Sprinkler and Drip Irrigation: Theory and Practice

Foreword
Preface
Acknowledgements
Contents
About the Author
Main Section
Sprinkler Irrigation Types and Components
Introduction
Advantages
Disadvantages
Classification of Sprinkler Irrigation Systems
Components of a Periodic Move Sprinkler Irrigation System
Pump
Pipes
Pipe Fittings
Sprinkler Heads
Valves
Control Valves
Air Release/Vacuum Breaker Valve
Non-return Valve
Pressure Relief Valve
Booster Pumps
Desilting Basins and Debris Screens
Summary
Assessment
References and Further Readings
Uniform Irrigation with Sprinklers
Introduction
Sprinkler Discharge Rate
Wetted Diameter
Spacing of Sprinkler Heads
Breaking of Jet
Application Rate
Application Efficiency
Sprinkler Head Selection
Uniformity Parameters
Design of Sprinklers Spacing
Summary
Assessment
References and Further Readings
Layout of Sprinkler Systems
Introduction
Maximum Area of Land Irrigated from a Water Source
Number of Sprinklers Operated at a Time (Nmax)
Time of Irrigation
Pressure Variation in a Lateral
Typical Layouts
Summary
Appendix
Assessment
References and Further Reading
Design of Periodic Move and Solid Set Sprinkler Systems
Introduction
Important Observations from This Problem
Friction Loss Equation in Sprinkler Lateral for a Uniform Diameter Pipe
Scallopi’s Correction Factor for Christiansen’s F
Average Friction Loss
Pressure Head Distribution in Sloping Laterals
Design of Laterals
Design of Submains
Design of Main
Summary
Appendix
Assessment
References and Further Reading
Selection of Pumps
Introduction
Reference States for Components for Energy
Pump
Total Dynamic Head (TDH)
Power of Pump
Operating Characteristics of Pump
Net Positive Suction Head (NPSH)
Selection of Pump Using Manufacturer’s Catalogue
Head Losses in Pipe Sections
Examining the Sufficiency of Existing Pump in the Field
Pumps in Parallel
Pumps in Series
Selecting a Suitable Diesel Engine for Pump
Summary
Assessment
References and Further Reading
Maintenance and Operation of Sprinkler Irrigation Systems
Introduction
Maintenance Tips for Sprinkler Irrigation System
Operation of SIS
System Characteristics
Matching the Impeller Speed and Diameter for Variable requirements
Changing the Speed of Rotation Alone
Changing the Diameter of Impeller Alone
Time of Sprinkler Operation
Soil Moisture Characteristics
Field Capacity
Permanent Wilting Point
Available Water Holding Capacity
Management Allowable Depletion (MAD)
Irrigation Scheduling
Plant Wilt Symptoms Method
Evapotranspiration Estimation Methods
Irrigation Requirements
Irrigation Depth
Gross Irrigation Depth
Irrigation Interval
Capacity of Pump
van-Genuchten’s Equation
Irrigation Scheduling Under Salinity
Summary
Assessment
References and Further Reading
Drip Irrigation Components
Introduction
Salinity Under Drip Irrigation
Classification of Drip Irrigation Systems
Point and Line Source
Online Drippers
Inline Drippers
Subsurface Drip
Emitters or Drippers
Bernoulli’s Law for Flow in Emitter
Orifice Emitters
Vortex Emitter
Long Path Emitters
Tortuous Path Emitters
Pressure Compensating Dripper
Self-flushing Drippers
Present-Day Drippers
Variation in the Emitters Discharge Due to Manufacturing
Filtration
Vortex Sand Separators (Hydro Cyclones)
Media Filter
Disc Filters
Screen Filter
Filter Selection
Hydraulics of Flow Through Filters
Chemical Injection Devices
Venturi Assembly
Pressure Differential Fertilizer Tank
Fertilizer Injection Pump
Pipes
PVC Fittings & Accessories
Pump
Automation Components
Relay Circuit
Solenoid Valve
Automatic Metering Valve
Pressure Management Valves
Controllers for Backwashing of Sand and Disc Filters
Sensor-Based Irrigation Systems
Automated Fertigation Systems
Pollution Prevention Accessories in Chemigation
Variable Frequency Drive (VFD)
Summary
Appendix
Assessment
References and Further Reading
Drip Irrigation—Planning Factors
Introduction
Crop Water Requirement
Maximum Area of the Land Irrigated
Maximum Area of One Subunit
Wetting Pattern of Drippers
Empirical Equation for Wetting Pattern
Semi-Empirical Equation for Wetting Pattern
Ponded Radius
Lateral Configurations
Emission Point Layouts for Widely Spaced Crops
Computing Percentage Wetted Area
Case Study
Dripper Discharge Rate
Spacing Between Drippers
Spacing of Lateral
Summary
Assessment
References and Further Reading
Hyraulics of Microirrigation Pipes
Introduction
Friction Loss Through Drip Laterals and Submains
Average Friction Loss
Ratio of Pressure Head Losses due to Friction Versus Ratio of Lengths
Locations of Maximum and Minimum Pressures in Uniform Slopes
Coefficient of Variation of Pressure and Discharge Rate in Uniform Slopes
Emitter Connection Head Losses
Summary
Assessment
References and Further Reading
Drip Subunit Design with Uniform Diameter Pipes in Uniform Slopes
Introduction
Relative Flow Difference Criterion
Maximum Length of a Horizontal Lateral
Maximum Length of Lateral/Submain on Slopes
Paired Lateral
Average Pressure Head
Average Pressure Head for Upslope
Average Pressure Head for Downslope
Average Friction Loss in a Paired Lateral
Average Elevation Loss in a Paired Lateral
Equal Average Pressure Heads on Both Sides of a Paired Lateral
Average Pressure Head for Upslope
Average Pressure Head for Downslope
Relative Pressure Head Variation in Downslope
Slope Profile Type
Statistical Variation Criterion
Relationship Between CVh and Vh
Evaluation of Drip Irrigation Systems with Statistical Criterion
Keller and Karmeli Emission Uniformity Criterion
Field Evaluation When Using Keller and Karmeli Criterion
Summary
Assessment
References and Further Reading
Design with Telescopic Pipes in Uniform and Non-uniform Slopes
Introduction
Trial-and-Error Method
Telescopic Pipe Design
Poly-Plot Method
Telescopic Pipe with Only Two Sections
Computer-Aided Design of Drip Subunits
Drip System Simulation Programme (DSSP)
Manufacturing Variation
Uniformity coefficient
Screens of the DSSP
Model Problem
Design of Lateral
Lateral Diameter (ϕ)
Design of Submain
Design and Evaluation of the Subunit
Lateral Data
Summary
Assessment
References and Further Reading
Design of Mains
Introduction
Water Hammer Management
Estimation of Surge Pressure Heads
Minimal Capital Method
Life Cycle Cost Analysis Method
Summary
Assessment
References and Further Reading
Fertigation
Introduction
Nutrient Elements
Nitrogen
Phosphorous
Potassium
Calcium, Magnesium and Sulphur
Micronutrients
Nutrients in Fertilizers
Fertilizers and Irrigation Water
Concentrations of Fertilizers Solution
Water Soluble Solid and Liquid Fertilizers
Fertilizer Injection Times
Fertigation Scheduling
Summary
Assessment
References and Further Reading
Maintenance and Operation of Drip Irrigation Systems
Introduction
Water Chemical Reactions
Bio-chemical Reactions with Water
Reaction of Fertilizers With Water
Acid Treatment
Acid Treatment for Prevention of Carbonate scales
Acid Treatment for Clogged Systems
Biological Plugging Removal
Continuous Treatment
Intermittent Treatment
Super Chlorination
Algae Control in Ponds and Wells
Remedy for Iron
Regular Maintenance of Accessories
Filters
Media Filters
Flushing Main and Laterals
Handling Rats and Squirrel Problems
Operation of Drip Irrigation System
Minimum Irrigation Duration
Maximum Duration of Irrigation
Irrigation for Germination
Irrigation Scheduling
Summary
Assessment
References and Further Reading
Evapotranspiration for Microirrigated Crops
Introduction
Reference Crop Evapotranspiration
Evapotranspiration Estimation by Climatological Data
Single Crop Coefficient Approach
Single Crop Coefficient Approach
Dual Crop Coefficient Approach
Summary
Assessment
References and Further Reading
Rhizosphere Modelling
Introduction
Derivation of Richards Equation
Boundary Conditions
Unsaturated Hydraulic Conductivity Parameters
Parameter Optimization
Inverse Modelling with a Double-Ring Infiltrometer Test
Soil Water Balance Methods for Estimation of Evapotranspiration
Water Balance Models
Single Cell–Single Step Model
Single Cell–Multiple Step Model
Drainage from Root Zone and Capillary Rise to Root Zone
Irrigation Depth (it)
Average Water Content in Root Zone
Results of the Case Study
Multiple Cell–Multiple Step Model
Derivation of Reactive Transport Solute Transport Equation
Diffusion
Convection
Hydrodynamic Dispersion
Adsorption
Chemical Reaction
Urea Reactions in Soil
Continuity Equations for Reactive Solute Transport
Boundary Conditions
Estimation of Dispersivity
Estimation of Urea Reaction Rate Constants
Experimental Set-up for Estimation of Urea Reaction Rate Constants
Parameter Set Needed for Rhizosphere Modelling
Development of Fertigation Schedule by Modelling with Hydrus
Summary
Appendix I
Appendix II
Introduction to Finite Difference Methods
Truncation Errors and Numerical Dispersion
References and Further Reading
Water Budgeting and Economic Evaluation
Introduction
Water Budgeting
Rainfall Analysis
Water Balancing
Basics of Economic Analysis
Summary
Assessment
References and Further Reading
Basic Section
Pressure, Energy and Power in Water
Introduction
Units and Terminologies Used
Laws of Newton
Pressure
Pressure Measurement
Energy of Water
Potential or Gravitational or Datum Energy
Kinetic Energy
Pressure Energy
Total Energy of Water
Power of Water
Summary
Solved Exercises
Assessment
References and Further Reading
Bernoulli’s Law
Introduction
Bernoulli’s Equation
Friction Head Loss
Friction Loss Formulae
Pressure Change Due to Elevation
Flow in Microirrigation Pipes
Summary
Points to Ponder
Solved Exercises
Assessment
References and Further Reading
Soil Texture and Soil Moisture
Introduction
Soil
Types of Soil Water
Hygroscopic Water
Capillary Water
Gravitational Water
Soil Moisture Specification Methods
Summary
Points to Ponder
Exercises
Solved Exercises
Assessment
Reference and Further Reading
Soil Water Movement
Introduction
Saturated Flow
Unsaturated Flow
Energy of Unsaturated Flow
Tensiometer
Correction of Tensiometer Reading
Summary
Points to Ponder
Solved Exercises
Assessment
Reference and Further Reading
Salinity
Introduction
Atom
Electro-Neutrality
Clay Particles
Salinity of Soil
Leaching Requirement
Cation Exchange Capacity (CEC)
Exchangeable Sodium Per Cent (ESP)
Sodium Adsorption Ratio (SAR)
Hydration
Summary
Assessment
Reference and Further Reading
Pumps
Introduction
Basic Physics to Understand Pumps
Angular Momentum
Torque
Rotational Power
Centripetal Force and Centrifugal Force
Centrifugal Pump Operating Principle
Components of Centrifugal Pump
Impeller
Casing
Suction Pipe
Foot Valve
Strainer
Delivery Pipe
Delivery Valve
Working of Centrifugal Pump
Priming
Volute Chamber
Volute Pump with Vortex Chamber
Casing with Stationary Guide Blades
Classification of Centrifugal Pumps
Radial Flow
Mixed Flow
Axial Flow Pumps
Self-priming Pumps
Centrifugal Pump Installation
Centrifugal Pump Troubles and Remedies
Pump Fails to Start Pumping
Pump Working but not Up to Capacity and Pressure
Multi-stage Pump
Turbine and Submersible Pumps
Propeller Pump
Jet Pump
Airlift Pump
Work Done by a Centrifugal Pump Impeller
Heads of a Pump
Static Head
Suction Dynamic Head
Delivery Dynamic Head
Total Dynamic Head
Minimum Speed Needed to Initiate Flow
Impeller Diameter
Diameter of Suction Pipe and Delivery Pipe
Limitation of Suction Lift
Loss of Head and Efficiencies
Mechanical Losses
Leakage Losses
Performance of Pumps—Characteristic Curves
Specific Speed of a Pump
Expression for Specific Speed
Specific Speed Versus Operating Characteristics
Assessment
References and Further Readings