The district plan’s flood map, 4,000 mapped
areas where the plan expects water: the managed catchments, the
high-hazard core, the ponding spots, and Te Waihora’s own flood
line. Where /floods is the record of the
water that came, this is the water the plan waits for.
Mapped areas
4,000
before overlaps, the standings stack
High hazard
2,579 ha
1,820 areas the plan expects deep or fast water
Catchments
14
the managed water, named by its river
Te Waihora
2.74 m
the contour the lake’s flood area is drawn to
Where the plan expects water
A pale wash for the managed catchments, deep
blue for the high-hazard core, dark marks where the models
expect water to sit, and the grey-teal mass to the south: Te
Waihora’s flood extent inside the 2.74 m contour. Hover any
area for its name. A point’s own answer is at
/before, and the record of water that has
actually come is /floods.
The standings
The managed water is named by its catchment,
the river whose flood it is. The high-hazard areas are the
ground the plan expects to take water deep or fast; the ponding
spots, where it sits.
The high hazard
Where the plan expects the water deep or fast, the standing that bites hardest on what gets built.
High flood hazard1.7K areas · 2.5K ha1,692 areas · 2,530 ha
High hazard, residential overlay128 areas · 49 ha
The managed water, by catchment
The broader watch, the flood-management areas, named for the waterway they belong to.
Avon River225 areas · 3.8K ha225 areas · 3,812 ha
Lower Styx River948 areas · 3.5K ha948 areas · 3,506 ha
Heathcote River222 areas · 3.4K ha222 areas · 3,425 ha
Lake Ellesmere4 areas · 1K ha4 areas · 1,037 ha
Halswell84 areas · 610 ha
Dudley Creek22 areas · 595 ha
Bells Creek525 areas · 508 ha
Lake Forsyth1 area · 411 ha
Avoca Heathcote Valley4 areas · 190 ha
Southshore4 areas · 179 ha
Sumner4 areas · 140 ha
Lansdowne38 areas · 86 ha
Moncks Redcliffs2 areas · 41 ha
McCormacks Bay1 area · 21 ha
The ponding spots
Small areas where the models expect water to sit and wait.
Lower Styx River44 areas · 759 ha
Hendersons Basin8 areas · 289 ha
Cranford Basin7 areas · 143 ha
Cashmere Stream Floodplain3 areas · 49 ha
Cashmere-Worsleys32 areas · 42 ha
Hoon Hay Valley1 area · 27 ha
The lake’s own line
Te Waihora’s flood area: everything inside the 2.74 m contour is the lake’s to reach.
Te Waihora 2.74 m contour1 area · 20.2K ha1 area · 20,219 ha
The suburbs under the waiting water
By share of outline inside the high-hazard
areas: read from a sampled join, so a sliver still counts.
The broader management areas are counted separately on each
suburb’s page.
Brooklands39% high hazard · 52% managed · 12 ponding spots
The district plan’s flood-hazard layers, 4,000 mapped areas covering 38,668 hectares before overlaps. Where /floods is the record of water that has actually come, this is the plan’s expectation, where the models say it can come again, and how the rules answer.
What do the standings mean?
The deep blue is the high flood hazard, the ground the plan expects to take water deep or fast, 2,579 hectares of it. The paler wash is the flood-management area, the broader watch, drawn by named catchment (14 in the record). The small dark marks are ponding spots: places the models expect water to sit. And the great southern shape is Te Waihora itself: everything inside the 2.74 m contour is the lake’s own flood extent.
Why by catchment?
Because floodwater follows the waterway it belongs to. The management areas carry the catchment’s name: Lower Styx, Bells Creek, the Avon, the Heathcote, so the rule reads as "this river’s flood", not an abstract zone.
Is ground outside the map safe?
Not proven, the layers are a model’s answer to the scenarios the plan regulates, drawn at the district’s scale. A storm bigger than the design event, a blocked culvert, a tide on top of the rain, all reach past any mapped edge. The map is where the plan’s rules bite, not a promise about where water can never go.
How does this differ from the flood record?
/floods counts what has been reported, the water that came, patched to the events on file. These layers are the plan’s forecast: modelled extents, mostly DHI’s flood work, that decide where building rules, floor levels and mitigation apply. The record and the expectation overlap, and the difference between them is the interesting part.
The record behind this
Christchurch City Council’s open data, the DistrictPlanB
service’s flood-hazard layers: the flood-management areas named
by catchment, the high-flood-hazard core (DHI’s flood modelling),
the ponding areas, the residential-overlay slivers, and the
Lake Ellesmere flood management area drawn to the 2.74 m
contour. A model’s map, not a memory, the record of water that
has actually come is /floods, the sea’s
mapped reach is /tsunami, and the water
itself is rolled at /waterways.