Macro Invertebrate Flow 

Experiment

Financial Impact on Hydropower: 

Process and Methods

Jerry Wilhite

Craig Ellsworth

TWG Meeting, October 12, 2021
“Request that WAPA provide additional 

information regarding purchase power 

cost estimates, including assumptions and 

uncertainty, such that effects to 

hydropower are minimized if Bug Flows 

are implemented in the future.”
Goal: Provide a general understanding of how 

CRSP hydropower financial impacts are 

estimated.

• Hydropower model 

overview

• Modelling process

• Bug Flow modelling

• Previous Estimates

• Looking forward

• Questions 
Goal: Provide a general understanding of how 

CRSP hydropower financial impacts are 

estimated.

• Hydropower model 

overview

• Modelling process

• Bug Flow modelling

• Previous Estimates

• Looking forward

• Questions 
GTMax SuperLite

• Modified version of original GTMax

Model and customized for the SLCA/IP 

system

• Models flow of electricity, water, and 

money

• Maximizes economic or financial value 

of electrical power generation while adhering to user-defined inputs and 

restrictions

• Produces “optimal” hourly generation 

patterns for 1 week each month

• Two formulations

• Flaming Gorge

• Other CRSP units

• Can optimize “bug flows” GTMax SL
Goal: Provide a general understanding of 

how CRSP hydropower financial impacts are 

estimated.

• Hydropower model overview

• Modelling process

• Inputs and assumptions 

• Model outputs

• Model accuracy

• Bug Flow modelling

• Previous Estimates

• Looking forward

• Questions 
GTMax SL

Energy Prices

• Palo Verde Hub

• Monthly on and 

off peak

• Convert to hourly 

prices

Electric Demand

• Hourly average 

customer 

schedule 2006-

2018

• Project use

Hydrology 

Forecasts

• 24-month 

study

• CRSS

• Monthly 

volumes

• Reservoir 

elevations 

Operating Criteria

• Water laws

• Ops plans

• Environmental 

laws

Power System Physical 

Properties

• Unit efficiency

• Max release

• Plant capacity

• Losses (8%)

• Outages

• Ancillary services
Example: GTMax SL Output

0

200

400

600

800

1,000

1,200

0

200

400

600

800

1,000

1,200

Sun Mon Tue Wed Thu Fri Sat

Total Load (MWh)

Generation (MWh)

Example GTMax SL Output with SHP Purchases

FN CY GC FG BM MP Other Total Load
GTMax SL Accuracy

• Used observed 

hydrologic data for WYs 

2009 – 2016

• Compared model 

predicted generation to 

observed generation 

(PO&M 59)

• Actual generation was 

less than modelled in 

all but one year

Water Year

Modelled 

Generation 

(MWh)

Observed 

Generation 

(MWh) % Difference

2009 4,799,959 4,711,766 1.9%

2010 4,655,393 4,575,425 1.7%

2011 6,925,842 6,855,827 1.0%

2012 5,345,123 5,219,578 2.4%

2013 4,109,416 4,003,033 2.7%

2014 3,923,947 3,873,198 1.3%

2016 4,996,324 5,011,928 -0.3%

Total 34,756,005 34,250,756 1.5%
Goal: Provide a general understanding 

of how CRSP hydropower financial 

impacts are estimated.

• Hydropower model overview

• Modelling process

• Bug Flow modelling

• 2021 Example

• Previous Estimates

• Looking forward

• Questions




15

Key Points
16

Goal: Provide a general understanding of 

how CRSP hydropower financial impacts are 

estimated.

• Hydropower model overview

• Modelling process

• Bug Flow modelling

• Previous Estimates

• 2018 – 2021

• Observed 2018 - 2019

• Looking forward

• Questions 
17

Previous “Bug Flow” Estimates
$15,000

$65,000

$135,000 $121,000

-$19,000

-$160,000

$210,000

$135,000

-$200,000

-$150,000

-$100,000

-$50,000

$0

$50,000

$100,000

$150,000

$200,000

$250,000

May June July August

Bug Flow Cost

2018 Monthly Cost of Bug Flows

Estimate

Observed

Cost Benefit
19
20

Goal: Provide a general understanding of how 

CRSP hydropower financial impacts are 

estimated.

• Hydropower model overview

• Modelling process

• Bug Flow modelling

• Previous estimates

• Looking forward

• 2022

• Beyond 2022

• Questions
21

Looking ahead to 2022

Ideas for reducing bugflows impacts to hydropower

Things we have learned:

H-value

• Higher = expensive

Number of 

days 

• Saturday = weekday

• 5 weekends/month

Daily 

fluctuation 

level

• Is limiting 

movement of 

onpeak water

Type of 

month

• Power months 

= expensive

Power prices & 

onpeak/offpeak

spread

• Higher = expensive
24

Goal: Provide a general understanding of how 

CRSP hydropower financial impacts are 

estimated.

• Hydropower model 

overview

• Modelling process

• Bug Flow modelling

• Previous estimates

• Looking forward

• Questions