Trial Balloon - Alberta method

Trial Balloon – 85% Flow-by with 20th Percentile Baseflow
General Description
This method is that used by the Government of Alberta for planning and as a default desktop method
for setting flow regimes without site-specific studies (Locke and Paul 2011). It is similar to the
environmental flow policy of Canada’s Department of Fisheries and Oceans (DFO 2013). Both are based
on the presumptive standard approach (Richter et al. 2012) and the percentage of flow with sustainable
boundary approach (Richter 2009). The Alberta and DFO methods are supported by field studies in
Canada, the US and elsewhere.
This simplified approach requires only hydrologic data. The flow recommendation consists of two parts
– a percentage of flow (POF) component and an ecosystem base flow (EBF) component. The POF
component is set at 85% of the daily natural flow (i.e., a 15% reduction from natural flow). The EBF
component is set as the 20th-percentile flow on a monthly time step. The attached graphs illustrate how
the two components are combined to set an ecological flow.
How this trial balloon helps the EFSAB to advise DENR in characterizing the aquatic ecology of different
river basins
This trial balloon does not address this aspect of the statutory charge, nor have any other trial balloons
presented to the EFSAB to date. The direct connection between characterizing basin ecology and
developing flow recommendations is not called for in the statute. Characterizing the aquatic ecology of
different river basins can be done separately from determining the flow recommendation framework.
See separate handout for more detail.
How this trial balloon helps the EFSAB to advise DENR in identifying the flows necessary to maintain
ecological integrity
The POF component generally retains the natural shape of the hydrograph, including all five
components of flow (magnitude, frequency, duration, timing and rate of change). The EBF component
protects aquatic systems during periods of low flows by reducing the duration that low flows would exist
just using the POB component.
The POF component is to be calculated on a cumulative basis at any point in a river basin. Due to the
language of the NC statute, the baseline would be the current condition, not the natural (unaltered)
flow. However, both baselines should be run to understand the degree to which the current condition is
already changed from the natural condition.
Limitations of this trial balloon and options for how to address those limitations
In order for this flow approach to work in a planning context with the basin models, decision criteria
must be developed to determine the timing (seasonality), frequency, and duration that water is
inadequate to meet: 1) yield for all needs; 2) yield for essential uses; and 3) ecological flows. There are
basically two ways to do this – develop timing, frequency and duration criteria for ecological flows, or
develop such criteria for water needs/uses.
The first approach would be done in the model by giving water use priority over ecological flows and
tabulating the timing, frequency and duration that the ecological flow standard is not met. While
appealing, this assumes that the EFSAB or DENR can determine the timing, frequency and duration
criteria that are protective of ecological integrity. Due to the varying nature of ecological conditions
throughout the state, this would be a difficult task. However, one could use statistical metrics from the
natural hydrology to determine frequencies and durations of events (by season) that are outside of the
norm.
The second approach would be done by giving ecological flows priority over water use in the model, and
tabulating the timing frequency and duration that water needs/uses are not met. It is understood that
this is actually the approach that is used in OASIS. If so, it will be up to DENR to determine if those
violations are unacceptable.
However, as a planning tool it really isn’t necessary to develop “acceptable violation” criteria for either
approach. If the model is run as understood in the second approach, DENR just needs to know that
there isn’t adequate water at a particular node, at a certain time, with a certain frequency and duration.
It will be up to DENR to work with appropriate parties to determine possible planning-level solutions to
situations where there is inadequate water to meet all needs.
References
DFO. 2013. Framework for Assessing the Ecological Flow Requirements to Support Fisheries in Canada.
DFO Canada Science Advisory Section, Science Advisory Report 2013/017.
Locke, A., and A. Paul. 2011. A Desk-top Method for Establishing Environmental Flows in Alberta Rivers
and Streams. Alberta Environment and Alberta Sustainable Resource Development, Edmonton.
Richter, B.D. 2009. Re-thinking environmental flows: from allocations and reserves to sustainability
boundaries. Rivers Research and Applications 25: 1–12.
Richter, B.D., M.M. Davis, C. Apse, and C. Konrad. 2012. A Presumptive Standard for Environmental
Flow Protection. River Research and Applications 28: 1312–1321.