Rain-bomb risks prompt caution on Matatā housing growth

A rain bomb in the hills above Matatā in March this year saw sediment and debris-laden water come over the top of Moore's Bridge, closing State Highway 2 and entering private properties. Photo / LDR

Whakatāne Mayor Victor Luca says building more homes within Matatā now would be a mistake due to the potential damage from “rain bombs” and worsening weather.

Matatā is one of the areas named in the draft Eastern Bay Spatial Plan as a key growth area for housing, with infill housing of up to 700 homes and the potential for development of up to 800 homes eastward of Pollen Street over the next 30 years.

At an infrastructure and planning committee meeting on Thursday, the council learned that since August, Whakatāne District Council has spent more than $300,000 clearing sediment and debris from Matatā catch-pits after it washed down from stream catchments due to localised “rain bombs”.

Most of the cost was incurred between February and May, due to several heavy rain events in the hills above the town during that period.

Rain bombs are usually associated with a burst of heavy rain that has the potential to do damage.

Luca said it would be a mistake to densify Matatā with what was going on there at the moment.

Whakatāne Mayor Victor Luca feels building further housing in Matatā would be a mistake until something is done to address flooding risks. Photo / LDR

“Climate change is the elephant in the room and we seem to have consistently underestimated the effects.

“There’s a micro-climate [in the Matatā catchment]. It’s not totally predictable, but it looks like things are going to keep getting worse.

“These rain bombs that come – this is the second in 20 years but they don’t have to be linear, there could be another one in a year or two.

“This has to be fixed and the people living there have to be given some comfort.”

After the 2005 debris flow, the council placed sediment and debris catch-pits in Matatā both at the Awatarariki Stream on the western side of the town and Waitepuru Stream on the northeastern side of the town.

A $70,000 annual maintenance budget is supposed to cover the cost of keeping these catch-pits clear so that the town and lagoon do not suffer debris-flooding events.

Despite this, earlier this year a heavy rainfall event localised in the hills above Matatā saw sediment and debris overwhelm Moore’s Bridge, which crosses the Awatarariki Stream, blocking State Highway 2 and entering properties on Pioneer Place.

Another view of the damage after the rain bomb in the hills above Matatā in March this year. Photo / LDR

While some of the cost overrun for removing debris was covered from an emergency stormwater fund, $112,000 of unbudgeted spending needed to be approved, which would likely come from an internal loan. This amount also included the repair of a blown-out stormwater pipe in Murupara.

Three waters manager Jim Finlay suggested this sediment and debris coming down the rivers could be mediated with rock weirs slowing the flow of the water, at an estimated cost to the council of $140,000.

“It’s terrible that we’re just sitting there waiting for this to happen and you have to clean up each time and if you don’t, you are possibly going to have flooding down the highway and through the town from both of those streams.”

Finlay likened it to “someone having a party in your house every week and you’ve got to go and clean up the mess”.

Councillor Gavin Dennis recently presented to the Bay of Plenty Regional Land Transport Committee about the Moore’s Bridge incident that resulted in a debris flood.

Dennis asked that the bridge be improved and that NZ Transport Agency Waka Kotahi (NZTA) and New Zealand Rail increase their maintenance on their State Highway 2 and railway bridges.

Finlay said New Zealand Rail had since cleared out its culverts on the Awatarariki Stream and had further work planned for clearing culverts on the Waitepuru Stream.

– LDR is local body journalism co-funded by RNZ and NZ On Air.