Philippine Agricultural Engineering Standards - General Irrigation Terminologies

Vocabulary flashcards covering key definitions and terminologies from the Philippine Agricultural Engineering Standards (PAES) for Irrigation.

Active Storage

Volume of water stored in reservoir b/w minimum water level and normal water level

Afflux Elevation

Rise in maximum flood level from original unobstructed flood level which result after an obstruction to the flow

Application efficiency

Ratio of average depth of water infiltrated and stored in the root zone to the average depth of irrigation water applied

Bearing capacity

Maximum average contact pressure b/w the foundation and the soil

Conveyance efficiency

Ratio b/w water received at the inlet to that released at the project’s headwork

Conveyance Loss

Loss of water from a channel during transport due to seepage and percolation

Critical depth

Depth of water flow where the energy content is at minimum hence, no other backwater forces are involved

Crop coefficient

Ratio of actual ET to its potential ET

Crop Evapotranspiration

Rate of ET of a disease – free crop growing in a large field under optimal soil conditions

Crop water requirements

Amount of water used in producing crops which is the sum of evapotranspiration or consumptive use plus seepage and percolation losses

Dam height

Vertical distance from lowest point of ground line to the dam crest

Dead Storage

Volume below the intake structure; sediment volume based on 25 years of accumulation in the reservoir

Designed Height

Actual height of the embankment after settlement

Design Irrigable area

Maximum area which an irrigation project can serve considering the extent of arable lands and available water supply

Distribution Uniformity

Numerical value on the uniformity of application for agricultural irrigation systems

Diversion dam

Structure or weir provided across the river or creek to raise its water level and divert the water into the main canal to facilitate irrigation by gravity

Diversion water requirement

Total quantity of water diverted or removed from the ground in order to irrigate a crop

Drip irrigation / trickle irrigation

Involves dripping water onto the soil at very low rates ($2\text{--}20\text{ L/hr.}$) from the emitters

Drop

In-line canal structure designed to convey canal water from a higher elevation to a lower level, duly dissipating the excess energy resulting from the drop in elevation

Effective rainfall

Amount of rainwater that falls directly on the field

Effective rooting depth

Soil depth from which the bulk of the roots of the crop extracts most of the water needed for ET

Effective Size

Particle diameter corresponding to a 10% sieve passing

Effluent standard

Any legal restriction or limitation on quantities, rates, and/or concentrations or any combination thereof, which a person or point source is allowed to delivery into a body of water or land

Elevated Flume

Water conveying conduit or trough which is supported on abutments by piers

Emitter Spacing

Spacing b/w emitters or emission points along a lateral line

Emitters

Applicator used in drip, subsurface, or bubbler irrigation designed to dissipate pressure and to discharge a small flow or trickle of water at constant rate that does not vary significantly because of minor differences in pressure

Energy grade line / Specific energy line

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

Evapotranspiration

Combination of water transpired from vegetation and evaporated from the soil, water, and plant surfaces

Filter Drain

Dam component which prevents migration of small particles and screen off fine materials that flow with seepage water and prevent piping

Finished Height

Height of the embankment to be attained during construction

Farm Water Requirement

Amount of water to replenish the crop water requirement and losses less the effective rainfall

Freeboard

Additional height of the dam provided as safety factor to prevent overtopping by wave action or other causes

Homogenous Embankment

Dam composed of a single kind of embankment material exclusive for slope protection

Hydraulic depth

Ratio of flow area to the wetted top width

Hydraulic Grade Line / hydraulic gradient

Profile of the free water surface

Hydraulic jump

Occurs when a thin sheet of incoming flow moving at high velocity strikes water of sufficient depth

Hydraulic radius

Cross-sectional area of flow divided by the wetted perimeter

Inverted siphon

Closed conduit designed to convey canal water in full and under pressure running condition, to convey canal water by gravity under roadways, railways, drainage channels and local depressions

Karst Topography

Geologic formation shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rocks such as limestone or dolomite

Land Preparation Water Requirement

Amount of water required in lowland rice production which includes water losses through evaporation, seepage, and percolation and land soaking

Land Soaking Requirement

Amount of water required in lowland rice production which is a function of the initial soil moisture and the physical properties of the soil

Leaching

Deep percolation of water beyond the root zone of plants, resulting in loss of salts or nutrients

Manufacturer’s Coefficient of Variation

Measure of the variability of discharge of a random sample of a given make, model and size of emitter, as provided by the manufacturer and before any field operations or aging has taken place determined through a discharge test of a sample of 50 emitters under a set pressure at 200 ͦC

Normal depth

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

Normal Storage Elevation

Maximum elevation of water surface which can be attained by the dam or reservoir without flow in the spillway

Open Channel Flow

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

Optimal emitter spacing

Drip emitter spacing which is 80% of the wetted diameter estimated from field tests

Pan Coefficient

Ratio b/w reference ET and water loss by evaporation from an open water surface of a pan

Percolation

Vertical flow of water below the root zone which is affected by soil structure, texture, bulk density, mineralogy, OM content, salt type and concentration

Reference crop ET

Rate of ET from a reference surface which is hypothetical reference crop with an assumed height of $0.22\text{m}$, a fixed surface resistance of $70\text{ s/m}$ and an albedo of $0.23$

Residual MC

Moisture left in the soil before initial irrigation water delivery which describes the extent of water depletion from the soil when the water supply has been cut-off

Shallow Tubewell

Tube or shaft vertically set into the ground at a depth that is usually less than 15m for the purpose of bringing groundwater into the soil surface whose pumps are set above the water level

Seepage

Water escaping below or out from water conveyance facilities such as open ditches, canals, natural channels, and waterway

Setback distance

Distance from the perimeter of the irrigation area to the community or area of concern that is sensitive to contamination

Storage ratio

Ratio of the storage capacity to the total earth volume required for embankment construction which indicates the relative cost of the different types of reservoirs

Structural height

Vertical distance measured from the top of the dam down to the bedrock

Surface Irrigation System

Application of water by gravity flow to the surface of the field, either the entire field is flooded (basin irrigation0 or the water is fed into small channels (furrows) or strips of land (borders)

Uniformity Coefficient

Ratio of the particle size at 60% passing to that at 10% passing

Uniform Flow

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

Unimodal rainfall pattern

Rainfall pattern with five wet months of more than $200\text{mm/month}$, five dry months of less than $100\text{mm/month}$, two transition months of $100\text{mm-}200\text{mm/month}$ and total annual rainfall above $1500\text{mm}$

Watershed

Area which contributes to runoff or drains water into the reservoir

Wetted diameter

Diameter of the circular area wetted by the sprinkler when operating at a given pressure and no wind

Wetted perimeter

Portion of the perimeter of the canal that is in contact with the flowing water

Zoned embankments

Dam consisting a central impervious core flanked b/w zones of more pervious materials

Crop Rotation

Crops are planted in succession

Multiple Cropping

Four crops are grown in sequence, one after the other

Intercropping

Short duration catch crops are grown b/w rows of long-duration crops

Relay Cropping

Different crops are planted in a tight schedule

Corrugation Irrigation

Water flows down the slope in small furrows called corrugations or rills which is used for germinating drill-seeded or broadcasted crops; no raised beds are used for crops

Zigzag Furrow

Shall increase the length that the water must travel to reach the end of irrigation run, thus, reducing the average slope and velocity of the water

Piping

Internal erosion induced by regressive erosion of particles from downstream and along the upstream line towards an outside environment

Rockfill Dam

Dam that relies on rock, impervious membrane is used as water barrier and can be placed either within the embankment or on the upstream slope

Check Dam

Small barrier built across the direction of water flow on shallow rivers and streams intended to convey runoff during peak flow and to slow and hold surface water long enough for the water to deposit sediment it is carrying

Angle of Inclination

Tilt of PV module with respect to the horizontal plane

PV Performance Ratio

Ratio of the input solar power to the PV module and the output power of the inverter/controller

Ray of Incidence

Angle where a ray of sunlight strikes the surface of the PV module, measured with respect to line perpendicular to said surface