Youth Justice Redevelopment Project

Transcription

1 Youth Justice Redevelopment Project Youth Justice Facility Cherry Creek, Victoria February 15, 2018

2 Document control record Document control Report title Document ID YJRP-REP-CC Project Number File path C:\pw_work\ashley.watson\audc1_01\dms98722\YJRP-REP-CC _B.docx Date Rev Revision details / status Author Approver 18/01/18 A Draft Issue A.Watson L.Bird 31/01/18 B Issued for Town Planning A.Watson L.Bird 15/02/18 C Issued for Town Planning A.Watson L.Bird Consultant Team Document control Architectural HDR Level 12, 360 Elizabeth Street, Melbourne Vic 3000 Civil, Structural, Building Services, Fire Safety, Vertical Transport, ESD, ICT, AV, Acoustics Aurecon 850 Collins St, Docklands Vic 3008 Security Umow Lai Level 4, 10 Yarra Street, South Yarra Vic 3141 Cost Planner Slattery Level 14, 160 Queen Street, Melbourne Vic 3000 BCA Consultant TBC February 15, 2018 Page i

3 Acronyms CWW DJR MW YJRP City West Water Department of Justice and Regulation Melbourne Water Youth Justice Redevelopment Project February 15, 2018 Page ii

4 Contents 1 Introduction... 2 Project overview... 2 Purpose... 2 Limitations & assumptions Site Conditions... 3 Existing Conditions... 3 Proposed Development Site... 4 Stormwater Management Objectives... 4 Proposed Stormwater Treatment System Catchment Catchment Catchments 3 & Stormwater Treatment Results Catchment Catchment Catchments 3 & Proposed Stormwater Detention System Catchment Catchment Catchment 3 & Tables Table 1 - Catchment 1 Composition... 4 Table 2 - Catchment 1 Stormwater Treatment Results Summary... 6 Figures Figure 1 Catchment 1 MUSIC Model... 5 Figure 2 - Catchment 1 Swale Effectiveness... 5 Figure 3 - Catchment 1 Bioretention Effectiveness... 5 Figure 4 - Overall Treatment Train Effectiveness... 6 Figure 5 Catchment 2 MUSIC Model... 6 Figure 6 - Catchment 2 Bioretention Effectiveness... 6 Figure 7 - Catchment 3 & 4 MUSIC Model... 7 Figure 8 - Catchment 3 & 4 Treatment Effectiveness... 7 Appendix A Sketches Appendix B Detention Calculations Appendices 4 Access Road... 9 Stormwater Management Objectives... 9 Proposed Stormwater Treatment System... 9 Stormwater Treatment... 9 Proposed Stormwater Detention System Conclusion February 15, 2018 Page 1

5 1 Introduction Project overview The scope of this project is to develop a youth justice facility with an initial capacity of 224 beds for remand and sentenced clients, a 12 bed mental health unit, an intensive supervision unit of at least eight beds, with scope for further expansion to a total of 300 beds within the allocated site. The Department of Justice & Regulation have engaged HDR as the lead consultants and architects for the delivery of this project. Aurecon are the engineering sub-consultants to HDR. The subject site is located north of Little River Road and west of Princes Freeway in Werribee. Presently, the subject site is a green-field site with no services infrastructure. The development site is approximate 67 hectares in size and is part of a 320 hectare site. Purpose The purpose of this report is to outline the stormwater management strategy and to detail how stormwater quality and quantity control will be achieved on the project. The report covers the stormwater management strategy for the site and the access road. Limitations & assumptions This report is based on the information available at the commencement of the Schematic Design phase of the project and is preliminary in nature. This report is reliant on the following information: HDR masterplan site layout Verbal advice received from Melbourne Water (MW) regarding detention requirements (dated 13/09/2017) Melbourne Water advice MWA (dated 13/11/2017) February 15, 2018 Page 2

6 2 Site Conditions Existing Conditions The site has a total area of 67ha. The site is bounded on all sides by a mixture of cultivated pasture and native grasslands. The Princes Freeway is located approximately 360m southeast of the southeastern corner of the site. The site is currently undeveloped with native grasses in the north and uncultivated pasture in the south. Two valleys run through the middle of the site, generally falling from west to east. The northern and southern parts of the site fall towards the valleys at a gentle slope of between 1 and 2%. The YJRP facility site will be confined to the southern part of the site (approximately 25ha) to avoid disturbance of the native grasslands. Proposed Development The proposed YJRP facility consists of an access road and the site. The site has the following main features: Staff and visitor carparks Primary hub building comprising security, admissions, health, staff areas, laundry, sitewide plant and equipment rooms Educational buildings (classrooms/workshops) Communal dining building Recreational buildings including indoor pool and court A number of clusters of accommodation buildings Outdoor recreational areas for each accommodation building cluster A small (AFL 9s size) oval A road network including: o External ring (outside the perimeter wall) road o Internal ring (inside the perimeter wall) road o Smaller accessways inside the site for golf cart sized vehicles A small (AFL 9s size) oval The proposed YJRP facility has been designed as a campus style facility, and as such will include sizeable open spaces between the buildings. February 15, 2018 Page 3

7 3 Site Stormwater Management Objectives The proposed for the development has been developed incorporating water sensitive urban design (WSUD) principles. Based on discussions with Melbourne Water the following minimum stormwater management objectives have been adopted: Total Suspended Solids (TSS) - 80% retention of typical urban annual load Total Nitrogen (TN) - 45% retention of typical urban annual load Total Phosphorus (TP) - 45% retention of typical urban annual load Litter (gross pollutants) - 45% retention of typical urban annual load Detention - storage of the difference between the predevelopment and post development runoff volumes for the 100 year ARI, 72 hour duration storm event The water quality objectives match the EPA Victoria Urban Stormwater Best Practice Environmental Management Guidelines (BPEMG). Proposed Stormwater Treatment System The site has been split into four catchments for the purposes of stormwater management: Catchment 1 1. The main catchment comprises the area enclosed by the perimeter wall. 2. The carparks located in the western corner of the site will be treated as a separate catchment from the rest of the site. 3. The southern part of the external perimeter road will discharge to the south of the site, and will be treated separately. 4. The northern part of the external perimeter road will discharge to the north of the site, and will be treated separately. Catchment 1 is by far the largest catchment on the site and contains a mix of buildings, pavements, sports fields, and landscaped areas. The stormwater system for Catchment 1 consists of the following: Downpipe network to collect roof runoff (100 year ARI) Dual-purpose rainwater harvesting/detention tanks to collect roof runoff In-ground stormwater pipe system to collect runoff from paved areas and overflows from the tanks Swales to collect runoff from the internal perimeter access roads The oval will be bunded to create a storage basin to provide detention storage for the non-roof impervious areas. The area composition of Catchment 1 is detailed in Table 1below: Table 1 - Catchment 1 Composition Sub-catchment Area (ha) Discharge Point Roof areas 3.2 To rainwater tanks, overflow to drainage network Internal Perimeter Road and sterile zone 1.7 To stormwater swales then oval Paved areas 3.7 To stormwater pipes/swales then oval Unpaved areas 7.3 To stormwater pipes/swales then oval The proposed stormwater strategy for Catchment 1 is to adopt a de-centralised approach to detention. The buildings will be provided with rainwater harvesting tanks (1 tank per building cluster). It is proposed to utilise these tanks as dual-purpose tanks providing detention of the 10 year ARI storm event, as well as providing non-potable water supply. The overflows from the tanks will be directed to the general site-wide stormwater system. The runoff from the remaining impervious and pervious areas inside the secure perimeter will be collected in a stormwater network that will consist of a mixture of open swales and underground pipes. In general, a swale will be provided adjacent to the internal perimeter road and the road through the central spine of the site. Wherever site contours allow it, drainage pipes will daylight to these swales. The swales will serve to convey stormwater flows but will also provide some stormwater treatment and attenuation. A number of bioretention areas will also be provided in order to provide additional stormwater treatment, as swales are typically insufficient to achieve the desired nitrogen and phosphorus removal. The drainage pipes and pits will be sized to convey the 10 year ARI storm event. The swales will be sized to convey the 100 year ARI storm event and overland flow paths will be provided to direct all flows in the 100 year ARI storm to the swales. The stormwater network will direct all runoff in storm events up to and including the 100 year ARI storm to the oval located in the northeast of the site. The oval will be utilised as a detention basin in storm events, and will be bunded to provide a storage volume equal to the difference between the predevelopment and post-development runoff volumes for the 100 year ARI, 72 hour duration storm event, minus the volume provided by the dual-purpose tanks Catchment 2 Catchment 2 consists of approximately 1.5ha of staff and visitor carparks. The carparks will discharge to bioretention areas which will provide stormwater treatment. The overflows and underdrains from the bioretention will discharge to a piped stormwater system which will discharge to a detention basin. The drainage pipes and pits will be sized to convey the 10 year ARI storm event and overland flow paths will be provided to direct all flows in the 100 year ARI storm to the detention basin. The detention basin will be designed to provide a storage volume equal to the difference between the predevelopment and post-development runoff volumes for the 100 year ARI, 72 hour duration storm event Catchments 3 & 4 Catchments 3 & 4 consist of the external perimeter road that runs around the outside of the perimeter wall. This road will most likely be constructed of unsealed crushed rock, and will be treated as an impervious area. The road runoff will be captured in an open swale which will provide stormwater treatment and conveyance. The swale will be graded to create small basins in some locations in order to provide a storage volume equal to the difference between the predevelopment and post-development runoff volumes for the 100 year ARI, 72 hour duration storm event. The swale February 15, 2018 Page 4

8 will discharge to the open grasslands to the north and south of the site. A number of discharge points will be provided to mirror natural flow patterns. provided in Catchment 1. The swales provide significant removal of all pollutants, particularly TSS and TP. This is summarised in Figure 2. Stormwater Treatment Results Stormwater treatment modelling was carried out using MUSIC software Catchment 1 The Catchment 1 MUSIC model nodes are shown in Figure 1. Figure 2 - Catchment 1 Swale Effectiveness Bioretention Bioretention systems (also known as raingardens) utilize a filter media to remove suspended solids, and plants to remove nutrients such as nitrogen and phosphorus. A total of 90m 2 of bioretention will be provided in Catchment 1. The bioretention will be located in the landscaped area in the centre of the site, and in the area around the oval. The bioretention systems provide very effective removal of all pollutants from the runoff, as shown in Figure 3. Figure 1 Catchment 1 MUSIC Model The proposed stormwater treatment train consists of three distinct elements: Swales Open swales Bioretention (raingardens) Detention basin (the oval) Swales are essentially open ditches that are shaped to convey stormwater, and grassed to slow down the flow and capture suspended solids and nutrients. Approximately 1100m of swales will be Figure 3 - Catchment 1 Bioretention Effectiveness Basin and Overall Treatment Train The bunded oval basin will provide minor stormwater treatment, although it is not designed for this function. This is due to some suspended solids settling out. The oval treatment train effectiveness is shown in Figure 4. February 15, 2018 Page 5

9 Figure 4 - Overall Treatment Train Effectiveness It can be seen from Figure 4 the proposed treatment train exceeds the stormwater treatment objectives, as summarised in Table 2 below: Table 2 - Catchment 1 Stormwater Treatment Results Summary Pollutant Objective Removal Achieved Catchment 2 Total Suspended Solids (TSS) 80% 93.9% Total Phosphorus (TP) 45% 77.1% Total Nitrogen (TN) 45% 49.1% Gross Pollutants (GP) 70% 100% The Catchment 2 MUSIC model nodes are shown in Figure 5. In terms of stormwater treatment only the bioretention is directly designed to remove pollutants. The swale is provided for conveyance and the pond is provided for detention (although these two features will both provide minor stormwater treatment for this catchment). Figure 5 Catchment 2 MUSIC Model Bioretention A total of 210m 2 of bioretention will be provided in Catchment 2. The bioretention will be within the carparks, with the carpark pavement graded such that surface runoff will be directed into the bioretention. The bioretention systems provide very effective removal of all pollutants from the runoff, as shown in Figure 6. Figure 6 - Catchment 2 Bioretention Effectiveness February 15, 2018 Page 6

10 It can be seen from Figure 6 that the proposed treatment train exceeds the stormwater treatment objectives, as summarised in Table 3 below: Table 3 - Catchment 2 Stormwater Treatment Results Summary Pollutant Objective Removal Achieved Catchments 3 & 4 Total Suspended Solids (TSS) 80% 89.3% Total Phosphorus (TP) 45% 71.6% Total Nitrogen (TN) 45% 65.1% Gross Pollutants (GP) 70% 92.3% Catchments 3 and 4 have the same composition and are of similar areas. The treatment train proposed is identical and is shown in Figure 7 below: Figure 8 - Catchment 3 & 4 Treatment Effectiveness It can be seen from Figure 8 that the proposed treatment train exceeds the stormwater treatment objectives, as summarised in Table 4 below: Table 4 - Catchment 3 & 4 Stormwater Treatment Results Summary Pollutant Objective Removal Achieved Total Suspended Solids (TSS) 80% 99.6% Total Phosphorus (TP) 45% 80% Total Nitrogen (TN) 45% 69.9% Gross Pollutants (GP) 70% 100% Proposed Stormwater Detention System Each catchment will be provided with a detention system as follows: Figure 7 - Catchment 3 & 4 MUSIC Model The unsealed perimeter road will be graded to discharge to a swale running parallel to it. The swale will discharge to the open grassland. A small area of bioretention (10m 2 ) will be provided at the downstream end of the swale to provide some additional polishing stormwater treatment prior to discharge to the receiving environment. 1. Catchment 1: Dual-purpose rainwater harvesting/detention tanks (10 year ARI) Bunded oval (100 year ARI) 2. Catchment 2: Basin 3. Catchment 3: Depressions in the swale to provide detention 4. Catchment 4: Depressions in the swale to provide detention The results of the Catchment 3 & 4 MUSIC model are shown in Figure 8 below: The exact storage volumes required will be determined as the design progresses and once the site layout is frozen, however approximate volumes have been calculated based on the masterplan layout sketch. The storage volume calculations are provided in Appendix A. February 15, 2018 Page 7

11 3.4.1 Catchment 1 The Catchment 1 detention storage will be provided by a combination of the dual-purpose rain tanks and the bunded oval. The approximate volumes are as follows: Storage volume required: 9033m 3 Detention in tanks: 1100m 3 Oval storage volume: 7933m 3 The tanks will be provided with flow control outlets at the base and overflow outlets at the top of the storage. The method of flow control for the oval will be developed during detailed design, but will most likely take the form of grated pits with orifices sized to enable storage of the design storm. An overflow spillway will be provided over the bund to cater for larger or higher intensity rainfall events. It is noted that the volume required to be stored by the oval is substantial and would equate to almost 500mm of water across the oval surface. It is suggested that a number of deeper swales and localized depressions around the oval be utilized as well in order to reduce the volume required to be stored on the playing surface Catchment 2 The Catchment 2 detention storage will be provided by a basin located north of the carparks. The storage volume required is 1575m 3 which will be provided entirely by the basin. The method of flow control for the basin will be developed during detailed design, but will most likely take the form of grated pits with orifices sized to enable storage of the design storm. An overflow spillway will be provided over the bund to cater for larger or higher intensity rainfall events. Due to the use of bioretention in the carparks it is anticipated that the amount of sediment entering the basin will be minimal, therefore a sediment pond or forebay is unlikely to be required Catchment 3 & 4 The Catchment 3 & 4 detention storage will be provided by depressions in the swales. A total of 231m 3 of storage will be required for each catchment. It is anticipated that this will be provided by a series of shallow depressions in the swale. A subsoil drain will be provided to drain the depressions gradually, no formal flow control structures will be provided. February 15, 2018 Page 8

12 4 Access Road Stormwater Management Objectives The proposed for the Access Road has been developed in accordance with the stormwater management strategy for the development site, incorporating water sensitive urban design (WSUD) principles. Based on discussions with Melbourne Water, Stormwater from the Access Road will be retarded back to pre-development rural levels before discharging to existing surface and to the swamp to the south (Paul & Belfrages Swamp) or drained to the south, to Princes Freeway. Treatment of the Road discharge will be analysed using MUSIC models to confirm Water Quality. The low flows and volumes are expected to show that the existing flow regime is not compromised including environmental flow requirements per Department of Environment, Land, Water and Planning (DELWP). Proposed Stormwater Treatment System The Access Road has up to five catchments for stormwater management. 1. The western catchment is land west of the Access Road, excluding approximately 7.5ha that drains across the Access Road to Paul s swamp on the eastern side of the Access Road. 2. The stormwater catchment north of Section B of the Access Road drains towards the development and into the main catchment. As the Access Road is built above the existing surface, small remnant catchments will be discharged by culvert to Paul s swamp. Discharge from the culverts will be to grassed swales with some sections acting as level spreaders to minimize concentration of storm water. 3. Approximately 7.5ha from the western catchment will discharge via culverts under the Access Road to the eastern catchment and spreader swales discharging to Paul s swamp. 4. Catchment 4 is the natural catchment draining to Paul s swamp and will remain unchanged. 5. The balance of the Access Road catchment discharges towards Little River Road and the Princes Freeway. Wyndham City Council and VicRoads are the responsible authorities for this area and their approvals will be sought. Typical cross section of the Access Road Proposed Stormwater Detention System Detention storage for the difference between the predevelopment and post development runoff volumes will be provided by depressions and minimal graded swales discharging to existing surface levels. Stormwater Treatment Stormwater Treatment will be based on MUSIC models and BPEM compliance. February 15, 2018 Page 9

13 5 Conclusion The proposed YJRP stormwater management strategy has been developed to minimise the adverse effects of the development on the environment. This report demonstrates that the proposed stormwater treatment train is able to achieve best practice environmental management guidelines for the removal of total suspended solids, total nitrogen, total phosphorus and gross pollutants. Detention storage in accordance with Melbourne Water s requirements is also provided. Therefore the proposed development is in accordance with the Melbourne Planning Scheme and Melbourne Water s requirements. February 15, 2018 Page 10

14 Appendix A Sketches The following table summarizes the sketches that have been developed as part of this Report. Document Number Rev Title YJRP-SKT-CC E Site wide stormwater system decentralized option February 15, 2018 Page 11

15 DETENTION BASIN SIZED FOR 100 YEAR ARI RUNOFF FROM CARPARKS. 1500m3 APPROX. STORAGE VOLUME LARGER DUAL-PURPOSE RAINTANK FOR ADMINISTRATION BUILDINGS (SIZE TBC) STORMWATER PIPES TO DISCHARGE TO SWALE, PROVIDE PRECAST CONCRETE WINGWALLS. SECURITY DETAILS TBC (TYP.) PERIMETER ROAD DRAINAGE SWALE (TYP.) OUTLET PIPE TO DISCHARGE TO EXISTING NATURAL FLOW CHANNEL, SECURITY DETAILS TBC. CARPARKS TO BE PROVIDED WITH MIN. 140m2 OF BIORETENTION. BIORETENTION OVERFLOWS AND SUBSOIL DRAINS TO DISCHARGE TO PIPED STORMWATER DRAINAGE SYSTEM OVAL TO BE UTILISED AS DETENTION STORAGE FOR RAINFALL EVENTS UP TO AND INCLUDING THE 100 YEAR ARI. PROVIDE BUND AROUND OVAL TO ACHIEVE REQUIRED VOLUME NOTES PITS FOR RAINWATER HARVESTING DRAINAGE ARE NOT SHOWN FOR CLARITY, REFER TO TYPICAL BUILDING PERIMETER DRAINAGE DETAILS. DUAL-PURPOSE RAINWATER HARVESTING/DETENTION TANK. REFER TO HYDRAULIC SKETCHES FOR RAINWATER HARVESTING VOLUME APPROX. 130m3 DETENTION VOLUME REQUIRED. TANK OVERFLOW TO DISCHARGE TO PIPED STORMWATER NETWORK (TYP.) LEGEND STORMWATER PIT STORMWATER PIPE WINGWALL STORMWATER SWALE PIPES TO BE TWIN WALL HDPE OR SIMILAR. MAXIMUM PIPE SIZE DN150. SITE WIDE STORMWATER SYSTEM DECENTRALISED OPTION E D C B A SITE LAYOUT UPDATED SITE LAYOUT UPDATED ISSUED FOR TOWN PLANNING DRAFT SKETCH DRAFT SKETCH AW AW AW AW AW AW YJRP-SKT-CC E

16 Appendix B Detention Calculations February 15, 2018 Page 12

17 STORMWATER DRAINAGE ANALYSIS - DETENTION CALCULATION Spreadsheet specific for this job only. Manning's n Client: DJR File No.: Minimum Velocity (m/s) Project: YJRP - CATCHMENT 1 Date: 20/12/2017 Maximum Velocity (m/s) Engineer: A.Watson Minimum Drop through Pit (m) Minimum Drop along Pipes (m) Minimum Freeboard at Pit (m) a b c d e f g Fraction Impervious Land NOTE: YOU SHOULD REVIEW ALL INPUT CELLS (SHADED IN BLUE) Pavement Roof C (100 Year) Catchment pre dev post dev Areas (m 2 ) C*A C*A Total duration I Qd Volume Land Pave Roof (m2) (mins) (mm/h) (l/s) (m 3 ) STORAGE VOLUME: m 3

18 STORMWATER DRAINAGE ANALYSIS - DETENTION CALCULATION Spreadsheet specific for this job only. Client: DJR File No.: Minimum Velocity (m/s) Manning's n Project: YJRP - CATCHMENT 2 Date: 20/12/2017 Maximum Velocity (m/s) Engineer: A.Watson Minimum Drop through Pit (m) Minimum Drop along Pipes (m) Minimum Freeboard at Pit (m) a b c d e f g Fraction Impervious Land NOTE: YOU SHOULD REVIEW ALL INPUT CELLS (SHADED IN BLUE) Pavement Roof C (100 Year) Catchment Areas (m 2 ) C*A C*A Total duration I Qd Volume Land Pave Roof (m2) (mins) (mm/h) (l/s) (m 3 ) pre dev post dev STORAGE VOLUME: m 3

19 STORMWATER DRAINAGE ANALYSIS - DETENTION CALCULATION Spreadsheet specific for this job only. Client: DJR File No.: Minimum Velocity (m/s) Manning's n Project: YJRP - CATCHMENTS 3 & 4 Date: 20/12/2017 Maximum Velocity (m/s) Engineer: A.Watson Minimum Drop through Pit (m) Minimum Drop along Pipes (m) Minimum Freeboard at Pit (m) a b c d e f g Fraction Impervious Land NOTE: YOU SHOULD REVIEW ALL INPUT CELLS (SHADED IN BLUE) Pavement Roof C (100 Year) Catchment Areas (m 2 ) C*A C*A Total duration I Qd Volume Land Pave Roof (m2) (mins) (mm/h) (l/s) (m 3 ) pre dev post dev STORAGE VOLUME: m 3