Construction
The low water crossing was developed from the traditional ford. A ford permits vehicular traffic to cross a waterway with wet wheels. The term “low water crossing” implies that the crossing is usually dry, while “ford” implies that the crossing is usually wet.
A simple low-water crossing can be constructed with culverts. Culverts (often concrete pipes) are used to carry the water in a stream keeping the crossing surface dry for most of the year. High flows, e.g. spring runoff or flash floods, flow over the top of the crossing, as the culverts are not large enough to carry these flood-type runoff events.
A more elaborate low-water bridge will usually be an engineered concrete structure. There are thousands of such structures in the western United States; some of them accommodate four-lane city streets or highways. Typically, a low-water bridge that accommodates a high daily volume of vehicular traffic will be underwater only a few days per decade.
Read more about this topic: Low Water Crossing
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