site instrumentation methods by jim richardson and mike vepraskas modified 9/08
TRANSCRIPT
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Site Instrumentation MethodsSite Instrumentation Methodsby
Jim Richardson andMike Vepraskas
Modified 9/08
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Overview
• Criteria for picking monitoring sites
• Selection of equipment and installation
• Data collection & interpretation
• Rainfall measurements
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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).
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Boundaries
In many cases you want to monitor across boundaries between:
• Wetland vs. Non-Wetland
• Hydric vs. Non-Hydric Soils
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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
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Hydric Hydric
Boundary?
Upland(Not hydric)
TRANSECT
PIEZOMETER AND WELL NESTS
TRAVERSE
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SOIL
Microtopography should be similar at an installation
Piezometers or wellswill give differentreadings
10 ft
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Where do you place your Instruments??
Potential hydric soil zone
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Where do you place your Instruments??
Monitoring Sites Hydric soil boundary
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Backswamp
Backplainflat Levee
Flood Plain
Till
Alluvium
Where do you place your instruments?
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Till
Alluvium
Flooding Depth and Duration are Important too
Flooded forShort duration(not hydric?)
Flooded and pondedFor long duration—Hydric soils
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Use Transects Across Hydric Boundaries
Wells and piezometers
Possible Boundaries
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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.
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Sand
Sand
Clay
Water drainsdown well,Saturation undetected
Well Piezometers
Shallow piezometercontains water, but lowerpiezometer does not. Perched water table detected.
Perched Water Table
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BwBw
AA
BkBkBtgBtg
Soil Descriptions Suggest Boundaries
Upland
BoundaryHydric Soil
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Overview
• Criteria for picking monitoring sites
• Selection of equipment and installation
• Data collection & interpretation
• Rainfall measurements
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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
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Wells and Piezometers
Wells aretubes thatcontain many holesto let waterin.
Piezometerscontain fewholes, and let water in mainly at theirbottom.
Wells showthe depthto the watertable
Piezometers showif soil aroundholes is saturated
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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
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Water flow
Dry
Ped
Dry
PED
Vertisols have large, continuous cracks that carry water deep into the soil when soil is dry
Wells havemany holes, and some holeswill be next to cracks
Water in well is from “Crack Flow”.Soil is not saturated
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AQUIFERSCONFINED & UNCONFINED
Confined aquifer- sand
Confining aquitard (clay)
SATURATEDZONE
UnconfinedAquifer- in soil
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0
Mucky Mineral
-75Sand
-169-170
Sand
Clay
Sand
Muck
“Domed” Organic Soil
Piezometer
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0 Surface
Mucky Mineral
-75Sand
-169-170
Organic
Sand
Clay
Sand
Muck
“Domed” Organic Soil forms over point of upwelling water?
Break in clayallows waterthrough
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Suffolk Scarp
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Dismal Swamp
Scarp
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Suffolk Scarp
Saturated Sand (confined aquifer)
Clay confining layer
Stream
Sandy loam
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Stream has cut throughConfining layer.Water from confinedsand flows into channel.
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If stream is dammed, water flows onto plain.
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Thick organicdeposits form on plain.Dismal Swamp
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Stratified Soil with Confined Aquifer
A-horizon (Loam)
E-horizon (Loam)
Bt-horizon (CLAY)
C- LOESS (silt)
Btb-PALEOSOL (CLAY)
SUGGESTION: Place wells in surface aquifers down to confining layer. Place piezometers in confined aquifers.
Where do you place your piezometers?
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A-(Loam
E-(Loam)
Bt (CLAY)
C- LOESS
Btb-PALEOSOL (CLAY)
slots
Avoid:Piez. Willnot fill in clays
Ideal:PiezometersIn permeablelayers
Well
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A-(Loam
E-(Loam)
Bt (CLAY)
C- LOESS
Btb-PALEOSOL (CLAY)
Recharge - EpiSATURATED or Recharge - EpiSATURATED or PERCHEDPERCHED
Water levels
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A-(Loam
E-(Loam)
Bt (CLAY)
C- LOESS
Btb-PALEOSOL (CLAY)
Discharge - EndoSATURATEDDischarge - EndoSATURATED
Water levels
Water in loessUnder pressure:Artesion Condition
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Basic PiezometerInstallation Method
Sand Pack~ 3” aboveslots
Backfill with soil, packed well
Loose Cap: usePop (soda) can
Surface ConeSoil or bentonite + soil
(2:1) mix for sandy soils. Carefully packed. Check
every visit.
Drill air holeIn tube if capIs tight
Bentonite Seal 3 to 6 inches
3+”
6” of Well Screen or slots
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Basic WellInstallation Method
Sand Pack
Loose Cap: usePop (soda) can
Surface ConeSoil or bentonite + soil
(2:1) mix for sandy soils. Carefully packed. Check
every visit.
Drill air holeIn tube if capIs tight
3+”
Bentonite Seal 3 to 6 inches
Well Screen or slots over depth of interest
Backfill with soil, packed well
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Fabric Covers or Socks for Wellsand Piezometers
Sand andSoil may fallinto holes in Wells andPiezometers.
Cover holesWith porousfabric.
Can use”•Geotextile,•Drain Sock, •Women’s nylons
Tape
Knot atbottom
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For Flooded Sites Use a Surface MarkerAlong with wells and piezometers
Gauge showingwater heightabove surface
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High Water TableIndicator
Stolt, Univ. Rhode Island Well pipe cut in halfTo see inside
Magnet
Steel rod
Cork Float
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High water mark, Reset after measurement
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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.
Another Type ofWell Recorder
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Overview
• Criteria for picking monitoring sites
• Selection of equipment and installation
• Data collection & interpretation
• Rainfall measurements
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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).
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Typical Wetland HydrographTypical Wetland Hydrograph
Time (Months)
SummerET
Fall Rising Limb
Winter Peak
SpringFalling Limb
Wat
er T
able
Dep
th (
cm)
Surfaceponded
Saturated < 30cm-30cm
Jan. July Dec
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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.
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Recharge
Discharge
Water levels in piezometers differ with depth in recharge and discharge areas
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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.
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2 ft.
6 ft.
Finding the Water Table with Piezometers
Piezometers
Where is the water table in this soil?
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2 ft.
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
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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.
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Influence of Drainable Porosity on watertable fluctuation
-250
-200
-150
-100
-50
0
N D J F M A M J J A S O N D J F M A M J J A S O N D J F M
Wat
er T
able
Dep
th (
cm)
Low drainable porosity (muchfluctuation)
High drainableporosity (littlefluctuation)
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Drainable Porosity
Is roughly the Volume of Air-Filled PorosityWhen 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.
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Low Drainable Porosity
1 inch of rain raiseswater tableby 10 inchesbecause of lowamount ofPore Space
Rock with nointernal pores
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High Drainable Porosity
1 inch of rain raiseswater tableby 2 inchesbecause of highamount ofPore Space
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Very porouslayer of organic
soil
1 inch of rainmust fill much
pore space to saturate
soil
Little water table Fluctuation in thiszone
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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.
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This device is bestfor soils withLow Drainable Porosity, where weeklyreadings are made
Magnet
Steel rod
Cork Float
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RECHARGE
FLOWTHROUGHDISCHARGE
Water Table Fluctuations in Discharge Areas
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Carolina Bays
Carolina BaysOval-shaped depressions oriented
In a NW-SE direction
N
1.6 km(1 mile)
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This Bay has ridges on westernand eastern sides”
Does GroundWater flowInto Bay here?
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Water Balance for Juniper Bay Today (2002-03)
Storage6 mm
WetlandGroundwater
Inflow-Outflow543 mm
SurfaceOutflow707 mm
Precip.1115 mm
PET845 mm
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Well on East Side of BayHourly water table levels
-50
-48
-46
-44
-42
-40
8/1 8/6 8/11
D
Dep
th (
in.)
Days
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-50
-48
-46
-44
-42
-40
8/1 8/6 8/11
D
Dep
th (
in.)
Days
Fall in water tableduring daydue to Et
Sawtooth PatternCaused by ground water inflow
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-50
-48
-46
-44
-42
-40
8/1 8/6 8/11
D
Dep
th (
in.)
Days
Rise in water tableat night
due to groundwater inflow
Wetland is Discharge Area
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Well at Center of Bay
-45
-40
-35
-30
-25
-20
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
Wat
er T
able
Dep
th (
in.)
No daily fluctuation: no ground-water inflow
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Discharge
Flowthrough
Recharge
Gi=Go
Gi>Go
Today
Gi<Go
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Overview
• Criteria for picking monitoring sites
• Selection of equipment and installation
• Data interpretation• Rainfall measurements
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Rain gauge
Net Radiometer
Solar Panel
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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
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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
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Rain gauge located in clearing at a distance from the trees that Is equal to twice the height of the trees
Gauge30 in. aboveground
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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.
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0
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F M A M J J A S O N D J F
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ain
fall
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Weather Station
Northwest
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Southwest
Rainfall Variability for a 750 acre Site
Gauges not working
How Many Gauges Do You Need?
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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.
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Acceptable RainfallAcceptable 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.
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WETS Station : GREENVILLE 2, NC3638 Creation Date: 10/23/2002 Latitude: 3537 Longitude: 07723 Elevation: 00030 State FIPS/County(FIPS): 37147 County Name: Pitt Start yr. - 1971 End yr. - 2000 -------------------------------------------------------------------------| | Temperature | Precipitation | | (Degrees F.) | (Inches) | |-----------------------|--------------------------------------| | | | | | 30% chance |avg | | | | | | | will have |# of| avg | |-------|-------|-------| |-----------------|days| total| Month | avg | avg | avg | avg | less | more |w/.1| snow | | daily | daily | | | than | than | or| fall | | max | min | | | | |more| | -------------------------------------------------------------------------| January | 52.0 | 31.0 | 41.5 | 4.42 | 3.53 | 5.33 | 8 | 0.9 | February | 55.8 | 33.2 | 44.5 | 3.45 | 2.34 | 4.16 | 6 | 1.4 | March | 63.9 | 40.2 | 52.0 | 4.07 | 3.19 | 4.83 | 7 | 0.6 | April | 73.0 | 47.9 | 60.5 | 3.19 | 2.18 | 4.31 | 5 | 0.0 | May | 79.9 | 56.8 | 68.3 | 4.04 | 2.79 | 5.01 | 7 | 0.0 | June | 86.2 | 64.7 | 75.5 | 4.46 | 3.00 | 5.25 | 7 | 0.0 | July | 89.9 | 69.4 | 79.7 | 5.24 | 3.75 | 6.45 | 7 | 0.0 | August | 88.1 | 67.8 | 77.9 | 5.89 | 3.65 | 7.03 | 7 | 0.0 | September | 82.9 | 61.9 | 72.4 | 5.50 | 2.78 | 7.13 | 6 | 0.0 | October | 73.5 | 48.9 | 61.2 | 3.27 | 2.00 | 4.34 | 4 | 0.0 | November | 64.7 | 40.4 | 52.6 | 2.85 | 2.03 | 3.46 | 5 | 0.0 | December | 55.6 | 33.6 | 44.6 | 3.23 | 2.10 | 4.02 | 6 | 0.4 | ----------|-------|-------|-------|--------|--------|--------|----|------| ----------|-------|-------|-------|--------|--------|--------|----|------| Annual | ----- | ----- | ----- | ------ | 44.45 | 52.35 | -- | ---- | ----------|-------|-------|-------|--------|--------|--------|----|------| Average | 72.1 | 49.7 | 60.9 | ------ | ------ | ------ | -- | ---- | ----------|-------|-------|-------|--------|--------|--------|----|------| Total | ----- | ----- | ----- | 49.61 | ------ | ------ | 75 | 3.4 | ----------|-------|-------|-------|--------|--------|--------|----|------| -------------------------------------------------------------------------| GROWING SEASON DATES --------------------------------------------------------------------------- | Temperature ---------------------|----------------------------------------------------- Probability | 24 F or higher | 28 F or higher | 32 F or higher | ---------------------|-----------------|-----------------|----------------- | Beginning and Ending Dates | Growing Season Length | 50 percent * | 2/22 to 11/28 | 3/15 to 11/16 | 3/28 to 11/ 1 | 280 days | 246 days | 218 days | | | 70 percent * | 2/16 to 12/ 4 | 3/ 9 to 11/23 | 3/23 to 11/ 6 | 293 days | 259 days | 228 days | | | --------------------------------------------------------------------------- * Percent chance of the growing season occurring between the Beginning and Ending dates.
WETS Data TableWETS Data Table
Precipitation data
Enlarged next slide
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WETS Station : GREENVILLE 2, NC3638 Creation Date: 10/23/2002 Latitude: 3537 Longitude: 07723 Elevation: 00030 State FIPS/County(FIPS): 37147 County Name: Pitt Start yr. - 1971 End yr. - 2000 -------------------------------------------------------------------------| | Temperature | Precipitation | | (Degrees F.) | (Inches) | |-----------------------|--------------------------------------| | | | | | 30% chance |avg | | | | | | | will have |# of| avg | |-------|-------|-------| |-----------------|days| total| Month | avg | avg | avg | avg | less | more |w/.1| snow | | daily | daily | | | than | than | or| fall | | max | min | | | | |more| | -------------------------------------------------------------------------| January | 52.0 | 31.0 | 41.5 | 4.42 | 3.53 | 5.33 | 8 | 0.9 | February | 55.8 | 33.2 | 44.5 | 3.45 | 2.34 | 4.16 | 6 | 1.4 | March | 63.9 | 40.2 | 52.0 | 4.07 | 3.19 | 4.83 | 7 | 0.6 | April | 73.0 | 47.9 | 60.5 | 3.19 | 2.18 | 4.31 | 5 | 0.0 | May | 79.9 | 56.8 | 68.3 | 4.04 | 2.79 | 5.01 | 7 | 0.0 | June | 86.2 | 64.7 | 75.5 | 4.46 | 3.00 | 5.25 | 7 | 0.0 | July | 89.9 | 69.4 | 79.7 | 5.24 | 3.75 | 6.45 | 7 | 0.0 | August | 88.1 | 67.8 | 77.9 | 5.89 | 3.65 | 7.03 | 7 | 0.0 | September | 82.9 | 61.9 | 72.4 | 5.50 | 2.78 | 7.13 | 6 | 0.0 | October | 73.5 | 48.9 | 61.2 | 3.27 | 2.00 | 4.34 | 4 | 0.0 | November | 64.7 | 40.4 | 52.6 | 2.85 | 2.03 | 3.46 | 5 | 0.0 | December | 55.6 | 33.6 | 44.6 | 3.23 | 2.10 | 4.02 | 6 | 0.4 | ----------|-------|-------|-------|--------|--------|--------|----|------| ----------|-------|-------|-------|--------|--------|--------|----|------| Annual | ----- | ----- | ----- | ------ | 44.45 | 52.35 | -- | ---- | ----------|-------|-------|-------|--------|--------|--------|----|------| Average | 72.1 | 49.7 | 60.9 | ------ | ------ | ------ | -- | ---- | ----------|-------|-------|-------|--------|--------|--------|----|------| Total | ----- | ----- | ----- | 49.61 | ------ | ------ | 75 | 3.4 | ----------|-------|-------|-------|--------|--------|--------|----|------| -------------------------------------------------------------------------| GROWING SEASON DATES --------------------------------------------------------------------------- | Temperature ---------------------|----------------------------------------------------- Probability | 24 F or higher | 28 F or higher | 32 F or higher | ---------------------|-----------------|-----------------|----------------- | Beginning and Ending Dates | Growing Season Length | 50 percent * | 2/22 to 11/28 | 3/15 to 11/16 | 3/28 to 11/ 1 | 280 days | 246 days | 218 days | | | 70 percent * | 2/16 to 12/ 4 | 3/ 9 to 11/23 | 3/23 to 11/ 6 | 293 days | 259 days | 228 days | | | --------------------------------------------------------------------------- * Percent chance of the growing season occurring between the Beginning and Ending dates.
WETS Data TableWETS Data Table
GrowingSeason
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USDA-NRCS’s WETS TABLEUSDA-NRCS’s WETS TABLE
Defines Normal RainfallDefines Normal Rainfall
Month 30th Percentile 70th Percentile
June 3.01 5.25July 3.75 4.31
August 3.65 6.45September 2.78 7.13
October 2.01 4.34
Normal rainfall for August is: 3.65 to 6.45 inches
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Summary
• Select sites that represent large areas
• Pay attention to microtopography
• Use wells for water table measuremens, and piezometers to find saturation depths
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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
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