Project Update on Colin Sherrard Wetland Development
Thursday, 02 February 2017
This project aims to restore a preferential hydrological regime to circa 14 hectares of degraded willow wetland. The core focus of the project is to compartmentalise the wetland between Opuatia stream and farmland by blocking historical drains and creating earth bunds along property boundaries. Some of the canopy will be opened up using excavators if the budget allows. The remaining open water will be created through a targeted aerial spray programme across approximately 6 hectares of grey willow canopy in the lowest lying part of the wetland. Once the existing drains that cut through the stopbank into the Opuatia are blocked, the area will be inundated with 300-500mm of open water.
Earthworks were completed in the 2015/16 construction season which comprised of blocking the historical drain and creating a small earth bund at the southern area of the wetland. Some of the willow has been opened up to create open water wetland area. Low points along the river stop bank were GPS’d during winter flood events using the boat for access.
It appears that the earthworks done to date has had the desired result of lifting water levels in the wetland, the area is being used by good numbers of ducks and swan. We will monitor water levels during summer and then decide whether or not further earthworks along the stop bank are necessary to fill any further low points. If no further earthworks are required, we will monitor the plant response. It appears that some of the crack willow is already starting to die from the increased inundation. Fish and Game staff will do a further GPS survey in the wetland to determine any low points still holding water. Willows in these areas may be targeted with aerial herbicide control if required to help open up further areas. These will be left standing and will begin to break down in the next 4-5 years. This woody debris will provide good structure for invertebrates, native fish and avifauna.
The work done is holding water to date in an area that was once dry due to historical drainage. At this point in time some more work may be required to ensure the water levels are held at the current level. However, we will learn more of the success once we have got through the dry summer/autumn period. The area is fenced off from stock and there will be a little more fencing done once the permanent water levels are identified. Regarding wildlife, I have never in the past 15 years seen as many ducks and swans in that area of our property along with pukekos and bittern. The waterfowl are breeding in and around recreated wetland. I have planted oak trees in the general area and oversewn the small areas of bare ground on the periphery of the site with millet to provide short term food for birds along with the seed produced by naturally occurring sedges, willow weed, flax and cabbage trees. By far the majority of the area is in willow trees. It is the intention to plant more flax and natives such as manuka once the permanent water level has been identified. To date I would have to say it is a very successful project.
Photo 1: one of the open water area where mechanical removal has occurred
Photo 2: Flooded willow area showing increased water level. Mechanical willow removal has occurred in background. Crack willows in foreground are showing signs of stress due to increased water levels