Hydrology, River Processes, and Hazards Vocabulary

Flashcards covering key hydrology and river process vocabulary terms defined in the lecture text.

Abrasion (corrasion)

The mechanical erosion of soil and rock by the abrasive action of particles set in motion by running water, wind, glacial ice, and gravity.

Aeration zone

The area of an unconfined aquifer above the water table where the pore spaces among soil particles and rock formations are filled with air.

Antecedent drainage (inconsequent drainage)

Refers to a river that maintains its course and direction even when the surrounding landscape experiences tectonic uplift or folding.

Aquiclude

A geological formation that can store water but does not transmit it at a rate sufficient to supply wells or springs.

Attrition

An erosional process where rocks and pebbles carried by water or wind collide and wear each other down, reducing their size and making them more rounded.

Bankfull discharge

The maximum discharge that a particular river channel is capable of carrying without flooding.

Baseflow

The portion of streamflow that originates from groundwater discharge, representing the sustained low flow in a river during dry or fair weather conditions.

Carboniferous limestone

A succession of limestones occurring in Great Britain and Ireland deposited during the Dinantian Epoch of the Carboniferous Period between $363$ and $325$ million years ago, composed primarily of calcium carbonate.

Cavitation

The implosion of bubbles or cavities, particularly during rapid, turbulent water flow, often downstream of an obstruction.

Critical erosion velocity

The minimum water velocity needed for a river to pick up and transport sediments of a specific size.

Drainage density

The total length of streams and rivers within a drainage basin divided by the total area of that basin.

Field capacity

The amount of water remaining in soil after excess water has drained away, usually within $1$ to $3$\,\text{days} after a rain or irrigation event.

Helicoidal flow

A corkscrew-like, spiraling movement of water within a river channel, particularly in a meander, resulting from friction with the channel bed and banks.

Hjülstrom curve

A curve showing the linkage between sediment size and the velocity needed to erode, transport, or deposit material.

Hortonian flow

A type of surface runoff occurring when rainfall intensity exceeds the soil's infiltration capacity, causing water to flow over the land surface.

Hydraulic radius

A measure of river channel efficiency calculated by dividing the cross-sectional area of the channel by its wetted perimeter.

Incised meander

A meandering river valley that has cut down its bed into bedrock due to uplift or a lowered base level.

Ingrown meander

A type of incised meander characterized by an asymmetrical valley shape with a steep, undercut slope on one side and a gentler slip-off slope on the other.

Intrenched meander

A river bend that has cut deeply into bedrock, creating a steep-sided valley or gorge with narrow, deep channels.

Manning’s equation

An empirical relationship defining depth-averaged velocity of water in open-channel conditions relative to hydraulic radius, slope of the energy grade line, and channel roughness.

Ox-bow lake

A crescent-shaped, free-standing body of water formed when a river's meander loop is cut off from the main channel by sediment deposition.

Percolines

A hollow at the base of a hillslope where water (soil moisture) seeps out onto the ground surface and becomes overland flow, also known as a seepage line.

Phreatic zone

The subsurface region of an aquifer where all pores and fractures are completely filled with groundwater.

Porosity

The amount of open space or void space within a rock or soil relative to its total volume, calculated as the ratio of void space volume to total volume.

Shingle

Coarse, rounded rock material, typically pebbles and gravel between $0.08$\,\text{inches} and $8$\,\text{inches} ($2$\,\text{mm} to $200$\,\text{mm}) in size, found along coastlines and near water.

Sinuosity

A measure of the winding nature of a river channel, calculated as the ratio of actual channel length to straight-line distance between source and mouth.

Superimposed drainage

A drainage pattern initially established on younger, non-resistant rocks that continues cutting through into pre-existing patterns in older, resistant bedrock below.

Thalweg

The line connecting the lowest points in a valley or river channel, representing the line of fastest flow or deepest water along a river's course.

Thermal spring

A natural spring issuing water significantly hotter than surrounding air and ground temperature, often at $21^\circ\text{C}$ ($70^\circ\text{F}$) or higher.

Throughflow

The lateral unsaturated flow of water in the soil zone, typically through a highly permeable geologic unit overlying a less permeable one.

Time lag

The time interval between the peak of rainfall and the peak of river discharge on a hydrograph.

Wilting point

The soil moisture level below which crops cannot absorb water and will wither, expressed as a ratio of moisture content to dry earth weight or volume.