Approaches_to_Flow_Recommendations_(Goudreau)

Ecological Flow Science Advisory Board
August 20, 2013

Chris Goudreau, N.C. Wildlife Resources Commission
Levels of Protection (pp 84-86 of IFC book)
No Protection
Threshold Protection
Partial Ecologically-Based Protection
Addresses 1-4 riverine components (hydrology, biology, water quality)
May address intra-annual variability, but not inter-annual
Comprehensive Ecologically-Based Protection
Addresses all 5 riverine components (hydrology, biology, water quality,
connectivity, geomorphology)
Maintains intra-annual and inter-annual variability
Full Protection (hands off)
General Approaches (Richter et al. 2011)
Minimum Flow Threshold
May be a single value (e.g., 7Q10) or
be seasonally adjusted (e.g., Tennant, South Carolina)
Statistically-based Standard
More on following slide
Percent of Flow Standard
Example - Alberta
Statistically-Based Standard
Flow components include:
Critical low, low, high flow pulses, small floods, high floods
Wet, normal, dry years
For each, includes magnitude, duration, frequency,
season
Tied to ecologically significant events
E.g., spawning, floodplain rejuvenation, fry/juvenile
growth, migration, sediment movement, channel
maintenance
Approaches of Proposals
Proposal Threshold Stat-Based POF Other
Modified SC 20/30/40 MMF
30/40/50 MMF
NC 80% Flow-by (daily)
Alberta 20%-tile EBF
(monthly)
85% Flow-by (daily)
TNC ~10%-tile pass-by
(monthly)
? 90% Flow-by (monthly)
95% Flow-by (monthly)
Headwater cutoff;
Wet/dry year values
Ad-Hoc

Regression of
ecodeficit with fish
diversity or EPT
richness
Examples of Applying Proposals
Simplified examples – DWR model takes into account
more realistic model constraints
Comparing POF and Minimum Threshold
Mean annual flow = 130 cfs
Assumes constant withdrawal of 10 cfs (6.4 mgd)
If not enough water to meet eco-flow, withdrawal is
reduced
Outflow is always between inflow and 80% flowby
Not enough water for withdrawal
Outflows lower than POF
Not enough water for withdrawal
Application of Proposals
Proposal Headwater Wadeable Large River Coastal
Non-Tidal
Coastal
Tidal
Modified SC    
NC    
Alberta    
TNC No
withdrawal
 ? ?
Ad-Hoc   ? ?