Focus Group Meeting: September 27, 2013 Truckee River Water Quality Standards Review

Overview of Topics for Discussion Feedback from previous workshop? Review of flow regime development – Adjustment to 10 th percentile flow regime Preliminary WQ results Interpretation of Results – Integration of results over range of flows Preliminary climate change sensitivity runs Next steps 2

Feedback from Previous Workshop

Topics for Comment from August 2013 Focus Group Meeting Approach for applying WARMF and TRHSPF to evaluate potential changes to the Truckee River Nutrient Water Quality standards Approach for establishing a flow regime based on TROM Future No Action scenario Approach for analysis and interpretation of model results Any overarching concerns regarding the water quality standards review process?

Review of Flow Regime Development

Selection of Representative Flow Conditions Derived “target flows” based on TROM Future No Action output Two representative flow regimes selected to date – Low Flow (10 th percentile) – Average Flow (50 th percentile) 6

1977 FNA Comparison of TROM, 10 th percentile flows, and TRHSPF 7 Only adjusted summer period for lower river ONLY Adjusted at TCID

Refining 10 th Percentile Flow Regime Closer to Target Preliminary runs performed with only minor adjustment to 1977 FNA (at Derby Dam) Working Group recommended further adjustment for 1977 above Derby Dam Final results with adjusted flows are “in process” Single test run completed – Biggest change in Reach 1 8

1977 FNA Comparison of TROM, 10 th percentile flows, and TRHSPF 9 Adjusted at WARMF-TRHSPF interface – July, August decreased flow – September increased flow Adjusted summer period for lower river ONLY Adjusted at TCID Adjusted at Sparks Jul - Sep Adjusted at TCID

Single Test Run with Adjusted 10 th Percentile Low Flow 10 Proceeding with running adjusted 10 th percentile flow for full suite of constituent concentrations Ortho-P TN

1985 FNA Comparison of TROM, 50 th percentile flows, and TRHSPF 11 No additional adjustment

Preliminary Results of 10 th Percentile Low Flow Condition (Does not include adjusted flow regime) 12

Set of Simulations Orthophosphate (mg/L) Total Nitrogen (mg/L) PLPT std x 0.65 x 0.75 NDEP/PLPT std xxxxx 0.85 x 1.00 x Total Phosphorus (mg/L) Total Nitrogen (mg/L) NDEP std x 0.65 x 0.75 NDEP/PLPT std xx xxxx 0.85 x 1.00 x

Options for Calculating Percent Violation of DO WQS 14 % of Hours: attainment is aggregation of all hours that have violated WQS X hours violated 8760 hours/yr % of Days: if 1 + hours violate WQS on a given day, that day is not in attainment X days violated 365 days/yr Reviewing attainment as “% of days” is more conservative approach

Spatial Aggregation for WQS Modeling 15

Preliminary Results Total P 10 th Percentile Flow: Reach Averaged 16 % of Days% of Hours TN = 0.75

Preliminary Results Ortho-P 10 th Percentile Flow: Reach Averaged 17 % of Days% of Hours TN = 0.75

Preliminary Results Total Nitrogen 10 th Percentile Flow: Reach Averaged 18 % of Days% of Hours

Preliminary Results: Longitudinal Plots TN = 0.75 mg/L, OP = 0.05 mg/L 19

Preliminary Results Total P 50 th Percentile Flow: Reach Averaged 20 % of Days% of Hours TN = 0.75

Preliminary Results Ortho P 50 th Percentile Flow: Reach Averaged 21 % of Days% of Hours TN = 0.75

Preliminary Results Total N 50 th Percentile Flow: Reach Averaged 22 % of Days% of Hours

Preliminary Results: Longitudinal Plots TN = 0.75 mg/L, OP = 0.05 mg/L 23

Preliminary Observations Reaches 1, 2, 3 show low level of DO violation Reach 4 is most critical at 10 th percentile flow – Sensitive to the phosphorus concentration – Not sensitive to the TN concentration – No violations for 50 th percentile flows Need further investigation of Reach 4 response 24

Integration of Results Over Full Flow Regime Working Group discussed potential merit of running a 90 th percentile (high flow) regime Could consider an “integration” of DO violations across all flow regimes Spreadsheet calculation based on preliminary results 90 th percentile year not simulated – Conservative assumption: high flow violations same as average year 25

Integration Over Flow Regimes: Compare Target Flows 26

Comparison of 10th and 50th Flow Regime Results: Total P th Percentile Flow 50 th Percentile Flow TN = 0.75

Preliminary Climate Change Scenario Identified by Focus Group as important consideration for sensitivity analysis Focus only on temperature increase – Given highly managed system, reservoir management could override climate change influences in upper watershed – Climate models predict wide variation in precipitation changes General approach for sensitivity runs – Only adjust TRHSPF air temperature inputs – air water exchange – Apply a 1° F air temperature increase across entire year – Present the results on a "per degree" basis – Although linear response not expected, reasonable first step 28

Basis for 1° F Temperature Increase USBR Truckee River Basin Study ( ) – Evaluate range of potential changes in water demands due growing population – Compare demands to existing supply under potential future uncertainties, including climate change Will include use of climate model projections 29 SOURCE: USBR, Truckee Basin Study, Technical Advisory Group Water Supply Workshop, June 24, Approximate 1° F increase over 20 years

TP Climate Sensitivity Example: 10 th Percentile Flow (TN 0.75 / TP 0.05) 30

Geomorphology Considerations Potential relationship between channel geometry and most critical segments Mapped selected parameters for each model segment – Reach slope – Water depth (summer average; 10 th percentile year) – Water velocity (summer average; 10 th percentile year) Developed an “indicator” of segment-specific diurnal swing – Calculated for two-segment average to account for influence by the diurnal in the prior segment 31

Justification for Indicator Violations are caused primarily by the magnitude of the diurnal swing Diurnal swing at steady state directly proportional to: gross plant productivity (g O 2 /m 3 /day) / [reaeration rate] Gross plant productivity = areal productivity (g O 2 /m 2 /day) / [water depth] Reaeration proportional to: [velocity * slope] Diurnal swing = areal productivity / [depth * velocity * slope] With similar periphyton productivity across segments, [depth * velocity * slope] should be a good indicator of segment-specific diurnal 32

Visually Determined “Bins” for Mapping Parameters 33

Average Depth (Summer Mean) 34 Vista (304) Tracy (315) Marble Bluff Dam (343) Below Derby Dam (320)

Channel Slope 35 Vista (304) Tracy (315) Marble Bluff Dam (343) Below Derby Dam (320)

Average Velocity (Summer Mean) 36 Vista (304) Tracy (315) Marble Bluff Dam (343) Below Derby Dam (320)

Reach Geometry Index 37 Vista (304) Tracy (315) Marble Bluff Dam (343) Below Derby Dam (320)

Next Steps Focus Group comments / feedback: – Technical approach Finalization of WQS model runs/output interpretation – Finalize “adjusted” 10 th percentile flow runs with all constituent concentrations – Climate sensitivity simulations Development of Technical Rationale Report 38

Upcoming Focus Group Workshops Early Nov, 2013 (TBD) *NEW DATE* – Final modeling results Jan 15, 2014 (W) – Technical Rationale document Additional Stakeholder / Focus Group meetings TBD in