Plans, policies and reports
Hauraki Gulf Islands review
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Issues and options papers
Impervious Surface Controls for Land Units 11 and 12
Issue
Apart from the controls on gross dwelling area and lot coverage that apply to
land development on the Gulf Islands, there are no controls on the total area of
impervious surfaces.
Impervious surfaces in a catchment decrease storm-water penetration into the
soil and increase flooding and erosion of neighbouring properties and streams.
Excessive areas of impervious surfaces may also cause damage to sewage disposal
fields.
Land Units 11 and 12 are the significant residential land units on Waiheke
Island with lot sizes averaging between 800m2 and 2000m2. These land units have
a permitted lot coverage limit (total building coverage) of 15 per cent and a
gross dwelling area limit of 10 per cent for lots less than 2000m2. There are no
controls on the area of concrete or other water-resistant surfaces that can be
used for driveways, paths, parking areas, barbecue areas, outdoor living courts
and so on.
As there is no infrastructure for storm water or wastewater, it is
particularly important that residential lots have enough permeable surface to
deal with runoff.
Soil type, degree of vegetation cover and the slope of the land moderate
absorption of storm water. Soils on Waiheke Island are Waitemata sandstone/clay
and in the absence of natural vegetation are easily waterlogged. Sixty-five
percent of vacant sites in Land Units 11 and 12 have at least 75 per cent
vegetation cover. Most existing vacant lots in Land Units 11 and 12 are 800-1500
m2 with an average of 1100-1200m2. Fifty-three per cent of vacant land is steep;
36 per cent is of moderate slope. (1 in 6 is a moderate to steep slope).
A slope of 1 in 6 is a threshold that is used in the Plan for the amount of
earthworks that are permitted (less earthworks are permitted above a slope of 1
in 6). This could also be used as a threshold for impermeable surfaces.
Possible approaches
You may have a better or alternative approach to those outlined below. If so,
we would like to hear from you.
- Status quo - do nothing.
- Develop a total impervious surface rule for Land Units 11 and 12 related
to the slope of the land.
- Develop a total impervious surface rule for Land Units 11 and 12 that
takes no account of slope: for example, 20 per cent or 25 per cent total
impervious surface for all sites.
- Develop a total impervious surface rule for all land units.
Note:
While this issue paper can be read in isolation, it is best read in
association with the issue papers relating to:
