The printout shows chainage, water surface elevation, energy level, velocity, Manning etc. The flood marks left by the severe 1975 flood served to calibrate the flood plain model.
In view of the relatively gentle gradient of the Vaal within the Barrage reach, the floods are not violent in character and most of the low-lying areas affected at high flood are inundated by slowly moving or stagnant water. Velocities even during high flood seldom exceed 2 m/s in the main channel or 0,5 m/s on the flood plains.
It was found that all existing bridges and the Barrage structure can be negotiated with negligible afflux by floods of up to 200-year return period.
In the execution of contracts for civil engineering works, disputes arise from time to time. This is not surprising if the nature of the works and the circumstances under which they have to be carried out are borne in mind. Most civil engineering contracts therefore make provision for the settlement of disputes.
These provisions will be discussed in this article with specific reference to the provisions of the General conditions of contract 1982 for use in connection with works of civil engineering construction (fifth edition), which are recommended for general use by the SA Institution of Civil Engineers, the South African Association of Consulting Engineers and the SA Federation of Civil Engineering Contractors.