Part 1 - Palmerston North City Council

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gemconsulting The proposed works have been designed by the MWRC River Engineers. The design has been peer reviewed by Gary Williams from G & E Williams Consultants Ltd. The peer review is attached to this report as Appendix C. It is intended to complete the works over one summer period (preferably the summer of 2012/13). However it is recognised that this timeframe depends on weather conditions and river flows. If we have another wet summer the works may need to be put off until more favourable conditions exist. It is also possible that the works proposed by the applicant occur in one summer and the majority of the works proposed by PMB Landco Ltd occur the following summer. 3.1 Reasons for the Proposed Works There are a number of reasons for carrying out the works in the river at the ANZAC Park Cliffs. As noted, the cliff has started to erode much faster than was anticipated, particularly since 2004, and it is estimated that some 20,000m 3 of soil is now being eroded from the cliff each year. The rate of erosion can be easily seen in the aerial photographs attached to this report as Appendix D. This erosion is a significant source of sediment that is released to the Manawatu River each year, thereby contributing to the rivers already high sediment loadings. Once the works are completed it is anticipated that the erosion and sedimentation from the cliff will cease. The retreating cliff is causing a change in the direction of the river flow to the extent that it will eventually start to erode the opposite river bank, threatening the stopbank protecting the city. Major and costly works will be required to protect the integrity of the stopbank to ensure that it continues to protect the city from floods in the future. If the cliff is left to erode it will eventually expose the existing residentially zoned land on top of the cliff to significant risk. At some point works similar to those currently proposed will become necessary. As the cliff erodes, increased costs can be expected due to the river channel alignment continuing to deteriorate making it more difficult to rectify. Also if the cliff advances too far towards any residential development it may not be possible to rectify without purchasing land and or dwellings to complete the works. There is a significant risk to public safety. The site is a popular recreation site with people using the river for swimming and kayaking. The cliff is extremely unstable and large slips can occur with little or no warning. People pursuing recreational activities in that stretch of the river are exposed to a high level of risk. In addition, risk is also present at the top of the cliff. As residential development continues in the vicinity people are attracted to the open rural landscape around the top of the cliff. While the cliff has been fenced, a recent visit to the site revealed that the cliff has now retreated beyond the fence and that it no longer offers any protection to the public. 3.2 Description of Activities To achieve the realignment of the river in a way that is physically possible, and to avoid or minimise effects on the river, certain works will be required to occur in a certain order. The following describes the main components of the works that will need to be undertaken to achieve the river realignment. A construction methodology has been developed that describes the works, the sequencing of works and mitigation methods in further detail. The methodology is attached to this report as Appendix E. Access and Stockpile Areas Approximately 30,000 tonnes of rock will be used in the construction of the rock lining, bed armouring and snub groyne. A stockpile area (Stockpile Site 1) will need to be created on the grassed area between the river and the Esplanade Walkway to accommodate up to 5,000 tonne of rock at any one time. This immediate supply of rock is required so that there are no delays once construction of the lining is initiated and also to smooth out any minor supply delays from the quarry should they arise. Stockpile Site 1 will be accessed from an existing track leading from the end of Albert Street. Up to 300 tonnes of rock will be transported to the site each day, equating to 15 truck and trailer loads per day. It will 4
gemconsulting take up to 150 working days (30 weeks) to deliver all of the required rock to the site. It is proposed to limit truck movements 1 to the hours of: Monday to Friday: 7:00am to 7:00pm Saturday: 7:30am to 1:30pm. A secondary stockpile area (Stockpile Site 2) is proposed to be developed on the left bank of the river and will contain approximately 2000 tonnes of rock. This area will be accessed from a newly constructed ford across the Manawatu River and access track from Stockpile Site 1. When the project is complete this stockpile site will be disestablished and replanted. A third small stockpile area (Stockpile Site 3) will be developed on land owned by the PNCC within the Pari Reserve. This will be a permanent stockpile accommodating up to 300 tonnes of rock for future maintenance of the rock lining if required. River Crossing and Access Track A ford will need to be constructed upstream of the proposed snub groyne to allow access to the left side of the river. The ford will be constructed from river gravels and be 0.7 metres below the typical low flow level of the river allowing for construction vehicles and machinery to pass. 300kg rock will be placed on the upstream face to protect the ford from scour. An access track will follow the existing beach from Stockpile Site 1 to the ford. The ford will access the Hargreaves land where a short access track will be constructed along the river bank to proposed Stockpile Site 2 and the rock lining site. Diversion of the Mangaotane Stream The Mangaotane Stream will be permanently diverted so that it enters the Manawatu River upstream of the snub groyne. A crossing will be constructed where the stream crosses the access track to allow for its passage to the river. Vegetation Clearance Clearance of vegetation will be required to allow for the access track, the new bed for the Mangaotane Stream and the construction of Stockpile Site 2. The vegetation in this area predominately consists of willow and poplar trees and other weedy species such as gorse and broom. Temporary River Channel A channel of at least 40 metres wide will be excavated through the gravel beach on the right bank of the river to act as a temporary river channel whilst the rock lining is completed. The excavation will start from the downstream end with the gravel from the excavation placed on the land between the current river channel and the excavation for later use as fill behind the rock lining. 20 metre wide areas of gravel will be left at each end of the channel to prevent water flow through the area while it is being excavated. These buffers will be removed once the channel is completed to allow the river to flow through the new channel. Snub Groyne Groynes are structures that protrude from the river bank so as to modify channel alignment by shifting higher velocity flows away from the bank. A snub groyne will be constructed a short distance upstream of the rock lining to help direct the water towards the temporary river channel. The snub groyne will remain in place permanently to help direct water along the rock lining once it is completed. The groyne will protrude into the river by 16 metres (the 1 "Movements" refers to a single entry and single exit 5
Page 1 and 2: good earth matters gemconsulting Ma
Page 3: APPLICATION FOR RESOURCE CONSENT Se
Page 7 and 8: gemconsulting TABLE OF CONTENTS 1 I
Page 9 and 10: gemconsulting 1 INTRODUCTION The Ma
Page 11: gemconsulting Some 400 metres of th
Page 15 and 16: gemconsulting 3.3 Monitoring and Ma
Page 17 and 18: gemconsulting 5 REGULATORY FRAMEWOR
Page 19 and 20: gemconsulting beaches which specifi
Page 21 and 22: gemconsulting Flood Protection Zone
Page 23 and 24: gemconsulting 5.4 Objectives and Po
Page 25 and 26: gemconsulting The extent and nature
Page 27 and 28: gemconsulting Other sources of nois
Page 29 and 30: gemconsulting This natural characte
Page 31 and 32: gemconsulting It is considered that
Page 33 and 34: gemconsulting Policy 16.2 requires
Page 35 and 36: gemconsulting existing stop banks o
Page 37 and 38: gemconsulting Policy 8 This policy
Page 39 and 40: gemconsulting fish, will ensure tha
Page 41 and 42: gemconsulting The Attractive Commun
Page 43 and 44: gemconsulting The Mangaotane Stream
Page 45 and 46: gemconsulting 8 RESOURCE MANAGEMENT
Page 47 and 48: gemconsulting the significance
Page 49: gemconsulting Appendix A LOCATION P
Page 53: FIGURE B: LOCAL PARKS, RESERVES & W
Page 57: FIGURE D: LAND HOLDINGS WHERE WORKS

Part 1 - Palmerston North City Council

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