A.KESHAV KUMAR,(ME12-007)R.LAVANYA,(ME12-008)

PRECIPITATION PROFILES OF SPRINKLER SYSTEM

Precipitation profiles of sprinkler irrigation

Meaning of precipitation:

The quantity of water falling to earth at specific

place within a specified period of time; “the

storm brought several inches of precipitation”

PRECIPITATION PROFILES OF SPRINKLER SYSTEM

Lateral movement of moisture is more in clay soils.

Linear and lateral movement of moisture is present to some extent in loamy soils.

Sandy soils having high linear movement when compared to loamy soils.

Precipitation profile is a function of many factors:

Nozzle pressure.

Nozzle shape & size.

Sprinkler head design.

Sprinkler rotation speed.

Trajectory angle.

Riser height.

Wind.

Head Design Description Usage

Fixed Spray • Produce a tight, constant fan of water• Fan out in a radius of 5'-15'

• Small lawns• Shrubs• Ground cover

Pop-Up • Pop up above grass when activated and disappear belowground when not in use

• Provide even water distribution and low spray angle

• Small lawns• Medium lawns• Large lawns• Side lawns• Gardens

Rotary • Deliver a single stream of water that rotates in a circle• Apply water more slowly than spray designs

• Medium lawns• Large lawns• Side lawns

Shrub • Mounted above foliage on risers, or extensions• Special pattern nozzles provide flexibility

• Ground cover• Planters• Shrubs• Gardens

Fixed Spray Pop-Up

Shrub Rotary

Rotational speed

• The rotational speed is about 2.5m/s

• Rotational speed of sprinkler head significantly affects the water distribution

Trajectory angle.

Risers are an important component of any irrigation system.

Since the main lines of irrigation systems do not always connect directly to the sprinkler heads themselves, risers fill the gap in between by providing the right connection

Risers are available in 1/2" and 3/4" diameters

Basic risers are rigid and best used for short distances

Basic risers offer more economical options

Cut-off risers allow you to make on-the-spot adjustments

Flexible-tubing risers provide flexibility for installing sprinkler heads in difficult spots

Risers

.

Riser Type Materials Points to Consider

Basic • Metal• PVC

• Best for short distances

Cut-Off • Polyethylene • Provide installation flexibility• Can be trimmed in 1/2" sections

Flexible • Polyethylene • Allow movement to reduce stress on sprinkler heads• Provide greater length

How to calculate a precipitation rate

Physically measuring using cups is a very simple method. You can purchase water-auditing cups (sometimes called a catchcan), a rain gauge, or use any non-tapered cup or can. Set the cup in the zone. Run that zone for several minutes- we recommend 5, 10, or 15 minutes.After the time is up, retrieve the can and check the water level. A rain gauge or catchcan will have measurements indicating the amount of water caught.

MOISTURE DISTRIBUTION CHARACTERISTICS

Moisture distribution characteristics:

1) Sprinkler spacing

2) Nozzle size

3) Operating pressure

4) Depth of water application

Operating pressure affects more to the wetting pattern of sprinkler irrigation.

Operating pressure of pressure head ranging from 3.5m to 70m.

Moisture distribution characteristics:

Spray distribution characteristics of sprinklers and their spacing will regulate the uniformity of water application .

The spray distribution characteristics of sprinkler heads are typical change with nozzle size and operating pressure .

In this distribution pattern , the depth of water applied surrounding the sprinkler, decreas as the distance from the sprinkler increases .

Wetting pattern

Normally the area wetted is circular . The heaviest wetting is close to the sprinkler .

For good uniformity several sprinklers must be operated close together so that their patterns overlap .

For good uniformity the overlap should be at least 65% of the wetted diameter.

If the pressure is above or below this then the distribution will be affected. The most common problem is when the pressure is too low. This happens when pumps and pipes wear.

If the pressure is too high then the distribution will also be poor.A fine spray develop which falls close to the sprinkler.

EFFECT OF WIND SPEED ON SPRINKLER SYSTEM

Effect of wind velocity on sprinkler system

The wind velocity and wetting pattern of the soil are closely related to each other .

The wind distorts the circular pattern of wetting in the shape of irregular ellipse .

Wind velocity more than 16kmph ,the wetting pattern , uniformity of application is adversely affected , as result sprinkler irrigation is not recommended at this velocity level.

Wind velocity from 0-8kmph , the application uniformity is not affected.

Wind velocity up to 13kmph is acceptable but beyond it the application uniformity gets significantly affected.

No wind

Elongated parallel pattern

Overlapped Sprinklers

Dry zone

effect of wind on sprinklers

s.no Wind velocity kmph Sprinkler spacing across the wind direction(m)

1. 0 65

2. 0 to 6 55

3. 7 to 13 40

4. More than 13 30