Types of environmental watering requirements

Patterns in defining environmental watering requirements

Environmental watering requirements are developed on a catchment-by-catchment basis by considering the specific water needs of individual environmental assets. These water requirements for individual assets are then combined to produce higher-level requirements that often provide benefits across multiple environmental assets. These higher-level water requirements are typically composed to allow the requirements to be operationalized within the constraints of a water supply scheme. These water requirements are called different things depending on the water regulation jurisdiction. In our world, we work across all jurisdictions so we simply call them ‘flow rules’.

There are thousands of individual flow rules developed for sites across Australia. To develop reporting systems, we need to categorise these into ‘flow rule’ types. In developing the eFlow Projector application, we had to come up with a taxonomy to capture rules with similar approaches and to structure a flow rule parameterisation that captures common features across rule types.

A taxonomy for flow rules

eFlow Projector has four main flow rule types that are used to capture the range of parameter configurations summarised below.

Reporting location

• A single location (usually a stream gauge) is used for assessing flow rule performance.
• One (or more) locations are often used for environmental flow release compliance assessment. This enables reporting on the contribution of water releases towards meeting a flow rule.
• Multiple additional locations can be used for more complex assessment such as when the flow requirement at a reporting location is contingent on the flow at some other location.

Analysis period

• Annual: most flow rules consider a single water year in isolation for assessment, generating a yearly result for success across rule components.
• Multi-year: flow rules that report on larger, less frequent events are often assessed across multiple years. These rules will require a certain number of events to occur n years, with the time between events to not exceed a certain duration. For example, a wetland should fill 3 times in ten years with the gap between filling events to not exceed 4 years.

Prevailing climate

Flow rules are developed to avoid local extinction during dry periods and to promote reproductive opportunity when times are good. Flow rules will often have variable parameters depending on the prevailing climate. The prevailing climate is typically defined at the commencement of the water year (although not always).

Event Type

• Freshes: these flow rules require multiple flow events over a threshold for a given number of days, with a minimum independence between events and a certain event count, during a specified season.
• Multi-year Freshes: these flow rules extend on freshes for longer term events, where an event doesn’t need to occur yearly and is instead required every n years, with a maximum time between events.
• Low flow: these flow rules require the total time over a threshold for a given season.
• Oversupply: these flow rules require the total time under a threshold for a given season.

Variable Success

For each of the parameters used to define freshes, multi-year freshes, low flow and oversupply rules, there is rarely a single absolute value that is meaningful. Rather, there is a continuum from acceptable to ideal conditions. We capture these ranges of suitability as continuous functions and quantify them across timing (season), magnitude, duration, count and independence. This allows reporting where the ideal condition is not met, but some benefit was still provided. For further information on partial success, see this story.

Importance

Not all flow rules are equally important, nor do they always require reporting. In this case eFlow Projector includes four reporting tiers to allow subsequent filtering to focus on just the high priority rules or all flow rules.