Sedimentation

Sediment (particularly muddy sediments) discharged into rivers, streams and harbours can negatively impact a range of values, including ecosystem health and the way people use water for recreational, cultural and spiritual purposes.

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Sedimentation rate

The depth of sediment overlying concrete pavers buried at discrete sites provides an indicator of estuary sedimentation. The map shows average sediment depth change (mm) from baseline (year pavers installed) at each monitoring site (displayed as circles) and over the whole harbour (shaded region). Positive values indicate where there has been sediment deposition (accumulation) and negative values indicate erosion.

See Stevens et al. 2022 for technical methods, data tables, and further information

Bathymetry

Contours displayed at 0.25 m intervals derived from depth databases gridded at 10 m resolution. Bathymetry depths (m) are referenced to Porirua Sounding Datum (SD) which is linked to Porirua Chart Datum (CD), defined as 2.55 m below Land Information New Zealand (LINZ) steel pin C1K1 at the Mana Cruising Clubrooms.

Due to the wide spaced survey lines and irregularly shaped seabed, some gridding artefacts can be seen along the outer edges of the survey area. For example, along the northern channel of the Onepoto Inlet where it appears there are ridges in the channel and along the southern edge of the Pāuatahanui Inlet where some flat areas show raised unnatural features.

See Waller & Stubbing 2019 - Bathymetry for technical methods, data tables, and further information

Bathymetry change

Contours derived from differencing the 10 m resolution depth databases from each combination of surveys. Red areas indicate sedimentation, while blue areas indicate general harbour erosion. Bathymetry depths (m) are referenced to Porirua Sounding Datum (SD) which is linked to Porirua Chart Datum (CD), defined as 2.55 m below LINZ steel pin C1K1 at the Mana Cruising Clubrooms.

Results show shoaling across the main Onepoto Basin, but generally little change along the shallow banks at the northern entrance. The Pāuatahanui Inlet has likely experienced general shoaling at the southern side and some possible erosion or deepening on the northern side.

See Waller & Stubbing 2019 - Bathymetry for technical methods, data tables, and further information