42 water and wastewater terms with concise definitions and links to relevant formulas. Norwegian terms are kept in parentheses for reference.
Characteristic height of irregularities on the pipe wall, expressed in mm. Used in Colebrook-White.
Scaling of pump characteristic with speed change: Q ∝ n, H ∝ n², P ∝ n³.
Measure of organic pollution — oxygen consumed by microorganisms over 5 days at 20 °C.
Multiplier on design rainfall to account for climate change towards 2100.
Measure of all oxidisable substances in water. Covers more than BOD, faster measurement.
Water depth where specific energy is at minimum and Froude = 1. Boundary between sub- and supercritical flow.
Temporary storage of stormwater to reduce peak runoff to the receiving water.
Nominal diameter in mm. DN150 ≈ 150 mm internal (actual size varies slightly with material).
Sum of elevation, pressure head and velocity head along a streamline. Bernoulli's principle.
Required flow and pressure for fire fighting. Class 1 (20 l/s), 2 (33 l/s), 3 (50 l/s) at 0.5 bar.
Minimum cover depth for water mains to avoid freezing. Varies 1.5–2.2 m in Norway.
Dimensionless ratio classifying open-channel flow. Fr<1 subcritical, Fr=1 critical, Fr>1 supercritical.
Iterative method for solving flow distribution in looped networks by adjusting flow until continuity and energy balance are satisfied.
Empirical coefficient covering both roughness and viscosity for water at 15 °C.
Sudden transition from supercritical to subcritical flow in an open channel — used for energy dissipation.
Intensity-Duration-Frequency: rainfall intensity for various durations and return periods.
Penetration of water into the soil. Horton's equation describes how capacity decays with time.
Water entering the wastewater system that is not sewage — pipe leakage, drainage, illegal connections.
Empirical formula for stones in still or slow-moving water at control structures.
Share of produced drinking water lost in the distribution network before reaching consumers.
Empirical roughness coefficient in Manning's formula — expresses friction between fluid and pipe or channel wall.
The value is constant for a given material and surface, but depends slightly on fill ratio and flow regime. Lower n means smoother surface.
Calculates earth load on buried pipe by considering friction along trench walls and the fill column.
Empirical method (US Army Corps) for sizing riprap in channels and rivers.
Energy losses in bends, valves, tees — expressed as ζ · v²/(2g).
Positive head above vapour pressure on the suction side. NPSHa > NPSHr avoids cavitation.
Intersection of pump characteristic and system curve. Q and H are determined geometrically.
Zone above the pipe where bearing capacity is critical — fill must be compacted to specification.
Load from one person — typically 150–200 l/day water use and 60 g BOD₅. Industry is converted to PE.
Area with pressure within set min/max. Often max 6 bar (at house), min 2 bar (at consumption point).
Empirical method for design runoff Q = C · i · A · K_f. Applies to small urban catchments (<2 km²).
Expected interval between events exceeding a given size. T_r = 10 years ≈ 10% probability per year.
Dimensionless ratio of inertial to viscous forces, classifies the flow regime.
Fraction of rainfall that becomes direct runoff. The remainder infiltrates or evaporates.
Multiplier on design value to cover uncertainty and future growth.
Empirical parameter (1–100) combining land-use, soil type and antecedent moisture.
Requirement that sediment shall not accumulate — typically τ ≥ 1.5 N/m² or v ≥ 0.6 m/s at daily fill.
Friction force per unit area on pipe or channel wall. τ = ρ · g · R · S in fully developed flow.
Dimensionless threshold for sediment incipient motion: τ*c ≈ 0.06 for coarse sand/gravel.
Classifies pump type: low (centrifugal), medium (mixed-flow), high (axial).
Time for water to flow from the most distant point in the catchment to the outlet.
Used as design rainfall duration in the rational method. Kirpich and SCS methods give empirical estimates.
Time water has spent in the network after treatment. High water age leads to growth of micro-organisms.
Pressure wave propagating from rapid velocity change, e.g. valve closure.