floods and streams Final!!

Trellis Drainage Network

when a drainage network develops across parallel valleys and ridges mako tributaries flow down a valley and join a trunk stream that its across the ridges. Resembles a trellis garden ***rectangular pattern controlled by ridges and valleys Notice difference from a rectangular drainage network. They both use the word rectangular...look at pics

Continental divide

Separates drainage that flows into one ocean from draining that flows into another. Stand on top of the continental divide at the crest of the Rocky mountains, if you pour water on one side of the divide vs the other ...one will flow to the pacific...the other to the atlantic

competence depends on what?

Water velocity!!! ***ON SLIDE KNOW fast moving turbulent streams has greater competence..it can carry bigger particles a stream in a flood has more competence then it does on a normal day!

Are streams an important component to the hydrologic cycle?

Yes they are!

Geologists refer to sediments transported by a stream as fluvial deposits OR

alluvium-may accumulate in different ways... as bars (elongated mounds) as point bars (along an inner edge of a meander) floodplain (during floods water accumulates over the borders of the stream) delta (water slows and a wedge of sediment accumulates )

How do streams erode?

1. scouring 2. breaking and lifting (he has other name) 3. abrasion 4. dissolution

Floodplains and Terraces (FROM HIS SLIDE)

A RISE IN BASE LEVEL CAUSES SEDIMENT DEPOSITION- CALLED ALLUVIUM A FALL IN BASE LEVEL LEADS TO EROSION AND TERRACE FORMATION

What makes water move?

Gravity

Braided Streams

In some pleas streams carry abundant sediment during floods but cannot carry this sediment during normal flow. Thus during normal flow, the sediment settles out and chokes the channel. As a consequence the stream divides into numerous strands weaving back and forth between elongate bars of gravel and sand The result is this braided stream. -entwines like hair in a braid note in pic the elongated bars of gravel that the things are pointing to.

MEANDERS FROM ALONG

LOW GRADIENT REACHES (NOT HIGH UP ON MOUNTAINS)

The growth of populations effects streams how?

Negatively

Many factors vary along the length of the stream and this gives us

the longitudinal profile.

Suspended sediment load

usually consists of tiny solid grains (silt and clay size) that swirl along with the water WITHOUT settling to the floor of the channel hence they are suspended in the water...not touching the ground

Drainage networks carry water that collects in a ___________ to the sea and have a variety of geometries, often reflecting the underling ________________________.

watershed (drainage basin) geology

Stream discharge depends on such factors as

watershed area and climate (obviously during rainy season discharge will be greater)

Flood hazard map

by looking at discharge during a flood and knowing the shape of the river channel and elevation of the land bordering the river hydrologists can predict the extent of land that will be submerged by such a flood. This data produces the flood hazard map Its important to keep in mind when thinking about flooding hazard that the term floodplain means what it says-its an area that will eventually FLOOD! KNOWING LIKLEY FLOOD RECURRENCE INTERVALS CAN HELP WITH DEVELOPMENT

abrasion (erosion)

clean water has little erosive effect BUT water with sediment in it acts like sandpaper and grinds away at the channel floor and walls

Scouring (eroding)

when running water can remove loose fragments of sediment (think of scouring a pan of dried on food)

Flood

when the supply of water entering a stream channel exceeds the channels capacity, water spills our and covers the surrounding land, thereby causing a flood.

Streams can be both permanent or

ephemeral (lasting for a short time)

Meandering stream

geologists refer to a stream with many meanders as this

To find out where water that enters a stream comes from, we must look at the

hydrologic cycle

Cut bank

in a meandering stream. on the outside edge of a meander erosion continues to eat away at the channel wall forming this

Larger floods are more destructive but less frequent which means they have a a

longer recurrence intervals which means they don't come very often) and lower probability **ovbiously the opposite is true for smaller floods that are more frequent. They would have shorter recurrence intervals and higher probabity

point bar

on the inside edge of the stream, water slows down and the streams competence (particle size)decreases so sediment will start to accumulate, forming a crescent shaped wedge called this

Stream

refers to any elongated body of water. Large streams are rivers, smaller streams are creeks. Waters flow from upstream reaches closer to the source or HEADWATER of the stream to the downstream reaches closer to the end or MOUTH

competence (ability to carry sediment)

refers to the MAXIMUM particle size it carries. A stream with high competence can carry LARGE particles. A stream with low competence can carry small particles.

dissolution (erosion)

running water dissolves soluble minerals and it carries the minerals away in solution DISSolution=DISSolves

Seasonal floods occur __________and build _______________. Flash floods are _________________ and _________________________.

seasonally slowly sudden shortlived

Geologissts refer to the total volume of sediment carried by a stream as its

sediment load

What effects discharge?

-In a temperate region, discharge INCREASES in the downstream direction because each tributary is adding more water to the flow (makes sense) -Yet in an arid dry region discharge decreases downstream for mores water seeps into the ground or evaporates. -Human activity can effect it. if people divert the rives water for irrigation, the rivers discharge decreases. -Even at a given location it can vary during spring when there is lots of rain vs. summer when there is less...a flood can increase the discharge by hundred times normal. Amazon River discharges at about 200,000 meters/sec (15%of the total amount of runoff in the world) whereas the Mississippi discharge is on 17,000 meters/sec

Types of Drainage Networks

1. Dendritic 2.Radial 3.rectangular 4. trellis 5. parallel

Societies depend on streams for

1. water supplies 2. irrigation 3. energy 4. transport.

longitudinal profile

A cross sectional image showing the variation in the river's elevation along its length, is roughly a concave-up curve. This curve emphasizes that typically a streams gradient is steeper near its headwaters (the beginning or source) than near it mouth. -Near headwaters, source an idealized stream flows down deep valleys or canyons, whereas near its mouth (the end) it flows over nearly horizontal plaines. Real longitudinal profiles are not perfectly smooth curves, but rather they display little plateaus and steps, representing interruptions by lakes or waterfalls.

Headward Erosion

As flow increases and time passes, a strew channel begins to lengthen at its head (the origin). This process is called this. Occurs for 2 Reasons! 1. happens when the surface flow converging at the entrance to a channel has sufficient erosive power to downcut (when extra flow deepens the channel relative to its surroundings) 2. takes place at locations where groundwater seeps out of the ground and enters the head of the stream channel. Such seepage is called "groundwater sapping" and will gradually weakens and undermines the soil or rock just upstream of the channel's head until the material collapses into the channel. Each collapse makes the channel longer.

The sediment load consists of 3 components what are they?

Dissolved load suspended load bed load

Radial Drainage Network

Drainage network forming on the surface of a cone-shpaed mountain flow outward from the mountain peak like SPOKES ON A WHEEL...defines a radial network Radius ...radius of a circle, wheel Radiating pattern from a point uplift. Volcano usually in the middle look at pic!

Raging Waters- flash floods

Events during which the floodwaters rise so fast that it may be impossible to escape from the path of the water are called flash floods. thy happen during unusually intense rainfall or as a result of a dam collapse or levee failure. (A SUDDEN EVENT)

Runoff

Geologists use these term for ALL water flowing on the surface of the Earth-runoff includes sheet wash plus the water in streams!

Describing the flow of streams: discharge and turbulance

If you have a large stream and water flows slowly or a smaller one in whig water flows rapidly, which one carries more water? NOT OBVOUS ANSWER.. geologists need to calculate a streams discharge!!

Beveling Topography

OVER TIME DOWNCUTTING AND MEANDERING BROADEN VALLEYS AND BEVEL (REDUCE TO A SLOPING EDGE) TOPOGRAPHY TO BASE LEVEL look at pic in book or slides

Parallel drainage network

On a steep uniform slope several streams with parallel courses develop simultaneously Look at picture lines run down like from a mountain to a less steep position.. parallel is used in all the terms so make sure you know the slight differences Parallel network on steep uniform slopes. Look at pic.

dissolved sediment load

Running water dissolves soluble minerals int he sediment or oak that it flows over and groundwater seeping into a stream brings dissolved minerals with it. THE Ions of these dissolved minerals make up the streams dissolved load

flood frequency graph

Shows the relationship between the recurrence interval and the discharge for and idealized river Annual probability= 1/recurrence interval so a 100 year flood has a 1/100 chance of happening in a given year.

How do streams form in the first place?

The process of channel initiation (beginning of a stream) begins when sheet wash starts flowing downslope due to gravity sheetwash-water that flows downslope in a thin film 2. Sheetwash will erode its substrate! substrate-the material it flows over 3. The efficiency of such erosion depend on the VELOCITY of the flow-faster flows erode more rapidly. Because of vegetation, the topography of the environment, the material in the substrate, the velocity of sheet wash also varies with LOCATION! 4. Where the flow happens a bit FASTER or the substrate is a little weaker, erosion carves a CHANNEL! 5. Since the channel is lower than the surrounding ground, sheet wash in adjacent areas starts to head toward it. With time, the extra flow depends the channel relate to its surroundings. A process called DOWNCUTTING and a stream forms!! 6. AS douncutting deepens the main channel, the surrounding land surface start to slope toward the channel. thus side channels, or TRIBUTARIES begin to form.These flow into the main channel. EVENTUALLY and array of linked streams evolves with the smaller tributaries flowing into a" trunk stream". 7. The array of interconnecting streams together constitute the DRAINAGE NETWORK....like all transportation networks or roads, drainage networks of streams reach into all corners of a region, providing conduits for removal of RUNOFF The configuration of tributaries and trunk streams defines the map patter of a drainage network...this pattern depends on the shape of the landscape and the composition of the substrate! Geologists recognize several types of networks on the basis of the networks pattern (dendritic, radial, rectangular, trellis, parallel)

Hydrologic Cycle 5 Reservoirs: In snow and ice. In the Atmosphere. In the Ocean (largest). In the land. In the subsurface.

Transfer of water between various reservoirs 1. Water circulates through a number of reservoirs (including the atmosphere) Largest reservoir is the OCEAN which cover 71% of the earth's surface 2. Water evaporates from the ocean where it remains for quite a while 3. Atmospheric water gradually condenses and forms clouds that drop rain or snow onto the oceans or lands. 4. Water that falls on land can be held in glacial ice or in surface water (lakes, rivers, streams and swamps) 5. These bodies of ice and water constitute the Earth's SURFACE-WATER RESERVOIR. 6. Some water flows back to the ocean, some evaporates into the air and some sinks into the ground. 7. Water can remain temporarily on the surface of soil grains or sink deeper into the ground and be trapped there as groundwater. 8. Groundwater fills the holes and cracks between grains of rock and sediment and flows very slowly. 9. THUS, the subsurface of the land is also a water reservoir. 10. Not all reservoirs are inanimate-some water becomes part of a living organism and returns to the atmosphere by transpiration from plants or respiration by animals. The overall circulation of water from reservoir to reservoir in the Earth System is called the hydrologic cycle

What determines the efficiency of the erosion?

Velocity and volume of water and on its sediment content ^volume+^velocity = more erosion ^=higher

Sediment carried and deposited by streams. The clast size (the size of the rock bits) depends on the streams

Velocity!!! look at pic from you slides if you can't read this one

Discharge

Volume of water passing through cross section of the stream at a given time. D=AxV D=discarge A=area v=volicity units in volume/second. the amount of water flowing in a channel

Dendritic Drainage Network

When river flow over a fairly uniform substrate, that develops a network that looks like the pattern of branches connection the trunk of a tree. (think uniform, flat piece of paper you would draw a tree as part of your landscape) Branching pattern over a uniform substrate.

Drainage Divide...what is it?

a relatively high ridge that separates two drainage basins From book: a highland or ridge that separates one watershed from another

Capacity is dependent on what

both its competence (size of particles ) and discharge

Living with floods We"cannot tame that lawless stream, cannot curb it or confine it, cannot say to it go or go there and make it obey" Mark Twain

building artificial levees(elongated monte of sand and clay) and built concrete flood walls, along the banks of the river, to increase the channels volume. Artificial levees and flood walls isolate a discrete area of the floodplain. Sometimes the river rose so high that levee undermining occurs. when this happens rising water level increase the water pressure on the river side of the levee, forcing water through sand under the levee. In susceptible areas, water begins to spurt out of the ground on the dry side of the levee, thereby washing away the levees support. the levee finally becomes so weak that it collapses and water fills in the areas behind it. Look at pick...water comes up so close to the edge that it starts to seep through the sand and create puddles. Look at Pic!

Bed sediment load

consists of large par tiles such as sand, pebbles or cobbles that bounce or roll along the stream floor. Usually involves SALTATION-multitude of grains bounce along in the direction of the flow within a zone that extends upward fro the surface of the streamed for a distance of several centimeters to tens of cent. Each salting grain in the zone follows a curved trajectory up throughout the water then back down to the bed. When it strikes the bed it knocks other grains upward and thus supplies more grains to the saltation zone.

Stream channels form by ________________________ and lengthen by _____________________________ erosion.

downcutting headward

A drainage basin collets water from a broad region...what are the names for these basins?

drainage basin, also known as catchment (like it catches the water) and watershed (a shed to store the water) which feed then into the trunk stream, which carries the water away

When does most erosion takes place?

during floods when a stream carries a large volume of fast moving sediment-laden water

Raging Waters...seasonal floods

floods that occur during an annual wet eason are called seasonal floods. Floods of this type typically take place in tropical regions, during intense monsoonal rains and in temperate regions during the spring when downpours drench the land frequently and or heavy winter snowpack melts. The seasonal floods submerge floodplains, they produce floodplain floods and then they submerge delta plains they produce delta plain floods. **FLOODS TYPICALLY BUILD SLOWLY DUE TO LONG PERIOUDS OF SUSTAINED, INTENSE RAINFALL SATURATING THE GROUND

Rectangular drainage network

in places where a rectangular grid of fractures (VERTICLE JOINTS) breaks up the ground, channel follow preexisting fractures and streams join each other at RIGHT ANGLES creating a rectangular network Rectangular joint controlled pattern. Look at pic!

The gravitational energy stored in water transforms into

kinetic energy...the energy of motion About 3% of this kinetic energy goes into the work of ERODING the walls and beds of streams and channels.

In places where turbulence produces long lived whirlpools, abrasion by sad or gravel carves a bowl shaped depression called what into the floor of the stream

pothole

Capacity (in the ability to carry sediment)

refers to the total QUANTITIY of sediment it can carry. Clearly a large river has more capacity than a small creek

Competence and capacity describe the ability to carry

sediment. They depend on velocity (Competence mainly) and discharge. Where velocity/competence decreases, sediment will settle out (fall to bottom), where velocity/competence increases, EROSION WILL occur. Because of the abrasive affects casued by the sediment and the speed at which it is going.

meandering streams and their floodplanes

snake like curves in a river is called a meander.How do they evolve?? Water in a stream starts out as a straight channel, natural variations in water depth will cause the fastest moving part of the current, called the thawed to swing back and forth. THe water erodes the side of the stream more effectively where it flows faster so it begins to cut away faster on the outer arc of the curve. Thus each curve begins to migrate sideways and grow more pronounced until it becomes a meander. -on the outside edge of the meander, erosion continues to eat away at the channel wall forming a CUT BANK. -on the inside edge where water slows down and stye streams competence(max particle size) decreases, so sediment accumulates forming a crescent shaped wedge called a POINT BAR his words: IN LOW GRADIENT reaches of a steam the channel loops back and forth forming meanders, with point bars and cut banks.

dischage is determined at a

stream gauging station where the instruments measure the velocity and depth of the water at several points across the stream pic is a little different than the book, but principals are the same

breaking and lifting (erosion) PLUCKING Is the term he uses different from my book

the push of flowing water can break chunks of solid rock off the channel wall or floor or walls. Also,the flow of a current over a clast can cause the clast to rise or lift off the substrate (floor)

Competence vs capacity

when describing the streams ability to carry sediment geologists distinguish between competence and capacity