Andrew Rosen Stream Drainage System:

Andrew Rosen
Stream Drainage System:
- The main stem is the principal channel in a drainage basin
- A drainage system is the pattern formed by the streams, rivers,
and lakes
- Dendritic drainage: Formed by homogeneous material
- Parallel drainage: Formed when there are slopes in surfaces
- Trellis drainage: Formed by folded topography (mountains).
Synclines are down-turns where the main channel resides
- Rectangular drainage: Formed by regions that have faulting.
Streams follow paths of least resistance and are concentrated
where exposed rock is weakest
- Radial drainage: Formed around a central point. Sometimes
- Centripetal drainage is the opposite of radial and flows down a
central depression
- Deranged or contorted drainage is formed from disruptions of preexisting drain patterns
- A tributary is a stream or river which flows into a main stem river
(doesn’t flow directly into a sea, ocean, or lake)
- Tributaries serve to drain the surrounding drainage basin of its
surface water and groundwater by leading the water out into an
ocean or other large body
- V-shaped valleys are formed by strong streams through
- A drainage basin is where a stream receives runoff, throughflow,
and groundwater
- Drainage basins are separated from each other by watersheds
- Watersheds represent all of the stream tributaries that flow to
some location on a channel
Channel Type:
- A stream is a body of water that transports rock particles and
dissolved ions and flows downslope on a path called a channel
- The deepest part is where the velocity is highest
- A straight channel is straight
- A meandering channel is curved
- A braided channel has islands
- Knickpoint: Change (rapid) in slope
- Laminar flow is when all water travels along similar parallel paths
- Turbulent flow is when they take irregular paths
- Streams erode because rock fragments are transported
- Turbulent flow keeps fragments in suspension longer
- Streams may erode by undercutting the banks
River Valley Forms and Processes:
- Long profile is a plot of elevation vs. distance
- Long profiles show a steep gradient near the source of the stream
and a gentle one towards the mouth
- If there is a dam, velocity decreases upstream so that deposition of
sediment occurs causing the gradient to become lower
- Base level is the limiting level below which a stream cannot erode
its channel
- For streams that empty into oceans, base level is sea level
- Local base levels can occur where streams meet a resistant body of
rock or artificial dam
- As streams overtop banks, velocity will be high but then decrease
- Because of this, the coarser grained suspended sediment will be
deposited along the riverbank to make a natural levee
- Terraces are exposed former floodplain deposits that result when
the stream begins down cutting into its flood plain (regional uplift of
lowering the regional base level)
- Alluvial fans are deposits formed due to gradient/velocity changes
like that of mountain streams that enter flat valleys
- When a stream enters a standing body of water, there is a
decrease in velocity, and the stream deposits sediment in a delta
(finger-like projections)
Stream Flow:
- Manning’s Equation:
(left) and Chezy
Formula (right)
- Stream discharge: Q = A x V
- As the amount of water in a stream increases, the stream must
adjust its velocity and cross sectional area in order to form a balance
- Discharge increases as more water is added to the system
- As discharge increases, depth and velocity increase
- The rock particles and dissolved ions carried are the load
- Suspended load are particles carried in the main part of the stream
- Bed load is with coarse an ddense particles on the bed of the
stream but move by saltation (jumping) as a result of collisions
- Dissolved load is when ions have been introduced by weathered
- Floods occur when the discharge is too high, the stream widens,
and the flooded areas are known as floodplains
- The surface below which all rocks are saturated with groundwater
is the water table
- Rain falls on the surface and seeps into the soil into a zone called
the zone of aeration (unsaturated zone) where pores are filled with
- They are eventually filled up to form saturated zones
- Porosity is the percent of volume of the rock that is open pore
- Well rounded, coarse sediments have high porosity while fine
sediments don’t (basically how much water can fit between the
- Poorly sorted sediments have low porosity because fine granules
fill spaces
- Porosity is low in igneous and metamorphic rocks because the
minerals are intergrown unless they’re fractured
- Permeability is the degree to which the pore spaces are
interconnected, and the size of these interconnections
- Ionic charges on the surface of rocks attract a think layer of water
(force of molecular attraction)
- If the size of interconnections is not as large as the zone of
molecular attraction, the water can’t move
- Coarse rocks are usually more permeable than fine grained rocks
and sands are more permeable than clay
- Vesicular volcanic rock has a high porosity and low permeability
because of the bubbles inside
- An aquifer is a large body of permeable material where
groundwater is present in the saturated zone (good aquifers have
high permeabilities)
- The rate at which groundwater moves through saturated zone
depends on the permeability and hydraulic gradient (difference in
elevation divided by the distance between two points on the water
- Unconfined aquifers have recharge areas (areas where water
enters the saturated zone) usually occurring in high areas
- A groundwater divide is formed by glacial moraines
- Discharge areas are areas where groundwater reaches the surface
Karst Features:
Karst topography: a distinctive landform assemblage developed as a
consequence of the dissolving action of water on carbonate bedrock
- Sinkholes are funnel shaped and open upward
- Solution valleys (Karst valleys) are the remains of former surface
stream valleys whose streams have been diverted underground
- Karst springs occur where groundwater flow discharges from a
conduit or cave (can discharge lots of water)
- Streams flowing along the surface may enter a sinkhole as a
disappearing stream and flow underground and then reappear
- Cavern formation: 1) initial excavation (dissolving and creation of
voids) 2) Decoration stage (water leaves behind compounds in
Lake Formation:
- Movement of Earth’s crust (fault lines)
- Grabens are formed when adjacent plates separate at fault lines
- A rift lake is a lake formed as a result of subsidence related to
movement on faults within rift zones (area of externsional tectonics
on continental) and are sometimes bounded by large cliffs
- Lakes formed by volcanoes are small
- Lakes are found in abundance in high latitudes where glaciers were
- Kettle and Finger lakes were formed by sediment damming
- Lakes eventually fill with sediments to form terrestrial ecosystems
Lake Features:
- Input: precipitation, runoff, channels and aquifers, and artificial
- Output: Evaporation, groundwater flows, artificial extraction
- Thermoclines are layers of changing temperature per depth
- Shorelines change: Tides, nearshore currents, sea level changes,
and sediments
- Waves: wind speed, distance of wind blow. Lakes and rivers have
small SA so they don’t have big waves
- Marshes form near ponds and lakes (reeds/grasses/soft-stemmed
- Bogs begin as shallow ponds that fill with rotting leaves and plants
- There is little air under the mat of plants so it takes long for things
to rot
Effects of Land Use:
- Damns can cause enhanced clarity and reduced variability due to
periphyton abundance
- Dams can change temperatures and thus insect development
- Dams isolate ecosystems and prevent migration of anadromous
and catadromous species
Hydrologic Cycle:
- Runoff = precipation – evaporation +/- changes in storage
- A lotic ecosystem is the ecosystem of a river, stream, or spring
(biotic and abiotic factor)
- Acid rain forms from sulfur dioxide and nitrous oxide
• A lake is a body of water completely surrounded by land.
• More than 90% of Earth’s surface waters are contained in lakes.
• Less than 1% of Earth’s surface waters are found in rivers and
streams at any moment in time.
• The origin of most lakes is not related to stream activity.
• Conditions necessary for the formation and continued existence of
a lake:
1. A natural basin with a restricted outlet.
2. Sufficient input of water to keep the basin at least partially filled.
• Most of the world’s lakes contain fresh water. Less than 40% of
lake waters are salty.
• Any lake that has no natural drainage outlet, either as a surface
stream or as a sustained subsurface flow, will become saline.
• The water balance of most lakes is maintained by surface inflow,
sometimes combined with springs and seeps from below the lake
• Lakes are most common in regions that were glaciated within the
relatively recent geologic past because glacial erosion and
deposition have deranged the normal drainage patterns and have
created innumerable basins.
• The series of large lakes in eastern and central Africa is due to
major crustal movements and volcanic activity.
• Thousands of small lakes in Florida were formed by sinkhole
collapse where rainwater dissolved calcium from massive limestone
• Most lakes are very temporary features in the natural landscape,
geologically speaking. Few have been in existence for more than a
few thousand years.
1. Inflowing streams bring sediments to fill them up.
2. Outflowing streams cut channels that progressively deepen and
drain lakes.
3. As lakes become more shallow, an increase in plant growth
accelerates the process of infilling.
• Dry lake beds located in desert regions are called playas. When
temporarily filled by intermittent streams these bodies of water are
called playa lakes.
• Permanent desert lakes are nearly always products of either
subsurface structural conditions that provide water from a
permanent spring or of exotic streams that have their source in
nearby mountain.
• Lakes may affect climate and weather.
1. It is generally more humid around lake areas.
2. Because water warms and cools more slowly than land,
temperatures near lakes are generally milder than temperatures at
the same latitude but more distant from lakes.
• Other lakes Science Olympiad participants may wish to research
include kettle lakes, moraine lakes, oxbow lakes and man-made
I. Hydrologic Cycle
A. ~ 50% of rain returns to the atmosphere through evaporation or
transpiration from plants
B. ~ 15% to 20% of rain normally ends up as surface runoff in rivers
II. Channel flow
A. A stream is a body of running water confined in a channel and
moving downhill under the influence of gravity.
B. Geologists use the term “streams” for any body of running water,
from a trickle to a huge river.
C. Headwaters are the upper part of a stream near its source in the
D. The mouth is where a stream enters the sea, a lake, or a larger
E. The cross profile of a stream in steep mountains is usually a Vshaped valley cut into solid rock.
F. Near its mouth, a stream usually flows within a broad, flat-shaped
G. The stream channel is surrounded by a flood plain of sediment
deposited by the stream.
H. The sides of a channel are called its banks; the bottom of the
channel is called the stream bed.
I. Water may run off as sheetwash, a thin layer of unchanneled
water flowing downhill. Sheetwash, along with the impact of
raindrops on the land surface, can produce sheet erosion.
J. Tiny streams, called rills, merge to form small streams.
III. A drainage basin is the total area drained by a stream and its
A. A tributary is a small stream flowing into a larger one.
B. A drainage basin can be outlined on a map by drawing a line
around the region drained by all the tributaries to a river.
C. A drainage basin is a ridge or strip of high ground dividing one
drainage basin from another.
IV. Flooding
A. A recurrence interval is the average time between floods of a
given size.
B. Flood erosion is caused by the high velocity and large volume of
waters in a flood.
C. Flood deposits are usually silt and clay; good for agriculture, but
bad for cities.
D. Flood control structures
1. Upstream dams
2. Artificial levees that are embankments built along the bands of a
river channel.
3. Riprap is protective walls of stone constructed along riverbanks.
V. Erosion and deposition
A. Stream velocity is the speed at which water travels in a stream.
B. A stream reaches its maximum velocity near the middle of a
C. Friction near a stream’s banks and bed slows the water.
D. When a stream goes around a curve, the region of maximum
velocity shifts to the outside of the curve.
E. Velocity is the key factor in a stream’s ability to erode, transport
or deposit.
VI. Gradient
A. Stream gradient refers to the downhill slope of a bed.
B. Channelization refers to artificially steepening a gradient to
increase the speed of runoff to help control flooding and improve
navigation on a river.
VII. Channel shape and roughness
A. The shape of the channel controls stream velocity.
B. Hard, resistant rock is difficult to erode, so a stream may have a
narrow channel in such rock resulting in more rapid flow.
C. Softer rock erodes more easily thus widening the channel and
slowing the water which, in turn causes the deposition of
D. Roughness of the channel
1. Streams can flow rapidly over a smooth channel.
2. A boulder-strewn channel creates more friction causing water
flow to
3. A ripply, wavy sand bottom is rougher than a smooth sand
VIII. Discharge
A. The discharge of a stream is the volume of water that flows past a
given point in a unit of time. Discharge = width x depth x velocity.
B. Discharge (cfs) = channel width in feet
x average channel depth in feet
x average velocity (feet per second)
C. Example: 100 ft. x 15 ft. x 6’/sec = 9000 cubic ft/sec
D. Discharge increases downstream
1. Water flows out of the ground into the river through the
2. Small tributaries flow into larger streams.
IX. Stream erosion
A. Hydraulic action is the ability of flowing water to pick up and
move rock and sediment.
B. Water may slowly dissolve rocks, especially limestone.
C. Abrasion is the grinding away of a stream channel by the friction
and impact of the sediment load.
X. Stream transportation of sediment
A. Bed load is large or heavy sediment particles that travel near or
on the streambed.
1. Traction refers to rolling, sliding or dragging.
2. Saltation refers to short leaps or bounces off the bottom.
B. A suspended load is sediment light enough to remain lifted
indefinitely above the bottom of a stream by water turbulence.
C. The dissolved load is the soluble products of chemical weathering
XI. Stream deposition
A. Bars are ridges of sediment deposited in the middle or along the
banks of a stream.
B. Deltas or alluvial fans are deposits of sediments near the ends of
XII. Braided streams
A. Bars may divert stream flow to cause a stream to widen. Many
such diversions may create a braided stream, a network of
interconnected rivulets around numerous bars.
B. Braided streams form particularly well in streams laden with
XIII. Meandering streams and point bars
A. Meanders are formed by fine-grained silt and clay.
B. Meandering is more common in the lower reaches of a river
where sediments tend to be finer.
C. Meanders develop because a stream’s velocity is highest on the
outside of curves where erosion is promoted.
D. Low velocity on the inside of a curve promotes deposition. These
becomepoint bars.
E. A meander cutoff is a new, shorter channel across the narrow
neck of a meander. The cutoff meander becomes an oxbow lake.
XIV. Flood plains
A. A floodplain is a broad strip of land built up by sedimentation on
either side of a stream channel.
B. Flood plains may be composed almost entirely of horizontal
layers of finegrained sediment interrupted by coarse-grained
channel deposits.
C. Other flood plains are dominated by meanders shifting back and
XV. Deltas
A. Deltas are bodies of sediment deposited near the mouths of
B. Distributaries are small, shifting channels that carry water away
from the main river channel and distributes it over the surface of a
XVI Alluvial fans
A. An alluvial fan is a large fan-shaped or cone-shaped pile of
sediment that usually forms where stream velocity decrease as it
emerges from a narrow mountain canyon onto a flat plain.
B. On large fans, deposits are graded in size within the fan, with the
coarsest sediments dropped nearest the mountains and the finer
materials deposited progressively farther away.
XVII. Valley development
A. Downcutting is the process of deepening a valley by erosion of
the streambed.
B. Base level is the theoretical limit for erosion of the earth’s
surface. For those streams that reach the ocean, base level is close
to sea level.
XVIII. Graded streams
A. Graded streams exhibit a delicate balance between its
transporting capacity and the sediment load available to it.
B. Lateral erosion widens a valley by undercutting and eroding valley
C. Headward erosion slows uphill growth of a valley above its
original source through gullying, mass wasting, and sheet erosion.
XIX Drainage patterns
A. Dendritic patterns resemble branches of a tree or the veins in a
Dendritic patterns develop on uniformly erodable rock.
B. Radial patterns resemble the radiating spokes of a wheel. These
form on high, conical-shaped mountains.
C. Rectangular patterned tributaries have frequent 90° bends and
tend to join other streams at right angles.
D. Trellis patterns are formed by parallel main streams with short
tributaries meeting at right angles.
Hydrologic Cycle:
The hydrologic cycle, better known as the water cycle, describes the
movement of water through the hydrosphere. The easiest place to
begin is with evaporation. As the sun heats up the Earth's surface,
water evaporates, meaning it changes from a liquid to a gas, and
enters the air. Another important way that water vapor can enter
the atmosphere is through transpiration, which is the loss of water
from parts of plants, mainly their leaves. Once water vapor is in the
atmosphere it goes through the process of condensation, where it
returns to a liquid state and forms clouds. Once water droplets in
the clouds become large enough they will begin to fall to the ground
as precipitation. Once precipitation reaches the ground some of the
water will become run-off and flow to a river or other body of
water. Also, some water will infiltrate the ground and become
groundwater, where it can replenish aquifers. Eventually the water
will again evaporate and the cycle will continue.
Stream Drainage:
Streams follow a general pattern based on topography. Drainage
Channels form where runoff cuts into the ground.
Dendritic Drainage is the most common
and looks similar to a tree. Dendritic
Drainage occurs where a region is above a
single type of bedrock (homogeneous).
Which gives the entire area a similar
resistance to erosion and therefore a
seemingly random placement of tributaries.
Most tributaries will join a larger stream at
an acute angle.
Parallel Drainage generally form where
there is a large hill.They develop in areas
with parallel regions of rock that are harder
to erode.
Trellis Drainage Patterns form where there
is a folded topography like the Appalachian
mountains. tributaries enter the main
Stream at near right angles.
Radial Drainage
Upon that thought, many of you are probably thinking the mouth of
a river, or sea level. You would be absolutely correct. In the case for
large rivers, a delta or Mouth of the river at sea level Is indeed a
"Base Level", in fact, sea level itself is considered the "Ultimate Base
Level". How then can a waterfall be a base level? Well, some
wonderfully drawn pictures (/sarcasm) should give some light on it.
This picture shows a Longitudinal Profile, or a General Profile of a
river as compared to Distance and Elevation. As you can see on this
picture, The origin Is at the highest Elevation, while the mouth is at
the Ultimate Base Level. By looking at this graphic, we can make
some general assumptions:
1. The closer to the origin you are, the faster the water will flow
2. The closer to the mouth you are, the slower the water will flow
3. Sediment will be scoured closer to the higher elevation
4. Sediment will be deposited at the lower elevations
5. There Is a higher stream gradient the closer to the origin you go
6. There is a lower stream gradient the closer to the mouth you go.
So how does this work into waterfalls? Let me show you with
another concept: Downcutting!
Downcutting is the deepening of a river channel relative to its
surroundings. That is, how far does it dig into the ground. As natural
examples tell us, The amount of downcutting on a river is
dependent on where on the river it forms. Look at this example on
the next page:
This picture shows what downcutting looks like on a normal river. At
point “A”, the river is very fast moving and at a higher elevation to
that of sea level, so it downcuts at a steady rate. At point “B”, the
river is slowing down some, and is getting closer to sea level, so
downcutting is considerably slower here than at Point “A”, and at
Point “C”, downcutting is almost non-existent. However, science has
shown us that downcutting does not continue down to sea level at
the same speed in all cases. This is where we dive into the base level
Let’s review what we have determined so far:
Base Level is the closest to sea level a river can go. Downcutting
helps a river in its descent to Ultimate Base Level
Now, if Downcutting doesn’t always continue to sea level, what
blocks its path? Well, in order to understand this, we have to add a
little onto our definition of a base level. Base Level is the closest to
sea level a river can flow at any one location. In other words, in real
time, the base level at Point “A” on our graphic could be different to
the Base Level of point “B”. It all depends on the rock layers. This is
where we get into the final focus point.
At any one time, rock layers can dictate base levels.
Geologically speaking, nothing impedes downcutting. However, at
our timescale, we can witness downcutting happening before our
very eyes. That is essentially what a waterfall is, an agent of
downcutting. Look at this graphic of a waterfall:
In actuality, this is what a longitudinal profile looks like, if you were
to make it precise. Though mine is a sloppy mess, hopefully you can
see what I’m trying to get across. It has these stair steps, base levels,
that act as a mini origin, restarting the morphological process. These
don’t have to be waterfalls. Lakes, other rivers, even man made
dams have this kind of effect.
Flood Plain
A flood plain is the flat area that tends to be covered in water when
the river rises. As a flood increases the rivers size it slows the river
down causing it to drop sediment which in turn allows for very
fertile soil.
Natural Levee
A natural levee is formed when sediment(alluvium) is deposited
along the edge of the stream forming a ridge
A Point Bar forms where the water going through a meanders drops
alluvium on the inner bank
The Neck is the point of land between the two edges of a meander.
The Cutoff occurs when the stream erodes through the neck causing
the river to be back to a straight course.
The result is an Ox-bow Lake which is a separate body of water from
the stream
Ground Water:
By looking at the graphic, we can determine a definition. A Waterfall
is a morphological feature defined by water flowing over a hard rock
layer. In the case of most waterfalls, the water that flows over the
falls erodes the softer layer at the base. Once it erodes enough, the
unsupported hard layer above collapses. This is what makes a
waterfall appear to “retreat”. So how does this fit into river
morphology? It acts like a new point of origin. Look at this final
graphic to the right:
Ground Water is water that is in the ground. It exists in the pore
spaces and fractures in rock and sediment. It originally was
rainwater or snow. Water will move down into the earth until it
reaches a layer of soil where it can not penetrate. This layer is called
the impenetrable layer. The uppermost reaches of this water is
called the water table.
Facts- Groundwater makes up about 1% of the water on Earth.
That's about 35 times the amount of water in lakes and streams! It
occurs everywhere beneath the Earth's surface, but is usually
restricted to depths less that about 750 meters. The surface below
which all rocks are saturated with groundwater is the water table
Formation of Lakes:
- Glaciers form lake basins by making holes in loose/soft soil,
depositing minerals across stream beds, or leaving buried chunks of
ice behind that melt
- Glaciers retreat and sediments accumulate from tributaries
(organic material from watershed and aquatic plant/algae)
- Used for dating (Pb-210 and C-14). Also can use sharp increases in
pollen in plants. Diatom abundance/composition is also used.
Light Variability:
- Light controls temperature (solar radiation) and photosynthesis
(for dissolved O2)
- Solar radiation determines wind pattern in lake basins and water
- Algae suspended in water (phytoplankton), algae attached to
surface (periphyton), and vascular plants (macrophytes)
- Organic C compounds absorb light and suspended materials
absorb and scatter
- Vertical extinction coefficient (k) is the percentage of the surface
light absorbed or scattered in a 1 meter long vertical column of
- Light penetrates deeper with low k-values (btw attenuation means
- The euphotic zone is the max depth where algae and macrophytes
can grow (0.5%-1% of the amount of light available at surface)
Density Stratification:
- After ice-out (Spring) the water column is cold and isothermal
- Because of nature of water, lakes tend to stratify in distinct layers
- When the temperature (density) of the surface water equals
bottom, it can be mixed easily. This is known as turnover
- As it becomes warmer and more buoyant, the top stops mixing
with the bottom
- Three layers: Epilimnion, metalimnion, and hypolimnion from top
to bottom
- Fetch is the exposure of lake to win and effects mixing (size does
- Spring turnover, summer stratification, fall turnover, winter
- Lakes with two mixing periods like above are dimictic as opposed
to polymictic
- Holomictic lakes are mixed from top to bottom. Partial is
- The nonmixing bottom layer is called the monimolimnion and the
one that mixes completely is the mixolimnion
- Monimolimnion has high [] of dissolved solids
The Watershed: Drainage basin (all land and water areas that drain
towards a lake)
- Water quality decreases with an increasing ratio of watershed area
to lake area
- Lakes with small watershed that are made from groundwater flow
are seepage lakes
- Lakes fed primarily by inflowing stream are drainage lakes
- Seepage lakes are susceptible to acid rain because of low buffering
Lake Chemistry:
- Function of the climate and basin gelology
- Has ion balance (sum of negative ions = sum of positive) of three
major anion and four major cations (HCO3 , SO4 , Cl /Ca , Mg , Na ,
- Hardwater lakes have a lot of calcium and magnesium and soft
water lakes don’t
- TDS (total dissolved salt) is the total amount of ions in the water
Lake Zones:
- Littoral zone is near the shore where sunlight fully penetrates
- The euphotic zone is from the surface depth to the depth where
light levels become too low for photosynthesis (occurs within the
- The limnetic zone is the open water area where light doesn’t reach
the bottom
- The bottom sediment is known as the benthic zone (has many
organisms (invertebrates))
Trophic Status:
- Eutrophic lakes have high nutrients and plant growth while
oligotrophic don’t. Mesotrophic are in the middle
Lake Inputs:
A. Precipitation directly upon lake surface
1.Normally a small proportion of total input
2.Large lakes can receive a large proportion from direct
precipitation (Lake Victoria >70%)
3.Dead Sea has nearly zero direct precipitation upon surface
B.Surface influents of drainage basin
1.Normally the major input
2.Quantity, timing, and quality affected by vegetation
C.Groundwater seepage
1.Commonly a major source in certain geological settings
a)Rocky, mountainous, high gradient basins
b)Glacial till
c)Karst and doline lakes in limestone
2.Difficult to accurately estimate
D.Groundwater as discrete springs
1.Calcareous regions
2.Fractured basalts
Lake outputs:
A.Surface outlets
1.Drainage lakes lose water mainly by flow from a surface outlet
2.Lakes with sediments composed mainly of clays and silts usually
have surface outlets
B.Seepage into groundwater
1.Normally occurring in shallow waters
2.Lake sediments can regulate this loss
1.Dependent on season and latitude
2.Wind velocity, humidity, temperature, etc. regulate the rates of
3.Lakes in closed basins lose water primarily by evaporation
1.Hydrophytes (water loving) plants can transpire great quantities of
water where present
2.Riparian and littoral vegetation main contributors to loss
3.Most important in shallow, small, relatively productive lakes,
ponds, ditches, and streams
Global Water Balance:
A.More evaporation from the oceans than returned via direct
precipitation -source of most terrestrial precipitation
B.Hydrologic regions among continental land masses
1.Exorheic -rivers originate and from which they flow to the sea
2.Endorheic -rivers arise but never reach the sea
3.Arheic -no rivers arise (deserts in the latitudes of the trade winds)
C.Continental average precipitation comparable except South
D.Global fluxes, content, and retention times
1.Retention time in atmosphere is ~9 days
2.57-80% of precipitation is returned to the atmosphere through
evaporation (world average is 65%)
E.Can humans modify the global water balance?
1.Dams, canals, diversions, agriculture, and basin modification
2.Global atmospheric CO2increase and warming
a.Melt 1% of global polar ice cap and sea level rises about 80 cm
b.Melt 10% of global polar ice cap and sea level rises about 8.0 m
A.Soil and geological substrate regulate the rates and pathways
ofhillslope runoff
1.Landscape form, land use, and management requirements should
be or are linked to these processes
2.Overland flow occurs when absorptive capacity is exceeded by
therate of rainfall or meltwater influx
B.Subsurface flow
1.Infiltration and percolation to the zone of saturation followed by
relatively slow movement to drainage channels
2.Subsurface stormflow is shallower and more rapid