Hydrology, River Systems, and Flooding

Comprehensive vocabulary flashcards covering hydrological principles, drainage systems, fluvial processes, sediment dynamics, channel landforms, and flood probability models.

Hydrology

The study of the distribution, movement, quantity, and quality of water on Earth.

Hydrological Cycle

The continuous movement of water between the atmosphere, Earth's surface, and underground.

Evaporation

The process by which liquid water changes into water vapour.

Transpiration

The process where plants release water vapour into the atmosphere.

Condensation

The phase change in which water vapour transforms into liquid water.

Precipitation

Water falling from the atmosphere to Earth's surface as rain, snow, or other forms.

Infiltration

The process by which water enters the soil directly from the surface.

Percolation

The downward movement of water through soil layers and permeable rock.

Surface Runoff

Water that flows across the land surface into streams and rivers.

Groundwater Flow

The subsurface movement of water underground.

Residence Time

The average time water remains stored in a particular component of the hydrological cycle.

Watershed (Drainage Basin)

An area of land where all precipitation and surface water drains toward the same river or outlet.

Drainage Divide

An elevated ridge of high ground that separates neighbouring watersheds.

Drainage Pattern

The geometric arrangement of stream channels within a drainage basin.

Dendritic Drainage

A stream network pattern resembling the branching of a tree.

Radial Drainage

A pattern where streams radiate outward from a central high point, such as a volcano.

Rectangular Drainage

A drainage pattern where streams follow bedrock fractures, forming sharp, right-angle bends.

Trellis Drainage

A pattern where main streams flow through parallel valleys with tributaries joining at near-right angles.

Drainage Density

The total length of all stream channels in a basin divided by the drainage basin area.

Stream Gradient

The change in channel elevation per unit distance, typically steeper near the headwaters.

Base Level

The lowest elevation to which a stream or river can erode, with sea level being the ultimate base level.

Fluvial Processes

The collective processes of erosion, transportation, and deposition of sediment by flowing water.

Graded River

A river that adjusts its longitudinal slope to balance available energy with the energy required to transport sediment.

Stream Discharge ($Q$)

The volume of water passing a given cross-section per second, calculated as $Q = w \times d \times v$ (width $\times$ average depth $\times$ average velocity) and measured in $\text{m}^3/\text{s}$.

Hydrograph

A graph illustrating river discharge as a function of time.

Rising Limb

The rising portion of a hydrograph where stream discharge increases following a precipitation event.

Peak Discharge

The maximum rate of river flow observed during a flood or precipitation event.

Recession Limb

The descending limb of a hydrograph during which river discharge progressively decreases after the peak.

Baseflow

Sustained streamflow supplied to a river primarily through groundwater seepage.

Lag Time

The time difference between peak rainfall intensity and peak river discharge.

Stream Competence

The maximum particle size of sediment that a river is capable of transporting, strongly governed by flow velocity.

Stream Capacity

The total volume or mass of sediment that a river can transport, primarily determined by discharge.

Shear Stress

The tangential force exerted by flowing water against the bed of a channel that can dislodge sediment.

Entrainment

The initial lifting and mobilization of loose sediment particles from the riverbed by moving water.

Dissolved Load

Ions and minerals transported downstream in chemical solution.

Suspended Load

Fine sediment particles carried aloft within the water column by turbulence.

Bed Load

Coarse sediment particles transported directly along or immediately above the riverbed.

Traction

A mode of bed-load transport where particles roll or slide continuously along the channel bed.

Saltation

The process by which sediment grains bounce and hop along the riverbed.

Abrasion

Mechanical wearing away and scraping of bedrock or sediment by particles carried in the flow.

Plucking

The hydraulic process by which flowing water lifts, dislodges, and carries away fractured rock fragments.

Incision (Downcutting)

Vertical erosional deepening of a river channel into its underlying bed.

Headward Erosion

Erosional extension of a stream channel progressively upstream at its origin.

Hjulström Curve

A graphical diagram illustrating the relationships among flow velocity, sediment grain size, erosion, transport, and deposition.

Straight Channel

A linear river channel form typically constrained by narrow valleys or underlying geological structures.

Meandering River

A single sinuous channel featuring looping curves, driven by outer-bank erosion and inner-bank deposition.

Braided River

A complex network of small intersecting channels separated by dynamic sediment bars, associated with high sediment load.

Thalweg

A continuous line tracing the deepest and fastest-flowing section along a river channel.

Cut Bank

The steep, eroding outer margin of a meander bend produced by localized high water velocity.

Point Bar

A crescent-shaped deposit of sand and gravel formed along the slow-moving inner bank of a meander bend.

Oxbow Lake

A curved, crescent-shaped standing water body formed when an abandoned meander loop is cut off from the main channel.

Floodplain

A low-relief land area flanking a stream channel that is periodically submerged and aggraded during overbank floods.

Natural Levee

An elevated ridge of coarse sediment deposited along channel margins during overbank flooding events.

Alluvial Fan

A cone- or fan-shaped accumulation of sediment deposited where a confined, steep mountain stream emerges onto a flat plain.

Delta

An accumulation of sediment deposited at the mouth of a river where it enters a standing body of water such as an ocean or lake.

Distributary

A divergent stream branch that flows away from the main channel without returning, commonly across a delta plain.

Regional Flood

An extensive inundation resulting from prolonged precipitation, widespread snowmelt, or rain-on-snow events.

Flash Flood

A sudden, high-velocity inundation triggered by intense, localized precipitation and rapid surface runoff.

Ice-Jam Flood

Flooding caused by floating river ice forming a barrier that impedes downstream flow and pools water upstream.

Dam-Failure Flood

Catastrophic, abrupt flooding initiated by the structural breach or collapse of an artificial dam or levee.

Floodway

A designated engineering channel constructed to divert excess floodwaters away from developed or vulnerable areas.

Recurrence Interval ($R$)

The statistical average time in years between flood events of a specified magnitude or greater, related to probability by $R = \frac{1}{P}$.

Annual Flood Probability ($P$)

The likelihood that a flood of a specific magnitude will be equaled or exceeded during any single calendar year.

100-Year Flood

A flood discharge that has an exceedance probability of 1% ($P = 0.01$) in any given year, rather than occurring precisely once per century.

Mean Annual Flood ($Q_{\text{maf}}$)

A benchmark flood magnitude possessing an empirical recurrence interval of approximately $2.33$ years and a 43% annual probability.