Wetland Management
Coastal Lakes Management, Strategies for a Sustainable Future
Contributor:
Philip Haines,
Manager,
WBM Oceanics Australia,
Newcastle, 2006
INTRODUCTION
The sustainable management of Intermittently Closed and Open Lakes and Lagoons (ICOLLs) is one of the most difficult tasks facing coastal managers today. This booklet provides ten scientifically based management strategies that address:
- Existing and future catchment development and associated pollutant inputs;
- Artificial entrance management;
- Foreshore inundation mitigation;
- Habitat loss;
- Waterway activities, and
- Institutional arrangements for ICOLL management and conservation.
The ten strategies are not designed to provide a complete management package for ICOLLs, rather they should be used to form the platform for individual Management Plans that are h4.specific to the features of each system.
ICOLLs
Intermittently Closed and Open Lakes and Lagoons are saline water bodies that have intermittent connection to the ocean. Some have entrances that are mostly open, on average, while the majority (>70%) have entrances that are mostly closed. When closed, ICOLLs have no tidal interaction and behave as terminal lakes, with water levels responding to catchment runoff, direct rainfall, evaporation and groundwater inflows and outflows.
There are approximately 60 Intermittently Closed and Open Lakes and Lagoons (ICOLLs) located along the NSW coastline, strongly biased towards the south coast. ICOLLs are recognised as the most sensitive type of estuary to human intervention due to their lack of tidal flushing and interaction with the ocean, particularly ICOLLs that have mostly closed entrances.
PRESSURES ON ICOLLS
There are many issues potentially compromising the values of coastal lakes including increasing coastal populations, growing tourism demands and climate change.
- The population of the non-metropolitan coastal zone is expected to increase by approximately 430,000 between 2001 and 2031. Development around coastal lakes and within their catchments increases pollutant loads and modifies natural processes, resulting in degradation of the waterway.
- The coastal zone continues to be a tourist destination which is increasing recreational demands on the ICOLLs and increasing loads to on-site sewage systems.
- Climate change is now widely accepted within the scientific community, and is a legitimate threat to the future management of the NSW coastal zone. One of the primary changes to the climate likely to impact on ICOLLs is sea-level rise. Current projections for future sea level rise suggest an increase in mean sea level of between 0.2 and 0.6 by then end of this century.
MANAGEMENT EXAMPLE: “DEFINING SETBACKS FOR DEVELOPMENT”
The booklet has identified 10 management strategies. As an example, strategy three states that “Buffers or offsets to development are required around coastal lakes that take into consideration the functionality of the biophysical ecosystem and the expected response to future climate change”.
The methodology for determining future development setbacks for ICOLLs is based on the following management principles:
- The ICOLL should be permitted to experience a full natural range of water level conditions;
- The net water levels in the ICOLL will increase in the future as a natural response to increasing sea levels, and associated increases in entrance berm conditions;
- Buffers should be provided around the ICOLL, beyond the natural range of water level condition, to allow for natural ecosystem functioning and interaction between the estuarine and terrestrial environments;
- Buffers around the ICOLL should be vegetated to maximise opportunities for ecological processes and for dissipating / assimilating the impacts of adjacent development; and
- Some ICOLLs, or specific parts of ICOLLs may be more sensitive than others, and thus may require additional buffering between the development and the waterway.
THE NEED FOR TWO BUFFERS
In defining appropriate setbacks from ICOLLs, two buffers need to be considered. Firstly, a vertical buffer to allow for the natural expansion and contraction of the waterway, with allowance for future sea-level rise. Secondly, a horizontal buffer to provide for sustainable functioning of fringing riparian ecosystems and to protect the waterway environment for impacts associated with urban development. To be effective, the buffers should contain dense vegetation.
Vertical buffer: As a default value, a vertical buffer of RL 3.5 should be applied to all ICOLLs in NSW, subject to more detailed site-specific assessments. This default buffer allows for a berm crest level of 2.5 to 3m AHD and an allowance of 0.5 to 1.0 meters for future sea-level rise, over a planning horizon of approximately 100 years.
Horizontal buffer: A minimum of 50m from the 3.5 AHD contour around the ICOLL is recommended. However when the foreshore ground level information is uncertain, or where ICOLLs are more sensitive to catchment pollutant inputs, the buffer should be larger.
Where existing development prohibits the return of natural water level regimes (eg. Manly Lagoon, Werri Lagoon and Lake Mummuga) horizontal buffers should be applied from the extent of the maximum permissible water levels in the ICOLLs.
CONCLUSION
The status quo on managing ICOLLs is contributing to their declining condition and we cannot afford to continue down this track. New initiatives are required and this booklet offers clear and practical solutions to on-going and future problems.
For More Information: Coastal Lakes Booklet (PDF – 1.3MB)
