Padma Multipurpose Bridge Project

ProjectActivitiesConstruction ofSubstructure(pile drivingandconcreting)EnvironmentalImpactsUnderwater noiseimpacts on fisheriesand other aquatic lifeImpact on the annualjuvenile Hilsamigration and otherfish species.Impact on dolphin andother aquatic life.Mitigation/Compensation MeasuresUse vibratory hammer. Under those conditions where impact hammersare required for reasons of seismic stability or substrate type, it isrecommended that the pile be driven as deep as possible with avibratory hammer prior to the use of the impact hammer.Monitor sound levels during pile driving to ensure that they do notexceed the NOAA or any other international recognized criteria. Implement measures to attenuate the sound when sound pressurelevels exceed the NOAA or any other international recognized criteria.Methods to reduce the sound pressure levels include, but are not limitedto:ooinstallation of underwater enclosures to minimize soundSurround the pile with an air bubble curtain system or air-filledcoffer dam.o Use a smaller hammer to reduce the sound pressure. Thesound produced in pile driving has a direct relationship to theforce used to drive the pile. A smaller hammer will have lessforce on the pile therefore, producing less sound.Use a hydraulic hammer if impact driving cannot be avoided. The forceof the hammer blow can be controlled with hydraulic hammers, andreducing the impact force will reduce the intensity of the resulting sound. A construction window is proposed for piling schedule to reduce theimpact on Hilsa migration. Since juvenile Hilsa migration in the bridgesite predominantly takes place during March-May through two deepchannels (>7m) located on Mawa side, it is recommended that no pilingactivity will be taken up during March to May in deep channels. It isrecommended that contractor has to conduct the bathymetric surveysevery year immediately after the monsoon season to locate these deepchannels and revise the piling schedule accordingly. Hilsa migration monitoring as per the schedule of ecological survey toconfirm the actual depth of migration at bridge siteRestrict piling during dolphin breeding period (April-July) in channels with>7m water column. During other season, an exclusion zone of 500m radiusshould be monitored for at least 30 minute before the start of piling. Ifdolphins are observed in the exclusion zone, piling works should be delayeduntil they have left the area. If dolphins enter the exclusion zone after pilingBudget,USD30,000(Ref:MonitoringBudget)and wild lifemonitoringbudgetPart of civilworkscontractand wild lifemonitoringbudgetPart of civilworkscontractInstitutionalResponsibilitiesImplementationContractorContractorContractorSupervisionCSC, PIU,ExternalMonitorCSC, PIUCSC, PIU,ExternalMonitor8-15