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 1:5. Batter slopes greater than 1:5 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 for both minor (20% AEP) and major (1% AEP), or the capacity of the downstream stormwater network, whichever is lesser. If the downstream flow path is through private residential lot in an infilled area, the permissible discharge rate (PSD) shall be restricted 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 Certification is issued.
Open drains providing interallotment drainage shall be in easements in favour of all relevant properties as well as GPSC.
Drainage flowpaths of public infrastructure, including road and recreation reserves, are not to enter private property whether or not in drainage easements. Subdivision layouts shall be provided to achieve this requirement. Drainage reserves will, otherwise, be required.
On Site Detention (OSD)
OSD to limit post-development runoff to a pre-development level is required for all subdivision developments. This is to avoid exceeding the capacity of downstream drainage infrastructure 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 limited to up to three (3) 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.
Centralised OSD systems, such as basin, underground pit/pit storage etc., is required for subdivisions with five (5) lots/units or over.
OSD calculation methods that assume a constant discharge, such as the Mass Curve
Council will accept, but not limit to, software packages such as OSD4, DRAINS or Excel Spreadsheets being used to generate OSD design system.
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.
Access - Vehicle Crossings and Drives
All vehicle crossings providing access off a sealed road are to be sealed or concrete paved unless outside of township zones and providing access solely for rural agricultural purposes.
All common driveways accessing a road within or abutting a township zone 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.
Crossing Culverts in Road Reserve
Endwalls for roadside culverts are not to protrude above the finished level of the crossing. Low-profile endwalls are allowed if the culvert is outside clear zone as per IDM SD255 and SD260.
Road design
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 verge for tree planting is to be provided to meet landscaping requirements. Trees are not to be planted in the clear zone or in table drains. Street lighting is not to be placed in the clear zone or in table drains. Any services installed in the tree zone are to be minimum depth 1m.
Roadside features
To avoid long term impact from roadside features to open drains, the followings shall be considered:
- No trees are to be planted within open drain and must be setback a minimum of 450mm from the top of swale.
- Tree must be setback a minimum 750mm from road edge, back of kerb and/or footpath.
- Trees and street lights shall be outside of clear zone and 3m minimum from traffic lane.