Christchurch, 17 May 2016

Flood threat for Christchurch City much bigger than previously assumed

Following the discovery by Empowered Christchurch several weeks ago that Council has been applying incorrect floor levels for an area in South Brighton, two further areas of concern have now emerged. These are:

Floor levels in tidally influenced areas, and

The extent of the tidally influenced area in Christchurch

According to the Christchurch City Council Plan, Policy 2.5.5, the "minimum floor level in tidally influenced areas should be set for a one-in-200 year event", (i.e. at 12.3 m above the Christchurch City Datum).

With the recent designation of the area downstream of the Avondale Road Bridge as a tidally influenced area1, the minimum floor level should now be 12.3 m above the Datum. This means that the house we highlighted on Bridge Street last week is now actually 1.03 m below the minimum height required. The owner has been given no indication of what the Council intends to do to remedy the situation and the higher floor level is likely to affect a large number of houses in the area.

Regarding the extent of the tidally influenced area in Christchurch:

While the City Council is in the process of updating its floor level requirements for the affected area and, indeed, the rest of the city, it appears that no allowance has been made for a tidal factor in the city-wide flood modelling. Tidal flooding would affect a significant area of Christchurch City. Meanwhile, during one of the driest periods in recent history, a brand new stop bank in the lower estuary north of the South Brighton area was less than 10 cm from being topped on Wednesday, 11 May 2016.

The vast majority of houses behind these flood banks have not been raised. This
1 Supplementary Agenda Council Meeting, Thursday, 12 May 2015; page 12, section 6.8 directly contradicts the City Council’s published recommendations from almost four years ago:

"Acknowledging that the minimum floor levels for homes set at one in 50-year flood event by the Building Act were not adequate for the city’s more flood-prone areas. These levels needed to be set at one in 200-year event."2

We believe that having the correct floor levels for housing is an absolutely critical factor for recovery after a natural disaster. For example, the purpose of the Resource Management Act is set out as follows:

"In this Act, sustainable management means managing the use, development, and protection of natural and physical resources in a way, or at a rate, which enables people and communities to provide for their social, economic, and cultural well-being and for their health and safety…"

The flood risk in Christchurch has significantly increased as a result of the earthquakes, yet it appears as though every effort is being made to build at lower levels.

A key mechanism for avoiding correct floor levels pursuant to regulations has been the application of existing use rights (EURs). We are investigating the history of this complex regulatory loophole in the Christchurch recovery and will be publishing the results in the near future.

ends

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