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Site Instrumentation Methods by Jim Richardson and Mike Vepraskas PowerPoint Presentation
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Site Instrumentation Methods by Jim Richardson and Mike Vepraskas

Site Instrumentation Methods by Jim Richardson and Mike Vepraskas

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Site Instrumentation Methods by Jim Richardson and Mike Vepraskas

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  1. Site Instrumentation Methods by Jim Richardson and Mike Vepraskas Modified 9/08

  2. Overview • Criteria for picking monitoring sites • Selection of equipment and installation • Data collection & interpretation • Rainfall measurements

  3. Selecting Sites to Monitor • Pick sites that are representative of a large area--both in terms of landscape position and microtopography • Pick at least one site in an area known to be hydric, and one site in the upland (transect). • Replicate sites at the same landscape position (traverse).

  4. Boundaries In many cases you want to monitor across boundaries between: • Wetland vs. Non-Wetland • Hydric vs. Non-Hydric Soils

  5. Think Shallow • Hydric soils are saturated either on the surface or within 12 in. of the surface. • Do not focus too deeply • Be sure to monitor within 12 in. of surface

  6. PIEZOMETER AND WELL NESTS TRAVERSE TRANSECT Upland (Not hydric) Hydric Boundary? Hydric

  7. SOIL Microtopography should be similar at an installation 10 ft Piezometers or wells will give different readings

  8. Where do you place your Instruments? Potential hydric soil zone

  9. Where do you place your Instruments? Monitoring Sites Hydric soil boundary

  10. Flood Plain Backplain flat Levee Backswamp Alluvium Till Where do you place your instruments?

  11. Flooding Depth and Duration are Important too Flooded and ponded For long duration— Hydric soils Flooded for Short duration (not hydric?) Alluvium Till

  12. Use Transects Across Hydric Boundaries Wells and piezometers Possible Boundaries

  13. Soils Considerations • Complete a profile description for each plot where equipment will be installed. • Estimate the depth to any layers that may perch water for long periods, and any sand deposits. • From the description, estimate the depths that wells and piezometers will be installed.

  14. Perched Water Table Piezometers Well Sand Clay Sand Shallow piezometer contains water, but lower piezometer does not. Perched water table detected. Water drains down well, Saturation undetected

  15. Upland Boundary Hydric Soil Soil Descriptions Suggest Boundaries A Bw Bk Btg

  16. Overview • Criteria for picking monitoring sites • Selection of equipment and installation • Data collection & interpretation • Rainfall measurements

  17. Finding the Water Table • Wells should be used to identify water tables. • Piezometers measure pressure, and not the free water surface. • Wells work best when they don’t penetrate a layer that is perching water or intersect large cracks

  18. Wells and Piezometers Wellsare tubes that contain many holes to let water in. Piezometers contain few holes, and let water in mainly at their bottom. Wells show the depth to the water table Piezometers show if soil around holes is saturated

  19. Piezometers vs. Wells • We suggest placing one well at each site whenever you need to know where the water table is. • Piezometers should be used to conform to the technical standard (one in the upper 10 in.) • Do not use wells in Vertisols or any other clayey soil where bypass (crack) flow can occur

  20. Vertisols have large, continuous cracks that carry water deep into the soil when soil is dry Water flow Wells have many holes, and some holes will be next to cracks Dry Ped Water in well is from “Crack Flow”. Soil is not saturated Dry PED

  21. AQUIFERSCONFINED & UNCONFINED Unconfined Aquifer- in soil SATURATED ZONE Confining aquitard (clay) Confined aquifer- sand

  22. “Domed” Organic Soil Piezometer Muck Sand Clay Sand 0 Mucky Mineral -75 Sand -169 -170

  23. “Domed” Organic Soil forms over point of upwelling water? Muck Break in clay allows water through Sand Clay Sand 0 Surface Organic Mucky Mineral -75 Sand -169 -170

  24. Suffolk Scarp

  25. Dismal Swamp Scarp

  26. Suffolk Scarp Stream Sandy loam Clay confining layer Saturated Sand (confined aquifer)

  27. Stream has cut through Confining layer. Water from confined sand flows into channel.

  28. If stream is dammed, water flows onto plain.

  29. Thick organic deposits form on plain. Dismal Swamp

  30. Stratified Soil with Confined Aquifer Where do you place your piezometers? A-horizon (Loam) SUGGESTION: Place wells in surface aquifers down to confining layer. Place piezometers in confined aquifers. E-horizon (Loam) Bt-horizon (CLAY) C- LOESS (silt) Btb-PALEOSOL (CLAY)

  31. slots Ideal: Piezometers In permeable layers Avoid: Piez. Will not fill in clays Well A-(Loam E-(Loam) Bt (CLAY) C- LOESS Btb-PALEOSOL (CLAY)

  32. Recharge - EpiSATURATED or PERCHED A-(Loam E-(Loam) Bt (CLAY) Water levels C- LOESS Btb-PALEOSOL (CLAY)

  33. Discharge - EndoSATURATED A-(Loam Water levels E-(Loam) Water in loess Under pressure: Artesion Condition Bt (CLAY) C- LOESS Btb-PALEOSOL (CLAY)

  34. Backfill with soil, packed well Surface Cone Soil or bentonite + soil (2:1) mix for sandy soils. Carefully packed. Check every visit. Bentonite Seal 3 to 6 inches Sand Pack ~ 3” above slots 6” of Well Screen or slots 3+” Loose Cap: use Pop (soda) can Basic Piezometer Installation Method Drill air hole In tube if cap Is tight

  35. Surface Cone Soil or bentonite + soil (2:1) mix for sandy soils. Carefully packed. Check every visit. Backfill with soil, packed well Bentonite Seal 3 to 6 inches Sand Pack Well Screen or slots over depth of interest 3+” Loose Cap: use Pop (soda) can Basic Well Installation Method Drill air hole In tube if cap Is tight

  36. Fabric Covers or Socks for Wells and Piezometers Cover holes With porous fabric. Tape Sand and Soil may fall into holes in Wells and Piezometers. • Can use” • Geotextile, • Drain Sock, • Women’s nylons Knot at bottom

  37. For Flooded Sites Use a Surface Marker Along with wells and piezometers Gauge showing water height above surface

  38. Steel rod Cork Float High Water Table Indicator Stolt, Univ. Rhode Island Well pipe cut in half To see inside Magnet

  39. High water mark, Reset after measurement

  40. Another Type of Well Recorder This is Circular 1409, http://edis.ifas.ufl.edu/CH151. B. J. Boman, and T. A. Obreza, Cooperative Extension Service, University of Florida Gainesville, FL 32611.

  41. Overview • Criteria for picking monitoring sites • Selection of equipment and installation • Data collection & interpretation • Rainfall measurements

  42. Time to Make Readings • Collect data weekly during a critical time of year when water levels are “high” (usually winter, spring, and fall). • Monthly readings may be adequate when water levels are low (e.g. in summer).

  43. Jan. July Dec Typical Wetland Hydrograph Winter Peak Summer ET ponded Surface Saturated < 30cm Water Table Depth (cm) -30cm Spring Falling Limb Fall Rising Limb Time (Months)

  44. How often do you make measurements? • Measure at least weekly • Daily measurements are needed for some modeling work • If you use automated systems, set for daily measurements, and visit monthly.

  45. Water levels in piezometers differ with depth in recharge and discharge areas Recharge Discharge

  46. Piezometer Readings • Data must be plotted separately for each piezometer. • Note when free water present at depth of slotted portion of tube. • Can plot depth of water or plot “saturated”or “not saturated” as a bar over time.

  47. Finding the Water Table with Piezometers Where is the water table in this soil? 2 ft. Piezometers 6 ft.

  48. If you must use a piezometer to identify a water table,then use the water level in the shallowest piezometer for your estimate Water table 2 ft. 6 ft.

  49. Water Table Fluctuations during rain events • In some soils, water tables move up and down quickly during and after a rain. • In other soils, there is much less fluctuation. • The amount the water table rises during a rain is related to the soils drainable porosity.