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

River and stream water quality and ecology in the Wellington region: State and trends
As mentioned in Section 2.3, the River Environment Classification (REC) has
been used to characterise natural variability (and that due to land use) in rivers
and streams represented in the RSoE programme (see Appendix 2 for details on
the REC environmental factors).
3.2 Intermittently flowing rivers and streams
The extent of ephemeral and intermittent 5 streams in the Wellington region is
unknown. However, an assessment undertaken in the Auckland region
estimated the extent of ephemeral and intermittent streams to be 11,590 km or
75% over and above the estimated perennial stream length (Storey & Wadwha
2009). A similar proportion could be expected in the Wellington region.
Ephemeral and intermittent streams typically occur in headwater catchments
and form the most upstream extent of rivers and streams. Intermittent streams
can also be found in the lower reaches of some rivers and streams where flow
runs beneath the surface of deep gravel substrates for part of the year. Larger
rivers or streams in the Wellington region with intermittently flowing reaches
include the Waipoua River and the Mangatarere Stream.
Although ephemeral and intermittent streams are not regularly monitored in the
Wellington region, a recent study conducted in the wet sediment and
intermittently flowing reaches of six forested Wellington streams found that
these habitats supported diverse macroinvertebrate communities (Figure 3.2).
Pollution sensitive Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa,
including a number of rare or geographically restricted taxa, were found in
both habitat types (Storey 2010). Similarly diverse macroinvertebrate
communities have been found in ephemeral and intermittent streams in other
parts of New Zealand (eg, Parkyn et al. 2006).
Figure 3.2: Intermittent (a) and wet sediment (b) reaches of a small stream in York
Bay, Eastbourne (sampled in 2010)
5 Ephemeral streams flow only for a short time during and, for a short time after, storm events while intermittent streams cease flowing for
part of the year, generally during dry periods (Hansen 2001).
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