Padma Multipurpose Bridge Project

L eq (1 hr) (dBA)Train SpeedDistance to Reciever (m)(km/h)25 50 75 100 20080 63.4 60.4 58.7 57.4 54.4100 64.2 61.2 59.4 58.2 55.2125 65.4 62.4 60.6 59.4 56.4Note : Based on Estimates in Transit Noise and Vibration Impact Assessment, FederalTransit Administration, 200697. Pier Scour: Natural scour occurs at certain points on a natural channel under the influence ofvarying flows, sediment transport, channel shifting and other fluvial processes. Local structureinducedscour results from interference with natural flows by bridge piers and abutments, river trainingstructures etc. Where a structure is in place, it is not always easy to distinguish between natural andstructure-induced effects. The deepest scour is usually, but not always, associated with the highestflows in the river, at least up to the bank-full stage. Once bankfull conditions are exceeded the flowmay tend to straighten out and the velocity may not increase appreciably. Therefore, on braided orhighly Anabranched Rivers the worst scour condition may occur near bankfull conditions. Provisionalestimates of natural scour have been determined as follows: Lowest bed level outside of the flood season: -37m PWD Provisional estimate natural scour level (2 year) -39m PWD Provisional estimate natural scour level (100 year) -50m PWDMajor Positive Impact98. The major positive impacts due to the construction of the bridge are:Transport CommunicationEconomic development99. Transport Communication: During O/M stage of the project the bridge will carry road and futurerail traffics which will have potential significant positive impact on transport. The projected road trafficshave been presented in Chapter 2. The bridge will provide significant travel time savings drivers inthe corridor, particularly between the Dhaka Division to the south-east of Bangladesh and possiblyonto India. These travel time savings are expected to be in the order of 2 hours for cars and bus, to10+ hours for trucks by 2014. Opening year traffic is expected to be 12,056 vehicles per day, growingover 75,636 in thirty two years.100. Economic Development: The Padma Bridge will provide a vital missing link and will supportdevelopment in an area that has to date been poorly serviced by the road network. The trafficforecast included induced traffic, which is arising from new landuse or economic development thatoccurs as a result of the implementation of the bridge. The cost of travelling for people living orworking in the vicinity of Padma Bridge will be reduced due to the better connection. This means theycan travel further and more often. The impact of additional and new trips has been applied by applyingan elasticity of induced passenger traffic, a 10% increase in passenger traffic is considered asinduced traffic in traffic analysis.7.2.3.2 River Training Works101. There will be significant positive impact with the construction of RTW in bank protection. InMawa side, about 2km and in Janjira side about 14.5km (3.76km optional) protection work will bringsignificant benefit to the people living close to the bank. The benefits will be immeasurable in Janjiraside where bank is very erosion prone. About 15,000 people will be directly benefitted due to theprotection work.102. RTW works predict two future impacts such as: additional flooding due to possible backwatereffects from the bridge and river training works, and additional erosion caused by the same works.While flooding impacts can be calculated using hydraulic models, it will be difficult to establish to whatextent upstream erosion might be ascribable to the bridge: Future River changes (whether bridge-7-28