01_Flow_Scenarios

Ecological Flows Science Advisory Board
June 21, 2011

Chris Goudreau, N.C. Wildlife Resources Commission
Instream Flow Status (pp 84-86 of IFC book)
No Protection
No legal ability to keep from drying up the stream
Rare in N.C., but there are examples
Threshold Protection (i.e., minimum flow)
May be a single value (e.g., 7Q10) or
have seasonal value (e.g., 20/30/40 percent of MAF)
Instream Flow Status (pp 84-86 of IFC book)
Partial Ecologically-Based Protection
Addresses 1-4 riverine components
Most likely hydrology, biology and 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
Statistically-based Standard
Typically partial protection, but could be comprehensive
Percent of Flow Standard
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
Spawning
Floodplain rejuvenation
Fry/juvenile growth
Migration
Sediment movement
Channel maintenance
Flow Components
Example – Trinity River
Example – Cheoah River
Example – Cheoah River
Table 2. High Flow Events – 5-year Repeating Schedule.
High Flows
Year 1

Year 2

Year 3

Year 4

Year 5

Magnitude
(cfs)3
Events
Total
Days
Per
Month
Events
Total
Days
Per
Month
Events
Total
Days
Per
Month
Events
Total
Days
Per
Month
Events
Total
Days
Per
Month
Day 1 Day 2 Day 3
January
February 1 2 1 2 1 2 1 2 1 2 1000 Var1
March 1 3 1 3 1 3 1 3 1 3 1000 6002 300
April 2 5 3 6 2 5 2 5 3 6 1000 850 300
May 2 4 2 4 3 6 3 6 3 6 1000 850
June 1 2 1 2 1 2 1000 850
July 1 2 1000 850
August 1 1 1000
September 1 1 1 1 1000
October 1 1 1 1 1 1 1000
November 1 1 1 1 1 1 1 1 1 1 1000
December
Total Per
Year:
10 19 10 19 10 20 10 19 10 20
1 600 cfs from hour 15 to hour 19, 400 cfs from hour 20 to hour 34; 200 cfs from hour 35 to hour 47; 100 cfs for hour 48 2 600 cfs from hour 16 to hour 36; 300 cfs from hour 37 to hour 48
3 12:00 a.m. (midnight) shall be the starting point for determining the appropriate time for initiating and changing flow releases

Flow Regime Tied to Ecology
Base Flows Subsistence Flows Overbank Flows High Flow Pulses
Conserve biological function
Conserve biological diversity,
habitat diversity and
water quality
Provide for life history and
geomorphic processes Maintain floodplain
Moisture and nutrients
to floodplain
Riparian recruitment
Water quality tolerances
Key habitat thresholds
Flow-dependent
species habitat
Bank storage/moisture
Suitable temperatures &
dissolved oxygen
Fish spawning cues
Maintain channel
Sediment/nutrient transport
Sound Ecological Environment
Percent of Flow Standard
Remove X% of water flowing by for a given time step
X generally 6 – 20% (Richter et al. 2011)
Alberta just releasing a standard of 15%
Time step can be daily, weekly, etc.
X can differ by season