Water Journal : Water Journal April 2013
WATER APRIL 2013 100 Feature Article need for ongoing maintenance due to re-mobilisation during minor ooding events. Due to this, trials were undertaken using open-weave jute mesh to prevent movement of the wrack when lake levels were higher. 3. Similarly to the passive saltmarsh program, community engagement was important and early lessons were learnt about the timing and breadth of stakeholder engagement so that all expectations could be considered and managed before works began. One of the most signi cant unforeseen issues that arose for the active saltmarsh rehabilitation work was with the original designs that had utilised years of data collected by Council. The estuary had been facing drought conditions for the previous decade and subsequently the vegetation communities around the lake had adapted to these conditions. Due to the continued low water level in the lake during the drought, the healthiest saltmarsh was growing at around 0.2m AHD; this resulted in the designs for the active sites being re-graded from this elevation to around 0.5m AHD (in some cases less). A number of the active rehabilitation sites had been constructed using this speci cation when the drought broke in 2010/2011. During 2011 and early 2012, the estuary received more frequent and heavier rain events, causing a higher average lake level. This higher level caused the two most recently constructed sites to be submerged for extended periods immediately after planting and has contributed to their slow rehabilitation. These challenges resulted in a redesign of the methodology for the remaining sites. Surveys of healthy saltmarsh in 2011 showed that the ideal elevation during the frequently higher rainfall was between 0.4m AHD and 0.5m AHD, with saltmarsh species present up to 0.8m AHD. The majority of these elevations were not captured in the original designs. Adopting lower levels of intervention has greatly reduced construction costs for acid sulphate soil treatment and spoil disposal and has permitted existing healthy saltmarsh to be retained in situ. The reduced excavation has allowed these sites to include higher elevation areas that will facilitate healthy bands of saltmarsh that can migrate landward or towards the lake edge in response to changes in rainfall patterns. Early observations in these elevated saltmarsh areas have, however, initially shown increased levels of weed species, which may be due to the lack of frequent inundation of saline/brackish water allowing the terrestrial weeds to compete with the newly planted saltmarsh. Monitoring and maintenance activities over the next few months should show if these sites are likely to become resilient over time. Trials are in the early stages of development for irrigating the saltmarsh and fringing exotics with lake water to help reduce the competing weeds. APPLYING AN ADAPTIVE MANAGEMENT APPROACH As noted previously in this article, saltmarsh rehabilitation in a non-tidal estuary is largely untested. As a result, many issues were encountered during on-ground works that required an adaptive management approach to be embraced. The saltmarsh sub-program has employed a regular monitoring program that is complemented by a regular review of ndings and adaption of activities as has been seen t. This is vital so that a regular feedback loop is maintained to ensure the most effective and ef cient delivery of the saltmarsh rehabilitation sub-program. For example, if the active saltmarsh sub- program was not analysing the monitoring information then signi cant design changes may not have been made and the desired outcomes not achieved or further signi cant investment of maintenance employed to achieve the outcomes. Monitoring of the sites will continue to provide important data on the response of the saltmarsh rehabilitation over a longer time-frame. ACKNOWLEDGEMENTS The Wyong Shire Council would like to acknowledge the Australian Government's Caring for our Country initiative that has enabled these important works to be able to be undertaken. REFERENCES Funnell SC & Rogers PJ (2011): Purposeful Program Theory: Effective use of theories of change and logic models. San Francisco, USA: Jossey-Bass. Love AJ (1991): Internal Evaluations: Building Organisations from Within (Vol 24). Newbury Park, USA: Sage. Owen JM (2006): Program Evaluation: Forms and Approaches. Crows Nest, Australia: Allen & Unwin. Patton MQ (2008): Utilization-Focussed Evaluation (4th edition ed.). Newbury Park, USA: Sage. Roberts DE & Dickinson TG (2005): Tuggerah Lakes Estuary Management Study. Bio-Analysis: Marine, Estuarine and Freshwater Ecology. Trochim WM (1991): Developing an Evaluation Culture for International Agricultural Research. Assessing the Impact of International Agricultural Research for Sustainable Development. Cornell University. Wyong Shire Council (2010): Tuggerah Lakes Estuary: Estuary Management Plan. Retrieved February 2013, from Wyong Shire Council: Central Coast: www.wyong. nsw.gov.au/environment/tuggerah-lakes- estuary/estuary-management-plan Figure 4. Passive activity (left) shown in Tuggerah Bay, and active saltmarsh (right) during rehabilitation -- works depicted include foreshore re-grading and spreading of wrack mulch prior to planting.
Water Journal February 2013
Water Journal May 2013