RISK-COST APPROACH TO INTERIM DRAINAGE STRUCTURE DESIGN

An interim drainage structure provides short service during the constr uction months of the permanent drainage structure. This study presents a risk-cost approach by which the design flood for an interim drainag e structure can be derived from the capacity of the permanent structur e, cost-capacity ratio, cost-damage ratio, and construction months dur ing a year. To accommodate various construction periods in a year, the design capacity for such a temporary drainage structure can be adjust ed to the monthly rainfall or runoff distribution at the project site. Design charts were produced for the break-even economic condition usi ng the Gumbel distribution for annual maximum analysis. Similar soluti ons were also achieved using the Exponential distribution for annual e xceedance analysis. Design methodology presented in this paper provide s an objective basis for selecting construction months and sizing the interim drainage structures.