Physical Constraints to Development Within Bayside

Any developments or civil works that involve the disturbance of soil below the groundwater table or the disturbance of sediments within Botany Bay have the potential to disturb actual or potential acid sulfate soils. The soils can form sulfuric acid that can leach into the surrounding area acidifying neighbouring drains, wetlands, creeks, estuaries and bays, causing severe environmental damage. It can also impact on infrastructure by causing serious damage to steel and concrete structures such as the foundations of buildings.

There are five classes of land when categorising risk from acid sulfate soils. Each Class has corresponding acid sulfate soil risk management requirements. Further information can be found at:

• Acid Sulfate Soil Risk Maps
• Acid Sulfate Soil Classes

All Development Applications are assessed for the likelihood of acid sulfate soils onsite, and depending on the risk class, appropriate management measures are required during demolition, excavation and construction.

Further general information on acid sulfate soils can also be found at:

Department of Agriculture, Water and the Environment

NSW Department of Planning, Industry and Environment - Environment, Energy and Science

Discharge of water containing sediment and contaminants can have a significant harmful effect upon the environmental health and amenity of creeks, wetlands, ponds and Botany Bay.

Disturbance of soil for building, construction and landscaping can cause pollution if not managed correctly. Bayside Council requires the implementation of controls for soil and water management for developments, as outlined in the Development Control Plans.

The following information must be provided as part of documentation of Development Applications to Council:

A Development Application must include an:

• Erosion and Sediment Controls Plan for sites with an area of 2500m2 or smaller, or
• Soil and Water Management Plan for sites with an area greater than 2,500m2.

Managing Urban Stormwater - Soils and Construction 4th ed. March 2004 and Planning for Erosion and Sediment Control on Single Residential Allotments provide guidelines for the preparation of these plans.

Bayside is located in the Botany Sands Aquifer with groundwater less than two metres below ground level in many other areas. Where a development is proposed to extend into the existing groundwater, it is critical that adequate site investigation is undertaken at an early stage.

To enable the work area to be kept dry while construction is being undertaken, groundwater inflows into any basement excavation are generally managed through dewatering. Dewatering is the process of removing groundwater from an aquifer to lower the water table below the lowest level of excavation. This allows construction to proceed safely by limiting the potential for excavation instability and preventing waterlogged ground conditions.

Dewatering within the Botany Sands Aquifer generally requires continuous pumping of groundwater for a prolonged period. Where significant dewatering is required to allow construction to proceed, you will need to apply for a licence from the Department of Primary Industries - Water .

Tailwater is the water produced through the extraction of groundwater during dewatering. To meet the requirements of the Protection of the Environment Operations Act 1997 tailwater must be disposed of in a manner that doesn’t contaminate surface waters.

If the dewatering system is not carefully designed and managed it can lead to adverse impacts on the environment including:

• inflow of contaminated groundwater resulting from excessive or prolonged pumping
• discharge of contaminated water into stormwater systems and waterways
• detrimental ‘downstream’ environmental impacts by potential chemical and physical contamination
• impacts on local businesses or residents due to the appearance of the discharge or the odours generated by the tailwater

When considering developing on your land, it is important to ensure that any development proposal which includes excavation or basement level works, or proposes an on-site retention system, considers the depth of the groundwater. Depending on the works, a geotechnical report may also be required.

Additionally, all works connected to a source of underground water and used for water supply, groundwater monitoring, dewatering, or any other purpose, must be licensed by the Department of Primary Industries.

It is also important to note that there are several groundwater sites in the former Botany Council area which contain polluted groundwater. Many of these are in the process of being cleaned up, or have a site management plan associated with the site.

Increased rainfall intensity and sea level rise due to climate change may make flooding and drainage issues more significant in Bayside.

Any development proposed within an area potentially affected by sea level rise, may therefore require Council to set habitable finished floor levels, may require a flood study which takes into account sea level rise, or may require a Risk Management Plan to be prepared.

Land contamination can occur due to leakage of pollutants into the ground and groundwater.  Land contamination is particularly prominent in the Bayside Council area, as it has been heavily used by industry.

Any development proposed on a potentially contaminated site must be considered in accordance with State Environmental Planning Policy 55 - Remediation of Land. Prior to development, the site must be demonstrated to be suitable for use, or that it will be suitable for use after remediation.

To ensure sustainable future growth and the safety of aircraft and airline passengers, airspace surrounding an airport must be protected from inappropriate development.  For this reason, the height of buildings in areas near Sydney Airport and under flight paths are restricted.

Additionally, Australian Noise Exposure Forecast (ANEF) charts are used to assist in identifying areas where noise sensitive development (such as residential and child care centres) should be controlled. ANEF charts are contour maps that show a forecast of aircraft noise levels.

If your property is located in these areas, your Development Application will need to consider these restrictions and considerations.

With increasing development and impervious areas within the Bayside local government area, there are less opportunities for infiltration, which results in increased stormwater runoff and flooding.

Council requires onsite stormwater retention as its principal method of stormwater management.  Retention aims to retain stormwater on the site through the permanent storage of roof or surface water runoff, discharging this stormwater into the groundwater system through the use of an absorption/infiltration system. Absorption systems are used on sites that have typically sandy soils with medium to high permeability rates. This includes the vast majority of the former City of Botany Bay Council area and the low-lying sandy regions of the former Rockdale City Council area.

If the soil does not permit a stormwater absorption/infiltration system, such as in an area with clayey soils, or due to the type of development, an on-site detention system will likely be required.  This system aims to control the impact of stormwater run-off on downstream properties/infrastructure, and is of particular consideration in highly impervious urban areas and areas located at higher points of the catchment.

In some instances a property may fall away from the street and the property may not have access to an existing drainage system, or it may not be feasible to install an absorption system on the site. In these cases, Council’s preferred method of stormwater management for the property is for the developer to negotiate for a private drainage easement to allow for gravity stormwater discharge to Council infrastructure. A Drainage of Low Level Properties form may be required. If a private drainage easement cannot be obtained when required, the developer will need to lodge a Private Drainage Easement Review.

Rainwater tanks are actively encouraged throughout the region as a matter of water sensitive urban design and are often mandatory for certain types of development. Rainwater tanks provide a building with a way to harvest roof stormwater for non-potable uses such as toilet flushing, reducing the buildings demand on the drinking water supply. For large scale redevelopments, the development will need to meet the water quality objectives as outlined by Council's Technical Specifications.

Design criteria and standards are contained within Council’s Technical Specifications.

Flooding can cause significant damage to property, infrastructure, roads and risk to life.  Being flood affected means a property has a risk of being flood affected in specific rainfall events.

Any development proposed within a flood affected area may require flood related development controls to be applied to the development consent, such as raising floor levels or using flood resistant materials. Any new development is not to increase the water level or hazard on adjoining properties. Opportunities should be investigated to design a development that is clear of the overland floodway and acts to reduce the impacts of these flows, possibly by removing inappropriate travel paths and/or reducing the hazard.

For sites subject to flooding in the 1% AEP flood or for flood planning requirements, the applicant is required to obtain Flood Advice from Council’s Strategic Planning Department. This letter will identify the minimum floor level and other requirements for development of the property, as well as any additional works or studies that will be required for the development of the property.

Council is actively working to reduce the impact of flooding and progressively preparing Flood Studies and Floodplain Risk Management Studies and Plans for all catchments.

The Denison Street Risk Study identifies risk related planning measures that will be used to inform existing and future developments in and around Denison Street, Hillsdale.

Any development proposed within this study area will be governed by the constraints and proposed controls / potential restrictions on the use of land within the area, for the continued safety of residents and workers in the area.