F1 Drainage fundamentals

Drainage Fundamentals

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Practical Drainage for Sportsturf, Golf, and Horticulture. Keith

McIntyre, Brent Jakobsen, Ann Arbor Press, 2000

Module A: Fundamentals

Pores space

Infiltration and Saturation & Field capacity

Gravity & Capillary action & Surface tension

Lateral movement, rising table and free water

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Soil Structure And Pore Space

Water content decreases due

to rate of drainage by

gravity

Remaining water held in narrow pores

Water is prevented from

moving: hydraulic

conductivity

HC is particle size transfer

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Drainage occurs when:

Pore spaces are filled

Gravity exceeds

surface tension

Gravity pulls water

downward

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Pore spaces

Soil particles fit imperfectly

Inter packing: sand/clays

Little room for air/water between particles

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Factors affecting Water intake and retention

Infiltration

Saturation

Field capacity

Hydraulic conductivityAdhesion and surface tension

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Infiltration rate

Irrigation should occur between stress point and

field capacity

Soil accepts water highest in this range Infiltration rate is variable

*if rain is falling faster than gravity can pull it down the profile, the surface will saturate

Runoff will occur

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Saturation

Saturation may occur at varying depths

Changes in soil profile affect saturation

Consistent soil profile is key to progressive water movement into

profile

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Field Capacity

Defn: moisture status of the soil, where gravity cannot pull more water from a

saturated profile.

Air space also critical for root growth.

Pore space allow roots to force their way through soil

% pore space = % root growth

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Water Adhesion to Soil particles

Coarse sand pores are large

Silt/clay pores are small

The finer the pores, the tighter the adhesion between particles

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Wilting point

Plants ceasing to extract water is called

“wilting point”

Only remaining water is held too tightly by

adhesion for plant use

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Surface Tension

Click icon to add clip art

The smaller the drop, the stronger

the tension

Dusts and insects on the water

surface shows tension

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Gravity

As depth increases, so

does the weight of water

All but capillary water is affected

by gravity

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Capillary Fringe

A saturated zone at the bottom of topsoil, above a

slow draining baseOften a winter problem

*if a hole is dug into the capillary fringe zone, no water will enter this hole even if the surrounding

soil is saturated

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Capillary Fringe

A saturated zone where no

lateral movement (to

drains) will occur

If a hole is dug into the capillary zone, it will NOT

fill with water

If a hole is dug below the

capillary fringe, it will fill with

water.(“head”)

Where head is greater than

surface tension, of menisci pores

it will drain

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Capillary action

Stronger than gravity

Water molecules are attracted to the

adhesive forces of surface molecules

Laterally pulled or vertically

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Capillary Action

If capillary sizes are the same

along the menisci, gravity will prevail

Water only moves as a result of

capillary forces until the soil reaches field

capacity.

Capillary water never moves through large

pores

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Lateral movement of water in soils

Lateral movement occurs slowly

Rarely moves more than 4” from source

Depends highly on pore space of soil

Capillary distances/movement is greater in silty clay vs sand (small vs large

pore space)

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Rising water table

Likely found in the middle of a

slope

Water at bottom of slope is

surface water problem

Flows along seams in gravel

profile

If shallow capped (with clay) it will

break the surface

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To alleviate rising water table (springs)

Locate the water source (piezometer)

Intercept at gravel layer

uphill

Install drainage to off-site

Result will avoid digging on

site/wet area

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Piezometer

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Natural Deep drainage

Non capillary pore spaces

Natural drainage through the subsoil

Into drain pipes installed (large

piping installed at construction stage)

Hydraulic conductivity greater

than.04mm/hr required in subsoil

Construction on dry soil is important for subsoil compaction

of pore space

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Free Water vs capillary fringe

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Drainage Fundamentals

Perched water table

Capillary Fringe and free water zones

Hydraulic conductivity

Drain Spacing: Hooghouts Formula

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Perched Water table

Fine textured material over a

coarse one

no water drains from a finer

material until capilary fringe is built above the

coarser material

If height of capillary fringe exceeds

topsoil, it will never drain

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How does a perched water table work?

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Height of Perched table

Determined by pore size distribution

Fine textured soil has deep saturated zone,

coarse is shallow29



Perched Heights

USGA sand = 5-9” perched table 1.5mm coarse

sand = 2” perched

4mm gravel = .75” perched

tableSurface tension (menisci) reaches equilibrium with

gravity and drainage stops

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Perched Water Table

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Perched water table

The saturated zone from bottom of profile to air entry point is called capillary fringe

Zero suction at base, no free water present

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Capillary fringe: Air entry point


McIntyre, Brent Jakobsen, Ann Arbor Press, 2000 33

The pull of gravity breaks surface tension of large pores,

which drains down profile

Field capacity is reached when no more water can be pulled from the profile-adhesion and

surface tension are equal

Capillary Fringe:

Click icon to add clip art



The only water that can move into subsoil

drains is from the free water zone

Capillary fringe



All movement of water ceases

when free water zone is drained

Continued drainage is

determined by rate of base

Movement into secondary profile

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Saturated Free water zone

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Saturated Free water zone

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Hydraulic conductivity: USGA spec( SHC)

Rate is affected by pore size

Water moves 100X faster

through a USGA sand root zone

than loam

When saturated, GRAVITY pulls

water downward faster

Field capacity is reaching

equilibrium of surface tension

and gravity

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Hydraulic conductivity: testing

Conductivity varies greatly by the amount of fines in the soil (silt)

Unusual for a soil to have greater than

2”/hr hydraulic conductivity

This conductivity requires a functioning perched water table

to grow turf

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Hydraulic Conductivity: Soil Types

• Surface grading and drainage critical

Silt/Clay Loam 20-45% fines particles<.1mm = .2-.4”/hr (5-10mm) *common on fairways

Sandy Loam >20%fines particles <.1mm = .4-2.0”/hr (10-50mm)

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Hydraulic conductivity:

Any sports turf field has to be drained to field capacity to allow play - top 2” of soil

Therefore: Free water zone must be drained down to field capacity

quickly

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Tube experiment: Moisture release curve



Hooghouts: Defined terms

D:

= drainage rate (“/hr) of saturated free water zone at midpoint

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Hooghouts Formula:

K:Saturated hydraulic conductivity of top soil in inches/hr

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Hooghouts Formula

H² is equivalent to Ha X Hb

Ha = height of saturated free water zone,Hb = height of saturated free water zone that water must flow through

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Hooghouts Formula

S² is equivalent to Sa X Sb

Sa = is the distance between drainsSb =distance between drains where component of the area water is collected

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Hooghouts formula: Calculating rate of drainage at midpoint

Calculations to reduce height of free water BETWEEN drains

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Practical Drainage for Sportsturf, Golf, and Horticulture. Keith McIntyre, Brent Jakobsen, Ann Arbor Press, 2000

Hydraulic conductivity

A description of various soils and conductivities

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Silt/Clay Loam

20-45% fines( particles less

than .1mm)

Common on fairways and sportsfields

Hydraulic conductivity:• .2-.4in/hr, 5-10 mm/hr

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Sandy Loam

Less than 20% fines (particles less than .1mm)

Contain fines, but sandier

Drain faster, but compact to low conductivity

Hydraulic conductivity:• .4-2in./hr, 10-50mm/hr

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Hydraulic Conductivity .2”/hr(no surface drainage)

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Slow draining base(no surface drainage)

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Hydraulic conductivity .8”/hr(no surface drainage)

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Hydraulic conductivity 2”/hr(no surface drainage)

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Summary: What does this tell us?

Water moves laterally very slowly

Traditional thinking of drainage is suspect

Drainage of base, is more important than

installing subsoil drains.

Explains why vibra-molling works so well•Opens up the base and makes it drain better

Subsoil must be sufficiently dry to

fracture – compaction while wet will make the surface impermeable.

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Summary

Effective drains need to be spaced close together, 3.3ft in

most soils

The base will remove water quicker than drains spaced

further apart

High organic soil content has high hydraulic conductivity

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Summary: Problem solving HC

Measure your soil

depth

Identify it’s hydraulic

conductivity

Test your drainage

base in a lab for

conductivity rate

Calculate drainage spacing using

Hooghouts

Determine if subsoil

drainage is really worth

it!

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Designing subsoil drains

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Discharge area: Subsoil drains

Decide where to discharge the waterDesign UP from discharge point (minimum 1:70)Have uniform fall on all pipes

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Discharge area: Subsoil drains

Open drainCreekBe aware what will happen during floodingDischarge must be above levelDesign the drain FROM the discharge point upwardUniform fall on all pipes

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Subsoil drain pattern:

Favoured design30-45% angleSmall laterals into larger mainFlexible corrugated tileJoints are offset from each other

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Determining pipe sizing

Manufacturers supply max flow performanceAs pipe length increases, friction loss increasesMain runs with the slopeLaterals run across slope

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A fall of .5ft in 49.5 ft is 1:99

Efficient and simpleLaterals same distance apartUniform drainage for the whole area

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Calculating pipe required

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How to size pipe

Assume area of 1ac (43,560ft sq)Uniform slope of 1:70, down 295 ft. no cross fallSubsoil drains spaced at 6.6ft, topsoil at 12” HC 2”/hrRainfall event of 2”/hr

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Example of racetrack drainage

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Sizing drains

High traffic area with subtle drain coverOff back of greenRealistic sizingNo additional labor for trimming/maintenance

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Principles of Subsoil Drainage

MigrationFilter material

Installation techniques

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Choosing the right filter material

Filter material should bemade on the basis of type or sand that will surround itIf the drain is in a fine soil, filter should be a coarse river sand-NOT GRAVEL!

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Migration of particles

Significant amount of fines enter the surrounding soilTHIS moves fines into the pipeQuickly collapses the drain, often during first few waterings

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Particle migration into coarser gravels

Common mistakes:Surround pipe with coarse gravel or crushPea gravel ¼ - 3/8” often specifiedOverall, these gravels are too large!!


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Filter material entering pipeWe are too worried about filter material entering the drain pipeIf gravel is used, smaller particles will migrate into the large pores

When to use gravel filter material

Only in USGA spec greens

D15 of the gravel must not exceed the D85 of the

sand zone

This is the “Bridging Factor”

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Clean filter material

Make sure no fines in the filter materialUse HC of the filter material >100”/hr (sand withought fines)Misconception: Sand will not enter drain pipe except from above. Surface area of slots is less that 1% of pipe surface area.

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Bridging factor

If gravel is too coarse, bridging factor will be too highUsing finer filter material prevents migration of particles from surrounding soil.

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Diameter rating

When installing subsoil drains, in any situation other than USGA sand, use clean washed sand. NOT pea gravel, or any gravel with a D15 less than 1mm. D15 means 15% of the filler is larger than the specified size, 85% spec.

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Installing subsoil drains

Cut into the area below the soil to be drainedMake sure sides are verticalAvoid subsoil contaminationProvide uniform slope

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Installing subsoil drains1. Clean vertical trenches2. 2” of sand at bottom of trench3. Even slope4. Correct high/low points 5. Lay slits on BOTTOM of trench

*water enters pipe from the bottom

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Installing subsoil drains

5. Cover the pipe with filter sand 2” surrounding

6. Firm down/light rolling7. Use commercial joints

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Geofabrics: Never wrap pipes

Fabric on drains are unnecessary

If correct sand has been used, fines will effectively pass through the drainage system

Geo textile drastically reduces drainage rates

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Types of pipes

Flexible slotted (agricultural)

2-8” diameterCommonly used is 4” outer diameterSlot size varyThese pipes self-clean, depositing fines though the ridgesThis process will not block pipes

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Types of drain pipes

PVC solid drain pipe – Improved

flow for collectors

Multi flow – slit drainage

Atlantis draincell http://www.atlantiscorp.com.au/video

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http://www.atlantiscorp.com.au/video



Common drainage mistakes

Incorrect backfill materialIncorrect pipe connectorsMisunderstanding of surface and subsurface drainage

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F1 Drainage fundamentals

Education

brent jakobsen

keith mcintyre

ann arbor press

drainage fundamentals

retention6practical

soils19practical drainage

saturation8practical

gravity13practical drainage