Site Instrumentation MethodsSite Instrumentation Methodsby

Jim Richardson andMike 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

Hydric Hydric

Boundary?

Upland(Not hydric)

TRANSECT

PIEZOMETER AND WELL NESTS

TRAVERSE

SOIL

Microtopography should be similar at an installation

Piezometers or wellswill give differentreadings

10 ft

Where do you place your Instruments??

Potential hydric soil zone

Where do you place your Instruments??

Monitoring Sites Hydric soil boundary

Backswamp

Backplainflat Levee

Flood Plain

Till

Alluvium

Where do you place your instruments?

Till

Alluvium

Flooding Depth and Duration are Important too

Flooded forShort duration(not hydric?)

Flooded and pondedFor long duration—Hydric soils

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.

Sand

Sand

Clay

Water drainsdown well,Saturation undetected

Well Piezometers

Shallow piezometercontains water, but lowerpiezometer does not. Perched water table detected.

Perched Water Table

BwBw

AA

BkBkBtgBtg

Soil Descriptions Suggest Boundaries

Upland

BoundaryHydric Soil

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 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

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

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

AQUIFERSCONFINED & UNCONFINED

Confined aquifer- sand

Confining aquitard (clay)

SATURATEDZONE

UnconfinedAquifer- in soil

0

Mucky Mineral

-75Sand

-169-170

Sand

Clay

Sand

Muck

“Domed” Organic Soil

Piezometer

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

Suffolk Scarp

Dismal Swamp

Scarp

Suffolk Scarp

Saturated Sand (confined aquifer)

Clay confining layer

Stream

Sandy loam

Stream has cut throughConfining layer.Water from confinedsand flows into channel.

If stream is dammed, water flows onto plain.

Thick organicdeposits form on plain.Dismal Swamp

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?

A-(Loam

E-(Loam)

Bt (CLAY)

C- LOESS

Btb-PALEOSOL (CLAY)

slots

Avoid:Piez. Willnot fill in clays

Ideal:PiezometersIn permeablelayers

Well

A-(Loam

E-(Loam)

Bt (CLAY)

C- LOESS

Btb-PALEOSOL (CLAY)

Recharge - EpiSATURATED or Recharge - EpiSATURATED or PERCHEDPERCHED

Water levels

A-(Loam

E-(Loam)

Bt (CLAY)

C- LOESS

Btb-PALEOSOL (CLAY)

Discharge - EndoSATURATEDDischarge - EndoSATURATED

Water levels

Water in loessUnder pressure:Artesion Condition

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

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

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

For Flooded Sites Use a Surface MarkerAlong with wells and piezometers

Gauge showingwater heightabove surface

High Water TableIndicator

Stolt, Univ. Rhode Island Well pipe cut in halfTo see inside

Magnet

Steel rod

Cork Float

High water mark, Reset after measurement

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

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 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

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.

Recharge

Discharge

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

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.

2 ft.

6 ft.

Finding the Water Table with Piezometers

Piezometers

Where is the water table in this soil?

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

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 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)

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.

Low Drainable Porosity

1 inch of rain raiseswater tableby 10 inchesbecause of lowamount ofPore Space

Rock with nointernal pores

High Drainable Porosity

1 inch of rain raiseswater tableby 2 inchesbecause of highamount ofPore Space

Very porouslayer of organic

soil

1 inch of rainmust fill much

pore space to saturate

soil

Little water table Fluctuation in thiszone

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 bestfor soils withLow Drainable Porosity, where weeklyreadings are made

Magnet

Steel rod

Cork Float

RECHARGE

FLOWTHROUGHDISCHARGE

Water Table Fluctuations in Discharge Areas

Carolina Bays

Carolina BaysOval-shaped depressions oriented

In a NW-SE direction

N

1.6 km(1 mile)

This Bay has ridges on westernand eastern sides”

Does GroundWater flowInto Bay here?

Water Balance for Juniper Bay Today (2002-03)

Storage6 mm

WetlandGroundwater

Inflow-Outflow543 mm

SurfaceOutflow707 mm

Precip.1115 mm

PET845 mm

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

-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

-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

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

Discharge

Flowthrough

Recharge

Gi=Go

Gi>Go

Today

Gi<Go

Overview

• Criteria for picking monitoring sites

• Selection of equipment and installation

• Data interpretation• Rainfall measurements

Rain gauge

Net Radiometer

Solar Panel

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

Gauge30 in. aboveground

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.

0

200

400

600

800

1000

1200

F M A M J J A S O N D J F

Month

Cu

mm

ula

tiv

eR

ain

fall

(mm

)

Weather Station

Northwest

Southeast

Southwest

Rainfall Variability for a 750 acre Site

Gauges not working

How Many Gauges Do You Need?

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 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.

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

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

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

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