Hydrologic Model of the Mayag üe z Bay Watersheds: Progress Report

1. Hydrologic Model of the Mayagüez Bay Watersheds: Progress Report Eric Harmsen, Associate Professor Dept. of Agricultural and Biosystems Engineering Marcel Giovanni Prieto, Graduate Student Dept. of Civil Engineering and Surveying

2. Acknowledgements • NASA-EPSCoR • US Geologic Survey • Sea Grant • U.S. Army Corps of Engineers (ERDC) • LARSIP Laboratory • Puerto Rico Water Resources and Environmental Research Institute • Professor Nazario Ramirez, UPRM • Students: Sandra Ortiz, Richard Diaz, Moises Angeles Malaspina, Christian Calderon

3. Some Water Issues in Puerto Rico • Water conflicts between agricultural and non-agricultural community (Lajas, PR) • Sediment transport is contaminating marine resources at numerous coastal areas in PR • Saltwater intrusion is threatening groundwater resources in the north and south coast of PR • Dropping groundwater elevations occurring in the South Coast. • Many of the principal reservoirs have become partially filled with sediment since their construction, reducing their effectiveness in providing water supplies and mitigating flood peaks.(e.g., Carraízo Reservoir which supplies San Juan) • Problems with the water supply service of 700,000 families at the present time in the island (Nuevo Día05 Feb. 2005)

4. Rio Grande de Anasco Outlet Sediment Discharge to the Mayagüez Bay

5. Water related issues will become even more serious in the future • Potential climate change • Urban growth • Increasing population • Increasing cost of water and energy • Contamination of water supplies • Environmental impacts from changing flows

6. Objective • To develop an integrated hydrologic model for the Mayaguez Bay Watersheds for the purpose of • Estimating the components of the hydrologic cycle • Evaluate the water balance under climate change conditions (uncoupled) • Longer-term objectives: • Apply an integrated hydrologic model coupled with a regional atmospheric model (e.g., RAMS/TOPMODEL) • Evaluate the water balance for the entire island

7. Integrated Hydrologic Modeling

8. MOTIVATIONWe will be able to address scientific and practical questions related to the hydro/atmospheric system • How might changes in global/local weather affect our water supply • How will urban growth effect the hydrology (land use change, Urban Head Island effect) • Evaluate the effect of specific types of storms on • Flooding • Landslide potential

9. Modeling Strategy • Multi-watershed model (short-term) • Develop and calibrate hydrologic model • Use output from climate change simulations from an atmospheric simulation model as input to the hydrologic model • Island-wide model (long-term) • Develop and calibrate hydrologic model • Hydrologic model coupled with RAMS

10. Qualification Model will be developed based on a rough calibration • Available groundwater elevations • USGS gauging station – Total daily volume (not hydrographs) • Overland flow only (no channel flow)

11. Model Selection Requirements • Should simulate • Overland flow • Vadose zone flow • Groundwater flow (preferably in 3-D) • 1-D channel flow • Should run on a supercomputer • Source code should be freely available Models we evaluated: • Mike She, WASH123D, IHM, GHSSA

12. Conceptual model development • Identification of data sources • Delineation of study area • Conceptualize surface, soil and subsurface systems • Development of GIS map • Perform simplified GIS water balance

13. Study Area • Requirements • Two or more watersheds • Boundary along coast • Large topographic relief • Include alluvial and bedrock aquifers • Various land use categories

18. GIS Water Balance of the Mayaguez Drainage Basin Precip = ET + RO + Rch +ΔS Precip = Precipitation ET = Evapotranspiration RO = Surface Runoff Rch = Aquifer Recharge ΔS = Change in soil moisture storage

19. Soil Moisture Content

20. Soil Moisture Content

21. Potential Evapotranspiration • Hargreaves-Samani Method PET = 0.0023 x Ra x (T +17.8) x (Tmax – Tmin)0.5 PET = potential or reference ET Ra = extraterrestrial evapotranspiration T = average daily air temperature Tmin = average daily minimum temperature Tmax = average daily maximum temperature

22. Hydrologic Model - Evapotranspiration Evaluation of Simplified Method Surface Elevation Air Temperature Reference Evapotranspiration

23. Hydrologic Model - Evapotranspiration Actual ET September Kc Literature Reference ET X NDVI Actual ET January

24. Hydrologic Model – Surface Runoff LAND COVER MONTHLY RUNOFF COEFFICIENT MONTHLY RAINFALL MONTHLY RUNOFF

25. Aquifer Recharge September January Aquifer Recharge was zero at all locations 59.7 mm Average

28. Global Warming http://www.gfdl.noaa.gov/~tk/climate_dynamics/fig1.gif

29. PET = 0.0023 x Ra x (T +17.8) x (Tmax – Tmin)0.5 “ There has also been a general trend toward reduced diurnal temperature range, mostly because nights have warmed more than days.” - Union of Concerned Scientists http://www.ucsusa.org/global_warming/science/early-warning-signs-of-global-warming-heat-waves.html

30. Global Climate Circulation Model – Caribbean Area DOE - Accelerated Climate Prediction Initiative

31. Some Climate Change Results

32. Conclusions from GIS Water Balance Analysis During the next 50 to 100 years: • ET can be expected to increase by 3 to 5 mm/month • In the worse case the aquifer recharge will also drop by this amount • The expected drop in the water table is between 13 to 27 mm. • Increase urban development may decrease aquifer recharge and increase surface runoff.

33. Numerical Model • MIKE SHE • Advantages • Easy to use • 3-D groundwater • Water balance analysis tools are excellent • Can simulate other processes: sediment and solute transport • Disadvantages • Only runs on a PC • Documentation is not complete OLF – Diffuse wave approximation of the Saint Venant equations UZ – Richards Equation, gravity method, 2 layer water balance SZ – standard groundwater equation (MODFLOW)

34. Simulation of average conditions for Mayaguez Bay Area • Rainfall – Time series for Hacienda Constanza weather station • Manning’s n: 0.07 • Soil: Loamy Clay • Potential ET: 4.4 mm/day • Aquifer • type: unconfined • thickness: 33 m • conductivity: 0.33 m/day • Initial groundwater elevation: 0 m below surface

43. Future Work • Model Calibration • Groundwater elevations • Daily Surface water Volumes • Climate Change scenarios • Decide which climate parameters to vary • Write Proposals for more funding (NASA-NEWS)