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Modeling Surface Water-Groundwater Interactions in Coastal Environments During Storm Events

This study simulates how surface water and groundwater interact during a 25-year/72-hour storm event in a coastal setting using the SEAWAT 2000 model. The research evaluates the effects of stormwater management on flow dynamics and the buoyancy impact of drainage well discharge on the water system. The hydrogeological characteristics of the area, including formations like Miami Limestone and Key Largo Limestone, are examined to understand water movement. Simulations include pre- and post-development hydrographs and well data to assess the impact of storm events on the local water system. Conclusions suggest that routing stormwater to drainage wells has a lesser impact on shallow groundwater flow, while discharging stormwater to lakes can lead to significant changes in water dynamics.

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Modeling Surface Water-Groundwater Interactions in Coastal Environments During Storm Events

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  1. Simulation of the Dynamics of Surface Water-Groundwater Interactions in a Coastal Environment During a 25-Year/72-Hour Stormby William C. HutchingsDavid L. Tarbox SWIM20 Meeting (2008) Naples, Florida

  2. Purpose • Obtain an Environmental Resources Permit that includes an evaluation of the potential effects of the 25-year/72-hour storm event. Requirements • 1. Evaluate potential effects of surface storm water • management on surface water/groundwater flow; • Evaluate the potential effects of buoyancy of • drainage well discharge on surface water/ • groundwater in the vicinity. Model SEAWAT 2000

  3. Model Characteristics • 6785 m (East-West) • 5270 m (North-South) • 81 columns and 76 rows • Variable grid (200 m to <50 m) and thickness • 17 Layers • Variable top elevation • Vertical extent approximately 3 to -55 NGVD

  4. 0 Total area: 291 acres

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  6. N S Range of Hydraulic Conductivity in Feet Per Day (ft/day) Blue ≥ 1000 ft/day Gray 100-1000 ft/day Green 10-100 ft/day Yellow ≤ 0.1 ft/day Site Hydrogeology Approximate Location of Site • The Site is underlain by the following formations in ascending order • Pamlico Sand • Miami Limestone • Key Largo Limestone • Anastasia Formation • Tamiami Formation From Fish & Stewart, 1991 WRI Report 90-4108

  7. Fence Diagram of Upper Biscayne Aquifer Pamlico Sand Miami Oolite Anastasia Ls North Part Note: LS to –50 ft NGVD South Part

  8. Fence Diagram of Upper Biscayne Aquifer (North Part of Fence Diagram) Pamlico Sand Miami Oolite Anastasia Ls

  9. Pamlico Sand Miami Oolite Anastasia Ls Fence Diagram of Upper Biscayne Aquifer (South Part of Fence Diagram)

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  12. Model Input Parameters Cont. Tracer tests conducted in four zones from water table to approximately –50 ft NGVD with Rhodamine WT Specific capacity tests conducted in several drainage wells.

  13. General Characteristics of Biscayne Bay • Generally a saline water body • Receives discharge of freshwater from the Biscayne aquifer • West part of Biscayne Bay exhibits less salinity than seawater due to the discharge of freshwater from Biscayne aquifer C.D. Langevin 2001 From WRI Report 00-4251

  14. Pre-Development Site Plan Ibis Lake Various Additional Lakes Southeast Lake Location of Tracer Tests

  15. 0 Interval 2 represents Miami Oolite

  16. 0 Interval 3 represents Anastasia Fm

  17. 0 Interval 4 represents Anastasia Fm

  18. 0 Interval 1 represents Pamlico Sand

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  25. Summary of Hydraulic Parameters Cont.

  26. Methodology Used for Simulating 25-Year 72-Hour Storm Event • Obtained results from Interconnected Channel-Pond Routing • Model (ICPR) or HydroCAD stormwater models including: • Lake stage elevations for pre and post-development • simulations; • Discharge rates for drainage wells; • Discretize model with respect to time to represent hydrographs

  27. Pre-Development Ibis and Southeast Lake Hydrographs

  28. Post-Development Ibis and Southeast Lake Hydrographs

  29. Post-Development Well Hydrographs Note: Representative set of wells

  30. Pre-Development Initial Hydraulic Heads in layer 2 Ibis Lake Southeast Lake

  31. Ibis Lake Southeast Lake Pre-Development Hydraulic Heads in Layer 2 at 72 Hours

  32. Steady State Distribution of TDS through North Part of Site (Ibis Lake) Lake W E 2.7 Landward Flow -55 0 Distance in meters (m) Note: Elevation in m NGVD 3500

  33. Pre-Development Distribution of TDS through North Part of Site (Ibis Lake) at 72-hours During Storm Event Lake Site Site 2.7 Landward Flow Seaward Flow -55 0 m W 3500 m E Distance in m Note: Elevations in m NGVD

  34. Pre-Development Hydraulic Heads in Layer 2 at 41 Days

  35. Post-Development Site Plan Ibis Lake Post-development lakes Southeast Lake

  36. Location of Drainage Wells Screened in the Lower Biscayne Aquifer Drainage wells

  37. Post-Development Hydraulic Heads in Layer 2 at 72 Hours (Design Stage)

  38. Distribution of TDS through North Part of Site (Ibis Lake) at 72-hours During Storm Event (Design Stage) Note Vertical upward flow induced by lake Lake W E 2.7 Landward Flow Seaward Flow -55 Drainage Well 0 Distance in meters (m) Note: Elevation in m NGVD 3500

  39. Distribution of TDS through North Part of Site (Ibis Lake) at 72-hours During Storm Event (Maximum Stage) Note downward vertical flow induced by lake Lake W E 2.7 Seaward Flow Landward Flow -55 Drainage Well 0 Distance in meters (m) Note: Elevation in m NGVD 3500

  40. Distribution of TDS in Lower Biscayne Aquifer (Layer 17) at 72 Hours 34 g/l 0.5 g/l Landward flow consistent with pre-development conditions General seaward flow (reversed) caused by discharge to drainage wells

  41. Post-Development Hydraulic Heads (Maximum Stage) at 12 days Ibis Lake Southeast Lake

  42. Post-Development Hydraulic Heads in Layer 2 at 41 Days

  43. Post-Development Variation in TDS Beneath Ibis Lake in Layers 4 & 7 at 72 Hours (Design Stage)

  44. Post-Development Variation in TDS Beneath Ibis Lake in Layers 4 & 7 at 72 Hours (Maximum Stage)

  45. Conclusions • Shallow groundwater flow is affected less when storm water is routed to drainage wells; • Storm water discharge to lakes results in strong downward vertical flow promoting solute transport; • Buoyancy of drainage well discharge may lessen downward solute transport; • 4. Deep groundwater flow is temporarily reversed (seaward) beneath the study area due to storm water discharge to lakes and drainage wells. • 5. Storm water discharge to drainage wells decreases loss to ET from • surface waters. • 6. Discharge of storm water to drainage wells along the coast may be a viable control for seawater intrusion.

  46. The End

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