Crossings
Topics
3 min read
Stream crossings on dairy farms prevent harm to aquatic habitats, reduce pollution, and boost livestock health.
Well planned and constructed crossings prevent damage to the stream bed and reduce the amount of sediment, nutrients and bacteria getting into waterways. They may also improve stock health and production by reducing stress, lameness and the potential of liver fluke.
Stock Exclusion Regulations
Stream crossings for livestock using bridges or culverts are required under the Stock Exclusion Regulations.
The Stock Exclusion Regulations 2020 require all dairy cattle to use a bridge or culvert if they cross a waterway more than twice a month. All other stock are required to use crossings by 1 July 2025.
Always consult your regional council before construction and pick a suitable location. Consider the waterway size and flow before choosing the location for a culvert or bridge. Create safeguards like nib walls and runoff drains to prevent water contamination. It's crucial to follow these guidelines for a well-constructed, compliant crossing, ensuring optimal farm management and environmental stewardship. You also need to ensure the crossing does not cause a barrier to fish passage up and down the waterway.
Planning before construction
Consult with your regional council to find out what their rules are around constructing crossings and whether you require a resource consent. If a proposed crossing is on a waterway managed by the regional council for flood protection purposes, restrictions may apply.
Fish passage requirements under both the National Environmental Standard for Freshwater and regional council plans may also need to be considered.
What to build: culvert or bridge?
The type of crossing constructed is dependent on waterway size and shape, high flow levels and the types of vehicles that need to cross. Bridges are preferred over culverts to ensure normal stream function, such as flows and fish passage.
Selecting a crossing location
Ideally, a crossing point should be at a narrow point of the waterway, with flat approaches on either side or approaches that slope away from the waterway.
Avoid locating crossings where there are steep slopes leading down to it. Flat or slightly rising approaches are safer for farm vehicles, reduce the risk of stock slipping, and reduce sediment and nutrient runoff into the waterway.
Choose a straight stretch of stream with a low gradient. Bends in the stream near culverts are more likely to cause erosion.
Diverting runoff from waterways
Crossings should be constructed so that stormwater runoff from the track leading to and from the crossing can be diverted away from the stream (using earth-cut-off drains) into a grassy area.
Raised edges (often called nib walls) on the crossing will help prevent direct runoff from entering the water.
Single barrel arch culvert
(no base)
Where suitable
- Waterway less 2m wide.
- Average rainfall less than 1800mm.
This is the most preferred option for culverts as there is no base to the culvert, meaning it will likely maintain the normal stream functioning, such as flows and fish passage, and create less erosion risk and therefore maintenance requirements.
Key considerations
- Can accommodate the full width of a small stream and some of the natural bank.
- Check for erosion regularly and maintain as required to ensure integrity of the structure, and that fish passage is maintained.
What to avoid
- Avoid using culverts less than 300mm in diameter.
Single barrel circular culvert
Where suitable
- Waterway less than 2m wide.
- Average rainfall less than 1800mm.
Key considerations
- Ensure a good-sized culvert is installed to allow for the full width of the stream.
- Check for erosion regularly and maintain as required to ensure the integrity of the structure and that fish passage is maintained.
What to avoid
- Avoid using culverts less than 300mm in diameter.
- Avoid constricting the stream width which will increase water velocities.
- Bury the bottom of the culvert below the stream bed to avoid creating a 'hanging' or 'perched' culvert, which could create a fish passage barrier, cause erosion and/or alter stream flows.
Box culvert
Where suitable
- Waterway less than 2m wide.
- Average rainfall less than 1800mm.
Key considerations
- Box culverts often accommodate the full width of a waterway.
- Check for erosion regularly and maintain as required to ensure the integrity of the structure and that fish passage is maintained.
What to avoid
- Avoid using culverts less than 300mm in diameter.
- Bury the bottom of the culvert below the stream bed to avoid creating a 'hanging' or 'perched' culvert, which could create a fish passage barrier causing erosion, and/or alter stream flows.
Multi-barrel circular culvert
Where suitable
- Dependent on the catchment area, but can be used in a higher rainfall area or larger catchment than a single barrel culvert of the same size.
- Generally, one large culvert is better than several small ones as debris blockage is less likely, and velocities will be lower.
Key considerations
- Used to accommodate larger flows, and can be a cheaper option than installing bridges across large waterways. However, they will collect more debris than bridges and require more maintenance.
- Check for erosion regularly and maintain as required to ensure the integrity of the structure, and that fish passage is maintained.
What to avoid
- Ensure that low-flow and high-flow events are covered.
- Bury the bottom of the culvert below the stream bed to avoid creating a 'hanging' or 'perched' culvert, which could create a fish passage barrier causing erosion, and/or alter stream flows.
Single span bridge
Where suitable
- Good for streams less than 10m wide and will be suitable for larger streams in many cases.
- Bridges are preferred over culverts to ensure normal stream function, such as flows and fish passage.
Key considerations
- Single-span bridges provide a long-term option when constructed well with quality materials.
- Engineering advice is usually required.
- Consent is almost always required.
What to avoid
- Avoid using recycled materials such as car bodies or trailer parts.
- Avoid installing a bridge in the flow path of flood events.
Multi-span bridge
Where suitable
- Large river systems.
Key considerations
- Not common on farms and expert advice is required.
What to avoid
- Avoid taking on this scale of project alone. Ensure resource consent is sought and engineers are involved.