SCE PE Water Resources & Environmental key terms

A simple rainfall-runoff formula estimating peak discharge as the product of a runoff coefficient, design rainfall intensity for the time of concentration, and drainage area.

The travel time for water to flow from the most hydraulically remote point of a drainage area to the outlet; used to choose design rainfall intensity.

An NRCS parameter from 0 to 100 representing the runoff potential of a soil-cover complex; higher values mean more runoff and less infiltration.

The direct runoff hydrograph resulting from one unit of effective rainfall (such as one inch) uniformly distributed over a watershed during a specified duration.

A graph showing rainfall intensity versus duration for several return periods at a location; used to select design storm intensity for a given duration.

The average number of years between events equal to or exceeding a given magnitude; the reciprocal of the annual exceedance probability.

A procedure that tracks a flood wave through reservoir or channel storage using continuity and a storage-discharge relationship to compute outflow hydrographs.

An empirical head-loss formula for water flowing full in pipes, relating friction loss to flow rate, diameter, length, and a roughness coefficient C.

A head-loss equation using a friction factor that depends on Reynolds number and relative roughness; it applies to any fluid and flow regime.

Head loss caused by fittings, valves, bends, expansions, and other disturbances, computed as a loss coefficient K times the velocity head.

A transient pressure surge caused by rapid changes in flow velocity in a pipeline, producing high and low pressures that can damage pipes.

Net positive suction head: the absolute pressure head at a pump suction, available from the system or required by the pump to avoid cavitation.

A plot of the total head required by a piping system versus flow rate, combining static lift and friction losses; the pump operates where it crosses the pump curve.

A line showing piezometric head, the sum of pressure head and elevation, along a pipe; it lies below the energy grade line by the velocity head.

An empirical formula for average velocity in open-channel or full-pipe flow using hydraulic radius, channel slope, and a roughness coefficient n.

The flow cross-sectional area divided by the wetted perimeter; a measure of channel efficiency used in Manning's and Chezy equations.

The uniform-flow depth at which gravity and friction balance for a given discharge, slope, and channel shape, computed with Manning's equation.

The depth at which specific energy is minimum for a given discharge; the Froude number equals one and flow can pass between subcritical and supercritical states.

A dimensionless ratio of inertial to gravitational forces in free-surface flow; less than one is subcritical, greater than one is supercritical.

The sum of flow depth and velocity head relative to the channel bottom for a given discharge per unit width; minimum at critical depth.

An abrupt transition from supercritical to subcritical flow marked by turbulence, energy dissipation, and a rise in the water surface.

The oxygen consumed by microorganisms while decomposing biodegradable organic matter in a water sample under specified conditions, commonly five days at 20 degrees Celsius.

The concentration of particulate matter retained on a filter after a water sample is filtered and the residue dried at a standard temperature.

A biological treatment process in which an aerated mixed microbial culture degrades organic matter, followed by clarification and return of settled biomass to the aeration basin.

Solids retention time: the average time microorganisms remain in an activated sludge system; a key design parameter controlling treatment performance and sludge production.

Sludge volume index: the volume in milliliters occupied by one gram of sludge after 30 minutes of settling, used to judge settleability and detect bulking.

The product of disinfectant residual concentration and contact time used to demonstrate pathogen inactivation credit, adjusted for temperature, pH, and other factors.

A water treatment step that destabilizes colloidal particles and dissolved organics by rapid mixing with chemicals so they can aggregate into settleable flocs.

The biological oxidation of ammonia to nitrite and then nitrate by autotrophic bacteria, consuming oxygen and alkalinity in aerobic wastewater treatment.

The equivalent value today of future costs or benefits discounted at a specified interest rate over a defined analysis period.

The total cost of a facility over its useful life, including capital, operation, maintenance, replacement, and salvage, expressed in present-worth terms.

A method comparing the discounted benefits and costs of a project, often as a ratio, to judge whether public investment is economically justified.

The time span for which a facility is sized to meet projected demand before expansion, balancing capital cost against future capacity needs.

A multiplier applied to average demand or flow to estimate the maximum rate a conveyance, storage, or treatment unit must handle.