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Influencing Floodplain Health

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Along the Goulburn River, Source Catchments is aiding management to identify the benefits and dis-benefits of floodplain inundation under a range of flow scenarios.

Flooding of dry floodplains can be beneficial or disastrous for floodplain ecosystems. Watering can rejuvenate river red gums and other vegetation. In refuge pools and floodplain wetlands, rewetting can be the kiss of life for waterbirds, resident fish and water bugs battling to survive the water scarcity, predation and habitat loss that accompany drought.

But the duration of wetting is vitally important. Unless the water stays long enough, the natural cycles that flooding initiates can stall. And the timing of watering matters too: for instance, delivering water during very hot summer weather can trigger ‘blackwater’ events fatal to fish and other aquatic fauna.

Willows on Goulburn River bank. Photographer Irene Dowdy courtesty MDBA.Willows on Goulburn River bank. Photographer Irene Dowdy courtesty MDBA.In Northern Victoria’s Goulburn and Ovens rivers, a team of researchers are trialling a landmark water quality and quantity software model while exploring the response of key ecological indicators to flow scenarios, including floodplain wetting events. The research integrates ecological and hydrological modelling science as it reviews current understanding of the role of overbank flows in maintaining riparian ecosystems.

 

 

The team is also investigating options for “piggybacking” of flow releases onto naturally occurring flow events.

“We will soon be in a position to increase our knowledge base on likely ecological effects of restoring such flows in the Goulburn river system,” says Northern Victoria Focus Catchment Coordinator Wayne Tennant, of the Goulburn-Broken Catchment Management Authority.

The research involves a range of influential partners. These are the Environment Protection Authority (Victoria), Department of Primary Industries (Victoria), Goulburn Broken Catchment Management Authority, North East Catchment Management Authority, Goulburn-Murray Water, and the University of Melbourne.

The project was instigated in part to help “road-test” Source Catchments, the first component of eWater’s landmark integrated water modelling suite, eWater Source, to be publicly released. A range of other water models is also being put to the test that combine rainfall-runoff, flow routing and hydraulic models, to explore the possible impact of various climatic conditions (based on historical and predicted events) in relation to rewetting off-channel habitats.

Ultimately the team expects to ensure better environmental outcomes without compromising consumptive needs and to improve operational management of environmental water reserves, whatever the prevailing climate.

Similar but different

The Ovens and Goulburn rivers contribute significantly to the water resources of the Murray-Darling Basin. The rivers have similar geomorphology, land use, and vegetation communities, yet the Ovens River is largely unregulated while the Goulburn is highly regulated. Both rivers have high environmental value and natural biodiversity. Irrigated and dryland agriculture are very important in both catchments, and contribute significantly to the Victorian and national economies.

Goulburn River. Photo Goulburn-Murray Water.Goulburn River. Photo Goulburn-Murray Water.In their natural state, both rivers’ off-channel floodplain wetlands, red gum forests, and other ecosystems were strongly influenced by seasonal flooding. Today the situation is very different: while the Ovens River still floods frequently, the Goulburn River, regulated by Eildon Dam, does not. This project is investigating the effects of changing land uses and climates on flow, and the way the combination of these processes and the management of environmental flows might affect river and floodplain ecology.

Four current eWater models have been tested in the Northern Application Project:

  •   Ecological Modeller;
  •   Eco Evidence (formerly Causal Criteria) Analysis to develop/evaluate ecological response models;
  •  Source Catchment models (formerly WaterCAST), on key Ovens and Goulburn River tributaries;
  •  Source Rivers Modelling, trial use on Goulburn River.

One output will be a hydrological model of the unregulated tributaries which feed into the Goulburn River between Lake Eildon and the Goulburn Weir.

The model is expected to provide:

  • a base model from which to develop an understanding of how landscape complexity and connection can improve our understanding and management of landscapes and water resources;
  • a base model from which to build and develop water flow and quality scenarios associated with fire in one of the tributaries;
  • inputs from the unregulated tributaries which could be fed into the Source Rivers model of the Goulburn River as required.

Identifying prioritiesOvens River. Photo James DominguezOvens River. Photo James Dominguez

There are a range of hypothetical outcomes which can be evaluated in the context of floodplain inundation. As a starting point, the Northeast CMA and Goulburn Broken CMAs are considering the response of floodplain vegetation to the delivery of water to floodplain wetlands. The four eWater models have been used to help demonstrate this hypothetical outcome.

Using Eco Evidence analysis the team has conducted an investigation to evaluate the relative strength of existing research before its incorporation into the conceptual model showing the benefits and dis-benefits of floodplain rewetting. The analysis shows there are numbers of research papers that confirm strong benefits to floodplain vegetation of inundation of floodplains.

Construction of a base Source Rivers model for the Goulburn River and tributaries – using another eWater tool: RiverManager - is now complete. Next the team will run a number of scenarios examining ways to utilise natural flood events, piggy-backing on the use of water within storages, to create a range of floods in the Goulburn River system. These will explore the effectiveness of techniques to enhance natural flow events to improve the frequency and extent of inundation without excessive flooding.

As a water quality and quantity model, Source Catchments is designed to help natural resource managers and consultants develop targets, prioritise improvement programs and measure the effectiveness of a broad range of catchment management activities.

Along the Goulburn River it is allowing creation of a management database identifying high priority areas for refuge management, based on the dynamics of groundwater-surface water interactions.

“One of the significant challenges faced in the management of water resources is balancing water use to maintain healthy water resources that support growing communities and a thriving economy now and into the future,” Tennant says. “Climate change and land use change impacts on these water resources represents an additional challenge in their management. By using a range of modelling tools the project contributes to our understanding and management of water resources in Victoria.

“This project is also an important first step in increasing our understanding of the importance of landscape connection and complexity in managing our water resources.”

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