The Heathcote River reached very high levels following the steady rain on Friday 21 July, combined with a King Tide and an unexpected late storm surge. These factors all combined to see the estuary reach record-breaking levels (flooding areas of Southshore), and in turn, water not draining out of the Heathcote River effectively.
Heavier rainfall in the hill catchments also caused significant runoff into the natural ponding basins around the foot of the Port Hills along Cashmere Stream, resulting in ponding Hoon Hay Valley, Worsleys Valley, Kennedys Bush Quarry reserve and Hendersons basins.
Storage basins in the upper Heathcote filled, and did reduce flood risk further down the river to some extent. But many streets and properties in the low areas along the Heathcote River flooded throughout Saturday. We have recorded 12 properties in these areas that had flooding above the floor.
While street flooding and road closures, and water through a garden or garage can be stressful and an inconvenience, flooding through living areas is extremely distressing, and can see people out of their homes for some time.
We are working to speak one-on-one with all of the people we know of who had floodwater through their homes during the July event. If you had flooding above your floor in this event, and think that the Council does not have your situation recorded, please email us on firstname.lastname@example.org
Many houses in flood prone areas along the Heathcote River have been rebuilt since the earthquakes to higher levels as a defence against flooding. We saw many cases in the July event where this prevented flood waters entering the home. However, these properties will often still see water in the section, and under the house.
We are working with the MetService and NIWA to try and obtain better weather forecasts, particularly for storm surges.
Part of the recovery is about community resilience planning, looking at how people in flood risk areas can minimise the impacts for them, their homes and their belongings. This will include advice such as moving valuables from under the house if heavy rain is forecast.