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U.S. Geological Survey R.I. Water Resources Board

EVALUATION OF ALTERNATIVE INSTREAM-FLOW CRITERIA AND WATER-SUPPLY DEMANDS ON GROUND-WATER DEVELOPMENT OPTIONS IN THE BIG RIVER AREA, RHODE ISLAND. U.S. Geological Survey R.I. Water Resources Board. MISSION.

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U.S. Geological Survey R.I. Water Resources Board

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  1. EVALUATION OF ALTERNATIVE INSTREAM-FLOW CRITERIA AND WATER-SUPPLY DEMANDS ON GROUND-WATER DEVELOPMENT OPTIONS IN THE BIG RIVER AREA, RHODE ISLAND U.S. Geological SurveyR.I. Water Resources Board

  2. MISSION • Provide actionable information and detailed ground-water withdrawal strategies that the RIWRB and public suppliers may use to maximize withdrawals while minimizing the probability of adverse effects caused by these withdrawals in the basin.

  3. ACTIONABLE INFORMATION • WHAT DO YOU NEED TO KNOW? Streamflow (probable) – Depletion = Probable Risk • WHEN DO YOU NEED TO KNOW IT? In Time to Affect Depletion • HOW DO YOU RESPOND? • Go to Alternate Withdrawal Plan • WHAT LIMITS RESPONSE? WSSMP Minimum Service Limit Volumes

  4. Develop DSS to Provide: • Estimated “Natural” Streamflow Record • Ground-water flow model • Actual Streamflow record(s) • Historical Streamflow Analysis • Response coefficients • Withdrawal plans • Drought Projection • Hydrologic predictors • Withdrawal plans

  5. Estimated “Natural” Streamflow Record • Use • Response Coefficients from Ground-Water Model • Withdrawal Records • Calculate Streamflow Depletion • Back Out Estimated “Natural” Streamflow • Extend Estimated “Natural” Streamflow Record beyond withdrawal records by MOVE.1/MOVE.3

  6. 0.048 cfsm

  7. Ground-Water Flow Near a Stream: Natural Conditions

  8. Ground-Water Withdrawals Reduce Streamflow

  9. Streamflow Depletion: An Example

  10. Example Instream-Flow Criteria

  11. Results: Ground-Water Withdrawals for Different Instream-Flow Criteria

  12. Average Annual Ground-Water Withdrawals For Alternative Instream-flow Criteria

  13. Typical Rhode IslandGround-Water Demand Patterns

  14. DRY-PERIOD STREAMFLOW ISSUES

  15. Information • Information and publications are available at URL: • http://ma.water.usgs.gov/projects/BigRiver.htm

  16. Transient Model: Potential Results • Understand impacts of withdrawals on streamflow depletion during drought: Streamflow depletion during drought caused by withdrawals Streamflow during drought with no withdrawals Streamflow during drought with current withdrawals - = • Understand gains in streamflow when drought plan implemented: Effect of demand management on streamflow depletion Streamflow during drought with current withdrawals Streamflow during drought with demand management - = • Evaluate effectiveness of demand-management practices • Use results to constrain optimization • Other comparisons that can be made between simulation results?

  17. Stream Depletion i Well j Stream Site k Preceeding months t Month *Note response coefficients should sum to almost 1 at the outlet of a closed basin. Reductions in ground water ET caused by drawdown account for some water Also, If a well gets water from a neighboring basin the depletions will not equal withdrawals

  18. RHODE ISLAND DROUGHT MANAGEMENT PLAN: WHO

  19. RHODE ISLAND DROUGHT MANAGEMENT PLAN: WHERE Normal Annual Precipitation Approximate location of the study area

  20. Time to Affect Depletion: Response Coefficients

  21. What is Basin Safe Yield? Safe Yield = Natural Streamflow ± Alterations - Flow to maintain ecosystem • Calculation of safe yield requires knowledge of: • Natural, unaltered streamflow (estimated) • Streamflow resulting from alterations in the basin (estimated) • Flow to maintain ecosystem (specified)

  22. Example of Basin Safe-Yield Graphical output • Natural flows or flow statistics • Altered (existing) flows • Target Flows • Effects of a particular withdrawal • Basin characteristics • Safe-yield estimate or appropriate safe-yield statistics Tabular Output Natural flow regime Log Streamflow, log Q Existing flow regime Target FDC Safe yield Exceedence probability*, in percent * Percent time streamflow exceeds a given level at a specified location

  23. Reservoir water balance and firm yield Water in storaget= Storaget-1+ Inflowst – Outflowst • Precipitation • Surface inflow • Ground-water inflow • Evaporation • Other withdrawals • Drinking-water yields • Required releases • Uncontrolled releases (spills) • Loss to ground-water The firm yield of a reservoir is the maximum drinking-water yield that can be withdrawn without the complete depletion of available storage. Illustration by: C. Mendelsohn, USGS

  24. Summary: The DSS is a Useful Tool • Provides quantitative forecast (probabilities) • Gives the RIWRB a method to report risks of low flows (decision makers decide based on risk) • Demonstrates/validates the need for conservation based on lagged depletions • Dynamic • The tool is applicable for various conditions • Forecasts can be modified as the situation evolves • Linked to management measures • User friendly • Based on proven methods

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