Environmental Water Requirements of Wetlands
within the Torbay Catchment, South Coast Region
EXECUTIVE SUMMARY
Background
The South Coast Regional Office of the Department of Water (DoW) is currently undertaking allocation planning for priority water resources located within the Torbay Catchments (within the Albany Drainage District). The program is being prepared with the purpose of preventing over-allocations and associated potential environmental, social and cultural impacts.
The Torbay Drainage System was highly modified during the 1950's to protect infrastructure from flooding and increase the area of productive horticultural land on the valley floor. Modifications consequently separated the lower section of the Torbay Catchments into three different hydraulic levels and local wetlands now have altered inflows, managed outflows and are kept at artificial levels
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1 For reasons explained in more detail elsewhere in the report, while this inland part of the Torbay Inlet is commonly regarded as "Lake Manarup", we will use the term Manarup Lagoon here to emphasise its continued functioning as a shallow, lagoonal estuarine basin
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The Centre for Ecosystem Management has been contracted to provide an assessment of the environmental water requirements within the Torbay Drainage System (TDS). The original contract brief identified two study sites, Lake Powell and Manarup Lagoon1. However, the scope of work was revised to include Marbellup Brook Drain, North Creek Drain (NCD) and Ewart Swamp since it seemed management of the larger wetlands could not be considered unless in the context of other significant structural components of the system.
Desk-based and field assessments were used to compile a knowledge base for the TDS and to identify ecological values and gaps. With this information, the level of water dependency of identified ecological values and the risks of impacts from changes in water regimes were evaluated and Ecological Water Requirements (EWRs) determined for all ecological values, features and processes.
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