Selection of an appropriate site for aquaculture development is critical to the success of the operation and ensures that the potential for environmental harm is minimised. When selecting a site, consider the following factors to minimise problems with containment structures.
Topography:
Consider the topographic relationship between the development area and adjacent sensitive environments and land uses.
There is likely to be a greater risk to properties down-slope of the proposed farm area, so the nature of the land use on these properties should be carefully considered.
Where practical, provide greater separation distances to sensitive areas down-slope of the development area. While the surface slope is not necessarily indicative of the direction of groundwater flow, it provides a good ‘rule of thumb’. Baseline monitoring of groundwater levels may confirm the direction of groundwater flow.
Flat coastal plains or sites where the ground level is less than approximately 5 m Australian Height Datum (AHD) may require treatment for soft organic, sandy or acid sulfate soils (see Section 2.5) and this could involve significant costs.
Geology:
Site geology is an important consideration in site selection. Shallow bedrock may interfere with earthworks adding to construction costs. Also, rock outcrops intersecting with containment structures may be a major source of leaks as water can travel through cracks and fissures in the rock.
Soils:
A low level of permeability is required to minimise the intrusion of saline and/or high nutrient water into the watertable or aquifer. Preferred sites for pond-based aquaculture would have sufficient in situ material to construct ponds to a high level of structural stability and impermeability. They would also be underlain by a consistent layer of low permeability soils. Suitable material characteristics may be obtained through one or both of the following:
- over-excavation and back-filling with suitable material obtained from borrow pits in proximity to the site
- mixing of heterogeneous materials from multiple sources or layers to produce a homogeneous material suitable for pond construction.
Further information on problematic soil types is included in Appendix 1.
In the absence of suitable material on site, or in close proximity, haulage of material from off site may be required. Otherwise, alternative pond construction techniques involving the use of impervious pond liners such as concrete or plastic may be necessary.
Consider these factors carefully, as longdistance haulage of materials or using synthetic lining for ponds may impose a significant financial cost, affecting the financial viability of the farm. It could also create other hazards such as increased risk of drowning.
Groundwater:
When selecting a site consider the following attributes of the groundwater:
- depth
- quality
- direction of flow
- resource value (see Section 2.7).
Consultation with local natural resource managers can be valuable in developing an understanding of local groundwater characteristics. So can the Groundwater Vulnerability Mapping, undertaken by the Department of Natural Resources and Water, which will help evaluate the risk of groundwater contamination.
This dataset integrates a number of attributes of the geology, soils and groundwater to predict the groundwater vulnerability assessment at a regional scale. (For further information contact your local Department of Natural Resources and Water office.
Other valuable sources of information include local earthworks contractors, geotechnicians and drillers who may have significant understanding of the groundwater environment and soils in the area.
Acid sulfate soils:
Most coastal aquaculture sites are found in areas where acid sulfate soils may be present and the State Planning Policy (SPP2/02) lists all shires in Queensland with acid sulphate soil issues. The extent to which acid sulfate soils affect aquaculture operations remains the subject of industry debate.
However, it is generally agreed that their presence should not be detrimental to the future viability of an operation, provided they are appropriately managed during the construction stage.
The desirable range of soil as well as water pH for aquaculture is 6.5 to 8.5. A pH lower than 6 is considered too acidic for most aquatic animals, and acid sulfate soil leachate is commonly less than pH 4. If acid sulfate soils are disturbed, the environment could be damaged and productivity could be significantly affected.
Therefore, under the State Planning Policy 2/02: Planning and managing development involving acid sulfate soils, development proposals in coastal locations will need to demonstrate that potential acid sulfate soils issues have been adequately addressed. There are a number of related guidelines and for further information, contact your local Department of Natural Resources and Water office.
In coastal areas the State Planning Policy is applicable to all land, soil and sediment at or below 5 m Australian Height Datum (AHD) where the natural ground level is less than 20 m AHD. In these areas, the State Planning Policy will apply where the proposed development involves:
- excavating or otherwise removing 100 m3 or more of soil or sediment
- filling of land using 500 m3 or more of material with an average depth of 0.5 m or greater.
The presence of acid sulfate soils may require detailed management to minimise environmental harm during the construction phase and may also require a level of on-going management during the operations phase. The presence of acid sulfate soils will not in most cases preclude development, but the level of treatment required will need to be considered when assessing the economic feasibility of the proposal, as the cost of management may be significant.
Sensitive environments:
Sites in close proximity to sensitive environments are likely to require more detailed assessment and management controls. Sensitive environments include:
- protected areas such as national parks, conservation parks and resources reserves
- significant coastal dunes
- significant coastal wetlands
- remnant vegetation
- freshwater wetlands.
Unsound containment structures may affect adjacent sensitive environments by causing problems such as:
- alterations to the hydrological cycle (wetting and drying) or water quality of freshwater wetlands
- vegetation dieback through waterlogging or salinisation
- changes in vegetation characteristics in response to changed soil properties.
Local and regional land use:
When determining the level of risk posed by containment structures, aquaculturalists need to consider the characteristics of adjacent environments and the nature of land uses in neighbouring areas including:
- activities such as cropping and grazing
- local and regional use of the groundwater resource – the consequences of an unsound containment structure will be more significant in sites where the local or regional groundwater is used as a resource for agricultural, domestic or stock watering purposes or is within a declared groundwater management area.
Separation distances:
The proximity of a containment structure to sensitive environments or land uses will affect the risk of environmental harm occurring should there be a problem with the structure. Where practical, the containment structure should be separated from sensitive environments by a reasonable distance.
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