Culverts are essential for draining water across a road. They only work if the culvert size matches its intended use.
Recommended maximum culvert spacing (metres) for non-ridge top roading
|Grade||Soil or rock erodibility|
|18% (1 in 6)||40||80||120||200|
|14% (1 in 7)||50||90||140||220|
|12% (1 in 8)||55||100||160||240|
|11% (1 in 9)||60||115||180||260|
|10% (1 in 10)||65||130||210||300|
|8% (1 in 12)||80||165||250||350|
- The culvert is located on hard ground.
- The solid bund at the culvert entrance helps to ensure water does not by-pass the culvert.
- The culvert mouth is easy to clean with an excavator.
- The culvert has a marker peg and is GPS located.
- The culvert inlet is easily blocked.
- The culvert is hard to keep clean.
- The culvert will be by-passed in heavy rain. This will damage the road and cause erosion.
- The culvert outlet is armoured by rock to reduce sedimentation.
- Installed during road construction, not after metalling.
- Set at a minimum of 20 degrees across the road and down slope to reduce blockage.
- The ground around the pipe has been compacted.
- The pipe has the correct amount of soil and metal above it to stop it being damaged by traffic.
- The culvert has sufficient fall so water drains from the pipe and doesn’t block easily.
- The trench is flat and to a depth recommended by the manufacturer.
- The culvert bed has been compacted.
- Pipe sections are joined in the trench.
- No sharp rocks or objects are in the backfill.
- Care is taken to compact soil around the pipe.
- Two non-marked culverts in a row have been wrecked.
- The culverts were not marked so grader damage was more likely.
- Water has by passed the culverts and is heavily scouring the road.
- The culvert inlet is protected from being blocked by slash.
- The culvert should not drain straight into the stream if there is no sediment control above the inlet.
- The road should not be built as close to the stream as this, unless there are no other feasible alternatives.