Morton West, Dacland. Hydrology / Stormwater Management Report Permit Application

Transcription

1 Morton West, Dacland Hydrology / Stormwater Management Report Permit Application February 2014

2 Document history Revision: Revision no. Author/s R01 Jonathon McLean Approved Jonathon McLean Distribution: Revision no. R01 Issue date 14 February 2014 Issued to Dacland (Jonathon Fetterplace) Description: Hydrology report Contact: Name Alluvium Consulting Pty Ltd ABN Contact Jonathon McLean person Ph Address Stewart Street, Richmond Victoria 3121 Ref: C:\Users\JMclean\Documents\panel\morton west\p113011_morton west hydrology report v1.docx

3 Contents 1 Introduction 2 2 The Site 2 3 The Stormwater Strategy Elements 3 4 Waterway Setbacks and Corridors 4 5 The Proposed Stormwater Quantity Strategy Minor drainage system Major drainage system 7 6 The Proposed Stormwater Quality Strategy 11 7 Conclusion 12 Appendix A 13 i

4 1 Introduction Alluvium Consulting Australia Pty Ltd (Alluvium) has been engaged by Dacland Pty Ltd (Dacland) to prepare a Stormwater Management Plan, in support of its permit application for the Morton West site. This report summarises the stormwater management strategy for the site and has adopted a water sensitive urban design philosophy to inform the preparation of the concept plan and subdivision layout plan. 2 The Site The Morton West site covers an area of approximately 69 hectares and is generally bound by Dohertys Road to the north, Derrimut Road to the east, the Regional Rail Link (RRL) to the south and adjoining properties to the west (refer to Figure 1). The subject site is traversed by Dry Creek, which flows from Dohertys Road in the north through to Derrimut Road in the north east. The topography of the site is characterised by moderate to gentle slopes with grades typically in the order of 0.5 to 2%. South and west of Dry Creek the site falls generally in an easterly direction whilst north of Dry Creek the site generally falls in a southerly direction. The Morton West site is located within PSP The Melbourne Planning Authority (MPA) engaged Spiire/CPG to undertake a hydrologic analysis of the entire Wyndham North growth area, which includes PSP Alluvium s report for the Morton West site has been undertaken in accordance with Spiire s/cpg s recommendations and more recent planning advice by Melbourne Water in relation to the preparation of Developer Services Schemes (DSS) for the area. Subject Site Figure 1 Site location 2

5 3 The Stormwater Strategy Elements The stormwater management strategy for the development can be considered in three parts: Waterway Corridor Stormwater Quantity Stormwater Quality There are two major catchments on the site, these are referred to as the Northern Catchment and the Southern Catchment. Refer to figure 2. Catchment 1 (external) 220ha Catchment ha Northern Catchment Catchment ha Southern Catchment Western Catchment Eastern Catchment Figure 2 Overall Catchment Plan 3

6 4 Waterway Setbacks and Corridors Waterways, whether natural or constructed, need to have an appropriate waterway corridor or reserve provided adjacent to development in order to accommodate objectives for flood protection, river health, biodiversity and amenity. A waterway corridor is defined as the waterway channel and its associated riparian zones. The riparian zones consist of two parts (see Figure 3): the vegetated buffer the core riparian zone Figure 3 Waterway corridor (source: Melbourne Water s Waterway Corridor Guidelines) According to Melbourne Water s Waterway Corridor Guidelines assigning a waterway corridor preserves areas of the riparian zone that protect or enhance native vegetation, river health and biodiversity, and provide space for recreational infrastructure and activities (e.g. shared paths and (in some cases) stormwater treatment systems. A fundamental principle is to provide continuity along the core riparian zone, therefore the strong preference is to locate shared paths and other infrastructure outside of the core riparian zone. However page 13 of the Waterway Corridor Guidelines states that in some instances, stormwater treatment systems such as constructed wetlands and bio-retention systems may be located within the core riparian zone but should form a relatively small proportion of the area of the core riparian zone so as not to degrade its ecological function. Following the MPA s circulation of the draft Tarneit North Precinct Plan (PSP) and draft Section 96A Subdivision Plans, Melbourne Water provided the following comment MW s waterway corridor line does not match the creek reserve shown on their plan. Refer to Figure 5 below. 4

7 We understand that Melbourne Water s initial process for determining the waterway corridor included the following background information and steps: SKM s 2012 report titled, Wyndham Vale & Truganina: Preliminary Geomorphic, Flora, Fauna and Socio-economic Assessment, which was commissioned by Melbourne Water. A desktop assessment that determined the presence of remnant native vegetation, to be incorporated into the waterway corridor. A Healthy Waterways Vision for Dry Creek: o Connect diverse and thriving communities of native plants and animals. o Provide amenity to urban and rural areas and engage communities with their environment. o Are managed sustainably to balance environmental, economic and social values. o Revegetating urbanised creeks extensively to improve vegetation and amenity. o Revegetating degraded streamside zones to improve habitat quality for fish and macroinvertebrates. o Improved amenity. On the 23 rd December 2013, a meeting was held at Melbourne Water to discuss the waterway corridor for Dry Creek. The stakeholders present at the meeting included Melbourne Water, Dacland and Alluvium. It was agreed at the meeting that a site visit be organised to walk the waterway corridor lines. The site meeting was held on the 20 th January To assist with the inspection and evaluation of the waterway corridor boundaries, a GPS tablet with the proposed layout and boundaries was used by Dacland s surveyors to determine the accurate location of proposed corridors. Following the field and desktop consultation, Melbourne Water has issued a revised waterway corridor boundary through the subject site (refer to figure 4), which is consistent with the corridor proposed by Dacland. This process has demonstrated that the waterway corridor will be sufficient in conveying flows along Dry Creek and providing for river health and amenity opportunities in a future urbanised landscape. Dry Creek is to remain in its natural form within this corridor. 5

8 Figure 4 Dry Creek waterway corridor (based on MWC supplied GIS files) 6

9 5 The Proposed Stormwater Quantity Strategy The proposed internal drainage system should be designed and constructed in accordance with the minor / major drainage system philosophy. For drainage assets within a catchment area of 60 hectares, Council design standards are expected to apply. For drainage assets greater than 60 hectares, Melbourne Water design standards are expected apply. 5.1 Minor drainage system The minor drainage system would consist essentially of an underground piped network and should be designed to accommodate a 1 in 5 year average recurrence interval event (ARI). 5.2 Major drainage system The proposed major drainage system should provide a flow path which safely and adequately conveys the 100 year ARI design flows through the site. These overland flow paths may be conveyed by the development s road reserves, where they may then outfall through a drainage or waterway reserve. Refer to overland flow plan, which is contained in Appendix 1. The subject site is located within PSP 1089, which is part of the Wyndham North Growth Area. The GAA engaged Spiire to undertake a hydrologic assessment and modelling exercise to determine the location and size of all the required retarding basins for the Skeleton Creek / Dry Creek catchment (Wyndham North Stormwater Management Strategy, May 2013). The purpose of this analysis was to inform the Precinct Structure Planning process and Melbourne Water s future Development Services Schemes. We understand that the stakeholders have agreed to the plan proposed in Figure 5, which will form the basis for retardation requirements within the catchment. As shown in Figure 5, there is no requirement for retarding basins (1 in 100 year ARI) to be located within the subject site of this application. Northern Catchment The Northern Catchment is contained within Melbourne Water s Dry Creek Upper DSS. The catchment is made up of the following subareas (refer to figure 6): Catchment 1 An external catchment area of approximately 3580 hectares that enters the northern boundary (Dohertys Road) of the subject site via the Dry Creek waterway corridor. Based upon the RORB model supplied by MWC/MPA/Spiire, the peak 1 in 100 year design flow is 84 cumecs. The development plan provides a waterway corridor along Dry Creek to accommodate this flow. It is expected that the waterway and riparian plantings will be the responsibility of Melbourne Water. Catchment 2 An internal catchment area of 10 hectares that drains directly to the Dry Creek waterway reserve. The overland flows will be conveyed by the development s road reserves. Some localised filling will be required within the south west corner of catchment 2 7

10 Subject Site Figure 5 Catchment requirements for retardation 8

11 Catchment 1 (external) 3580 ha Catchment 2 (internal) Catchment 3 (external) Refer to fig 7 Catchment 5 (internal) Catchment 4 (external) Refer to fig 7 Figure 6 Northern catchment Catchment 3 Subject Site Catchment 4 Catchment 6 Figure 7 External catchments to the west 9

12 Catchment 3 An external catchment area of approximately 42 hectares that enters the western boundary of the subject site. The peak 1 in 100 year design flow is estimated at 7.3 cumecs, of which the 100 gap flow (or overland flow) is about 4.4 cumecs. The 5 year flows will be conveyed by the stormwater pipe network in Morton West, whilst the 100 year gap flow can be accommodated within the 25.5 metre road reserve or 16 metre road reserve within the Morton West site. These overland flows will then outfall to Dry Creek. Catchment 4 An external catchment area of approximately 50 hectares that enters the western boundary of the subject site. The peak 1 in 100 year design flow is estimated at 8.7 cumecs, of which the 100 gap flow (or overland flow) is about 5.2 cumecs. The 5 year flows will be conveyed by the stormwater pipe network in Morton West, whilst the 100 year gap flow can be accommodated within the 31 metre road reserve or the 18 metre road reserves between the proposed schools. The overland flows along the 31 metre road reserve will continue along this road alignment through the property to the east. Catchment 5 An internal catchment area of 33hectares. The overland flows will be conveyed by the development s road reserves. Southern Catchment The Southern Catchment is contained within Melbourne Water s Truganina DSS. The catchment is made up of the following subareas (refer to figure 8): Catchment 6 An external catchment area of approximately 36 hectares that enters the western boundary of the subject site. The peak 1 in 100 year design flow is estimated at 8 cumecs, of which the 100 gap flow (or overland flow) is about 4.8 cumecs. The 5 year flows will be conveyed by the stormwater pipe network in Morton West, whilst the 100 year gap flow can be accommodated within the two road reserves proposed on the western boundary. These overland flows will then flow through the development to the east. Catchment 7 An internal catchment area of 15.9 hectares. The overland flows will be conveyed by the development s road reserves. 10

13 Catchment 7 (internal) Catchment 6 (external) Refer to fig 7 Figure 8 Southern catchment 6 The Proposed Stormwater Quality Strategy The subject site is located within PSP 1089, which is part of the Wyndham North Growth Area. The GAA engaged Spiire to undertake a hydrologic assessment and modelling exercise to determine the location and size of all the required retarding basins for the Skeleton Creek / Dry Creek catchment. The Spiire strategy also considered the location of stormwater quality treatment assets to meet the Best Practice Targets, namely: 70% removal of the total Gross Pollutant load 80% removal of total Suspended Solids 45% removal of total Nitrogen 45% removal of total Phosphorus To meet the environmental requirements, stormwater runoff will need to be treated to best practice before discharge to Skeleton Creek. The Spiire strategy and Melbourne Water s proposed Developer Services Schemes (DSS) include three distributed stormwater treatment within the Morton West region. The proximity of the three assets are shown on figure 9 and are located within catchments 2 and 5. Dacland are currently in discussions with Melbourne Water regarding the exact configuration of the stormwater treatment assets. A number of options are being worked through as a work in progress. 11

14 Area under investigation Figure 9 : Stormwater quality treatment locations under investigation 7 Conclusion The Morton East site has been based upon achieving best practice stormwater management whist being consistent with the principles and objectives proposed as part of the overall MPA/Spiire Wyndam North Stormwater Strategy and Melbourne Water s planning for its DSS s in the region. This assessment has considered the three main issues and impacts relating to: Waterway corridor Stormwater quantity Stormwater quality The urban design layout will integrate stormwater treatment within the landscape design of public open spaces (not road reserves). The permit plan has also responded to the need for overland flow conveyance through the provision of roadways and drainage reserves. 12

15 Appendix A 13

16 Overland flow Overland Flow Path Plan 14