THE PORIRUA HARBOUR and ITS CATCHMENT: a LITERATURE SUMMARY and REVIEW Report for Porirua City Council & Wellington City Council
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THE PORIRUA HARBOUR AND ITS CATCHMENT: A LITERATURE SUMMARY AND REVIEW Report for Porirua City Council & Wellington City Council Paul Blaschke Josephine Woods Frances Forsyth Blaschke and Rutherford Environmental Consultants February 2010 ISBN 978-1-877548-24-6 (print) ISBN 978-1-877548-25-3 (online) Cover photos: Upper: Overlooking Porirua Harbour and Paremata ca. 1920. Photographer: Sydney Charles Smith. PA Collection-3082-5, Alexander Turnbull Library Lower: Paremata Vista, 2009. Photographer: Keith Calder. Pukerua Bay SH1 am Rewarewa Point Stre Taupo m am rea t S ri Stre Karehana Bay aho O u t e r Horoki Plimmerton Kak H a r b o u r k Grays Rd on Cree Goat Camborne Point Rati P a Mana u a t Motukaraka Whitireia Point Ngati Toa Bank a Rocky Bay Park h a n u Ration Point Point Domain I n l e Pauatahanui Mana i Wildlife Reserve Marina Browns Bay t Paremata Stream Judgeford SH58 Browns Bay Pauatahanui Stream O n er mp o t o A Porirua CBD Kenepuru S tream Cannons Creek Canno reek Duck C chell Stream ns C Mit reek tream rirua S o P Linden Tawa kapu Stream Ta SH1 m s Strea g in tebb S ream St nt o m el onville B Literature review of Porirua Harbour and catchment CONTENTS Executive Summary............................................................................................................ 1 Introduction......................................................................................................................... 3 Acknowledgements......................................................................................................... 4 Physical dimensions, components, characteristics and significance of Porirua Harbour and its catchment................................................................................................................. 5 Tectonic and geological/geomorphic history, including current movement rates.......... 8 Geology....................................................................................................................... 8 Faults........................................................................................................................... 8 Geomorphic evolution .............................................................................................. 10 Mana Spit evolution.................................................................................................. 11 Drainage systems ...................................................................................................... 11 Environmental setting................................................................................................... 11 Summary of literature on Porirua Harbour catchment...................................................... 12 Catchment land use, vegetation and soils ..................................................................... 12 Soils........................................................................................................................... 14 Stream geomorphology and hydrology......................................................................... 15 Freshwater quality......................................................................................................... 16 Stream biota including macroinvertebrates and freshwater fish................................... 19 Terrestrial biodiversity.................................................................................................. 20 Birds.......................................................................................................................... 22 Summary of literature on Porirua Harbour ....................................................................... 23 Water quality................................................................................................................. 23 Sediment characteristics (quality and quantity)............................................................ 25 Sediment contamination and Harbour contaminants .................................................... 27 Harbour hydrodynamics................................................................................................ 29 Flow constrictions, including bridges and reclamations........................................... 29 Harbour flushing....................................................................................................... 30 Dredging and impacts ............................................................................................... 31 Biota.............................................................................................................................. 31 Habitats and vegetation............................................................................................. 32 Plankton species........................................................................................................ 33 Benthic fauna ............................................................................................................ 33 Cockle surveys.......................................................................................................... 35 Fish............................................................................................................................ 36 The degree of contamination of biota by toxic contaminants....................................... 36 Alien biota..................................................................................................................... 38 Patterns and quantity of human use .............................................................................. 38 Maori use .................................................................................................................. 38 Harvesting................................................................................................................. 39 Access ....................................................................................................................... 39 Report for Porirua City Council & Wellington City Council February 2010 Blaschke and Rutherford Environmental Consultants Literature review of Porirua Harbour and catchment Water sports .............................................................................................................. 39 Other activities.......................................................................................................... 40 The effects of roading ................................................................................................... 40 Summary of literature on Inlet exchange and outer harbour dynamics ............................ 42 Tidal inflow and outflow dynamics .............................................................................. 42 Effects of Mana Marina on the inlet and both arms of the Harbour............................. 43 Impacts boats and moorings may have in either arm of the Harbour ........................... 43 Patterns and quantity of human use .............................................................................. 43 Beach development and coastal erosion ....................................................................... 43 Sand bar dimensions and dynamics .............................................................................. 45 Effluent dispersal characteristics and potential impacts on the Harbour from the wastewater treatment pipeline discharges..................................................................... 45 Stormwater management .................................................................................................. 46 The effects of catchment land use on sedimentation and water quality ....................... 46 Rural impacts ............................................................................................................ 46 Urban impacts ........................................................................................................... 47 Industrial impacts...................................................................................................... 48 Sewerage infrastructure overflows and stormwater outfalls discharging into the Harbour ......................................................................................................................... 48 Current knowledge of impacts of stormwater on the Porirua Harbour and catchment 49 Sediment and nutrient transport........................................................................................ 51 Catchment erosion and inputs to streams...................................................................... 51 Sediment transport and delivery to the Harbour........................................................... 52 Estuarine inputs and Harbour discharge ....................................................................... 55 The relationship between sedimentation and Harbour hydrodynamics........................ 56 Climate change and sea level rise ..................................................................................... 57 Predicted changes and sea-level rise characteristics for the Harbour catchment.......... 57 Likely impact of predicted climate change and sea-level rise on the Harbour and catchment ...................................................................................................................... 58 Summary of relevant New Zealand soil erosion literature and knowledge...................... 60 Catchment erosion and sedimentation .......................................................................... 60 Methods for assessing estuarine