Sacramento Functional Flow Analysis

The Reorienting to Recovery Structured Decision Making group proposed a functional flow (FF) scenario. To this date, there is no available CalSIM FF run so we cannot model full FF on the entire system. This document outlines our approach to piloting a FF on the Sacramento River.

In the Balanced round of modeling, this methodology was adapted for the San Joaquin River basin and further documentation is available here.

Pilot FF Approach on the Sacramento River

The R2R technical team is working collaboratively with a flow sub group to develop a FF hydrograph for the Sacramento River. We are building off of the Nature Conservancy’s Natural Flows Database to develop a wet and dry year monthly EFF hydrographs. We will compile these wet and dry year FF into a 20 year synthetic timeserries based on the historical water year types between 1980 and 2000, the current R2R model timeframe.

Planned Improvements and Next Steps

• The technical team is working to review existing literature on pulse flows and expand pulse flow routing logic in the model. This will increase the granularity of flow related model effects despite the monthly timestep of our CalSim flow input data and the model.

• The technical team is also working with MBK to incorporate FF logic into a CalSIM Run that we can use directly in the model.

What is an FF

California’s FF includes 5 distinct components of a natural flow regime: fall pulse flows, wet season peak flows, wet season base flows, spring recession flows, and dry season baseflows.

For more information on FF please refer to additional sources:

• Modeling Functional Flows in California’s Rivers
• California Environmental Flows Framework
• Natural Flows Database

How can we tailor FF to our system

FF are hypothesized to be the best flows for salmon in our historical system. However, our system is highly managed so we may need to alter FF slightly from their historical values to maximize benefit to salmon.

The R2R technical team developed proposed FF monthly flows by combining the Natural Flows Database values with critical flow to survival migratory thresholds on the Sacramento River (from Michel 2021). This original attempt did not maximize habitat so the technical team revised their approach to maximize modeled habitat and survival using the following principles:

1. Optimize spawning habitat during full spawning timeframe (October, November, and December)

2. Fix dry season base flow at a low value to maximize water for Juveniles, use Natural Flows Database as a guide (August, September)

3. Optimize outmigration survival in last 3 model outmigration months (May, June, July). If water volume allows set migratory survival above 50%. If volume of water limited, set migratory survival above 20% (based on migratory survival flow survival thresholds on the Sacramento River (from Michel 2021).
4. Utilize additional flows for maximizing FP habitat in (January, February, March & April)

Proposed Model FF

Wet Year FF

The table below shows the monthly flow CFS for a wet-year model FF on the Sacramento River. This table was constructed using the Natural Flows database and model survival thresholds.

month	flow_cfs	description
Jan	40000	Utilize remaining water for FP habitat
Feb	40000	Utilize remaining water for FP habitat
Mar	40000	Utilize remaining water for FP habitat
Apr	40000	Utilize remaining water for FP habitat
May	10700	Optimize for migratory survival (10,700 for mig surv ~50%)
Jun	10700	Optimize for migratory survival (10,700 for mig surv ~50%)
Jul	10700	Optimize for migratory survival (10,700 for mig surv ~50%)
Aug	1000	Set at 1000 to increase acreage for available for Juv flows
Sep	1000	Set at 1000 to increase acreage for available for Juv flows
Oct	4750	Optimize for spawning habitat based on flow area WUA
Nov	4750	Optimize for spawning habitat based on flow area WUA
Dec	4750	Optimize for spawning habitat based on flow area WUA

The plot below shows the CalSIM modeled flows for the Sacramento River of an existing representative wet year: 1996. 1996 has the median water year index as provided by DWR out of all the “Wet” and “Above Normal” years within our model time frame.

The table below shows the annual total volume of water needed for each flow scenario. The wet year EFF uses more water than the Natural Flows database EFF and then the representative CalSIM year.

Scenario	Annual Acre Ft Water
Natural flows Database flows	16380382
Proposed Model FF	12578235
calsim	12625023

Dry Year FF

The table below shows the monthly flow CFS for a dry-year model FF on the Sacramento River. This table was constructed using the Natural Flows database and model survival thresholds.

month	flow_cfs	description
Jan	18500	Utilize remaining water for FP habitat
Feb	18500	Utilize remaining water for FP habitat
Mar	18500	Utilize remaining water for FP habitat
Apr	18500	Utilize remaining water for FP habitat
May	4500	Keep high for migratory survival (4,350 for mig surv ~20%)
Jun	4500	Keep high for migratory survival (4,350 for mig surv ~20%)
Jul	4500	Keep high for migratory survival (4,350 for mig surv ~20%)
Aug	500	Set summer base flow to 550 based on Natural flows tool and to increase acreage for available for Juv flows
Sep	500	Set summer base flow to 550 based on Natural flows tool and to increase acreage for available for Juv flows
Oct	4750	Optimize for spawning habitat based on flow area WUA
Nov	4750	Optimize for spawning habitat based on flow area WUA
Dec	4750	Optimize for spawning habitat based on flow area WUA

The plot below shows the CalSIM modeled flows for the Sacramento River of an existing representative dry year: 1987 1987 has the median water year index as provided by DWR out of all the “Critical”, “Dry”, and “Below Normal” years within our model time frame.

The table below shows the annual total volume of water needed for each flow scenario. The dry year FF uses less water than the Natural Flows database FF and then the representative CalSIM year.

Scenario	Annual Acre Ft Water
Natural flows Database flows	4967965
Proposed Model FF	6203089
calsim	6208945

Creating a synthetic flow timeserries

In order to incorporate these FF into the model data inputs we combined wet and dry years to make a synthetic timeserries over the full 20 year period. We started by classifying years as “Dry” or “Wet” based on DWR water year type classifications. All “Dry”, “Critical”, or “Below Normal” years fall into the “Dry” category and all “Wet” or “Above Normal” years fall into the “Wet” category.

The plot below shows this synthetic timeserries for the Sacramento River over the 20 year simmulation period.