Irrigation and Drainage midterm 1

Mutated Lemon · 100問 · 2年前

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is the application of water to create a condition in the soil that is favorable for plant growth.

Irrigation

provides the moisture needed by the crop that is not satisfied by rainfall.

Irrigation

refers to the controlled application of water from agriculture through man-made systems.

Irrigation

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

Drainage

refers to the relative proportion of various size groups of individual soil grains. It is determined by the relative proportion of sand, silt, and clay fractions present 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. It is denoted by the letter “n”.

porosity

The measure of the amount of water in the soil. It can be expressed as a dry mass basis or volume basis.

Moisture content

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

Dry Mass Basis

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

Volume Basis

methods in measuring soil moisture

Gravimetric Method, Soil Moisture Sensors, Remote Sensing

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

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

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

Saturation Point

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

Available Moisture

the soil moisture content when plants permanently wilt. The soil moisture tension at this point is about 15 atmospheres

Permanent Wilting Point

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

Readily Available Moisture

is a continuous movement of water between hydrosphere, atmosphere, and lithosphere in a cyclic manner.

The Hydrologic Cycle

the process of a liquid's surface changing to a gas.

Evaporation

the process of a gas changing to a liquid.

Condensation

describes any liquid or solid water that falls to Earth as a result of condensation in the atmosphere.

Precipitation

takes place when the water is absorbed by vegetation cover and trees, absorbed into the ground, or stored in puddles and land formations such as furrows and streamlets.

Interception

physical process involving the slow passage of water through the soil.

Infiltration

the flow of water through the soil and rocks by the influence of capillary and gravity forces.

Percolation

is a process in all plants that normally takes place during the day, giving off water vapor from the leaves openings.

Transpiration

as the portion of rainfall, snowmelt, and/or irrigation water that runs over the soil surface toward the stream rather than infiltrating into the soil.

Runoff

kinds of runoff

Surface Runoff, Interflow – subsurface runoff, Baseflow

Water used for irrigation comes from?

surface water or groundwater

Water Sources for Irrigation

Surface water, Groundwater

Refers to the water that is above the Earth’s surface. Includes lakes, rivers, and man-made reservoir such as dams. It is highly prone to pollution.

Surface water

Refers to the water that is below the Earth’s surface. Less prone to pollution

Groundwater

are used all over the world as sources of irrigation water

Rivers

water is directly diverted from the river without any structures, dams or other devices. The off-take canal is directly excavated through the river bank and no gate is provided

Direct River Diversion

To avoid the problems caused by fluctuating water levels in a river, a weir can be built across the river.

River diversion using weir

is an artificial lake. It can be formed by building a dam across a valley, by excavating the land or by surrounding apiece of land with dykes

Reservoir

are supplied with water by rainfall that falls directly on the surface of the lake, by water run-off from the adjacent landand small streams, or by groundwater that seeps through the soil to the lowest point which is the lake.

Lakes

an important source of irrigation water, especially for small-scale irrigation projects. Because it is only available below ground level, it must be lifted, or pumped before it can be used

groundwater

a body that does not allow transmission of a significant amount of water, such as clay, a till, or a poorly fractured igneous or metamorphic rocks.

Aquitard

any water bearing, permeable geological formation that stores and transmits water

Aquifer

an impermeable body of rock which contains no interconnected openings or interstices and therefore neither absorbs nor transmits water

Aquifuge

impermeable formation which contains water

Aquiclude

Types of Aquifer

Unconfined Aquifer, Confined Aquifer, Perched Aquifer

An aquifer that is exposed at the ground surface that is the aquifer formation extends essentially to the land surface.

Unconfined Aquifer

It is the one in which groundwater is confined under pressure greater than the atmospheric pressure by overlying and underlying impervious layers.

Confined Aquifer

Special type of unconfined aquifer and occurs when the ground water body is separated from the main ground water by a relatively impermeable stratum of small aerial extend and by the zone of aeration above the main body of groundwater.

Perched Aquifer

A well that brings groundwater to the surface without pumping because it is under pressure within a body of rock and/or sediments known as an aquifer.

Artesian Wells

is the movement of irrigation water from a source. It is usually done using a simple earth canal or a network of control structures,channels, and distribution system

Water conveyance

usually a reservoir, surface water such as swamps, rivers, or lakes, or a pumping station with either a surface or groundwater source. It directs water into the irrigation system.

Main intake structure

transports water from the main intake structure or main pumping station up to the farm ditches.

The conveyance system

is on the transport of water through field ditches to the fields to be irrigated

distribution system

assures the transport of water within the fields

field application system

removes the excess water from the fields.

drainage system

are due to operator or technician skill, which may affect the volume delivered to the farm

Operation losses

sometimes, this is considered negligible and are not included in the estimation process.

Evaporation losses

this is the most significant loss that should be considered for efficiency improvement. It is defined as the downward and lateral movement of water into the soil.

Seepage losses

cross sectional area of a conveyance channel measured perpendicular to the direction of flow

Area

elevation drop per unit length of the channel bottom

Channel bed slope

depth of water in the channel cross section

Depth

grade line of the water surface profile plus the velocity head in open channels.

Energy grade line

vertical line from the top of the channel to the water surface at the design condition.

Free board

ratio of flow area to the wetted top width

Hydraulic depth

cross sectional area of flow divided by the wetted perimeter

Hydraulic radius

canals with impermeable material for channel stabilization and/or reduced seepage.

Lined channel

constant flow depth along a longitudinal section of a channel under a uniform flow condition

Normal depth

water flow that is conveyed in such a manner that top surface is exposed to the atmosphere such as flow in canals, ditches, drainage channels, culverts, and pipes under partially full flow conditions.

Open channel flow

slope of the free water surface

Slope of the hydraulic grade line

slope of the water surface profile plus the velocity head in open channels

Slope of the energy grade line

ratio of the horizontal to vertical dimension of the channel wall

Side slope

width of the channel cross-section at the free surface

Top width

occurs when flow has a constant water area, depth, discharge, and average velocity through a reach of channel.

Uniform flow

portion of the perimeter of the canal that is in contact with the flowing water.

Wetted perimeter

are very common in the construction of concrete-lined canals

Rectangular channels

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