Lecture 7B: Micro-Irrigation System

Drip and Sub Drip Irrigation

Prepared by

Husam Al-Najar

The Islamic University of Gaza- Civil Engineering Department

Irrigation and Drainage- ECIV 5327

Micro- irrigation

• Delivery of water at low flow rates through various types of water

applicators by a distribution system located on the soil surface, beneath

the surface, or suspended above the ground

توصيل المياه بمعدالت تدفق منخفضة من خالل أنواع مختلفة من أجهزة تطبيق المياه عن طريق نظام •

توزيع يقع على سطح التربة أو تحت السطح أو معلق فوق سطح األرض

• Water is applied as drops, tiny streams, or spray, through emitters,

sprayers, or porous tubing

يتم تطبيق الماء على شكل قطرات أو تيارات صغيرة أو رذاذ من خالل بواعث أو رشاشات أو أنابيب •

مسامية

Water Application Characteristics of Micro- irrigation

خصائص تطبيق المياه

Low rates معدالت منخفضة

Over long periods of time على مدى فترات طويلة من الزمن

At frequent intervals على فترات متكررة

Near or directly into the root zone بالقرب من منطقة الجذر أو مباشرة

At low pressure عند ضغط منخفض

عادة الحفاظ على نسبة عالية من الماء

نسبياUsually maintain relatively high water content

/ تستخدم في المحاصيل الزراعية

البستانية ذات القيمة األعلى وفي المناظر

الطبيعية والمشاتل

Used on higher value agricultural/horticultural

crops and in landscapes and nurseries

كفاءة تطبيق عالية

High application efficiency

High yield/quality جودة عالية/ عائد

Decreased energy requirements انخفاض متطلبات الطاقة

Reduced salinity hazard تقليل مخاطر الملوحة

Adaptable for chemi-gation قابل للتكيف مع المعالجة الكيميائية

Reduced weed growth and disease انخفاض األعشاب الضارة ومشاكل المرض

problems

Can be highly automated يمكن أن يتم تشغيله بنظام التشغيل الذاتي

Advantages of Micro- irrigation

مزايا الري الدقيق

High initial cost تكلفة أولية عالية

Maintenance requirements (emitter .(انسداد الباعث ، إلخ)متطلبات الصيانة

clogging, etc.)

Restricted plant root development تقييد في تطور جذر

على طول )تراكم الملح بالقرب من النباتات

(حواف المنطقة المبللة

Salt accumulation near plants (along

the edges of the wetted zone)

Disadvantages of Micro- irrigation

مساوئ الري الدقيق

Salt Movement Under Irrigation with Saline Water

Salt accumulation leached downward

by successive water applications

Salt accumulation leached radially

outward from drip tubing

Subsurface Drip Sprinkler/Flood

Types of Systems

1. Surface trickle (drip)

– Water applied through small emitter openings to the soil surface

(normally less than 3 gal/hr per emitter)

– Most prevalent type of micro-irrigation

– Can inspect, check wetting patterns, and measure emitter discharges

2. Spray

– Water applied (spray, jet, fog, mist) to the soil surface at low pressure

(normally less than about 1 gal/min per spray applicator)

– Aerial distribution of water as opposed to soil distribution

– Reduced filtration and maintenance requirements because of higher flow

rate

3. Bubbler

– Water applied as a small stream to flood the soil surface in localized areas

(normally less than about 1 gal/min per discharge point)

– Application rate usually greater than the soil's infiltration rate (because of

small wetted diameter)

– Minimal filtration and maintenance requirements

4. Subsurface trickle

– Water applied through small emitter openings below the soil surface

– Basically a surface system that's been buried (few inches to a couple feet)

– Permanent installation that is "out of the way"

76 cm

152 cm

Typical Subsurface Drip Tubing Installation for Row Crops

30 – 35 cm

Non Wheel-

Track Row

Wetting Pattern

Drip Tubing

152-cm dripline spacing is satisfactory on silt loam & clay loam soils

System Components

• Pump

• Control head

– Filters

– Chemical injection equipment (tanks, injectors, backflow prevention, etc.)

– Flow measurement devices

– Valves

– Controllers

– Pressure regulators

• Mainlines and Submains (manifolds)

– Often buried and nearly always plastic (PVC)

• Laterals

– Plastic (PE)

– Supply water to emitters (sometimes "emitters" are part of the

lateral itself)

Schematic of a Typical Micro-irrigation System

Applicator Hydraulics

• General

– Need pressure in pipelines to distribute water through the

system, but the applicator needs to dissipate that pressure

– qe = emitter discharge

– K = emitter discharge coefficient

– H = pressure head at the emitter

– X = emitter discharge exponent

(varies with emitter type)

xKHe

q

Emitter Hydraulics

Emitter Type

Coefficient, K - Exponent, X

Emitter Discharge (Liter/minute)

Operating Pressure (m)

5.6 m

8.4 m

11.2 m

Porous Pipe - 0.112 1.00

9.0

13.6

18.2

Tortuous Path 0.112 0.65

3.3

4.3

5.2

Vortex/Orifice 0.112 0.42

1.7

2.0

2.2

Compensating 0.112 0.20

0.9

0.9

1.0

xKHe

q

Other Design and Management Issues

• Clogging

– Physical (mineral particles)

– Chemical (precipitation)

– Biological (slimes, algae, etc.)

• Filtration

– Settling basins

– Sand separators (centrifugal or cyclone separators)

– Media (sand) filters

– Screen filters

Filtration Requirements for Drip Emitters

Filter openings should be 1/7th –

1/10th the size of the emitter

orifice

0.020-inch orifice

Plugging Potential of Irrigation Water for

Microirrigation

• Chemical treatment

– Acid: prevent calcium precipitation

– Chlorine

• control biological activity: algae and bacterial slime

• deliberately precipitate iron

• Flushing

– after installation or repairs, and as part of routine maintenance

– valves or other openings at the end of all pipes, including laterals

• Application uniformity

– manufacturing variation

– pressure variations in the mainlines and laterals

– pressure-discharge relationships of the applicators

Advantages of Subsurface Drip Irrigation

• High water application efficiency

• Uniform water application

• Lower pressure & power requirements

• Adaptable to any field shape

• No dry corners (vs. center pivot)

• Adaptable to automation

Disadvantages of Subsurface Drip Irrigation

• High initial cost

• Water filtration required

• Complex maintenance requirements

– Flushing, Chlorination, Acid injection

• Susceptible to gopher damage ( القوارض)

• Salt leaching limitations

Schematic of Subsurface Drip Irrigation (SDI) System

Pump

Station

Backflow

Prevention

Device

Flowmeter

Chemical

Injection

System

Air & Vacuum

Release Valve

X X

Pressure Gage

X X

Flush Valve

X X

Dripline

Laterals

Zones

1 and 2

Submain

Flushline

Filtration

System

x

X Zone Valve

SDI System Maintenance

• Lateral flushing schedule (sediment)

• Chlorine injection schedule (biological growths)

• Acid injection schedule (chemical precipitates & scaling)

Trenching across the drip tubing ends for PVC manifold

installation

Flush Risers on Distal End

Ball Valve for Manual Flushing

of Drip Laterals

Air Vent to Release Trapped Air

from Laterals

SDI Water Application Rates (mm/hr)

(152 cm tubing spacing)

cm30.5

cm45.7

cm61.0

mm/hr

0.60 Liter/hr 1.10 0.86 0.66

0.78 Liter/hr 1.4 1.1 0.86

1.24 Liter/hr 2.2 1.8 1.4

2.0 Liter/hr 3.6 2.9 2.2

Emitter Spacing

Emitter Discharge 1

52

cm

30.5 cm