High water mark at Grey Street gardens

RAIN GARDENS: Auckland man Junayed Aamir views the water treatment system known as rain gardens at the beach-end of Grey Street. The left hand garden remained empty after the heavy downpour of the past two days but the garden on Captain Morgan's side was nearly full. The system is working how it was expected to, says GDC project manager David Wilson. Picture by Liam Clayton

THE sunken water treatment system known as rain gardens at the bottom of Grey Street is working as it should, says Gisborne District Council project manager David Wilson.

After downpours, The Gisborne Herald receives inquiries about why the rain garden on the Captain Morgan’s side of the road is almost full, while the one on the other side of the road is empty.

This is because the sunken garden on Captain Morgan’s side of the road has a far bigger catchment area than the one the other side, says Mr Wilson.

“The gutter runs around the corner and into Salisbury Road.”

The natural fall of the road also means stormwater is inclined to flow into that rain garden, he said. The catchment area for the rain garden on the other side of the road extends only as far as the entrance to the Waikanae Beach holiday park about 30 metres from the sunken garden.

The already-established drainage system under the road deals with some stormwater on that side of the road, so reconstruction of the road was not a cost-effective option, Mr Wilson said.

Before installation of the rain gardens, the fall from Grey Street meant stormwater piped on to the beach scoured out the sand.

The diffuse discharge system provided by the rain gardens means stormwater seeps slowly into the dunes as planned.

An outflow grill at the top of the right hand garden means no stormwater will pond on the road, Mr Wilson said.

“The downpour from the other day was a good test for the system. We are happy it is working the way we wanted it to.”

A replacement fence for the temporary one is expected to arrive in the near future and litter that blows into the rain gardens is taken care of under the council’s maintenance programme.