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.
The eight indicators of the Index of Flow Deviation