Draft Spokane River Allocation Scenarios: May 22, 2009
Note to reviewers: This table is the list of proposed scenarios to be run in June 2009, listed in sequence of completion. Items in BOLD show changes in specific scenario details as the model runs are
carried out from top to bottom.
DRAFT Lake Spokane Dissolved Oxygen Scenarios
Name
Groundwater
Stormwater
Point Sources
Tributaries
Comments
Phosphorus
Flow/Conc.
Flow
TP, NH3, CBOD5
Flow
TP, NH3, CBOD
Baseline Scenarios
Calibration
Existing
condition for
2001
No Source
2001
(range of 6
ppb to 23 ppb
TP)
Zero (implicit
in GW flow)
2001
2001
2001
2001
Core model work. PSU will update to current version of W2, check the
calibration of the combined Idaho and Washington models and incorporate
new information where appropriate.
Estimated
natural
(lowest mean
concentration
in core model
(6 ppb))
Zero
Zero
NA
2001
Estimated natural
(based on
headwater
concentrations)
This is the baseline model run for the TMDL. All scenario run results are
compared to this baseline DO condition in Long Lake.
Mainstem flows conditions for this scenario are 2001 conditions, without
adjustment related to recently changed FERC minimum flows (see FERC
flow scenario below).
Sediment oxygen demand set to reduced level of 0.25 g DO/m2-day for
baseline and all TMDL scenarios.
TMDL Scenarios
TMDL Scenario
#1/ Flat 50
2001
Estimated
mean monthly
SW flow
2001 Conc.
TP=310 ppb
NH3=50 ppb
CBOD=3 ppm
Design
TP = 50 ppb
CBOD5 = 5 ppm
NH3 = (see
technical
specifications)
Exception:
Kaiser TP=35
ppb
2001
% reduction in
human
contribution in
2001
Hangman/Coulee:
20% (Mar-May)
40% (June)
50% (July -Oct)
Little Spokane:
36% (Mar-Oct)
This is a TMDL scenario where point and nonpoint values are fixed values
and both assessment points (riverine, reservoir) are evaluated. Point
sources are set to a total phosphorus concentration of 50 ppb (exception:
Kaiser at 35 ppb). Nonpoint sources are set to estimated achievable
reductions.
Analysis incorporates riverine assessment approach. Water quality is
checked at an assessment point at the riverine reach immediately upstream
of Lake Spokane.
The DO improvement required from Avista to meet the standard in the
reservoir is determined by analyzing volume-weighted DO levels and
comparing to volume-weighted DO levels in the NO SOURCE scenario.
Name
TMDL Scenario
#2 / Lower Level
Treatment
Groudnwater
Phosphorus
Same as
TMDL #1
Stormwater
Point Sources
Flow/Conc.
Flow
TP, NH3, CBOD
Same as TMDL Design
Same as TMDL
#1
Scenario #1
except:
Tributaries
Flow
2001
TP, NH3, CBOD
Same as TMDL #1
Comments
2001
Same as TMDL #1
This scenario is identical to TMDL Scenario #2 except potential re-use
facilities (Hayden) are adjusted to higher spring TP limits (150 ppb) and
lower summer TP limits (10 ppb).
2001
Same as TMDL #1
This is similar to the NO SOURCE scenario but includes nutrients at the
level of the TMDL allocations from nonpoint sources (tributaries and
groundwater).
This scenario is identical to TMDL Scenario #1 except Washington point
sources are adjusted to 35 ppb.
WA sources:
TP = 35 ppb
ID sources:
TP= 50 ppb
TMDL Scenario
#3 / Idaho Reuse
Same as
TMDL #1
Same as TMDL Design
#1
Same as TMDL
Scenario #2
except for re-use
facilities
(Hayden)
Re-use facilities
Spring
TP = 150 ppb
Summer
TP= 10 ppb
Source Assessment Scenarios
Nonpoint Impact
(TMDL
conditions with
zero point
sources)
Same as
TMDL #1
Storm Water
Impact
(TMDL
conditions with
zero storm water)
Same as
TMDL #1
Name
Groudnwater
Phosphorus
Zero
Zero
Zero
Design
NA
Proposed TMDL 2001
allocations
Same as TMDL #1
This scenario provides the estimated nonpoint source contribution to
dissolved oxygen impacts in the reservoir at TMDL conditions.
This scenario allows for the isolation of the stormwater contribution to the
downstream water quality condition under the proposed TMDL conditions.
This scenario is run after the TMDL Scenarios (#1-#3) and prior to public
notice of the TMDL, after the proposed allocations are selected.
Stormwater
Flow/Conc.
Point Sources
Flow
TP, NH3,
Tributaries
Flow
Comments
TP, NH3, CBOD
Flow Impact
(TMDL
conditions with
with FERC
Flows)
Same as
TMDL #1
Same as TMDL Design
#1
CBOD5
Proposed TMDL
allocations
Same as TMDL #1
2001
adjusted
to meet
new FERC
minimum
flows
This scenario will show the effect of the new FERC flow requirements on
water quality under the proposed TMDL conditions. It is run after the
TMDL Scenarios (#1-#3) and prior to public notice of the TMDL, when the
agencies decide on the proposed allocations.
Note that the TMDL baseline condition will be the 2001 flow regime,
which underlies all other scenario runs. This particular scenario is the only
model run with a different flow regime.