Field Estimation of Wetland Soil Saturated Hydraulic Conductivity Peter Caldwell SSC570 12/2/03

1. Field Estimation of Wetland Soil Saturated Hydraulic ConductivityPeter CaldwellSSC57012/2/03 Causeway Bay

2. Agenda • Background • The Bouwer-Rice Method • Field Procedures • Office Procedures • Results • Conclusions

3. BackgroundHydrology Modeling • Research project involves modeling the hydrology of three Carolina Bays • Each bay has 4-7 wells used to collect data for model calibration • Each well location will be modeled • Model requires Ksat of all soil layers to 1 m depth

4. BackgroundReference Bays Bladen County, NC Charlie Long Bay Tatum Millpond Bay Causeway Bay

5. The Bouwer-Rice Method • Slug test method to determine Ksat in-situ • Only works at depths below water table

6. The Bouwer-Rice Method • Soil at Field Location Ground Surface Unsaturated Soil Saturated Soil Impermeable Layer

7. The Bouwer-Rice Method • Bore a hole to desired depth

8. The Bouwer-Rice Method • Insert well casing and screen

9. The Bouwer-Rice Method • Drop in slug

10. H The Bouwer-Rice Method • Record height of water in tube vs. time

11. The Bouwer-Rice Method • Calculate Ksat H 2rc Where, Lw h Le 2rw A and B are dimensionless parameters based on Le/rw Note: Use straight line portion of graph of H vs. time for t, Ho, Ht

12. Field ProceduresField Conditions Thick

13. Field ProceduresField Conditions Deep

14. Field ProceduresEquipment- Well Casing • 4” PVC Pipe with holes drilled in lower 20 cm • Holes less likely to get clogged than slots • Duct tape allowed fine tuning of screen length

15. Field ProceduresEquipment- slug Slug • 2” PVC, 24” long • Filled with gravel

16. Field ProceduresEquipment- Level-logger Level-logger • Made by Solinst • Records height of water above logger • Records every 0.5 second

17. Field ProceduresProcedure • Wanted Ksat values for all soil horizons to a depth of 1 m • Had soil profile descriptions from previous study • Depths/Thicknesses • Texture

18. Field ProceduresProcedure- Augering Hole • Based on profile descriptions, tape screen to appropriate length • Auger through root mat • Set well casing into hole created • Auger inside casing • Push casing down • Repeat until screen is positioned at desired depth

19. Field ProceduresProcedure- Insert Level-logger • Wait until water inside casing equalizes with water table • Drop level-logger inside casing

20. Field ProceduresProcedure- Inserting Slug • Wait 2-3 minutes for water to equilibrate from level-logger drop • Insert slug smoothly but quickly

21. Field ProceduresProcedure- Wait • Allow time for water level to lower (usually 10-15 minutes) • Approximately long enough for one game of crazy eights

22. Field ProceduresProcedure- Download data

23. Field ProceduresProcedure • Performed procedure 3 times for each horizon • Auger down to next horizon • Repeat procedure for remaining horizons • Repeat for each well location

24. Office Procedures • Compile H vs. time data for each horizon • Fit straight line for points on curve • Calculate Ksat

25. Office ProceduresH vs. Time data

26. ResultsKsat Values for Various Textures

27. ResultsKsat Vs. Depth by Soil Type

28. Conclusions • Slug test method was a relatively simple and straightforward method to estimate Ksat • Ksat values were reasonable, though slightly high • Will run further tests to validate the results