DRIP IRRIGATION SYSTEM

1
DRIP IRRIGATION SYSTEM

• by
• Albert Jarrett
• Professor of Biological Engineering
• Penn State University

2
The Pennsylvania Protocol

• In Chapter 73 (Conventional).
• In-Ground Systems (Limiting Zone gt60 in).
• Beds.
• Trenches.
• Subsurface Sand Filters.
• Elevated Sand Mounds (Limiting Zone gt20 in).
• Individual Residential Spray Irrigation System
• Bedrock Limiting Zone gt 16 in.
• Water Table Limiting Zone gt10 in.

3
Drip Irrigation

• Drip Irrigation is an Alternate On-Lot Disposal
  System.
• The followings present the drip irrigation
  system concept in some detail.
• This presentation ends with an example that shows
  the design process.

4
Soil Conditions

• Rock Limiting Zone 26 inches.
• Seasonal High Water Table Limiting Zone 20
  inches.
• Slope 25.

26 inches
20 inches
5
Soil Conditions

• No Perc Test is required.
• Soil profile must be evaluated by a licensed soil
  scientist who evaluates the probes.
• Soils must be well drained or moderately well
  drained.

6
Soil Conditions

• Soil Scientists Report
• Maximum soil linear load rate (Gal/ft/d) based
  on maximum daily flow
• Horizontal linear load (Gal/d) based on average
  daily flow.
• Depth of drip tubing.
• Minimum spacing between drip tubes.

7
Drip Irrigation Overview w/ Aerobic Tank
Hydraulic Unit

• Major Components

Hydraulic Pump Tank
Filtration
Treatment Tank
Zones
8
Drip Irrigation Overview w/ Sand Filter
Hydraulic Unit

• Major Components

Hydraulic Pump Tank
Treatment Tank
Zones
Filtration
9
Treatment Processes

• From Home to Treatment Tank.
• Septic Tank
• Solids settle
• Scum floats to surface
• Two Chamber Septic Tanks required.

10
Treatment Tank

• Two-Chamber Septic Tank

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Treatment Processes

• From the Treatment Tank to the Filtration Unit.
• Secondary Treatment is required if Limiting Zone
  lt 48 inches.
• Aerobic Treatment Tank
• Free Access Sand Filter (5 gal/d/ft2)
• Subsurface Sand Filter (0.8 gal/d/ft2)

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Aerobic Treatment Tank
13
Free Access Sand Filter (side view)
14
Free Access Sand Filter (top view)
15
Subsurface Sand Filter (partial side view)
16
Subsurface Sand Filter(top view)
17
Treatment Processes

• From the Filtration Unit to the Hydraulic Unit to
  the Drip Zones.
• The filtered effluent flows by gravity into the
  Hydraulic Unit Pump Tank
• Here a series of float switches controls the flow
  of partially treated wastewater to the Hydraulic
  Unit.
• The Hydraulic Unit is 2 (or 3) disc filters that
  provide final filtration before application to
  the soil.

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Hydraulic Unit Pump Tank

• Pump Tank
• Receives Filter Unit effluent
• Doses effluent to Hydraulic Unit and Zones.
• Contains pump-control switches.

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Hydraulic Unit

• Contains 2 (or 3) disc filters.
• Provides final filtration before going to drip
  zones.
• Must have at least 2 zones.

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Drip Zones
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Drip Zones

• Each long section of a zone is on the contour.
• Each zone may have more than one lateral.
• Each lateral may have more than one zone.
• Each zone must have a supply and return line.
• Air vents are also required on each zone.

22
Drip System

• With Water Limiting Zone 20 inches.

20 inches
0 to 12 in deep 6 to 12 in of cover over the
tubing.
Emitters spaced 2 feet apart 0.68 gal/d/em
Maybe as small as 8 in
23
Drip System

• With Rock Limiting Zone 26 inches.

20 inches
0 to 12 in deep 6 to 12 in of cover over the
tubing.
Emitters spaced 2 feet apart 0.68 gal/d/em
24
Drip System 3rd Configuration

• With Rock Limiting Zone 20 inches.

Driplines laid on soil surface and covered with
native topsoil.
Emitters spaced 2 feet apart 0.65 gal/d/em
20 inches
25
Simple Example

• A site with a 3-bdrm home has a well drained
  soil with a rock limiting zone at 35 inches and a
  seasonal high watertable at 25 inches.
• The site has a 10 slope.
• Soil Scientist report states
• Maximum soil linear load rate 0.25 gal/ft/d.
• Horizontal linear load 3.5 gal/ft/d.
• Drip tubing spacing to be at least 2.0 feet.
• Tubing to be buried at least 6 inches deep.

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Example

• Site Geometry
• Width of lot along the contour 130 ft.
• Distance from dose tank to Hydraulic Unit 20
  ft.
• Hydraulic Unit is 7 feet above the enabler float
  in dose tank.
• Distance from Hydraulic Unit to zones 100 feet.
• Distance from zones to bldg sewer 140 feet.
• Elevation increase from Hydraulic Unit to drip
  zones 20 feet.

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Soil Conditions

• Rock Limiting Zone 35 inches.
• Seasonal High Water Table Limiting Zone 25
  inches.
• Slope 10.

35 inches
25 inches
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Soil Conditions

• Rock Limiting Zone 35 inches.

6 inches
29 inches
35 inches
29
Soil Conditions

• Seasonal High Water Table Limiting Zone 25
  inches.

6 inches
25 inches
19 inches
30
Example

• Soil Scientists Report
• Maximum linear loading rate 0.25 gal/d/ft.
• Horizontal linear load 3.5 gal/d/ft

31
Example

• The septic tank is sized as per Chapter 73 for a
  3 bdrm home.
• This is a drip system so a Secondary Treatment
  unit is needed. The choices are
• Aerobic Treatment Tank
• Free Access sand filter.
• Subsurface sand filter.
• See the Secondary Treatments for sizing
  guidelines for these units.

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Example

• Following the Pre-treatment unit the effluent
  will flow into a Dose/Pump tank.

33
Example

• The Pump/Dose Tank must be at least 2 times
  larger than the maximum daily flow.
• The maximum daily flow from a 3-bdrm home is
  taken to be 400 gpd.
• Therefore the Pump/Dose Tank must be at least 800
  gallons in size.

34
Example

• In a Drip Irrigation system the effluent is
  pumped from the Dose/Pump Tank to the Hydraulic
  Unit and on to the drip zones.

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Example

• The Hydraulic Unit controls the flow to zones and
  backflushing. Two units are available 2-disc and
  3-disc units.
• The two-disc unit supports
• 1200 ft of drip tubing/zone.
• Tubing forward flush rate 15 gpm.
• 4 zones and one return connection.
• 4800 ft of drip tubing (4x1200).

36
Example

• Forward Field Flush Flow Rate
• Dose flow rate to the drip emitters
• PLUS
• Field Flush flow rate needed to maintain a
  velocity in the drip tubing of 2 fps. This is set
  to 1.6 gpm/lateral within each zone.

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Example

• Length of drip tubing required
• Max daily flow/linear loading rate
• 400 gpd/0.25 gal/d-ft 1600 ft.
• We will use 2 zones.
• 1600 ft/2 800 ft/zone

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Example
Supply Line
Return line

• Each zone will consist of
• 8 runs of 100 ft each.
• 4 laterals each 200 ft long. (2 runs/lateral).

Run
Air Vent Check Valve
Lateral (4)
39
Example

• Check to make sure the runs are long enough.
• Based on the Average daily flow
• 400 gpd (.5) 200 gpd.
• Horizontal linear load 3.5 gal/g-ft
• Minimum run length 200/3.5 57 ft.
• Our runs are 100 ft long Okay.

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Example (Summary)

• Peak daily flow 400 gpd.
• Soil linear load 0.25 gal/d-ft.
• Total tubing length required 1600 ft.
• 2 zones used.
• Hydraulic Unit used 2 disc.
• Tubing length/zone 1600/2 800 ft.
• No. Laterals/zone 4
• Lateral length 800/4 200 ft.
• Run length 100 ft.
• Horizontal linear load 3.5 gal/d-ft.
• Minimum run length 200/3.5 57 ft.

41
Example

• Flow required to each zone during Forward Field
  Flush Hydraulic Condition.
• Need
• Dose flow rate PLUS
• Field flush flow rate

42
Example

• Dose flow rate (for each zone)

43
Example

• Field flush flow rate/zone 1.6 gpm/lateral (to
  maintain a velocity of 2 fps in drip tubes)
• 1.6gpm/lat x 4 laterals 6.4 gpm/zone
• Total flow required during Forward Field Flush is
  4.3 6.4 10.7 gpm.

44
Example (Pump Selection)

• The remaining task is to size the pump.
• This means that we must determine
• Systems total head
• Systems maximum flow rate.

45
Example (Bernoulli Analysis)

• The Total Head for the pump in the Dose Tank is
  the sum of three components
• Head Loss in all the pipes.
• Pressure needed to run the system either the
  emitters or the Hydraulic Unit.
• Elevation difference between the water level in
  the dose tank to the drip zones.
• The Total Head is the SUM of these three values.

46
Example (Friction HL)

• The Head Loss (or Friction) is the most difficult
  to determine. This must be done in parts
• HL in the pipe from the dose tank to the
  Hydraulic Unit.
• HL in the Zone supply pipes.
• HL in the drip lines.
• HL in the Zone return pipes.

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Example (HL from tank to HU)

• First size this pipe to carry the maximum flow.
• During dosing the pipe will carry 10.7 gpm.
• During back flushing this pipe will carry 15 gpm.
• Size for the 15 gpm.

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Example (Size the pipe to HU)

• With a design flow rate of 15 gpm and using
  PVC-schedule-40 pipe we will need a 1.5-inch
  pipe to keep the velocity above 2.0 fps. (V
  2.35 fps).
• This 1.5-in PVC pipe has a friction factor Fc
  0.63 psi/100 ft or 1.46 ft/100 ft.

49
Example (HL from tank to HU)

• Before we can determine the HL in this pipe we
  must determine the length of the pipe including
  the equivalent length for the various elbows
  valves etc.
• The length of pipe was given at 20 ft.
• The equivalent length is specified as 50 ft.
• The total length is 20 50 70 ft.

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Example (HL from tank to HU)

• The HL is calculated from
• HL FcL
• HL 1.46 ft/100 ft(70ft) 1.02 ft.

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Example (HL in Supply Pipe)

• First size the Supply pipe to carry the maximum
  flow.
• During dosing the pipe will carry 10.7 gpm.
• Not used during back flushing.
• Size for the 10.7 gpm.

52
Example (Size the Supply Pipe)

• With a design flow rate of 10.7 gpm and using
  PVC-schedule-40 pipe we will need a 1.25-inch
  pipe to keep the velocity above 2.0 fps. (V
  2.20 fps).
• This 1.25-in PVC pipe has a friction factor Fc
  0.70 psi/100 ft or 1.62 ft/100 ft.

53
Example (HL in Supply Pipe)

• Before we can determine the HL in this pipe we
  must determine the length of the supply pipe
  this is assumed to be a straight pipe.
• The length of pipe was given at 100 ft.

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Example (HL in Supply Pipe)

• The HL is calculated from
• HL FcL
• HL 1.62 ft/100 ft(100ft) 1.62 ft.

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Example (HL in Drip Zone)

• We desire to deliver 10.7 gpm to each zone. Of
  this water
• 4.3 gpm will go out the emitters.
• 6.4 gpm will flush through the drip lines and be
  returned to the building sewer.

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Example (HL in Drip Zone)

• The drip supplier specifies that for 200-ft
  laterals the losses in the drip lines will be 18
  ft (Table 3A).

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Example (HL in Return Pipe)

• First size the Supply pipe to carry the maximum
  flow.
• During dosing the return pipe will carry 6.4 gpm.
• Not used during back flushing.
• Size for the 6.4 gpm.

58
Example (Size the Return Pipe)

• With a design flow rate of 6.4 gpm and using
  PVC-schedule-40 pipe we will need a 1.0-inch
  pipe to keep the velocity above 2.0 fps. (V
  2.30 fps).
• This 1.00-in PVC pipe has a friction factor Fc
  0.95 psi/100 ft or 2.19 ft/100 ft.

59
Example (HL in Return Pipe)

• Before we can determine the HL in this pipe we
  must determine the length of the supply pipe
  this is assumed to be a straight pipe.
• The length of pipe was given at 140 ft.

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Example (HL in Return Pipe)

• The HL is calculated from
• HL FcL
• HL 2.19 ft/100 ft(140ft) 3.07 ft.

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Example (HL Summary)

• The Head Loss (or Friction) for these four
  sections of our system is
• HL Dose Tank to the HU 1.02 ft.
• HL Supply Pipe 1.62 ft.
• HL Drip Lines 18 ft.
• HL Return Pipe 3.07 ft
• Total HL 23.7 ft.

62
Example (Pressure Requirements)

• The Pressure needed to operate the various
  components of the system
• Pressure to Back Flush the Hydraulic Unit.
• Pressure to Operate the Emitters.
• At this time these requirements are not provided
  by the manufacturer.

63
Example (Pressure Requirements)

• Without having worked with this system I would
  assume the following
• The pressure needed to run the HU should be 10 to
  20 psi (23 to 46 ft).
• The pressure needed to make the emitters function
  properly is generally about 10 psi (23 ft).
• The total pressure requirement 46 23 69 ft.

64
Example (Elevation Difference)

• Elevation differences include
• Rise from enabler float in dose tank to Hydraulic
  Unit ( 7 ft).
• Rise from the Hydraulic Unit to the drip Zones
  (20 ft).
• Total elevation rise 7 20 27 ft.

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Bernoulli Summary (Dosing)

• The total energy needed to run this system is
• HL 23.7 ft.
• Pressure 69 ft.
• Elevation rise 27 ft.
• Total during dosing 120 ft.
• Flow rate 10.7 gpm.

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Bernoulli Summary (Back Flushing)

• The total energy needed to run this system is
• HL 115 1.02 116 ft.
• Pressure 0 ft.
• Elevation rise 7 ft.
• Total during dosing 123 ft.
• Flow rate 15 gpm.

67
Example (Pump Requirement)

• For Dosing
• HT 120 ft
• Q 10.7 gpm
• For Back Flushing
• HT 123 ft.
• Q 15 gpm.
• Pump Design
• HT 123 ft.
• Q 15 gpm.

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Example (Time/Dose)

• Average daily flow 200 gpd
• Each zone accounts for 50 of flow.
• Zone 1 100 gpd
• Zone 2 100 gpd
• At 4 doses /zone/day each dose must apply 25
  gal.
• Time/dose 25 gal/dose/4.3 gpm 5.8 min

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Example (Time/Dose)

• Summary
• We dose 5.8 min 4 times each day to supply 25
  gal/dose or 100 gal/day to each zone.
• With 2 zones we apply 200 gal/day the avrage
  daily flow from the 3 bdrm home.

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Example (Time/Dose)

• Under condition of Maximum daily flow (400 gpd)
• We apply 200 gal/zone/day
• At 4.3 gpm (25 gal/dose).
• 200/25 8 doses/day.

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Thank You