What Are The Primary Sizes Of Grains That Make Up The Suspended Loads Of Most Rivers And Streams?

EENS 111	Physical Geology
Tulane University	Prof. Stephen A. Nelson
Streams and Drainage Systems

Streams

A stream is a body of water that carries stone particles and dissolved ions and flows downward slope along a clearly defined path, called a aqueduct . Thus, streams may vary in width from a few centimeters to several tens of kilometers. Streams are important for several reasons:

• Streams carry most of the h2o that goes from the state to the sea, and thus are an of import part of the h2o cycle.
• Streams carry billions of tons of sediment to lower elevations, and thus are one of the main transporting mediums in the production of sedimentary rocks.
• Streams bear dissolved ions, the products of chemic weathering, into the oceans and thus make the sea salty.
  

• Streams are a major function of the erosional procedure, working in conjunction with weathering and mass wasting. Much of the surface mural is controlled by stream erosion, evident to anyone looking out of an airplane window.
• Streams are a major source of water, waste matter disposal, and transportation for the earth's man population. Most population centers are located next to streams.
• When stream channels fill with water the excess flows onto the the land as a alluvion.  Floods are a common natural disaster.

The objectives for this discussion are as follows:

1. How do drainage systems develop and what do they tell the states about the geology of an surface area?
2. How practice stream systems operate?
3. How do streams erode the landscape?
4. What kinds of depositional features result from streams?
5. How do drainage systems evolve?
6. What causes flooding and how tin we reduce the damage from floods?

Development of Streams - Steamflow begins when water is added to the surface from rainfall, melting snow,and groundwater.  Drainage systems develop in such a way as to efficiently move h2o off the land. Streamflow begins as moving sheetwash which is a thin surface layer of water.  The h2o moves down the steepest gradient and starts to erode the surface by creating pocket-size rill channels. Every bit the rills coalesce, deepen, and downcut into channels larger channels form. Rapid erosion lengthens the channel upslope in a procedure called headward erosion . Over fourth dimension, nearby channels merge with smaller tributaries joining a larger torso stream. (See figure 17.3 in your text). The linked channels become what is known equally a drainage network . With continued erosion of the channels, drainage networks change over time.

Drainage Patterns - Drainages tend to develop along zones where rock blazon and structure are most easily eroded. Thus various types of drainage patterns develop in a region and these drainage patterns reflect the structure of the rock. Dendritic drainage patterns are nearly common.  They develop on a land surface where the underlying stone is of uniform resistance to erosion. Radial drainage patterns develop surrounding areas of high topography where elevation drops from a cardinal high expanse to surrounding low areas.

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. Trellis drainage patterns develop where registrant rocks break up the landscape (see figure 17.4 in your textbook).

Drainage Basins - Each stream in a drainage arrangement drains a certain expanse, called a drainage basin (also chosen a catchment or a watershed). In a single drainage bowl, all water falling in the basin drains into the same stream. A drainage divide separates each drainage basin from other drainage basins.  Drainage basins can range in size from a few km2, for small streams, to extremely large areas, such as the Mississippi River drainage basin which covers about forty% of the contiguous United States (meet figure 17.5c in your text). Continental Divides - Continents tin can be divided into large drainage basins that empty into different ocean basins. For example: North America can be divided into several basins west of the Rocky Mountains that empty into the Pacific Ocean. Streams in the northern part of North America empty into the Arctic Sea, and streams East of the Rocky Mountains empty into the Atlantic Ocean or Gulf of Mexico. Lines separating these major drainage basins are termed Continental Divides. Such divides usually run along loftier mountain crests that formed recently enough that they have not been eroded. Thus major continental divides and the drainage patterns in the major basins reflect the recent geologic history of the continents. Permanent Streams - Streams that flow all year are called permanent streams.   Their surface is at or below the water table.  They occur in humid or temperate climates where there is sufficient rainfall and low evaporation rates.   Water levels rise and autumn with the seasons, depending on the belch. Ephemeral Streams - Streams that but occasionally have water flowing are called ephemeral streams or dry washes. They are higher up the water table and occur in dry climates with low amounts of rainfall and high evaporation rates. They catamenia mostly during rare flash floods.

Geometry and Dynamics of Stream Channels

Belch

The stream channel is the conduit for water being carried by the stream. The stream can continually adjust its aqueduct shape and path as the amount of water passing through the aqueduct changes.   The volume of h2o passing any indicate on a stream is chosen the discharge . Discharge is measured in units of volume/time (m³/sec or ft³/sec).

Q = A x V

Discharge (k³/sec) = Cross-sectional Area [width x average depth] (k²) x Boilerplate Velocity (thousand/sec).

As the amount of water in a stream increases, the stream must adjust its velocity and cross sectional area in order to form a residuum. Belch increases every bit more water is added through rainfall, tributary streams, or from groundwater seeping into the stream . As discharge increases, more often than not width, depth, and velocity of the stream likewise increase.

Velocity

A stream's velocity depends on position in the stream channel, irregularities in the stream channel caused past resistant rock, and stream gradient. Friction slows h2o along channel edges. Friction is greater in wider, shallower streams and less in narrower, deeper streams.

In direct channels, highest velocity is in the center. In curved channels,The maximum velocity traces the outside curve where the aqueduct is preferentially scoured and deepened.  On the inside of the bend were the velocity is lower, deposition of sediment occurs.  The deepest part of the channel is called the thalweg, which meanders with the curve the of the stream. Flow around curves follows a spiral path.

Stream menses can be either laminar, in which all h2o molecules travel along similar parallel paths, or turbulent, in which individual particles take irregular paths. Stream menstruation is characteristically turbulent.  This is chaotic and erratic, with arable mixing, swirling eddies, and sometimes high velocity.  Turbulence is caused by catamenia obstructions and shear in the water. Turbulent eddies scour the channel bed, and tin proceed sediment in pause longer than laminar menstruum and thus aids in erosion of the stream bottom.

Cantankerous Exclusive Shape

Cross-sectional shape varies with position in the stream, and discharge. The deepest part of aqueduct occurs where the stream velocity is the highest. Both width and depth increase downstream considering discharge increases downstream. As belch increases the cross sectional shape will modify, with the stream becoming deeper and wider.

Erosion by Streams

Streams erode because they take the ability to pick upward stone fragments and transport them to a new location. The size of the fragments that can be transported depends on the velocity of the stream and whether the flow is laminar or turbulent. Turbulent flow can keep fragments in break longer than laminar flow.

Streams can also erode by undercutting their banks resulting in mass-wasting processes like slumps or slides. When the undercut material falls into the stream, the fragments can be transported away by the stream.

Streams tin cut deeper into their channels if the region is uplifted or if there is a local change in base level. As they cut deeper into their channels the stream removes the cloth that one time fabricated up the channel bottom and sides.

Although slow, as rocks motility along the stream lesser and collide with one some other, abrasion of the rocks occurs, making smaller fragments that can then be transported past the stream.

Finally, because some rocks and minerals are easily dissolved in water, dissolution also occurs, resulting in dissolved ions being transported by the stream.

Sediment Send and Deposition The rock particles and dissolved ions carried by the stream are the called the stream'due south load. Stream load is divided into 3 categories. Suspended Load - particles that are carried along with the water in the main part of the streams. The size of these particles depends on their density and the velocity of the stream. Higher velocity currents in the stream tin can carry larger and denser particles.

Bed Load - coarser and denser particles that remain on the bed of the stream most of the time but move by a process of saltation (jumping) every bit a result of collisions betwixt particles, and turbulent eddies. Note that sediment can motion between bed load and suspended load equally the velocity of the stream changes.

• Dissolved Load - ions that have been introduced into the water by chemical weathering of rocks. This load is invisible considering the ions are dissolved in the h2o. The dissolved load consists mainly of HCO₃ ^{- two} (bicarbonate ions), Ca^+two, And so₄ ^-2, Cl^-, Na⁺ⁱⁱ, Mg⁺ⁱⁱ, and K⁺. These ions are eventually carried to the oceans and give the oceans their salty character. Streams that have a deep hugger-mugger source mostly have higher dissolved load than those whose source is on the Earth'southward surface.

The maximum size of particles that tin exist carried as suspended load past the stream is called stream competence .   The maximum load carried by the stream is called stream capacity .  Both competence and capacity increase with increasing discharge. At high discharge boulder and cobble size fabric can motion with the stream and are therefore transported.   At low discharge the larger fragments become stranded and only the smaller, sand, silt, and clay sized fragments move.

When flow velocity decreases the competence is reduced and sediment drops out. Sediment grain sizes are sorted by the water. Sands are removed from gravels; muds from both. Gravels settle in channels. Sands drop out in near channel environments. Silts and clays drape floodplains away from channels.

Changes Downstream

As one moves along a stream in the downstream management:

• Discharge increases, as noted above, because h2o is added to the stream from tributary streams and groundwater.
• As belch increases, the width, depth, and average velocity of the stream increment.
• The gradient of the stream, however, volition decrease.
  

It may seem to exist counter to your observations that velocity increases in the downstream direction, since when one observes a mountain stream about the headwaters where the slope is high, it appears to have a college velocity than a stream flowing forth a gentle gradient. But, the water in the mountain stream is probable flowing in a turbulent way, due to the large boulders and cobbles which make up the streambed. If the flow is turbulent, and then it takes longer for the water to travel the same linear distance, and thus the average velocity is lower.

Besides as 1 moves in the downstream management,

• The size of particles that brand upward the bed load of the stream tends to decrease. Even though the velocity of the stream increases downstream, the bed load particle size decreases mainly considering the larger particles are left in the bed load at college elevations and chafe of particles tends to reduce their size.
• The limerick 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.

Long Contour

A plot of height versus altitude. Unremarkably shows a steep gradient or slope, nigh the source of the stream and a gentle gradient as the stream approaches its mouth.  The long profile is concave upwards, as shown by the graph below.

Base of operations Level Base level is defined equally the limiting level below which a stream cannot erode its channel. For streams that empty into the oceans, base level is sea level. Local base levels tin occur where the stream meets a resistant body of rock, where a natural or artificial dam impedes further aqueduct erosion, or where the stream empties into a lake.

When a natural or artificial dam impedes stream flow, the stream adjusts to the new base level past adjusting its long profile. In the instance here, the long contour higher up and below the dam are adjusted. Erosion takes place downstream from the dam (especially if it is a natural dam and water tin menses over the superlative). Just upstream from the dam the velocity of the stream is lowered so that deposition of sediment occurs causing the gradient to get lower. The dam essentially get the new base level for the part of the stream upstream from the dam. In general, if base level is lowered, the stream cuts downwardly into its channel and erosion is accelerated.   If base level is raised, the stream deposits sediment and readjusts its contour to the new base level. Valleys and Canyons Land far above base level is subject to downcutting past the stream.  Rapid downcutting creates an eroded trough which can get either a valley or canyon.   A valley has gently sloping sidewalls that evidence a V-shape in cross-department.   A Canyon has steep sidewalls that form cliffs.  Whether or valley or coulee is formed depends on the rater of erosion and forcefulness of the rocks.   In full general,  tiresome downcutting and weak, hands erodable rocks results in valleys and rapid downcutting in stronger rocks results in canyons. Considering geologic processes stack strong and weak rocks, such stratigraphic variation often yields a stair step contour of the canyon walls, as seen in the Grand Canyon.  Stiff rocks yield vertical cliffs, whereas weak rocks produce more than gently sloped canyon walls. Agile downcutting flushes sediment out of channels.  Just after the sediment is flushed our tin can farther downcutting occur.   Valleys store sediment when base of operations level is raised. Rapids Rapids are turbulent h2o with a rough surface.  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 aqueduct. Sudden alter in slope may occur where an active mistake crosses the stream channel.   Large clasts may be transported into the stream by a tributary stream resulting in rapids where the two streams join.   Abrupt narrowing of the stream may occur if the stream encounters strong rock that is not easily subject area to erosion. Waterfalls Waterfalls are temporary base levels acquired by strong erosion resistant rocks.   Upon reaching the strong rock, the stream and then cascades or free falls downwards the steep slope to form a waterfalls.  Because the rate of flow increases on this rapid change in slope, erosion occurs at the base of the waterfall where a plunge pool forms.  This tin can initiate rapid erosion at the base, resulting in undercutting of the cliff that caused the waterfall. When undercutting occurs, the cliff becomes bailiwick to rockfalls or slides.   This results in the waterfall retreating upstream and the stream eventually eroding through the cliff to remove the waterfall. Niagara Falls in upstate New York is a skilful case.   Lake Erie drops 55 yard flowing toward Lake Ontario. A dolostone caprock is resistant and the underlying shale erodes.  Blocks of unsupported dolostone plummet and fall. Niagara Falls continuously erodes south toward Lake Erie. In  temporary diversion of the water that flows over the American Falls department revealed huge blocks of rock.  The rate of southward retreat of Niagara Falls is soon 0.5 thou/yr.   Eventually the falls will achieve Lake Erie, and when that happens Lake Erie will drain.

Aqueduct Patterns

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 stone, like a fault or joint organization.

Even in straight channel segments water flows in a sinuous style, with the deepest function of the aqueduct changing from near i banking concern to near the other. Velocity is highest in the zone overlying the deepest office of the stream. In these areas, sediment is transported readily resulting in pools . Where the velocity of the stream is low, sediment is deposited to form bars .

The banking company closest to the zone of highest velocity is usually eroded and results in a cutbank .

Meandering Channels - Because of the velocity structure of a stream, and specially in streams flowing over depression gradients with hands eroded banks, directly channels will somewhen erode into meandering channels . Erosion will accept place on the outer parts of the meander bends where the velocity of the stream is highest. Sediment deposition will occur along the inner meander bends where the velocity is low. Such deposition of sediment results in exposed confined, chosen point bars . Considering meandering streams are continually eroding on the outer meander bends and depositing sediment along the inner meander bends, meandering stream channels tend to migrate dorsum and forth across their flood plain.

If erosion on the outside meander bends continues to take identify, somewhen a meander bend tin can get cut off from the balance of the stream. When this occurs, the cutoff meander curve, considering it is still a depression, will collect water and course a type of lake called an oxbow lake .

Braided Channels - In streams having highly variable discharge and easily eroded banks, sediment gets deposited to form bars and islands that are exposed during periods of depression discharge. In such a stream the water flows in a braided pattern around the islands and confined, dividing and reuniting as information technology flows downstream. Such a channel is termed a braided channel . During periods of high discharge, the entire stream channel may contain water and the islands are covered to get submerged bars. During such loftier discharge, some of the islands could erode, but the sediment would exist re-deposited every bit the discharge decreases, forming new islands or submerged confined. Islands may become resistant to erosion if they go inhabited by vegetation

Stream Deposits

Sudden changes in velocity tin result in deposition by streams. Inside a stream we have seen that the velocity varies with position, and, if sediment gets moved to the lower velocity office of the stream the sediment volition come out of pause and be deposited. Other sudden changes in velocity that affect the whole stream can also occur. For case if the discharge is suddenly increased, every bit it might be during a flood, the stream volition overtop its banks and flow onto the floodplain where the velocity volition and then all of a sudden subtract. This results in deposition of such features as levees and floodplains. If the gradient of the stream suddenly changes by elimination into a apartment-floored basin, an ocean basin, or a lake, the velocity of the stream will of a sudden subtract resulting in degradation of sediment that can no longer be transported. This can result in deposition of such features every bit alluvial fans and deltas.

• Floodplains and Levees - As a stream overtops its banks during a flood, the velocity of the overflowing will first be high, but volition suddenly decrease as the h2o flows out over the gentle slope of the floodplain. Because of the sudden decrease in velocity, the coarser grained suspended sediment will be deposited along the riverbank, eventually edifice up a natural levee. Natural levees provide some protection from flooding because with each flood the levee is built higher and therefore discharge must exist higher for the next alluvion to occur. (Note that the levees we see along the Mississippi River here in New Orleans are not natural levees, but man fabricated levees, built to protect the floodplain from floods.  Still, the natural levees practice form the high ground as evidenced by the flooding that occurred as a result of levee breaches during Hurricane Katrina).

Terraces - Terraces are exposed former floodplain deposits that effect when the stream begins downward cutting into its flood plain (this is usually caused by regional uplift or by lowering the regional base level, such equally a drop in sea level).

Alluvial Fans - When a steep mountain stream enters a flat valley, in that location is a sudden decrease in gradient and velocity. Sediment transported in the stream will all of a sudden become deposited forth the valley walls in an alluvial fan. As the velocity of the mount stream slows information technology becomes choked with sediment and breaks upwards into numerous distributary channels.
Deltas - When a stream enters a standing body of h2o such as a lake or ocean, again there is a sudden subtract in velocity and the stream deposits its sediment in a eolith called a delta. Deltas build outward from the coastline, but volition only survive if the bounding main currents are not strong enough to remove the sediment.

Every bit the velocity of a stream decreases on entering the delta, the stream becomes choked with sediment and conditions become favorable to those of a braided stream channel, only instead of braiding, the stream breaks into many smaller streams called distributary streams.

Over the last 1,000 years, nearly of the state that makes up southern Louisiana has been built by the Mississippi River depositing sediment to form delta lobes.  These delta lobes take shifted back and along through fourth dimension every bit the River'due south form inverse in response to changes in ocean level and the River trying to maintain the shortest and steepest path to the Gulf of United mexican states (see figure 17.25a)

Drainage Development

Landscapes on Earth's surface evolve over time with the main crusade of alter being streamflow and the resulting erosion and deposition.  For example:
Uplift sets a new base level which causes streams to cut deeper, resulting in widening of valleys and erosion of hills.  If these erosional processes were to continue, the landscape would be eroded to base of operations level.

Stream Piracy

Stream piracy is where one stream erodes headward to capture the drainage of some other stream. The stream with more than vigorous erosion (steeper gradient), intercepts another stream and water from the captured stream no flows into the pirating stream (see figure 17.26 in your text).

Drainage Reversal

Drainage reversals can occur every bit a issue of tectonic processes.  For instance, in the early Mesozoic when Africa and Due south America were role of the same continent, South America tuckered westward.  Eventually Africa separated from South America to course the Atlantic Ocean on the eastern side of South America.   On the west coast, subduction began and the resulting compression acquired the uplift of the Andes mountains.  As the uplift occurred, the drainage had to opposite to flow to the east into the Atlantic Ocean (see effigy 17.27 in your text).

Superposed and Antecedent Streams

In looking at the landscape, information technology is ofttimes evident that streams sometimes cut through deformed terrain seemingly ignoring the geologic structures and hardness of the rock.  If a stream initially develops on younger flat strata made of soft textile and then cuts down into the underlying deformed strata while maintaining the course adult in the younger strata, it is referred to equally a superposed stream , because the stream design was superposed on the underlying rocks.    In such cases much of the original soft strata is removed.  (see effigy 17.29 in your text).

If tectonic uplift raises the basis beneath established streams and if erosion keeps footstep with uplift, the stream will cutting downward and maintain its original course.  In such a instance, the stream is called an antecedent stream, because the stream was present before the uplift occurred . (See figure 17.30 in your textbook).

Some antecedent streams take incised meanders.  The meanders initially develop on a gentle gradient and then uplift raises the landscape (dropping the base level) and the meanders cutting downward into the uplifted mural (meet figure 17.28 in your text for an example).

Floods

Floods occur when the discharge of the stream becomes too high to exist accommodated in the normal stream channel. When the discharge becomes too loftier, the stream widens its channel by overtopping its banks and flooding the low-lying areas surrounding the stream. The areas that become flooded are chosen floodplains .

Floodwaters are devastating to people and property.  During a flood discharge exceeds the storage book of the stream aqueduct.  Velocity (thus, competence and capacity) increase and water leaves the channel and flows onto next land. Water slows abroad from the thalweg, dropping sediment.

Causes of Flooding

1. Heavy rains dump large volumes of water on the landscape increasing the amount of h2o flowing into the stream.
2. If the soil has become saturated as a result of rain so that at that place is no room in the soil for h2o to infiltrate, the water instead volition see stream channels and increase the belch.
3. In the winter, if a sudden increase in temperature speedily melts snowfall causing an influx of water into the drainage organisation.
4. When a natural or bogus dam breaks or levee breaks, releasing water into a channel with a sudden increment in discharge or releases h2o from the channel onto the surrounding floodplain.
   

Inundation Stage

• The term stage refers to the height of a river (or whatsoever other bounding main) above a locally defined elevation.  This locally defined elevation is a reference level, often referred to as datum.  For example, for the lower part of the Mississippi River, reference level or datum, is sea level (0 anxiety).  Currently the Mississippi River is at a stage of nigh 12.5 feet, that is 12.5 feet above sea level.  Other river systems have a reference level that is not bounding main level.  Most rivers in the U.s. have gaging stations where measurements are continually fabricated of the river's phase and discharge.  These are plotted on a graph called a hydrograph , which shows the stage or belch of the river, every bit measured at the gaging station, versus time.
• When the belch of a river increases, the aqueduct may become completely total.  Any discharge higher up this level will result in the river overflowing its banks and causing a flood.  The phase at which the river will overflow its banks is called bankfull stage or inundation phase. For example, the graph beneath is a hydrograph of the Mississippi River at St. Louis, Missouri during the time period of the 1993 flood.  Discharge is plotted on the Y-axis, and dates are plotted on the x-axis.  Annotation that stages corresponding to various discharges are shown on the left-mitt y-axis, and that the spacing between equal units of phase are not equal along the y-axis.

Annotation that for the 1993 Mississippi River Flood, the river reached flood stage of xxx feet above datum on near June 26 and peaked (or crested) at just under l feet higher up datum on August i.  The sudden drops seen in discharge around July 15 and July 20 corresponded to breaks in the levee organization upstream from St. Louis that caused water to menses onto the floodplain upstream, thus reducing both the phase and discharge measured at St. Louis. To illustrate, for the Mississippi River flood at St. Louis, arcadian cross sections of the River are shown below for points a, b, and c in the diagram higher up.

Lag Time The time difference between when heavy precipitation occurs and when superlative discharge occurs in the streams draining an area is chosen lag fourth dimension. Lag time depends on such factors as the amount of time over which the pelting falls and the amount of water that can infiltrate into the soil.

If the corporeality of rain is high over a brusk time period, lag fourth dimension is short.  If the corporeality of rain is high over a longer time period, lag time is longer. Lack of infiltration and interception reduce lag time

Flash floods occur when the rate of infiltration is low and heavy rains occur over a short period of time.   Because they come with footling warning, flash floods are the well-nigh dangerous to human lives. Such floods stem from unusually intense rainfall or dam failures, strike with little warning,an they are often mortiferous.  (See the example of the Big Thompson Canyon flash flood in your text, p. 644).

Any time the surface materials of the Earth are covered with impermeable materials similar physical, asphalt, or buildings, the infiltration of water into the soil is prevented.  Urbanization tends to reduce infiltration, and thus h2o must collect in tempest sewers and eventually in the main drainage systems.  Thus, extensive urbanization also decreases the lag time and increases the acme discharge fifty-fifty further.  Urbanization can therefore pb to a college incidence of flash floods.

Flooding Risk Discharge data collected over a long period of time on streams tin exist used to calculate flood probability.   The data are plotted on a graph of Elevation Discharge for each yr versus recurrence interval.  Note that the logarithm of the recurrence interval is used.   As an case, such a graph is shown for the Red River of the North at Fargo, N Dakota below.

From such a graph one can determine the stage or discharge for unlike recurrence intervals.   The x year flood is defined as the discharge that would take a 10% probability of occurring every year.  Similarly, the 100 year inundation is the belch that has a 1% run a risk of occurring every year.    Note that the 100 year overflowing does not necessarily occur just in one case every 100 years.  For example, the graph for the Blood-red River of the N, higher up, shows that two 250 year floods occurred in an 8 year menses. F lood Run a risk Mapping Food hazard mapping is used to make up one's mind the areas susceptible to flooding when belch of a stream exceeds the bank-full phase.  Using historical data on river stages and discharge of previous floods, forth with topographic information, maps can be synthetic to evidence areas expected to exist covered with floodwaters for diverse discharges or stages.

Overflowing Control Response to flood hazards tin can be attempted in two main ways:  An engineering approach, to command flooding, and a regulatory arroyo designed to decrease vulnerability to flooding. Engineering Approaches Aqueduct modifications - Past creating new channels for a stream, the cantankerous-exclusive surface area can be enlarged, thus create a state of affairs where a higher stage is necessary before flooding.  Channelization likewise increases water velocity, and thus reduces drainage time. Dams - Dams tin can be used to hold h2o back then that discharge downstream can be regulated at a desired rate.  Homo synthetic dams accept spillways that can be opened to reduce the level of water in the reservoir backside the dam.  Thus, the water level can exist lowered prior to a heavy rain, and more water can be trapped in the reservoir and released later on at a controlled discharge. Retention ponds - Memory ponds serve a like purpose to dams.  Water tin exist trapped in a memory pond and and so released at a controlled belch to prevent flooding downstream. Levees, Dikes, and Floodwalls  - These are structures congenital along side the aqueduct to increment the stage at which the stream floods. Floodways - Floodways are areas that tin can exist built to provide an outlet to a stream and let it flood into an area that has been designated as a floodway.  Floodways are areas where no construction is immune, and where the country is used for agricultural or recreational purposes when in that location is no threat of a flood, but which provide an outlet for flood waters during periods of loftier discharge.  The Bonnet Carrie Spillway w of New Orleans is such a floodway.  During depression stages of the Mississippi River the state between the River and Lake Pontchartrain is used for recreational purposes - hunting, fishing, and dirt bike riding for example. During high stages of the River when there is a potential for the River to rising to flood phase in New Orleans, the spillway is opened so that water drains into Lake Pontchartrain.  This lowers the level of water in the Mississippi and reduces the possibility of a levee break or water overtopping the levee. Regulatory Approaches With a better understanding of the beliefs of streams, the probability of flooding, and areas likely to be flooded during high discharge, humans tin undertake measures to reduce vulnerability to flooding.  Among the regulatory measures are: Floodplain zoning - Laws can be passed that restrict structure and habitation of floodplains.  Instead floodplains can be zoned for agronomical apply, recreation, or other uses wherein lives and property are non endangered when (note that I did not apply the discussion if) inundation waters re-occupy the floodplain. Floodplain building codes - Structures that are allowed within the floodplain could be restricted those that can withstand the loftier velocity of alluvion waters and are loftier enough off the ground to reduce take chances of contact with water. Floodplain buyout programs - In areas that have been recently flooded, it may be more cost effective for the government, which commonly pays for flood damage either through subsidized flood insurance or directly disaster relief, to buy the rights to the country rather than pay the cost of reconstruction and and so have to pay once more the next time the river floods. Mortgage limitations - Lending institutions could refuse to requite loans to purchase or construct dwellings or businesses in flood prone areas.

Case of a Flood During Hurricane Katrina in 2005, much of New Orleans flooded, mainly as a issue of levee and floodwall failures that occurred on human made drainage and navigation canals.   In lecture, this event volition exist discussed in some item.   For details on the geological aspects of the flood events see the following web page and its included links - www.tulane.edu/~sanelson/Katrina.

---

Examples of questions on this material that could be asked on an exam

1. Define the following: (a) ephemeral stream, (b) stream slope, (c) stream discharge, (d) suspended load, (e) bed load (f) dissolved load (g) drainage basin, (h) drainage divide
2. What happens to a stream's discharge as one moves down stream?  Explain why this occurs.
3. List and give a cursory description of the various types of drainage net works..
4. What conditions are necessary for stream to be meandering stream and a braided stream?
5. How do streams erode?
6. Define the following: (a) alluvial fan, (b) delta, (c) floodplain, (d) point bar, (east) stream piracy, (f) floodstage, (g) hydrograph, (h) flash flood, (i) stream terrace.
7. What are the main causes of floods?
8. What is the probability that the 100 year flood will occur in any given year?
9. How does human development affect inundation hazards?
10. What engineering approaches are available to reduce the chance of flooding?
11. Also engineering solutions, what other steps can be taken to reduce vulnerability to flooding?

---

Return to EENS 1110 Page

What Are The Primary Sizes Of Grains That Make Up The Suspended Loads Of Most Rivers And Streams?,

Source: https://www.tulane.edu/~sanelson/eens1110/streams.htm

Posted by: montanodrationotled.blogspot.com

Share this post