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Fluvial-12: Mathematical Model for Erodible Channels
Author: Howard H. Chang, Ph.D., P.E.
Presented by:
Amir K. Ilkhanipour, P.E., Sr. Civil Engr.
County of Orange/OC Public Works/Public Works/Flood Control Division
Note: This document is also available as a PowerPoint
presentation.
San Diego State University
Department of Civil and Environmental Engineering
Dr. Chang's research is in the area of water resources engineering pertaining to river hydraulics, sedimentation, and erosion. He is the author of several computer models for channel design and river hydraulics as well as the book, Fluvial Processes in River Engineering, published in 1988 by John Wiley & Sons.
Among them, the FLUVIAL-12 program for river sedimentation was evaluated by the National Academy of Sciences as a national standard for river engineering. The program is now used worldwide by professionals to simulate stream scour for the design of channels and hydraulic structures such as bridges and levees. Among professional activities, he has taught short courses on river and sedimentation engineering, hydrology and hydraulics for flood control facilities, and the use of the HEC-2 and FLUVIAL-12 programs.
AGENDA
PROGRAM SUMMARY FOR FLUVIAL-12
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INTRODUCTION
-
PHYSICAL FOUNDATION OF FLUVIAL PROCESS RESPONSE
-
CHANNEL WIDTH ADJUSTMENTS DURING SCOUR AND FILL
-
ANALYTICAL BASIS OF THE FLUVIAL MODEL
-
WATER ROUTING
- SEDIMENT ROUTING
- Determination of Sediment Discharge
- Upstream Boundary Conditions for Sediment Inflow
- Numerical Solution of Continuity Equation for Sediment
- SIMULATION OF CHANGES IN CHANNEL WIDTH
- Direction of Width Adjustment
- Rate of Width Adjustment
- SIMULATION OF CHANGES IN CHANNEL-BED PROFILE
-
SIMULATION OF CHANGES DUE TO CURVATURE EFFECT
-
TEST AND CALIBRATION OF FLUVIAL-12
-
INPUT DESCRIPTION (Record Cards)
-
OUTPUT DESCRIPTION
-
RUNNING THE MODEL
-
IMPORTANT MESSAGES FOR INPUT PREPARATION
PROGRAM SUMMARY
-
Fluvial-12 is a mathematical model developed by Dr. Howard Chang
for water and sediment routing in natural and man-made channels
-
Changes
simulated by Fluvial-12 include channel bed scour and fill, width
variation, and changes in bed topography induced by curvature effects
-
These
inter-related changes are coupled in the model for each time
step (of hydrographs)
-
While
this model is for erodible channels, physical constraints,
such as bank protection, grade-control structures and bedrock outcroppings
may also be modeled in the program
-
Applications of Fluvial-12 also include
evaluations of general scour at bridge crossings, sediment delivery,
channel responses to sand and gravel mining and channelization
-
Fluvial-12
has been applied to many designs for bank protection and grade-control
structures which must extend below the potential scour depth
-
Fluvial-12
has been tested and calibrated with field data from several rivers
and waterways
-
Fluvial-12 is an "erodible-boundary" model which is different from
an "erodible-bed model", such as HEC-6, in the following ways:
-
An erodible-bed model does not simulate changes in channel width,
and since the profile is closely related to changes in width, the
results may not reliable
-
The change in bed profile in an erodible-bed
model is assumed to be uniform in the erodible zone and all
the points adjust up and down by an equal amount during aggradation
and degradation. This is not true in actuality.
-
An erodible-bed
model does not consider the channel curvature. In reality,
the bed topography is highly non-uniform in a curved channel, especially
during a high flow.
-
The erodible zone needs to be specified
at all cross sections in an erodible-bed model. This means the
model does not provide the extent of erosion in the channel, but
the user has to inform the model about the erodible part of the channel
bed. Fluvial-12 computes the boundary changes with the discharge
and time.
-
Sediment inflow into channel reach needs to be specified
for many other models. This requires the sediment rating curve
which is usually not available for stream channels. In Fluvial-12
model, sediment inflow may be specified and it may also be computed
based on hydraulics of flow at the upstream section at every time
step.
I. INTRODUCTION
-
Alluvial rivers/channels are self-regulatory and adjust their
characteristics in response to any change in the environment. Such
changes distort the natural quasi-equilibrium of a river; therefore,
in the process of restoring the equilibrium, the river will adjust
to the new conditions by changing its slope, roughness, bed-material
size, cross sectional shape, or meandering pattern.
-
Within the existing
constrains, any one of the above characteristics may adjust
as the river seeks to maintain the balance between its ability
to transport sediment and the sediment load providing.
II. PHYSICAL FOUNDATION OF FLUVIAL PROCESS-REPONSE
-
The principles of continuity, flow resistance, sediment transport
and bank stability in relations with time and spatial variations
of channel configurations are used.
-
Generally, width adjustments
occur concurrently with changes in river bed profile, slope,
channel pattern, and roughness. These changes are closely interrelated
and are delicately adjusted to establish or to maintain the
dynamic state of equilibrium.
-
Although under changing discharge,
true equilibrium may never be attained, for a short river reach
of uniform discharge, the conditions for dynamic equilibrium
are:
-
Equal sediment discharge along the channel
-
Uniformity in Power
Expenditure (gQS), where g is unit weight of water-sediment
mixture, Q is discharge and S is energy gradient.
-
A river channel undergoing changes usually does not have a uniform
sediment discharge, but river channel adjustments are such that non-uniformities
in water surface profile and sediment discharges are effectively
reduced. The rate of adjustment is limited by the rate of sediment
movement and subject to rigid constraints such as grade-control structures,
bank protection, bedrock, etc.
-
Because sediment discharge is a direct function of gQS, channel
adjustment in the direction of equal power expenditure also favors
the uniformity in sediment discharge. The sediment discharge in a
reach will match the inflow rate when the equilibrium is reached.
III. CHANNEL WIDTH ADJUSTMENTS DURING SCOUR AND FILL
-
A stream's adjustment in the direction of equal power expenditure,
or straight water surface profile, provides the physical basis for the
modeling of channel
width changes.
-
However, this adjustment does not necessarily mean movement
toward uniformity in channel width. For one thing, the power expenditure
is also affected by channel
roughness and channel bed elevation, in addition to the width.
-
Adjustment
toward uniformity in power expenditure is frequently accomplished
by significant variations in width. Such width variations generally
occur concurrently with streambed scour or fill.
-
The streambed area
undergoing scour has a steeper energy gradient (or water surface
slope) than its adjacent areas. Formation of
a narrower and deeper channel
is effective to reduce the energy gradient due to decreased
boundary resistance and lowered streambed elevation. In addition,
the cross
section develops a somewhat
circular shape, which conserves power as a result of being
closer to the best hydraulic section.
-
On the other hand, the streambed
area undergoing fill has a lower streambed elevation and a flatter
energy gradient. Channel widening
at this area is effective
to steepen its energy gradient due to the increasing boundary
resistance and rising streambed elevation.
IV. ANALYTICAL BASIS OF THE FLUVIAL MODEL
River channel changes simulated by the model include channel
bed scour and fill (or aggradation and degradation), width variation,
and changes caused by curvature effects. Because changes in channel width
and channel bed profile are closely inter related, modeling of erodible
channels must include both changes. The FLUVIAL-12 model has the following five major components:
(1) Water routing, (2) sediment routing, (3) changes in channel width,
(4) changes in channel bed profile, and (5) changes in geometry due to
curvature effect.
[Flow chart showing major steps of
computation for FLUVIAL-12 model]
V. WATER ROUTING
Water routing provides time and spatial variations of the depth,
discharge, energy gradient and other hydraulic parameters in the channel.
The water routing component has the following three major features: (1) Numerical
solution of the continuity and momentum equations for longitudinal flow,
(2) evaluation of flow resistance due to longitudinal and transverse flows,
and (3) upstream and downstream boundary conditions.
[Picture showing continuity and momentum equations]
The longitudinal energy gradient can be evaluated using any valid flow resistance
relationship. If Manning's formula is employed, the roughness coefficient
n must be selected by the modeler. However, if a formula for alluvial bed
roughness (e.g., Brownlie's formula, 1983) is used, the roughness coefficient
is predicted by the formula. Method for evaluating the transverse energy
gradient by Chang (1983) is used in the model. The longitudinal energy
gradient can be evaluated using any valid flow resistance relationship. If
Manning's formula is employed, the roughness coefficient n must be selected by the
modeler. However, if a formula for alluvial bed roughness (e.g., Brownlie's
formula, 1983) is used, the roughness coefficient is predicted by the formula.
Method for evaluating the transverse energy gradient by Chang (1983) is used
in the model.
VI. SEDIMENT ROUTING
The sediment routing component for the FLUVIAL model
has the following major features: (1) Computation of sediment transport
capacity using a suitable formula for the physical conditions, (2) determination
of actual sediment discharge by making corrections for sorting and diffusion,
(3) upstream conditions for sediment inflow, and (4) numerical solution
of the continuity equation for sediment. These features are evaluated
at each time step, and the results are used in determining the changes
in channel configuration. FLUVIAL-12 program divides the bed material
at each section into several, say five, size fractions; the size for
each fraction is represented by its mean diameter. For each size fraction,
sediment transport capacity is first computed using a sediment-transport
formula. The FLUVIAL-12 model provides the choices of six sediment formulas: (1)
Engelund-Hansen formula (1967), (2) Yang's unit stream power formula
(1972, 1986), (3) Graf's formula (1970), (4) Ackers-White formula, (5)
Parker, et al. formula for gravel (1982), and (6) Meyer-Peter and Muller
bedload formula. The actual sediment rate is obtained by considering sediment material
of all size fractions already in the flow as well as the exchange of
sediment load with the bed using the method by Borah et al. (1982). If the stream carries a load in excess of its capacity, it will deposit
the excess material on the bed. In the case of erosion, any size fraction
available for entrainment at the bed surface will be removed by the flow
and added to the sediment already in transport. The rate of sediment
inflow into the study reach is provided by the upstream boundary condition
for sediment. If this rate is known, it may be included as a part of
the input and used in the simulation. Unfortunately, sediment rating data are rarely very reliable or simply
not available. For such cases, it is assumed that the river channel remains
unchanged above the study reach, and sediment inflow rate is computed
at the upstream section at each time step, the same way they are computed
at other cross sections. For this reason, the study reach should extend far enough upstream so
that the channel beyond may be considered basically stable. -
Changes in cross-sectional area, due to longitudinal and
transverse imbalances in sediment discharge, are obtained
based upon numerical solution of continuity equations for
sediment in the respective directions. First, the continuity
equation for sediment in the longitudinal direction is
[Picture of equation]
-
where l is
the porosity of bed material, Ab is the cross sectional area of channel within
some arbitrary frame,
Qs is the bed-material discharge, and qs is the lateral inflow
rate of sediment per unit length. According to this equation,
the time change of cross sectional area ¶Ab/¶t is related to the
longitudinal gradient in sediment discharge ¶Qs/¶s and lateral
sediment inflow qs.
[Diagram simulating changes in channel bed profile depicting aggradation and
degradation.]
VII. SIMULATION OF CHANGES IN CHANNEL WIDTH
The change in cross sectional area DAb obtained in sediment
routing represents the correction for a time increment Dt that needs to
be applied to the bed and banks. With DAb being the total correction, it
is possible for both the bed and banks to have deposition or erosion; it
is also possible to have deposition along the banks but erosion in the
bed and vice versa. The direction of width adjustment is determined following
the stream power approach and the rate of change is based upon bank erodibility
and sediment transport. A reduction in width at a cross section is usually associated with a
decrease in energy gradient for the section, whereas an increase in width
is accompanied by an increase in energy gradient. Formation of a narrower
and deeper channel at the degrading reach decreases its energy gradient
due to reduced boundary resistance. On the other hand, an aggrading reach is usually lower in channel bed
elevation and energy gradient. Widening at the aggrading reach increases
its energy gradient due to increasing boundary resistance. These adjustments in channel
width reduce the variation in energy gradient and total power expenditure
along the river. For a time increment, the amount of width change depends
on the sediment rate, bank configuration and bank erodibility. The slope
of an erodible bank is limited by the angle of repose of the material,
and the rate of width change depends on the rate at which sediment material
is removed or deposited along the banks. An increase in width at a channel section depends on sediment removal
along the banks. The maximum rate of widening occurs when sediment inflow
from the upstream section does not reach the banks of this section while
bank material at this section is being removed. River banks have different degrees of resistance to erosion; therefore, the
bank erodibility factor is used as an index for the erosion of bank material
and the four bank types reflecting the variation in erodibility are classified
as follows:
(1) Non erodible banks (0)
(2) Erosion resistant banks, characterized by highly cohesive
material or substantial vegetation, or both (.2)
(3) Moderately erodible banks
having medium bank
cohesion (.5)
(4) Easily erodible banks with noncohesive material (1) Values of the bank erodibility factor vary from 0 for the first type
to 1 for the last type of banks. The values of 0.2 and 0.5 have been empirically
determined for the second and third types, respectively, based upon test and
calibration of the model using field data from rivers in the western U. S.
VIII. SIMULATION OF CHANGES IN CHANNEL-BED
PROFILE
After the banks are adjusted, the remaining correction for DAb is applied to the bed. In the model, the allocation of scour and fill across a section during each time step is assumed to be a power function of the effective tractive force to - tc, i.e.
[Picture of equation]
[Diagram simulating changes in channel bed profile depicting aggradation and
degradation.] where Dz is the local correction in channel-bed elevation, to (given by gDS) is the local tractive force, tc is the critical tractive force (using Duboys formula), m is an exponent, and y is the horizontal coordinate, and B is the channel width. The value of tc is zero in the case of fill. The m value in the above equation is generally between 0 and 1; it affects the pattern of scour-fill allocation. A small value of m, say 0.1, would mean a fairly uniform distribution of Dz across the section; a larger value, say 1, will give a less uniform distribution of Dz and the local change will vary with the local tractive force or roughly the depth. The value of m is determined at each time step such that the correction in channel bed profile will result in the most rapid movement toward uniformity in power expenditure, or linear water-surface profile, along the channel.
IX. SIMULATION OF CHANGES DUE TO CURVATURE EFFECT
From the dynamic equation for the transverse velocity, an equation governing
the streamwise variation in transverse surface velocity, v, was derived (Chang,
1984). In finite difference form, the change in v over the distance Ds is given
by
[Picture of equation]
where v is the transverse surface velocity along discharge centerline,
U is the average velocity of a cross section, i and i+1 are s coordinate indices,
F1
and F2 are functions of ¦ (friction factor) and depth, and the overbar denotes
averaging over the incremental distance between i and i+1. The above equation
provides the spatial variation in v, from which the mean flow curvature may
be obtained using the transverse velocity profile.
[Diagram of simulation of changes due to curvature effect]
[Picture of Serrano Creek]
[Picture of Serrano Creek]
X. TEST AND CALIBRATION OF FLUVIAL-12
-
Field data are generally used for test and calibration of a model. The required information includes channel configuration before and after the changes, a flow record, and sediment characteristics. Data sets with more complete information are also more useful.
-
The FLUVIAL-12 has undergone test and calibration using many data sets. Such studies together with their respective references are given below:
(1) Test and Calibration Study Using Data from the San Diego River in Southern
California. Chang, H. H., 1982, "Mathematical Model for Erodible Channels"
(2) Test and Calibration Study Using Data from the
Inlet Channel of San Elijo Lagoon in Southern California. Chang,
H. H., and Hill, J. C., 1977, "Minimum Stream Power for Rivers and Deltas,"
(3) Test and Calibration Study Using Data from the
San Dieguito River in Southern California. Chang, H. H., 1984, "Modeling of River Channel Changes"
(4) Test and Calibration Study Using Data from the
San Lorenzo River in Northern California. Chang, H. H., 1985, "Water and Sediment Routing through Curved Channels"
(5) Test and Calibration Study Using Data from San
Juan Creek in Southern California. Chang, H. H., 1987, "Modeling Fluvial Processes in Streams with Gravel Mining,"
(6) Test and Calibration Using the Missouri River
Data in Iowa. Chang, H. H., 1988, "Test and Calibration Study of the FLUVIAL Model Using the Missouri River Data"
(7) Test and Calibration Study Using Data from the
Santa Clara River in Southern California. Chang, H. H. and Stow,
D., 1989, "Mathematical Modeling of Fluvial Sediment Delivery", Journal of Waterway, Port, Coastal, and Ocean Engineering
(8) Test and Calibration Study Using Data from the
Fall River in Colorado. Chang, H. H., 1991, "Simulation of Bed Topography in a Meandering River"
(9) Test and Calibration Study Using Data from the
San Luis Rey River in Southern California. Chang, H. H., 1991, "Computer Simulation of River Channel Changes Induced by Sand Mining"
(10) Test and Calibration Study Using Data from Stony
Creek in Northern California. Chang, H. H., Harris, C., Lindsay,
W., Nakao, S. S., and Kia, R., 1993, "Selecting Sediment Transport Equation for Scour Simulation at Bridge Crossing"
XI. INPUT DESCRIPTION
-
The basic data requirements for a modeling
study include:
(1) topo map of the river reach from the downstream end to the upstream
end of study
(2) digitized data for cross sections in the HEC-2 format with cross-sectional
locations shown on the topo map
(3) flow records or flood hydrographs and their variations along the study
stream reach, it any
(4) size distributions of sediment samples along the study reach
Additional data are required for special features of a study river reach.
-
The HEC-2 format for input data is used in all versions of the FLUVIAL model. Data records for HEC-2 pertaining to cross-sectional geometry (X1 and GR), job title (T1, T2, and T3), and end of job (EJ), are used in the FLUVIAL model.
-
If a HEC-2 data file is available, it is not necessary to delete the unused records except that the information they contain are not used in the computation. For the purpose of water- and sediment-routing, additional data pertaining to sediment characteristics, flood hydrograph, etc., are required and supplied by other data records. Sequential arrangement of data records are given in the following:
| Records |
Description of Record Type |
| T1,T2,T3 |
Title Records* |
| G1 |
General Use Record |
| G2 |
General Use Records for Hydrographs |
| G3 |
General Use Record |
| G4 |
General Use Record for Selected Cross-Sectional Output |
| G5 |
General Use Record |
| G6 |
General Use Record for Selecting Times for Summary Output |
| G7 |
General Use Record for Specifying Erosion Resistant Bed Layer |
| GS |
General Use Records for Initial Sediment Compositions |
| GB |
General Use Records for Time Variation of Base-Level |
| GQ |
General Use Records for Stage-Discharge Relation of Downstream Section |
| GI |
General Use Records for Time Variation of Sediment Inflow |
| X1 |
Cross-Sectional Record* |
| XF |
Record for Specifying Special Features of a Cross Section |
| GR |
Record for Ground Profile of a Cross Section* |
| SB |
Record for Special Bridge Routine* |
| BT |
Record for Bridge Deck* |
| EJ |
End of Job Record* |
-
T1, T2, T3 Records - These three records are title records that are required for each job.
-
G1 Record - This record is required for each job, used to enter the general parameters listed below. This record is placed right after the T1, T2, and T3 records.
-
G2 Records - These records are required for each job, used to define the flow hydrograph(s) in the channel reach. Up to 10 hydrographs, with a maximum of 120 points for each, are currently dimensioned. These records are placed after the G1 record.
-
G3 Record - This record is used to define required and optional river channel features for a job as listed below. This record is placed after the G2 records.
-
G4 Record - This is an optional record used to select cross sections (up to 4) to be included at each summary output. Each cross section is identified by its number which is counted from the downstream section. This record also contains other options; it is placed after the G3 record.
-
G5 Record - This is an optional record used to specify miscellaneous options, including unsteady-flow routing for the job based upon the dynamic wave, bend flow characteristics. If the unsteady flow option is not used, the water-surface profile for each time step is computed using the standard-step method. When the unsteady flow option is used, the downstream water-surface elevation must be specified using the GB records.
-
G6 Record - This is an optional record used to select time points for summary output. Up to 30 time points may be specified.
-
G7 Record - This is an optional record used to specify erosion resistant bed layer, such as a caliche layer, that has a lower rate of erosion.
-
GS Record - At least two GS records are required for each job, used to specify initial bed-material compositions in the channel at the downstream and upstream cross sections. The first GS record is for the downstream section; it should be placed before the first X1 record and after the G4 record, if any. The second GS record is for the upstream section; it should be placed after all cross-sectional data and just before the EJ record. Additional GS records may be inserted between two cross sections within the stream reach, with the total number of GS records not to exceed 15. Each GS record specifies the sediment composition at the cross section located before the record. Sediment composition at each section is represented by five size fractions.
-
GB Records - These optional records are used to define time variation of stage (water-surface elevation) at a cross section. The first set of GB records is placed before all cross section records (X1); it specifies the downstream stage. When the GB option is used, it supersedes other methods for determining the downstream stage.
-
GQ Records - These optional records are used to define stage-discharge relation at the downstream section. The GQ input data may not be used together with the GB records.
-
GI Records - These optional records are used to define time variation of sediment discharge entering the study reach through the upstream cross section. The GI input data, if included, will supersede other methods for determining sediment inflow.
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X1 Record - This record is required for each cross section (175 cross sections can be used for the study reach); it is used to specify the cross-sectional geometry and program options applicable to that cross-section. Cross sections are arranged in sequential order starting from downstream.
-
XF Record - This is an optional record used to specify special features of a cross section.
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GR Record - This record specifies the elevation and station of each point for a digitized cross section; it is required for each X1 record.
-
SB Record - This special bridge record is used to specify data in the special bridge routine. This record is used together with the BT and GR records for bridge hydraulics. This record is placed between cross sections that are upstream and downstream of the bridge.
-
BT Record - This record is used to compute conveyance in the bridge section. The BT data defines the top-of -roadway and the low chord profiles of bridge. The program uses the BT, SB and GR data to distinguish and to compute low flow, orifice flow and weir flow.
-
EJ Record - This record is required following the last cross section for each job. Each group of records beginning with the T1 record is considered as a job.
XII. OUTPUT DESCRIPTION
-
Output of the model includes initial bed-material compositions, time and spatial variations of the water-surface profile, channel width, flow depth, water discharge, velocity, energy gradient, median sediment size, and bed-material discharge. In addition, cross-sectional profiles are printed at different time intervals. Symbols used in the output are generally descriptive, some of them are defined below:
| SECTION |
Cross section |
| TIME |
Time on the hydrograph |
| DT |
Size of the time step or Dt in sec |
| W.S.ELEV |
Water-surface elevation in ft or m |
| WIDTH |
Surface width of channel flow in ft or m |
| DEPTH |
Depth of flow measured from channel invert to water surface in ft or m |
| Q |
Discharge of flow in cfs or cms |
| V |
Mean velocity of a cross-section in fps or mps |
| SLOPE |
Energy gradient |
| D50 |
Median size or d50 of sediment load in mm |
| QS |
Bed-material discharge for all size fractions in cfs or cms |
| FR |
Froude number at a cross section |
| N |
Manning's roughness coefficient |
| SED.YIELD |
Bulk volume or weight of sediment having passed a cross section since beginning
of simulation, in cubic yards or tons. |
| WSEL |
Water-surface elevation, in ft or m |
| Z |
Vertical coordinate (elevation) of a point on channel boundary at a cross-section,
in ft or m |
| Y |
Horizontal coordinate (station) of a point on channel boundary at a cross-section,
in ft or m |
| DZ |
Change in elevation during the current time step, in ft or m |
| TDZ |
Total or accumulated change in elevation, in ft or m |
XIII. RUNNING THE MODEL
-
The executable file of FLUVIAL-12, FL12.EXE, may be run on a Personal Computer or a main-frame computer. To run it on a PC, just type the command FL12. The computer will respond by requesting the input file name and then the output file name.
XIV. IMPORTANT MESSAGES FOR INPUT PREPARATION
-
The computing time of this program is sensitive
to the reach length between two adjacent cross sections, DX. Very
small reach lengths which may result in excessive computing time
should be avoided. In HEC-2, a downstream section and an upstream
section are usually used at each bridge crossing, but these two sections
should be combined into one, if possible, for the FLUVIAL application.
-
The GR points used to define the ground profile should be
selected to provide an accurate definition of the initial profile. As
such, sufficient points should be used for each cross section. Also,
large spacing between adjacent points should be avoided even if there
is no difference in initial elevation. Detailed results rely upon the
adequate number of points used. Use Field 10 of G5 record to insert points
by interpolation.
-
The number of GR points used in defining the ground
profile also affects the computing time because these points are
executed a great number of times for each job. Points that are definitely
outside the flow boundary level should be deleted during initial
editing. However, because of the possibility for bank erosion, there
should be sufficient points to cover any such potential changes.
-
Ineffective flow areas should be specified, either
by excluding them from the GR points or by raising the GR elevations
above the water level.
-
Very fine sediments with a grain size less than 0.0625
mm constitute the wash load and should normally be excluded from the size-fraction
data on GS records.
-
The bank erodibility factor, BEF, in Field 5 of Record
G1, is a control for the rate of channel widening. A small value
slows down widening. This value should be calibrated against field
data
whenever possible.
[Graph of Serrano Creek - Spatial Variations in Sediment Delivery
During 100-Year Time Span.]
[Graph of Serrano Creek - Series of Floods in 100-Year Time Span.]
[Graph of Serrano Creek - Simulated Changes During Flood Series at Section 159+43
- Proposed Plan 2]
[Graph of Serrano Creek - Simulated Changes During Flood Series at Section 179+43
- Proposed Plan 2]
The proposed restorations/improvements reduce the amount of sediment washing down the Creek to about 30,000 tons within a 100-year duration (reduction of about 45%)
[Map of Serrano Creek (Facility Number F19)]
[Photo of proposed location of Slope Protection (loose riprap) Unit U2]
[Photo of Serrano Creek]
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