Diagnostic study of failures of hydraulic structures in Bangladesh - case studies of failures in Chittagong district

Abstract

Many hydraulic structures such as regulators, drainage sluices, weirs, water retention structures etc. have been constructed in Bangladesh for water resources development aimed at flood control, irrigation and drainage. Many such structures are under construction or at planning and design stage. However, many of the completed structures are not functioning properly due to various reasons. This study was taken up to establish the factors leading to such failures in functioning. Although there are evaluation reports on the performance of water resources development projects, which have identified the causes of failures to hydraulic structures, no indepth study was carried out. With an aim to quantify the contribution of various factors this diagnostic performance evaluation was carried out. In this study, a critical evaluation of the present practice of the design, construction and operation and maintenance for various hydraulic structures was also carried out. Under this study a global survey of all hydraulic structures in Chittagong area was condllcted. Chittagong area was selected because it contains hilly region as well as deltaic flood plain. All structures were first located with the help of concerned officials responsible for their operation and maintenance and then their present performance levels were evaluated with the help of a questionnaire. In depth analysis of failures was then carried out for four selected structures which included two water retention structures in the hill streams and two tidal sluices in the deltaic flood plain. The factors contributing to the failures have been categorised under (a) design and planning issues, (b) construction deficiency and"(c) improper operation and maintenance. This study found that about 50 per cent of the completed structures were not functioning properly to provide with the intended benefit. Due considerations were not given to the detailed hydrological analyses. Attention given to hydraulic analyses was also inadequate. In general much attention was paid to structural design. The design of hydraulic structures are based on the available water level and rainfall data. But there are a lot of errors in data collection. There are structures built across ungauged hilly streams without appropriate data of the catchment hydrology. Many of these structures were damaged due to flash floods. It was observed that repairs were done based on original design without investigating the reasons for failure and thus the repaired structure remained vulnerable to future events. Construction deficiency have caused serious damage to hydraulic structure leading to tota! failure and such deficiencies were observed in many structures. The main construction deficiency was in concreting; in many cases the constructed thickness of section was less than the design thickness. This was confirmed by measurement during field visits. Often absence of quality control, poor supervision and difficult working conditions led to poor concrete quality. The absence of proper operation and routine maintenance arrangements were common to all completed hydraulic structures. Thus the conditions of the Structures deteriorated gradually and eventually many of them became inoperative. There were no operators engaged at the structure sites and the gates and fall boards were not opened during flash floods. " In such situations the structures failed due to overflanking. There were Project Committee in some of the structures who were responsible for operation but they were ineffective. Indepth studies were carried out for Mondakini and Harwal Chari water retention Structures in Fatikchari, and Bamansunder and Ichakhali sluices in Polder 61/2, Mirsharai. The major cause , of failure of water retention structures was the absence of proper operation and for tidal sluices, construction deficiency was the major cause of failure.