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

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

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).

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

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

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

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

Where do you place your Instruments? Potential hydric soil zone

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

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

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

Use Transects Across Hydric Boundaries Wells and piezometers Possible Boundaries

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.

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

A Bw Bk Btg Soil Descriptions Suggest Boundaries Upland Boundary Hydric Soil A Bw Fig. 3.32. Based on Knuteson et al. 1989, Seelig and Richardson, 1992 and Richardson et al. 1992 we developed a generalized soil-landscape model with Simmonson’s (1959) generalized theory of soil genesis conditions or losses, gains, and translocations marked. Bk Btg

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

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

Wells and Piezometers Wells are Piezometers 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

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

Wells have many holes, and some holes will be next to cracks 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 Fig. 3.7 By-Pass flow based on Bouma ( ). The factors influencing by pass flow are listed above the figure. High rain intensity, low water quality, steep relief, silt loams versus sands, water repellent soils, and wet soils have lower by pass flow than their counterparts. Water in well is from “Crack Flow”. Soil is not saturated Dry PED

AQUIFERS CONFINED & UNCONFINED Aquifer- in soil SATURATED ZONE Confining aquitard (clay) Confined aquifer- sand

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

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

Suffolk Scarp

Dismal Swamp Scarp

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

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

If stream is dammed, water flows onto plain.

Thick organic deposits form on plain. Dismal Swamp

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)

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

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

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

Soil or bentonite + soil Carefully packed. Check Loose Cap: use Pop (soda) can Basic Piezometer Installation Method Drill air hole In tube if cap Is tight 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 ~ 3” above slots 6” of Well Screen or slots 3+”

Soil or bentonite + soil Carefully packed. Check Loose Cap: use Pop (soda) can Basic Well Installation Method Drill air hole In tube if cap Is tight 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+”

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

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

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

High water mark, Reset after measurement

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.

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

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).

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

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.

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

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.

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

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.

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.

Influence of Drainable Porosity on water table fluctuation High drainable porosity (little fluctuation) Low drainable porosity (much fluctuation)

Drainable Porosity Is roughly the Volume of Air-Filled Porosity When soil is wet to Field Capacity. It is related to the volume of macropores, or large cracks, root channels, and pores between sands and gravels.

Low Drainable Porosity 1 inch of rain raises water table by 10 inches because of low amount of Pore Space Rock with no internal pores

High Drainable Porosity 1 inch of rain raises water table by 2 inches because of high amount of Pore Space

Very porous layer of organic soil 1 inch of rain must fill much pore space to saturate soil Little water table Fluctuation in this zone

Soils with Low Drainable Porosity Water table fluctuation is large: Water tables may rise 2 ft. or more after a large rain event, and also fall within several days. Water tables need to be read weekly or more often in these soils. Unless water tables are read daily, you aren’t recording maximum level.

This device is best for soils with Low Drainable Porosity, where weekly readings are made Steel rod Magnet Cork Float

Water Table Fluctuations in Discharge Areas RECHARGE FLOWTHROUGH DISCHARGE Fig. 3.20. Illustrations of recharge and discharge in a landscape (after Richardson et al. 1992).

Oval-shaped depressions oriented Carolina Bays 1.6 km (1 mile) Carolina Bays Oval-shaped depressions oriented In a NW-SE direction N

This Bay has ridges on western and eastern sides” Does Ground Water flow Into Bay here?

Water Balance for Juniper Bay Today (2002-03) PET 845 mm Precip. 1115 mm Surface Outflow 707 mm Storage 6 mm Wetland Groundwater Inflow-Outflow 543 mm

Well on East Side of Bay Hourly water table levels Days Depth (in.)

Sawtooth Pattern Caused by ground water inflow Days Depth (in.) Fall in water table during day due to Et

Wetland is Discharge Area Days Depth (in.) Rise in water table at night due to groundwater inflow

Well at Center of Bay Water Table Depth (in.) 8/1/02 8/2/02 8/3/02 8/4/02 8/5/02 8/6/02 8/7/02 8/8/02 8/9/02 8/10/02 8/11/02 8/12/02 8/13/02 8/14/02 -20 No daily fluctuation: no ground- water inflow -25 -30 Water Table Depth (in.) -35 -40 -45

Recharge Today Flowthrough Discharge Gi=Go Gi<Go Gi>Go

Overview Criteria for picking monitoring sites Selection of equipment and installation Data interpretation Rainfall measurements

Rain gauge Solar Panel Net Radiometer

Rainfall Daily rainfall measurements are critical for identifying years or “normal” rainfall Each site should be instrumented with an automatic recorder A manual recordering gauge is needed (essential) for backup

Rainfall Locate the gauge on level ground, about 30 in. or more above the surface. The gauge needs to be in the clear, at a distance of twice the height of the nearest obstruction

Rain gauge located in clearing at a distance from the trees that Is equal to twice the height of the trees Gauge 30 in. above ground

Rainfall cont’d. Nearest available weather stations usually aren’t “near enough” for daily data Be sure to protect gauges against bird droppings--install wires that cut feet.

Rainfall Variability for a 750 acre Site How Many Gauges Do You Need? Gauges not working

Points on Rainfall Rainfall data are just as important as water table data. One gauge per 750 acres is adequate—if the gauge is working More rain gauges are fine, but they increase the chance that one or more gauges will fail. Use only the amount of equipment you can keep in working order.

Acceptable Rainfall Rainfall can be within a range that is either normal (or drier than normal). Wetter than normal rainfall is not acceptable Normal rainfall is defined as a range on the WETS Tables.

WETS Data Table Precipitation data Enlarged next slide

WETS Data Table Growing Season

USDA-NRCS’s WETS TABLE Defines Normal Rainfall Normal rainfall for August is: 3.65 to 6.45 inches

Summary Select sites that represent large areas Pay attention to microtopography Use wells for water table measuremens, and piezometers to find saturation depths

Summary Install wells and piezometers so they don’t leak by by-pass flow from surface. Read instruments weekly, and be sure to visit site monthly if using automated equipment Measure rainfall whenever possible