Streams & Floods

Unit 1

Streams + rivers

concentrated flows of water in channels

erodes, transports, then deposits sediments

transfers mass from continents to ocean basins

Uses of stream flow

gathering water, growing food, drinking, transporting, gaining energy (electricity)

Hyrdrologic Cycle

condensation from clouds falls (rain), flows down through channels into ocean, evaporates back into clouds

Stream Bank

along the edges of the channel, kinda the surface

parts of a stream

Streambed

floor of the channel, deepest part of the stream

parts of a stream

Reach

a defined length of the channel, prob in a unit

parts of a stream

Runoff

sheet-like flow over the land surface

happens if a stream is not in a channel

Efficiency of erosion

depends on:

velocity of flow, steepness of the slope, type of soil or rock present, and presence of vegetation

Downcutting

process where water flowing in a channel cuts into the substrate and deepens the channel

basically digging into the ground, making a deep crevice

as _____ continues, channel depends and surrounding land begins to slope down towards channel

Headward erosion

process in which river water erodes in an upstream direction, lengthening the river valley

lengths it more forwardly

Lateral Erosion

process in which river water erodes laterally, widening the river valley

Tributary

a smaller stream that flows into a larger stream

Dendritic

branching or tree-like

common in regions of uniform material

Type of Drainage Pattern

Radial

Draining in all directions away from a point (mountains, hills)

Type of Drainage Pattern

Rectangular

channels aligned primarily in two directions

follows fractures in rock, looks like a puzzle piece

Type of Drainage Pattern

Trellis

develops across parallel valleys and ridges

surface alternates between erodible and resistant materials

basically said idgaf im going through all these valleys

Type of Drainage Pattern

Parallel

develops steep, uniform streams with parallel courses

goes like:

I I I I

Type of Drainage Pattern

Drainage Basin (watershed)

land areas draining into the main stream or body of water

Drainage Divide

A ridge separating two drainage basins

Abrasion

the “sandblasting” of rock by particles in fast-moving water

Type of erosional process

Scouring

removal of loose fragments of sediment (HM: dissolution and breaking and lifting)

Type of erosional process

Sediment load

material moved by running water

affected by water velocity + the sediments being transported

Base Level

the lowest point to which a stream can erode

stream loses all potential energy, so velocity drops to zero when it reaches base level

gradient is nearly flat, discharge is high, sediments are fine, meandering channels, velocity may be slower

Headwaters

most rivers start near a headwater, which may contain a patch of snow that starts it

gradient is steep, discharge is low, sediments are coarse and younger, channels are mainly straight, velocity may be higher

Braided Streams

trunk stream consisting of many channels

high sediment load, usually coarse sediments, channels weave back and forth between bars of sediment

Floodplain

a relatively flat area in between hills or ridges, prone to flooding

Delta

forms when a stream enters standing water
think Nile River

spans out into the ocean, can form into different shapes

(triangle-shape forms where waves or offshore currents redistribute sediment entering the standing water)

Straighter-shaped delta

currents are stronger, less sediment accumulates so the edge becomes straight

Outward arc-shaped delta

currents are weaker, more sediment accumulates, causing edges of delta to arc outward

Delta Lobes

formed during different time intervals

lobes form when a stream’s given path over time starts to become too gentle of a slope, so a new one forms

Flood

occurs when volume of water flowing down a stream exceeds the volume of the stream channel
spreads over floodplain

triggered by torrential rains, rapid snowmelt, and/or failure of a dam or levee

Flood Prevention

expensive and only temporary (ultimately futile)

levees + flood walls prevent overflow for floodplains

**levees: can be man-made or sometimes created naturally through sediment deposition

Permanent Stream

water flows all year at or below the water table

humid or temperate climate

sufficient rainfall, lower evaporation

Ephemeral Stream

Dries up part of the year, above the water table, found in drier climates, flows intermittently

lower rainfall, high evaporation

Cut Bank

High velocity flow where erosion takes place

Point Bar

Place of low velocity where deposition occurs

Oxbow Lake

Remnant of a meander that has been cut off from the flow of a river

Meandering Streams

sinuous, looping curves

low gradient

broad floodplain

Discharge of a Stream

“volume per some given time”

ex:

width = ___m

depth =___m

velocity =____m/sec

discharge = ____m³/sec

Gradient (slope)

“drop in elevation over distance flowed”

△E/D

△E= ___ft

D = ____ mi

Grad=____ft/mi