Geology Unit #4

River and Streams

Major sources of water that support agriculture but also pose flood risks.

Drainage Basin

The entire area surrounding a river where all water flows downhill into the main river.

Channel

The main path that water travels in a river or stream.

V-shaped Valley

A valley shape formed by river erosion, typically narrow and steep.

Levee

Slightly elevated land directly next to a river channel, higher than surrounding areas.

Floodplain

Flat land beyond the levees that floods when water overflows the channel.

Tributary

A smaller stream or river that flows into a larger river.

Dendritic Pattern

Branching drainage pattern that looks like tree branches, tributaries meet at angles less than 90°.

Radial Pattern

Drainage pattern where streams flow outward from a central high elevation point.

Rectangular Pattern

Drainage pattern that forms right angles due to cracks in underlying rock.

Steep Elevation Gradient

Rapid change in elevation causing fast-moving, straight river channels.

Low Elevation Gradient

Gentle slope causing slower water movement and meandering channels.

Meander

A curve or bend in a river formed as water moves side to side.

Cutbank

Outer edge of a meander where erosion occurs and water moves faster.

Point Bar

Inner edge of a meander where sediment is deposited and water moves slower.

Meander Migration

The gradual movement of a river’s bends over time due to erosion and deposition.

Oxbow Lake

A U-shaped lake formed when a river meander is cut off from the main channel.

Mississippi River Example

River artificially controlled to flow through New Orleans, causing economic benefits but increased flood risk and costs.

Discharge

The amount of water flowing past a point per unit time (velocity × area).

Flooding

Occurs when discharge exceeds the channel’s capacity.

Recurrence Interval

The average time between floods of a certain size.

Flood Probability

The chance a flood occurs in a given year (1 ÷ recurrence interval).

5-Year Flood Example

Has a 20% chance (1/5) of occurring in any given year.

River Mouth

The location where a river empties into a larger body of water.

Distributaries

Smaller channels that branch off at a river’s mouth.

Delta

A triangular landform created by sediment deposition at a river’s mouth.

Subsidence (Delta)

Sinking of land due to heavy sediment accumulation.

Water Quality

The safety and usability of water for consumption and irrigation.

Potable Water

Water that is safe to drink and tastes acceptable.

EPA Standards

Limits set by agencies to determine safe levels of substances in water.

Biological Contamination

Presence of harmful microorganisms in water.

Fecal Coliform Count

Measure of bacteria per 100 mL used to assess water contamination.

Drinking Water Standard

Must have 0 coliform bacteria per 100 mL.

Swimming Water Standard

Can have up to 200 coliform bacteria per 100 mL.

Chemical Contamination

Pollution from substances like pesticides, fertilizers, and pharmaceuticals.

Water Clean-Up

Process of removing contaminants, often expensive and time-consuming.

Water Availability

The amount of water accessible for human use.

Catawba River Case Study

Conflict between South Carolina and North Carolina over water usage.

Savannah River Case Study

Water dispute between South Carolina and Georgia.

Georgia vs Tennessee Case

Proposal to shift state border to access Tennessee River.

Colorado River Case Study

Long-standing disputes among western states over water usage.

Colorado River Overuse

Supplies 30 million people but is heavily depleted and shrinking.

Water Wars

Potential conflicts over water scarcity in the future.

Coastline

The area where land meets the ocean, still part of continental crust.

Tides

Regular rise and fall of sea levels.

Tidal Range

Difference between high and low tide.

Hawaii Example

Small tidal range (1–2 ft).

Bay of Fundy Example

Large tidal range (~40 ft).

Waves

Water movements that increase in height and slow down near shore.

Wave Refraction

Bending of waves as they approach shallow water.

Longshore Current

Water current moving parallel to the shoreline.

Longshore Drift

Movement of sediment along the coast.

Emergent Coastline

Coastline rising due to tectonic uplift, steep with small beaches.

Stack

Steep, isolated rock formation offshore.

Terrace

Flat, step-like landforms representing former shorelines.

Submergent Coastline

Coastline sinking or sea level rising, creating irregular land.

Spit

Narrow strip of sand extending into water.

Barrier Island

Detached sand formation parallel to the coast.

Continental Margin

The submerged outer edge of a continent.

Active Margin

Located near plate boundaries with tectonic activity (ex: California).

Passive Margin

Far from plate boundaries with little tectonic activity (ex: East Coast US).

Continental Shelf

Shallow underwater extension of the continent.

Continental Slope

Steeper drop-off beyond the shelf.

Continental Rise

Gentle slope leading to the deep ocean floor.

Coastal Erosion

The removal of land by wave action.

Cape Hatteras Case Study

Lighthouse moved inland due to shoreline erosion.

Zoning

Building restrictions to reduce damage from erosion.

Erosion Line (E-line)

Predicted future shoreline position.

Seawall

Structure built to block wave energy.

Groin

Structure extending into water to reduce sediment movement.

Beach Nourishment

Adding sand to eroded beaches.

Miami Beach Case Study

Successful beach restoration but harmful to wildlife.

Groundwater

Water stored beneath Earth’s surface.

Runoff

Water that flows over land.

Infiltration

Water that soaks into the ground.

Porosity

Percentage of open space in soil/rock.

Intergranular Pores

Spaces between grains.

Fractures

Cracks in rock that store water.

Vugs

Holes formed by dissolution in rock.

Sorting

Arrangement of particles affecting porosity.

Cementation

Binding of particles reducing porosity.

Permeability

Ability of water to flow through material.

Water Table

Boundary between saturated and unsaturated ground.

Zone of Aeration

Area above water table with air in pores.

Phreatic Zone

Area below water table fully saturated with water.

Aquifer

Underground layer that stores and supplies groundwater.

Well

Structure used to extract groundwater.

Unconfined Aquifer

Aquifer open to surface infiltration.

Aquitard

Layer with low permeability that restricts water flow.

Confined Aquifer

Aquifer trapped between aquitards.

Artesian Well

Well where pressure pushes water to surface naturally.

Perched Aquifer

Small aquifer above an aquitard within a slope.

Recharge

Water entering an aquifer.

Discharge

Water leaving an aquifer.

Overdrafting

Removing water faster than it is replenished.

Cone of Depression

Lowering of water table around a well.

Subsidence (Groundwater)

Ground sinking due to water removal.

Salinity Contamination

Saltwater entering freshwater supply.

Desalinization

Process of removing salt from water.

Love Canal Case Study

Toxic waste contamination leading to health crisis and Superfund Act.