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Functional flows: A practical strategy for healthy rivers Stewart Rood University of Lethbridge. Fundamental principle: river ecosystems require instream flow. Trees. Trout. Science: Instream Flow Needs – Flow amount and pattern required to sustain an organism
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Functional flows: A practical strategy for healthy rivers Stewart Rood University of Lethbridge
Fundamental principle: river ecosystems require instream flow Trees Trout
Science: Instream Flow Needs – Flow amount and pattern required to sustain an organism Environmental Flow Needs – Flows to sustain the aquatic and riparian ecosystems AbEnv-IFN group: 85% of natural flow Management: Old: Minimum Flow for survival Instream Objective – Flow target for human use & the environment New (2006): Water Conservation Objective (WCO) = Instream Objective + 10%; or 45% of natural flow
Tennant (Montana) method Oldman River – pre-Dam good poor 85% 60% 45%
another empirical approach St. Mary ‘the proper way to do toast … … wait ‘til it burns, then 5 seconds less’ (Ogden Nash?)
conservation vs. restoration decline recovery but … hysteresis condition discharge
Riparian Ecosystem Aquatic Ecosystem Hydrograph components for: 1. Channel Formation 2. Riparian (Streamside) Community 3. Aquatic (Instream) Community 4. Water Quality
Scaled to the Bow River at Banff 1. High flows for Channel development 2. Riparian Post-flood ramping for cottonwood recruitment Discharge = Flow Rate (m3/s) 3. Aquatic Sufficient flow for T & O2 O2 under ice 4. Water Quality Winter Spring Summer Autumn
BioScience 1997 … yes, but it’s not feasible to restore natural flow regimes …
Functional Flows High flow functions occur in high flow years The Paradox of Water Management Demand is high when supply is low Wet 1/4 Normal 2/4 Dry 1/4 High flows for Channel development Riparian Post-flood ramping for cottonwood recruitment Discharge = Flow Rate (m3/s)
A management opportunity: Storage is proportionally greater in low flow years Dry 1/4 Uniform reduction to 45% = system stress Functional Flow = flow when most needed Riparian Survival Discharge = Flow Rate (m3/s) Aquatic Sufficient flow for T & O2 O2 under ice Water Quality
Oldman River near Monarch July 1988 – pre-Oldman Dam Insufficient flow = degraded system
Oldman River Dam Project 1991 increased minimum flows 1993 flow ramping 1995 flood People cared
350 300 Recruitment Box 250 survivable stage decline (2.5 cm / day) 200 River stage above base (cm) 150 potential recruitment band 100 50 seed release 0 MAY JUN JUL AUG SEP Month
S. Sask. Oldman 1995
Science: Instream Flow Needs – Flow to sustain an organism Environmental Flow Needs – Flows to sustain aquatic and riparian ecosystems - The Natural Flow Regime AbEnv-IFN group: 85% of natural flow Management: Water Conservation Objective (WCO) 45% of natural flow Functional Flows 1. Deliberately non-natural pattern 2. Support aquatic and riparian populations 3. Environmental benefit during wet years to compensate for Environmental stress during dry years
Decrepit population 1988 Rejuvenating the Oldman 2008 Healthy population
Functional flows: A practical strategy for healthy rivers Stewart Rood University of Lethbridge