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| Environmental Flow Assessments Holistic Environmental Flow Assessments
The Process
Bringing it all Together
Environmental Flow Assessment Reports
Further Information
Throughout Australia, environmental flow assessments are used to estimate the quantity and timing of flows required to sustain identified aquatic values in riverine environments. Typically, water management planning and other natural resource planning processes use environmental flow assessments to make informed decisions about water management.
There is no single standardised method for estimating environmental flows in Australia or in other countries. Rather, there are many methods available, which are usually tailored to meet the specific requirements of each assessment. Environmental flow assessments have been undertaken for a number of Tasmanian rivers and streams, using the most appropriate methods available at the time. Previously, these assessments have focused largely on minimum flow requirements for instream fauna (such as fish and invertebrates). However, new methodologies that incorporate natural variability in stream flow, and the high flow water requirements of entire riverine ecosystems, are now being used by DPIPWE to develop environmental flows for catchments.
Environmental flows are descriptions of the flow regime that maintain the ecosystem values at a low level of risk. In Tasmania, environmental flow assessments often focus on several ecosystem values including instream fauna (e.g. fish, platypus and invertebrates; especially threatened or unique species), instream plants, riparian plants and geomorphic features of the river channel.
The overall objective of environmental flow recommendations is to ensure that sufficient water is made available to support the needs of the entire riverine ecosystem. Recently, DPIPWE developed the Tasmanian Environmental Flows Framework (TEFF), which reflects the growing understanding in the scientific community that riverine ecosystems are more than just channels and instream biota. They are comprised of a range of components, such as riparian vegetation, floodplain wetlands, geomorphological features and estuaries, which depend on a range of flow components that are present in a natural flow regime. By incorporating a range of natural flow events, it is likely that environmental flow provisions will also support lesser-known ecosystem processes, such as seasonal triggers for fish spawning and the transport nutrients to estuaries.
Currently, DPIPWE is conducting a research project, the Tasmanian Environmental Flows Project (TEFlows project) which aims to test and refine the new framework (the TEFF) by investigating the influence of variability in flow on the physical and biological structure of freshwater-dependent ecosystems. It will build on the known flow requirements of freshwater-dependent biota and processes, and will contribute to the development of appropriate indicators to measure the effectiveness of implemented environmental flows.
The TEFlows Project is being conducted by the Water Assessment Branch (Water Resources Division, DPIPWE) for NRM South and NRM North, and is funded under the National Action Plan for Salinity and Water Quality. The Project commenced in July 2006 and will be completed in June 2009.
■ TEFlows Project
 Tasmanian catchments that require environmental flow assessments are prioritised using information on current water use, river and estuarine health indicators, and water management planning activities. For each assessment, DPIPWE identifies water demand at different times of the year and uses the most appropriate environmental flow assessment method on a case by case basis. Generally, a desktop approach is used to determine environmental flows in smaller systems where water use is minimal, and more detailed field-based methods are employed in catchments where there is a high demand for water.
The new methodology developed by DPIPWE (TEFF) outlines the methods that are used in catchments with high water demand. Broadly, the TEFF aims to link the biological components and physical heterogeneity present within a river to specific flow events, and to link these flow events to specific environmental flow objectives. The process involves four main steps:
- Identify freshwater ecosystem values in each catchment in order to define the objectives of the environmental flow assessment. Develop conceptual models that identify the ecosystem processes that support these values.
- Identify representative river reaches, conduct assessments using hydraulic and hydrological models to characterise physical habitat and biological diversity of the system, and identify specific flow events that relate to these attributes.
- Conduct hydrological analyses of flow data to define the pattern of occurrence of important flow events and the availability of important habitats for fauna.
- Recommend a flow regime that meets the objectives of the environmental flow assessment, including rules for water abstraction.
 Ecosystem values in each catchment are derived from an assessment of the freshwater-dependent ecosystems defined within the Conservation of Freshwater Ecosystem Values (CFEV) database. All major freshwater-dependent ecosystems are included in the CFEV database: rivers, waterbodies, wetlands, saltmarshes, karst and estuaries.
The CFEV database provides conservation management priorities for individual freshwater-dependent ecosystems based on their current condition, representativeness and distinctiveness in comparison to other similar ecosystems in Tasmania. Because of this robust, landscape-scale approach, CFEV objectively identifies areas of conservation significance and high freshwater-dependent ‘value’ within a catchment. Conceptual models are then developed to illustrate the dependence of the identified ecosystem values on the movement of water through the landscape. These models help define the elements of the ecosystem and the flow regime which should be targeted in the environmental flow assessment.
Link to CFEV site
Once the objectives of the environmental flows have been identified, the hydrology of the catchment is characterised using hydrological models. This is done in order to assess the degree to which the current flow regime has been altered from that of the ‘natural’ (modelled pre-abstraction) flow regime, and allow risk to the various ecosystem values to be identified. Field sites are then selected for assessments to determine the flow events required to meet the environmental flow objectives.
Sites used in the assessment are representative of river reaches in the catchment (e.g. headwaters, lowland reaches, etc.) and, thus, incorporate the range of habitats (such as pools and riffles) and hydraulic conditions found throughout the river. In catchments where water use is high, sites must also occur in locations that are relevant to water management. Site assessments involve surveying the physical structure and heterogeneity of reaches, and constructing hydraulic models to determine the specific flow magnitudes associated with a range of physical features.
Site assessments enable the magnitude of flow events that influence the physical heterogeneity of the river to be determined (such as flows at which over-bank flooding occurs). Once the magnitudes of particular flow events have been determined, the frequency, duration, timing and rate of change of these events are determined. Additionally, the flow conditions that provide important habitats for fauna are also identified. Based on these analyses, monthly minimum flows and high flow thresholds that maintain healthy physical habitats and suitable instream habitat conditions for faunal assemblages are derived.
The final step in the TEFF is to combine the important flow events that were identified in the previous steps into a flow regime to meet the objectives of the assessment. Environmental flow regimes typically comprise:- Large-scale flow events, which in many systems will be essentially natural
- Small- and intermediate-scale flow events which will be explicitly linked to the habitat and life history requirements of the system’s biota, the physical heterogeneity of the system, and retain characteristics of the natural flow regime as much as possible
- Minimum flows (depending on season) to maintain hydrological connectivity during periods of high water abstraction
These events are defined by their hydrological parameters (i.e. magnitude, frequency, duration, timing and rate of change) and are combined to describe the recommended environmental flow regime.
Environmental flow assessments essentially describe the importance of different flows to the aquatic values of riverine systems. It is critical when interpreting environmental flow assessments that they are considered in the context of the community’s environmental, economic and social objectives for the river(s) being examined. Thus, assessments provide an essential input into DPIPWE’s water management planning process; however, all water users within a catchment are considered by DPIPWE during the development of water management plans. During this process, environmental water requirements are negotiated and implemented as environmental water provisions, which aim to balance economic, social and environmental values within catchments.
DPIPWE has undertaken several environmental flow assessments. Reports detailing these assessments can be found here:
■ Environmental Flow Assessment Reports
■ Conservation of Fresh Water Ecosystem Values Program (CFEV)
■ TEFlows Project
■ Water for Ecosystems Policy
■ Water Management Plans
Contact: EcohydrologyBryce Graham
Section Head (Ecohydrology)
Water Assessment Branch
13 St Johns Avenue
NEW TOWN TAS 7008
Phone: 03 62335308
Fax: 03 62336881
Email: Bryce.Graham@dpipwe.tas.gov.au
DPIPWE switchboard: 1300 368 550 (local call cost within Australia)
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