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Reporting partially successful environmental watering events

Summary

Environmental outcomes are rarely binary. However, our traditional approach to reporting on environmental watering success is based on meeting all water requirements (magnitude, duration, timing, count) as a binary pass or fail. eFlow Projector allows the creation of continuous functions for scoring success so that partially meeting different components of a flow objective can be accounted for. The partial success functions allow performance close to the ideal performance to be given at least some partial credit in assessing the environmental watering performance.

5 min read

Author: Zach Marsh

Defining environmental water requirements

Environmental watering requirements are typically described as a combination of characteristics of the hydrologic regime (timing, magnitude, duration, independence, frequency, count). For example, to achieve spawning and movement requirements for a particular fish species, flow requirements through winter may require 50ML/day to allow adequate passage across riffles, that last for at least 4 days to allow the fish to traverse the river, find a mate, spawn, then to allow dispersal. We may ideally need two of these ‘events’ each year (separated by at least 2 weeks) for a successful water year. The environmental water requirement is:

Water requirement parameter	Value
Season	Winter
Magnitude	50 ML/day
Duration	4 days
Independence	14 days
Count	2 per year
Frequency	Annual

Across the Murray Darling Basin there are around 800 environmental water requirements like this to keep track of.

Traditional reporting is binary — either success or failure

For the fish spawning and movement example, how should we report when the duration of one of the events is 3 days instead of 4? Or if we got one event and not two? Or if the events were only 12 days apart and not 14 days? Or if everything was a success across both events, except the very last day of the second event was 49.5ML/day instead of 50ML/day? Or the second event finished in August not July?

The standard way of reporting environmental watering success is binary – either success or failure. So, for each of these cases when any part of the flow requirement is not fully met, then the environmental watering requirement has not been met, and we report a failure to meet the environmental watering requirement.

However, from a biological perspective, there has been value to the fish in all the above cases. Our knowledge of the requirements to achieve an environmental outcome are not precise and the specification of absolute criteria is somewhat arbitrary. This approach works well in quantifying water requirements for water planning. However, it is too restrictive in reporting performance in a biologically meaningful way.

eFlow Projector reports a range that allows partial success to be considered

Truii has created eFlow Projector that allows partial success of watering events to be considered.

Environmental outcomes are rarely binary. The eFlow Projector tool allows the creation of continuous functions for scoring progress towards meeting a flow objective. The partial success functions allow performance close to the performance target to be given at least some partial credit in assessing the environmental watering performance. The partial success functions in eFlow Projector can also be set to the traditional ‘binary’ approach to allow comparison with traditional reporting approaches.

Further to reporting the overall partial success, eFlow Projector reports partial success across each of the hydrological parameters so that it is clear if the failure to meet watering objectives is due to magnitude, duration, independence or count. More details on how the partial success approach works can be found in a paper presented at the 10th Australian Stream Management conference.