STANDARDS FOR ENGINGEERING WORKS

STORMWATER DRAINAGE DESIGN HANDBOOK

MARCH 2013

SCOPE This handbook provides information additional to Council’s Stormwater Drainage Design specification within its Standards for Engineering Works. The clauses referenced below refer to that specification.

The following design criteria are given:

1. Design IFD rainfalls (Clause D5.04(3)) 2. Rational Method, Design Impervious Areas and Coefficients of Runoff (D5.06(4)) 3. Conduit material standards (D5.18(1)) 4. Conduit jointing details (D5.18(3)) 5. Batter slope treatments and fencing guidelines for constructed wetlands and detention basins

(D5.16) Design information is also provided in the standard drawings. If any criterion is not specified, then other references such as AR&R or ACT Urban Services’ “Design Standards for Urban Infrastructure, Stormwater” may be adopted. In addition to the above, the Stormwater Drainage Design Handbook also provides Council’s requirements on the following stormwater issues:

6. Clearance Requirements for Structures Adjacent to Sewer and Stormwater Mains (Clause D5.16) 7. On-site Stormwater Detention 8. On-site Stormwater Management 9. Stormwater Treatment Facilities on Council Property

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1 Design Rainfall Data (Clause D5.04 (3)) Design Intensity-Frequency-Duration (IFD) data are provided in the tables attached.

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2 Rational Method, Design Impervious Areas and Coefficients of Runoff (D5.06 (4)) (i) The table below provides typical impervious areas for composite sites:

Development Type Design Impervious Area (%) Single Residential 45 Multi-unit 60 Commercial 70 CBD 90 Industrial 90

(ii) Impervious areas are deemed to have a runoff co-efficient of 0.90. (iii) The following relation shall be used for pervious areas in residential developments with

densities in the range of 10-15 lots per hectare: Cp = 0.91 – 3.14 i-0.594

Where, Cp = runoff coefficient for impervious surfaces i = design rainfall intensity (mm/h) (iv) Appropriate pervious area runoff coefficients can be obtained from Fig 1.1 attached (ACT Urban Services) for other land use types. 3 Conduit Material Standards (D5.18 (1)) Stormwater pipelines shall be constructed with:

• Steel reinforced concrete pipes (SRCP) • Fibre reinforced cement pipes (FRC) • Steel Reinforced Concrete Pipes (SRC) • Ductile Iron Cement Lined (DICL) • Unplasticised Polyvinyl Chloride Pipes (uPVC) • Vitrified Clay Pipes (VC) • Galvanised steel pipes (GS).

Alternative pipe materials may be acceptable. All pipes shall comply with the most recent appropriate Australian Standard. 4 Conduit Jointing Details (D5.18 (3)) All pipe jointing shall be rubber ring, with the exception of 100mm uPVC which may be solvent weld.

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5 Batter slope treatments and fencing guidelines for constructed wetlands and detention basins (D5.16)

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6 Clearance Requirements for Structures Adjacent to Sewer and Stormwater Mains (Clause D5.16)

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Clearance & Easement Requirements for Structures

Adjacent to Sewer & Stormwater Mains Policy

POLICY OBJECTIVE The objective of this policy is to provide guidelines for clearance requirements for structures adjacent to sewer and stormwater mains. LEGISLATIVE PROVISIONS New South Wales Code of Practice Plumbing and Drainage 2006 Australian Standard AS3500 2005 Plumbing and Drainage Sewerage Code of Australia WSA 2002 Version 2.3 Public Works Act Water Supply Authorities Act POLICY STATEMENT RATIONALE A clearance between a structure and a sewer or stormwater main is required for the following reasons: • To allow access for maintenance equipment to inspect manholes, house connections, drainage

pits, and for the possible repair / replacement of the sewer or stormwater mains. • To protect the stability of the adjacent buildings: • To protect the sewer or stormwater main from damage by having it located within the zone of

influence of structure footings. • To minimise the potential for trench instability due to the presence of nearby footings. The provisions of this policy apply regardless of the recent developments in construction techniques i.e. the provisions apply even with the advent of non-surface disruptive techniques such as pipe bursting. APPLICATION Structures including dwellings, buildings, garages, store rooms, tool sheds, garden sheds, green/glass houses, gazebos, rainwater tanks (see exceptions below), verandas, decks, pergolas, aviaries, pools, electrical and gas appliances, supports for building overhangs and parallel retaining walls cannot be constructed over, or within, the clearance zone of Council sewer and stormwater mains. CLEARANCE SPACE REQUIREMENTS Single Main A single sewer or stormwater main requires a clearance of 1.5m from the centre of the main to the closest point of the structure. Where the main is over 1.5m deep, the clearance is to be equal to the depth of the main. Twin Mains Where a sewer main and a stormwater main are close and parallel to each other, a clearance of 1.5m is required from the centre of either main to the closest point of a structure. Where the main is over 1.5m deep, the clearance is to be equal to the depth of the main. A minimum clearance of 1m is required between the two mains. EASEMENT WIDTHS Easements over mains shall be the same space as the total clearance requirements of this policy.

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EXEMPTIONS Interlot Drainage Interlot drainage requires a total clearance zone of 1.5m provided a 1m clearance is provided to a council main. Carports Carports are permitted to be built over sewer or stormwater mains under the following conditions: • The carport’s members are to be secured by bolts allowing easy disassembly • Should a problem occur with the sewer or stormwater main requiring the removal of the carport,

the owner of the property is to bear all costs associated with removing and reinstating the carport

• The carport must be open on at least 3 sides Rainwater Tanks Rainwater tanks are permitted to be built over sewers or stormwater mains under the following conditions: • The tank must be plastic moulded type of capacity equal to or less than 5,000L • The tank must be founded on appropriate flat bedding material, at or just above natural surface

level, to distribute loads evenly. Elevated tanks supported on structures are not permitted • The tank must be able to be readily disconnected and removed from the vicinity. • The tanks must not be connected to the town water supply • Electrical pumps must be located outside the easement. Should a problem occur with the

sewer or stormwater main requiring the removal of the tank, the owner of the property is to bear all costs associated with removing and reinstating the tank

Town Centre Zone Buildings may be erected over sewer (but not stormwater) mains in the ‘Commercial Core’ zone. In these instances, the following conditions must be met: • The footings are to be piered and beamed to the design of a structural engineer or otherwise

designed to alleviate stress on the main • The main must be renewed / replaced / relined, at the developer’s cost, over a distance

determined by individual assessment, at a size to suit ultimate capacity • The main is to be physically located prior to any excavation, including boring of the piers • The structure is not to be constructed over or within 2m to the centre of a manhole,

maintenance shaft, or sewer dead end Miscellaneous • Paved areas in concrete, asphalt or unit pavers are permitted provided an expansion joint is

placed either side of the line of the covered main • Cantilevered overhangs, including eaves are permitted • Shrubs and groundcover type vegetation is permitted • Building over the sewer or within the sewer easement may be permissible on community based

land or community based facilities where sewer or building relocation is not possible. For such cases Council will review any application and base any decision on the specific circumstances. In these cases, if approval is granted, the conditions outlined for the Town Centre Zone must be met

DAMAGE TO SEWER AND STORMWATER MAINS Any damage caused to sewer and stormwater mains shall be the responsibility of the person undertaking the work and will be fully recovered by Council.

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Version Council Meeting Date Resolution Adoption Date Effective From

1 15 May 2007 07/230 15 May 2007 15 May 2007 2 19 May 2009 09/264 6 July 2009 6 July 2009 3 17 November 2009 09/698 17 November 2009 17 November 2009 4 21 June 2011 11/220 17 August 2011 17 August 2011 5

All policies can be reviewed or revoked by resolution of Council at anytime. This document is scheduled for review in September 2016

DIVISION: Executive BUSINESS UNIT: Executive Management POLICY AUTHOR: General Manager

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7 On-site Stormwater Detention

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On-Site Stormwater Detention

OBJECTIVE To limit stormwater flows from new developments and redevelopments using on-site detention systems (OSD) to ensure that there is no loss of life; no damage to property; and no environmental harm. LEGISLATIVE PROVISIONS Nil STATEMENT Background Development that increases the amount of impervious area results in an increase in stormwater runoff, possibly causing local and downstream flooding. On-site detention aims to compensate for this increased runoff by limiting the rate of stormwater discharge by requiring temporary storage and the controlled release of stormwater generated within a site. OSD is only one aspect of the management of the water cycle on a site. Under the heading of Water Sensitive Urban Design (WSUD), water management now needs to consider the opportunities to better mimic the natural water cycle by addressing issues such as on-site retention (e.g. rainwater tanks), the use of infiltration where appropriate, the quality of stormwater runoff and the impact on natural creeks and watercourses. This OSD requirement aims to ensure that new developments and redevelopments do not increase peak stormwater flows in any downstream area during major storms up to and including the 100 year ARI (1% Annual Exceedence Probability) storm events. Applicability This policy applies to all developments that drain to council’s stormwater infrastructure, excepting: • Developments on single residential lots or dual occupancies, which are adequately addressed

by BASIX requirments • Minor re-developments, such as change-of-use developments, not involving a significant

increase to impervious areas Elements The following lists the elements of this policy: • Permissible Site Discharge (PSD) –specifies a maximum allowable discharge from the

developed site. See specific section below. • Site Storage Requirement (SSR) – the volume of storage that needs to be provided. See

specific section below. • Maximum permissible surface ponding depth – maximum 600mm (potentially deeper where

safety is ensured) for public health and safety reasons. • Safety Fences – fencing required when gentle side slopes cannot be accommodated. • Overland flow paths created to ensure a failsafe system is put in place. Permissible site discharge To ensure that new developments and re-developments do not increase peak stormwater flows during storms up to and including the 100 year ARI event, the stormwater discharge rate from the site is to be kept to no higher than the rate from the area in its natural state,as estimated in the table below. The peak stormwater flow from the site in its natural state therefore becomes the Permissible Site Discharge (PSD) for the developed site.

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To control the amount of stormwater discharged from a site.to the PSD measures such as an orifice plate shall be fitted to the discharge point of the OSD tank or storage basin The permissible site discharge (l/s/ha) for on-site detention systems is given in the table below for varying impervious areas and areas bypassing the system.

Permissible Site Discharge (l/s/ha)

Percentage of Development Area Draining to OSD System Percent

Impervious 100 95 90 85 80 75 70

10 277 273 268 262 255 254 253 20 264 259 254 249 243 242 241 30 251 245 240 236 232 230 228 40 238 232 225 223 220 218 216 50 225 218 211 210 208 206 203 60 222 215 208 204 201 195 190 70 219 212 205 199 194 185 177 80 215 208 201 194 187 175 163 90 212 205 198 189 180 165 150

Area is total site area in hectares Site storage requirement The Site Storage Requirement (SSR) is the volume of water to be detained to achieve the PSD. The storage can be either above or below ground. The site storage requirement (cum/ha) for on-site detention systems is given in the table below for varying impervious areas and areas bypassing the system.

Site Storage Requirement (cum/ha)

Percentage of Development Area Draining to OSD System

Percent Impervious

100 95 90 85 80 75 70

10 20 26 32 36 39 41 43 20 37 43 50 54 58 62 66 30 53 61 68 73 77 83 89 40 70 78 86 91 96 104 111 50 86 95 104 110 115 125 134 60 103 112 121 127 133 142 152 70 119 129 138 144 150 160 169 80 136 145 155 161 168 177 187 90 152 162 172 179 185 195 204

Contribution to on-site detention by rainwater tanks On-site retention facilities such as rainwater tanks that are plumbed into the development’s water supply system can be included as counting towards the on-site detention storage requirement at a volume of 50% of its capacity (only 50% since the tank is likely to be at least partially full when a rain event occurs). Stormwater detention works Construction details of works must be in accordance with the Upper Parramatta River Catchment Trust’s guidelines or other recognised authorities.

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References Upper Parramatta River Catchment Trust (1999). On-site Detention Handbook – 3rd Edition Storm Consulting Pty Ltd. Water Sensitive Urban Design for Ducks Lane Precinct, Goulburn, April 2004

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8 On-site Stormwater Management

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On-site Stormwater Management Policy

POLICY OBJECTIVE To provide guidelines for the permissibility and requirements for the on-site management of stormwater. LEGISLATIVE PROVISIONS Public Works Act Environmental Planning and Assessment Act, 1979. Local Government Act, 1993 NSW Code of Practice for Plumbing and Drainage POLICY STATEMENT Scope Where it is infeasible for a development to drain its stormwater to stormwater infrastructure or a natural watercourse it may be possible to manage the stormwater on site. This policy provides guidelines for the on-site management of stormwater. Normal Requirements for Stormwater Management for Development As stated in the Stormwater Drainage Design section of Council’s Standards for Engineering Works, new development must cater for stormwater by:

• For the “major” system (100 year ARI (average return interval)) – provide a safe, well-defined overland flow path

• For the “minor” system (5 year ARI for residential areas and 10 year ARI for industrial areas) – provide a system of carrying and controlling the flows. This involves a piped system.

The piped system can comprise a “charged” line, provided hydraulic analysis indicates sufficient flow. Permissibility The use of an on-site stormwater management system is only permissible where it is infeasible to connect to stormwater infrastructure or a natural watercourse, even though such connection may require easements across private property. On-site stormwater management is permissible for isolated developments, such as single dwellings, dual occupancies, garages, sheds etc. It is generally not permissible for more intense developments such as multi-units. Permission to use on-site stormwater management must be sought from and provided by Council for each instance. Conditions The guidelines below apply to the on-site management of stormwater. They may be amended by professional analysis.

1. Rainwater tank: • Capacity sized at 1kL per 20sqm of roof area (minimum size 3kL) for retention /

detention. • A small diameter discharge pipe (no larger than 13mm) to be positioned at the mid-

height level of the tank(s) draining to the infiltration trench. • For new dwellings, the tank to be plumbed to the WCs, washing machine, and garden

taps etc.

2. An infiltration bed or trench: • Sized at 1sqm on the top surface per 10sqm of impervious area draining to it (including

roof area draining to the rainwater tank).

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• The bed / trench should be 600mm deep, level on bottom and top. • A trench would include domes, and a bed would include distribution aggregate and

perforated pipes. • The long axis of the bed / trench shall be placed across the fall of the land. • The bed / trench shall not be placed within the clearance zone of a sewer main.

3. Contour banks (or similar) placed:

• Downstream of the trench / bed to prevent overland flow onto an adjacent lot. • Upstream of the trench / bed to prevent overland flow to the trench / bed.

4. A pervious buffer area surrounding the trench / bed sized as equal to the impervious area

draining to the trench/bed (including the roof area). The trench / bed shall be centrally located in the buffer area. Additionally, there shall be a distance of at least 2m from the edge of the infiltration trench to the edge of a structure.

5. If an overland flowpath or dam exists on the property, an easement in favour of the upstream lots.

6. The creation of a restriction as to user, requiring the installation, retention and maintenance of

the stormwater management features.

Note that the any requirements of the Sydney Catchment Authority override this policy. The SCA may require additional treatment such as a raingarden.

Version Council Meeting Date Resolution Adoption Date Effective From

All policies can be reviewed or revoked by resolution of Council at anytime. This document is scheduled for review in September 2016

DIVISION: Planning and Community Services BUSINESS UNIT: Development Control POLICY AUTHOR: Ian Aldridge – Manager Engineering Services

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9 Stormwater Treatment Facilities on Council Property

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Stormwater Treatment Facilities on Council Property Policy

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POLICY OBJECTIVE To provide guidelines for the permissibility and requirements for locating stormwater treatment facilities on council property LEGISLATIVE PROVISIONS Local Government Act, 1993 Environmental Planning and Assessment Act, 1979 POLICY STATEMENT

Permissibility The installation of a stormwater treatment facility on Council land, to be ultimately maintained by Council, will be considered in the following circumstances: • The development serviced by the facility is significant in size and/or involves multiple owners • The site for the facility is available for use by Council for operational purposes

Permission to use on-site stormwater management must be sought from and provided by Council for each instance.

Direct Works to be Carried out by the Developer • Construction

All construction shall be arranged by the developer at their own cost. This shall included but not be limited to: survey, design, legal fees, earthworks, access road, discharge arrangements, fencing, and landscaping.

• Initial Maintenance The initial maintenance period shall be carried out by the developer at their own cost. The minimum duration for this period is 2 years from the date of the completion of the final stage of the development being serviced by the facility.

Contributions Required from the Developer Due to the use of public land, and future operation and maintenance costs to be incurred by Council, the developer contributions listed below apply. These contributions are payable at subdivision certificate stage and are separate and additional to other s94, s94A and s64 contributions. • Compensation for Use of Land

The developer shall pay to Council compensation of $20/sqm (CPI adjusted) of the land to be used. If the developer wishes to dispute this figure, a valuation (by agreed certified valuer) shall be carried out at the developer’s cost.

• Capitalised Operation and Maintenance Costs The developer shall contribute the present value of future operation and maintenance costs for the facility over a period of 40 years (subsequent to the initial maintenance period) at the discount rate of the 10 year Treasury bond rate (as at June 2012, this was 3.04%).

• Capitalised Renewal Costs The developer shall contribute the present value of the future renewal of the facility after an assumed life of 40 year at the discount rate as above.

Example

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By way of example, a bioretention pond of 100sqm, with an estimated operational and maintenance cost of $1,000 per year, an estimated renewal cost of $20,000, an assumed life of 40 years and a discount rate of 3.4%, would incur the following costs: • Land value: 100sqm @ $20/sqm = $2,000 • Capitalised Operation and Maintenance Costs: The discount rate of 3.04%

gives a present value of future annual costs factor of 23.7. Therefore the operation and maintenance cost of $1,000 per year results in a capitalised cost of $23,700

• Capitalised Renewal Costs: The discount rate of 3.04% gives a present value of expenditure in the future factor of 0.335. Therefore the estimated renewal cost of $20,000 results in a capitalised cost of $6,700

• Total: $2,000 + $23,700 + $6,700 = $32,400

Version Council Meeting

Date Resolution Adoption Date Effective From

1 2 3 4 All policies can be reviewed or revoked by resolution of Council at anytime.

This document is scheduled for review in September 2016 DIVISION: Planning and Community Services BUSINESS UNIT: Development Control POLICY AUTHOR: Manager Engineering Services