1. Field Estimation of Wetland Soil Saturated Hydraulic Conductivity Peter Caldwell SSC570 12/2/03
Causeway Bay

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

3. Background Hydrology 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. Background Reference 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. The Bouwer-Rice Method
Record height of water in tube vs. time H

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 Procedures Field Conditions
Thick

13. Field Procedures Field Conditions
Deep

14. Field Procedures Equipment- 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 Procedures Equipment- slug
2” PVC, 24” long
Filled with gravel

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

17. Field Procedures Procedure
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 Procedures Procedure- 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 Procedures Procedure- Insert Level-logger
Wait until water inside casing equalizes with water table
Drop level-logger inside casing

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

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

22. Field Procedures Procedure- Download data

23. Field Procedures Procedure
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 Procedures H vs. Time data

26. Results Ksat Values for Various Textures

27. Results Ksat 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