Streams

The Mississippi River drainage basin covers about _______ of the contiguous United States

40%

4 Common Types of Drainage Patters

Dendritic Radial Rectangular Trellis

2 types of stream flow.

Laminar and Turbulent

Discharge Formula

Q = A x V Discharge (m3/s)= Cross-sectional Area [width x average depth](m2) x Average Velocity (m/sec)

Permanent Streams

Streams that flow all year

3 Types of Stream Load

Suspended Load, Bed Load, Dissolved Load

Bed Load

coarser and denser particles that remain on the bed of the stream most of the time bt move by a process of saltation as a result of collisions between particles, and turbulent eddies.

Continental Divides

continents can be divided into large drainage basins that empty into different oceans.

Downstream, the size of particles that make up the bed load of the stream tends to..

decrease.

As one moves along a stream in the downstream direction, the gradient of the stream

decreases.

The most common drainage pattern...

dendritic drainage patterns

On the inside of the curve where the velocity is lower...

deposition of sediment occurs.

If base level is raised, the stream

deposits sediment and readjusts its profile to the new base level.

Radial Drainage Patterns

develop surrounding areas of high topography where elevation drops from a central high area to surrounding low areas.

Trellis Drainage Patterns

develop where linear zones of resistant rocks break up the landscape.

Rectangular Drainage Patterns

develop where linear zones of weakness, such as joints or faults cause the streams to cut down along the weak areas in the rock.

Water levels rise and fall with the seasons, depending on the...

discharge.

Because some rocks and minerals are easily dissolved in water...

dissolution also occurs, resulting in dissolved ions being transported by the stream.

Land far above base level is subject to...

downcutting by the stream.

Both width and depth increase _______ because discharge increases _______.

downstream

Erosion takes place _____ from the dam.

downstream.

The linked channels become a...

drainage network.

Drainage Basin

each stream in a drainage system drains a certain area, called a drainage basin (also called a catchment or a watershed).

Streams that only occasional have water flowing are called...

ephemeral streams or dry washes.

When stream channels fill with water the excess flows onto the land as a

flood.

Rapid erosion lengthens the channel upslope in a process called...

headward erosion.

Continental divides usually run along...

high mountain crests that formed recently enough that they have not been eroded.

Streams that have a deep underground source generally have a...

higher dissolved load.

Permanent streams occur

in humid or temperate climates where there is sufficient rainfall and low evaporation rates.

Pools

in straight channels, velocity is highest in the zone overlying the deepest part of the stream. In these areas, sediment is transported readily resulting in pools.

In straight channels, highest velocity is...

in the center.

Discharge _______ as more water is added through rainfall, tributary streams, or from groundwater seeping into the stream.

increases

Competence and capacity increase with...

increasing discharge

Dissolved Load

ions that have been introduced into the water by chemical weathering of rocks.

Saltation

jumping

As the rills coalesce, deepen, and downcut into channels....

larger channels form.

Over time, nearby channels merge with smaller tributaries joining a _____ ______ ______.

larger trunk stream.

When a natural or artificial dam impedes stream flow, the stream adjusts to the new base level by adjusting its...

long profile

Radial drainage patterns usually consist of...

many dendritic drainage patterns.

Streamflow begins as _______ _______

moving sheetwash

Turbulence is caused by

obstruction and shear in the water.

In meandering channels, erosion will take place

on the outer part of the meander bends where the velocity of the stream is highest.

In curved channels, maximum velocity traces the ______ _____ where the channel is ....

outside curve, preferentially scoured and deepened

Suspended Load

particles that are carried along with the water

A stream's velocity depends on...

position in the stream channel, irregularities in the stream channel caused by resistant rock, and stream gradient.

Ephemeral streams flow mostly during

rare flash floods.

Thus, major continental divides and the drainage patterns in the major basins reflect the...

recent geologic history of the land.

Thus various types of drainage patterns develop in a region and these drainage patterns...

reflect the structure of the rock.

Water moves down the steepest slope and starts to erode the surface by creating small _______ ________.

rill channels.

Drainages tend to develop along zones where...

rock type and structure are most easily eroded.

For streams that empty into the ocean, base level is...

sea level.

Turbulent eddies scour the channel bed, and can keep

sediment in suspension longer than laminar flow and thus aids in erosion of the stream bottom.

Even in straight channel segments water flows in a...

sinuous fashion, with the deepest part of the channel changing from near one bank to near the other.

Flow follows a...

spiral path

Straight Channels

straight stream channels are rare. Where they do occur the channel is usually controlled by a linear zone of weakness in the underlying rock, like a fault or joint system.

Laminar

stream flow in which all water molecules travel along similar parallel paths.

Turbulent

stream flow in which individual particles take irregular paths.

Importance of Streams (human use)

streams are a major source of water, waste disposal, and transportation for humans - most population centers are located next to streams.

Importance of Streams (Oceans)

streams carry dissolved ions into the oceans and make the sea salty

Meandering channels

streams flowing over low gradients with easily eroded banks

Waterfalls

temporary base levels caused by strong erosion resistant rocks.

Thalweg

the deepest part of the channel which meanders with the curve of the stream.

Point bars

the deposition occurring along the inner meander bends where the velocity is low, results in exposed bars, called point bars.

Even though the velocity of the stream increases downstream, the bed load particle size decreases mainly because...

the larger particles are left in the bed load at higher elevations and abrasion of particles tends to reduce their size.

Base level

the limiting level below which a stream cannot erode its channel.

Stream Capacity

the maximum load carried by the stream.

Stream's load

the rock particles and dissolved ions carried by the stream.

In a single drainage basin, all water falling in the basin drains into...

the same stream.

In general, if base level is lowered...

the stream cuts downward into its channel and erosion is accelerated.

Rapids occur where...

the stream gradient suddenly increases, where the stream flows over large clasts in the bed of the stream, or where there is an abrupt narrowing of the channel.

The deepest part of channel occurs where...

the stream velocity is the highest.

The size of the rock fragments that can be transported by a stream depends on...

the velocity and flow-type of the stream.

Discharge

the volume of water passing any point on a stream.

Waterfalls danger...

the water can cause rapid erosion/undercutting at the base of the waterfall, making it subject to rockfalls or slides. The waterfall slowly retreats upstream and eventually is removed.

These ions are eventually carried to the oceans and give the oceans...

their salty character.

Importance of Streams (Erosion)

they are a major part of the erosional cycle- much of the surface landscape is controlled by stream erosion.

Importance of Streams (Sedimentary Rocks)

they carry billions of tons of sediment to lower elevations- the main transporting medium in the production of sedimentary rocks.

Importance of Streams (Water Cycle)

they carry most of the water that goes from the land to the sea- important part of the water cycle

Stream flow is characteristically...

turbulent

Rapids

turbulent water with a rough surface

Streams can cut deeper into their channels if the region is _______ or if there is a ....

uplifted, local change in base level.

Slow downcutting and weak, easily erodible rocks results in

valleys.

Sediment can move between bed load and suspended load as the ______ of the stream changes.

velocity

As the amount of water in a stream increases, the stream must adjust its _____ and ______ in order to form a _____.

velocity, cross-sectional area, balance

Strong rocks yield ______ cliffs, whereas weak rocks produce more _________ ______ canyon walls.

vertical, gently sloped.

Streamflow begins when

water is added to the surface from rainfall, melting snow, and groundwater.

Friction is greater in _____, _____ streams.

wider, shallower

As discharge increases, generally ___,___,____, of the stream also increase.

width, depth, and velocity.

The surface of permanent streams is...

at or below the water table.

Valleys store sediment when...

base level is raised.

The dissolved load consists mainly of

bicarbonate Ions

Rapid downcutting in stronger rocks results in...

canyons.

With continued erosion of the channels, drainage networks...

change over time.

Turbulent streams can be characterized by...

chaotic and erratic, with abundant mixing, swirling eddies, and high velocity.

_____ slows water along channel edges

Friction

Bicarbonate ions in a dissolved load.

HCO3, CA, SO, CL, NA, MG, K

Bars

Where the velocity of the stream is low, sediment is deposited to form bars.

Stream

a body of water that carries rock particles and dissolved ions and flows down slope along a clearly defined path, called a channel.

A _____ _______ separates each drainage basin from other drainage basins.

Drainage Divide

_______ ________ develop to efficiently move water off the land.

Drainage systems

Competence

The maximum size of particles that can be carried as suspended load by the stream.

Dendritic Drainage Patters

They develop on a land surface where the underlying rock is of uniform resistance to erosion.

Active downcutting flushes sediment out of channels. Only after the sediment is flushed out can further downcutting occur (t/f).

True

The stream can continually adjust its channel shape and path as the amount of water passing through the channel changes. (T/F)

True

The stream channel is the conduit for water being carried by the stream. (T/F)

True

The composition of the particles in the bed load tends to change along the stream as different bedrock is eroded and added to the stream's load (T/F).

Trues

Streams may vary in width from...

a few centimeter to several tens of kilometers.

Long Profile

a plot of elevation versus distance, usually shows a steep gradient or slope, near the source of the stream and a gentle gradient as the stream approaches its mouth.

Ephemeral streams are...

above the water table and occur in dry climates with low amounts of rainfall and high evaporation rates.

Sudden change in gradient may occur where an...

active fault crosses the stream channel.

In meandering channels, sediment deposition occurs

along the inner meander bends where the velocity is low.