Revealed: movie. Courtesy of Anneberg
Media, URL <http://www.learner.org/resources/series78.html>. Requires
Windows media Player. Sign in and view #19 Running Water I:
Rivers, Erosion and Deposition, and #20 Running Water II: Landscape
Fluvial Geomorphology (pdf)
and Sediment Transport Appendix (pdf),
Habitat Restoration Guidelines, 2004, Washington Department of
Fish and Wildlife, Site URL: http://wdfw.wa.gov/hab/ahg/shrg/index.htm.
Aquatic Habitat Guidelines:
An Integrated Approach to Marine, Freshwater, and Riparian Habitat Protection
and Restoration, Washington Department of Fish and Wildlife, Site URL:
http://wdfw.wa.gov/hab/ahg/ explore the appendices to the Integrated
Streambank Protection Guidelines (ISPG), Stream Habitat Restoration Guidelines
(SHRG) - the appendices to these manuals have excellent
summary overview to hydrology, fluvial geomorphology and sediment transport
flow and Fluvial Processes, Dr. Michael Pidwirny, University of
British Columbia Okanagan, Fundamentals of Physical Geography (PhysicalGeolgraphy.net),
page URL: http://www.physicalgeography.net/fundamentals/10y.html
and Deposition, Dr. Michael Pidwirny, University of British
Columbia Okanagan, Fundamentals of Physical Geography (PhysicalGeolgraphy.net),
page URL: http://www.physicalgeography.net/fundamentals/10w.html
on topographic Maps (view Landforms due to streams), Dr. Susan
California State University, Sacramento, page URL: http://www.csus.edu/indiv/s/Slay
NASA Geomorphology From Space: Chapter 4 Fluvial
Landforms , site URL: http://disc.gsfc.nasa.gov/geomorphology/GEO_COMPLETE_TOC.shtml
landform Simulation Model, Northern Illinois University, URL: http://www.niu.edu/landform/home.html. Java
base drainage network simulator that allows input on variables such
as erodibility, climate, and tectonics.
The impact of the hydrologic cycle on landscape development cannot
be underestimated. Not only does it illustrate the movement of water
between the land, oceans, and atmosphere, it is also an energy
cycle, responsible for shaping and creating landforms. Through
evaporation solar energy is converted to potential energy that
is eventually released by rainfall. Raindrop impact loosens soil and
rock particles, and incrementally water moves these particle downslope,
into channels, and eventually to the ocean. When water flows downhill
potential energy converts to kinetic energy, the energy
of motion responsible for carving landscapes. Fluvial activity
shapes mountains, river valleys, gullies, and slopes, and transports
nearly 90% of all sediment entering the oceans. Solar energy also
drives wind and waves that perform their own work.
Terms and concepts:
Ground water: water within the zone of aeration (vadose
water) and the zone of saturation (phreatic
water). The groundwater table is
the upper boundary of the zone of saturation.
Overland flow is surface runoff and is categorized
using a variety of terms. If all soil beneath the surface is
saturated the term saturated overland flow applies.
If surface runoff is occurring because precipitation exceeds infiltration
then that is refered to as Hotonian overland flow.
The general term for overland flow that moves over the surface as a
thin muddy sheet is called sheetflow.
Throughflow: The water the flows through the undersaturated
zone during storms. Considered a component of storm runoff.
Surface water (runoff): All terrestrial water in lakes, ponds,
sheet flow and stream flow.
Stream: The general term for any natural channel
through which water flows. A stream can flow all year around
(perennial stream) or only when it rains (ephemeral stream). The
term includes the smallest gully to the largest river.
Baseflow: the groundwater contribution to streamflow.
Alluvium: The sediment deposited by streams.
Basel Level: Base level is the elevation below which a stream
cannot erode. The valley floor of a river is graded to whatever the
local baselevel may be. Aggredation accompanies a rise in base level.
Degradation (erosion) accompanies a lowering of baselevel.
What work is accomplished by streams?
weathering - solution and abrasion
erosion - scouring
transportation - movement of sediment from one place to another
deposition - laying down sediment
A stream accomplishes all of these, however one or more process may
dominate depending on geology of the basin, climate, and base level.
For example deposition prevails where a braided stream flows across an
arid alluvial fan, and solution where a tropical stream flows through
limestone. Within a basin these processes will vary both spacially
and temporially. Weathering and erosion dominate in finger tip tributaries
extending headward into steep slopes. The sediment is then transportion
through the river trunk and eventually deposited at its mouth. Scouring
and sediment transport occurs during floods, and during low flows deep
scoured pools are made shallow by deposition.
How is streamflow measured?
Stream discharge (Q), the rate at
which water flows through a given cross-sectional area of a channel,
is calculated using the equation below. In the field discharge is measured
using a current meter and a tape measurer. At a gauging station, stage
height is continuously recorded by a recorder attached to a float resting
on the water's surface in a stilling well. Discharge is then determined
from the rating curve (plot of Q vs depth) for that area of the channel. River
Bollin Field Work - Watch geomorphology students measure discharge
of a small stream.
Q (discharge) = wdV
w = width (usually measured at the top) d = average depth (taken at defined intervals
and average) V = average velocity
Velocity is taken at defined intervals:
if depth is <2.5 ft velocity is measured at 6/10
the total depth measured from the top
if depth is >2.5 ft velocity is measured at 2/10 and 8/10
With the exception of groundwater piping, which will be discuss later, overland
flow (sheet flow) is necessary for channel
formation. The rate at which a channel forms depends on vegetation,
storm intensity, slope, permeability, and erodibility
of the surface.
Sheet flow is dynamically unstable and small irregularities in
the surface will cause local concentrations of flow. Eddy formation
and flow diversion around obstructions or into hollows initiate
scouring. Once developed, a scoured trough or rill is
perpetuated by the continued concentration of flow and migrates
upstream by headward erosion of the nickpoint,
the inflection where scouring is greatest. Eventually the rill
grows into a gully, and if the gully deepens to
intersect the groundwater table it will become a permanently flowing perennial stream. A
gully may take only a few days or years to form. However,
a large integrated stream network can take thousands to several
millions of year to develop.
Because sheetflow is easily deflected it can concentrate in linear depressions,
joints, mudcracks, hiking trials or even cow paths. Every irregularity
on a slope can potentially influence channel development. Large
slope depressions created by landslides are also popular sites for water
to concentrate. Over time streams may establish paths in structural
troughs, faults, rift valleys, or linear depressions formed on weak lithologies. Over
time discontinuities in structure and lithology will become etched into
Formation by spring sapping, subsurface piping,
Spring sapping, subsurface piping, and artesian sapping,
are all forms of erosion by ground water discharge. This is process
is common along contact springs where groundwater flowing along an impermeable
bed discharges along a slope and slowly removes the material around it. The
seepage pressure of water flowing from a slope will loosen and and removed
sediment. If the spring is deep in the slope it will undermine and collapse
the overlying material. Spring discharge continues to erodes the channel
downslope, while sapping drives headward migration and channel lengthening
upslope. Small mountain creeks that terminate at slope springs
are typical formed by this process.
all material carried by a stream. It is introduce to the channel
through solution, abrasion, mass-wasting,
and channel scouring. The average load of
a stream is a function of the climate, geology and slope of
its drainage basin.
Bedload is that portion of the particulate load
that is transported along the bed by sliding, rolling or hopping.
It moves at velocities slower than the flow, and spends most of
its time on or near the stream bed.
Bedload transport move filmed
and edited by John Gaffney (U of Minn) (more)
mechanisms of grain motion:
traction (rolling and sliding)--important
factors: frictional drag, lift forces exerted by the flow,
saltation (hopping)--grains are temporarily
suspended by fluid vortices or by ballistic impact and then
Grain movement may be continuous or intermittent
depending on the flow regime (strength of flow as defined by Froude
Number) and grain size.
Suspended load is fine sediment carried
in the body of the flow (fig.3). Suspended load moves at the same
velocity as the flow and typically includes clay and fine silt
particles having large relative surface areas. The electrostatic
attraction between the charges on the particles and the water molecules
keeps these particles in suspension. For clay and fine silt
this electrostatic force is large compared to the weight of the
particle. However, once deposited cohesion between particles
will inhibit entrainment. (See Hjulstrom curve below.)
Washed load is that component
of suspended load composed of particle sizes not found in the channel
The quantity and quality of the particle load
is defined in terms of competence and capacity. Competence is
the largest size clast that a stream can carry, whereas capacity is
the volume of sediment carried. Competence (caliber) is a function
of velocity and slope whereas capacity is determined by of velocity
and discharge (volume rate of flow).
Dissolved load includes the
chemically dissolved ions carried by the water, and is dependent
on climate and rock solubility.
Figure 3. Suspended load makes the waters of the Cold River (Alstead,
NH) murky after rainfalls. Coarse gravel along the banks is bedload
deposited at a higher water level. Movement of cobbles and
boulders transported along the bed can generally be heard but not
seen. The greatest amount of channel scouring occurs during
floods. Floods also precipitate mass movement by removing
the stabilizing toes of landslides.
The load of a stream varies with discharge and
is greatest during times of flood. At times a landslide in
an upstream tributary may introduce an unexpected pulse of sediment
Figure 4. The Hjulstrom curve (below) shows the velocities
required to move and transport sediment. Note that a higher velocity
is required to entrain cohesive clay and fine silt than coarse sand,
which is cohesionless. However, once fine sediment is entrained a
much lower velocity is required to keep it in suspension. (Vist
the USDA Stream
Systems Technology Center for a good review of the phi
particle size classification.)
Factors that govern the % dissolved and suspended
Climate: temperature, precipitation (volume, timing
Type and amount of vegetation (dependant on climate)
Geology: rock solubility: (e.g. abundance of carbonates
or evaporite deposits)
erodibility and permeability of materials in the drainage basin
Relief and slope: Affects the potential and kinetic
energy of runoff and stream flow
Human activities such as mining, constructure, clear
cutting, development, etc.
Go to the FAO
World River Sediment Database and record the sediment yields,
watershed areas, runoff and rainfall of the following rivers:
Ganges, Mississippi, Hudson, and Colorado. What is the
sediment yield/area for each. How do the vary? What
hypotheses can you make to explain your observations?
Laminar vs. turbulent flow
Fluid flow is either laminar or turbulent (fig 5). If flow is laminarwater
particles follow parallel paths that don't cross.Turbulent
flow, on the other hand is chaotic, characterized by instantaneous
changes in both particle direction and velocity. Flow paths cross
and interact. Variations in velocity, local channel dimensions, roughness,
and sediment load produce a variety of turbulent flow phenomena. Bank
and bottom rollers, and helical flow are examples, as are vortices caused
by flow separation around obstacles. Helical flow is
a spiral, cross-channel and downstream motion of flow, which is important
to point bar development in meandering streams. Eddies and vortices are
important to sediment scouring processes and pothole (fig.
The conditions under which these flows occur are described using a dimensionless
number known as Renold's number, shown below. The Re# for
laminar channel flow is around 500. Streams have Re#s >2000 and are
therefore characterized by turbulent flow. However, groundwater flowing
through a granular aquifer is typically laminar. Re# varies for different
systems, such as water flowing through channels or pipes, or smoke rising
from a stack.
Renold's Number= pvd/u
p = density (m/l3) v = velocity (l/t)
d = average depth of flow (see below) (l)
u = viscosity (m/lt)
Figure 5. Vertical velocity profiles depicting the differences
in laminar and turbulent flow. (R#<500 = laminar flow; R#>2000=fully
a laminar flow condition and a constant flow velocity. What adjustment(s)
would result in the flow becoming turbulent?
Figure 6. Potholes carved into the Wingate Sandstone by the
Freemont River, near Fruita UT. The basins are carved by turbulent
eddies armed with sediment that drill through the bedrock. (Click
Many large high-level potholes in New England
stream were carved by aggressive, sediment-laden glacial meltwater
stream that accompanied deglaciation. (Examples: Shelburn
Falls in the Deerfield River, MA: Sculputured
Rocks on the Cockermouth River, Groton, NH; Screw Auger Falls, Gulf
Hagas on the West Branch Pleasant River, Maine.)
Flow regime: Three progressive states of turbulent flow, or flow
regime, are defined by another dimensionless number call Froude Number (described
Froude # = v2/(gd)
v = velocity (l) d = average depth of flow (l) (see below) g = acceleration due to gravity (l/t2 ) (32
ft/sec2 or 9.8 m/sec2)
F# is often viewed as the ratio of the inertial force (the force acting
to sustain the flow) and the gravitational force (the force acting to
dampen the flow), as such froude number reflects the strength of the
flow. F# is also viewed as the ratio of kinetic (~v2) and
potential (gd) energy .
Froude number defines the type of turbulent flow, whether it's shooting (upper
flow regime) or tranquil (lower flow regime). For
a given grain size, bedforms in a channel or on a beach will reflect
flow regime. Therefore, once a relationship is determine
through experimentation, usually in a flume, bedforms can be used to
interpret past conditions of flow strengh and depth. Flow regime
can be observed in the field by noting whether the water surface is in
phase (upper flow regime) or out of phase (low flow regime) with the
Flow regime affects the type of bedform that develops and certain
characteristics of sediment transport.
Under low-flow regime conditions the bedload moves intermittently
because it is temporarily incorporated in bedforms, such as ripples
and dunes. This means that a large amount of sediment can be
stored in the bed even though over time it is slowly moved downstream.
In upper flow regime conditions that typically occur during flooding
the movement of sand and granule-size particles is continuous. The
greatest amount of channel scouring occurs during floods. Deep
pools scoured by floods are typically filled in or made shallow during
low flow conditions.
Problem: Measuring streamflow on the San Pedro
movie from the Arizona Water Science Center). The flume
used to measure flow is specially designed so the the froude # of
the flow is equal to 1. How does this design facilitate the
determination of discharge? If the water in the stilling well
is 2 inches what is the flow velocity?
How streams erode their channels
Mechanisms of stream erosion
Abrasion (corrasion) : Wearing away by debris carried in
the flow. Potholes are formed by debris swirling against the bedrock in
Solution (corrosion): Erosion by chemical solution. Prominent
in karst terrains where bedrock is soluble.
of rock by tiny shockwave produced by bubbled collapse.
Cavitation and hydraulic lift are explain by Bernoulli's Law, which
explains the relationship between velocity and pressure in a flow.
The law assumes that the total energy of the system is constant and
equal to its potential energy + kinetic energy and
existing pressure. Because density and gravity are
constant the only two variables are velocity and pressure. As
one increases the other must decrease.
An increase in velocity caused by water flowing over a falls or
through a constricted portion of a channel forces a decrease in
pressure and an rapid bubbling. The bubbles implode when the velocity
is again decreased sending shock waves that chip the rock.
Hydraulicking: The lifting and removal of loose
material by the force or impact of water (reactive force
+ lift force). The shear stress exerted by the flow is dependent
on the weight of the water, which increases with flow depth, and
the slope of the bed. As depth and slope increase so does
shear stress. Lift force is related to the vertical pressure
and velocity gradient in the flow (see Bernoulli's Law below).
Total Energy =ph + (1/2) pv2 + P = constant
cp=density; g=9.8m/sec2; ah=height
above base level; v=velocity; P=pressure
A simplified version of the equation is: P + pv2 =
Potential energy is PE=ph
Kinetic energy is 1/2 pv2 Pressure F/A is F=ma
When v increases, P must decrease and visa versa. Therefore
high flow velocity over particle reduces the overlying pressure
and aids in the lifting of the grain from the bed.
Question to ponder: How is Bernoulli's
Law also be used to explain the hydraulic lift experienced
by particle on the stream bed?
5. Ballistic impact is chipping caused by grains hitting the rock (i.e.
formation of chatter marks). This process is more effective in an aeolian
environment where grains are small (e.g. fine sand). Water hydrostatically
bonded to a grain will cushion its impact in a streams. Ballistic
impact also aids in sediment entrainment.
Hydraulic Geometry (Leopold and Maddock, 1953) is
an empirical method used to illustrate the relationship between channel
geometry (width, depth, and slope), flow velocity, and stream discharge
within a particular drainage basin. As mentioned above, Stream
discharge (Q) is the product of width, depth, and flow velocity.
Q = AV = wdV
Q = discharge (ft3 /sec or m3 /sec)
A = cross-sectional area = width x depth
V = Velocity
Empirical regression equations describe the geometric changes
experienced by a channel while adjusting to changes in discharge.
Discharge can increase during a flood (at a station)
or when tributaries meet (downstream). These
geometric changes can be mathematically and graphically displayed. Exponents
will differ slightly from one river system to another depending
on climate and local geology.
Leopold and Maddock (1953) obtained the following results:
2. Manning equation: v = (1.49/n) *R2/3S1/2 :
n = empirically derived roughness coefficient (manning
calculator from LMNO Engineering, Research, and Software, Ltd.)
Questions: Although the slope of a river
decreases down stream, flow velocity increases. This is evident
from the above equations.
What adjustments can you predict a stream will make after
flowing from a silt-dominated channel to one dominated by sand
List and briefly described at
least two conditions that may lead to changes in channel composition.
Summary of changes that occur in the downstream
1. Discharge increases
2. slope decreases
3. n (manning roughness) decreases; C (Chezy smoothness increases)
4. net forward velocity increases
5. Area increases
6. load increases
7. particle size decreases*Question: If the gradient of a river
decreases downstream, why does the downstream velocity often increase.
Wetted Perimeter and hydraulic radius
Wetted perimeter(Pw) = w + 2d: Approximates the
length of the channel boundary.
Hydraulic radius (R)= A/Pw: ratio of the area
of the stream channel to the wetted perimeter. This value
approximates average channel depth. Measuring
wetted perimeter of a small stream
An increase in R results in a decrease in frictional resistance
exerted by the channel walls
Streams and Energy
Energy is the ability to perform work (Force x distance; or
mass x acceleration x distance). The energy in a stream consists
of potential energy (PE=pgh), which is stored energy, and kinetic
energy (KE=1/2 mv2), which is the
energy of motion. The potential energy of a river decreases
downstream while its kinetic energy increases.
Energy transformations: As water moves down slope potential
energy changes to kinetic energy. The work preformed on a stream
is accomplished by KE. The rate of transfer of PE to KE, which performs
the work of stream flow, is a function of gradient.
The amount of work preformed is a function of available kinetic
energy. In a graded profile, the stream has adjusted so that the
work needed to transport the sediment through the system is equal
to the available energy.
KE is lost by internal friction (fluid friction; governed
by both fluid and eddy viscosity), external friction (drag induced
by channel walls, and by sediment erosion and transportation. KE
is gained by an increase in slope and by an increase in discharge.