Lowflow – variable success
About Lowflow
Lowflows (or baseflows) provide a continuous stable, sustained low level flow in a river. The flow may be limited to a narrow area of the river channel but is important as it connects habitats within the channel and supports plants and animals that only live in water. Low flows also keep the river bed and lower banks wet helping to maintain native plants and trees that live beside waterways.
Water requirements
This model captures the total duration that a flow requirement is met during a specifed period of the year (typically, Autumn-winter, summer-spring).
Model purpose
The purpose of the model is to represent the most common way that low flows are prescribed. The model extends this traditional prescription to also allow the consideration of the prevailing climate as well as the representation of partial success.
Development context
This model was developed initially in the eFlow Projector application (Marsh et. al. 2021) to support performance reporting by the Victorian Environmental Water Holder.
Spatial application
This model can be applied anywhere that low flow requirements can be described in terms of magnitude, duration and timing.
Model description
Ecohydrological rules
The flow time series is analysed to identify all event opportunities within the prescribed sub-period of the year (typically, Autumn-winter, summer-spring), where the flow is above the specified threshold. The best set of event opportunities is combined to provide an overall magnitude and duration score for the period. The output is an overall performance (0 to 100%) for each water year of the record.
Assessment method
A continuous yearly value is determined by combining all scores (magnitude and duration) into a summary score. These results are then aggregated to a binary yearly result, then to a temporal result based on the defined assessment parameters.
The temporal results are then analysed across locations to report an overall landscape risk by considering the simultaneous occurrence of failures across the system.
Inputs
Data
- Daily flow data
Parameter Sections
- Data – parameters to describe the variable season. This includes the start month (to determine the year) and the success % of each month. A binary season can be achieved by using only 0 and 100% season scores.
- Rules – the rules for each possible climate type. This included a magnitude (flow threshold) and duration (% of season) target.
- Partial tables – the tables to define how partially achieving the rules can still carry some level of success. This includes a table for both magnitude and duration.
Outputs
- Yearly time series of performance, including the magnitude, duration, compliance and summary scores
- Events file containing all events identified, including start date, end date and duration.
- Yearly time series of assessment results
- Temporal time series of assessment results
- Spatial time series of assessment results
User interface
Underlying code
This plugin is written in Python and its underlying code is publicly available from the Eco Risk Projector computation repository.
References
Marsh, N., Marsh, Z., Stacey, M., and Toomey, M. (2021) Eflow Projector: Assessing th Perfomance of environmental watering, Proceedings of the 10th Australian Stream Management Conference 2020, Kingscliff, NSW
Source: Victorian Environmental Water Holder. https://www.vewh.vic.gov.au/news-and-publications/stories/understanding-flows-some-terminology-explained 
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