evaluation of load translator for chatfield reservoir jim saunders wqcd standards unit 14 february...
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Evaluation of Load Translator for Chatfield Reservoir
Jim SaundersWQCD Standards Unit14 February 2008
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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
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For Today….
What is a load translator? The data set Review history of load translator Evaluate performance of load
translator(s) Discuss approach and path forward
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What is a Load Translator?
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
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Data Needs
Phosphorus concentrations in lake Phosphorus loads Hydraulic data (volume, area,
computed inflow, outflow) Phosphorus export
Flow * concentration in release Must include manifold, too Assume concentrations same in
manifold and release to SP
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Phosphorus in Outflow
0.001
0.010
0.100
1.000
Jan-87 Sep-89 Jun-92 Mar-95 Dec-97 Sep-00 Jun-03 Mar-06
Ou
tflo
w T
ota
l P
ho
sph
oru
s, m
g/L
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Outflow P: Expectations and Concerns
Large volume of reservoir buffers outflow P concentration
MDL issues (esp. 2002) Are there patterns in concentration?
Over years Between seasons
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Annual Distributions
0.001
0.01
0.1
1
1987 1989 1991 1993 1995 1997 1999 2001 2003 2005
To
tal P
ho
sp
ho
rus
, mg
/L
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Seasonal Differences
0.001
0.01
0.1
1
1-Jan 20-Feb 10-Apr 30-May 19-Jul 7-Sep 27-Oct 16-Dec
Ordinal Day
Lak
e B
ott
om
Ph
osp
ho
rus,
mg
/L
1987-1991 1992-1996 1997-2001 2002-2006
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Aggregating Data
Sampling program: ~13 samples/y How best to assign concentrations to all
flows? Can’t aggregate across years Aggregate within seasons (just in case)
Oct-Mar Apr-Sep (stratification season) Assume constant concentration (median) within
each season in each year Seasonal Load = Seasonal median*Σ(flows)
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Phosphorus Balance
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
1988 1990 1992 1994 1996 1998 2000 2002 2004 2006
Ph
osp
ho
rus,
lbs/
y
Retained Export
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Previous Load Translator
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
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Vollenweider Model
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
z
LTP
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Estimating P Retention Coefficient
Canfield-Bachmann Artificial lakes To match 1982 data,
multiply σ by 3.6 Yields modified
Canfield-Bachmann
589.0
114.0
z
L
589.0
410.0
z
L
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Derive “new” C-B from data?
Plot σ vs. L/z; No real pattern Influential extreme flows
y = 0.0284x1.0249
R2 = 0.5963
0
10
20
30
40
50
60
0 200 400 600 800
R atio of External Load to Mean D epth
Sig
ma
fro
m O
bs
erv
ed
Ex
po
rt
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Does it Predict Well?
Use constant σ=6 (NB: differs from text) Note 5 yrs at right (’88, ’95, ’98, ’99, ’05)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
0.050
0.000 0.010 0.020 0.030 0.040 0.050
Predicted TP, mg/L
Ob
se
rve
d E
xp
ort
TP
, m
g/L
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Try Another Model: Dillon-Rigler
Load
ExportLoadR
)(
zRL
TP)1(
Commonly used
for reservoirs Retention is
fraction of load Median R=0.64
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P Retention (and Extreme Flows)
y = 0.7147x
R2 = 0.9594
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 10000 20000 30000 40000 50000 60000
External P Load, lbs/y
Re
tain
ed
P, l
bs
/y
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Can We Predict R?
Not encouraging based on common approach (OECD for shallow lakes)
Probably better to use a constant
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.0 0.2 0.4 0.6 0.8
OECD R
Ob
se
rve
d R
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Performance of Dillon-Rigler?
Use constant R=0.64 (median) Alignment OK, but precision not so good
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035
Predicted TP, mg/L
Ob
se
rve
d E
xp
ort
TP
, m
g/L
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Alternate View of Precision
Compare predictions of summer median P (bootstrap) Five peculiar years predict very high 1996 predicts low
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
1988 1990 1992 1994 1996 1998 2000 2002 2004 2006
Su
mm
er M
edia
n T
ota
l P
ho
sph
oru
s, m
g/L
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Is Load Translator Ready to Use?
Would prefer it to be stronger Plan to continue exploring options Especially interested in 5 odd years Consider two main tributaries from
hydrologic perspective Flows largely uncorrelated SP always the dominant flow Loads closer to being equal due to
higher concentrations in Plum Creek
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Plum Creek and the “Odd” Years
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1000 10000 100000 1000000
Flow, AF/y
Res
iden
ce T
ime,
y
Total Inflow Waterton Plum Full Pool
2002
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Thinking Out Loud…
High flow years for Plum Cr (>20,000 AF) stand out: over-predict phosphorus
What’s different about Plum Cr load? Normal stream that carries particulates
at high flow Contrast with SP that has been decanted
through series of reservoirs Can the retention be partitioned?
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Next Steps
Refine load translator Flows and TMAL
What scenario for inflows? Is 261,000 AF scenario appropriate? TMAL not exceeded even in 1995 (336K AF)
Does worst case for in-lake concentration represent highest load scenario?
Next meeting Mar 13: Hydrologic considerations for TMAL