CASE STUDY
FLOOD MODELLING AND ANALYSIS SAVES PROPERTY DEVELOPER $30,000-40,000 AND ENSURES THE SITE’S ENTIRE FOOTPRINT IS COMMERCIALLY VIABLE As engineers we appreciate that the architect’s design is not always an easy task. The developers purchase a lot (site) intending to build with a certain idea of their financial return and we need to try to make that work. We have produced fantastic results in stormwater and flood modelling with mid to high density developments due to our extensive design experience and standards. Our expertise with design and familiarity with the local council requirements, made us an ideal fit for this six storey development, which was referred to us through a former client and architect we have worked with previously in the Penrith. The specific issue with this development was OVERLAND FLOW FLOODING. Flooding may have restricted the footprint of the design which in turn could have great implications for the financial potential of the project. Our clients relies on us to provide the best possible solution to optimise their chosen design within the financial constraints whilst ensuring it will pass through council.
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Although the site had an existing onsite detention tank, the council requested a new system to be installed with the new development layout. It became evident to us that the onsite detention tank was not suitable for this particular site and would not function for its intended purpose. The purpose of the onsite detention tank is to restrict discharge so that properties downstream of the site are not detrimentally affected by flooding. This particular site was in fact affected by floods and we determined that the onsite detention tank would in fact be inundated should a major storm event occur. Proposed Architectural Site Plan
BASED ON OUR MODELLING, the major storm event resulted in half the site to become affected by an overland flow. We approached council to explain the reason behind our logic that the onsite detention tank was not the right solution in this particular case
15 Parkes St Parramatta, NSW 2150 x T: 02 9806 3000 x F: 02 9891 2806 www.DonovanAssociates.com.au
CASE STUDY because the design intention of the onsite detention tank would not address the magnitude of the calculated flooding. We know the council requires a design model for this condition which we were able to represent with our modelling.
Pre development flood depth
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Pre development flow direction
Often, councils propose generic solutions at the early planning stages to issues without investigating the sites in much detail. For this development, we were able to demonstrate the solution proposed was not suitable for this project and the council accepted our recommendation for the removal of the onsite detention tank, SAVING THE CLIENT $30,000 - $40,000 WITHOUT COMPROMISING SAFETY OR DAMAGE TO THE PROPERTY. With respect to managing the flooding for this site, our innovative solution was to manipulate the flood waters around the site while maintaining the same footprint for the client. We had to adhere to the council’s requirements that whatever is done onsite cannot impact the neighbouring properties. Therefore we ensured that any flooding would be contained completely on the existing site through different systems, allowing it to continue through the same path, as it had previously. We prepared an overland flow report which required a two dimensional flood model that demonstrated that the pre-existing and post development conditions were achieved in accordance with council’s planning controls. WE RECEIVED DA APPROVAL WITHOUT COMPROMISING THE DESIGN AND VALUE OF THE DEVELOPMENT FOR OUR CLIENT.
Post development flood depth
Another interesting outcome achieved for this project was dealing with an existing easement through the site. An easement is a parcel of land over which an existing pipe is used for stormwater discharge to pass through the site. Due to the developer’s proposal to build over this existing easement, we had to divert the easement and connect it back to where it would pass through the storm water pipe on the adjoining property. This was a difficult task to divert at a right angle, requiring both a design and a DRAINS (software) analysis to estimate the height of the water and potential energy throughout the pit and the pipe system to ensure the water would not surcharge out of the pit. In addition, the proposed pipe sizes had to match the existing system.
Post development flow
15 Parkes St Parramatta, NSW 2150 x T: 02 9806 3000 x F: 02 9891 2806 www.DonovanAssociates.com.au
CASE STUDY DEALING WITH THESE POTENTIAL NATURAL AND MAN-MADE HAZARDS IS WHAT WE DO EACH AND EVERY DAY FOR OUR CLIENTS. It is what clients entrust us to uncover and resolve so they can be certain that all reasonable care and attention have been given to provide an optimal solution.
DRAINS output for easement analysis
Stormwater Management Site Plan
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It was necessary to undertake the specific modelling of the existing easement and ensure the system had the capacity to convey the site’s stormwater flows, otherwise the entire system would need upgrading which would have been a very expensive task, not to mention the potential damage caused with the associated liability and legal considerations. The council stipulates that a developer must cover the costs as part of their responsibility for the development. Usually, developers are not willing to pay the enormous cost to assess and analyse all the neighbouring properties to their site. We were able to mathematically demonstrate through our modelling, that the existing system was capable of managing all the expected flows, including the 1 in a 100 year flood to the council’s satisfaction. The final challenge for this project was ensuring water quality. This is another requirement the council insists be achieved and the percentages and targets were reached.
Proposed Architectural Elevation Plan
MUSIC Water Quality Model Output
There was an increase pollutants as a result of impervious areas of concrete and roofing that caused pollution from run-off with dirt, chemicals and solid materials that were deemed detrimental to the natural waterways. This can be treated though bio retention, rain gardens, proprietary systems (such a filter traps and grease traps) and rain water tanks. To solve this problem, we used “MUSIC” modelling software to demonstrate how all the impervious areas and systems were being treated to REDUCE THE POLLUTANTS from pre to post construction. “MUSIC” modelling software provides various options for us to select and design the most suitable solution for each development site. Since the site fell to the rear, the discharge flowed through the redirected easement pipe, making it a very cost-effective solution for this situation.
15 Parkes St Parramatta, NSW 2150 x T: 02 9806 3000 x F: 02 9891 2806 www.DonovanAssociates.com.au
CASE STUDY MODELLING IS AN ESSENTIAL AND EFFECTIVE TOOL that provides the clearest data and analysis, particularly in the case of flooding. This is always recommended because every site is ultimately affected by flooding in a 1 in 100 year storm unless you’re sitting on top of a mountain!
Initial flood model prepared
The expertise and efforts we put into this design saved our client a major redesign and potentially the reduction of the development’s footprint by as much as half. For a development with these technical constraints, the value that could have been lost could have been in the MILLIONS OF DOLLARS. As Engineers, it’s important WE ACHIEVE RESULTS THAT PROVIDE OUR CLIENTS WITH COST EFFECTIVE SOLUTIONS THAT CAN PASS THROUGH COUNCIL AND ACHIEVE THEIR FINANCIAL AND COMMERCIAL OUTCOMES.
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STORMWATER MANAGEMENT PLAN (FOR DA) PROPOSED RESIDENTIAL BUILDING GENERAL NOTES 1. FINAL LOCATION OF NEW DOWNPIPES TO BE DETERMINED BY BUILDER/ARCHITECT AT TIME OF CONSTRUCTION.
3D view of proposed development
2. THESE DRAWINGS TO BE READ IN CONJUNCTION WITH ARCHITECTS AND OTHER CONSULTANTS DRAWINGS. ANY DISCREPANCIES TO BE REFERRED TO THE ENGINEER BEFORE PROCEEDING WITH WORK.
DRAINAGE NOTES
6. ALL STORMWATER DRAINAGE PIPES ARE TO BE uPVC AT MINIMUM 1% GRADE UNLESS NOTED OTHERWISE. 7. IT IS THE CONTRACTORS RESPONSIBILITY TO LOCATE AND LEVEL ALL EXISTING SERVICES OR OTHER STRUCTURES WHICH MAY AFFECT/BE AFFECTED BY THIS DESIGN PRIOR TO COMMENCEMENT OF WORKS.
3. ALL MATERIALS AND WORKMANSHIP TO BE IN ACCORDANCE WITH AS/NZS 3500.3:2003 STORMWATER DRAINAGE, BCA AND LOCAL COUNCIL POLICY/CONSENT/REQUIREMENTS.
8. ALL PITS WITHIN DRIVEWAYS TO BE 150mm THICK CONCRETE OR EQUAL. 9. THIS PLAN IS THE PROPERTY OF DONOVAN ASSOCIATES AND MAY NOT BE USED OR REPRODUCED WITHOUT WRITTEN PERMISSION FROM DONOVAN ASSOCIATES.
4. ALL DIMENSIONS AND LEVELS TO BE VERIFIED BY BUILDER ON-SITE PRIOR TO COMMENCEMENT OF WORKS. THESE DRAWINGS ARE NOT TO BE SCALED FOR DIMENSIONS NOR TO BE USED FOR SETOUT PURPOSES.
SURFACE INLET PIT
5. LOCATION OF SURFACE STORMWATER GRATED INLET PITS MAY BE VARIED OR NEW PITS INSTALLED AT THE CONSTRUCTION STAGE PROVIDED DESIGN INTENT OF THIS DRAWING IS MAINTAINED
ABSORPTION TRENCH
ACCESS GRATE
SP
PROPOSED DOWNPIPE SPREADER
450 SQUARE INTERVAL
450 X 450
GRATE LEVEL = 75.50
SL 75.50
INVERT LEVEL = RL 75.20
IL 75.20 DP 90
10.00
SUBSOIL PIPE
INSPECTION RISER RAINWATER HEAD
MINIMUM COVER
SUBJECT TO VEHICLE LOADING UNDER A SEALED ROAD
100mm SINGLE RESIDENTIAL 300mm ALL OTHER DEVELOPMENTS
a
a
a
SW
a
SW
IR RWH
a
MINIMUM PIT SIZE (mm)
450 x 450 600 x 600 600 x 900 900 x 900 (WITH STEP IRONS) 1200 x 1200 (WITH STEP IRONS)
PITS GREATER THAN 600mm DEEP SHALL HAVE A MINIMUM ACCESS OPENING OF 600 x 600mm THE GRATED COVERS OF PITS LARGER THAN 600 x 600mm ARE TO BE HINGED TO PREVENT THE GRATE FROM FALLING INTO THE PIT.
·
TRENCH DRAINS: CONTINUOUS TRENCH DRAINS ARE TO BE OF WIDTH NOT LESS THAN 150mm AND DEPTH NOT LESS THAN 100mm. THE BARS OF THE GRATING ARE TO BE PARALLEL TO THE DIRECTION OF SURFACE FLOW.
·
STEP IRONS: PITS BETWEEN 1.2m AND 6m ARE TO HAVE STEP IRONS IN ACCORDANCE WITH AS1657. FOR PITS GREATER THAN 6m OTHER MEANS OF ACCESS MUST BE PROVIDED.
450mm WHERE NOT IN A ROAD 600mm
UNSEALED ROAD
750mm
PAVED DRIVEWAY
100mm PLUS DEPTH OF CONCRETE
SEE AS2032 INSTALLATION OF UPVC PIPES FOR FURTHER INFORMATION. CONCRETE PIPE COVER SHALL BE IN ACCORDANCE WITH AS3725-1989 LOADS ON BURIED CONCRETE PIPES, HOWEVER A MINIMUM COVER OF 450mm WILL APPLY.
CONNECTIONS TO STORMWATER DRAINS UNDER BUILDINGS: SHALL BE CARRIED OUT IN ACCORDANCE WITH SECTION 3.10 OF AS3500.3-1990
STORMWATER PIPE 100mm DIA. MIN. UNO
EXISTING STORMWATER PIPE
LOCATION NOT SUBJECT TO VEHICLE LOADING
WHERE INSUFFICIENT COVER IS PROVIDED, THE PIPE SHALL BE COVERED AT LEAST 50mm THICK OVERLAY AND SHALL THEN BE PAVED WITH AT LEAST: · 150mm REINFORCED CONCRETE WHERE SUBJECT TO HEAVY VEHICLE TRAFFIC; · 75mm THICKNESS OF BRICK OR 100mm OF CONCRETE PAVING WHERE SUBJECT TO LIGHT VEHICLE TRAFFIC; OR · 50mm THICK BRICK OR CONCRETE PAVING WHERE NOT SUBJECT TO VEHICLE TRAFFIC.
GRATED TRENCH DRAIN
PROPOSED ROOF GUTTER FALL
(WITH ENVIROPOD 200 MICRON)
NATURAL GROUND FINISHED DESIGN LEVEL
4. THIS DRAWING IS NOT TO BE USED FOR SET-OUT PURPOSES - REFER TO ARCHITECTURAL DRAWINGS
LEGEND
SURFACE INLET PIT
PROPOSED DOWNPIPE 90mm DIA. OR 100mm x 50mm MIN.
3. ALL ROOF GUTTERS TO HAVE OVERFLOW PROVISION IN ACCORDANCE WITH AS 3500.3:2003 AND SECTIONS 3.5.3, 3.7.5 AND APPENDIX G OF AS 3500.3:2003
DEPTH (mm)
UP TO 450mm
450mm TO to 600mm 600mm TO 900mm 900mm TO 1500mm 1500mm TO 2000mm
THE BASE OF THE DRAINAGE PITS SHOULD BE AT THE SAME LEVEL AS THE INVERT OF THE OUTLET PIPE. RAINWATER SHOULD NOT BE PERMITTED TO POND WITHIN THE STORMWATER SYSTEM
DEPTH OF COVER FOR PVC PIPES: MINIMUM PIPE COVER SHALL BE AS FOLLOWS:
2. TREE PRESERVATION: IT IS THE RESPONSIBILITY OF THE CONTRACTOR TO OBTAIN ANY PRIOR APPROVAL REQUIRED FROM COUNCIL WITH RESPECT TO POTENTIAL IMPACT ON TREES FOR ANY WORKS SHOWN ON THIS DRAWING PRIOR TO THE COMMENCEMENT OF THOSE WORKS
PIT SIZES AND DESIGN:
ALL PIPES SHOULD BE CUT FLUSH WITH THE WALL OF THE PIT.
ANCHOR BLOCKS ARE DESIGNED ACCORDING TO CLAUSE 3.5.3 OF AS3500.3-1990
PLAN SPECIFIC NOTES
(WITH ENVIROPOD 200 MICRON)
PIPE GRADE: THE MINIMUM PIPE GRADE SHALL BE: · 1.0% FOR PIPES LESS THAN 225mm DIA (UNO) · 0.5% FOR ALL LARGER PIPES (UNO) PIPES WITH A GRADIENT GREATER THAN 20% WILL REQUIRE ANCHOR BLOCKS AT THE TOP AND BOTTOM OF THE INCLINED SECTION; AND AT INTERVALS NOT EXCEEDING 3.0m
5. ALL SURVEY INFORMATION AND PROPOSED BUILDING AND FINISHED SURFACE LEVELS SHOWN IN THESE DRAWINGS ARE BASED ON LEVELS OBTAINED FROM DRAWINGS BY OTHERS.
1. ROOF DRAINAGE NOTE: AS 3500 ROOF DRAINAGE REQUIRES EAVES GUTTERS TO BE SIZED FOR 20 YEAR 5 MIN. STORM = 205mm/hr. FOR EAVES GUTTERS, AS 3500.3:2003 THEN HAS THE FOLLOWING REQUIREMENTS: i) FOR TYPICAL STANDARD QUAD GUTTER WITH Ae = 6000mm² AND GUTTER SLOPE 1:500 AND STEEPER, THIS REQUIRES ONE DOWNPIPE PER 30m² ROOF AREA. ii) DOWNPIPES TO BE MINIMUM 90mm DIA. OR 100 x 50mm FOR GUTTERS SLOPE 1:500 AND STEPPER. iii) OVERFLOW METHOD TO FIGURE G1 OF AS 3500.3:2003 IT IS THE RESPONSIBILITY OF THE PLUMBER AND / OR BUILDER TO COMPLY WITH THIS. THIS DRAWING SHOWS PRELIMINARY LOCATIONS / NUMBERS OF DOWNPIPES ONLY WHICH ARE TO BE VERIFIED BY BUILDER / PLUMBER
PIPE SIZE: THE MINIMUM PIPE SIZE SHALL BE: · 90mm DIA WHERE THE LINE ONLY RECEIVES ROOFWATER RUNOFF; OR · 100mm DIA WHERE THE LINE RECEIVES RUNOFF FROM PAVED OR UNPAVED AREAS ON THE PROPERTY THE MINIMUM PIPE VELOCITY SHOULD BE 0.6 m/s AND A MAXIMUM PIPE VELOCITY OF 6.0 m/s DURING THE DESIGN STORM.
·
PVC PITS: PVC PITS WILL ONLY BE PERMITTED IF THEY ARE NOT A GREATER SIZE THAN 450 x 450mm (MAXIMUM DEPTH 450mm) AND ARE HEAVY DUTY
·
IN-SITU PITS: IN-SITU PITS ARE TO BE CONSTRUCTED ON A CONCRETE BED OF AT LEAST 150mm THICK. THE WALLS ARE TO BE DESIGNED TO MEET THE MINIMUM REQUIREMENTS OF CLAUSE 4.6.3 OF AS3500.4-1990. PITS DEEPER THAN 1.8m SHALL BE CONSTRUCTED WITH REINFORCED CONCRETE.
·
GRATES: GRATES ARE TO BE GALVANISED STEEL GRID TYPE. GRATES ARE TO BE OF HEAVY-DUTY TYPE IN AREAS WHERE THEY MAY BE SUBJECT TO VEHICLE LOADING.
CONNECTIONS TO COUNCIL SYSTEM: IF PROPOSED DRAINAGE SYSTEM IS DESIGNED TO CONNECT TO COUNCIL'S DRAINAGE SYSTEM, IT IS ADVISED THAT A 'WORKS PERMIT' IS OBTAINED FROM THE RESPECTIVE COUNCIL PRIOR TO COMMENCEMENT OF WORKS ABOVE GROUND PIPEWORK: SHALL BE CARRIED OUT IN ACCORDANCE WITH SECTION 6 OF AS3500.3-1990
DRAWING TITLE:
DETAILS, NOTES & LEGEND COPYRIGHT - THIS DRAWING REMAINS THE PROPERTY OF DONOVAN AND MAY NOT BE ALTERED IN ANY WAY WITHOUT DONOVAN ASSOCIATES WRITTEN CONSENT.
DRAWN Y.RIAD
DATE
Y.RIAD
DESCRIPTION
02.03.2017 ISSUED FOR DA
S.SINGH 28.06.2017 13.07.2017
PROJECT
ISSUE
B C
PROPOSED RESIDENCE
FOR
APPROVED BY:
DESIGNED BY: CHECKED BY:
A
PROPOSED EASEMENT LOCATION AMENDED ARCHITECTURALS AMENDED
SCALE
SITE ADDRESS:
SHEET SIZE CLIENT REF.
SCOTT SHARMA. M.I.E. Aust.
YR SS
A1 DRAWING No.
E291644
ISSUE
C SHEET No.
D1
Stormwater management plan documentation
15 Parkes St Parramatta, NSW 2150 x T: 02 9806 3000 x F: 02 9891 2806 www.DonovanAssociates.com.au