streams and floods

Question 1

flooding due to climate change

Answer 1

higher temp -> ocean temo higher -> more evaporation -> more cloud cover and moisture -> more precipitation

Question 2

hydrologic cycle

Answer 2

EPTSIMR
evaporation
precipitation
transportation
sublimation (solid to gas)
infilitration
melting
runoff

Question 3

drainage networks

Answer 3

configuration of tributaries and trunk streams
geometry influenced by topography, rocks types, jointing, and differences in chemical weathering and erodibility
patterns: dendritic, radial, rectangular, parallel, trellis

Question 4

drainage basin

Answer 4

land areas drain into trunk stream or body of water
watershed: area of land that drains into stream
ridges and peaks separate drainage basins

Question 5

discharge

Answer 5

amount of water flowing in channel
m^3 /s
cross-sectional area x average water velocity
not uniform in a channel (friction)

Question 6

turbulence

Answer 6

twisting, swirling motion of fluid
caused by
irregularities in bank and bottom
objects in water
steep gradients

Question 7

how do streams erode?

Answer 7

scour: water picks up and move sediment
breaking and lifting: fast water breaks chunks of rock off channel, lifts rock off channel bottom
abrasion: sandblasting of rock by particles in fast water
dissolution: running water dissolves soluble minerals

Question 8

sediment load

Answer 8

material moved by running water load
dissolved: ions from chemical weathering
suspended: fine particles in water
bed: large particles move along bottom

Question 9

sediment transport (competence and capacity)

Answer 9

slow water: fine sediments and solutes
fast water: move boulders and clasts
COMPETENCE: ability to move large clasts
CAPACITY: amount of sediment carried

Question 10

how does decrease in water velocity affect sediment transport?

Answer 10

competence reduced, sediment drops out
channel bottoms filled
sands form inside banks
silts and clays drape floodplains

Question 11

sediment deposition

Answer 11

fluvial deposits are sediments transported by streams (alluvium)
sediment accumulation in channel and point bars
flood: sediment accumulates on floodplain

Question 12

stream gradient

Answer 12

change in elevation per distance flowed (ft/mile)

Question 13

longitudinal changes (gradient, dischargem competence, channels)

Answer 13

character of stream changes along its length
near source: steep gradient, low discharge, high competence, straight channels
near base: flat gradient, high discharge, low competence, curved channels

Question 14

base level

Answer 14

lowest point to which stream can erode
velocity drops to zero at base level
ultimate base level is sea level but a lake is a temp or local base level

Question 15

valley

Answer 15

• gently sloping sidewall and wider bottom
• _/ shaped

Question 16

canyons

Answer 16

• steep sidewalls and narrow bottom
• variation in resistance to erosion results in stair-step profile
• strong rocks -> steep, weak -> gentle slopes
• |_| shaped

Question 17

waterfalls

Answer 17

• super steep gradient so water is in free fall
• scours a deep plunge pool
• temp base levels

Question 18

alluvial fans

Answer 18

• build at canyon mouths
• sediment drops out as water spreads from mouth (coarsest material first, close to mouth)
• strong flood smoothes fan surface

Question 19

braided stream

Answer 19

interfingering channels
high sediment load, shallow channel
sediment is deposited, chokes channel in normal flow

Question 20

meandering streams

Answer 20

sinuous looping curves
form where gradient is low and substrate is soft and easily eroded
meanders evolve during floods

Question 21

how is a channel modified during periods of flood?

Answer 21

curves migrate downstream
fast water erodes the outside stream bank
slow water deposits points bars on inner part of curve
floodwaters may cut an outside bank to create shorter pathway downstream
cut off meander neck -> oxbow lake

Question 22

deltas

Answer 22

forms when a stream enters standing water
stream divides into a fan of distributaries
velocity slow, sediment drops out
morphology is balance of sediment load, waves and storms, tides and slumping

Question 23

avulsion

Answer 23

when a river’s flow is abruptly diverted from its established channel to a new course (more direct path)

Question 24

stream piracy

Answer 24

one stream captures the flow of another
stream with vigorous headward erosion and steeper gradient intercepts stream with gentler gradient
captured stream flows into new stream

Question 25

flash flood triggers

Answer 25

• torrential rains (runoff when precipitation>infiltration)
• long period of continuous rain (ground is saturated)
• rapid snowmelt
• failure of dam or levee

Question 26

limiting flood damage

Answer 26

• levees and flood walls prevent overflow
• rain/sponge gardens help soil absorb water and decrease runoff
• creating bypasses (room for river)
• calculating flood risks

Question 27

flood recurrence interval

Answer 27

100 year flood means 1% risk of such flood in 1 year
occurrence of a severe flood in one year does not decrease risk of similar occurrence the following year

Question 28

vanishing rivers

Answer 28

humans overuse/abuse rivers
pollution
dam construction
overuse of water
urbanization and agriculture