River and stream water quality and ecology - Greater Wellington ...

River and stream water quality and ecology in the Wellington region: State and trends
(c) River and stream works
A range of riverbed and riverbank works are undertaken in the Wellington
region for flood protection and erosion control purposes such as channel realignment,
bed contouring and gravel extraction. Greater Wellington holds
several resource consents to undertake such works in rivers across the region
(eg, Otaki, Waikanae, Hutt, Ruamahanga, Waiohine and Tauherenikau rivers).
Other consented activities in the beds of streams in the Wellington region
include diversions (temporary and permanent), installation of instream
structures (eg, weirs) and piping and reclamation. A considerable amount of
stream piping and reclamation in recent years has been associated with
residential and roading development in urban areas of Wellington, Porirua and
Hutt cities. 11
(d) Water abstraction
Surface water is abstracted for a variety of uses throughout the region,
including irrigation, public water supply, water race water supply and industrial
uses. Water abstraction places pressure on rivers and streams by reducing the
amount of water available for aquatic habitat, physical, chemical and biological
processes, recreational activities, and other instream uses and values. Large
scale abstraction of groundwater that is hydraulically connected to surface
water also has the potential to impact on rivers and streams. The demand for
water is often greatest during dry periods in summer when river and stream
flows are at their lowest and temperatures are warm, further exacerbating the
pressures placed on these ecosystems.
According to Keenan et al. (2012), as at the end of 2010, consented water
abstraction in the Wellington region equated to approximately 414 million
m 3 /year; this represents a 54% increase on the 269 million m 3 /year of water
allocated in 1990. Surface water (ie, lakes, rivers and streams) makes up
around two-thirds of the allocated water resource, of which community water
supply has the greatest annual allocation (41%). Other major uses of surface
water resources are irrigation (with 24% of the annual allocation), Wairarapa
water races (19%) and hydroelectricity generation (14%). In contrast, the main
uses of groundwater allocation are irrigation (60%) and public or community
water supply (36%), although overall – from all groundwater and surface water
sources – water supply and irrigation are allocated similar amounts of water on
an annual basis (Keenan et al. 2012).
Most (77%) of the increase in water allocation between 1990 and 2010 was for
irrigation; a further 20% was for public water supply. Further, most (83%) of
the region’s increase in water allocation occurred in the Wairarapa, mainly for
dairying (Keenan et. al 2012). Under the current allocation policies of Greater
Wellington’s existing RFP (WRC 1999), the only rivers with significant
(>30 L/s) remaining allocation available during normal to low flows are
Tauherenikau, Hutt (lower reach), Wainuiomata (lower reach) and Otaki rivers
(see Keenan et al. 2012 for further discussion).
11 Based on Greater Wellington’s consent records (excluding consents for culverts less than 20 m in length), it is estimated that between
2003 and 2005 a total of 14.9 km of stream length was lost due to piping or reclamation in the Wellington region.
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