Irrigation: Advantages and Basics

Irrigation

• Irrigation constitutes the science of artificially applying water to land.
• This application aligns with crop requirements throughout their growth period.
• It ensures crops receive full nourishment.

Advantages of Irrigation

• Increased food production results from higher crop yields, leading to self-sufficiency.
• Optimum benefits occur through maximized crop yield with the required water amount.
• Mixed Cropping Gets Eliminated When irrigation is reliable, eliminating the need for mixed cropping.
• Mixed cropping involves sowing two or more crops together in the same field.
• General prosperity arises from revenue returns due to developed irrigation systems.
• Hydro-electric power can be generated more cheaply through water development projects.
• Domestic water supply is augmented through irrigation facilities in nearby villages and towns.
• Communication improves with embankments and inspection roads along irrigation channels.
• Inland navigation is enabled and developed using larger canals.
• Afforestation promotes the growing of trees along channel banks.
• Timber resources in the country increases.

Disadvantages and Ill-Effects of Irrigation

• Water pollution can result through various ways.
• Climate may become colder and damper, leading to marshy lands and mosquito breeding.
• Over-irrigation results in water-logging and potentially reduced crop yields.
• Procuring and supplying irrigation water becomes complex and expensive.

Types of Irrigation

• Surface Irrigation, where flow irrigation utilizes gravity to supply water from a higher level to a lower one.
• Perennial irrigation assures a constant water supply to crops.
• Direct irrigation involves direct runoff from a river.
• Storage irrigation involves damming rivers to store water for monsoons.
• Flood irrigation (or inundation) keeps soil submerged and thoroughly flooded.
• Sub-surface irrigation occurs without wetting the soil surface.
• Water nourishes plant roots by capillarity.
• Natural sub-irrigation comes from leakage water from channels underground.
• Artificial sub-irrigation employs open-jointed drains artificially laid below the soil to supply water to crops by capillarity.

Techniques of Water Distribution in Farms

• Free flooding (ordinary or wild flooding) uses ditches excavated in the field along contours or up and down slopes.
• Border flooding divides land into strips separated by borders (low levees), typically 10-20m wide and 100-400m long.
• Supply ditches (irrigation streams) can be earthen, lined, or underground concrete pipes.

Time Required to Irrigate a Land Strip

• Time = 2.3 * log10(Q / (Q - f * A)), where Q is the discharge, f is the infiltration rate, and A is the area of land strip.
• Maximum Area that can be irrigated = Q/f

Flood Control Methods

• Check flooding is similar to ordinary flooding but controls water by surrounding the check area with low, flat levees.
• Basin flooding represents a specific type of check flooding adopted for orchard trees.
• Furrow irrigation wets only one-fifth to one-half of the land surface
• Sprinkler irrigation applies water in the form of spray through a network of pipes and pumps.
• Sprinkler Irrigation is favored:
• Where land topography is irregular,
• Or where land gradient is steeper,
• Or where soil is easily erodible,
• Or where land soil is excessively permeable,
• Or where the water table is high,
• Or the seasonal water requirement is low (near the coast),
• Or humidity control is needed (e.g., tobacco),
• Or crops have shallow roots,
• Or crops require high and frequent irrigation
• Or where water is scarce
• Or where water is available with difficulty.

Sprinkler Systems

• Permanent systems have permanently buried pipes.
• Semi-permanent systems have main lines buried.
• Portable systems have both mains and laterals as portable.

Advantages of Sprinkler Irrigation

• Seepage losses in surface irrigation are eliminated.
• Land leveling is unnecessary.
• No cultivation area gets lost to ditches.
• Water gets applied at a rate less than the soil's infiltration capacity.
• Fertilizers can be applied uniformly.
• Salts are leached down to prevent water-logging or salinity.
• System is less labor-intensive.
• Efficiency can reach up to 80%.

Limitations of Sprinkler Irrigation

• High winds can distort the sprinkler pattern.
• High temperatures and winds can cause considerable evaporation losses.
• It suits not crops requiring frequent and larger depths of irrigation.
• The initial cost of the system is high.
• Only sand and silt-free water can be used.
• The system requires larger electrical power.
• Heavy soil with poor intake cannot be irrigated efficiently.
• Constant water supply is needed for commercial equipment use.
• Drip irrigation (or trickle irrigation) constitutes the latest field irrigation method

Irrigation Water Impurities

• Sediment concentration of water in irrigation affects the type of irrigated land.
• Total Concentration of Soluble Salts can be composed of salts of calcium, magnesium, sodium, and potassium.
• Salinity is generally expressed by parts per million (ppm) or milligrams per liter (mg/l).
• Amounts exceeding 700 ppm can be harmful to some plants.

Conductivity Class of Water

• Low Conductivity Water (C1) has a conductivity of up to 250 micro mhos/cm at 25 deg C.
• Medium Conductivity Water (C2) ranges from 250-750.
• High Conductivity Water (C3) ranges from 750-2250.
• Very High Conductivity Water (C4) exceeds 2250.
• Low sodium water (S1) has a SAR value between 0 to 10.
• Medium sodium water (S2) has a SAR value between 10 to 18.
• High sodium water (S3) has a SAR value between 18 to 26.
• Very high sodium water (S4) has a SAR value above 26.

Classifications of Saline and Alkaline Soils

• Saline soil (or white alkali) has an electrical conductivity > 4000, ESP is 15, and pH is ≤8.5.
• Alkaline soil (or Non-saline alkali or Sodic soil or Black alkali) has an electrical conductivity 4000, ESP is > 15 pH is 8.5 to 10.0.

Irrigation Water Quality

• Concentration of Potentially Toxic Elements such as boron and selenium can be toxic to plants.
• Bicarbonate Concentration must be related to the concentration of calcium plus magnesium.
• High bi-carbonate ions may result in precipitation of calcium and magnesium bicarbonates.
• Bacterial Contamination is not a serious problem unless the crops are directly eaten.
• The SAR(Sodium Absorption Ratio) formula is SAR = [Na+] / sqrt(([Ca++] + [Mg++]) / 2).

Water Requirements of Crops

• Total water quantity and manner in which a crop requires from sowing to harvest are key.
• Crop period is total time between sowing and harvesting.
• Base period is duration from the first watering to the last watering before maturity.
• Delta signifies the total water depth required for a crop during the entire crop period in the field.
• Frequency of irrigation (or Rotation period) is the time interval between consecutive waterings

Crop delta Calculation

• The Total depth of water needed by a crop over its entire life in the field, is the Delta.
• It is equal to the number of irrigations multiplied by the depth of water applied with each irrigation

Duty

• Duty is used to defines the area of land fully irrigated and matured by a unit volume of water over a specific period.
• Duty is equal to 8.64B/D

Factors Affecting the Duty of Water

• The Type of crop is a main factor, as different crops require different amounts of water.
• The Climate and season affect water loss in evaporation,
• Useful rainfall directly contributes to crop growth.
• Permeability of Soil: High permeability leads to more water loss due to percolation.
• The Efficiency of cultivation methods determines water waste.

Measures for Improving Duty of Water

• Leveling ensures uniform irrigation.
• Proper ploughing increases water absorption.
• Modern methods can be used.

Irrigation Method

• Porous soils should be treated before sowing.
• Alkaline soils should be leached for water retention.
• Manure and fertilizers increase soil's water-holding capacity.
• Prioritize crop rotation.

Handling Irrigation Supplies

• Sources should be within limits and provide quality.
• Canals must be lined.

River Engineering

• River Engineering is a discipline that studies human intervention in the course to produce benefits.
• It consists of construction of bridges,
• Generating hydroelectricity, building dams,
• Regulating channels, using sediments for construction, reducing reservoir deposits.
• Rivers need hydroelectricity from hydropower, dams for irrigation, regulated navigation, sediments for construction, and controlled water capacity.
• River is a natural flowing watercourse toward an ocean, sea, lake, or another river

River Characteristics

• Rivers range widely in size.
• Water and sediment discharge varies
• Are seldom straight.
• Shift place and have a history.
• River are classified by - topography - flood hydrographs

River Topography

• Rivers have a wide range in size and discharge, are curvy, shift positions, and have a long history.
• Rivers in Hills (Upper reaches) originate in mountains, incised/rocky, or boulder stages.
• Rivers in alluvial flood plains (Lower reaches) meander, are either aggrading, degrading, or stable.
• Braided rivers flow in multiple channels around alluvial islands due to deposition.
• Delta rivers form deltas shape as they join the sea, dividing into branches.
• Tidal rivers are affected by ocean tides in their tail reaches.
• Flashy rivers have sudden flood rises and falls.
• Virgin rivers in arid zones may dry up completely.
• There are 3 loads in the river as sediment is transported: dissolved, suspended, and bed load.
• There 2 types of bed load: sliding and saltating
• The wash load has fine sediments
• River basins drain an are consisting of:
  • the Main river,
  • the Tributaries
    • the Watershed Divide,
      • Areas prone Floodplains,
      • the Outflow Point.
• Sub-catchment refers to a smaller land that drains into a specific tributary
• Basin areas affect water volume; larger basins need complex hydrology.
• Basin shape : Elongated basins reduces flood risk while circular basins increase it
• Topography helps identify areas prone to flooding.
• Climatic and Rainfall Patterns contribute to events in the river basion.
• Hydrological characteristics include discharge, runoff, infiltration, and recharge.
• Geological aspects help plan for ground storage.
• Erosion sediments should be taken into account while planning for a basin.
• There are two types of flow in river engineering:
  • Steady flow occurs when discharge is constant and
  • Unsteady flow indicates variances in the rate.

Steady and Unsteady Flow

• Steady flow discharges do not change over time and occur when inflow and outflow are balanced.
• Common in controlled systems includes weirs and flumes.
• Unsteady Flow has varied flow rates, and water levels fluctuate over time due to precipitation and tides.
• The River is a natural channel. The river carries sediment based off the flow rates.
• There are 3 Types of waves:
  • Hydraulic Waves: Caused from Fluid Dynamics
  • Hydrological Waves: Can Be used for rainfall.
  • Kinematics Waves: Dominate the force of inertia.