ECONOMIC APPROACH TO OPTIMIZING DESIGN PARAMETERS

For coastal engineering works, as for other structures, the designer must search for the economic optimum point. This point represents the minimum in the sum of direct cost and cost of possible future damage. By setting up functional representations of these costs the optimum can be obtained directly. This approach is illustrated by models developed independently in the Netherlands and in Canada. At this stage the output of the models may be denoted as the 'perfect knowledge' optimum, in the sense that parameters of the cost functions are assumed to be known with complete accuracy. In the 'real world' case, however, the estimated values of the parameters will be subject to considerable uncertainty. It is shown that because of this uncertainty the 'real world' design optimum will generally be shifted to give a structure larger than that indicated by the 'perfect knowledge' assumption. The novel contribution of the present paper consists of analyzing this shift to obtain simple expressions for the apparent overdesign due to uncertainty and for the resulting cost increase. An illustrative example is presented.