Wetland Creation at Ash Island, Newcastle, NSW
Client: Department of the Environment and Climate Change (National Parks and Wildlife Service)
Project Reference: 05111
WRL Technical Report: Wetland Cration at Ash Island: Hydraulic Advice and Design Aspects (2006/08)
Ash Island is one of several islands located in the lower Hunter River Estuary. Previously the site was modified, drained and cleared for largely agriculture purposes. The site is now managed by National Parks and Wildlife Service and is adjacent to the Ramsar Listed Kooragang Nature Reserve. As part of a wetland compensation agreement, a number of investigations were undertaken to determine the design of a series of proposed tidal ponds and connecting channels. To design the tidal system, soil, groundwater, surveying and hydraulic studies were undertaken by the Water Research Laboratory.
The final design of the tidal ponds is provided below. Three ponds were designed, each with different bed levels and tidal flushing regimes. The various pond designs were derived to account for the range of onsite objectives.
Major field investigations were undertaken prior to finalising the pond design. RTK-GPS surveying was undertaken using a roving quad bike to maximise coverage. The resultant digital terrain model assisted in determining the excavation volumes. A preliminary Acid Sulphate Soil assessment was also undertaken to determine the extent of potential and actual acid soils in the floodplain soils.
To determine the impact of increasing the tidal prism within the adjoining channel network a range of onsite measurements and hydraulic calculations were undertaken. The onsite measurements focused on comparing the tidal prism versus the channel dimensions. This information was tabulated within a computer model to determine how the channels may evolve with an increased tidal prism.
Once the pond designs, culverts and impact studies were finalised, on-ground specifications were developed. This included cross-sectional diagrams of the proposed wetland, engineering specifications on the entrance structures and additional information on managing acid sulphate soils. In an interesting turn of events, a critically endangered grass owl was recorded onsite prior to commencing construction works. As such, on-ground works have been postponed until further information is obtained.
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