The Editor, Sir:

I have noted a few letters to the editor in recent times on the matter of 'fixing' the Flat Bridge in the Bog Walk gorge. Suggestions such as raising the bridge or somehow fixing it have been brought forward, and the common thread running through these letters is, more or less, that if Jamaican engineers cannot do it, bring in the foreigners.

As a Jamaican engineer, I would suggest these letter writers consider the following:-

1. The roads leading up to, and following the bridge are, in many places almost at the level of the river. So, if you're going to raise the bridge, you also have to raise a good part of the roadway as well. Then, consider how high you will have to raise the roadway. Kindly look at the high water marks, the bamboo roots that floated on top of the flood water and lodged in the tree branches. Maybe 10 meters high? You would have to build high, erosion-resistant walls to protect the sides of your raised roadway. Not so practical or cheap, eh?

2. Install handrails? The debris the river carries when it is in spate includes stones, tree trunks, and the like. These hit the leading edge of the bridge facing the flow with considerable force. Look at the little half round concrete bumps on either aside. Have you noticed that every time they fix them, and a flood occurs, that the upstream side is hammered away again by rocks in the water? To put handrails on the sides of the bridge is possible, but, if you can afford to rebuild them every time the river floods, well, go ahead.

A wider bridge as might be needed to carry two lanes of traffic, designed to survive such extreme conditions would have to have a very hard upstream edge (that is, a heavily armoured edge) and handrails that would fold into pockets in the upper surface when the river begins to flood. This, as it is practically impossible to construct handrails that stick up into the flooding river, straining out the tree trunks, small boulders and other debris. If you did manage to construct such invulnerable handrails, consider the new foundations required to resist the force of water on the trapped debris. Look at the train rails used to make the handrails on the bridge over the Sandy Gully on Waterloo Rd. Aren't they bent into shapes looking more like pretzels? And that is in a flow less than the Rio Cobre.

Making the bridge wider and installing handrails is easy, raising the bridge and roadways, is not. It takes only the Government to have enough confidence in Jamaican engineers such as myself and others, to design an improved bridge, understanding the practical limitations on the design, and not automatically believing that foreign engineers are always superior, to get the job done.

The limitations being, don't drive into the gorge if there is heavy rainfall in the upstream area, expect to have to take a route when it does flood, and expect to have to clear some debris off the road afterwards. The roadway as is, has considerable load-carrying capacity and is very useful.

I am, etc.,

HOWARD CHIN, P.E.,

Member Jamaica Institution of Engineers