All Crossings need to consider:
- Peak Flows – Will the crossing allow enough water through during high flows?
- Will debris or ice be able to flow through?
- Fish / Aquatic Life Forms Passage – Will the crossing allow fish and/or aquatic life forms to move freely?
- Weight Allowance – Will the crossing be able to handle the weight of trucks that may not be frequent (i.e. a fire truck)?
- Span – Bridges are generally for wider crossings. Culverts are for narrower/smaller crossings.
- If a span is greater than 20′, a bridge may be required.
- Proper Siting – A stable, relatively-straight crossing is critical.
- Flood Plain – If the crossing is in a flood plain, you will want to contact your local city/county floodplain manager for their regulations and permits.
Well-Designed Bridges are the preferred crossing and, typically, have the least impact on the stream. They are best for large streams and those plagued with floatable debris or ice jam problems. Bridges have the least impact on fish.
Culvert Size depends on the size of the drainage above the culvert site; the average stream width, depth, and gradient at the crossing site; the amount of debris loading anticipated; and the performance of the crossing. Culverts need maintenance so they don’t get clogged.
Fords are best located in shallow areas with gravelly bottoms and little traffic. Even small Montana streams may become uncrossable during the spring/early-summer snowmelt.