Part 1 - Palmerston North City Council

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gemconsulting channel as it is excavated. Once the bulk of the channel is excavated the remaining downstream and upstream portions will be removed allowing the river to flow through. This will likely see a ‘flushing flow’ of water containing higher than normal loads of sediment from the disturbed gravels for a short time. Accessing the site from the right bank will necessitate carting most of the rock across the river. A crossing (ford) will be established upstream of the work site to allow for this. It is expected that sediment in the river bed will be disturbed and released during the construction of the ford. Numerous trips across the river by off‐road trucks will be required and while these crossings may cause disturbance of the gravels in the ford, initially resulting in a small amount of sediment discharge, it is expected that this will soon settle and any discharge will be minimal. It is noted that the trucks themselves will not introduce new contaminants into the river environment. The construction of the snub groyne and cofferdam will be constructed in the active river channel and there is expected to be some sediment released from the river bed and gravels while this work takes place. Past experience has shown that sediment discharges from this type of work is short term and any discoloration is expected to dissipate within 200 to 300 metres of the site. The groyne and coffer dam will be wide enough to allow heavy vehicle access from the central island created between the new river channel and the old channel and will be used to transport gravels between the island and the work site. A further cofferdam will be constructed downstream of the worksite to prevent the free flow of river water from entering the site. The construction of the majority of the rock lining and the bed armouring will take place in the dry 2 river bed contained within the cofferdams minimising the release of sediment into the river. The unnamed tributary that runs from the central valley between Waicola and Cashmere Drives will run into the ‘dry’ area. This stream only flows during wet weather and only has a small volume of flow. As the works progress past this stream, it will be channelled so that it can flow directly over the rock lining and to the river. A cross section of the proposed stream channel is shown on Figure 5 of the engineering plans attached as Appendix B. The Mangaotane Stream will be diverted so that it runs to the Manawatu River upstream of the proposed works thereby avoiding any issue of inflow and associated outflow of sediment laden water from the work area. The lower portion of the rock lining will be constructed within the flowing river but will be done so from the left bank and from the platform created from the previously completed works. Excavations of the river bed to reach the founding depth of the rock lining will cause unavoidable sediment release to the river. Once the lower portions of the wall are constructed it is expected that sediment release will be minimal. River gravels will be carted from the central island over the upstream coffer dam and to the construction site thereby requiring no river crossings during this phase of construction. An additional potential cause of an adverse effect on water quality is the accidental release of oils or other chemicals from machinery working in the riverbed. All machinery working in this environment is required to be of good condition and properly maintained and is not to be parked or left unattended in or near the river. The risk of this type of spill is considered to be extremely low. All fuels and oils will be required to be stored well away from any surface water bodies and in bunded facilities to avoid the likelihood of such contaminants entering water bodies. Unclean machinery can also spread weed species into new terrestrial and aquatic environments. This has been observed in the South Island with the rapid spread of Didymo throughout several water bodies. To minimise such risk all machinery will be required to be cleaned prior to entering any water bodies on the site to prevent the spread of pest species. 2 The term 'dry' is used here but is a loose term as the bed will still contain water but it will not be running into the river. It would be more of a pool of still water. 16
gemconsulting The extent and nature of the disturbance to the river bed The proposed works will disturb the bed of the river in the immediate location of the works. As described in Section 3.2 above, it is intended to excavate a temporary river channel through the beach on the right bank of the river and to eventually use this gravel to support the rock lining. The proposed works will disturb the river bed for much of its width in places and for a length of some 550 metres in total. Some of the proposed works will be permanent, e.g. the rock lining, the snub groyne, bed armouring and re‐alignment of the River and Mangaotane Stream. Other components will be removed once works are complete, e.g. cofferdams. It is expected that the beach on the right river bank will reform over time after completion of the works however, it will not reform to the same extent that it is now due to the river being closer to the right bank. Effects on in‐stream habitats, spawning habitats and fish passage The proposed method of construction will ensure that fish passage is maintained in the Manawatu River at all times during the construction period. Fish passage will also be maintained for the Mangaotane Stream. The unnamed tributary only flows during wet weather and it has a small waterfall of about two metres in height as it joins the river. When the works are complete it is expected that it will continue to have a similar fall into the river at low flow conditions. Any habitats in the immediate area of the works will likely be destroyed, however it is expected that such habitats would quickly reform in this area once the works are complete as has occurred near other rock linings along the river. Downstream habitats could potentially be affected by sediment released from the river bed during the works but it is expected that this will be limited to 200 to 300 metre downstream of the site. Past experience has shown that sediment can be released from such works but that it is minimal and does not stay in suspension for any great distance. Adherence to the construction methodology will mitigate the severity of the effects on downstream habitats with the majority of the works taking place out of the active river channel. The ‘in river’ construction works are programmed to start in September 2012 and are expected to be complete by April 2013 thus avoiding the spawning season of trout (May to September). Effects on flood flows The works will not restrict or affect flood flows of the river itself, however, the possibility of floods during the construction phase presents challenges to the project. If a flood were to occur during the construction, it is possible that stockpiled gravel could be lost downstream. To help mitigate this, the work is to proceed quickly once commenced. Also, the shape of the stockpile, following the curvature of the river, and the addition of larger rocks at the upstream end of the stockpile are expected to minimise any losses during a flood event. Some gravel recovery may be required from downstream if losses are experienced. Effects on water levels and passage of flows The passage of flows will be maintained throughout the construction stages of the project. Once the river is diverted through the temporary channel the works will proceed in the "dry" river bed with no effect on the river flow. Water levels are not expected to alter as a result of the proposal. The river will still rise and fall naturally in accordance with rainfall in its catchments. It is intended to realign the Mangaotane Stream so that it joins the river just upstream of the snub groyne. Once the initial re‐alignment is completed the only further effects on this stream will be from machinery crossing it via a ford on the access track to the site. The rock lining will be designed to accommodate the smaller unnamed tributary so that it will join the river in the approximate location and level that it does now. Effects on public access to the river and recreation During construction, public access to the site, in particular the river, beach and rock stockpile area will need to be restricted. Currently there are signs restricting access to the river in this location due to the existing safety concerns in the area so effectively there will be little change from the current situation. 17
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 and 12: gemconsulting Some 400 metres of th
Page 13 and 14: gemconsulting take up to 150 workin
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: gemconsulting 5.4 Objectives and Po
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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