What are the environmental impacts of building a railway bridge over a river?

Question

may i know the environmental impacts to the river bed and water quality when a railay bridge is constructed over a river . also how to manage the river bed to its original natural state.

Answer 1

The answer all depends on the physical aspects of the river (i.e. soft bottom, rocky bottom, hieght of banks from river, width of river etc).

There are also hydrological considerations such as water velocity, storm surges, amount of water flowing down river etc.

Also what wildlife and vegetation is present on the site.

The impacts can be divided into short-term and long-term.

Short-term

The loss of riparian habitat within the construction area.

Increased sediment load which may smoother aquatic organisms downstream.

Water quality would be effected by increased sediment load and the release of any substances either bound in soil or introduced by building materials used.

Disturbance during construction works (noise, vibration etc)

Long-term

Shadow, which may prevent re-colonisation (Depends on bridge width and height above river)

Habitat fragmentation - The bridge may act as an obstacle for migratory species or species with paths running accross the area (otters etc)

Increased erosion on banks and around footing or bridge.

Vibration may also cause some disturbance.

There are several options that can be used to restore the riverbed and surrounds to its original state.  This might range from replanting the riparian habitats to help bind the banks, planting marginal species, providing areas for natural recolonisation to occur, the use of shelving to provide walkthroughs under the bridge for otters etc and possibly providing nooks and crevices to provide nesting sites for birds and bats.

It all depends on what the habitat is and what wildlife occurs.  A survey should be carried out to assess what is present and what impacts the construction will have, to enable a decision to be made as to the best option for restoring the habitat, or if the bridge is in a suitable location.  A Environmental Impact Assessment might be required to take into account the questions you have asked.

There are several case studies that examine river habitats restoration, you may have to look for these either in past construction works or on-line.