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Estuary Edge Condition Inventory, by Jacobs NZ LTD

Estuary Edge condition

Not withstanding that the terms of reference for this work was supplied by the client (CCC) and that the focus in part was to prove wither there was earthquake legacy damage to the edge or not, it is a solid and useful piece of work.

It gives good reference to past work and the present the state of the Estuary edge and structures. CCRU believe this is a study that should have been undertaken well before now. This is a useful starting point for information building and more work on solution possibilities is now required. What Jacobs found was interesting, the format and information is an approachable read and is well worth a look at.

“In total the 7.1km of shoreline surveyed was categorised into 145 sections, of which 117 were structures covering a length of 4.5km. Shoreline sections represent lengths of similar condition, hence an individual structure could have multiple sections covering different conditions.

Approximately 3km of the structures (60%) were graded as being in a good condition ranking of ‘A’ or ‘B’ (no or limited evidence of damage), predominantly being council stopbanks that have had repairs post-CES north of Bridge Street (Area 1) and at Ebbtide Street (Area 4), and repaired gabion baskets and reno mattress in the South New Brighton Park (Jetty to Pleasant Point Yacht Club and the Jellicoe Marsh Boardwalk). Additional estuary inundation protection structures not on the estuary edge, being the stopbank around the eastern side of Jellicoe Marsh and the LINZ bund along the Southshore RRZ were also graded as condition ‘B’ and ‘A’ respectively, although the Jellicoe Marsh stopbank was being upgraded following the survey.

Approximately 1.3km of the shoreline, making up 28% of length of structures were given a condition ranking of ‘D’ or ‘E’ (severe or extensive damage resulting in significant loss of functionality). These structures were predominantly found in Area 3 - South New Brighton Park and Area 5 - Southshore. Within Area 3 half of the 600 m of unrepaired reno mattress between the Yacht Club and Jellicoe Marsh, is ranked Condition ‘D’ and ‘E’. The worst section RM2-I, covering a length of 186m to the north of the South Brighton Holiday Park has slipped down onto the estuary bed with lateral spread to now sit below MWHS level, and the land behind has suffered the greatest post CES erosion over the whole study area (average -8.5m, maximum -13.4m).

In Area 5, there is 1km of former private structures, being a collection of still standing concrete walls, informal revetments and informal fill (many from collapsed former walls), that have been graded as being condition ‘D’ or ‘E’. These structures make up 70% of the length of structures within the Southshore area. Conversely, none of the structures in this area have been graded condition ‘A’ and only 6% (83m) have been graded condition ‘B’.

One 40m of the stopbank in Area 1 (fronting Kibblewhite Street) was also given a condition ‘D’ rating due to the significant erosion occurring on the front face of the stopbank. No structures with ‘D’ or ‘E’ rankings were found in Areas 2, 4 or 6.”

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