Multi criteria prioritization of storm water drain works for an urban area in the Chittagong hill tracts

Abstract

Stonn water flood hazard due to inadequate drain is a major concern in the Paurashavas in the Chittagong Hill Tracts (CHT). To address the issue of urban storm flood hazard, drainage master plans have been prepared for the three Paurasbavas in the CHT nnder the Urban Governance and Infrastructure Improvement Project (UGIIP) ofl..ocal Government Engineering Department (LGED). The plan would be implemented over a period of 10 years. The availahle fund for drain construction in each year is a fraction of the total requirement. Therefore, a method for prioritization of drain construction in the intermediate years is needed. Development of Multi Criteria framework for prioritization of storm drain works is the ultimale goal of this research. This research has been carried out by selecting Bandarban Paurashava as the study area. A questionnaire survey has been carried out to assess public response on stonn water flood hazard. The survey has covered 190 households which was obtained on the basis of statistical sampling formula. The distribution of J 90 households among 9 Wards is in the proportion 10 Ward population. The purpose of the survey is 10 assess flood situation and its consequences. The respondents identified location of flood affected area, causes of stonn water flood and public life disruption due to storm water flood. Area-elevation relationship has been developed based on the contour map of the study area. Volume-elevation relationship has been derived from the area-elevation relation. A rainfall depth of 123 mm has been used to estimate runoff volume. Based on runoff volume, flooded area has been identified using volume-elevation and area-elevation relationships. Besides flooding, nmoff ways along hill slope areas make disruption to the public and private properties. The runoff ways along hill slope areas have been identified based on contour map. A total of 17.8 kID of new drains have been proposed in the Master Plan for Bandarban Paurashava. The new drains consist of 78 independent drains. Five criteria have b<;en selected to represent storm flood hazard that would serve as the basis for prioritization of drain construction. These criteria are drain deficiency, flood magnitude, population suffcring, damage characteristics and social vulnerability. Magnitude of five criteria have xlii , been calculated for every drain. Standardized value of each criteria arc added for a drain to get total score for the drain with the help of Linear Additive Model. The scores of 78 drains are ranked in order of decreasing magnitude, and the rank represents priority order. The scrics of 78 ranks is to be divided into 10 segments to set the year-wise implementation sehedule of78 drains over 10 years. The segments are to be such that the total drains in a segment ean be implemented using the budget for that year.