Transcript SURFACE WATER

SURFACE WATER
water cycle (hydrological cycle) = continuous movement of water
between atmosphere and earth’s surface
STEPS:
1. evapotranspiration = processes of evaporation and transpiration
occurring together
a. evaporation = when liquid water changes into water vapor
1) heat from sun causes change to occur
2) usually on surface areas
b. transpiration = plants give off water
vapor to the atmosphere
1) occurs through pore spaces
of plants as they breathe
2. condensation = water vapor cools and expands becomes tiny water
droplets
a. air is saturated
b. will form clouds
3. precipitation = process by which water falls from clouds to earth’s
surface
a. clouds can no longer hold water vapor
b. can be rain, snow, hail, or sleet
c. 75% falls in the oceans
d. 25% falls on land surface
Water goes in several directions:
1. runoff = water that flows over land into streams and
rivers; usually downslope
2. soak into ground forming groundwater
3. absorbed by plants → transpiration
4. evaporation → surface areas such as lakes and streams
5. may be added to a glacier
Factors that determine runoff:
1. amount of rainfall
a. rate of precipitation exceeds infiltration
b. ground may already be saturated
2. time span over which rain falls: torrential downpours too
fast for water to infiltrate ground
3. slope of land:
a. steep slopes cause more water loss
b. steeper the slope, faster the water
flows
4. amount of vegetation: low vegetation or barren areas have more
water loss
5. physical and chemical composition of soil affects water-holding
capacity
a. soils with high percentage of coarse particles has large pores
between particles to hold water and allow it to pass through
b. soils with high percentage of fine particles (clay) tends to clump
together and has few or no spaces between particles therefore
water cannot pass through as easy
water budget = gains and losses of water from a region
1. precipitation is a gain
2. evapotranspiration and runoff are losses
3. world water budget is balanced due to amount of precipitation
equaling amount of evapotranspiration and runoff
4. local water budget = one of a particular area
a. usually is not balanced
b. factors that affect:
1) temperature
2) presence of vegetation
3) wind
4) amount of rainfall
5) duration of rainfall
6) season of the year
c. factors can vary geographically
STREAM/RIVER SYSTEMS
1. made up of a main stream and all feeder streams
a. all flow downslope to lower elevations
b. path varies depending on slope of land and type of material
through which stream flows
2. tributary = feeder stream that flows into main stream
a. each one increases size of stream it is joining and adds water to it
b. large stream is called a river
c. small streams are called brooks or creeks
3. development:
a. local precipitation exceeds evapotranspiration
b. gully forms = narrow ditch eroded into land surface by running
water
c. each time it rains gully is eroded wider and deeper
d. eventually a fully developed valley with permanent stream forms
4. watershed (drainage basin) = all of land area whose water drains into
a stream system
a. can be small or extremely large areas
b. divides = ridges or elevated regions of high ground that separate
watersheds
c. each tributary has its own
watershed and divides but are all
part of larger stream system
stream loads = materials carried by a stream
1. dissolved load = mineral matter carried in liquid solution
a. how much is carried in solution depends on material through which
water has passed
b. groundwater adds most of dissolved load to stream, while runoff
adds small amounts
c. expressed as parts per million (ppm)
2. suspended load = sediment carried in suspension, free from contact
with stream bed
a. particles of fine sand and silt
b. amount of material suspended varies with volume and velocity of
water
c. faster moving water can carry
larger particles
d. as water slows, heavier particles
will begin to settle out
3. bed load = sediment transported on or immediately above stream bed
a. larger, coarser material like gravel and pebbles
b. saltation = movement of material by short jumps
c. material is also moved by sliding or rolling on stream bed
d. greatest erosional effect due to abrasion
e. pothole = bowl shaped cavity in bed caused by large rocks being
scraped over one area in a whirlpool motion
STREAM CHARACTERISTICS
1. banks = edges of stream channel above water level
2. bed = part of stream channel below water level
4. carrying capacity = ability of stream to transport materials
a. depends on both velocity and amount of water moving
b. channel’s slope, depth, & width all affect speed & direction of water
movement
5. discharge = volume of water that flows over a specific location within
a given time period
a. affected by velocity of water
b. high velocity = high discharge = high erosion
c. discharge = width X depth X velocity
(m3/s)
(m)
(m)
(m/s)
d. as discharge increases, carrying capacity increases, erosion increases
6. gradient = change in elevation of stream over a given horizontal
distance
a. determines velocity of stream
b. can vary along a stream channel
c. headwater region will have steep gradient → high velocity
7. water gap = deep notch left where stream erodes through mountain
as it is uplifted
8. wind gap = water eroded notch in mountain through which water no
longer flows
flood = when water spills over sides of stream’s banks onto adjacent
land
1. floodwater carries large amounts of eroded sediments
2. as floodwater recedes, its volume and speed decrease, causing water to
drop sediments
3. flood stage = level at which a stream overflows its banks and crest of
stream is maximum height
4. it takes time for runoff to collect in streams, which causes water to
continue to rise and may reach its crest days after precipitation has
stopped
5. upstream flood = flooding of a small area, cause a lot of damage in
short period
6. downstream floods = heavy accumulations of excess water from
large regional drainage systems; heavy water volume, extensive
damage
7. flood monitoring and warning system
a. monitored by National Weather Service
b. have established gauging stations = provide continuous record of
water level in each stream
c. warning system is first step in implementing emergency
management plans
d. allows people to safely
evacuate an area in advance
of the flood
Stream Development:
1. changes in shape, width, size, and landscapes over which it flows
2. first and most important condition is adequate supply of water
3. headwaters = region where water first accumulates to supply a
stream
a. usually high in mountainous areas
b. path not well defined when first begins to flow
4. stream channel = narrow pathway carved into sediment or rock
a. network formed by main streams and its tributaries
b. widens and deepens as more water accumulates and cuts into
surface
5. stream banks = ground bordering stream on each side which holds
water within area of stream
6. mouth = area of stream that leads into ocean or another large body
of water
a. streambed’s gradient flattens out and its channel becomes very wide
Stream Erosion: water erodes more sediment than any other erosional
agent
1. headward erosion = process of lengthening and branching of
stream
a. usually at upper ends, extends river system and watershed
b. carries away sediments from slopes of watershed
c. usually relatively small and narrow, often form waterfalls over
steep inclines
d. also called headward extension
2. stream piracy (stream capture) =
capture of a stream in one watershed by stream with higher rate of
erosion in another watershed
3. rill erosion = water swiftly running down a slope creates small channels
in soil
a. begins when small stream forms during heavy rain
b. leaves a scar on slope
4. gully erosion = rill channel that becomes broader and deeper
5. sheet erosion = water flowing over a gentle slope slowly removes
sediment from entire land surface
6. erodes a V-shaped channel into region
a. continue to erode until it reaches base level = elevation at which it
enters another stream or body of water
b. lowest base level = sea level
STAGES OF A RIVER SYSTEM
1. young rivers = produces a V-shaped valley with
steep sides
a. found in mountainous or hilly regions
b. may have white water rapids and waterfalls
c. high level of energy
d. erodes bed more than banks
e. few tributaries and usually carries a small volume of water
2. mature rivers = curving stream that flows down a gradual slope
and erodes its sides
a. well established tributaries and carries more water
b. gradient less steep = flows less swiftly → channel gets wider
c. erodes valley walls and widens valley
floor gradually forming U-shaped valley
d. velocity of water in a river is fastest at the center
1) increases on outside of river bends
2) decreases on inside of curves
e. forms meanders = wide curves that form in streams
1) will continue to develop and become wider over time
2) after some degree of winding common for stream to cut off
f. oxbow lake = water remaining in an isolated meander in a floodplain
1) crescent shaped lake forms
2) ends become plugged with sediment
3) will eventually dry up
Oxbow lake formation
g. found at bottom of
mountains and hills
3. old rivers = flows very slowly through a very broad, flat floodplain
that it has carved
a. gradient and velocity decrease
b. no longer erodes land
c. causes changes in the meanders
d. fewer tributaries
e. begins to deposit sediment in channel and on banks
4. rejuvenated river = gradient has been made steeper by movement of
earth’s crust
a. stream will resume process of downcutting toward its base level
b. cut more deeply into valley floor
c. cause increase in stream’s flow rate and channel
will become V-shaped again
d. if meanders are present then deep side
canyons could be formed
STREAM DEPOSITION
1. as water velocity decreases the ability to carry sediment
decreases
2. delta = triangular shaped deposit at mouth of a stream
a. shape and size determined by waves, tides, off-shore
depths, and sediment load of stream
b. occurs when a stream or river slows as it empties into
an ocean, gulf, or lake
c. sediments build up & slow stream water, sometimes
even blocking its movement
d. usually made up of consist of
silt and clay
e. surface is relatively flat
3. alluvial fan = fan shaped deposit with its tip pointing upstream
a. occurs where stream descending steep slope reaches a flat plain
b. common in arid and semiarid regions; dry, mountainous regions
Ex: Death Valley, CA
c. deposited on dry ground
d. contains coarse, angular sand and gravel
e. form at the base of slopes
4. bar = elongated mound of sediment in stream channel
5. floodplain = broad, flat valley floor carved by a meandering stream
a. often covered with water if stream floods
b. spring floods common near headwaters in areas where the winters
are harsh
c. ice jams increase chance of spring flooding
d. human activities contribute to flooding
- removal of natural ground cover
e. commonly swampy areas
6. natural levee = raised riverbank that results when a river deposits its
load at river’s edges
a. can be quite high and prominent
on old channels
b. usually coarser sediment
c. can be on both banks
LAKES & FRESHWATE R WETLANDS
1. lake = depression in surface materials of landscape that collects and
holds water
a. gain water from streams and runoff
b. get water from local precipitation, springs, and other sources
c. most have outlets from which water flows to rivers and to ocean
d. reservoirs = lakes made for primary purpose of storing water for
community’s use
e. ponds = manmade lake used for watering livestock, attracting
wildlife, natural beauty, etc.
2. lake formation
a. oxbow lakes form when meanders get cut off from main stream
b. could also be formed when stream flow becomes blocked by
sediment from landslides
c. could be remnants of prehistoric lakes that have receded to lower
lying areas
d. some are formed by glacier movement
e. kettle lakes = formed when blocks of ice left by melting glaciers
eventually melted in depression
f. can also be found in areas where
limestone bedrock is located →
water dissolves holes and
forms caverns
3. undergo change
a. precipitation, runoff, and underground sources maintain a
lake’s water supply
b. depression that receives more water than it loses to evaporation or
use by humans will exist for a long period of time
c. considered temporary water-holding areas
d. over hundreds of thousands of years, usually fill with sediment
and become part of new landscape
Volcanic lake
4. eutrophication = process by which lakes become rich in nutrients
from surrounding watershed causing a change in the kinds of
organisms in the lake
a. animals that live in lake use water’s oxygen and add waste products
to water
b. amount of dissolved oxygen helps determine quality of water and
ability to support life
c. can be sped up with the addition of nutrients (fertilizers)
d. may cause excess algae and
excess organisms that feed
on algae which may use too
much dissolved oxygen
causing fish and other
sensitive organisms to die
5. wetland = land area that is covered with water for large
part of year
a. bogs = receive water from precipitation, waterlogged soil rich in
peat moss, acidic soil
b. freshwater marshes = form along mouths of streams and in areas
with extensive deltas
c. swamps = low lying areas often located near streams
1) may develop from marshes
2) prehistoric swamps formed
coal reserves used today
6. wetlands improve water quality
a. act as filtering system that traps pollutants, sediments, &
pathogenic bacteria in water sources
b. provide vital habitats for migratory waterbirds
c. provide homes for many other types of wildlife
7. in the past humans have filled in wetlands to create more
land to build on
8. preservation of these have now become a global concern
FLOOD CONTROL
1. flooding is natural stage of development of stream
a. will continue to occur as stream matures
b. best to leave floodplains in natural state in areas
2. indirect methods: forest and soil conservation that prevents excess
runoff during heavy rainfall
3. direct methods
a. building of a dam
b. building of artificial levees
c. create floodway = permanent
overflow channel
PREVENTING LAND EROSION:
1. planting vegetation
2. build terraces = broad, steplike cuts made into the side of
a slope
3. put up retaining walls
Terraces
Stream retaining wall