Flow Health Hydrology Assessment Tool

Flow Health is an application to assist in the assessment, design and management of river flow regimes. Its main purpose is to provide a score for hydrology in river health assessments, but it can also be used as a tool to assist environmental flow assessment. The tool was developed by Fluvial Systems and Yorb as part of the River Health and Environmental Flow in China Project and is available for free.

Flow Health has three main functions:

  1. To provide the hydrology indicator in river health assessment: Flow Health analyses time series of flow data based on a comparison with a reference condition (i.e. pre-regulation flow time series, or modelled unregulated flow) to derive scores for 8 pre-defined indicators of flow deviation. A score of 1 is close to reference and a score of 0 is distant from reference. The indicator scores are aggregated to form an overall Flow Health score for each year of record.
  2. To recommend a low risk minimum monthly environmental flow regime: Flow Health automatically produces the minimum monthly flow regime that has a Flow Health score of 1. Users can also produce a regime with a lower score.
  3. To test the hydrological health of any monthly flow regime for environmental flow assessment: Flow Health can be used interactively to design a monthly flow regime, with continuous updating of Flow Health indicator and overall scores. Any monthly flow regime can be tested.

Science behind flow health

The Flow Health hydrology assessment tool uses the Index of Flow Deviation (IFD) to assess the hydrological health of a river health. The IFD relies on a suite of eight indicators, shown in the graphs below. These represent different aspects of flow regime that are recognised as being of universal importance for river health – periods of cease-to-flow, base flows during low- and high-flow periods, high flows, and the timing or seasonality of flows.

For each parameter, a score from 0 to 1 was calculated for a given year, based on the degree of deviation beyond a range of natural variability, derived from a reference period. An indicator was given a score of 1 where the value fell within the 25th and 75th percentile range of the reference distribution. The method uses monthly flow data, and is relatively easy to calculate for any river with adequate flow data.

A detailed report describing the method is available here.

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