Project 2. Awatarariki Dam
Frequently Asked Questions
That EBOP/Whakatane District Council sanctioned forestry and logging operations in the watershed areas of geologically unstable and earthquake prone country behind the village was irresponsible.
There was no sanctioned forestry logging in either of the catchments (Waitepuru and Awatarariki). Sanctioned logging was undertaken in catchments further around the Manawahe Road towards Awakaponga. GNS demonstrated that this event was of such an extreme nature that the landslides and subsequent debris flows occurred even on highly vegetative slopes. These slips were deep into the bedrock. Indications are that in some circumstances, vegetation will actually add to the instability with increased water retention that heavy vegetation has on slope stability. John Douglas (EBOP) will be able to discuss in some detail, at the Matata Open Forum Day, catchment management in the catchments behind Matata.
That a debris dam (of logs and forestry waste) had built up, creating a large lake which had been reported to the authorities out of concern for the threat it posed to the community below – yet no-one took any interest or even bothered to check it out.
GNS did not believe there was any evidence that there was a “large water body” retained by a previous landslip. Discussions with EBOP support this with visual inspections of the catchment being flown every 12 weeks. Investigations to establish who reported this have proven difficult, and there was no formal reporting ever made of this sighting. A demonstration of what happens when large bodies of water are discovered occurred recently at Ohinekaoa (Herepuru Road). The small lake that was created by a landslip at Ohinekoao was monitored very closely. To the point estimates of water quantity were made (John Douglas took depth samples) and failure and implication calculations were made regarding downstream culvert capacities. No action taken due to results.
The Debris Dam
In supporting the concept of a 17m debris dam and other protective measures, WDC have voted to secure Matata’s future. The people of Matata appreciate that; however, a host of questions and concerns remain inadequately discussed.
Of the other 3 options which were pursued can you demonstrate to us why they were considered unsuitable for Matata?
This is related to cost and the social implications of properties lost in other options. The cost of each proposal is described in two parts:
i) the capital cost of works; and
ii) the acquisition cost of properties for works.
This will be clearly outlined at the Community Forum being facilitated by Whakatane District Council on 23 July 2006.
Could we have a list of the options considered?
11 engineered options were considered. A number of ‘non’ engineering options were also investigated (weather forecasting/warning systems).
The Matata Open Forum Day is designed to further explain these to the Community.
Where will the debris dam be built?
Detailed design will determine this after geological investigations. It will be somewhere upstream of the railway near the old quarry. (See map).
How will it be constructed and anchored in this unstable, earthquake prone area?
Detailed design will determine this after geological investigations. All engineering will be checked and reviewed through a “Peer Review Process” of independent specialists in this field. The regulators (EBOP and WDC) will appoint independent engineers, international if necessary, to ensure the design is in line with the scope of its function, (i.e. it will stop a certain sized event).
What will it look like?
Detailed design will determine this after geological investigations. Schematic drawings will be available as part of the Resource Consent process.
How will it work?
It will arrest debris flows whilst still allowing water and finer silt to pass through – the silt traps will capture this.
How will it be maintained and serviced?
A maintenance contract will be entered with a service provider – funding has been allocated as part of the LTCCP and funding/risk options being assessed. Annual Reports can be tabled at the Community Board for review per Resource Consent conditions.
Will an extreme flow path to allow for storm water to be diverted away from the lagoon, possibly out to sea or to the west, be provided?
No, all flow from the Awatarariki Stream will be routed to the lagoon (as historically occurred).
Silt from a storm event carried into the silt traps at the front of the lagoon will be captured before entering the western lagoon.
Will work on the lower Awatarariki Stream provide a series of silt traps to protect the reinstated lagoon/wetland area?
Yes, silt management measures will be incorporated in the design.
View other community questions with a focus on general issues.