Urban Water Management Final Exam Review

Vocabulary practice flashcards covering core urban hydrology, flood defence engineering, groundwater dynamics, drought indices, and nature-based solutions.

Watershed

The land area that drains to a common outlet, bounded by a drainage divide (ridge line); also referred to as a catchment or basin.

Drainage divide

A ridge line marking the topographic boundary that separates two adjoining watersheds.

Impervious cover

Any artificial surface through which water cannot infiltrate (such as roofs, roads, and car parks), which converts rain into rapid surface runoff.

Connected (effective) impervious area

The portion of impervious ground that drains directly into gutters and storm pipes, having a far greater impact on hydrograph peaks and lag times than total impervious area.

Hydrograph

A continuous plot of stream discharge (flow rate) against time at a specific cross-section of a channel.

Rising limb

The ascending portion of a hydrograph that shows the rapid increase in stream discharge following rainfall.

Falling (recession) limb

The declining segment of a hydrograph where stream discharge gradually drops back toward pre-storm baseflow.

Lag time

The time delay between peak rainfall intensity and peak stream discharge.

Baseflow

The sustained, slow, groundwater-fed contribution to streamflow between precipitation events.

Quickflow

The direct storm runoff component appearing above the baseflow separation line on a stream hydrograph.

Combined sewer overflow (CSO)

The direct discharge of untreated industrial wastewater, domestic sewage, and stormwater runoff into watercourses when storm runoff exceeds sewer system capacity.

Pluvial flood

Urban flooding generated by intense, high-volume rainfall before the water reaches an established river channel or drainage conduit.

Return period

The statistical average time interval between flood events of a specified magnitude (e.g., a $100$-year flood has a $1\%$ annual exceedance probability).

Sunny-sky flooding

Flooding occurring without rainfall (also known as tidal, nuisance, or king-tide flooding) when high tides force water backward through gravity drainage outlets and onto low-elevation land.

Piping

Subsurface mechanical erosion where concentrated water seepage carries fine soil particles out from beneath or within an earthen dike or levee, forming subterranean channels.

Levee effect

A hazard paradox identified by Gilbert White (1945) wherein protective levees foster an exaggerated perception of safety, stimulating dense floodplain development and exponentially elevating damages when a structural failure occurs.

Relative sea level rise

The net change in water level relative to the local land surface, calculated as the sum of global eustatic sea level rise and local ground subsidence.

Aquifer

A water-bearing body of permeable rock, sand, or gravel that yields commercially or domestically exploitable quantities of groundwater.

Aquitard

A geological formation of low hydraulic conductivity (such as dense clay or shale) that retards groundwater movement between aquifers.

Unconfined aquifer

An aquifer whose upper boundary is the open phreatic water table under atmospheric pressure, replenished by direct vertical rainwater infiltration.

Confined aquifer

An aquifer bounded above by a low-permeability aquitard, maintaining groundwater under artesian pressure derived from elevated or distant recharge outcrops.

Potentiometric surface

The imaginary piezometric surface representing the hydraulic level to which water in a confined aquifer would rise inside a borehole.

Artesian well

A borehole penetrating a confined aquifer in which internal hydrostatic pressure elevates the groundwater column above the upper confining geological boundary.

Non-revenue water

Treated potable water produced by municipal water treatment plants that is lost to pipeline leakage or non-metered consumption prior to billing.

Subsidence

The gradual or rapid downward settling or sinking of the Earth's surface caused by groundwater over-extraction, organic soil oxidation, or heavy structural loads.

Differential subsidence

Non-uniform, uneven settling of the ground surface across short horizontal distances, which inflicts severe shearing and structural failure on buildings, canals, and pipelines.

Green roof

A multi-layered engineered vegetated roof system designed to capture, store, and evapotranspire stormwater, reducing peak runoff volumes and mitigating urban heat.

Extensive green roof

A lightweight green roof profile characterized by a thin substrate depth, minimal maintenance requirements, and low-growing flora like sedum, mosses, and grasses.

Intensive green roof

A heavy, deep-substrate urban roof garden capable of supporting shrubs and trees, requiring regular irrigation and continuous maintenance.

Stormwater retention

The permanent on-site containment and removal of stormwater runoff through biological evapotranspiration or ground infiltration.

Stormwater detention

The temporary detention of peak storm runoff in engineered storage facilities to dampen the hydrograph peak before controlled, delayed release.

Grey infrastructure

Conventional, single-purpose engineered civil structures such as concrete conduits, pipes, pumps, culverts, and floodwalls that convey or hold back floodwaters.

Green-blue infrastructure

A nature-based urban network combining natural vegetated features (green) and hydrologic water bodies (blue) that slowly slows, filters, and infiltrates water.

Nature-based solutions (NBS)

Interventions that mimic, protect, or restore natural ecological functions to address water management challenges while simultaneously securing co-benefits for human health and biodiversity.

Sponge city

An urban hydrological design framework aimed at absorbing, storing, infiltrating, and purifying stormwater where it precipitates, epitomized by the philosophy: slow it, spread it, sink it, store it.

Bioswale

A gently sloped, vegetated drainage channel engineered to filter, slow, and infiltrate urban stormwater runoff.

Wolman's (1967) cycle

A conceptual model tracking river sedimentation from stable pre-development, through massive sediment yields during land-clearing construction, to clean erosive runoff and channel incision following catchment urbanisation.

Urban stream syndrome

The systematic morphological and ecological degradation of streams in urban catchments, characterised by flashy hydrographs, high pollutant loads, channel enlargement, and habitat destruction.

Hydric soil

Soil developed under conditions of prolonged flooding, ponding, or saturation during the growing season, sufficient to establish anaerobic conditions in the root zone.

Gley

A drab grey, bluish-grey, or greenish soil color formed by the continuous chemical reduction and mobilization of iron under persistent anaerobic water saturation.

Redoximorphic features

Morphological color patterns in soils caused by alternating cycles of iron and manganese reduction, leaching (depletions), and oxidation (concentrations) driven by fluctuating water tables.

Meteorological drought

A prolonged deficit in precipitation compared to long-term climatological averages for a given region, quantified via indices such as SPI, SPEI, and PDSI.

Hydrological drought

A deficiency in subsurface and surface water volumes, marked by abnormally low river discharges, depleted reservoirs, and fallen groundwater levels.

Agricultural drought

A condition where plant-available root-zone soil moisture drops too low to support healthy crop growth and physiological development.

Socioeconomic drought

A drought condition reached when the physical shortfall in water resources directly compromises municipal, industrial, and agricultural supplies necessary to meet human economic demand.

Ecological drought

An ecologically disruptive water shortage that pushes natural aquatic and terrestrial ecosystems beyond vulnerable survival thresholds.

Verdringingsreeks

The formal Dutch water displacement sequence determining national allocation priorities during critical shortages: (1) safety and prevention of irreversible damage, (2) utilities, (3) small high-value usage, (4) other broad economic sectors.

Landelijk Coördinatiecommissie Waterverdeling (LCW)

The Dutch national water allocation body that monitors drought levels and issues national water shortage alerts (Level 1, Level 2, and Level 3).

Delta Works

A massive civil flood protection scheme in the southwest Netherlands enacted by the Delta Act 1958 following the 1953 flood, designed to shorten the coastline and provide protection against a $1\text{-in-}10{,}000$-year storm surge.

Waterschap (Water board)

An independent regional Dutch governmental authority responsible for regulating surface water levels, supervising polder defences, and maintaining water quality.

Normaal Amsterdams Peil (NAP)

The vertical reference datum utilized throughout the Netherlands, roughly corresponding to mean sea level.

Managed aquifer recharge (MAR)

The intentional, purposeful recharge of treated surface water or purified wastewater into subterranean aquifers to bolster reserves and halt coastal saltwater intrusion.

Mississippi River-Gulf Outlet (MRGO)

A man-made navigational canal south of New Orleans that destroyed protective coastal wetlands and funneled Hurricane Katrina's storm surge directly toward the city in 2005.

Sustainable Drainage Systems (SuDS)

Decentralized water drainage sequences that mimic natural catchment processes by reducing impervious runoff through local retention, infiltration, and surface storage.