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Species specific water requirements

Flow assessment

Generalised and process models

Spell Analysis

About Spell Analysis

Spell analysis allows the identification of events in hydrological data where certain criteria are met. These events may need to be identified for many reasons, including:

  • Species specific watering requirements (flow above a threshold for a certain period of time)
  • Checking compliance with water release restrictions

Model purpose

The purpose of the model is to identify events within time series data and report a range of summary statistics based on these events. Although commonly used on daily flow data, this model can be used on any time series data loaded into Eco Risk Projector. The model reports a range of summary statistics:

  • Count
  • Mean magnitude of peaks
  • Total duration
  • Mean duration
  • Max duration
  • Total duration between spells
  • Mean duration between spells
  • Max duration between spells

For each season present in the data (The season is defined by the input parameters).

The modal also provided a list of all the identified events, along with an overall summary of these events containing the following statistics:

  • Threshold
  • Total duration
  • Mean duration
  • Max duration
  • Mean duration between spells
  • Max duration between spells

Development context

This model has been developed based on the expertise of industry experts.

It was developed as a general tool to support the Queensland Department of Environment and Resource Management.

Spatial application

This model is applicable to any location where spells are being assessed independently across locations.

Model description

Ecohydrological rules

This model analyses the data to find events which fit the provided parameters. This means the event must occur within the specified season, meet the specified flow requirements (above, below, range), meet the minimum and maximum length requirements and finally have sufficient independence from all other events. These events are then used to calculate the summary statistics.

Assessment method

Assessment is based on one of the summary statistics (continuous annual value). The summary statistic to be used for assessment is selected via the “Assessment Metric” parameter. 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.


  • Daily time series data. This can be any type (flow, depth, rainfall, evaporation, etc.) provided it is at the daily or sub-daily time step.
Parameter Sections
  • Data – define the data type to run analysis on. All time series data types are valid options.
  • Season – define the season to split data into. Specify the start date and end date,
  • Event – define the parameters which determine a spell event. Includes the spell type (above threshold, below threshold, range), the threshold (either a set value or the ARI value), the minimum independence between events, the minimum spell length (optional) and the maximum spell length (optional)


  • Daily time series of spell occurrences
  • Yearly time series of summary statistics for the given season (As defined in the parameters)
  • Event list of all identified events
  • Summary results for all events across the analysis period
  • 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.


Cockayne B, McGregor G, Marshall J, Lobegeiger J, and Menke N 2010, ‘Fitzroy Water Resource Plan review technical report 3: ecological risk assessment’, Department of Environment and Resource Management, Queensland Government, Brisbane.