A Time Series Approach to Instream Flow Mitigation Forecasting. Presented by Alan Keizur

Transcription

1 A Time Series Approach to Instream Flow Mitigation Forecasting Presented by Alan Keizur

2 Agenda Brief background on project Brief overview of model Some results and application GoldSim highlights

3 Introduction Task: Clients: Develop a forecasting model to project the amount of water that will be needed to mitigate (replace) net withdrawals by the city and water district from the Snoqualmie river over the next 50 years. Law Offices of Thomas Pors City of North Bend, Washington Sallal Water District

4 Map of Area Map Courtesy Of USGS Redmond Seattle

5 North Bend, Washington Photo courtesy of City of North Bend website

6 Background City currently exceeding current water right (Mt. Si springs) In process of negotiating a new water right with Washington Dept. of Ecology Instream flow requirements in effect on Snoqualmie River (minimum flow) Are required to mitigate new consumptive use (withdrawals returns) on days when instream flows not met Negotiating purchase from Seattle Public Utilities (SPU) and investigating groundwater supply as sources for mitigation

7 Objectives Project consumptive use trend over next 50 years to full build-out Project mitigation requirements over time, accounting for variability in stream flow Support negotiations with Seattle Public Utilities and Dept. of Ecology Estimate compensation requirements to Puget Sound Energy for lost generating capacity at Snoqualmie Falls

8 Wrinkles Triggering and operational criteria for mitigation have not been defined: Number and location of comparison points (Snoqualmie, Carnation, Monroe?) Potential time lags between pumping and return Undefined operational factors (real-time instrumentation?) Groundwater yield for mitigation is currently uncertain Groundwater modeling (MODFLOW) to investigate aquifer characteristics

9 Input Data Annual demand forecast (from City of North Bend) Daily pump and WWTP flow data Daily streamflow records Daily instream flow criteria (follows seasonal pattern) Expert judgment on expected groundwater yield for summer mitigation, including uncertainty

10 Modeling Approach Simulate next 50 years on a daily timestep Determine if instream flows are being met Calculate daily consumptive use based on growth, seasonal withdrawal and return patterns Track mitigation water from SPU and groundwater Incorporate variability in stream flow using historical data Monte Carlo simulation Randomly sample starting point and then loop through record Convert daily values to annual for reporting purposes

11 Model Demo

12 Time History Chart Annual Mitigation

13 SPU Block Purchase Profile 1.4 Million Gallons per Day (mgd) % 5% Mean Year

14 Monthly Mitigation at Year 50 3 Million Gallons per Day (mgd) % 5% Mean 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

15 GoldSim Highlights Benefits Comment: Why not just use a spreadsheet? Very easy to implement model and modify logic Provides tremendous flexibility to expand analysis (e.g., time lags, surfacegroundwater interactions, uncertainty) Easy to explain model to stakeholders (clients, regulators, third parties) Dashboard capability for what if analysis, model handoff (built but not yet used on this project) Limitations Difficult to extract result data for result preparation (e.g., statistics at various timepoints) This should be addressed by improved spreadsheet functionality in next version

16 Next Steps Provide further analysis and support during negotiations e.g., Incorporate SPU price structure to project expenditures for City Incorporate results of groundwater investigation Aquifer yield and response characteristics Ongoing updates and refinements (e.g., sensitivity analyses)

17 Potential Water Resource Applications Water supply and delivery systems Instream flow assessments Water rights negotiations Aquifer storage and recharge Population dynamics (e.g., salmon) Hydropower

18 Thank You