Golden Plains Shire Council has adopted the Infrastructure Design Manual to provide guidance and civil standards to developers and engineering designers as to the expectations and standards for new estates construction and subdivisions within the Shire.
The IDM(Infrastructure Design Manual) is an online system that provides a reference guide to the standards and requirements for infrastructure. This has been used for land development and infrastructure upgrades from 14 July 2013.
The following are notes intended to provide guidance for subdivisions in Golden Plains Shire to provide clarification to general or minimum IDM specifications.
Drainage
New open drains are to be established at a minimum grade of 1:300. This is an amenity requirement and was adopted by Council resolution.
Batter slopes are to be maximum 1:6 within the road reserve. Open drains providing interallotment drainage shall have desirable maximum batter slope of 1:6. Batter slopes greater than 1:6 will only be permitted where there is a site constraint or limitation. Drainage easements are to be made wider to accommodate open drains.
Drainage of subdivided lots will be restricted to the pre-developed rate, or the capacity of the downstream stormwater network, whichever is lesser. This may restrict outflows to a 20%AEP (5-year ARI, approx.) rate at pre-development level and require Onsite Stormwater Detention (OSD) of stormwater volumes for a 1%AEP (100-year ARI, approx.) storm.
Unless otherwise specified on title, drainage calculations for new development will be expected to allow for: dwelling roofs 400m² and shed roofs 200m² per new lot, hardstand (e.g. crushed rock driveway etc.) 500m² per new lot.
Lots shall be gravity drained from the lowest point of the lot. Pumped systems will not be supported.
Legal drainage rights such as easements or drainage reserves will need to be obtained where discharging through other freehold titles. A legal drainage flowpath will need to be secured either:
- prior to a Permit being issued, or
- as a condition of Permit before Compliance is issued.
Open drains providing interallotment drainage shall be in easements in favour of all relevant properties as well as GPSC.
Drainage flowpaths from the public realm, including road and recreation reserves, shall be via drainage reserves and discharge is not to enter private property whether or not in drainage easements. Subdivision layouts shall be designed to achieve this requirement.
On Site Detention (OSD)
OSD to limit post-development runoff to a pre-development level or the capacity of the existing drainage infrastructure, whichever is lesser, is required for all subdivision developments. This is to avoid exceeding the capacity of the downstream drainage flowpath and control discharge to waterways.
The use of rainwater tanks for OSD purposes can occur where control of roof-water is sufficient to provide the required detention volumes. This is can usually be achieved for up to three dwellings after which the uncontrolled runoff from associated driveways, paved areas, etc, usually cannot be compensated by increased control of roofwater.
In these situations, surface water from driveways and paved areas must be captured and detained. i.e. a basin or similar will be required with the associated access, discharge and safety provisions. A landscaped solution may be preferable to underground storages or regular basins.
OSD calculation methods that assume a constant discharge, such as the Mass Curve
Analysis, require a factor to be applied to the constant discharge to determine the detention volumes - the adjustment factor for aboveground storage is 0.75 and for belowground storage is 0.6.
The time of concentration (Tc) used for OSD calculations is to be the Tc for the catchment of the drainage network that the property is discharging into.
Access - Vehicle Crossings and Drives
All vehicle crossings providing access off a sealed road are to be sealed unless outside of township growth or settlement zones or areas and providing access solely for rural agricultural purposes.
All common driveways accessing a road within or abutting a township growth or settlement zone or area will be sealed.
Where there is concrete kerb and/or concrete footpath then the vehicle crossing shall be constructed in concrete.
A common property or carriageway access arrangement for battle-axe blocks will need to be wide enough to accommodate the required features which may include:
- Pavement with width 5.5m and 3.5m seal. Widening will be required for any CFA access requirements or as required for traffic volumes or vehicle classification.
- Landscaping space 2m wide.
- Open drain(s).
- Service trench.
- Clearances to obstructions.
- Utility meters and post boxes.
Vehicle or Pedestrian Crossing Culverts in Road Reserve
Endwalls for roadside culverts are not to protrude above the finished level of the crossing. Low-profile endwalls are available.
Road design and Roadside Features
Design life for pavements is 50 years.
Concrete kerb and channel shall be provided on the returns of intersections and the inner radius of road bends.
A 3m wide (minimum) verge for tree planting is to be provided where landscaping is required. Trees are not to be planted in the clear zone or in table drains. Any services installed in the tree zone are to be minimum depth 1m.
Street lighting is not to be placed in the clear zone or in the table drains.
Service pits are not to be located in the table drain. Where open drains are used, the driveway culverts can be extended to create flat areas for the installation of service pits.
Court bowls must be minimum ø21m and sealed with asphaltic concrete to provide for tandem steer waste collection vehicles to turn and manoeuvre for bin collection.
Trees
It is a strategic goal of GPSC to achieve a minimum of 30% canopy coverage in townships within the Shire. At least 90% of all properties must have a tree planted within the adjacent nature strip to demonstrate that tree planting is occurring and contributes to strategic goals.
To maximize tree canopy and demonstrate how canopy coverage can be achieved, the following guidelines are provided:
- The House Drain connection point should be to vehicle crossing wingwalls or 0.6m from the crossing.
- Water and gas, etc, service connections should be 0.6m from the property side boundary on the opposite side of the crossover.
- Trees should be shown green in colour, with a canopy size 3m in diameter and indicative locations not shown in direct conflict with local connections.
- Services installed below trees must be installed with a minimum cover of 1m.
- A minimum of one (1) tree should be shown on the frontage of each property and minimum of two (2) on each side boundary.
- No trees are to be planted within an open drain and must be set back a minimum of 450mm from the top of the swale.
- Tree must be set back a minimum 750mm from the road edge, back of kerb and/or footpath.
- Trees must be planted a minimum of 2m clear from any upright structure, e.g. fences, bollards, seating, as measured from the edge of the mulch ring