Coastal Acid Sulfate Soils Program (CASSP) projects

Background

Frogmore DrainFrogmore Drain Union FloodgatesUnion Floodgates opened to facilitate improved aquatic habitat Aerial image of the Frogmore/Darkwater flood mitigation drainage network draining into the Belmore River The Frogmore/Darkwater flood mitigation drainage network draining into the Belmore River Landholders assist in positioning in-system structures Landholders assist in positioning in-system structures Typical in-system structure that was required to be positioned to accommodate increased water levels Typical in-system structure that was required to be positioned to accommodate increased water levels Landholder working bee Landholder working bee

In December 1998, the Federal Minister for the Environment and Heritage, Senator the Hon Robert Hill, launched Australia’s Ocean Policy. The policy recognised that agricultural, residential and tourism development along Australia’s coastline has led to disturbance and exposure of acid sulfate soils, which in turn led to the reduction in inshore water quality, habitat degradation and loss of biodiversity.

To address this serious environmental issue, Australia’s Ocean Policy initiated the Coastal Acid Sulfate Soils Program (CASSP).The primary focus of the CASSP is to provide catalytic funding for projects with on-ground works that demonstrate options for the management of coastal acid sulfate soils for the improvement of water quality.

The MRFP submitted a CASSP funding application in March 2000 to address environmental and land management issues pertaining to two (2) sites within the Macleay River Floodplain.The application was submitted by the MRFP on behalf on Kempsey Shire Council, in partnership with NSW Fisheries (conservation Division, Northern Region), Department of Land & Water Conservation, NSW Agriculture and the Macleay Acid Sulfate Soils Local Action Group (MASSLAG).

Lower Macleay Acid Sulfate Soils Rehabilitation Project

Frogmore/Darkwater project

The Frogmore Darkwater water quality, aquatic habitat improvement project has been developed to address environmental issues associated with a major flood mitigation network, servicing a large lowland/backswamp area of the Belmore River.

The flood mitigation system is controlled by a large nine (9) cell floodgate structure.The floodgates control over 14km o flood mitigation drains with the entire drainage network through acid sulfate soil landscapes.

The objective of the project is to facilitate tidal movement behind the Union Floodgate structure and into the drainage network. To achieve this one (1) of the nine (9) floodgates on the Union structure will be opened and remain open in non-flood periods. To accommodate the increased water volumes/levels in the system a series of smaller in-system water control structure were positioned at strategic location to avoid undesirable pasture inundation. In total 20 smaller in-system water control structures were required to be positioned in low points and washouts within the systems banks and levels To gain an understanding of how the system would respond to increased water levels, a series of trial floodgate openings was undertaken during specific tidal regimes.

Before more permanent structures were positioned, a landholder ‘working bee’ was held. Landholders filled and position sand bags in the predetermined low or washout points. Once the sand bags were positioned the floodgates were opened to allow tidal exchange. After a two week period the gates were then closed, where an inspection of the water marks on the sand bags provided an understanding of to what levels water could be expected to reach given varying tidal levels.

The location and positioning of the structures was based on the results obtained via the trial floodgate openings. The in-system structure inverts were calculated based on the capacity to retain water in the drainage network, reduce the volume of ground water drainage and provide a mechanism for the farmers to lift the smaller structures to accommodate backswamp and pasture (via flood irrigation) management.

Results to-date indicate that, the effects on water quality within the drainage network improves significantly with then the gates are opened and tidal water movement assist in decanting the acidic water discharges.

Scott's Drain/Killick Creek Project

The Scott’s Drain/Killick Creek project is an acid sulfate soils/saline scald rehabilitation project. The project has been developed to remediate a scalded landscape in the Upper Belmore River area.

The Scott’s Drain floodgates are the controlling structure on the northern outlet of the system. The Killick Creek Cut floodgate structure is the controlling structure on the southern outlet. There is approximately ten (10) km of mitigation drains between the two outlets. All of which drain acid sulfate soil landscapes.The objectives of this project is to retrofit the existing Scott’s Drain floodgates to facilitate active water management in the drains and subsequently over the scalded areas.

The design modifications include a safe working platform, a lifting device and a mini sluice gate. The methods adopted involved lifting the Scott’s Drain gates to allow high tide to push fresh water from the Belmore River into the drain and over the scald. Once the desired depth of water is obtained, the floodgates are closed and the mini sluice gate is opened for more precise water level management.

Results

Results to-date have been very positive with lush re-vegetation now growing over the once barren scalded landscape and improved water emanating from the system. As a result of the successful outcomes, this method of scald rehabilitation will be implemented to address other nearby acid sulfate soil scalded landscapes.

Aerial view of the Scott's Drain/Killick Creek flood mitigation drainage systemThe Scott's Drain/Killick Creek flood mitigation drainage system
Scott's drain acid sulfate soil scalded area Scott's drain acid sulfate soil scalded area
Scott's Drain floodgate Scott's Drain floodgate
Revegetation over scald after intentionally flooding the scald with fresh water from the Belmore RiverRevegetation over scald after intentionally flooding the scald with fresh water from the Belmore River
Acid sulfate soil scald area
Trial plot positioned in scalded area
Improved wetland environment