Lake Sumner Levels

Examining HWP claims for extent of shoreline drowning.

Presentation to Hurunui Waiau Zonal Committee, May 12th 2011Sumission; Edward Snowdon, BA, NZCE (mech), on behalf of Loch Katrine Association Inc.

Personal background; My family and I have a continuous association with Lakes Sumner and

Katrine since the 1950s. I am a precision engineer, not a registered surveyor. It has always been

our contention a neutral survey, apart from HWP, of the proposed levels should have been

conducted using commonly recognised datums.

From Pattle Delamores hydrology; and Boffa Miskel's ecology (March) we have:

HWP RL LINZ survey

historic low 541.8 m 521.99

historic high 544.99 m 525.2

proposed design storage level 543.8 m 523.99

design storage range 2 m

Assuming HWP's RLs relate to the original Christchurch Hydrological Survey of 1956, LINZ

survey,and the associated bench marks at the outlet of Sumner, as above, we can relate the original

record to HWP consultant's work by conventional survey.

2 meters added to the historic low level allows us to put a stake in the ground at the design storage

level. However, in the March work presented by Boffa Miskell for HWP we have an assessment of

the forest and shoreline of Lake Sumner, which will be inundated. We are provided with tables,

transects and illustrated aerials, demonstrating inundation of a large area of forest, shoreline scrub,

and beach (of Lake Sumner, without mention of the similar effect upon Loch Katrine).

Our contention is: this graphic line is drawn 500mm lower than the design storage level, ie. a

third of the effective inundation and its impacts are missing.

And the effect on the aerial photos would be;

Boffa Miskell appear to justify the drawing anomaly by calling it the line of long term inundation

and arrive at it by averaging modeled heights upon the historical data. Refer figure A.

Trees, shrubs and vegetation have a well recognised period of tolerance to inundation. It is not a

matter of average height, but an actual event of inundation exceeding the level of tolerance.

Once will kill (permanently!).

If HWPs' scheme were to be effective and achieve a suitable volume of storage with reliability, it

would have to hold water at the design storage level for months at a time as per above levels graph.

p.3

To quantify the proposed design level; 2 meters represents a rarely occuring flood height.

The recent 'weather bomb' of Dec. 28th, produced one of the five highest flows recorded in the thirty

years of the NIWA Mandamus recorder. The resultant flood at Sumner did not reach HWP design

storage level and lasted for a few hours, as observed.

To quantify the losses; Boffa Miskell claim Lake Sumner will lose 4.4 ha of trees and shrubs. This

is not correct. It is well known that plants are not killed by “average” water levels but by maximum

inundation levels and durations. Using the proposed storage levels and including Loch Katrine it is

easily shown that the area of 'kill' is actually at least 7 times larger ( not less than 30 Ha). This will

include virtually all of the Kowhai fringe, the Rata, much mature Red and Mountain Beech; indeed

it is the essential, pristine and unique part of the landscape which will be killed. This is only

including the effects to the wetted line, not ongoing influences of wave action.

We are contemplating another Lake Monowai, which was raised 2.4 meters in 1926 and holds

iconic status for environmental catastrophe marked by a shore lined with tree stumps.

This country is unlikely to accept another Monowai.

Boffa Miskel now concede large scale mitigation will be required as well as losses which cannot be

mitigated. Where are the costings? Should this proposal make it through Environment Court

scrutiny it could well be the single biggest loss of unmodified environmental value in New

Zealands' RMA history.

Ref.

Boffa Miskel: Lake Sumner Water Storage and edge inundation: Ecological Aspect: January 2011

and appended cross sections and aerial graphic photos.

Lake Sumner Value, and Lake Sumner edge inundation reports; March 2011

Pattle Delamore Partners; Summary of Scheme Description and Operating Rules for Lake Sumner

Weir: December 2009.

Mark, Johnson, Wilson: Mortality of Plants along the Te Anau Shoreline; NZES 1977.

Christchurch Hydrologic Survey 1956: Hurunui river at Lake Sumner, and ammendments 1991.

LINZ Survey Office; Wellington.

(final draft May 4) p.4