2. Mangatawa catchment consents for earthworks, storm water ...

NZ Transport Agency and Tauranga City Council
Mangatawa Drain Flood Bypass and TEM Stormwater AEE
a) Vegetation
The salt-marsh occupies the landward half of this area, and mangrove the seaward half. There is a distinct
gradation in the salt-marsh vegetation: a landward community of sea-rush and open sandy areas with patches
of glasswort (Sarcocornia quinqueflora) and Samolus repens gives way seawards to a marsh dominated by
jointed rush. Salt-marsh ribbonwood (Plagianthus divaricatus) is conspicuous as an emergent towards the
western end of the searush zone, as youthful-looking bushes of c.1-1.5 m tall. Salt-marsh ribbonwood and
sea-rush are also common along the foot of the rubble berms that define the western and southern edges of
most of the SES. Native species of much less cover in the SES include Cotula coronopifolia, Triglochin striatum,
Selliera radicans, Isolepis cernua, I. nodosa, Lobelia anceps, Juncus pallidus and Baumea juncea. The mangrove
canopy is a nearly continuous one, and increases slightly in height seawards, reaching c.1.5 m high along the
tidal inlet just inside the shore-parallel bund of the sewage ponds. Judging by the considerable amount of
lichen on their branches, conditions are less than ideal for mangroves.
The SES seems to have no especially noteworthy botanical features and an increase in the amount of treated
stormwater discharged through it seems likely to result only in changes to the zonation of the dominant
species only.
b) Avifauna
The SES is Site No.13 in Owen (1993), which is the source reference for the Tauranga District Plan. One pair of
banded rail plus a juvenile were observed in that survey (1990) with Pukeko, NZ kingfisher, mallard and whitefaced
heron. No fernbirds were reported and the habitat quality was described as moderate – stock damage;
rubbish tip leachates; rats and feral cats common. Banded rail (Gallirallus philippensis assimilis; moho-pereru)
is also considered to be sparse (i.e. at risk) on a national basis. In this survey fernbird was recorded in marsh
ribbonwood – searush – jointed rush habitat adjacent to the access-track from the stormwater management
area and adjacent to the Vector Gas pipeline route. Fernbirds were both seen and heard on either side of the
access track.
Fernbird calls were also played throughout the rushmarsh habitat but no further birds were located. Accessible
areas of silt and sand substrate were inspected for banded rail foot-prints and recorded calls were played
throughout both the rushmarsh and mangrove – dominated habitat; no footprints were found and no calls
elicited.
In the 1990 survey (Owen, 1993) a pair of banded rail had been observed in this area and four individuals were
recorded in similar habitat near the end of Tip Lane together with fernbirds. The combination of rushmarsh
habitat abutting low, dense mangroves would provide good potential habitat and it would be unusual if banded
rail did not utilise the area at least on an intermittent basis.
Other birds observed using the habitat were harrier, NZ kingfisher, pukeko (common throughout), welcome
swallow and white-faced heron. In addition, five pied stilt and two grey reed herons were observed feeding on
the intertidal flats around the channel edges and two paradise shelduck were observed resting on exposed
intertidal sand.
Overall the rushmarsh – mangrove habitat is a high value area for marshbirds and is presently in an
undisturbed condition – the wetland vegetation has recovered following installation of the gas pipeline, and
farm stock has been excluded.
Status: Final Page 56 April 2009
Project Number: 3932036
NZ1-1552092-Mangatawa Drain Flood Bypass and TEM Stormwater AEE