Page 31 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Climate Systems and Climate Change xxvii tools for structured learning
Geosystems provides a structured learning path that helps students achieve a deeper understanding of physical geography through active learning.
concepts
KEY LEARNING
After reading the chapter, you should be able to:
• Sketch a basic drainage basin model, and identify different types of drainage patterns by visual examination.
• Explain the concepts of stream gradient and base level, and describe the relationship between stream velocity, depth, width, and discharge.
• Explain the processes involved in fluvial erosion and sediment transport.
• Describe common stream channel patterns, and explain the concept of a
graded stream.
• Describe the depositional landforms associated with floodplains and alluvial
450 part III The Earth–At • List and describe several types of river deltas, and explain flood probability
estimates.
fan environments.
▶ A Quantitative Solution at the end of each 15a
chapter leads students through an exercise by using a quantitative approach to solve a problem.
. Key Learning Concepts Review at the end of each chapter concludes the learning path and features summaries, narrative definitions, a list of key terms with page numbers, and review questions.
6.
Chapter 15 river Systems Describe drainage patterns. Define the various pat-
terns that commonly appear in nature. What drain- age patterns exist in your hometown? Where you attend school?
ba str
am e oc
am sl
it
ea
y ch
g e cr wnstream
concepts review
KEy LEArnIng
different types of drainage patterns by visual different types of drainage patterns by visual
level, and describe the relationship between velocity, depth, width, and discharge.
examination.
examination.
tional flow.
Drainage density is determined by the number and
pattern refers to the arrangement of channels in an area as and below Earnthd’sbesluorwfacEea.rFthlu’svsiaulrfparcoec.eFslsuevsiarlepsrtorceeasmse-s are stream- elevation limit of stream erosion in a region. A l
determined by the steepness, variable rock resistance, vari- related. The brealsaitcedfl.uTvhiael bsaysitcemfluivsialdsryasitneamgeisbasdinra, ionrage basin, or level occurs when something interrupts the stre
able climate, hydrology, relief of the land, and structural watershed, wwhaicthersihseadn, wopheicnhsiysstaenm.opDernaisnyasgtemd.ivDidreasinage divides ity to achieve base level, such as a dam or a land
controls imposed by the landscape. Seven basic drainage define the cadtecfhimnentthe(wcatecrh-rmeceenitvi(nwga)tearr-ereaceoifviangd)raairne-a of a drain- blocks a stream channel.
age basin. Inagaenybadsriani.nIangeanbaysidnr,aiwnatgeer binasitiina,llwyamteorviensitially moves
radial, parallel, rectangular, annular, and deranged.
Discharge, a stream’s volume of flow per un downslope in a thin film of sheetflow, or overland flow. ISSUES FOR THE 21ST CENTURY
downslope in a thin film of sheetflow, or overland flow. is calculated by multiplying the velocity of the str This surface runoff concentrates in rills, or small-scale hydrology (p. 454)
only outlets being evaporation and subsurface gravita-
urban areas rienscurletaisninhgigruhneorfpfeaankdffllowodsidnugriinagffelocotedds.rIengions. Rising sea level will make
tional flow.
Drainage density is determined by the number and
length of channels in a given area and is an expression
of a landscape’s topographic surface appearance. Drain-
delta areas more vulnerable to flooding.
ing or just after a rainstorm is a flash flood. gradient (p. 427)
base level (p. 427)
and moves it to new locations in the process of erosion. Sediments are laid down by the process of deposition. Hydraulic action is the erosive work of water caused by hydraulic squeeze-and-release action to loosen and lift
age pattern refers to the arran c Geosystems Connection at
area as determined by the stee t h e e n d o f c h a a n c p e t , e v r a s r i a h b e l e l p c l i s m t a u t d e , e h n y dt s r o l o
15c
patterns are generally found in nature: dendritic, trellis,
This surface runoff concentrates in rills, or small-scale width and dep•thIncforreassinpgecpifoicpuclraotsisonsewctililointoefntshife
downhill grooves, which may develop into deeper gIunll2i0e1s1, Americafnlus vspiaelnt(p$.4245m4i)llion
downhill grooves, which may develop into deeper gullies Streams may whoarvledwpiedre,nensipael,cieapllhyeimn edreavl,elorpint
and a stream course in a valley. High ground that osnepfisah-ing-relatedaractivniatiegse. bSatrseianm(sp. 454)
and a stream course in a valley. High ground that sepa- flow regimes. Discharge usually increases in a do
in Montana, Missouri, Michigan, to flood impacts. rates one valley from another and directs sheetflow is sheetflow (p. 455)
rates one valley from another and directs sheetflow is direction; however, in rivers in semiarid or ari
basins. Some regions, such as the Great Salt Lake Basin,
have internal drainage that does not reach the oceanas, twhaeter quality adnrdaiqnuangteityp,attern (p. 458)
have internal drainage that does not reach the ocean, the
Utah, and Wisconsin are of high
an interfluve. Extensive mountain and highland regions continental divide (p. •45S5t)ream restoration will continue, i an interfluve. Extensive mountain andenhoiugghhlaqnuadlitryetghiaotnthsey aredischarge may decrease with distance downstrea act as continental divides that separate major drainage internal drainage (p. 4fl5o7w) restoration, vegetation reesta
act as continental divides that separadtesimgnajtoerd d“brluaeinriabgbeon fishiserlioes”t to evapotranspiration and water diversions. basins. Some regions, such as the Great Salt Lake Basin, drainage density (p. 45g8e)omorphology.
b a s e d o n s u s t a i n a b i l i t y c r i t e r i a s Au c h g r a p h o f s t r e a m d i s c h a r g e o v e r t i m e f o r
place is calle•dGlaobhayldclriomgartaepchh.anPgrecmipaityatiniotenns accessibility, and the specific species
b Key Learning Concepts
at the beginning of every chapter help students identify the key knowledge and skills they will acquire through study of the chapter.
AQuantitativeSOLUTION Flood Frequency Analysis
re Interface
ovide water
fo
The degree to which any phenomenon is a hazard depends on its magnitude and its frequency of occurrence. The frequency with which a flood of a certain magnitude or higher can be expected to occur is called its recurrence interval. Recurrence intervals can
Statistically, we then expect a flood of magnitude 425 m3 · s−1 (or higher) to occur on average once every 7 to 8 years. On average is emphasized, as it is incorrect to expect a flood of this magnitude or higher to occur on a regular cycle of once every 7 to 8 years. Sometimes the interval between floods of this magni-
(n
humanDEN TOR 15
be determined wherever long-term river-gauging records are
available, and are given by the formula: tude or higher will be shorter than 7 to 8 years, and sometimes
where Tr is the recurrence interval, n is the number of years of
record, and m is the number of floods of the given magnitude or
This is the reciprocal of the recurrence interval, expressed as a
nual peak discharge is independent of other values in the table. The If we want to calculate the recurrence of a flood of magnitude
425
= 31 * 100
r
municipal and
+1
)
it w
ill be
longe
r. A recu
rren
ce inte
o
t
be
used to predict
OMINA
u
rva
Tr = m when a flood of a certain magnitude will occur in the future.
farmed fertile floodplain soils for • Dams and diversions alter river flows and sediment loads, a
higher during the years of record.
percentage:
Table AQS 15.1 shows peak discharges for a river-gauging
station for a period of record from 1980 to 2009. Note thaet ecaochsayns- tems and habitaPt. R m
r(
odplainspeaknindonde eyelatradsoe.s not influence the peak value in thernexsttyoear.e ecosystems and thre4atened species.
= 12.9%
that m3 · s−1 was exceeded four times in the 30-year period. For this river, based on these data, there is a 12.9% chance
−
3
425 m · s or higher, for example, we note in Table AQS 15.1
1
(30 + 1)
In June 2013, flood4waters
runoff, peak flows, and sediment loads in streams.
of a flood of magnitude 425 m3 · s−1 or higher occurring in any
• Levee construction affects floodplain ecosystems; levee fail
Tr(425) =
given year.
= 7.75 following days of heavy = 7.8 years
destructive flooding.
rainfall inundated Germany, Austria, Slovakia, Hungary,
lc
The relationship can also be expressed as the probability
ann
HUMANSof a floodRoIf VgivEenRmaSgYnitSudTe EocMcurrSing in any given year (Pr ).
S
b
t
i
t
le
) =iver re*st1o00ration efforts include da (n + 1)
TABLE AQS 15.1 Peak Discharges for a River, 1980–2009 and the Czech Republic.
Acc
wat
Ger e
any r1e98c2orded in the1p70ast 1992
500M
AP Ph1o98t4o.]
1986 1988
ording to
Year
er levels i
Peak Discharge
local residents,
(m3 ∙ s−1) n Passau,
Year
Peak Discharge (m3 ∙ s−1)
Year
Peak Discharge (m3 ∙ s−1)
1980 113 1990
227 2000 119 411 2002 112 255 2004 184 113 2006 991 212 2008 28
many, w
1981
re higher than
71
1991
2407
2001
241
y19e8a3 rs. [
atthias2S12chrader/
1993
198
2003
311
85 1994 297 1996 1770 1998
1985
42
1995
311
2005
198
1987
57
1997
595
2007
71
1989
57
1999
227
2009
283
RIVER SYSTEMS
HUMANS
• Humans use rivers for recreation and have centuries.
• Flooding affects human settlements on flo • Rivers are transportation corridors, and pr industrial use.
ffecting river m removal to
ures cause
. Critical Thinking Activities integrated
throughout chapter s1e5cb tions give students anRivers in Madagascar
mosphe
THE
effect
erode se CRITICALthinking 15.1 chan
eam Locate Your Drainage Basin carrie
disru
al baissethe river’s mouth? Use Figure 15.3 to locate the larger ’s abdirla-inage basins and divides for your region, and then take
■ Sketch a basic drainage basin model, and identify ■ Explain the concepts of stream gradient and
only outlets being evaporation and subsurface gravita-
H y d r o l o g y i s H t h y e d r s o c l i o e g n y c e i s o f t h w e a s t c e i r e a n n c e d o i t f s w g a l o t e b r a l a n c d i r c i t u s l a g - l o b a l l e c n i r g c t hu l o a f - c h a n T n h e e l g s r i a n d a i e g n i v t e o n f a a r s e t r a e a a n m d i i s s t a h n e e s l x o p p r e e , s o s i r o t n h e o f s t r e tion, distributtiion,, dainsdtripbruotpioenrt,ieasn—d spreocpifeirctaiellsy—, wspaetceirfiactally, awlatnedr sactape’sintoeploegvraatpiohnicpseur rufanciet dapispteaanrcaen. cBe.asDeraleinvealgeis th
I Sketch a basic drainage basin model, and identify
present. [Karl Weatherly/Corbis.]
deserts, a torrent of water that fills a stream channel dur-
geosystemsconnection pness, variable rock resist- hydrograph (p. 429)
gement of channels in an discharge (p. 428)
’s drDoeptermine the name of the drainage basin within which ecosy
loweysotu- r campus is located. Where are its headwaters? Where Schaf
ide that TM a look at this region on Google Earth
any regulatory organization oversees planning and coordi-
of time,
d regions,
451
opportunity to stop, check, and apply their understanding.
carry an enormous sediment load as a result of deforestation The trees anchor the soil with their roots; when that stabilizing
is gone, soil
s into river nels and is
d into oceans, pting coral reefs
ther aquatic stems. [Kevin
er/Alamy.]
NASA.
. Investigate whether
nation for the drainage basin you identified. Can you find
m by its
huamnnatoenlp.soetgtrleampheinctmonapflosodnplilnaeinsthaantdcodeveltrasthis region? • omuinttterniets, making more people vulnerable
ncluding dam decommissioning and removal,
m as water
blishment, and restoration of stream
a specific
eivfyenstos rmin systems, including hurricanes,
and o
structural controls imposed bridge concebpatssic bderatiwnaegenpatterns are g dendritic, trellis, radial, para
chapters, reminding them where
and deranged.
t h e y h a v e b e e n ha y nd dr o l wo g hy e ( pr . e 4 2t 2h ) e y fluvial (p. 422)
are going. drainage basin (p. 422) sheetflow (p. 423)
continental divide (p. 423) internal drainage (p. 425) drainage density (p. 426) drainage pattern (p. 426)
1. Define the term fluvial. What is a fluvial process?
2. What role is played by rivers in the hydrologic cycle?
xxvii
gy, relief of the land, and flash flood (p. 429)
b y t h e l a n d Ws c h a i pl e e . f o Sl l oe v w e i n n g t h e f l o w o f w a t e r t h r o u g h s t r e a m s , w e e x a m i n e d f l u v i a l p r o c e s s e s a n d l a n d f o r m s
7. Explain the base level concept. What happens to a
and the river-system outputs of discharge and sediment. We saw that a scientific understanding
enerally found in nature:
stream’s base level when a reservoir is constructed?
and one from an urbanized area.
llel, rectangular, annular,
of river dynamics, floodplain landscapes, and related flood hazards is integral to society’s ability
8. What was the impact of flood discharge on the chan-
to perceive hazards in the familiar environments we inhabit. In the next chapter, we examine the
nel of the San Juan River near Bluff, Utah? Why did
e r o s i o n a l a c t i v i t i e s o f w t h a e v s e e s , c t h i da n e g s e , s c u t a r k r e e n p t l s a , c a e n ? d w i n d a s t h e y s c u l p t E a r t h ’ s c o a s t l i n e s a n d d e s e r t regions. A significan9.t pDoirftfeiornenotifattheebhetuwmeaen paonpautulartailosntrlievaems ihnycdoraosgtralpahreas, making the difficulties
of hazard perception and the need to plan for the future, given a rising sea level, important aspects
of Chapter 16.
■ Explain the processes involved in fluvial erosion and sediment transport.
Water dislodges, dissolves, or removes surface material
FPO
3. What are the five largest rivers on Earth in terms of
discharge? Relate these to the weather patterns in
rocks and sediment. As this debris moves along, it me- M15_CHRI6982_09_SE_C15.indd c4h5a0nically erodes the streambed further through a pro-