India's Bridges: Highway 4 Culvert Bridge near Lodai, Gujarat (1) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.
|February 2001( 23.3893 Degrees, 69.7708 Degrees) Highway 4 Culvert Bridge|
In an earlier blog (August 26, 2011) I discussed the options available when two roads cross (stop sign, turnabout, bridge, interchange, etc.). In this blog I want to briefly discuss the options available when a river and a road cross.
For dry or shallow riverbeds, an economical option is a ford. The ford (also called a causeway) is carefully designed to carry the occasional storm runoff without flooding or eroding the road and without endangering the passing motorist. The roadway usually dips down and a concrete slab is provided across the roadway to carry the water.
Probably the most common solution for carrying low volumes of water is providing a culvert under the road. Culverts can vary from small diameter pipes (shown above) to 10 ft by 10 ft multi-cell boxes.
When the flow is too large to be safely carried by a ford or a culvert, a bridge is provided. The area (and height) under the bridge is designed to handle the 100 year runoff (I think the criteria varies depending on the agency you have to satisfy). I learned how to calculate runoff using nomographs, which allowed me to pass my engineering license exam many years ago. The term 'bridge' usually refers to a water crossing.
What other options are there? I've seen a bridge carrying a river (with boats) over a road but that's not too common.