Irrigation and Drainage Flashcards
Knowledge on farm irrigation and drainage will equip the individual with the understanding of the relation between crops and the amount and timing of both irrigation and drainage.
the relative proportion of primary particles (sand, silt and clay) in the soil
Soil Texture
the arrangements of primary particles in the soil into units or peds
Soil Structure
the ratio of the void volume to the total soil volume (unitless)
Porosity (n)
the ratio of the weight of water to the dry weight of the soil
Moisture content on a dry weight basis (mcw)
the ratio of the volume of water to the total soil volume
Moisture content on a volume basis or volumetric moisture content (mcv)
the ratio of the dry weight of the soil to the total soil volume
Bulk density
the ratio of the dry weight of the soil to the volume of the soil particles
Particle density
– ratio of the bulk density of the soil with the density of water; it is the ratio of the weight of soil to the weight of water with volume equal to the total soil volume
Apparent Specific Gravity (As)
ratio of the particle density of the soil with the density of water; it is the ratio of the weight of soil to the weight of water with volume equal to the volume of the soil particles alone
Real Specific Gravity (Rs)
the equivalent depth of water in the soil at a given condition
Depth of water present in the soil
Requred to increase the moisture content from an initial value (mci) to a final value (mcf)
Depth of water needed
volume of water to be applied to increase a the soil moisture content from an initial to final value (units: liters, cm3, m3)
Volume of irrigation water (Viw)
Value of the density of water, ρw
1 g/cm3 or 1,000 kg/m3
the time rate at which water will percolate into the soil and can be expressed in terms of the following empirical equations
Infiltration Rate
the amount of water the soil profile will hold when all its pore spaces are filled up with water
Saturation Point
(1) the amount of water a soil profile will hold against drainage by gravity at a specified time (usually from 24 to 48 hours) after a thorough wetting. (2) the moisture content of the soil when gravitational water has been removed (after irrigation by flooding). It is usually determined few days after irrigation. The soil moisture tension at this point is normally between 1/10 to 1/3 atmosphere.
Field Capacity
the soil moisture content when plants permanently wilt. The soil moisture tension at this point is about 15 atmospheres. Permanent wilting percentage can be estimated by dividing the field capacity by a factor ranging form 2.0 top 2.4, with the value higher for soils with higher silt content.
Permanent Wilting Point (or wilting coefficient)
the difference in moisture content of the soil between field capacity and the permanent wilting point.
Available Moisture (AM)
that portion of the available moisture that is most easily extracted by plants; this is approximately 75% of the available moisture.
Readily Available Moisture (RAM)
the ratio between the water delivered to the farm and the water diverted from a river or reservoir expressed in percent.
Water Conveyance Efficiency
the ratio between water stored in the soil root zone during irrigation and the water delivered to the farm expressed in percent.
Water Application Efficiency
the ratio of water beneficially used on the project, farm or field to the amount of water delivered to the farm expressed in percent.
Water-use Efficiency
the ratio of water stored in the root zone during the irrigation to the water needed in the root zone prior to irrigation, expressed in percent.
Water Storage Efficiency
the ratio of the normal consumptive use of water to the net amount of water depleted from the root zone soil.
Consumptive Use Efficiency
- the power theoretically required to lift a given quantity of water each second to specified height.
Water horsepower
water horsepower divided by pump efficiency, in decimal.
Brake Horsepower
- the difference in elevation of the water surface in a pond, lake, or river from which pumped water is taken, and the water surface of the discharge canal into which the water flows from a submerged discharged pipe. In pumping from groundwater source, static head is the difference in elevation between the water surface in the well and the water surface of the discharged canal.
Static Head
the sum of total static head, pressure head, velocity head and friction head.
Total Dynamic Head
(in a well) is the difference in elevation between the groundwater table and the water surface at the well when pumping.
Drawdown
graphs that show interrelations between speed, head discharge, and horsepower of a pump.
Characteristic Curve
expresses the relationship between speed in rpm, discharge in gpm, and head in feet.
Specific Speed
- is the sum of transpiration and water evaporated from the soil, or exterior portions of the plants where water may have accumulated from irrigation, rainfall, dew, or exudation from the interior of the plants. Consumptive use is identical with evapotranspiration, for practical purposes. Consumptive use only includes water retained in the plant tissue.
Evapotranspiration
the process by which water vapor escapes from living plants, principally by leaves, and enters the atmosphere.
Transpiration
The ability of the stream to provide water determines the extent of the total service area of a national irrigation system. To compute for the service area, the stream’s dependable flow (to a certain percent of dependability) is divided by the diversion water requirement.
Canal Capacity
the fraction of the irrigation water that must be leached through the root zone to control soil salinity at specified level.
Leaching Requirement (LR)
refers to the amount of water used for the non-consumptive demands such as land soaking and land preparation, and for the consumptive demands such as evapotranspiration requirements of the crop during its entire growth period.
Crop Water Requirement (CWR)
- depends on the type of crop being grown, type of soil, climatic conditions and farming practices and techniques.
- include seepage and percolation losses
Crop Water Requirement (CWR) Non-consumptive uses
includes evaporation and transpiration, lumped together as evapotranspiration.
Crop Water Requirement (CWR) Consumptive uses
the amount of water to be applied to the field as irrigation. It can be computed by deducting the effective rainfall (ER) from the total crop water requirement.
Irrigation Water Requirement (IWR)
include the seepage and percolation losses along the canals as well as losses due to evaporation. To account for these losses, the design farm requirement is computed with the application efficiency in consideration.
Application losses
the ratio of the amount of water entering the tertiary canal and the amount of water that reaches the field.
Application efficiency
the ratio of the amount of water entering the main canal and the amount of water that reaches the tertiary canal.
Conveyance efficiency
which is the quantity of water to be obtained from the source.
design diversion water requirement
irrigation systems that have relatively large service areas and are managed by government agencies
National Irrigation Systems (NIS)
managed and operated by farmers’ or irrigators’ associations
Communal Irrigation Systems (CIS)
pipes vertically set into the ground that abstract groundwater to be used for irrigation, usually owned and operated by individual farmers
Shallow Tubewell Irrigation Systems (STW)
irrigation, wherein the soil is moistened in much the same way as rain
overhead irrigation
It is accomplished by running water through small channels or furrows while it moves down or across the slope of the field. The water sips into the bottom and sides of t he furrows to provide the desired wetting. Careful land grading for uniform slopes is essential with this method.
Furrow irrigation
It is a variation of the furrow method and it uses small rills or corrugations for irrigating closely spaced crops, such as small grains and pastures. The water seeps laterally through the soil, wetting the area between the corrugations.
Corrugation irrigation
Irrigation which wets the entire land surface
flooding
Water is applied from field ditches to guide its flow and it is difficult to attain high irrigation efficiency using this method. The chief advantage of this method is its low initial cost of preparing the land.
Ordinary flooding
A field is divided into a series of strips by borders or ridges running down the predominant slope or on the contour. To irrigate, water is released into the head of the border. The water, confined and guided by two adjacent borders, advances in a thin sheet toward the lower end of the strip. The objective is to allow a sheet of water to advance down the narrow strip of land, allowing it to enter the soil as the water advances.
Border-strip flooding
Water is supplied to level plots surrounded by dikes or levees. This method is particularly useful on fine-textured soils with low permeability, it is necessary to hold the water on the surface to secure adequate penetration.
Level-border or basin irrigation
It involves controlled flooding from field ditches along the contour of the land, which allows the water to flood down the slope between field ditches without employing dikes or other means that guide or restrict its movement.
Contour-ditch irrigation
irrigation wherein the water is directed to the base of the plant. Water is applied to the soil through small orifices. The small orifices, often called emitters, are designed to discharge water at rates of 1 to 8 liters per hour. Water is delivered to the orifices through plastic pipelines, which are generally laid on the soil surface or buried. The rate of discharge is determined by the size of the orifice and the pressure in the pipelines. This method is particularly beneficial for young orchards, vineyards, closed-spaced perennials, and other crops of high value and in areas where water is scarce or has a high salt content. A highly efficient water utilization can be achieved with this method, bit it is very expensive.
drip or trickle irrigation
removal of excess water in the soil to create conditions suitable for plant growth
Drainage
The soil type largely influences the width of bed to be used. The furrows drain to collection ditches.
Bedding System
This system is adapted to areas that have depressions which are too deep or too large to fill by land leveling. The ditches meander from one low spot to another, collecting the water and carrying it to an outlet ditch.
Random Ditch System
This resembles terracing in that the drainage ditches are constructed around the slope on a uniform grade according to the land topography. The ditches should be constructed across the slope as straight and parallel s the topography permits.
Interception or Cross-slope System.
This is suitable on flat, poorly drained soils that have numerous shallow depressions. In general, the ditches are 185 m to a maximum of 370 m apart (not necessarily equidistant) and the land in between the parallel ditches is sloped and smoothed to eliminate any minor depressions or obstructions to the overland flow of the water.
Diversion or Parallel Ditch System
This system is used in rolling topography where drainage is necessary only in small valleys
Natural System.
Used if the entire area is to be drained and is usually more economic. Laterals enter the submain from one side only to minimize the double drainage that occurs near the submain.
Gridiron Layout
The submain is laid in a depression and the laterals join the submain from each side alternately. The land along the submain is double drained, but since it is in a depression, it probably requires more drainage.
Herringbone Pattern
This system is often used if the bottom of the depression is wide since it reduces the lengths of the laterals and eliminates the break in slope of the laterals at the edge of the depression.
Double-main System
This is used if the main source of excess water is drainage from hill lands. The drains are placed along the toe of the slope to protect the bottom land.
Intercepting Drain
the composite parts of the irrigation system that divert water from natural bodies of water such as rivers, streams, and lakes
Headworks
lands which display marked characteristics justifying the operation of an irrigation system
Irrigable Lands
a system of irrigation facilities covering contiguous areas
Irrigation System
an association of farmers within a contiguous area served by a National Irrigation System or Communal Irrigation System
Irrigators’ Association (IA)
the channel where diverted water from a source flows to the intended area to be irrigated
Main Canal
composite facilities that permit entry of water to paddy areas and consist of farm ditches and turnouts
On-Farm Irrigation Facilities
a tube or shaft vertically set into the ground for the purpose of bringing groundwater to the soil surface from a depth of less than 20 meters by suction lifting
Shallow Tubewell (STW)
the channel connected to the main canal which distributes irrigation to specific areas
Secondary Canal
