Restoring a wetland - where to begin

How do I restore a wetland?

All wetland restoration work should be as simple as possible. Your goal is a wetland that takes care of itself with little input from you.

The steps that follow are a general guide for swamp restoration (estuaries and peat bogs will have different management needs).  Please make sure you seek advice if you are restoring a bog, fen or salt marsh. Each wetland is unique, so some steps may not be necessary in your situation. We recommend you seek professional help for detailed information and advice. There is a list of contacts at the back of this booklet.

Under Northland Regional Council rules, you cannot undertake works within or near a significant indigenous wetland as they could cause adverse effects. This includes building structures, drainage, clearing or excavating. Please seek advice before you start work, as most wetlands in Northland are classed as ‘significant’. Check that you do not require a resource consent before you start work in your wetland.

  1. Look, learn and plan - Consider the wetland type, what you want to achieve and what suits your situation. Seek advice and take your time.
  2. Investigate the wetland’s water supply - If water levels and flows need restoring, this will be your first step. Many wetlands become dry and weedy because of drainage on adjacent land. You may need to manage a drain or culvert to restore water. Seek advice first as you may need a resource consent (see section 11, Wetland rules).
  3. Keep stock out, particularly at critical times of the year - However, be aware that if there is a nearby population of pateke (brown teal), they will benefit from some adjacent pasture being grazed.
  4. Control weeds.
  5. Control animal pests.
  6. Consider providing ‘extras’ for wetland wildlife.
  7. Plant in and around your wetland, focussing first on replacing species which have been removed or grazed out -  See the planting guide at the end of this booklet for plants to use for the different wetland types.
  8. Maintain the area with weeding and pest control.
  9. Monitor your progress.
  10. If you wish to protect your investment of time and energy, you can place a covenant on the site – where you or subsequent owners retain ownership and control, but the wetland is protected forever.
  11. Know and comply with rules about wetlands.

(1) Look, learn and plan

No two wetlands are alike – how they look and the plants and animals they contain will vary with local conditions (e.g. soils, climate and water flow). Larger wetlands may contain several different types of plant and animal communities, and all wetlands change with environmental conditions.

Before you start restoring your wetland, develop a site plan and ask yourself:

  • What’s there now? Plan to protect and encourage any naturally occurring native plants first.
  • What was there originally? Look at wetlands of a similar type in the area. Stock may have grazed out species such as cabbage tree, flax and raupo. Restore these “missing elements” first.
  • What would you like to see in the future?
  • What are your aims? Trapping sediment? Attracting wildlife? A water source?
  • How much time and what resources do you have?
  • What effect will your activities have on neighbouring properties, both upstream and down?
  • Could you work with neighbours?
  • Is your wetland changing? Check out the water supply. Your wetland may be getting wetter or drier depending on what you or your neighbours are doing.
  • Are you going to be doing any works that may cause damage or effects in the wetland? If so, you will need a resource consent.

Seek advice and help
Talk to the Northland Regional Council and the groups listed at the back of this guide about your goals. They can advise you on what to plant and options for funding. The Northland Regional Council may be able to provide copies of aerial photographs, if staff time allows.

See Waikato Regional Council’s wetland restoration template –
www.waikatoregion.govt.nz

and Landcare Research’s Green Toolbox Species Selector –
www.landcareresearch.co.nz/resources/tools/greentoolbox

Fenced swamp near Whāngārei

(2) Investigate the water supply

Your wetland and its water
Wetlands are covered or soaked for at least part, and often all, of the year. They depend on a natural supply of water – from tidal flows, springs, streams, flooding rivers, connections with groundwater, rainfall or a combination of these.

The water level in your wetland and how much it fluctuates will determine the plants and animals it can support.

Before you decide what sort of approach should be taken, spend some time monitoring the source and amount of water, especially over the seasons. Use a ‘depth marker’ (such as a wooden post) to mark water levels at different times of the year and use stakes to mark the edges of the winter water levels and summer water levels. This will help you decide if the water levels need restoring, what to plant and where. When wetlands become drier, weeds such as gorse, Mexican devil weed and pampas move in. Restoring water levels can help manage these weeds.

A number of things can damage a wetland’s natural cycle of flooding and drying. They happen at two key places:

  • At the ‘‘wetland’’ level, the cycle can be affected by drainage (including the construction of drainage ditches and culverts) or filling and levelling of low-lying areas.
  • At the ‘‘catchment’’ level (the source of the wetland’s water), the cycle can be affected by fewer floods than normal (if rivers are stopbanked), water takes from streams and groundwater, and the drainage of nearby wetlands.

If the wetland has been partially drained, you’ll probably need to increase its water levels by filling in or blocking ditches or drains. Weirs are an effective way to manage water levels, but require a resource consent. If there have been changes within the catchment you may need to increase water levels by building a low bund, weir or dam, or other earthworks.

Before you make any changes to water levels in a wetland or undertake any earthworks, contact the Northland Regional Council and your district council, as you will need a resource consent.

Raising water levels may kill vegetation around edges. Raising water levels may kill vegetation around edges.

Creating areas of open water
It’s not a good idea to create areas of open water by excavating material out of, or damming, existing wetlands. Areas of open water can be difficult to keep free of weed and algae in summer and dams can block fish access. Often wetlands do not have sufficient water flow to support good ponds. Seek advice before you create a pond.

Avoid damming or excavating wetlands that have not been disturbed and that support native plants and animals. If you want to create open water, choose bare paddocks or badly degraded wetland areas. And make sure you create some gently sloping, irregular shorelines as well as areas of water three metres deep. This allows birds, particularly waders, chicks and ducklings, easy access to and from the water and will extend the belt of reeds and rushes growing around the edge. Fallen trees and stumps can provide good roosts.

You may require a resource consent for this work, so check first with your district council and the Northland Regional Council.

(3) Keep stock out

Stock that venture into wetland areas will increase the soil’s nutrient levels, pug (compact) the soil, cause erosion, disturb the wildlife and eat and trample wetland plants. Cattle, in particular, tend to gather near water and wade into it. Stock grazing over time can completely change the vegetation type of a wetland.

Fencing stock out will encourage plants to regenerate from natural seed sources, prevent stock getting trapped and, in some areas, may reduce the incidence of liver fluke. If you can, aim to exclude not just the wetland itself, but also a buffer strip of 10-12 metres around it. A two or three wire electric fence may be sufficient for cattle.

If you don’t wish to keep stock out for the whole year – for example, if you want to keep surrounding plants cropped short for feeding waterfowl, such as pateke and pied stilt – it’s better to graze a small number of sheep as they are less likely to enter water, pug soil or ring-bark trees. The best time is mid-summer to mid-autumn, as your wetland will be drier and most bird breeding activity will be over.

From mid 2009 it became compulsory to fence stock out of the Coastal Marine Area (all tidal areas). For more information see fencing stock out of waterways.

The Northland Regional Council’s Environment Fund can help fund fencing of wetlands on private land.

The difference a fence can make. The difference a fence can make.

(4) Control the weeds

Weeds are one of the greatest threats to wetlands and, in many cases, weed control will be the most important thing you can do. If you’re planning any planting, you must control weed species in and around the area first – and continue weed control once your planting is complete.

The first step is a weed audit, in which you use a map of the wetland to locate and identify weed infestations. The next step is to gather information on how to control the weed species. You can then decide where to start the weed control, and when – and remember, it may take several seasons to control a serious weed infestation.

You may find you need help from a specialist qualified to use herbicides in wetlands.

Contact the Northland Regional Council’s Biosecurity Officers for information and advice on how to control wetland weeds. Always follow the herbicide manufacturer’s instructions.

Yellow flag iris is a serious wetland weed. Yellow flag iris is a serious wetland weed.

Pest willows

Pest willows were originally introduced to New Zealand for bank stability, shelterbelts and fodder. However, their dense growth can block stream flow and shade out native species. Crack willows and hybrids with weeping willows are particularly invasive – broken branches take root easily in muddy soils. Not all willows are pests – some non-seed producing willows are currently being recommended for erosion control.

Pest willows can be controlled in a number of ways – we recommend you first seek specialist advice from Northland Regional Council's Biosecurity Officers.

Helpful hints on weed control

  • When working with spades and machinery in weedy areas, wash them down before using them elsewhere on the farm to prevent weed spread.
  • Fence out stock to reduce the spread of weeds. The fence should be set back far enough from the water’s edge to allow for seasonal fluctuations in water level. This fenced off riparian margin will need to be managed to control weeds.
  • Barley straw reputedly inhibits algal growth and boosts aquatic insect life in slow-moving water. Two bales should keep around half a hectare of shallow, open water free of algae for six months. Either spread it out or anchor it in one position – eventually it will sink and decompose.

If your wetland is drying out from a change in water supply or drainage, weeds such as gorse, pampas and Mexican devil weed will move in. If this happens you may need to restore water levels. Old drain tailings are good places for weeds such as pampas grass to colonise. These areas may need special attention and restoration with native planting.

Find out more about weed and pest control

(5) Control animal pests

Some wildlife such as paradise shelduck will respond positively to a basic improvement in wetland habitat. However, other species such as pateke and bittern will require additional help, particularly in the control of animal pests. Some animal pests in wetland areas include:

  • Possums, hedgehogs, stoats, weasels, ferrets, cats and rats. 
    They take birds’ eggs and most will also eat chicks and adult birds.
  • Rabbits, hares, goats and possums eat wetland plants.
  • Dogs can harass and kill wetland birds. High-tensile net fencing will discourage dogs from entering the wetland and provide a more secure area for birds to nest.

Effective pest control can sometimes lead to an increase in pukeko numbers.  Although a native to New Zealand and a natural part of a wetland ecosystem, pukeko nibble on and uproot newly planted seedlings. To deter them, use large and heavy potted plants. Alternatively, try placing a hedge of short sticks around the plants, or
use plant protectors.

Regular animal pest control will enhance bird life in your wetland and protect young plants.

Contact the Northland Regional Council for practical advice and information on the best animal pest control methods for your situation.
www.nrc.govt.nz/nasties

Pest stoat (Photo: DOC).