Padma Multipurpose Bridge Project

About 2 km length through riverbed with average level of 0.0m PWD About 1 km length through chars with average level of +3m PWD Maneuvering areas – about 300m x 300m in 20 locations per year, average dredged depth 5m (equiv to from +0.0m PWD average to -5.0m PWD)27. Above activities will generate substantial quantity of dredged material – depending on contractor’sdetailed methodology and plant/equipment. During Stage 1 of the “limited 2-stage” bidding process itis expected that each prequalified bidder will describe its methodology of construction and it will thenbe possible to estimate these quantities more reliably (the bidders are expected to put a lot of effortinto optimizing their overall costs and reducing their risks) for this type of work activity. The tender andeventual contract documents will require the contractor to submit its temporary works proposals(including temporary access channels/maneuvering areas) at the appropriate times for assessmentand acceptance by the Engineer. The improper disposal of dredged material in the river water mightpose potential threat to aquatic habitats and siltation in navigation channel in downstream. A dredgematerial disposal plan is prepared and presented in Chapter 8.28. Impact of Pile Driving on Important Taxa: Hilsa, Gangetic dolphin, and winter birds (migratory)were identified during the bi-monthly ecological surveys in relatively high abundance close to theproject site (Table 3-15) and are considered to be the most likely taxa to be affected by pile driving. Inthe following section, impacts of pile driving on Hilsa, dolphin, and migratory birds are discussed ingreater detail. Impact on Hilsa Migration29. Pile driving will have a significant impact on the Hilsa migration. The annual Hilsa migration hasthe potential to be affected by construction especially during piling on their migratory routes. It ispossible that these activities may result in temporary changes in migratory patterns when constructionis being carried out. Juvenile Hilsa migration in the bridge site predominantly takes place duringMarch-May. Further, Hilsa uses deep channels (>10m) for their migration and there are two suchdeep channels in the Project alignment near the left bank as per the August 2008 and August 2009bathymetry. So any piling activity in the deep channels of the river during their migration period willhamper their migration pattern.South Bank: Janjira.North Bank: Mawa.Forty One @ 150m Truss Spans Across the Padma River from Bank to Bank.Month 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41Jan 1Feb 2Mar 3Apr 4May 5 Hilsa Migration &Jun 6 Dolphin Breeding SeasonJul 7Aug 8Sep 9Oct #Nov #Dec #Jan #Feb #Mar #Apr #May # Hilsa Migration &Jun # Dolphin Breeding SeasonJul #Aug #Sep #Oct #Nov #Dec #Jan #Feb #Mar #Apr #May # Hilsa Migration &Jun # Dolphin Breeding SeasonJul #Aug #Sep #Oct # Schedule of SubstructureNov # Piling Activity that Impacts Hilsa River bed (Aug 09) along Bridge alignmenDec # Schedule of Superstructure Migration & Dolphin Breeding River bed (Aug 08) along Bridge alignmenFigure 7-6: Impact of piling schedule on Hilsa Migration and dolphin breeding30. A construction window is proposed for piling schedule to reduce the impact on Hilsa migration.Since juvenile Hilsa migration in the bridge site predominantly takes place during March-May throughtwo deep channels located on Mawa side, it is recommended that no piling activity will be taken upduring March to May in deep channels. Location of the deep channels (as observed from thebathymetry survey during 2008 and 2009) and the proposed piling restriction is given in Figure 7-6. It543210‐1‐2‐3‐4‐5‐6‐7‐8‐9‐10‐11‐12‐13‐14‐15‐16‐17‐18‐19‐20‐21‐22‐23‐24‐25‐26‐27‐28‐29‐30Elevation, m PWD7-12