Transcript Technical Review of Chatfield Reservoir Control Regulation

Evaluation of Load Translator
for Chatfield Reservoir
Jim Saunders
WQCD Standards Unit
14 February 2008
Roadmap for Technical Review
Month
Topic
Sep-07 Technical comparison of existing control regulations
Oct-07
Existing chlorophyll target, incl magnitude, frequency, duration
Nov-07 Evaluation and discussion of concentration translator
Dec-07 Water budget and appropriate concentrations for each flow source
as precursor to common set of phosphorus loads
Jan-08
Phosphorus load estimates; produce common set by source
Feb-08 Evaluation and discussion of load translator
Mar-08 Hydrologic considerations for TMAL
Apr-08
Discuss chlorophyll-phosphorus-load linkages as basis for proposal
Jun-08
WQCD to finalize proposal and circulate
Jul-08
Notice due
Nov-08 WQCC RMH
For Today….
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What is a load translator?
The data set
Review history of load translator
Evaluate performance of load
translator(s)
Discuss approach and path forward
What is a Load Translator?
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Quantitative linkage between
phosphorus load to the reservoir
and the resulting phosphorus
concentration in the reservoir
A necessary component for:


Establishing the load consistent with a
chlorophyll (or TP) standard
Predicting the response (chlorophyll)
for future P load scenarios
Data Needs
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Phosphorus concentrations in lake
Phosphorus loads
Hydraulic data (volume, area,
computed inflow, outflow)
Phosphorus export
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Flow * concentration in release
Must include manifold, too
Assume concentrations same in
manifold and release to SP
Phosphorus in Outflow
Outflow Total Phosphorus, mg/L
1.000
0.100
0.010
0.001
Jan-87
Sep-89
Jun-92
Mar-95
Dec-97
Sep-00
Jun-03
Mar-06
Outflow P: Expectations and Concerns
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Large volume of reservoir buffers
outflow P concentration
MDL issues (esp. 2002)
Are there patterns in concentration?
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Over years
Between seasons
Annual Distributions
Total Phosphorus, mg/L
1
0.1
0.01
0.001
1987 1989 1991 1993 1995 1997 1999 2001 2003 2005
Seasonal Differences
Lake Bottom Phosphorus, mg/L
1
0.1
0.01
0.001
1-Jan
20-Feb
10-Apr
30-May
19-Jul
7-Sep
27-Oct
Ordinal Day
1987-1991
1992-1996
1997-2001
2002-2006
16-Dec
Aggregating Data
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Sampling program: ~13 samples/y
How best to assign concentrations to all
flows?
Can’t aggregate across years
Aggregate within seasons (just in case)
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Oct-Mar
Apr-Sep (stratification season)
Assume constant concentration (median) within
each season in each year
Seasonal Load = Seasonal median*Σ(flows)
Phosphorus Balance
50000
45000
Phosphorus, lbs/y
40000
35000
30000
25000
20000
15000
10000
5000
0
1988
1990
1992
1994
1996
Retained
1998
2000
Export
2002
2004
2006
Previous Load Translator
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Clean Lakes Study used a mass
balance model (Vollenweider)
Modified a component so prediction
would match the datum from 1982
No subsequent changes
Now have ample data for review
Vollenweider Model
L
TP 
z    
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TP, phosphorus concentration in lake (mg/m3)
L, external phosphorus load (mg/m2/y)
Z, mean depth (m)
σ, phosphorus sedimentation coefficient (y-1)
ρ, reservoir flushing rate (inflow/volume; y-1)
All terms known for historical data except σ
Estimating P Retention Coefficient
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Canfield-Bachmann
Artificial lakes
To match 1982 data,
multiply σ by 3.6
Yields modified
Canfield-Bachmann
 L
  0.114 
z
0.589
 L
  0.410 
z
0.589
S ig m a fro m Ob served E xp ort
Derive “new” C-B from data?
60
50
40
1.0249
y = 0.0284x
2
R = 0.5963
30
20
10
0
0
200
400
600
R atio of E xternal Load to Mean D epth
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Plot σ vs. L/z; No real pattern
Influential extreme flows
800
Does it Predict Well?
0.050
Observed Export TP, mg/L
0.045
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.000
0.000
0.010
0.020
0.030
0.040
0.050
Predicted TP, mg/L
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Use constant σ=6 (NB: differs from text)
Note 5 yrs at right (’88, ’95, ’98, ’99, ’05)
Try Another Model: Dillon-Rigler
L(1  R)
TP 
z
( Load  Export )
R
Load
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Commonly used
for reservoirs
Retention is
fraction of load
Median R=0.64
P Retention (and Extreme Flows)
45000
Retained P, lbs/y
40000
y = 0.7147x
35000
2
R = 0.9594
30000
25000
20000
15000
10000
5000
0
0
10000
20000
30000
40000
External P Load, lbs/y
50000
60000
Can We Predict R?
0.9
0.8
Observed R
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.0
0.2
0.4
0.6
0.8
OECD R
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Not encouraging based on common approach
(OECD for shallow lakes)
Probably better to use a constant
Performance of Dillon-Rigler?
0.040
Observed Export TP, mg/L
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.000
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
Predicted TP, mg/L
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Use constant R=0.64 (median)
Alignment OK, but precision not so good
Alternate View of Precision
Summer Median Total Phosphorus, mg/L
0.070
0.060
0.050
0.040
0.030
0.020
0.010
0.000
1988
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1990
1992
1994
1996
1998
2000
2002
2004
2006
Compare predictions of summer median P (bootstrap)
Five peculiar years predict very high
1996 predicts low
Is Load Translator Ready to Use?
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Would prefer it to be stronger
Plan to continue exploring options
Especially interested in 5 odd years
Consider two main tributaries from
hydrologic perspective
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Flows largely uncorrelated
SP always the dominant flow
Loads closer to being equal due to
higher concentrations in Plum Creek
Plum Creek and the “Odd” Years
0.8
2002
0.7
Residence Time, y
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1000
10000
100000
1000000
Flow, AF/y
Total Inflow
Waterton
Plum
Full Pool
Thinking Out Loud…
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High flow years for Plum Cr
(>20,000 AF) stand out: overpredict phosphorus
What’s different about Plum Cr load?
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Normal stream that carries particulates
at high flow
Contrast with SP that has been decanted
through series of reservoirs
Can the retention be partitioned?
Next Steps
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Refine load translator
Flows and TMAL
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What scenario for inflows?
Is 261,000 AF scenario appropriate?
 TMAL not exceeded even in 1995 (336K AF)
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Does worst case for in-lake concentration
represent highest load scenario?
Next meeting Mar 13: Hydrologic
considerations for TMAL