St Marys Bay and Masefield Beach Improvement Project Overview

Transcription

1 St Marys Bay and Masefield Beach Improvement Project Overview uckland Council Healthy Waters team, in conjunction with Watercare and Panuku propose to undertake a major infrastructure project to reconfigure the existing combined sewer and stormwater network at St Marys Bay and Masefield Beach as the first step in a programme to improve water quality and remove combined sewer overflows from uckland s Beaches We plan to lodge for Resource Consents this year and start building next year making tangible improvement by 221 Why are we doing it? The historic combined stormwater and wastewater network utilised in St Marys Bay and Herne Bay catchments is designed to over flow from time to time but today existing outfalls discharge frequently to local beaches St Marys Bay and Masefield Beach The outfall at St Marys Bay discharges at the shoreline and one outfall at Masefield Beach is broken and needs replacing We are undertaking this project in order to make tangible progress in improving water quality for these local environments, to make an overall reduction in combined sewer overflows to the Harbour and to pave the way for future improvements that will further improve water quality This project came out of the programme of work that was undertaken last year between Healthy Waters, Watercare, Panuku, uckland Transport and members of the Panuku Mana Whenua forums B How will it work? The project works by collecting flows from London Street and Hackett Street near St Marys Bay and Sarsfield Street near Masefield Beach in new pipelines which terminate in a common collection point near Pt Erin The pipeline from St Marys Bay is big enough that it can store flows so that these can be returned to the main sewer when it has capacity new outfall will be constructed from the common collection point so that flows can be safely discharged to the harbour when there is no spare sewer capacity The project is being designed so that it will integrate into long-term network improvement plans being developed by Watercare and Healthy Waters, which will further reduce combined sewer overflows and improve water quality The next page shows more detail of how the project will work when it is built

2 St Marys Bay and Masefield Beach Improvement Project Overview How does it work? 1 new collector system takes overflows from the existing Hackett, London and New Street overflows and conveys them to a new connection near Pt Erin Park (black and yellow) 2 New collector pipes take the existing Sarsfield Street overflows to the same point (pink) 3 new pump station at this point returns low flows back to the main branch 5 sewer (blue) 4 new marine outfall (to replace the existing outfall) is used to discharge high, dilute flows to the receiving environment (light blue) What are the benefits? The number of overflows at St Marys Bay is reduced from around 7 per year to around 2 4 per year The number of overflows at Masefield Beach is reduced from around 7 per year to zero The new outfall will discharge in high rainfall events around 3 times per year

3 St Marys Bay and Masefield Beach Improvement Project Overview C What will it achieve? The project will work in two ways Firstly, it will resolve the issues of overflows to both of these local beaches by replacing the existing old outfalls with a single new outfall that will discharge much further out in the harbour, away from the beaches Secondly, the project will also significantly reduce the total number of overflows to the harbour by returning low flows to the main sewer when spare capacity (or room ) is available to take extra flow It will reduce combined sewer overflows to St Marys Bay from over 7 per year to around 2 4 per year It will reduce combined sewer overflows to Masefield beach from over 7 to zero per year It will replace the existing old outfalls at Masefield Beach with a single new outfall This new outfall will discharge away from all beaches out into the Harbour This new outfall will discharge around 3 times per year The project will be a first step towards overall improvement of the combined sewer network (which will reduce overflows from other locations ) and it can work with any future solution that is proposed for the wider network How will overflows be reduced? The overflows can be reduced because there is a large storage volume in the tunnel between St Marys Bay and Pt Erin This means that the overflows can be stored in the tunnel until there is enough spare capacity in the main sewer to return the flows there, where they can be taken to Mangere Wastewater Treatment Plant to be treated When there are very high rainfall events (such as those uckland experienced during March) then the outfall will discharge out into the harbour There will still be a small amount of wastewater in this discharge How will the remaining overflows change? There will be fewer overflows so stormwater and wastewater will enter the harbour much less often than it does now The overflows will be screened so they will have some degree of treatment before discharging Because of the storage and return component, the total annual load of wastewater to the receiving environment will be reduced o It is very difficult to accurately quantify the different amounts of wastewater and stormwater in any one overflow because this depends on so many different variables how much rain there is, how full the sewer was at the time, if there are any blockages, if there are other flows in the network causing problems etc It is more useful to think in overall terms that the total load will be reduced What will happen in the long-term? We are replacing infrastructure that is up to 1 years old The infrastructure built as part of this project will be part of uckland s water infrastructure for the long-term, either as part of an improved combined network or as stormwater-only infrastructure s additional projects are undertaken to improve the situation, this project will become part of the wider solution

4 D Where exactly will it be built? The Healthy Waters team has spent some time looking at where it could be possible to build all this new infrastructure In particular, we have been looking at how we could construct the various parts of the project safely, minimising impacts on the community and the environment We have also needed to consider the safety of our operations team and ongoing impacts on the community and environment once the infrastructure is commissioned We now believe that we have enough meaningful information to seek feedback from the community Part of this is looking at the location of the main pump station near Pt Erin and where the new outfall could go The next pages show the options we are considering The first sketch shows one overall alignment from London St through to Pt Erin There are not many options for the pipe between London St and St Marys Reserve due to the lack of space The next sketch shows potential options for the final pump station and collection shaft The route of the pipeline between St Marys Reserve and Pt Erin is determined by this pump station location The Healthy Waters team prefers the northernmost location as it is the safest from a construction and operations perspective and has the least impact on neighbouring communities The final sketch shows options for the new marine outfall The Healthy Waters team prefers the blue option that discharges out by the Harbour Bridge This is because there is the least amount of construction in the marine environment, this option avoids existing mussel beds and at this stage it looks the easiest and safest to construct No final decisions have been made and feedback is sought at this stage

5 Sketch 1 Overview of the pipelines LEGEND: PREFERRED PIPELINE ROUTE TRENCHED PREFERRED PIPELINE ROUTE DRILLED SRFIELD St CONNECTIONS TRENCHED SHFT LOCTIONS CURR N ST ON RM P MN WHENU RE OF SIGNIFICNCE MIRI ST LO ND ON ST PROPOSED PUMP STTION SHELLY RING TER RC E BECH RD KET T ST DE HC LP R ST RY SR CIV PER D Plot Date: 24/5/217 1:2:51 PM Office: NZKL EM ME T TS T Filename: P:\2-BST\ HCKETT DIVERSION\5 DELIVER DESIGN\54 CDD\DWG\ DRG-CC-111DWG M m SCLE 1:15 CLIENT REV DTE REVISION DETILS FOR CONSULTTION PPROVED SCLE SIZE 1:15 1 DRWN M TUIKOLOVTU DESIGNED CHECKED M COBELDICK PRELIMINRY NOT FOR CONSTRUCTION ST MRYS BY PROJECT GENERL LIGNMENT PPROVED DTE TITLE DRWING No PROJECT No WBS TYPE DISC NUMBER REV DRG CC 12

6 Sketch 2 Options for the new pump station and tunnel shaft LEGEND: PREFERRED PIPELINE ROUTE LTERNTIVE PIPELINE ROUTE CURR N ST ON RM P MN WHENU RE OF SIGNIFICNCE MIRI ST PUMP STTION 1 SHELLY BE CH RD TT ST Filename: P:\2-BST\ HCKETT DIVERSION\5 DELIVER DESIGN\54 CDD\DWG\ DRG-CC-115DWG PUMP STTION 3 Plot Date: 24/5/217 1:24:9 PM Office: NZKL EM ME PUMP STTION m SCLE 1:1 CLIENT REV DTE REVISION DETILS FOR CONSULTTION PPROVED SCLE SIZE 1:1 1 DRWN M TUIKOLOVTU DESIGNED CHECKED M COBELDICK PRELIMINRY NOT FOR CONSTRUCTION ST MRYS BY PROJECT GENERL LIGNMENT PPROVED DTE TITLE DRWING No PROJECT No WBS TYPE DISC NUMBER REV DRG CC 115

7 Sketch 3 Locations for the new outfall -4-5 LEGEND: MRINE PIPELINE DRILLED OPTION MRINE PIPELINE TRENCHED OPTION MRINE PIPELINE DRILLED OPTION MRINE PIPELINE TRENCHED OPTION 2 MRINE PIPELINE DRILLED OPTION MRINE PIPELINE TRENCHED OPTION OUTFLL MN WHENU RE OF SIGNIFICNCE CUR 3 N RM 4RN ST O m ST MRYS BY ST MRYS BY CONCEPT DESIGN OUTFLL OPTIONS TITLE DRWING No SCLE 1: P Filename: \\URECONINFO\SHRES\NZKL\PROJECTS\2-BST\ HCKETT DIVERSION\5 DELIVER DESIGN\54 CDD\DWG\ DRG-CC-14DWG M COBELDICK DTE CHECKED PROJECT PPROVED 3 DESIGNED PRELIMINRY NOT FOR CONSTRUCTION 15 1 DRWN SIZE 1:15 BECH RD 25 SCLE M TUIKOLOVTU PPROVED SHELLY PRELIMINRY FOR CONSULTTION B REV DTE REVISION DETILS POINT ERIN PRK SHFT OUTFLL MH SWMH CLIENT 4 SWMH OUTFLL Office: NZKL Plot Date: 24/5/217 1:56:7 PM SWMH PROJECT No WBS TYPE DISC NUMBER REV DRG CC 14