Newsline 298 - 10 May 2013

Friday 10 May 2013

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A Very Heavy Rain Indeed 

The recent rainstorm in Richmond and Stoke was one of the most intense ever measured in New Zealand. The extreme rain that fell from Hope to Stoke on 21 April 2013 was measured by six rain gauges, with the maximum one hour total being 101 mm/hr in the Roding catchment at the Caretakers house.

Richmond and Stoke were not the only areas hit by the rain burst with the conveyor belt of rain first hitting land in Golden Bay at approximately 2.00 pm on Sunday. As it moved across the District heading towards the Richmond Hills, it left an increasing amount of water in its path.

In this event the rainfall duration, and the size of the catchments it fell in, were well matched. It’s very likely that the flow from the upper parts of the catchment had time to reach the lower watershed while heavy rain was still falling in the lower catchment. This meant that all of the catchment was contributing in each case and building upon itself, thus causing the sheet flooding.

The sheet flooding was then compounded by the fact that a number of streets in Richmond and Stoke run across the flow path of the water, once it overran the stormwater system. This is more than likely the cause of the high number of houses and businesses flooded.

Damage

While the damage throughout the District was still being assessed as this article went to press, it is very clear that private homes and businesses bore the brunt of the flooding.

Parks, roads and stormwater systems need to be restored in a number of places but the damage is superficial compared to the private cost. Nearly, if not, all of the tracks in the Richmond Hills have to be restored or recut and, in typical Tasman community style, there have been volunteers doing a great deal of this work already.

Roads on the whole have come through relatively unscathed with a small number needing some resealing. The exceptions are in Riwaka and Graham Valley, which had been suffering from a previous slip.

Metservice Forecast

The severity of this event caught nearly everyone off-guard as its sheer intensity was not forecast, although a general rain warning was in place. The latest update of this forecast came at 12.57 pm on 21 April 2013:

Area/S Affected: Ranges Of Nelson West Of Motueka – Heavy rain has set in and is expected to continue through Saturday and Saturday night. In the 24 hours from 9.00 am Saturday expect a further 130 to 160mm of rain to accumulate. Peak intensities of around 15mm per hour.”

The forecast also mentions the possibility of intense rain from thunderstorms in western Bay of Plenty, but not in the Tasman region. The difficulty of forecasting the location of thunderstorms in advance must be acknowledged.

What actually happened?

The first sign of exceptional rain occurred around 4.00 pm when 53mm were recorded in one hour prior in the Kotinga raingauge in Takaka. Heavy rain was beginning in the Hope area around this time. Prior to this however, around 45 mm of rain had already fallen, so ground conditions were already wet.

Around 4.00 pm the ‘conveyor belt’ of rain extended from east of Takaka across to Hope, and rainfall records from Tasman and Riwaka Valley show the heaviest rain there occurred from around this time. Following this, the heavy rain band shifted north to lie over central Richmond, the worst rain occurring there from 5.00 pm - 6.15 pm. As the rain band continued north, the Stoke area was assaulted by similar intensities from 5.30 pm – 6.45 pm. The earlier Takaka rainfall is also shown on the graph for interest. Each vertical gridline is 30 minutes.

Effectively this means that the ability to respond as one would in previously experienced events was near impossible. In an extremely short time the situation went from light rain to pulling people out of houses and attempting to protect life and property.

In a mixed blessing kind of way, the floods disappeared as quickly as they arrived as the beleaguered stormwater system could once again cope. Once the rain stopped falling the system could catch up. What was left, however, were the scars of the deluge, water, silt and debris were scattered throughout the area.

Questions we need to consider

The Council has a number of questions to answer:

  • Was the stormwater system sufficient?
  • Can we bear the cost of building a system to a far higher than current specification?
  • Are we able to bear the cost?
  • Are these weather bombs becoming the ’new normal’?

These are all questions the Council will be investigating in the aftermath.

Historic Perspective – how does this fit?

The most extreme rainfall over one hour measured in New Zealand occurred high in the Southern Alps in the Cropp Valley, in the Hokitika catchment. This total was 134mm over one hour.

The next highest one hour rainfall occurred in Leigh, north of Auckland in May 2001, when 109mm fell for the hour, and 134mm for a 24 hour period. Another high rainfall total of 94.5 mm over one hour was seen in the Matata area near Whakatane in 2005 when the 24 hour rain total was 308mm. This was a good example of a particularly damaging storm – the most intense rain falling when the ground was saturated. That storm resulted in boulders up to 7m in diameter being moved by floods and debris flows and 27 homes destroyed. The most intense rainfalls measured in the world are seen in the higher latitudes. Spare a thought for the town of Holt in Missouri where 305mm was dumped in one 42 minute period.

Flood flows

The only flood information available for the Richmond and Stoke foothills comes from the Orphanage Creek just above Suffolk Road. A water level recorder has operated here since 2004 and has recorded two large floods in this time (an intense rainstorm also affected this area in 2007). High flood flows have not been measured at this location to calibrate the water level record but these can be indirectly estimated using engineering equations and experience. It is considered that the flow reached 57 cubic metre per second on this occasion, well above the 25 cumecs registered in 2007.

What is different about this flood compared to December 2011?

A very damaging event also occurred in December 2011 and parallels have been drawn between the two storms. In fact the two storms were quite different. In 2011 the rainfall was less intense but continued for a much longer period and the primary issue that arose was land slippage, debris flows and choking of riverbeds. The flooding that occurred was often because rivers channels were choked with sediment and debris and were unable to carry the flows. In contrast, this year landslips were rare, but the large volume of water resulted in widespread flooding.

This time, damaging flows not only originated from defined rivers and creeks, but sheet flow occurred off the Richmond and Stoke foothills. Stormwater systems had little hope of draining this water away and it continued downhill in pathways previously unused to water flow. It accumulated where culverts were blocked or overwhelmed and backed up in areas behind streets, highways, landscaping or natural contours.

What is a return period?

The rainfall totals experienced exceeded the limits of the design software that is used to calculate recurrence statistics. Based on all previous data collected across our district, there is around a 1% chance of 60mm falling in an hour in any given year, in the Richmond/Stoke area. The totals experienced in the recent event approached 100 mm/hr and extrapolating the statistics shows that the probability of this occurring is about 0.2% in any given year. The common way of expressing this probability is to say this was a 500 year event, although this incorrectly implies that such a rain will only happen every 500 years.

Flood photos and rainfall readings

Tasman District Council would like to archive photos, video and rainfall readings from the flood on 21 April 2013 for the areas badly affected from Takaka through to Richmond.

The email address to contact Council is rainfall2013@tasman.govt.nz. Information could also be mailed to the Council’s Richmond office.

If you have flood photos please include the time photo is taken, the exact location, along with contact details (phone or email).

If you have video, please send a link where the video can be viewed or uploaded, or how it can be collected by other means.

If you have rain gauge readings, please send the readings, the time over which the rainfall fell, and the exact location, along with contact details.

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Message from the Mayor 

Our hearts go out to the many people affected by the recent devastating flash flood. Since the deluge on Sunday 21 April 2013 myself, councillors, staff and contractors have been out visiting affected families and businesses to witness first-hand the impact of the ensuing flood.

The reality is that the stormwater system was overrun and the water turned to the planned secondary flow paths which in turn were overloaded, which then sometimes took it through private property.

We are conscious that in a number of the places we visit that this is not the first time they have dealt with floods, and the frustration and anger expressed in some areas is easy to understand. Many people we have visited have provided comments, ideas and things to follow up on and we thank them for taking the time to do so especially as many were surrounded by their possessions and the mess on their properties.

This is another ‘weather-bomb’ to hit the District over the last three years. The damage recorded was similar but the causes were quite different – heavy rain in the mountain catchments, tropical rain over a long period in a defined area and a deluge over the space of two hours.

We will be looking to possible solutions, but we need to balance these with the risks the community is prepared to accept and/or pay to avert. When we look to what can be done, we need to look District-wide. Recent news focused on Richmond and Stoke, however, Takaka and Motueka, while not breaking records, received a great deal more rain than was expected with a number of people flooded as well. We also remember recent flooding in the Motueka Valley, Murchison and Maruia/ Shenandoah/Glengarry where people have also felt the brunt of floods in the last three years.

As we process the information and input from residents throughout the District, one also must acknowledge the community spirit that dwells in Tasman. We are a District that helps one another. On nearly every one of our visits we heard stories of selflessness of neighbours, family and friends helping those in need. We may not be able to control the weather, but we can certainly rely on and help each other.

Mayor Richard Kempthorne

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Commercial Subcommittee to Have First Meeting 

Tasman District Council has completed the formation of a Commercial Subcommittee, which will oversee the Council’s forestry, camping grounds, aerodromes and commercial property portfolio.

Council’s Commercial Subcommittee, which will report to the current Corporate Services Committee, will hold their first meeting on 14 May. The Subcommittee is made up of three external appointees Alan Dunn, Phil Grover and Roger Taylor, and two current councillors, Tim King and Brian Ensor.

The Commercial Subcommittee has the important task of providing sound commercial direction to the Council to ensure it achieves the greatest return possible from its forestry and property holdings, as well as other commercial investments like the jointly owned port and airport.

“The Tasman District is blessed with well qualified residents. The three appointed Subcommittee members will bring a wealth of experience as well as a high level of knowledge to the table”, said Tasman Mayor Richard Kempthorne.

“The Council has a responsibility to garner a sustainable return to offset the impact of growth and provision of essential services to our ratepayers. While the Subcommittee is not a decision-making body their advice and direction will make the achievement of this challenging task easier.”

“With a clear focus and onus on delivering greater returns from the commercial portfolio we are expecting a positive outcome to the Council’s bottom line which, in turn, benefits all Tasman residents.”

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Tasman’s Junior Army 

Amid the misery of the flood clean-up in Richmond, a Park Drive resident had her heart warmed by a group of enterprising local boys.

From her house she views the neighbourhood playground and saw that most of the bark had been washed away after a stormwater pipe overflowed. Not an urgent repair job, yet one that still needed doing. So she grabbed a shovel and a rake to do her bit.

The woman returned home for a break and a quick cuppa, and from the kitchen window saw half a dozen young lads bowled up with wheelbarrows and tools to finish the task. This they did with no direction from anyone.

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Draft Annual Plan Submissions Closed 

Submissions to the Draft Annual Plan 2013/2014 have closed with over 390 submissions received, covering the full range of services provided by Council. Topics included tourism services, library facilities, undergrounding of powerlines, pest control, cycleways, protecting the environment, arts and culture, and everything in between. For the first time submissions are available for viewing on Council’s website. Copies of submissions are also available for viewing at Council offices and at Council libraries.

Submissions Received on the Draft Annual Plan 2013-2014

The Council thanks everyone who has made a submission and appreciates the time and effort that people and businesses have put into helping shape our work programme for the next twelve months. Included in the submissions are a number directly related to the consequences of the deluge experienced throughout the District on Sunday the day before submissions closed. The Council has accepted these as they directly relate to the allocation of funding and prioritisation of work over the coming year.

The next step is the public hearings and over 100 people have asked to speak to their submissions. Submitters who indicated a desire to speak to their submission have been sent a letter with a proposed time.

The hearings are public meetings and have been scheduled as follows:

  • Motueka Memorial Hall, 8 May 2013, 9.30 am – 12.00 pm
  • Takaka Fire Station Hall, 8 May 2013, 2.00 pm – 4.00 pm
  • Richmond – Council Chambers, 10 May 2013, 9.30 am – 12.30 pm, then 1.10 pm – 4.30 pm (last speaker 4.20 pm)
  • Richmond – Council Chambers, 13 May 2013, 9.30 am – 12.30 pm, then 1.10 pm – 4.00 pm (last speaker 3.50 pm)
  • Richmond – Council Chambers, 15 May 2013, 9.30 am – 12.30 pm
  • Murchison Sports Recreation and Cultural Centre, 16 May 2013, 10.30 am – 1.00 pm.

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Safer Crossing Facility Proposed for High Street 

Tasman District Council and the New Zealand Transport Agency (NZTA) have identified a preferred solution to improve pedestrian safety in Motueka’s busy shopping district along State Highway 6.

The busy section of High Street opposite New World and The Warehouse has to contend with oncoming traffic, cars entering and exiting driveways and pedestrians. Increasing the safety of pedestrians on this busy section of road while maintaining traffic flow, and hopefully decreasing the stress for drivers, was a priority.

After looking at a number of possibilities, including a pedestrian crossing, it was decided that the preferred solution is a pedestrian refuge made up of two traffic islands with handrails to provide pedestrians with a safe place to wait between traffic lanes. This allows pedestrians to negotiate only one stream of traffic at a time without disrupting the flow of traffic. At this stage funding approval still needs to be sought for this facility but finding a preferred solution is a great step forward in the process. Although a zebra crossing was looked at as a possible solution it was thought that a zebra crossing would in fact make crossing less safe because pedestrians could cross the road thinking that they have priority but drivers turning onto the road may not see them because they are watching for oncoming traffic.

“Hopefully the refuge will supply a win-win for all three parties,” said Motueka Community Board Chairman David Ogilvie. “Those turning on to High Street by car, those already driving down High Street and pedestrians crossing the road.”

“This is very very good news. I’m sure the whole community will greet this result with enthusiasm and it will be a very welcome change.”

The support from the Motueka Community Board includes ensuring NZTA of $15,000 from its Community Projects Fund, however at this stage the process and costs of construction have to be fully identified before construction is guaranteed.

NZTA Central Operations Manager Mark Owen said the NZTA and Council have been heartened with the response from the community to the proposed facility.

“The Motueka Community Board have been fantastic to work with and we’d like to thank them for their positive, constructive and informed participation.”

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Moutere Hills Community Centre Opens its Doors 

The Moutere Hills Community Centre opened its doors on ANZAC day for the first time since the first fire severely damaged the main hall back in January.

Catering to the service attendees from the recently converted kitchen, the community has been drawn back to the Centre.

The Electrical Engineer’s report on the second fire, which took place in April, found there was no evidence that the electrical work that been done on the distribution board had contributed to causing the fire. The cause was identified as a faulty component in the switch box.

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Higher Density Housing – Have Your Say 

The Council is thinking about encouraging higher density housing in Richmond and is currently looking for community input.

The Council has had a display at the Richmond library, which is now housed in the Council’s Richmond office, about the subject and will be involving the local community in any decision-making.

The conversation with Richmond residents continues with the opportunity to fill in a questionnaire gathering thoughts and opinions. This questionnaire has been delivered to all Richmond residents.

The process has already attracted attention from the segments of the community who believe the plan involves building high rise apartments and offices in the heart of the CBD. At this stage there are no such plans and certainly no decisions have been made at any level. This process is about involving the community in the future planning of the town.

What is higher density?

Higher density residential development encompasses a wide range of housing resulting in a population density greater than provided by the conventional 3 or 4 bedroom dwelling on allotments around 600m2 or greater.

Outside of the conventional form there are a number of options including compact townhouses and duplex designs.

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