First flood issue meeting of year held

The Whanganui Flood Management Review Group met in its first meeting in 2016, to report on progress around investigations into flooding issues highlighted during the 19-20 June flood event of 2015.

The Group, comprising representatives from Horizons Regional Council, Whanganui District Council and Whanganui River iwi, met last week to discuss work completed, underway and next on the list. 

Horizons group manager river management, Allan Cook says work completed includes surveying of the river channel between the Whanganui River mouth and Upokongaro; and a thorough survey of the Matarawa Stream channel condition through Whanganui East.

“Completion of the channel survey provides us with the information needed to re-calibrate our flood prediction models at the Whanganui City Bridge and from Pipiriki to Whanganui and also the hydraulic model used to provide design flood levels throughout the city. That work has a high priority and is now well underway,” says Mr Cook.

“We have found the area where the Matarawa Stream flows through residential properties to be extremely restricted and a substantial programme of work, dealing with difficult access, will be required to address that. We will now look at options for undertaking and funding that work.”

Other work currently underway includes analysing the survey data to report on channel capacity and flood conveyance issues.

“Many people have commented on localised siltation of the river and we need to better understand the overall scale and how readily it may be scoured out in future high river flows. We expect a report on that issue by the end of March,” says Mr Cook.

“A study of the Awarua catchment and its impacts on State Highway 3 and the Wikitoria Road area, is also underway with findings expected by the end of March as well.”

Whanganui District Council group manager infrastructure, Mark Hughes, says “the data from the event has been used to validate the overland flow path mapping throughout the urban area”.

“Work has commenced on the Westbourne/Gonville catchments and the ponding behind stopbanks at Balgownie and Gilberd Street. These findings are expected by the end of May.

“We have also made the channel survey data available to our port engineers to assist them in their investigation of river siltation effects on stormwater outlets and navigation in the lower river,” he says.

Overall the Group believes there has been good progress made to date due to both Horizons and Whanganui District Council reallocating funding from other programmes at short notice in order to get investigation work underway.

“Prioritising work to ensure it’s undertaken as efficiently as possible continues to be at the forefront of our mind,” says Mr Cook.

“We will continue to provide updates after our meetings, or as significant pieces of work are completed, and wish to remind the community if there hasn’t been an update for a while then this is because we are still waiting on reportable progress.

“Finally, we understand there are some members of the community who are still dealing with the aftermath of the June floods or are unable to make important decisions for the future.  As we work through the priority list, and investigation reports become available, we hope to provide them with the information they need to make informed decisions,” he says.

The Group also plans to make presentations on their work to the Whanganui Navigation and Water Safety Group and possibly to other interested community groups. The next Whanganui Flood Management Review Group meeting is to be held at the end of March.

The Whanganui Flood Management Review Group consists of executive and flood management staff from Horizons Regional Council and Whanganui District Council, Hera Smith as the Lower Whanganui River iwi representative and Chris Shenton as the Whanganui River local iwi representative. The role of the Group is to identify key flood management issues in the Whanganui District highlighted during the 19-20 June 2015 flood event and facilitate initial investigation of these issues.

In December 2015 the Group identified 23 total areas of investigation to address flooding issues highlighted in June.