A guide to managing and restoring wetlands in Western Australia Wetland hydrology In Chapter 2: Understanding wetlands A guide to managing and restoring wetlands in Western Australia Chapter 2: Understanding wetlands i Wetland hydrology A guide to managing and restoring wetlands in Western Australia Chapter 2: Understanding wetlands Contents of the guide Introduction Introduction to the guide Chapter 1: Planning for wetland management Wetland management planning Funding, training and resources Chapter 2: Understanding wetlands Wetland hydrology Conditions in wetland waters Wetland ecology Wetland vegetation and fl ora Chapter 3: Managing wetlands Managing hydrology Wetland weeds Water quality Secondary salinity Phytophthora dieback Managing wetland vegetation Nuisance midges and mosquitoes Introduced and nuisance animals Livestock Chapter 4: Monitoring wetlands Monitoring wetlands Chapter 5: Protecting wetlands Roles and responsibilities Legislation and policy These topics are available in PDF format free of charge from the DEC website at www.dec.wa.gov.au/wetlandsguide. ii Wetland hydrology A guide to managing and restoring wetlands in Western Australia Chapter 2: Understanding wetlands ‘Wetland hydrology’ topic Acknowledgments Authors: Christina Mykytiuk, Justine Lawn and Romeny Lynch, DEC. Reviewers and/contributors The following people have been consulted in the development of this topic: Dr Brad Degens, Department of Water Robyn Loomes, Department of Water Alisa Krasnostein, DEC Dr Lien Sim, DEC Dr Ken Atkins, DEC The valuable contribution of each of these people, and people who have contributed their photos, is gratefully acknowledged. Symbols used in figures are courtesy of the Integration and Application Network (http:// ian.umces.edu/symbols/), University of Maryland Center for Environmental Science. Project manager: Justine Lawn, DEC Publications management: Joanna Moore Graphic design: Stuart Ridgway, Stuart Ridgway Design Cover photo: DEC gratefully thanks Professor Jenny Davis for permission to reproduce her photo of Manning Lake, Cockburn. Recommended reference When referring to the guide in its entirety, the recommended reference is: Department of Environment and Conservation (2012). A guide to managing and restoring wetlands in Western Australia. Department of Environment and Conservation, Perth, Western Australia. When specific reference is made to this topic, the recommended reference is: Department of Environment and Conservation (2012). ‘Wetland hydrology’, in A guide to managing and restoring wetlands in Western Australia, Prepared by C Mykytiuk, J Lawn and R Lynch, Department of Environment and Conservation, Perth, Western Australia. Disclaimer While every effort has been made to ensure that the information contained in this publication is correct, the information is only provided as a guide to management and restoration activities. DEC does not guarantee, and accepts no liability whatsoever arising from, or connected to, the accuracy, reliability, currency or completeness of any material contained in this guide. Sections of this topic were drafted by November 2009 therefore new information that may have come to light between the completion date and publication date may not have been captured in this topic. iii Wetland hydrology A guide to managing and restoring wetlands in Western Australia Chapter 2: Understanding wetlands Contents Introduction .............................................................................................................................1 What are the hydrological characteristics of Western Australia’s wetlands? ....................1 Wetland hydrology ...............................................................................................................2 Hydroperiod .........................................................................................................................2 Wetland water regime ........................................................................................................10 How does a wetland’s hydrological characteristics affect it? ............................................11 Water availability ................................................................................................................12 Oxygen availability ..............................................................................................................16 Light availability ..................................................................................................................18 Salt availability ....................................................................................................................18 Nutrient availability .............................................................................................................19 Organic carbon availability ..................................................................................................20 pH (acidity/alkalinity) ...........................................................................................................20 What determines a wetland’s natural hydrological characteristics? ................................22 Climate ..............................................................................................................................22 Water in the landscape - surface water and groundwater ...................................................25 Surface water flows ...................................................................................................25 Groundwater .............................................................................................................31 Investigating surface and groundwater interaction with wetlands .................................43 Quantifying wetland hydrology ..........................................................................................47 Sources of more information on wetland hydrology .........................................................56 Glossary ..................................................................................................................................57 Personal communications .....................................................................................................60 References .............................................................................................................................61 Case studies The hydrology of the Mandora Marsh system ....................................................................52 The hydrology of Lake Gore .................................................................................................54 The hydrology of Lake MacLeod ..........................................................................................55 iv Wetland hydrology A guide to managing and restoring wetlands in Western Australia Chapter 2: Understanding wetlands h Before you begin Before embarking on management and restoration investigations and activities, you must consider and address the legal requirements, safety considerations, cultural issues and the complexity of the ecological processes which occur in wetlands to ensure that any proposed actions are legal, safe and appropriate. For more guidance, see the topic ‘Introduction’. Introduction Over time, wetlands have formed where water has accumulated at or close to the ground surface for periods sufficient to form wetland characteristics. Water creates and defines wetlands and distinguishes them from dryland ecosystems, affecting every physical, chemical and biological process in wetlands and, in doing so, shaping their ecological character. An understanding of the natural patterning of water in a wetland, and the role it plays in shaping the wetland, is essential when managing it, particularly when the natural water patterns have been, or have the potential to be, affected by human-induced changes. Wetland water regime has been identified as the highest priority issue in the management of Western Australian wetlands by the WA Environmental Protection Authority.1 Changes to natural wetland water regimes have resulted from widespread changes to the landscape of WA, such as clearing, development and drainage, as well as water abstraction and climate change. Managing the natural water regime of a wetland of conservation value is the most essential activity a wetland manager can undertake. Where the purpose of wetland management is nature conservation, the role of a wetland manager is generally to minimise potential human-induced changes to intact natural water regimes. If altered by human activities, restoration and management of a wetland may involve reinstating or improving the water regime, or, if this is not feasible, managing a changing ecosystem. These tasks can be challenging for wetland managers without expertise in hydrology, and in many circumstances it can be essential for wetland managers to liaise with relevant qualified professionals such as hydrologists and hydrogeologists. This topic provides information on the natural hydrological characteristics of WA wetlands. This understanding forms the basis for managing wetland hydrology. The topic ‘Managing hydrology’ in Chapter 3 provides more detailed information on the actions that can be taken to manage or restore wetland hydrology. WHAT ARE THE HYDROLOGICAL CHARACTERISTICS OF WESTERN AUSTRALIA’S WETLANDS? Water is naturally variable across the Earth, but especially so in Australia, a land ‘of droughts and flooding rains’.2 Its variability in terms of presence and absence, timing,