Evaluation of operation and maintenance practice of flood embankments

Abstract

Embankment, one of the earliest civil engineering structures, is still the most favoured option for flood control due to it's simple construction method and use oflocallabour and material. The recorded history of construction of embankments in Bangladesh dates back to thirteenth century. Effectiveness of the embankment is very important in delivering benefits and for this purpose effective operation and maintenance (O&M) of embankment needs utmost care. Failure of embankment is a common phenomenon in Bangladesh. This study was taken up to evaluate the present day O&M position of flood control embankments. The main causes of failure of embankments have been identified as: erosion, overtopping, public cut and improper maintenance. Embankments normally do not fail due to design deficiency. Failures due to river erosion, breaches etc., in turn can be linked to poor O&M. Many of the O&M related problems are linked to poor planning and construction. Incomplete evaluation of hydro-morphological impact inside/out side the poldered area often forces people to make public cut to remove drainage congestion. For evaluation of effectiveness of then maintenance procedure, the performance of the polder and the O&M approach as prevailed in the Meghna-Dhonagoda Irrigation Project (MDIP) was taken up. RRA of the project revealed that either operational requirements and operational problems were not considered during planning/construction stage; or committees proposed for O&M were not functioning & water control structures were under the domination of vested interest groups; or officials were not trained nor did attend to their duties properly. The study found the absence of systematic accounting of O&M expenditure on project basis. The average O&M expenditure has been found to be more than the standard rate; and yet the maintenance were of poor quality. Identification of arrangement for O&M financing was neglected as usual. The constraints to the achievement of an acceptable level of project operation and maintenance are lack of motivation, organizational & institutional difficulties. O&M resource constraint is part of a more complex problem involving lack of public consultation, construction time and cost over-run, non-availability of proper & suitable O&M manual in the field level; tasks, responsibility & accountability of concerned officials not being defined/poorly defined etc. The major issues with respect to proper operation and maintenance are: non availability of sufficient fund which affects the physical work programme, failure to recover cost, non involvement of beneficiaries, incomprehensive planning, poor construction, compaction not being done .upto required degree and overlapping of construction and operation. Deficiencies in BWDB's organizational arrangements, procedures and lack of training of field staff negates O&M activities whatever is possible within the practical circumstances. Maintenance of embankments is grouped as preventive maintenance, periodic maintenance and emergency maintenance. The O&M stage should directly involve the local population. The routine preventive maintenance has to be done by Embankment Maintenance Groups (EMGS) and periodic maintenance has to be done by Landless Contracting Societies (LCCs). The group formation may be done through Bangladesh Rural Development Board (BRDB) or NGOs. However technical supervision will have to be the responsibility of 'Bangladesh Water Development Board (BWDB)' Emergency maintenance has to be got done by engaging contractors. The study revealed that the difference of flood heights of 25 years and 100 years return periods is less than I meter. The embankment with 25 years return period if properly constructed with Im freeboard should be able to withstand flood of 100 years return period. However in extreme cases, some extra measures like flood wall of gunny bag etc., may be required to prevent overtopping. The study also revealed that there was not much difference in achievement of degree of compaction between the uncompacted and conventionally compacted embankments. The increase in cost of construction, if the conventional 4.2m wide compacted embankment is changed to the 6.5m wide road cum flood control embankment is about 2% more only. Design of embankments with dual purposes of flood control and road communication can partially mitigate the adverse impact on navigation. Construction of embank.ment-cum-public road; will ensure constant use, more attention of local people and better maintenance of the embankment itself. This type of wide embankment can be used for afforestation without any risk of damage to the hydraulically/structurally min'imum required section.