When it rains hard a treasured Kāpiti Coast waterway, Wainui Stream turns very brown. Home to some of the best native fish biodiversity in the Wellington region the stream, says freshwater ecologist and advocate Mike Joy, has long been abused. It is now likely being damaged by Transmission Gully work upstream after measures requested by the Environmental Protection Agency were not put in place.
The Wainui Stream, including its Western tributary the Te Puka Stream, is undoubtedly a local and regional taonga. It contains some of the best native fish biodiversity in the Wellington Region including rare fish, but it has had a sad history of appalling abuse.
I have been interested in the Wainui Stream for about twenty years now. It started for me around the end of last century when I sampled it as part of data collection for my Freshwater Ecology PhD at Massey University. That work was funded by the Ministry for the Environment and Greater Wellington Regional Council. The Wainui stream is home to many rare and threatened freshwater species. They include longfin eels, Giant kokopu, Giant bullies, redfin bullies, torrentfish, banded kokopu and koaro as well as freshwater crayfish (koura).
Back then I found some big problems for the native fish communities. These were caused first by the historic forest clearance in the catchment and later exacerbated by native vegetation clearance and grazing of hillslopes. This land use and other development upstream was driving increased sedimentation all the way to the sea.
The photos here show the increase in the amount of material coming down. They lifted the stream bed very quickly. You can see a few metres of sediment buildup over just a few years, from 2008 to 2013.
Another issue, particularly for the fish are the culverts under State Highway 1. They have a double-whammy effect on the native fish and freshwater ecology. Our native fish are mostly diadromous, that means they need to migrate to and from the sea at different lifestages and this process is severely restricted by the current culverts. This is because the pipes project out into space and the water falls from the end of the pipes into a pool. While our native fish are great climbers they cannot fly or leap to get up into the pipe to get upstream. Thus, this culvert is effectively a barrier against upstream fish migration.
The other problem caused by the culvert is the buildup of rocks and cobbles just upstream of them, meaning that the flow disappears underground so there is no surface flow at low flows. The stream appears dry, but water still flows underneath. Some small fish can negotiate this, but it is a restriction on upstream migration and stops downstream movement for larger fish.
The most recent impact on the Wainui and its tributary Te Puka has been the construction of the Transmission Gully Highway. I became involved in this project when I was engaged by the Kapiti Coast District Council to be their consultant freshwater ecologist for the negotiations around Transmission Gully. KCDC were not opposing the development but I was employed to make sure that the Wainui stream was protected. There were mountains of material prepared by the applicant, The Land Transport Authority (NZTA) and they had engaged ecological consultants to prepare an Assessment of Environmental Effects. The application was to be heard before the Environmental Protection Authority’s Board of Inquiry. I was involved in caucusing between NZTA, ecological consultants and other ecologists including myself who were there to protect the environment.
It was an interesting process. The applicant wanted a consent to shift the Te Puka Stream many metres from its current bed into an artificial channel to allow the Highway foundations to sit where the current bed is. The applicant’s ecologists claimed this could be done without any major environmental impacts (this is the usual process; they are employed to do this). I made it clear that this was not possible – there would be major impacts. I emphasised the harm that the current State Highway 1 culverts were having on fish migration and habitat already, and that that must be fixed. I made it clear that It was crucial the new highway must have a bridge and not a culvert so the natural bead of the strain could remain so that there would be no impact on fish migration or on sediment movement.
Very surprisingly the NZTA seemed accepting of the mitigations I asked for, but I guessed it was taxpayer money and they would just agree to what was needed to make progress. They agreed to taking all the native fish away from the construction area and moving them to the Wainui stream during construction, and the stipulation that the current perched culvert on the highway be removed, as otherwise those transferred fish would have no access to the sea.
When the decision on the project finally came out from the EPA Board of Inquiry, they included all the conditions around moving fish, providing access and including a bridge and not culvert for the new highway and SH1 culvert.
Much later, to my surprise and disappointment I found that the roading contractor applied to Greater Wellington Regional Council to weaken the consent conditions. They were then given permissions to not do what was stipulated by the board of inquiry decision. They instead proposed a culvert with a fish pass and other unspecified changes to consent conditions. To this day I do not understand how a statutory process like a Board of Inquiry decision can be undermined in this way.
Since construction began, I have noticed increases in fine sediment build-up on the bed of Wainui Stream in Queen Elizabeth Park. For example, in the most recent rainfall in April, I was appalled to see how turbid the stream was after just a small amount of rain and very little increased flow in the stream. The sediment was clearly coming from the Te Puka tributary (see photo). I cannot be sure what the source was exactly, I can only say it’s very likely to have come from the road construction given the huge amount of exposed soil and roading material there is up there. Given the Covid-19 restrictions I don’t know whether the sediment control infrastructure is being maintained and couldn’t get any assurance on this from Greater Wellington Regional Council staff I contacted.
The Our Freshwater 2020 Report released in April by the Ministry for the Environment highlights the huge freshwater crisis we have in New Zealand. The Wainui is an example of the failure of regional and central government to protect freshwater.