Restricting use
Keeping stock off and away from the abutments of bridges can be a problem. Although a bridge should be able to withstand knocks and use as a rubbing post by cattle, stock will puddle the ground around the bridge and damage the stream bank. Fencing can be used, but this is troublesome to build, requires stiles or gates, and looks rather ugly. A better solution may be to surface the ground around the bridge and revet the bank to prevent damage by puddling, and put a gate or stile on the bridge if it is necessary to keep stock off it.
The inner step support is attached to the main beam as shown below.
Single beam bridges usually only require a single bar to keep stock off. Some situations may require a watergate underneath to prevent stock going up or downstream.
Steps
Construct steps with care so they do not spoil the appearance of the bridge. Two methods are shown below, using stone or cast concrete.
The following two examples show how the appearance of a bridge can be spoiled by poorly constructed steps, especially where several different types of materials are used.
Design and construct carefully the approach to the bridge. Often this acts as a gathering point where walkers wait to cross or admire the view, and an area may need to be surfaced for this purpose.
Scour protection
This may be needed for a metre or so upstream and downstream of the abutment on fast-flowing streams. The downstream side can become scoured as water eddies around the abutment.
Boulders
These are simply piled up on either side of the abutment. This is the simplest but least durable method.
Stone pitching
Set the stones with their long axis into the bank. Make sure the profile is smooth so that the water flows unimpaired.
Revetments
These are described more fully in Chapter 11 – Erosion control and vegetation restoration. Listed below are products designed for bank stabilisation, and which could be used to protect banks around bridge abutments and end seats.
Gabions are plastic coated wire mesh cages, which are filled with rock from the site. They are not attractive initially, but will become hidden with vegetation in suitable habitats after a year or two. They can be planted with clumps of reed, reed canary grass or other marginal vegetation.
Enkamat is a lightweight three-dimensional polyamide matting, used for surface protection and root reinforcement, and available in various grades. It is rolled out onto the bank, pegged down, seeded and filled with topsoil. For greater protection below the water, Enkamat A can be used. This contains bitumen-bound gravel, through which plants can grow.
Wyretex no. 7 or 8. Rake the slope, then lay the Wyretex and pin at 500mm intervals. Cover with a 50mm layer of soil, tamp down, and seed.
