Chapter 8 Streams and Flooding

streams and rivers are critical for___, the process in which Earth materials are removed in a given area; assisted by wind and ice, and even gravity when water enters a meander bend of a river, it is forced to slow down on the inner part of the bed (inner bank), only to speed back up on the outer part (outer bank) the raised velocity along the outer bank enhances erosion, forming a___that results in an unstable___

erosion cutbank; overhang

stage flood stage *always referenced to some site because a channel is steadily lowering in elevation downstream stream discharge calculation in ft^3/s

height of water in a channel relative to a reference plane, usually sea level height at which a channel starts to overflow its banks velocity of water * cross-sectional area of water flow

an overhang caused by enhanced erosion along the outer bank of a meander will eventually fall via some___event and will become part of the sediment being transported to a lake, reservoir, bay, gulf, sea, or ocean, or even another stream or river along the inner bank, where velocity decreases, sediments tend to build up and form deposits called combination of inner bank deposition and outer bank erosion results in? bed of stream is what?

mass wasting point bars (sand bars) lateral migration of channels that make up a drainage basin over time;widening of river valleys bottom

the younger stream terraces that are closer above active flood plains are more or less likely to be flooded? hence, humans have used the older kinds to build settlements and developing agriculture

more

located at mouths of drainage basins are___fans, which are large fan-shaped deposits that form where steep mountain streams empty out at valley floors hint: alluvium this leads to the channel choking due to sediment build up, and the channel is called a___ this channel migrated back and forth across the valley entrance, hence the mentioned fan-shaped deposit

alluvial braided stream

___failures are commonly triggered when water flows under or through the structures such that some of the levee material is removed by___ *overspilling is actually less common **due to zones of weakness or if built on a naturally permeable zone of surface where retention basins built? *hint: urban and suburban

artificial levee; erosion 1.adjacent to parking lots 2.residential areas 3.at construction sites prior to major

after flooding, when water levels fall, natural levees act as barriers as they block some floodwater from returning to the channel + floodplain drainage is further hampered by the fact that it is underlain by fine-grained material that is not very permeable; the poorly drained vicinity becomes a___, and can remain wet long after a flood

back swamp

kinds of stream deposits deltas formation can lead to land subsidence, which in turn, causes the deltas to grow further toward the alternate concentration of water, thereby creating new___

1.bars-mound shaped 2.point bars-crescent shaped bars; form on the inside of meander bends where water velocity decreases 3.delta deposits-form where a river enters another water body where water velocity decreases, and where the river splits land

ways to reduce flooding

1.dams-allows the control of stream discharge with reservoirs daily or seasonally; used for hydroelectric energy, freshwater, and recreation; bad for environment, especially downstream even though it stores sediments upstream 2.artificial levees-levees created by humans to keep streams from overflowing their banks and inundating their floodplain; made as earthen materials or large concrete flood walls; make floods worse upstream; sediments are prevented from being deposited on floodplains so flooding gets worse period over time 3.channelization-straightening and deepening a channel in order to increase stream discharge capacity by raising water velocity or cross-sectional area; stream gradient also raised; bad for environment since section becomes dominated by fast current, uniform channel depth, smooth bed, and no vegetation, thus increasing water temperature; worsens flooding downstream without it; more downcutting in channelized sections upstream that makes steeper banks more prone to mass wasting 4.retention (detention) basins-excess water from urban flooding stored in man made depressions for short time; made within networks of tributaries; works like small dams that store water from upstream before releasing at controlled rates 5.erosion controls-minimize mass wasting by keeping sediments in place or making physical barriers to trap sediments before they are transported throughout drainage basin 6.wetland restoration-restoration and preservation; reconnecting to water supply via filling in ditches and canals, and removing artificial levees; build new 7.flood proofing-build infrastructure above flood stage, surround with natural or artificial levees, or make emergency levees with sandbags 8.floodplain management-political policies that reduce flood losses and flood insurance claims 8.education-most cost effective strategy; raise risk awareness; those who choose to gamble with their lives need to know what they can due to reduce their risk of death

basic roles of streams and rivers? when a stream's or river's ability to carry water is overwhelmed, the water volume overflows its banks and creates a___ out of all the natural disasters, which has likely killed the most humans to date and caused the most economic loss? why?

1.drain water off the landscape (transport) g. 2.transport sediment flood floods 1.floods happen quite frequently 2.human settlement and activity clustered around watercourses that are waterways

types of precipitation-induced floods

1.flash floods-rapid flooding of small channels; also known as upstream floods since most smaller channels are located upstream in drainage basins; water level and velocity greatly increased in short time period 2.downstream floods-rivers in lower parts of drainage basins overflow their channels and inundate valley floors; mostly caused by accumulation of water upstream i.e. long precipitation events

downstream flooding water volume, lag time, and length of time channel (river) remains above flood stage compared to flash flooding, usually why are flash floods typically more hazardous than downstream floods while downstream floods typically produce more property damage?

1.larger water volume 2.longer lag time 3.above flood stage longer flash floods happen quicker downstream floods inundate more land and keep land inundated longer

precipitation-induced flooding factors

1.nature of precipitation events-based on intensity and duration 2.ground conditions-based on infiltration capacity (ability of land surface to absorb water) that is based on slope steepness and soil content 3.vegetation-reduces overland flow and thus flooding by intercepting some of the precipitation, or increases infiltration and this reduces overland flow too

why fatalities and property damage not used to measure flood severity? instead these are used

1.population density not uniform 2.human settlement not uniform 1.stream discharge 2.elevation

what causes conventional floods? what allows streams and rivers to have a minimum water volume that flows, better known as a base flow conditions, and is critical for the health of ecosystems?—keeps them from not drying up during periods of low precipitation fall

1.precipitation fall (rain, snow, sleet, hail, or slurry) 2.rapid melting of snow or ice 3.ice jams 4.dam failures groundwater base flow

land use flooding factors

1.removal of natural vegetation-causes sediment pollution when precipitation knocks soil particles into channel along with erosion, decreases infiltration, and increases overland flow 2.wetland destruction-land loses porosity to store water; similar to 1 3.construction activity-removing vegetation and destroying wetlands; buildings and roads built over channels block water flow; culverts (steel pipes) can only carry so much water and can clog 4.urbanization-biggest factor; based on 1-3; decreases infiltration and increase overland flow via buildings, roads, parking lots, etc.; channels reach flood stage more; flash flooding increases due to the decreasing lag time; sewers and drainage ditches transports excess water to channels quicker than groundwater flow

when stream discharge and water velocity increase, the 1st particles lifted are the? when stream discharge and water velocity decrease, the 1st particles to fall to the bed are the? the process whereby water separates particles (sediment grains mainly) based on their size, density, and shape

1.smallest 2.least dense 3.most angular 1.largest 2.most dense 3.most rounded hydraulic sorting

what are the erosion controls? most flood deaths occur in flash floods and 50% of these deaths are___related

1.stream buffers- planted vegetation lines banks and trap sediment; needed when land cleared by logging or agriculture 2.silt fences-synthetic fiber that traps sediments but allows water to pass; can be overwhelmed 3.silt basins-ponds made to trap sediments; sometimes deposits must be removed 4.wetland restoration vehicle

how people die in vehicles during floods, namely flash ones? only 2ft (0.6m) is needed to make a typical car float what about for a typical truck, SUV, or van?

1.trapped in vehicles 2.crashes 3.floating vehicles that are swept away 4.drive off roads 5.structural collapse 2-3ft (0.6-0.9m)

stream transportation and deposition factors suspended load vs bed load vs dissolved load

1.velocity 2.what is deposited suspended load is the sediments that are held in suspension and moving at the same velocity as flowing water bed load is the sediment that roll, bounce, or remain stationary on the stream bed dissolved load is the dissolved ions in flowing water

U.S. flash flood capital and why? another name for a river or main channel

Central Texas because 1.prone to storms from Gulf of Mexico 2.prone to storms from Great Plains becoming more intense as they draw moisture from the Gulf of Mexico; converging storm fronts 3.Hill Country in Central Texas has thin soil, so not a lot of infiltration, plus lots of limestone that breaks down easily 4.Hill Country has lots of steep valleys and steep canyons that moves water into streams fairly fast trunk stream

this is the recurrence interval formula recurrence interval (RI)=(N + 1)/M what is N and M? break up of ice and subsequent formation of__cause flooding upstream—temporary dams

N=number of yearly values recorded M=maximum stream discharge rank;determined from highest to lowest *M=1 is always highest ice jams

during overland flow, water will eventually move into low-lying terrain and begin a___; the sinuous pathway of the flowing stream is the___

stream channel

velocity of a stream is controlled by its steepness of its channel known as the___; direct relationship plus with stream discharge *also applies to rivers when a river empties into another water source, the slope of the area is 0, and this causes the water to no longer___, and___ceases base level what is the ultimate base level and why?

stream gradient (grade) flow;erosion lowest level to which a stream or river can erode sea level since the ocean represents end or lowest point for most rivers

lateral expansion due to undercutting that is due to lateral erosion, and, downcutting due to abrasion creates new floodplains like stairs, with each new plain being a step with lower elevation the older floodplains gradually dried out as a channel (river is the best case) migrates and are? *well-defined ones develop due to base level change from tectonic uplift or sea level drop

stream terraces

how are canyons formed? *not the water itself but the sediment that physically wears away rock via abrasion potholes are created during periods of high___when the water columns develop vortices called___that causes sediments to slowly rotate, thus grinding deeper progressively into solid rock; basis of abrasion

streams or rivers cutting into rock that makes up the beds of them over time (downcutting) stream discharge; eddies (eddy currents)

over time, abrasion and hydraulic sorting produces sediment that is progressively finer, more angular, and more uniform in size heading__towards/away from/nowhere/none related to___the mouth of a drainage basin

towards

as streams flow downward, they merge with other channels, and the smaller ones are called? network of channels; merging tributaries form progressively larger streams largest stream within a drainage system that serves as the principal channel upper portion of drainage system? lowest in which a river empties?

tributaries drainage system (drainage network) river (main channel) headwaters () mouth (river mouth)

hydrologic cycle (water cycle) what ultimately drives the hydrologic cycle? 75% of precipitation falls where?

continual transfer of water between subsystems and sub-subsystems of the Earth system solar energy oceans

the historic floods of 1993, 2008, and 2011 of the Mississippi River Drainage Basin occurred in less than 20 years but had recurrence levels on the order of centuries, some climatologists believe such floods are happening more frequently because? *just 1 example of this human modifications to the natural environment has overall lowered the risk for flooding, true or false a___consists of the sides of the channel, between which the flow is confined and where land follows channel course

current period of global warming is warming the atmosphere, and the atmosphere contains more water vapor that can fall as precipitation false bank (river bank)

as channels, mainly rivers, flow towards the world ocean, they may encounter___which forms when their ability to cut downward is reduced by resistant rock structures, lakes, inland seas, etc. generally, stream gradient decreases (becomes less steep and more flat) as the channel gets closer to some base level; resulting in___less/more/the same amount of___downcutting via abrasion and a tendency for more meandering, which in turn, leads to more undercutting via erosion that widens the river valley

deltas less

stage and stream discharge share an inverse or direct relationship? predicting floods is similar to?

direct predicting earthquakes since based on statistical probability

downcutting vs undercutting

downcutting-vertical erosion that increases the depth of a stream or valley due to sediment as water flows (abrasion) undercutting-lateral erosion that increases the width of a stream or valley due to water that flows *canyon too

imaginary line that follows crests in topography and separates chunks of the entire drainage system land area that collects water from a stream or river true or false, a drainage basin can be continuously subdivided into progressively smaller basins down to the level of tributaries?

drainage divide drainage basin (watershed) true

how to find flood frequency using percent probability? reoccurrence interval values tell how often we can expect floods of a certain size to happen, and percent probabilities indicate the___ *both based on long term averages

find reciprocal (inverse) of recurrence interval and multiply by 100% the chance that floods will happen

___involves identifying areas adjacent to a channel that will be inundated by a 100-year recurrence interval level flood based on recurrence level computing done to identify flood prone areas that are divided into flood fringes and floodways -within flood fringes, new buildings are allowed, but must be built at or above the 100-year recurrence interval level flood estimation, thus elevated -within floodways, no buildings or other obstructions that can impede water flow and raise flood height are allowed; instead they become future parks, golf courses, etc. why is this so for floodways?

floodplain management floodplain zoning floodways are where floodwaters are the deepest and fastest since these parts of floodplain zones have the least elevation

identify the type of stream based on this sequential scenario 1.in humid climates, more water infiltrates and reaches the water table since precipitation is more plentiful 2.increased infiltration causes humid regions to have water tables that are higher than their stream channels 3.groundwater forced into streams a lot

gaining streams

when soil accumulates enough water, gravity is able to begin pulling it from pore spaces, allowing infiltrating water to reach the water table and enter the saturated zone this water in the saturated zone is called? groundwater base flow

groundwater flow of groundwater to the surface and oceans

how is groundwater base flow different than stream discharge in terms of movement? stream hydrograph lag time lag time is contingent of?

groundwater base flow is pretty much continuous graph that plots stream discharge over time time difference between precipitation fall that increases overland flow and the spike in stream discharge from its base volume 1.distance between precipitation fall site 2.channel of interest

if 2 basins are equally sized but exist within 2 distinct climate zones, the one in the more arid climate zone will have___stream discharge naturally? largest drainage basin on Earth? stream discharge factors for drainage basins alluvium

less Amazon drainage basin 1.drainage basin size 2.climate stream sediment

identify the type of stream based on this sequential scenario 1.in arid climates, less water infiltrates and reaches the water table since precipitation is less plentiful 2.decreased infiltration causes arid regions to have water tables that are lower than their stream channels 3.water in streams flow into the groundwater system a lot *except for the world's larger rivers, this is true

losing streams

headwater streams are generally small and fast moving (flowing) and occupy narrow valleys closer to the mouth, streams become rivers and become slow moving while growing larger as they occupy wider valleys the main channel of the drainage system begins to develop right S shaped curves called___closer to the mouth

meanders

deposition on inner banks help build___, flat plains on valley floors *when overflow occurs, this area is the 1st to be inundated when a river overflows its channel, velocity suddenly drops as water moves onto the natural floodplain, forcing the largest, densest, and most rounded particles to immediately fall out of suspension and be deposited, creating___that run parallel to the banks

natural floodplains natural levees

flood floodplain, not natural floodplain *per US government since smaller tributaries far above sea level often do not have well-developed natural floodplains but still experience floods **and used to designate all areas at risk for floods while not necessarily implying natural floodplains

normally dry area of landscape becomes inundated with water any landscape susceptible to flooding

why are alluvial fans dangerous? where does dissolved loads originate from? what are the dissolved ions known as?

possibility of flooding, mass wasting, and land subsidence weathering of minerals that releases ions that bind with water molecules salts (ionic salts)

overland flow overland flow example stream discharge stream discharge typically measured in what units?

precipitation on land moves downslope in thin sheets via gravity water volume flowing downslope along a sloped parking lot water volume flowing through a channel over a given time interval ft^3/s

flood frequency is determined by 1st acquiring historical discharge of a river for as many years as possible and making a data table next, is to find___ for each maximum discharge, which is the frequency at which a particular discharge can be expected to recur over time hydrographs are also known as flood frequency curves -x-axes measure recurrence intervals -y-axes measure stream discharge or? -Z-axes measures percent probability, if included

recurrence interval stream stage

the actual water part of a stream discharge explain elevation flow of water

runoff 1.water flows from higher elevation to lower elevation, and most stream discharge is directed to oceans 2.once in oceans, water evaporates and returns to the atmosphere, completing the part of the water cycle that involves water traveling on the landmasses