Stream Processes, Hydrology, and Water Quality

Vocabulary flashcards covering stream dynamics, channel morphologies, flood equations, groundwater hydrology, and water quality concepts.

Stream

Any surface water whose flow is confined to a channel and is moving down gradient; represents a high-energy system that is not size-dependent and includes brooks, creeks, and rivers.

Drainage Basin

The land area that contributes water to a stream system; it is not size-dependent.

Drainage Divide

The high ground or topographic barrier that separates neighboring drainage basins.

Cutbank

An erosional feature formed on the outside of a stream curve where the fastest water current strikes the bank.

Point Bar

A depositional feature formed on the inside of a stream curve where slower-moving water deposits sediment.

Straight Channel

A channel type characterized by a moderately straight path, moderately high gradient and velocity, and down-cutting erosion that forms a V-shaped valley.

Meandering Stream

A channel type characterized by low gradient and velocity, where lateral erosion dominates to form cutbanks and point bars.

Braided Stream

A sediment-choked channel type characterized by very high gradient and velocity with interweaving channels.

Oxbow Lake

An isolated water body formed when a river cuts through the narrow neck of a meander loop during high flow or flooding, after which sediment seals off the abandoned bend.

Stream Rejuvenation

A process occurring when land is uplifted or base level falls, giving a mature stream renewed vertical erosional energy to down-cut into its channel and produce entrenched meanders or stream terraces.

Delta

A fan-shaped sediment deposit formed where a stream enters a standing body of water (such as an ocean or lake) and rapidly loses velocity.

Stream Gradient

The slope of a stream calculated as relief (high elevation minus low elevation) divided by horizontal distance, typically expressed in feet per mile ($\text{ft/mi}$), where $5{,}280\text{ feet} = 1\text{ mile}$.

Stream Discharge ($Q$)

The volume of water moving through a channel per unit time, calculated using the equation $Q = W \times D \times V$ (Width $\times$ Depth $\times$ Velocity) with units of cubic feet per second ($\text{cfs}$ or $\text{ft}^3/\text{sec}$) or $\text{m}^3/\text{sec}$.

Recurrence Interval (RI)

The average frequency of a flood event of a given magnitude, calculated as $RI = \frac{n + 1}{m}$, where $n$ is the total number of years of record and $m$ is the magnitude ranking ($1 = \text{largest}$).

Annual Flood Percentage Chance

The annual probability of a flood occurring in any given year, calculated from its recurrence interval as $\left(\frac{1}{RI}\right) \times 100$.

Floodplain

A flat valley floor adjacent to a stream channel that is built up by flood sediment.

Levee

A ridge of sediment deposited parallel to stream banks that functions to retain water.

Stream Terrace

A step-like abandoned floodplain left higher up along a valley as a stream cuts downward.

Zone of Aeration

The unsaturated upper subsurface layer where rock and soil pore spaces hold both air and water.

Zone of Saturation

The lower subsurface layer where all pore spaces are filled completely with water.

Water Table

The boundary separating the zone of aeration from the zone of saturation, which mimics the land surface and feeds lakes and streams.

Groundwater Recharge

The process of surface water infiltrating down into the subsurface to replenish an aquifer.

Groundwater Discharge

The process of water exiting an aquifer into streams or springs, or being pumped out by wells.

Porosity

The volume percentage of open pore space within a rock or sediment material.

Permeability

The capacity of a material to transmit fluid, determined by the interconnectedness of its pore spaces.

Aquifer

A water-bearing subsurface body requiring high porosity and high permeability (or high fracturing) to yield usable quantities of groundwater.

Aquitard

An impermeable rock or sediment layer that stops or significantly slows the flow of groundwater.

Unconfined Aquifer

An aquifer whose upper surface is open to the atmosphere through permeable material above.

Confined Aquifer

An aquifer sandwiched between aquitards under high water pressure.

Artesian Well

A well penetrating a confined aquifer in which water rises above the aquifer on its own under pressure.

Cone of Depression

A circular drop in the water table that develops around an actively pumping well, potentially drying out adjacent shallow wells.

Land Subsidence

The irreversible compaction of sediment layers that occurs when supportive groundwater pressure is permanently removed through over-pumping.

Saltwater Intrusion

The migration of deep coastal saltwater into freshwater wells caused by excessive groundwater pumping.

Karst Topography

A distinctive landscape created by the dissolution of soluble rocks (such as limestone) by weak carbonic acid ($H_2CO_3$) via the reaction $H_2O + CO_2 \rightarrow H_2CO_3$, featuring caves, sinkholes, solution valleys, disappearing streams, springs, stalactites, and stalagmites.

Point Source Pollution

Pollution discharged from discrete, easily identifiable origins, such as septic tanks, factory pipes, or industrial plants.

Nonpoint Source Pollution

Pollution that originates from broad, diffuse, and widespread sources, such as agricultural runoff, road salt, or tailing piles.

Oxygen-Demanding Waste

Organic matter introduced into water that consumes dissolved oxygen during decomposition by aerobic bacteria.

Pathogens

Disease-causing microorganisms found as water pollutants, including bacteria, viruses, and parasites.

Persistent Organic Pollutants (POPs)

Toxic synthetic compounds, such as DDT and PCBs, that resist environmental breakdown and biomagnify in food chains.

Biochemical Oxygen Demand (BOD)

The quantity of dissolved oxygen required by aerobic bacteria to break down organic matter in a given volume of water; high values indicate heavy organic pollution.

Oxygen Sag Curve

A graphical representation showing the sharp drop in dissolved oxygen downstream from an organic waste discharge point due to rapid bacterial consumption during waste decomposition.

Eutrophication

An environmental process in which excess plant nutrients (nitrates and phosphates) enter water bodies and trigger massive algal blooms, which subsequently decompose, consume dissolved oxygen ($O_2$), and create dead zones that suffocate aquatic life.