GATE AG key terms

The portion of water withdrawn for a use that is not returned to the source because it evaporates, transpires through plants, or is incorporated into products or crops.

The volume of irrigation water required to mature a crop over its growing season, usually expressed in hectares per cubic metre per second of continuous flow.

The total depth of irrigation water needed to raise a crop over its whole growing period, commonly stated in centimetres or millimetres of water depth.

The rate at which water is lost from a standardized grass or alfalfa surface under given weather conditions, used as a baseline for estimating crop water demand through crop coefficients.

A stable alluvial channel design concept in which sediment transport and boundary friction balance, giving silt factor, regime width, depth, and slope relationships for an unlined canal.

A dimensionless index in Lacey's regime theory representing the average particle size of sediment carried by a canal, influencing the designed width, depth, and slope.

The boundary shear stress at which bed sediment particles begin to move, used to check whether a canal bed or channel lining will remain stable against scour.

A rapid transition of open-channel flow from supercritical to subcritical state, producing a rise in water surface and energy dissipation used in stilling basins below spillways.

A dimensionless ratio of inertial to gravitational forces in open-channel flow; values below one indicate subcritical flow and above one indicate supercritical flow.

The total head of flowing water in an open channel measured relative to the channel bed, equal to flow depth plus velocity head, and used in critical-depth analysis.

A structural pool downstream of a spillway or outlet designed to dissipate excess kinetic energy of high-velocity flow before it reaches the natural channel.

A curved-crested overflow structure shaped to follow the lower nappe of flow over a sharp crest, allowing high discharge capacity with controlled pressures on the crest.

A dimensionless factor that corrects the theoretical flow rate through an orifice, weir, or spillway to account for real contraction, friction, and velocity distribution effects.

A flow-measuring structure that narrows the channel to create a measurable upstream-to-throat depth difference, giving discharge from a calibration relation with little head loss.

A simplification in fluid mechanics and soil mechanics that treats density variations as negligible except where they drive buoyancy, enabling simpler governing equations for flow and consolidation problems.

A classical formula giving the ultimate bearing pressure of a shallow footing as a sum of cohesion, surcharge, and unit-weight terms, each multiplied by bearing capacity factors.

An in-situ soil test in which a split spoon sampler is driven by a standard hammer, and the blow count for a set penetration is used to estimate soil strength and density.

Loss of shear strength in saturated loose sandy soil when cyclic loading raises pore water pressure until effective stress approaches zero, causing the ground to behave like a fluid.

Time-dependent volume decrease of saturated fine-grained soil as excess pore water is squeezed out under an applied load, computed from compression index and void ratio change.

A soil parameter describing the rate at which excess pore pressure dissipates during consolidation, used with drainage path length to predict settlement versus time.

The intergranular stress carried by a soil skeleton, equal to total stress minus pore water pressure, and the governing quantity for strength and compressibility.

The moisture content at which a fine-grained soil transitions from plastic to semi-solid behaviour, forming the lower bound of the plastic range used in soil classification.

The water content at which a remoulded fine-grained soil closes a standard groove under a specified number of blows, marking the boundary between liquid and plastic states.

The numerical difference between liquid limit and plastic limit, indicating the range of water content over which a soil remains plastic and its sensitivity to moisture change.

The ease with which freshly mixed concrete can be placed, compacted, and finished without segregation, commonly assessed by slump, compaction factor, or Vee-Bee tests.

The mass ratio of water to cement in a concrete mix, which inversely controls strength and strongly influences durability, permeability, and workability of the hardened material.

Two defects of fresh concrete: separation of coarse aggregate from mortar, and upward migration of water to the surface, both reducing uniformity and surface quality.

The ratio of the elastic modulus of steel reinforcement to that of concrete, used in working-stress design to transform a composite section into an equivalent concrete area.

The distance from the extreme compression fibre to the level of zero bending stress in a reinforced concrete section, central to both working-stress and limit-state flexural design.

A structural design philosophy that checks a member against specified failure conditions, such as collapse and serviceability, using partial safety factors on loads and material strengths.

The capacity of a reinforced concrete member to undergo large inelastic deformation before failure, promoted by under-reinforced sections and adequate confinement of concrete.

A permanently fixed point with a known reduced level established by precise levelling, serving as a reference for vertical control in topographic and engineering surveys.

The elevation of a survey point expressed relative to a chosen datum, obtained by adding or subtracting observed level differences from a benchmark.

The surveying operation of determining height differences between points, typically using a level instrument and graduated staff, or by trigonometric and total-station methods.

A surveying method that determines horizontal distance and elevation of a point from instrument readings and vertical angle, without chaining along the line.

The field procedure of pegging out a horizontal or vertical curve by offsets, deflection angles, or coordinates so that a road or railway follows its designed alignment.

Biochemical oxygen demand measures oxygen consumed by microbes degrading organic matter, while chemical oxygen demand measures oxygen consumed by a strong oxidant; together they indicate organic pollution load.

A biological wastewater treatment unit in which sewage trickles over a bed of attached-growth media, and microorganisms oxidize organic matter as air diffuses through the bed.

The final treatment step that destroys pathogenic microorganisms in water, commonly by chlorination, ozonation, or ultraviolet irradiation, leaving a residual where required.