**Course Title: Floodplain Management**

**Module 2:** Stream Systems on Dynamic Earth

**Session 7**: Stream Management Framework -- The Physical Principals
and Practice

**Author**: Dr. Donald R. Reichmuth, P.E., President, Geomax, P.C.,
Spokane, WA

(E-mail -- <Geomax@comcast.net>)

**Time 75 minutes**

# 

# Objectives: (PP 1 -- 2, Title and Objectives)

At the end of this session, the students will be able to:

7.1 Explain the stream sediment cycle in terms of source, transport and
deposition.

7.2 Contrast the difference between the engineering and geologic
approaches in developing analytical tools for stream management.

7.3 Show the effect that channel blockages have on overall stream
stability.

7.4 Examine the behavior and stabilization methods used in drainages
showing vertical instability.

7.5 Illustrate common problems associated with horizontal stream channel
migration.

7.6 Compare management practices to determine how to insure low impact
development.

7.7 Present floodplain as a product of the geological floodplain \--
case study exercises

7.8 Complete the Module 2 examination.

**Scope:**

Humans have a long history of altering catchment areas. During the last
150 years, these alterations have taken on immense proportions due to
the availability of large machinery and the desire to accommodate an
ever-increasing human population. In this short time frame, there have
been two distinct approaches (engineering and geological) applied to the
understanding and exploitation of watercourses. The engineering approach
started in the late 1800s with English engineers designing irrigation
canals in India and Egypt. The geological approach started in the U.S.
in the 1870s with explorers such as F.V. Hayden with the U.S. Geological
Survey and J.W. Powell with the Smithsonian Institution. At that time
the science of geomorphology, the study of the earth's surface features,
began.

The engineers developed mathematical formulas to help them design and
construct irrigation systems. The geomorphologists developed physical
models that attempted to explain the evolution of stream systems. One
fundamental difference exists between irrigation canals and natural
streams. Irrigation canals attempt to move water as high as possible
along a hillside. This requires that canal flow neither scours the bed
nor allows suspended sediment to deposit in the channel. This condition
is sometimes referred to as being "**in regime**". Additionally,
**friction losses** in the canal were to be minimized. Natural streams,
on the other hand, move both water and sediment downhill on as steep a
path as possible. It is necessary that sufficient **friction losses** be
generated to keep the stream's **terminal velocity** below the
**threshold value** that would cause destructive bed and bank erosion.

This session presents concepts from both disciplines that are useful and
practical for field-oriented floodplain management. Theoretical
considerations that lack in-the-field applications will not be
considered.

This session will be equally divided between lecture material and
student presentations.

**Readings:**

***Student and Instructor Reading:***

**[Class Handout]{.underline}**

Reichmuth, D.R. 2004. "Brief Analysis of the Analytical Basis of River
Mechanics," Geomax, P.C.

**[Grand Canyon]{.underline}**

Konieczki, Graf & Carpenter. 1997. "Streamflow and Sediment Data
Collected to Determine the Effects of a Controlled Flood in March and
April 1996 on the Colorado River between Lees Ferry and Diamond Creek,
Arizona," *USGS Open File Report*, OFR 97-224

Summary Report Also Available At:
<http://az.water.usgs.gov/floodrpt.html>

Dolan, Howard & Gallenson. 1974. "Man's Impact on the Colorado River in
the Grand Canyon," *American Scientist* Vol. 62, No. 4, Jul-Aug 1974,
pages 392-401.

***Instructor Reading:***

**[Basic Hydraulics]{.underline}**

Chow, V.T. 1959. *Open-Channel Hydraulics*, McGraw-Hill. Chapter 3,
"Energy and Momentum Principals" and Chapter 5, "Development of Uniform
Flow and Its Formulas."

These chapters provide a basic understanding of the engineering approach
to open channel hydraulics.

Additionally, there are excellent footnotes throughout the book that
describe the history of the development of the concepts that are
discussed.

**[Field Exploration]{.underline}**

Powell, J.W. 1961. *The Exploration of the Colorado River and its
Canyons*, Dover Publications

This volume is a reprint of the original book written by Powell in 1895,
titled *Canyons of the Colorado*.

**[Random Error Propagation]{.underline}**

Moffitt & Bouchard. 1987. *Surveying*. Eighth edition, Harper & Row.
Chapter 5 "Random Errors" (especially Section 5-7 Propagation of Random
Errors).

This chapter provides the rigorous mathematical theory for determining
the accuracy of an answer derived from an equation whose inputted values
contain random measurement errors.

**General Requirements:**

The students should start to apply the concepts learned in this session
to their individual Case Studies. The instructor should spend a short
time in class checking student progress with their Case Studies and
answering questions that they may have.

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**Objective 7.1** **Explain the stream sediment cycle in terms of
source, transport and deposition. (PP 3, Elements of Channel
Formation)**

**Requirements:**

The information in this section is presented as a lecture using Power
Point slides:

**Remarks:**

This section explores the various parts of the stream system. The
instructor should always keep the student's focus on a system and not
allow the discussion to evolve into a discussion of the site specific
parts that impact the entire stream

I.  **The basic sediment cycle operates on two different time scales.**

    A.  Tectonic forces act to uplift headwater areas in drainage
        basins.

        1.  These forces act over long time periods.

        2.  As the uplift occurs, potential energy is generated that
            allows the erosive processes to begin to work.

    B.  Sediment generation, transport, and deposition by streams act on
        much shorter time scales.

        1.  Variations in the rate that sediment is mobilized is
            dependent on changes in climatic conditions.

            a.  Glacial cycles can be tens of thousands of years.

            b.  Weather cycles (both drought and local temperature) can
                vary over tens and hundreds of years.

            c.  Depending on the drainage's latitude and elevation
                yearly cycles can occur.

        2.  The drainage basin rock type and vegetative cover also
            influence rates of these processes.

        3.  Human activity can have major impact on these processes over
            very short time spans.

II. **Source Areas are found primarily at the higher elevations in the
    drainage basins or by reworking earlier deposits.**

    A.  Typical sites can involve breakdown of bedrock and mobilization
        of older alluvial deposits.

        1.  Erosion of bedrock is the primary source of sediment

            a.  Rock type strongly influences the type of sediment that
                is produced.

            b.  Site temperature and moisture control whether chemical
                or mechanical weathering predominates.

        2.  Inactive stream terraces can become a source area when they
            are undercut by a shifting channel.

        3.  Stream banks often become local sediment sources.

            a.  Devegetating the stream banks can trigger bank erosion.

            b.  Human directed channel manipulation can cause banks to
                be attacked.

    B.  Problems can develop that change the rate of sediment
        production.

        1.  Landslides can occur in the drainage basin that
            significantly increase sediment availability.

        2.  Poor logging practice can trigger an erosive cycle within
            the drainage.

        3.  Construction activity, such as road building, can generate
            sediment sources.

        4.  Bank vegetation can be removed for numerous reasons and
            expose the banks to increased erosion.

III. **Sediment transport by streams** begins once a sediment supply is
     mobilized.

     A.  There are normally two types of channels involved in sustained
         sediment transport.

         1.  Vertically stable channels often occupy bedrock valley
             floors

             a.  Virtually all sediment that enters the stream channel
                 is flushed downstream.

             b.  The channel normally shows little tendency to shift.

             c.  The stream gradient can be quite steep.

         2.  Laterally shifting channels (meandering streams) occupy
             wide floodplains.

             a.  This steam type usually occurs in alluvial valleys

             b.  Sediment fed into the main valley from side tributaries
                 is moved downstream at an equal rate.

                 1.  Specific sediment deposits on the main valley floor
                     can remain stationary for long periods until the
                     stream shifts laterally into the deposit.

                 2.  Over time this "steady-by-jerks" mobilization of
                     sediment creates the overall sediment balance.

     B.  Problems associated with the sediment transport part of the
         stream system include:

         1.  Local bank failure and meander loop cutoffs can occur when
             the channel shifts laterally.

         2.  Structures built on the floodplain can be undermined as the
             channel shifts laterally.

         3.  Culverts on roads crossing stream channels on bedrock
             valley floors can become plugged by the sediment in
             transport.

IV. Deposition must ultimately occur when the sediment is taken out of
    the stream system.

    A.  Typical sites of deposition almost always involve lower gradient
        reaches along the stream system.

        1.  Normally these sites will be alluvial valley floors.

        2.  The channel will tend to break into multiple channels.

        3.  Often a delta will form when the stream enters a body of
            water.

    B.  Problems associated with depositional reaches include:

        1.  Flood levels and water tables often raise as the deposition
            fills the stream channels.

        2.  Individual distributary channels are often short lived and
            new distributary channels form.

        3.  In coastal areas channel changes can impact shellfish beds.

V.  **Base Level Control ultimately marks the end of an individual
    stream sediment cycle.**

    A.  Local base level occurs when some condition is imposed on the
        stream system that reduces the stream gradient to nearly level.

        1.  Geologic accidents such as landslides or volcanic lava flows
            can block a drainage.

        2.  Manmade dams can become local base level control.

        3.  Particularly erosion resistant bedrock can create partially
            effective base level control.

    B.  Absolute Base Level Control occurs at the ocean when the
        stream's energy is reduced to zero.

    C.  Both local and absolute base level control can change with time.

        1.  Bedrock blockages can erode away or be bypassed.

        2.  Manmade structures can fail or be removed.

        3.  Climate change, such as glaciation and global warming, can
            change sea levels.

**Supplemental Considerations:**

The instructor should identify a local sediment cycle going from source
area to depositional site.

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**Objective 7.2 Contrast the difference between the engineering and
geologic approaches in developing analytical tools for stream
management.**

**Requirements:**

The information in this section is presented as a lecture using Power
Point slides:

**Remarks:**

The literature is full of descriptions of hydrologic and geologic
studies dealing with streams, flumes and irrigation canals. In most
cases these studies relate to specific experiments that are not often
easy to generalize. Additionally in many cases, it is either impossible
or prohibitorily expensive to collect the required field data to use the
methodology presented. The discussion that follows will only present the
most widely used equations that are required to understand the
fundamental basics and that are the basis for many of the computer
programs that are widely available.

I.  Analytical Methods used to describe physical behavior are always
    approximations of reality (PP 4, Analytical Methods)

    A.  Engineering approach is usually highly mathematical.

        1.  This approach was initiated by English irrigation engineers
            over one hundred years ago.

        2.  Most of the equations that were developed were mathematical
            approximations of the physical phenomenon that was observed.

            a.  Some equations were based on first principals that
                described water falling under the influence of gravity.

            b.  Other equations were based on laboratory and field
                experiments.

        3.  Only a few of the equations that were generated are now in
            general use.

    B.  Geologic approach tries to explain the behavior of natural
        systems that were observed in the field.

        1.  This approach was advanced by early geologists that explored
            the arid Southwest United States.

        2.  Their writings tried to explain the physical principals that
            they observed.

        3.  These descriptions, while inexact, did help explain the
            phenomenon that was observed

II. Energy and momentum equations that have been derived, are based on
    first principals that have wide application. (PP 5, Energy
    Equations)

    A.  The Bernoulli equation relates potential energy, kinetic energy
        and friction losses for flow in a gravity system.

        1.  Energy cannot be created or destroyed; therefore it is
            possible to equate the total energy at one section with the
            total energy at a second section downstream.

        2.  If there is a difference in the total energy between the two
            sections, then work (friction losses) must have occurred
            between the two sections.

        3.  When the work (friction losses) is small, it expected that
            the stream velocity (kinetic energy) will increase because
            the potential energy (water height) drops when going from
            Section 1 to Section 2.

        4.  Stream velocity (kinetic energy) can only increase to some
            threshold in natural stream systems.

            a.  Increased turbulence will mobilize the stream bed and
                banks.

            b.  The channel will become unstable and work will be done
                to reshape the channel. This action will convert kinetic
                energy to work (friction loss) so there is a limit to
                the buildup in kinetic energy.

            c.  Streams are most stable when there is sufficient
                friction loss in the system to use up all of the
                potential energy available when the water falls from the
                elevation at Section 1 to Section 2.

    B.  When Section 1 and Section 2 have different sizes, a Variable
        Section Modification is often applied to the Bernoulli Equation.

        1.  This modification involves adding a second energy loss term.

            a.  The term is a constant (K) times the change velocity
                head between the two sections.

            b.  When the downstream section (Section 2) gets smaller
                (contracts), the constant (K) equals zero and there is
                no effect.

            c.  When the downstream section (Section 2) gets larger
                (expands), the constant (K) equals one-half and there is
                an additional energy loss.

        2.  The extra energy loss in expanding sections is caused by
            additional turbulence that develops during expansion.

        3.  When the sections contract, no additional turbulence occurs;
            therefore no extra energy loss develops.

        4.  In streams that have a pool-riffle configuration, energy
            loss occurs when flow goes into the pool and energy is
            conserved going into the riffle.

            a.  The pool is excavated by the excess kinetic energy
                available.

            b.  Pool-riffle sequences are common on natural stream
                systems and help keep kinetic energy (velocity) from
                building up.

    C.  In some instances it is preferred to use Momentum Principals to
        generate flow equations.

        1.  The equations that result are almost identical in form to
            the Bernoulli Equation.

        2.  The main difference is that the variables have slightly
            different definitions.

        3.  Because the general relationship between potential energy,
            kinetic energy and energy loss remain essentially the same,
            this method will not be discussed in detail.

III. Manning's experimentally based equation is now widely used to
     determine Flow Rate (Q). (PP 6, Manning Equation)

     A.  The basic form of this equation was experimentally derived
         during the late 1800's.

         1.  Physical parmeters involving channel shape and slope are
             required.

         2.  An additional parameter called "channel roughness" (n) is
             also needed.

         3.  A constant (1.486) is needed when using English units.

             a.  This constant converts the equation from metric to
                 English units.

             b.  When this value is used the "roughness" (n) term
                 remains the same in both systems.

             c.  The fact that this constant is often carried to four
                 significant places does not imply that the equation
                 will have four place accuracy.

     B.  The "roughness" value (n) cannot be physically measured.

         1.  There are approximate correlations between channel surface
             roughness and the value (n).

         2.  Considerable effort has gone into studies trying to define
             values for (n).

         3.  Essentially the value of (n) must be adjusted in each
             application so that the calculated results match what
             actually occurs in the field.

         4.  College students who have taken lab courses, might
             recognize this variable as similar to the "Lab Constants"
             that they might have used to make their work fit what was
             expected.

     C.  Rigorous error analysis can be performed on any equation that
         contains physical variables that are subject to measurement
         errors.

         1.  The derivation of the error analysis equations is beyond
             the scope of this course.

         2.  Sample results are, however, given for three cases shown of
             Slide PP7.2-3.

             a.  These examples closely match the original experimental
                 configuration that was used to derive this equation.

             b.  The probable errors (at one standard deviation) in the
                 answers for these three cases vary between 10 and 20
                 percent.

             c.  The probable errors are expected to be much larger if
                 the calculations were based on more realistic field
                 conditions and channel shapes.

     D.  The effect of input measurement error on the error in the Flow
         Rate Value (Q) can be analyzed further.

         1.  It is possible to determine how the error in each input
             value contributes to the error found in the answer (Error
             in Flow Rate (Q) in this case).

         2.  As seen at the bottom of Slide PP7.2-3, errors in the
             values of roughness (n) and in the energy line slope (S)
             contributed over 90% of the error in the value for (Q).

         3.  Errors in the values for the physical dimensions (H and W)
             only contributed small errors in the answer.

     E.  Many computer programs that calculate flow rates and water
         surface elevations use versions of Manning's Equation.

         1.  HEC-2 and related computer programs are based on Manning's
             Equation and are used extensively by FEMA to establish
             flood elevations.

             a.  Output data is most accurate when it is calibrated
                 using actual measured flood heights for given flow
                 rates. This is accomplished by "adjusting" the
                 roughness value (n) to make the computer output match
                 reality.

             b.  Even when calibrated against actual field measurements,
                 significant errors can develop when the data is
                 extrapolated to different stream flow conditions.

             c.  Because stream systems are dynamic, site conditions
                 change over time. These changes cause additional errors
                 to be introduced into the data at dates after the
                 calculations were made.

         2.  Uncalibrated computer output can contain significant errors
             and should be used with great caution when predicting flood
             height or areas that will be submerged when specific flows
             occur.

**Supplemental Considerations:**

The instructor should discuss local FEMA floodplain mapping programs in
light of the error analysis calculations given above. It would be best
if the instructor picked a specific local area that had been mapped by
FEMA and that is readily accessible to the students. The students would
then be directed to search the "FEMA Flood Map Store" which can be found
on FEMA's website ([www.fema.gov](http://www.fema.gov/)) for the reports
and mapping data that were available concerning the site. The students
could then explore what collecting the raw data would have cost and what
the potential accuracy of the published data would be.

**General Comment:**

Three distinct classes of stream problem will be discussed in the
following three sections: **(Sections 7.3, 7.4, & 7.5)** These problem
types are channel blockages, vertical channel changes and horizontal
channel changes. Each problem requires different methods of analysis and
data collection before management decisions can be made. **(PP7, Stream
Problem Types)**

**Objective 7.3 Show the effect that channel blockages have on overall
stream stability. (PP 8, Channel Blockages)**

**Requirements:**

The information in this section is presented as a lecture using Power
Point slides:

**Remarks:**

I.  **Small in-stream obstructions effect flow directions, scour, and
    bank erosion. (PP 9, Effects of In-stream Obstructions)**

    A.  Submerged obstructions could be anything (logs, rocks, debris,
        manmade structures, etc.) that is located on the stream bed and
        is overtopped by the flowing water during periods when higher
        flows occur.

        1.  The obstruction can be of any shape.

        2.  The downstream face of the structure controls the local flow
            behavior.

        3.  Flow tends to be directed perpendicular to the downstream
            face of the structure.

        4.  Secondary currents in the area will be disrupted and flow
            throughout the entire water column will be affected.

        5.  In the example shown on the slide, the flow would be turned
            into the bank and increased bank erosion could occur.

    B.  Exposed obstructions stick out of the water at virtually all
        flows.

        1.  A bridge pier would be an example.

        2.  Flow past the obstruction becomes very turbulent.

        3.  This turbulence often causes bed scour to occur next to the
            obstruction.

        4.  In some cases, sufficient bed scour occurs to undermine the
            obstruction.

II. **Geologic accidents can cause stream blockages to occur.**

    A.  Some events can cause rapid change in streams.

        1.  Earthquakes can cause vertical motion to occur that
            obstructs stream flow.

        2.  Mud and debris flows can fill entire channels. Examples
            include:

            a.  Electron & Osceola Mudflow in Washington State. **(PP
                10, Mount Rainier)**

            b.  Amero, Colombia Debris Flow in Central Amerial. **(PP
                11,Debris Flow Example)**

        3.  Landslides can block river valleys as occurred on the
            Madison River during the 1959 Hebgen, Montana, earthquake.

        4.  Catastrophic channel changes have occurred on large rivers.
            Examples include:

            a.  TheYellow River in China jumped hundreds of miles to a
                new outlet to the sea and caused widespread death and
                destruction.

            b.  The Mississippi River has changed course a number of
                times. See slide PP 6.3-6 for details.

        5.  Volcanic Eruptions such as occurred at Mt. St. Helens in May
            1980 wiped out much of the Toutle River.

    B.  Some events can cause slow change in a stream to occur.

        1.  Glaciation can slowly block river valleys and force streams
            to flow elsewhere. Examples include:

            a.  The Teays (now the Ohio) River Basin significantly
                altered during the last ice age. See slide PP3.1-4.

            b.  During the last ice age, the Missouri River was diverted
                from flowing to Hudson's Bay and joined the Mississippi
                River.

            c.  The Clark Fork River that originates in Montana was
                blocked by ice coming from Canada in the Idaho
                panhandle. This blockage triggered the Lake Missoula
                Floods that raised havoc in eastern Washington State.

        2.  Tectonic Uplift can slowly alter stream behavior as seen in
            the Grand Canyon. **(PP 12, Regional Uplift Erosion
            Patterns)**

            a.  Canyon has shifted into an anticline structure. **(PP
                13, Cross-Section View)**

            b.  Colorado River maintains grade as uplift occurs.

            c.  Canyon formed to maximize erosive energy. **(PP 14,
                Canyons of the Colorado)**

            d.  Undercutting destroys harder formations. **(PP 15,
                Erosion Patterns)**

III. **Manmade dams come in all sizes**

     A.  General impacts on stream channels. **(PP 16, Effects of
         Dams)**

         1.  Downstream from the dam.

             a.  Clean water discharge is very erosive

             b.  Seepage forces can destroy banks if rapid drawdown
                 occurs when the dam is used as a peaking power
                 facility.

             c.  Unregulated side drainages that enter the main stem
                 below the dam can form new deltas in the main stem
                 channel.

         2.  Upstream from the dam.

             a.  The dam creates a new local base level.

             b.  Sediment is deposited at the head of the dam causing a
                 delta to form.

             c.  The impounded water can cause serious erosion to occur
                 along the reservoir shoreline.

     B.  Large dams create multiple impacts (Lake Powell example)

         1.  River hydrograph is radically changed. **(PP 17, Colorado
             River Hydrograph)**

         2.  Clean water discharge causes downstream erosion. **(PP 18,
             Clean Water Releases)**

         3.  Unregulated, downstream side-drainages enlarge causing
             rapids to increase in size and height.

     C.  Small dams create smaller but significant problems.

         1.  Low head, irrigation diversion dams have been built on many
             rivers in the arid west. (Town Diversion Dam is an example)
             **(PP 19, Typical Fish Passage Problem)**

             a.  Rigid concrete structures are relatively expensive.

             b.  Upstream migrating headcuts can undermine the base.

             c.  Turbulent, high-velocity (high-energy) water created by
                 the vertical drop can scour the dam's base.

             d.  Maintenance costs are high. **(PP 20, Typical
                 Concrete/Steel Design)**

             e.  Fish passage is difficult. **(PP 21, Irrigation
                 Diversion Dam)**

             f.  The vertical drop and excessive turbulence usually
                 create a **hydraulic jump**, which is a serious safety
                 hazard.

         2.  Low head concrete structures can be improved.

             a.  When fall heights are less than 9 feet, it is possible
                 to use large rock to eliminate the vertical drop. **(PP
                 22, Cedar River Example)**

             b.  Repair cost is generally lower when large rock is used
                 instead of concrete.

             c.  Eliminating the vertical drop and hydraulic jump
                 significantly improves safety. **(PP 23, Improved
                 Safety)**

             d.  Fish passage is assured and habitat is greatly
                 improved. **(PP 24, Fish Passage Proof)**

**Supplemental Considerations:**

The instructor should describe problems (if any) associated with a local
dam and indicate what has been (or what should be) done to improve
conditions.

**Objective 7.4 Examine the behavior and stabilization methods used in
drainages showing vertical instability. (PP 25, Vertical Change)**

**Requirements:**

The information in this section is presented as a lecture using Power
Point slides:

**Remarks:**

I.  Headcuts cause stream grades to be lowered. (PP 26, Headcuts)

    A.  During the last glaciation, sediment production was high and
        most drainages aggraded.

    B.  Now that the climate has become dryer and warmer, primary
        sediment production is low.

    C.  In many regions, streams are in the process of excavating their
        valleys and returning to preglacial grades.

    D.  Many changes in the landscape that have accelerated headcutting
        were triggered by human activity.

        1.  The loss of beaver in most drainages has been especially
            destabilizing.

        2.  Converting woodlands to cropland has reduced the stabilizing
            benefits of vegetation.

        3.  Cattle grazing in arid areas of the West have diminished
            what little stabilizing vegetation that existed.

        4.  The Southeast was further destabilized by widespread
            channelization of the streams.

    E.  Widespread channel degradation has caused:

        1.  The irreplaceable loss of alluvial fill.

        2.  Diminished water storage in alluvial valleys.

            a.  This loss creates flashier peak flows.

            b.  This loss reduces base flows.

            c.  The water table is lowered causing dry site vegetation
                to dominate.

        3.  Infrastructures, such as culverts, are damaged. (PP 27,
            Headcut Caused Failure)

    F.  In smaller drainages, headcut control is not particularly
        expensive.

        1.  Reintroducing and/or protecting resident beaver can be
            extremely successful.

        2.  Almost any material can be used to create small low-head
            check structures in the degraded channels. (PP28, Erosion
            Control Treatments)

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I.  Grade control structures can dissipate excess energy. (PP 29,
    Vertical Grade Stabilization)

    A.  Often channel degradation develops when channels are too steep.

    B.  One cost effective way of increasing frictional losses is to
        install drops in the channel.

        1.  Large rocks and trees are often the most environmentally
            friendly material to use for constructing these structures.

        2.  Maximum drop heights (i.e. the water surface elevation
            difference across the structure) must be limited.

            a.  When large rocks are used, fish passage requirements
                will limit the drop height to about 2.5 feet.

            b.  Structural stability can become a problem on larger
                streams if plunging flow develops; therefore, skimming
                flow should be maintained. (PP 30, Rock Drop
                Characteristics)

                1.  Skimming flow normally occurs if the drop height is
                    less than 1.5 feet.

                2.  Boater safety is improved because standing waves
                    (hydraulic jumps) do not occur.

    C.  Drop structure alignment determines downstream flow behavior.
        (PP 31, Effects of Structure Alignment)

        1.  Flow is directed perpendicular to the downstream face of the
            structure.

        2.  Specific shapes create different downstream conditions.

            a.  Straight Shapes

            b.  "V" Shapes (PP7 32, Rock Drop Example)

            c.  Non-symmetrical Shapes.

    D.  Rock Drops have many advantages. (PP 33, Summary)

        1.  Built rapidly in-the-wet at less cost

        2.  Esthetically pleasing with improved habitat

        3.  Easy to maintain and/or modify

    E.  This class of structures comes close to duplicating beaver dams.

        1.  Raise watertables

        2.  Retain gravel for fish spawning.

            Supplemental Considerations:

The instructor should identify some local site-specific examples where
raising floodplain watertables would impact (for good or bad) the
landscape, habitat or infrastructure.

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**Objective 7.5 Illustrate common problems associated with horizontal
stream channel migration. (PP 34, Horizontal Change)**

**Requirements:**

The information in this section is presented as a lecture using Power
Point slides:

**Remarks:**

I.  **Meander loops systematically migrate downstream.**

    A.  Normally, it is possible to define a **meander belt** within the
        alluvial valleys that mark the maximum lateral channel motion.

    B.  Meander loops in a given stream normally have a unique size and
        shape.

        1.  Pattern is defined by flow, sediment, and gradient.

        2.  When altered, the system will respond by attempting to
            regain its more stable size and shape.

        3.  Rules-of-thumb exist regarding size and shape but more
            accurate information can usually be gained by finding a
            nearby reach on the same stream that is stable.

    C.  Migrating meander loops can impact infrastructure.

        1.  Buildings constructed within the meander belt can be
            attacked.

        2.  Roads and bridges crossing floodplains are particularly
            vulnerable. **(PP 35, Downstream Meander Loop Migration)**

            a.  Loops can fold in against the embankments and erode the
                road fill. **(PP 36, Poor Bridge Entry Problems)**

            b.  Flow through the bridges becomes extremely turbulent.
                This causes serious scour to occur.

II. **Meander loops can be cutoff.** **(PP 37, Meander Loop Cutoff)**

    A.  The shortened channel has less friction loss.

    B.  The extra available energy accelerates bed scour and bank
        erosion.

    C.  For stability to be reestablished, new friction loss elements
        must be added to the system.

        1.  The channel can simply be allowed to erode until the lost
            channel length is restored. (The original friction loss
            method regained).

        2.  Grade control structures can be added that consume the newly
            released energy.

        3.  Other friction loss elements can be added to the system to
            use up the newly released energy.

        4.  Any combination of the above methods of reducing the newly
            released energy would be effective in restoring stability.

III. **Differential Displacement can erode stream banks. (PP 38, Bank
     Erosion)**

     A.  This process occurs when an upstream sediment source that is
         coarser than the attacked bank material is mobilized.

     B.  The coarse material is deposited on the inside of the bend and
         the bank is eroded.

     C.  The channel size remains unchanged.

     D.  The finer eroded sediment is then more readily carried
         downstream.

     E.  Stabilizing the coarser sediment source best solves the
         problem.

     F.  Armoring the eroding bank (applying a "**band-aid**") only
         causes the mobilized coarser sediment to continue moving
         downstream in search of a different depositional site.

**Supplemental Considerations:**

The instructor should identify local areas where encroachment within a
stream's meander belt has created infrastructure loss.

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**Objective 7.6 Compare management practices to determine how to insure
low impact development. (PP 39, Cumulative Impacts)**

**Requirements:**

The information in this section is presented as a lecture using Power
Point slides:

**Remarks:**

I.  **There are two fundamental choices that can be made in floodplain
    management.**

    A.  A "**quick flush**" system can be used. **(PP 40, Quick Flush)**

        1.  Confines the stream with dikes and levees.

        2.  Straightens the channels and removes frictional loss
            elements.

        3.  Armors the channel to stop erosion and scour.

        4.  Many problems are created.

            a.  Flood peaks are passed downstream to hurt others.

            b.  Water storage in the alluvial valley is lost.

            c.  Habitat is destroyed.

            d.  The work is costly and requires considerable
                maintenance.

            e.  Encourages unsound floodplain development.

        5.  This method has been promoted by the Corps of Engineers to
            many communities. Examples are:

            a.  Portneuf River at Pocatello, Idaho

            b.  Santa Ana River in Orange County, California

    B.  A **" floodplain utilization"** system can be used. **(PP 41,
        Floodplain Utilization)**

        1.  Puts flood water into temporary storage. This reduces
            downstream flood peaks.

        2.  Causes flood water to infiltrate into the valley alluvium.

            a.  Slow release of this water improves base flow.

            b.  Local water supplies are improved

            c.  Creates higher watertables that better support riparian
                vegetation.

        3.  Slows downstream sediment movement.

        4.  Creates and/or maintains good habitat.

        5.  This method most closely imitates conditions that beaver
            created before Europeans arrived.

        6.  In some areas, high water is diverted totally out of the
            channel and floodplain.

            a.  The water can be used to water crops or to recharge a
                depleted aquifer. For example, water from the Santa Ana
                River in the Los Angles, California, Basin is used to
                recharge the aquifer and limit saltwater intrusion into
                the area.

            b.  The term "Water Spreading" is used for this process.

            c.  Problems can develop within the stream channel if Water
                Spreading becomes excessive or is used when the stream
                flow is low and the stream becomes dewatered.

    C.  Drainages must be treated as large-scale systems.

        1.  The impacts cannot be isolated to individual communities.

        2.  Communities must work together to determine the "**best
            path**" for development. **(PP 42, Long Range Goals)**

    D.  **FEMA** floodplain regulations can conflict with desirable
        management at times.

        1.  **Zero rise** requirements can make certain **Floodplain
            Utilization** techniques difficult to permit.

        2.  **Floodplain fill** is allowed /encouraged on the
            floodplain. When this happens the **Floodway** is turned
            into a **quick flush** conduit.

        3.  Little is done to encourage intercommunity cooperation in
            floodwater storage.

II. **Cumulative impacts often are not thoroughly considered.**

    A.  **Low impact development** can only occur when entire systems
        are evaluated.

    B.  Often individual actions have only small or immeasurable impact
        but when a number of these actions occur in a limited area,
        serious impacts develop.

        1.  Basalt, Colorado is an example **(PP 43, Cumulative
            Impacts)**

            a.  Early encroachment caused little harm. It could even be
                argued that the original road (Old Road) across the
                floodplain created temporary flood storage.

            b.  The final projects (New Highway and Bank Dike) virtually
                eliminated the ability for floodwater to reach much of
                the floodplain. Peak flow velocities were increased
                along earlier developments (especially the Commercial
                Buildings) causing serious bank erosion to develop.
                **(PP 44 Roaring Fork River, 1985 Aerial View; PP 45,
                Roaring Fork River, Bottleneck Area; and PP 46, Roaring
                Fork River, Ground Photo)**

        2.  Current FEMA regulations do little to control incremental
            impacts from accumulating.

**Objective 7.7 Present floodplain as a product of the geological
floodplain \-- case study exercises.**

**Remarks:**

A.  Teams will be expected to present a description of their floodplain
    case study as the product of geological processes. (See Task 1 in
    the Geological Exercise Template) Their written reports should be
    restricted in 1 to 2 type-written pages and 5-minute presentations.
    PowerPoint presentations should be optional and limited to 3 to 5
    slides per case study.

B.  The questions included with Tasks 2 and 3 of this module template
    are identical to those in the Biological module. The instructor may
    decide whether these questions should be raised twice, once within
    the context of geology and then again within a biological framework.
    There is merit in both approaches if there is sufficient time. We
    have written the course such that these questions will be presented
    in Session 14 and from a combined geological and biological
    perspective.

**Objective 7.8 Complete the Module examination**.

**Remarks:**

A.  The Module 2 examination included with in the next session
    (session 8) may be distributed at the end of the class to be
    completed at home. If it is distributed, a few minutes should be
    allowed for explanation.

B.  The instructor need not give all questions in the examination, but
    should include questions pertaining to concepts the instructor feels
    might not have been understood by some students. The instructor may
    also prepare a unique examination.

C.  A discussion of examination is included within the next session.

D.  The instructor should also allow students to discuss their team
    assignments.

**Supplemental Considerations:**

The instructor should consider discussing local interacting projects
that had cumulative impacts that exceeded the sum of the individual
impacts.

**References:**

Dalrymple, T., & Benson, M. 1967. *Measurement of Peak Discharge by the
Slope-Area Method,* Chap. A2, Book 3, "Applications of Hydraulics",
USGS. Can be found on the Internet at:

<http://water.usgs.gov/pubs/twri/twri3-a2>

Davidian, J. 1984. *Computation of Water-Surface Profiles in Open
Channels,* Chap. A15, Book 3, "Applications of Hydraulics," USGS. Can be
found on the Internet at:

<http://water.usgs.gov/pubs/twri/twri3-a15>

Barnes, H.H. 1967. "Roughness Characteristics of Natural Channels," USGS
Water Supply Paper 1849, 213p. Can be found on the Internet at:

<http://water.usgs.gov/pubs/wsp/wsp_1849/html/pdf.html>

Arcement & Schneider. 1989. "Guide for Selecting Manning's Roughness
Coefficients for Natural Channels and Flood Plains," USGS Water Supply
Paper 2339. Can be found on the Internet at:

<http://www.fhwa.dot.gov/bridge/wsp2339.pdf>

U.S. Corps of Engineers. 1994. *Methods for predicting n Values for the
Manning Equation,* Manual EM 1110-2-1601, Chapter 5. Can be found on the
Internet at:

<http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-1601/c-5.pdf>

Trieste, D.J. 1995. "Manning's Equation and the Internal Combustion
Engine," U.S. Forest Service, Stream Notes. Can be found on the Internet
at:

<http://stream.fs.fed.us/news/streamnt/apr00/apr00_2.htm>