Irrigation and Drainage

Question 1

the relative proportion of primary particles (sand, silt and clay) in the soil

Answer 1

Soil Texture

Question 2

the arrangements of primary particles in the soil into units or peds

Answer 2

Soil Structure

Question 3

the ratio of the void volume to the total soil volume (unitless)

Answer 3

Porosity (n)

Question 4

the ratio of the weight of water to the dry weight of the soil

Answer 4

Moisture content on a dry weight basis (mcw)

Question 5

the ratio of the volume of water to the total soil volume

Answer 5

Moisture content on a volume basis or volumetric moisture content (mcv)

Question 6

the ratio of the dry weight of the soil to the total soil volume

Answer 6

Bulk density

Question 7

the ratio of the dry weight of the soil to the volume of the soil particles

Answer 7

Particle density

Question 8

– 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

Answer 8

Apparent Specific Gravity (As)

Question 9

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

Answer 9

Real Specific Gravity (Rs)

Question 10

the equivalent depth of water in the soil at a given condition

Answer 10

Depth of water present in the soil

Question 11

Requred to increase the moisture content from an initial value (mci) to a final value (mcf)

Answer 11

Depth of water needed

Question 12

volume of water to be applied to increase a the soil moisture content from an initial to final value (units: liters, cm3, m3)

Answer 12

Volume of irrigation water (Viw)

Question 13

Value of the density of water, ρw

Answer 13

1 g/cm3 or 1,000 kg/m3

Question 14

the time rate at which water will percolate into the soil and can be expressed in terms of the following empirical equations

Answer 14

Infiltration Rate

Question 15

the amount of water the soil profile will hold when all its pore spaces are filled up with water

Answer 15

Saturation Point

Question 16

(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.

Answer 16

Field Capacity

Question 17

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.

Answer 17

Permanent Wilting Point (or wilting coefficient)

Question 18

the difference in moisture content of the soil between field capacity and the permanent wilting point.

Answer 18

Available Moisture (AM)

Question 19

that portion of the available moisture that is most easily extracted by plants; this is approximately 75% of the available moisture.

Answer 19

Readily Available Moisture (RAM)

Question 20

the ratio between the water delivered to the farm and the water diverted from a river or reservoir expressed in percent.

Answer 20

Water Conveyance Efficiency

Question 21

the ratio between water stored in the soil root zone during irrigation and the water delivered to the farm expressed in percent.

Answer 21

Water Application Efficiency

Question 22

the ratio of water beneficially used on the project, farm or field to the amount of water delivered to the farm expressed in percent.

Answer 22

Water-use Efficiency

Question 23

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.

Answer 23

Water Storage Efficiency

Question 24

the ratio of the normal consumptive use of water to the net amount of water depleted from the root zone soil.

Answer 24

Consumptive Use Efficiency

Question 25

- the power theoretically required to lift a given quantity of water each second to specified height.

Answer 25

Water horsepower

Question 26

water horsepower divided by pump efficiency, in decimal.

Answer 26

Brake Horsepower

Question 27

- 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.

Answer 27

Static Head

Question 28

the sum of total static head, pressure head, velocity head and friction head.

Answer 28

Total Dynamic Head

Question 29

(in a well) is the difference in elevation between the groundwater table and the water surface at the well when pumping.

Answer 29

Drawdown

Question 30

graphs that show interrelations between speed, head discharge, and horsepower of a pump.

Answer 30

Characteristic Curve

Question 31

expresses the relationship between speed in rpm, discharge in gpm, and head in feet.

Answer 31

Specific Speed

Question 32

- 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.

Answer 32

Evapotranspiration

Question 33

the process by which water vapor escapes from living plants, principally by leaves, and enters the atmosphere.

Answer 33

Transpiration

Question 34

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.

Answer 34

Canal Capacity

Question 35

the fraction of the irrigation water that must be leached through the root zone to control soil salinity at specified level.

Answer 35

Leaching Requirement (LR)

Question 36

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.

Answer 36

Crop Water Requirement (CWR)

Question 37

- depends on the type of crop being grown, type of soil, climatic conditions and farming practices and techniques. - include seepage and percolation losses

Answer 37

Crop Water Requirement (CWR) Non-consumptive uses

Question 38

includes evaporation and transpiration, lumped together as evapotranspiration.

Answer 38

Crop Water Requirement (CWR) Consumptive uses

Question 39

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.

Answer 39

Irrigation Water Requirement (IWR)

Question 40

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.

Answer 40

Application losses

Question 41

the ratio of the amount of water entering the tertiary canal and the amount of water that reaches the field.

Answer 41

Application efficiency

Question 42

the ratio of the amount of water entering the main canal and the amount of water that reaches the tertiary canal.

Answer 42

Conveyance efficiency

Question 43

which is the quantity of water to be obtained from the source.

Answer 43

design diversion water requirement

Question 44

irrigation systems that have relatively large service areas and are managed by government agencies

Answer 44

National Irrigation Systems (NIS)

Question 45

managed and operated by farmers’ or irrigators’ associations

Answer 45

Communal Irrigation Systems (CIS)

Question 46

pipes vertically set into the ground that abstract groundwater to be used for irrigation, usually owned and operated by individual farmers

Answer 46

Shallow Tubewell Irrigation Systems (STW)

Question 47

irrigation, wherein the soil is moistened in much the same way as rain

Answer 47

overhead irrigation

Question 48

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.

Answer 48

Furrow irrigation

Question 49

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.

Answer 49

Corrugation irrigation

Question 50

Irrigation which wets the entire land surface

Answer 50

flooding

Question 51

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.

Answer 51

Ordinary flooding

Question 52

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.

Answer 52

Border-strip flooding

Question 53

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.

Answer 53

Level-border or basin irrigation

Question 54

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.

Answer 54

Contour-ditch irrigation

Question 55

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.

Answer 55

drip or trickle irrigation

Question 56

removal of excess water in the soil to create conditions suitable for plant growth

Answer 56

Drainage

Question 57

The soil type largely influences the width of bed to be used. The furrows drain to collection ditches.

Answer 57

Bedding System

Question 58

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.

Answer 58

Random Ditch System

Question 59

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.

Answer 59

Interception or Cross-slope System.

Question 60

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.

Answer 60

Diversion or Parallel Ditch System

Question 61

This system is used in rolling topography where drainage is necessary only in small valleys

Answer 61

Natural System.

Question 62

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.

Answer 62

Gridiron Layout

Question 63

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.

Answer 63

Herringbone Pattern

Question 64

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.

Answer 64

Double-main System

Question 65

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.

Answer 65

Intercepting Drain

Question 66

the composite parts of the irrigation system that divert water from natural bodies of water such as rivers, streams, and lakes

Answer 66

Headworks

Question 67

lands which display marked characteristics justifying the operation of an irrigation system

Answer 67

Irrigable Lands

Question 68

a system of irrigation facilities covering contiguous areas

Answer 68

Irrigation System

Question 69

an association of farmers within a contiguous area served by a National Irrigation System or Communal Irrigation System

Answer 69

Irrigators’ Association (IA)

Question 70

the channel where diverted water from a source flows to the intended area to be irrigated

Answer 70

Main Canal

Question 71

composite facilities that permit entry of water to paddy areas and consist of farm ditches and turnouts

Answer 71

On-Farm Irrigation Facilities

Question 72

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

Answer 72

Shallow Tubewell (STW)

Question 73

the channel connected to the main canal which distributes irrigation to specific areas

Answer 73

Secondary Canal