REPORT. Draft Erosion and Sediment Control Plan. He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) - PDF

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REPORT Draft Erosion and Sediment Control Plan He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) Prepared for Prepared by Date Job Number v1 ASB Tower, Level 4, 2 Hunter Street,

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REPORT Draft Erosion and Sediment Control Plan He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) Prepared for Prepared by Date Job Number v1 ASB Tower, Level 4, 2 Hunter Street, Wellington 6011, New Zealand PO Box 2083, Wellington 6140 P F E Distribution: Horizons Regional Council (FILE) 1 copy 1 copy 1 copy Table of contents 1 Background Objectives Project description Anticipated construction programme 2 2 Principles to minimise effects 2 3 Erosion and sediment control for bulk earthworks Commencement ESC planning Stabilised site entrances Clearance of vegetation Progressive stripping of topsoil and subsequent earthworks Dust control Stockpiling Decanting earth bund Grit traps Localised surface ponding Silt fences Super silt fence Diversion of site run-off Water control bunds Decommissioning 8 4 Stabilisation Tracking and top soiling Additional methods of stabilisation 8 5 Maintenance Improvements 9 6 Erosion and sediment management of riverbed disturbances Manawatu River River situation at project site Manawatu River flows Water quality In-River works River diversion (Preferred Option) 12 7 Site management Timing of works In-River Winter works Adaptive site management Rainfall trigger events Water quality monitoring Water quality assessment Flooding contingency Inspections and audits Accidental discovery 16 8 Review and updating 16 9 Site responsibilities Applicability 18 Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) Appendix A : Appendix B : Appendix C : Ruha Street Design B - concept design drawings Erosion and sediment control indicative sketches Supplementary information Rev. Status Prepared by Checked by Date 1-00 Draft Issue for client review S Parackal A Kennedy/ P Roan Draft Issue for resource consent S Parackal This Draft Issue has been prepared by T+T based on our understanding of existing site conditions and design concept plans included as Appendix E to the Detailed Business Case prepared by Opus 1 and information on anticipated construction methodologies provided by Opus 2. The Contractor is to update the ESCP as required based on the Contractor s construction methodology. 1, He Ara Kotahi Detailed Business Case. Consultancy report prepared by Opus for the. 2 from Peter Kortegast to Andrea Harris dated 11. Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) 1 1 Background (PNCC) is undertaking the design and construction of a 6.6 km shared cyclepath and walkway running from Fitzherbert Bridge to Linton Army Camp in Palmerston North, following the left bank of the Manawatu River (referred to as He Ara Kōtahi). The entire area of works principally drains directly to the Manawatu River or to its tributaries. A new pedestrian and cycle bridge across the Manawatu River is proposed as part of these works and is the subject of this Draft Erosion and Sediment Control Plan (Draft ESCP). The proposed works will enable a secondary crossing downriver from Fitzherbert Bridge. The Draft ESCP is prepared to demonstrate the approach taken to erosion and sediment control for these works. The plan provides a framework for the management of earthworks to avoid accelerating or causing the generation of sediment, and, where this is not possible effective and efficient treatment. The Draft ESCP is prepared to support an application for resource consent, based on expected site conditions and method of works. It will require updating based on the appointed Contractor s construction methodology. 1.1 Objectives The primary objective for erosion and sediment control is to avoid causing or accelerating erosion and the subsequent generation of sediment. Where the primary objective is not possible, the secondary objectives are: To limit the extent and duration of any erosion or sediment generation; The effective and efficient treatment of sediment discharges using regional council accepted erosion and sediment control techniques; and To implement an adaptive management strategy which combines routine site auditing with monitoring of the receiving environment. The structure of the Draft ESCP has been set in accordance with Greater Wellington Regional Council (GWRC s) guidelines for erosion and sediment control 3 which are the adopted guidelines used by Horizons Regional Council (HRC). In summary, the draft ESCP covers the following matters: Section Content 1 Introduction and project description 2 Principles for minimising sediment discharge from site 3 Erosion and sediment control for bulk earthworks 4 Stabilisation 5 Maintenance of standard erosion and sediment control measures 6 Erosion and sediment management of riverbed disturbances 7 Site management, monitoring and reporting 8 Reviewing 9 Site responsibilities 3 Greater Wellington Regional Council (June 2006);Erosion and Sediment Control Guidelines for the Wellington Region Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) 2 1.2 Project description Proposed activities for the He Ara Kōtahi Bridge works at Ruha Street will include: Tree removal, topsoil stripping and vegetation clearance on both sides of the river banks, up to approximately 1,200 m 3 soil disturbance over approximately 1 ha area. Construction of a new pedestrian and cycle bridge, which includes two bridge piles within Manawatu River and one bridge pile on the true right hand bank (city side). Approximately 3,000 m 3 of fill e.g. gravel material with limited fines [fill specification to be confirmed] over approximately 0.8 ha area for the new bridge embankments and widening of the river stop bank on the city side of the river; Approximately 6,200 m 3 of linear excavations to form connecting shared pathways on both sides of the river; Minor upgrades to the road intersection of Dittmer on the city side; and Minor shaping earthworks to upgrade the parking area at the end of Dittmer Street Anticipated construction programme The total expected duration of the works is 52 weeks. Earthworks and river bed disturbance works are proposed to be undertaken in the first 25 weeks. Following this (weeks 25 35), the bridge deck and rails will be installed with permanent stabilisation activities expected to commence week 35 onwards with: Paving of the linear path excavations (weeks 35 45); and Grass and planting of the new stop bank, bridge embankments and pathway berms (weeks 45 52). This anticipated construction programme will require confirmation once a Contractor is appointed for the works. 2 Principles to minimise effects The principles for minimising sediment discharges will be as follows: Minimise disturbance by staging works; Prompt stabilisation of disturbed areas using temporary and permanent techniques as appropriate; Use of best practice erosion and sediment control techniques; Allowing for the ESCP to evolve in response to experience gained on site or new technologies; Ensuring regular inspections and audits of erosion and sediment control measures; and Regular planning meetings and updating of plans to suit changing site conditions. Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) 3 The following sections have been set out to address erosion and sediment control management of: Bulk earthworks on the river banks to construct new stop bank, bridge embankments and connecting shared pathways on both sides of the river - see Sections 3-5. Works within the river for constructing of two bridge piles located within the river channel see Section 6. 3 Erosion and sediment control for bulk earthworks ESC methods and measures which meet the principles set out in Section 2 and are considered appropriate for the proposed works are summarised in Table 3-1. These are discussed in more detail in the sections below. A sketch demonstrating appropriate ESC measures applied for the bulk earthworks is attached as Appendix B (refer Sketch 1). The E&SC methods implemented for any given part of the works will be modified and improved in response to detailed design and site conditions as works proceed, and specific E&SC measures will be implemented as required. Specific E&SC will be discussed at site meeting and daily checks will be undertaken by the contractor based on weather conditions. Table 3-1: Summary of E&SC measures and methods E&SC measures/methods Progressive clearing and stripping Dust control Application To reduce extent of disturbed areas To avoid generation of nuisance dust emissions Decanting Earth Bund (DEB) For catchments between 500 m m 2 Grit trap For catchments less than 500 m 2 Silt fences Diversion of site run-off Bunds/drains Localised surface ponding 3.1 Commencement Where sheeting flows are likely (the cycle way/ shared path or fill embankments) For catchments where site run-off needs to be directed to a DEB or grit trap for treatment prior to discharge. Where temporary flow diversion is required OR where cause scouring on batter faces is observed. Where the existing topography enables ponding of water. Prior to commencement of work a site meeting will be held with HRC s compliance and technical team, PNCC and Contractor. The purpose of the meeting is to confirm that all parties confirm method of works and programme, and assist in preparing the final ESCP for certification from HRC, and confirmation of any standing HRC River Management/PNCC asset protection agreements. 3.2 ESC planning Prior to commencement of works and implementation of any ESC measures, the plan/sketch for each stage will be prepared by appropriately qualified and experienced staff and be submitted to HRC. This will confirm the size and location, and that the device will be built in accordance with the ESCP and the adopted ESC guidelines. Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) 4 3.3 Stabilised site entrances The Contractor shall ensure a stabilised area with aggregate is constructed and maintained at all vehicle access entrances to and from the site. These entrances will be built in accordance with the adopted E&SC guidelines, as reproduced below: Figure 1 : Stabalisaed construction entrance (reproduced from GWRC E&SC guidelines) 3.4 Clearance of vegetation Vegetation will be cleared at the start of each stage of works. Clearance will comprise the removal of tree roots, flax and/or other vegetation, and the existing topsoil and grass will be maintained such that the surface is considered stabilised. 3.5 Progressive stripping of topsoil and subsequent earthworks Progressive stripping of topsoil will be undertaken. Stripping will comprise of removing the surface cover and creating an erodible surface. Following stripping, placement of fill material and/or cut excavations will commence. The Contractor shall ensure that areas stripped do not exceed the design areas of the E&SC measures set out in Table Dust control A construction objective will be to ensure there are no nuisance dust emissions from the project site. For the proposed works, dust generated at the site is likely to have the greatest effect on residential properties on the true right hand of the river and vehicles travelling along Dittmer Drive. To achieve no nuisance dust emissions, the following preventive measures will be used: Damping down of potential dust generation areas with water spray; Grassing down stockpiles where practicable; Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) 5 Ensuring that surfaces are constructed to their final design requirement as quickly as practicable; and Controlling vehicle speeds. On the true right side of the river, source of water for dust control is likely to be from the PNCC water supply. The contractor shall liaise with PNCC and comply with any water supply regulations (to prevent back flow). On the true left side of the river, water will be pumped from the river. Polymer may also be applied as a contingency if required. Wind conditions may be monitored to assist in daily planning of works to minimise the potential for nuisance dust emissions. 3.7 Stockpiling If required, any stockpiled soil material shall be moved to a designated area at the end of each working day. This area shall be atleast 30 m from the river, and a silt fence will be installed on the river side of the stockpile. The Contractor shall confirm proposed stockpiling areas, duration of stockpiles, and any associated controls prior to works commencing. 3.8 Decanting earth bund Where possible, site run-off will be directed to a decanting earth bund prior to discharge into the Manawatu River. Decanting earth bunds will serve as the primary treatment for the works. DEBs will be sized by volume to 2-3% of the catchment area. The detail of the DEBs will be as outlined in Auckland Regional guidelines (2016) 4, reproduced in Detail 2 below: Detail 2: Earth bund with floating T-bar dewatering device (reproduced from Auckland Region guidelines) Where possible, DEB s will be constructed with a length to width ratio between 3:1 5:1, however this may be constrained by site space limitations. Should the design and implementation of any DEB s fall outside the guidelines, certification from HRC will be obtained prior to works proceeding. 4 Erosion and Sediment Control Guide for Land Disturbing Activities in the Auckland Region (June 2016), Guideline Document 2016/005 Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) 6 Typically, the outlet structure of these DEBs will comprise of a floating T-Bar dewatering device (decanting arm with anti-seep collar, as shown in Detail 2 above) which discharging to stabilised ground. Where possible, the discharge end of the pipe will be perforated to disperse flows past the working area to stabilised or undisturbed ground. 3.9 Grit traps Grit traps may be used to capture and discharge flows for the linear pathway excavations, where the upslope catchment is less than 500 m 2. Grit traps may either be an excavated pit with a stabilised lip to discharge (as set out in the Waikato Regional Council E&SC guidelines), or a bunded pit with a pipe outlet. Grit traps will typically be between 3-5m 3. Where possible if a pipe outlet is used, the discharge end of the pipe will be perforated to disperse flows past the working area to stabilised or undisturbed ground. If discharges from these grit traps to the Manawatu River are observed to be discoloured, grit traps will be replaced with a DEB sized for 3% of the catchment Localised surface ponding During construction, there may be areas where localised ponding will occur (e.g. behind the true left embankment, refer Sketch 1). Water will be left to settle undisturbed for as long as practical in these areas. If the area is required to be drained, water will be decanted using a pump and discharged to ground. If the ponded water is discoloured with sediment, it will be pumped to the nearest DEB or grit trap Silt fences Silt fences may be installed as a treatment measure where sheeting flows are considered likely: - Toe of fill embankments, where it is not practical to divert flows to a DEB or if significant scour occurs in the embankment following rainfall; and - Cycleway/shared path, constructed with a cross-fall Silt fences will be built in accordance with the adopted E&SC guidelines, as reproduced below: Detail 3: Silt fence (reproduced from GWRC E&SC guidelines) Returns on the silt fences or rock checks may be used where some movement of water parallel to the silt fence may occur. Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) Super silt fence Super silt fences may be installed as a treatment measure to intercept debris, soil and sediment laden run-off. Super silt fences will be used for earth embankment works within 15 m of the river bank, where installation of a grit trap or DEB is not practical. Silt fences will be built in accordance with the adopted E&SC guidelines, as reproduced below: Detail 4: Super silt fence (reproduced from GWRC E&SC guidelines) 3.13 Diversion of site run-off Dittmer Drive Intersection: Bunds (300 mm minimum height) or shallow drains will be installed to direct water from the intersection to the downstream DEB or grit trap. These bunds (or drains) are likely to be temporary as these surfaces may change as fill operation progresses. Where there is potential for the discharge to result in erosion, drains may be replaced with piping. Cycleway/shared pathway: In most instances, the cycleway/shared pathway will be constructed with a cross-fall to encourage sheeting of water away from the working area where it can be treated by silt fences. Where this is not possible, bunds (300 mm minimum height) or shallow drains will be installed to direct water to the downstream DEB or grit trap. Temporary bunds (or drains) may be installed on a daily basis if required, but definitely in advance of rain or if the site is going to be left unattended for more than 24 hours Water control bunds On completion of the city side stop bank and true left embankment if significant scour is observed following rainfall, a 300 mm high compacted earth bund will be placed along the top of the batter. The purpose of the bund is to prevent any surface flow over the batter face of the fill. The water intercepted by a bund will be directed to the nearest DEB or grit trap. Draft Erosion and Sediment Control Plan - He Ara Kōtahi: Ruha Steet Pedestrian and cycle bridge (Option 1B) Decommissioning The removal of any erosion or sediment control measure shall only occur after HRC are satisfied that the area serviced by the erosion and sediment control structure has been stabilised (refer section 4 below). 4 Stabilisation General definition: Stabilised is defined as inherently resistant to erosion or rendered resistant, such as by the application of base course, rock, polymer, grassing, mulch, or another method. Where hydro seeding or grassing is used on a surface that is not otherwise resistant to erosion, the surface is considered stabilised once 80% vegetative cover has been established, or polymer is applied and visual observations suggest that run-off is clear. Specific application: Permanent stabilisation works will commence following the construction of the bridge and new road intersection and will comprise: Paving and concrete on the shared pathways and new carpark; Top soiling and grass at the pathway berms; Planting of the earth embankments and stop bank; and Rock armouring at river bank, around each abutment In some cases, highly compacted granular fill may be rendered resistant to erosion once works are completed. This will be monitored and if evidence of erosion is present, temporary stabilisation may be required if significant scouring following rainfall is observed. This could comprise polymer stabilisation, application of hydroseed and/or a temporary cover of tree mulch. 4.1 Tracking and top soiling The placement of top soil over disturbed areas is an effective way of starting the stabilisation of surfaces and assists with soil moisture retention and breaking up overland flow. The thickness of topsoil will be approximately 100 mm. Top soiling will be undertaken when areas are completed to the final design profile. 4.2 Additional methods of stabilisation Stabilisation is not limited to the methods set out above. Additional methods and technologies may be investigated during the course of works, to improve the effectiveness of stabilisation. Should a new method be proposed, certification will be sought from HRC prior to implementing. 5 Maintenance Table 5.1 identifies the maintenance requirements for all erosion an
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