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Scenario generation for long-term water budget analysis using the TOPMODEL rainfall-runoff model 2007 Alabama Water Resources Conference Perdido Beach Resort, Orange Beach, Alabama. Precipitation. Infiltration. Direct. Saturated Areas. Water Cycle. Baseflow. Evaporation. ET. Q out.

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  1. Scenario generation for long-termwater budget analysis using the TOPMODEL rainfall-runoff model2007 Alabama Water Resources ConferencePerdido Beach Resort, Orange Beach, Alabama

  2. Precipitation Infiltration Direct Saturated Areas Water Cycle Baseflow Evaporation ET Qout

  3. TOPMODEL Overview • TOPography-based hydrological MODEL • Developed by Beven and Kirkby, 1979 • “Physically-based watershed model that simulates the variable-source-area concept of streamflow generation.” (Wolock, 1993) • Many variations/improvements to the original model since 1979 • Three fundamental assumptions Beven, K.J. and M.J. Kirkby. 1979. A physically based, variable contributing area model of basin hydrology. Hydrological Sciences Bulletin, v. 24, pp. 43-69. Wolock, David M. 1993. Simulating the variable-source-area concept of streamflow generation with the watershed model TOPMODEL. USGS WRI 93-4124.

  4. TOPMODEL assumptions • Steady-state recharge to the groundwater • Hydraulic gradient of the water table is approximately equal to the surface slope • Transmissivity profile is exponential with depth

  5. TOPMODEL topographic wetness index (TWI) High values of TWI High potential for saturation Low values of TWI Low potential for saturation TWI = ln(a/tan b) Grid cells with the same TWI are hydrologically similar

  6. TOPMODEL topographic wetness index (TWI) Calculations need not be performed on every single grid cell. Grid cells with approximately the same TWI have similar hydrologic response

  7. General concept of TWI Mean TWI = 11 10-m cell Mean TWI = 12 Mean TWI = 15 Mean TWI = 14

  8. TOPMODEL Code • FORTRAN Code used by Leon Kaufmann and Dave Wolock (TOPMODEL executable) • Java GUI, Pre- and Post-processing, provides a Java wrapper for the TOPMODEL executable • ArcMap used to create topographic wetness index ASCII grid file

  9. TOPMODEL Features • Hydrographs on a daily time step • Monthly and annual water balances • Breakdown or flow components • Flow duration curves • Flow statistics and TNC IHA analysis • Hydrologic conditions can be mapped back using the topographic indices • Future “What-if” scenarios

  10. Total area Lake area Stream length Soil depth Permeability Water holding capacity Field capacity Porosity Percent impervious (S) Centroid latitude (ET) Groundwater withdrawal (S) Surface water withdrawal (S) Surface discharge (S) Area upstream of lakes Depth of root zone Partial list of Basin Characteristics

  11. Basin information Basin Characteristics Topographic Index 12-digit HUCs

  12. TOPMODEL User Interface Levels Single (S) or Nested (N) Basin Calibration Scenario-1 Basin Characteristics Scenario-1 Scenario-1 Scenario-n Future Scenario Hydrographs

  13. Program Flow Watershed Linkage Basin Characteristics OUTPUT OPTIONS ___________ Hydrographs Statistics Flow Duration Tabular Graphical User Request S or N? Edits for Scenarios Builder TOPMODEL Wetness Index Climate Data

  14. TOPMODEL Basin Characteristics + Edit basin characteristics + Save and Retrieve different basin characteristics files + Access the scenario builder

  15. Future Scenarios (Forecasting and What-ifs) • Climate variability • Long-term trends in precipitation • Long-term trends in temperatures • Population and Land use • Impervious area • Surface water withdrawals • Groundwater withdrawals • Surface water discharges

  16. TOPMODEL Scenario Builder Tab access to scenarios Static Trend Seasonal Step

  17. Historical climate record Historical record used to build a future scenario or use past extreme events directly

  18. Rainfall Scenario Using a historical record and assuming a stationary mean, Adjust the annual totals to some trend.

  19. TOPMODEL Main Menu + User friendly + Choose State + Choose gage + Message log reports status and errors

  20. Hydrograph overlay

  21. Flow duration overlay

  22. Calibration statistics Correlation coefficient Mean absolute error Bias Std Err of estimate Nash-Sutcliffe model-fit efficiency Flow statistics Low-flow Peak-flow Graphics Monthly water balance Annual water balance Custom plotting menu Karst component Work-in-progress

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