Resource Consents

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Stream Crossings

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With the intensification of all types of farming and increasing farm size more vehicles and stock now have to cross streams and creeks.

Herds crossing streams have a major impact on the water quality of rural waterways. However by installing properly designed crossings, farmers can help protect the quality of Taranaki’s waterways.

Improving the quality of our waterways is a priority for farmers and is the basis of the Dairying and Clean Streams Accord which is endorsed by Fonterra and government agencies such as regional councils, district councils, Ministry for the Environment and Ministry of Agriculture and Forestry. The ultimate goal of the Accord is for water quality to be suitable for fish, stock drinking and recreational swimming.

To help achieve this goal one of the targets of the Accord is to exclude all stock from waterways. This potentially means a large number of stream crossings still need to be installed on Taranaki farms.

Many native fish such as whitebait and eels migrate between the sea and freshwater as part of their lifecycles. Fish passage needs to be provided along the length of waterways to enable native fish and trout to access important habitats and small streams. Incorrectly installed or eroded fords and culverts can create waterfalls, high jumps or swift water. These barriers restrict natural migration and will ultimately lead to the decline of these fish.

Bridges or culverts are the best options for keeping stock and animal waste out of waterways.

                     

The advantages of well designed and installed stream crossings are:

• Less erosion and maintenance.
• Easier access during floods.
• Quicker travel times around the farm.
• Healthier stock, e.g. less stress, lameness and incidence of liver fluke.
• Cleaner water (less bacteria and sediment discharges, safer for swimming and stock drinking water).
• Better fish habitat.
• Access for fish upstream and downstream.
• Improved value.
• New opportunities for farm management.Return to top

Well designed stock crossings are not only good for the environment, they also make good business sense, save time and money and improve stock welfare and farm profits.                

Do I need a consent?

If you are building a bridge or a culvert on your farm you may need a building consent from us or a resource consent from Taranaki Regional Council. 

We consider regulations under the Building Act 2004 and look at the safety and structural integrity of the culvert or bridge. The regional council considers the effects the culvert or bridge may have on the stream flow, aquatic life and erosion, within the Resource Management Act 1991.  

Your culvert or bridge may not require a consent if:

• The cross-section area of the stream channel (width of stream x height of banks) is less than 10m².
• The culvert diameter is less than 1m and there is less than 1m of fill above the culvert.
• The bridge has no abutemetns in the stream bed and the deck is above the stream bank.
• Your bridge will not carry vehicles.
• A footbridge is that than 1m from the streambed.

Note: No in-stream work is allowed between 1 May and 31 October as this is a fish spawning period.

If your culvert or bridge does not meet these requirements a consent may be required. However, ensuring your bridge or culvert design follows these recommendation getting a resource consent will be much simpler.

If you have several crossings on your property, you can apply for just one consent from the Taranaki Regional Council to cover all the crossings.

Bridges

Bridges are the best option for stream crossings. Although they may be more expensive initially, this is often made up for by many benefits.

• Bridges reduce work in the streambed during construction.
• The effects on water quality are minimal, with less sediment and habitat disturbance.
• Very little ongoing maintenance is required.
• Bridges can be used in most conditions, e.g. floods.
• The natural streambed is retained and there is no barrier to fish passage.
• A bridge does not alter the natural course of the stream or reduce the channel capacity, thereby minimising erosion and flooding.

Bridges are best for:

• Large streams
• Streams with large amounts of debris (branches, logs, etc) or rock movement.
• High banks.Return to top

When designing a bridge consider:

• What you are going to use the bridge for (e.g. herd size, vehicle weights). This will determine what size and design.
• The best location for bank height and channel width. Ideally the bridge should cross at right angels to the stream. Consider moving the race to a better location if necessary,
• The need for solid foundations on the river banks.
• The length of the bridge should be greater than the width of the stream so that the abutments don’t encroach on the stream and restrict flows (this could cause erosion).
• The height of the bridge should be adequate to cope with flood flows and debris.
• Abutments and wing-walls should extend above flood levels and be buried well below streambed depth to prevent undercutting.
• If possible centre piers should not be used.
• Prefabricated concrete decks and standard designs may reduce costs.
• Minimising the runoff to the stream to protect water quality. To do this:
  • Raise the bridge slightly above the approaches to direct runoff away from the stream
  • Construct a lip on the edges of the deck.
• Include safety requirements in the design (e.g. edge railings and signage for bridge loading factors).

Culverts

Culverts often provide a cheaper option for streams that do not carry a lot of sediment or have high floods.

Different types of culverts are suitable for different types of streams:

• Single round culverts suit small streams or streams with medium to high banks.
• Arch or bottomless culverts are good for wider streams with low to medium banks. These culverts also help retain a natural streambed which is good for fish.
• Box culverts can be used in wider streams with low banks, or streams with medium bank heights. Due to wider openings they may not block as much as multi-barrel culvert crossings, however they can be a barrier to fish if water is very shallow. Install the culvert on an angle to create a deeper channel on one side for fish passage or bury the bottom of the culvert into the streambed.
• Multi-barrel culverts are generally not recommended as they block easily, require a lot of maintenance, and erosion is common. These culverts often create a barrier to fish passage. Consider installing a bridge or single larger culvert instead.

Getting the sizing and installation of culverts right will generally save you money in the long term by avoiding failure and the need for replacement, not to mention erosion and damage to the stream.

Location
Choose a straight stretch of stream with a low gradient (bends in the stream near culverts are more likely to cause erosion).

Pipe size
Pipe size is very important and generally bigger is better. The culvert width should be equal to or greater than the average stream bed width so that the culvert does not restrict flow (this will increase water velocity and the potential for erosion). Check other culverts nearby that are functioning correctly and use a similar size.

Materials
Suitable materials for culverts in order of preference are:

• Rough concrete – provides variable velocity for fish passage.
• Corrugated aluminium – slows velocity and provides rest areas for fish.
• Corrugated galvanised steel (note: bottom may rust, particularly in areas with agricultural runoff).
• Plastic – flexibility suits softer soils; corrugated preferred.

Culvert length
This should be less than 25m and ideally as short as possible (a consent may be required if it is longer). Water flow through the culvert should be slow enough to ensure better fish access up stream. Rocks placed in the stream just below the downstream end of a culvert can increase water level and reduce water speed to help fish passage.

Gradient and alignment
Position the culvert so that the gradient and alignment are the same as the existing stream. This prevents scouring and erosion at the inlet and outlet.Return to top

Streambed characteristics
Try to retain or simulate the natural streambed to help fish passage – use rocks where possible. The bottom of the culvert should be burled below the existing streambed level by at least 20% of the culvert diameter. This helps to ensure that no waterfalls will develop downstream of the culvert.

Banks
Armour with rock riprap or a headwall at the outlet and inlet if erosion is likely. This will help to retain earth fill and will prevent undermining, improving conditions for fish passage long term.

Fill
The fill over a culvert should be less than 1m high. Higher fills will create  greater water depths if water backs up resulting in high velocity and erosion and you are also likely to require resource consents from district and regional councils. Also check pipe manufacturer recommendations.

Pipe bedding
What the pipe sits on is very important for maintaining the culvert for the long term. Bedding should include approximately sized gravel, be firm and support the pipe. Build up the embankment and fill with 200mm soil layers and compact each layers. Culvert suppliers and contractors can help with installation information.

Spillway
Install a spillway to control overtopping of the culvert in large floods. Install to the side of the stream away from fill materials. The spillway should be wide and level across the access track, so that water flows over it at a shallow and even depth.

Other considerations

During construction and installation of your bridge or culvert also consider:

• Using an excavator and an experienced operator for site preparation and placement of pipes, thereby minimising soil disturbance and cost.
• If practicable, de-watering or diverting water from the site during construction will reduce the amount of sediment that enters the stream.
• All in-stream work should be conducted as quickly as possible during low flows to reduce disturbance and effects on water quality and ecology. Generally the Taranaki Regional Council only permits construction between 1 November and 30 April, to protect fish at spawning times.
•  Keep contaminants (eg: concrete, fuel, soil stockpiles) out of the stream channel.
•  Re-seed disturbed areas after construction.
• Runoff from tracks/races should be diverted away from the stream using earth cut-off drains, to direct runoff into paddocks where the grass can act as a filter.
• Set the bridge or top of culvert slightly higher than the approaches so that runoff is directed away from the crossing and the stream.

Regular maintenance
Keep the culvert or bridge clear of debris, as this reduces flow capacity, resulting in additional flooding and possible damage. Check regularly, especially after heavy rain events.

Related links

• Dexcel
• Federated Farmers
• Fish and Game New Zealand
• Fonterra
• Stratford District Council
• MAF Sustainable Farming Fund
• Taranaki Regional Council

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