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Limited Flood Study
FOR
Creek Meadows Subdivision
Section 7, Phase One & Two
AND
Peach Creek South -Tributary 16.4.3
R.S. 1 +51 to R.S. 9+89
March 27, 2015
Prepared For:
Creek Meadow Partners, L.P.
3988 Greens Prairie Road
College Station, TX 77845
Prepared By:
RME Consulting Engineers
Texas Firm Registration No. F-4695
P.O. Box 9253
College Station, TX 77845
RME No. 26-0551
Limited Flood Study
FOR
Creek Meadows Subdivision
Section 7, Phase One & Two
AND
Peach Creek South -Tributary 16.4.3
R.S. 1 +51 to R.S. 9+89
March 27, 2015
Prepared For:
Creek Meadow Partners, L.P.
3988 Greens Prairie Road
College Station, TX 77845
Prepared By:
RME Consulting Engineers
Texas Firm Registration No. F-4695
P.O. Box 9253
College Station, TX 77845
RME No. 26-0551
Limited Flood Study
Creek Meadows Subdivision
Section 7, Phase One & Two
Peach Creek South -Tributary 16.4.3
TABLE OF CONTENTS: PAGE
1.0 General Information .....................................................•........•....................................................................... 1
1. I Scope of Report ....................................................................................................................................... I
I .2 General Location ..................................................................................................................................... I
I .3 Description of Existing & Developing Conditions .................................................................................. 1
1.4 FEMA Information .................................................................................................................................. 3
2.0 Watersheds & Sub-Drainage Basins ...........................................•................................................................. 3
2.1 Peach Creek South -Tributary 16.4.3 ..................................................................................................... 3
3.0 Hydrologic Modeling ..................•.•.......•..............•...............•............................•...••....................................... 3
3.1 SCS -TR20 Formula & Methodology .................................................................................................... 3
3.2 Cumulative Precipitation "P" .................................................................................................................. 5
3.3 SCS Runoff Curve Numbers "CN" ......................................................................................................... 5
3.4 Time of Concentration & Lag .................................................................................................................. 6
4.0 HEC-HMS Computations & Results .............................................................................•...........•.................. 8
4.1 Basin Model Summary ............................................................................................................................ 8
4.2 Meteorological Model Summary ............................................................................................................. 9
4.3 Control Specification Summary .............................................................................................................. 9
4.4 Storm water Runoff Quantities ................................................................................................................. 9
5.0 Hydraulic Modeling ..................................................................................................................•.................. 10
5.1 HEC-RAS Modeling & Methodology ................................................................................................... I 0
5.2 Geometric Data ...................................................................................................................................... 10
5.3 Manning's "N" Coefficient. ................................................................................................................... 11
5.4 Flow Data .............................................................................................................................................. 12
5.5 Plan Data ............................................................................................................................................... 12
6.0 HEC-RAS Computations & Results ............................•.•..•......................................................................... 12
6.1 Existing Floodplain Model .................................................................................................................... 12
6.2 Proposed Floodplain Model. .................................................................................................................. 12
7.0 Certification ...............•.........•................................•....................................................................................... 14
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LIST OF TABLES: PAGE
Section 3.0 -Hydrologic Modeling
Table #1: Rainfall Depth ........................................................................................................................................ 5
Table #2: Composite Curve Number ...................................................................................................................... 6
Table #3: Tu -Overland Sheet Flow ..................................................................................................................... 7
Table #4: T 12 -Shallow and/or Concentrated Flow ................................................................................................ 7
Table #5: Tc Summary ........................................................................................................................................... 7
Table #6: SCS TL Summary ................................................................................................................................... 8
Section 4.0 -HEC-HMS Computations & Results
Table #7: Routed Runoff Values .......................................................................................................................... 10
Section 6.0 -HEC-RAS Computation & Results
Table #8: Existing vs. Proposed Conditions Floodplain Comparison .................................................................. 13
LIST OF FIGURES: PAGE
Section 1.0 -General Information
Figure 1 -Standard Unit Hydrograph ..................................................................................................................... 2
Figure 2 -Routed Unit Hydrograph w/Detention ................................................................................................... 2
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ATTACHMENTS:
Appendix A -General Information
Vicinity Map
DFIRMMap
Appendix B -Watersheds & Sub-Drainage Basins
Limited Flood Study -Hydrologic & HydrauJjc Data
Appendix C -Hydrologic Modeling
GLO Location "P" Parameter Map
GLO Scale "a" Parameter Map
GLO Shape"µ" Parameter Map
Hydrologic Soil Group Data
Appendix D -HEC-HMS Computations & Results
50% Simulation Run
20% Simulation Run
10% Simulation Run
4% Simulation Run
2% Simulation Run
1 % Simulation Run
0.2% Simulation Run
Appendix E -Hydraulic Modeling
GP-0 I: Site Grading & Drainage Plan
Limited Flood Study -Hydrologic & Hydraulic Data
Appendix F -HEC-RAS Computations & Results
HEC-RAS Model Output Data
260-0551 Flood Study.docx Page -iii
Limited Flood Study
Creek Meadows Subdivision
Section 7, Phase One & Two
Peach Creek South -Tributary 16.4.3
1.0 GENERAL INFORMATION
1.1 Scope of Report:
This drainage study' s scope includes the hydrologic and hydraulic evaluation, for
LIMITED floodplain modeling, of Peach Creek South -Tributary 16.4.3 at
current/existing conditions, and the proposed conditions with the channel realignment. All
standard rainfall events were analyzed, however, the design and analyzed frequencies were
the 4% and 1 % rainfall frequencies. This report, or proposed improvements, does not
require procurement through the Federal Emergency Management Agency (FEMA) since
the proposed improvement is unmapped floodplain. However, this report will be utilized
as "better data" for modeling of the proposed channel realignment, to insure no-adverse
impacts (zero-rise) to adjacent upstream landowners. The hydro logic and hydraulic models
were analyzed in accordance with the criteria outlined in the "Unified Stormwater Design
Guidelines" (USDG) manual of the City of College Station (CoCS) and acceptable FEMA
standards.
1.2 General Location:
The unstudied portion of Peach Creek South -Tributary 16.4.3, is located within the
southern portion of Brazos County, Texas (and located within the corporate city limits of
College Station). At this location the tributary generally runs north and south (north being
upstream), within the project area. Ultimately the tributary discharges into the main stem
of Peach Creek and thence into the Navasota River. The subject channel realignment is
generally identified on the Vicinity Map, with its relationship to Bryan/College Station
area, and is also approximately located at latitude 30°31'37.12"N and longitude
96°17'0. l O"W. This exhibit is contained in the "Attachment -Appendix A" section of this
report.
The specific portion of Peach Creek South -Tributary 16.4.3 that will be studied, in this
report, is described by River Station (RS) 1 +51 (downstream limit of Creek Meadows
Sudivision) to RS 9+80. At RS 1 +51 the creek has an approximate flowline of 281 .2 feet
Mean Sea Level (MSL) and an upper flowline of 283.7 feet at RS 9+80. At Bridge 0.245
the flowline is approximately 181 feet. The studied length of creek is approximately 829
feet of river.
1.3 Description of Existing & Developing Conditions:
EXISTING CONDITIONS:
Currently, Peach Creek South -Tributary 16.4.3 has a very low to moderate
developed/urbanized watershed with very little of its rivervine system experiencing
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Creek Meadows Subdivision
Limited Flood Study
RME Consulting Engineers
March 27, 2015
channel modifications and minor disturbances due to upland urbanization. The vast
majority of the tributary watershed is unimproved and rural in nature. The Brazos County
soil maps, as reported on the NRCS Web Soil Survey web-based program, indicates that
the watershed area is primarily comprised of Type C and D soils. These soils generally
consist of clays or silty clay/sand mixtures with low absorption rates.
DEVELOPING CONDITIONS:
As mentioned above the Peach Creek South -Tributary 16.4.3 watershed is for all practical
purposes undeveloped and primarily rural. However, some of the upstream limits of the
watershed has experienced noticeable development. Therefore, as it is typical with
urbanization, the low flow/high frequency rainfall events ( < 2-Yr Storm) generally flow
through the detention facilities, where they exist, unimpeded and thus create greater
occurrences of "bank-full" flows in the creek and therefore destabilize the creek creating
scouring and erosion. Also typical with urbanization the recession limb of the hydro graph
will grow in volume and length as the upstream detention facilities attenuate increased
impervious runoff. This is further illustrated in Figure 1 -"Standard Unit Hydrograph"
and Figure 2-"Routed Hydrograph w/Detention".
WI.OW
HYOflOGRAPH
Time to Peak ,._ ...
P ak
Rec uionUmb
Buetlow
TI me
TimeBaa•
Figure I -Standard Unit Hy drograph
.301--~-+--E~l~--t~~+--~+-~-t-~--t~~t-~-t-~-1 -" I
0 201----lf---o'.
260-0551 Flood Study.docx
12 13 14 15 16
TIME -HOURS
Figure 2 -Routed Hydrograph w/Detention
Page -2
Creek Meadows Subdivision
Limited Flood Study
1.4 FEMA Information:
RME Consulting Engineers
March 27, 2015
Peach Creek South -Tributary 16.4.3 is currently unmapped floodplain as graphically
depicted on the Federal Emergency Management Agency (FEMA)-Flood Insurance Rate
Map (FIRM) Community/Panel number 480083 0325E, with an effective date of May 16,
2012. A portion of the FIRM Panel Map, with the studied limits of Thompson Creek
identified, is illustrated on DFIRM Map and is located in the "Attachment-Appendix A"
portion of this study.
There are no known hydrologic and hydraulic studies performed on this portion of the
tributary.
2.0 WATERSHEDS & DRAINAGE AREAS
2.1 Peach Creek South -Tributary 16.4.3:
As previously discussed the tributary is a secondary drainage system of the Navasota River.
An exhibit of this watershed is provided and is entitled Limited Flood Study -Hydrologic
& Hydraulic Data. This exhibit is contained within the "Attachment-Appendix B" section
of report. As shown, the studied portion of the tributary is located within the upper reach
of the Peach Creek main stem. Details of this secondary drainage basin is as follows:
• Peach Creek South -Tributary 16.4.3 runs generally from south to north and
encompasses an area of approximately 0.512 square-miles of drainage area;
• The watershed of Peach Creek South -Tributary 16.4.3 has a approximate
elevation range of 281' to 358' (MSL);
3.0 HYDROLOGIC MODELING
3.1 SCS -TR 20 Formula and Methodology:
The Natural Resources Conservation Service (NRCS), formerly the Soil Conservation
Service, developed the runoff curve number method as a means of estimating the amount
of rainfall appearing as runoff. The SCS-TR 20 formula calculates the peak discharge and
volumes in a reliable fashion for moderate sized (50 to 400 acres) watersheds.
The SCS unit hydrograph procedure (also known as the TR-20 runoff method) generates a
runoff hydrograph by the following basic steps. (For brevity, this is a simplified
description.) The SCS-TR20 methodology was employed for hydrologic computations of
the Thompson Creek watershed.
1. A rainfall distribution is selected which indicates how the storm depth will be
distributed over time. This is usually a standardized distribution, such as the SCS ~
III storm, and often a standardized duration of 24 hours is selected;
2. The design storm depth is determined from rainfall maps, based on the return period
being modeled. Combined with the rainfall distribution, this specifies the cumulative
rainfall depth at all times during the storm;
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Creek Meadows Subdivision
Limited Flood Study
RME Consulting Engineers
March 27, 2015
3. Based on the Time-of-Concentration (Tc), the storm is divided into "bursts" of equal
duration. For each burst, the SCS runoff equation and the average Curve Number (CN)
are used to determine the portion of that burst that will appear as runoff;
The SCS runoff equation determines the precipitation excess runoff that results from a
given cumulative precipitation:
(P-fa)2
Q= ------------(Q=O if P<la)
(P-Ia)+S
1000
S= ----------10
CN
with Ia= 0.2 s
(P-.2S)2
Q= ------------
(P+. 8S)
where,
Q =Precipitation excess runoff (inches);
P =Cumulative precipitation (inches)-Table C-6 of the USDG-further discussion
in the next sub-section;
Ia= Initial abstraction (inches);
S =Potential maximum retention (inches);
CN =Curve Number -The Antecendent Mositure Condition (AMC) 1 and 3 are
implemented by adjusting the Curve Numbers. The AMC specifies the
moisture level in the ground immediately prior to the storm. Four
conditions are defined:
1 - I Dry
2 -II Normal
3 -III Wet
4 -Frozen or Saturated
It is common policy to use AMC 2 for most design work. Other values
should be used only under special circumstances. AMC 3 is sometimes
used to study wet conditions, such as a spring rainfall event. AMC 3 usually
causes a dramatic increase in runoff, and is not normally used for design
purposes. Unless otherwise specified AMC 3 will be utilized for all
hydrologic computations that employ the SCS-TR 20 method since it will
yield the most conservative flood conditions.
4. A Unit Hydrograph, in conjunction with the Tc, is used to determine how the runoff
from a single burst is distributed over time. The result is a complete runoff hydrograph
for a single burst;
5. Individual hydrographs are added together for all bursts in the storm, yielding the
complete runoff hydro graph for the storm.
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Creek Meadows Subdivision
Limited Flood Study
3.2 Cumulative Precipitation "P":
RME Consulting Engineers
March 27, 2015
As sited earlier the NRCS SCS-TR20 methodology utilizes rainfall depth "P" at various
storm durations for the various storm frequencies that will be analyzed. The information
reported in the SCS TP40 is provided in Table C-6 of the USDG, for Brazos County, TX,
and is summarized as follows in Table #1 -"Rainfall Depth".
However, these distribution maps do not include the 500-year rainfall frequency which is
also required to be studied and modeled by FEMA. Therefore, in order to determine the
rainfall depth "P" for this recurrence interval the Generalized Logistic Distribution
equation, found in the USGS Water Resources Investigations Report 98-4044, will be
utilized and is as follows.
GLO, Xd(t) = p +(a/µ.)* {1 -((1-F) I F]ll} where,
Xct(f) =Precipitation Depth for a give Rainfall Frequency (inches);
~' a, µ=Location, Scale, and Shape Parameters for the GLO Distribution. The
appropriate maps are attached in the "Attachment -Appendix C" section
of report;
F = Annual non-exceedance probability;
TABLE #1
Rainfall Depth
Storm
Duration 2-YR 5-YR 10-YR 25-YR 50-YR 100-YR 500-YR
24-hr 4.50 6.20 7.40 8.40 9.80 11.00 16.17
Where, ~ = 3 .50 a = 0.85 µ = -0.25 F = 0.998
3.3 SCS Runoff Curve Numbers "CN":
The Soils Conservation Service (SCS) runoff Curve Number, for each sub-drainage basin,
was determined by composite method of percentage of land cover to the total sub-drainage
basin. These CNs were estimated from the NRCS, Urban Hydrology for Small
Watersheds, TR 55 (June 1986) by comparison of runoff surface types. Runoff surface
types where determined by field reconnaissance, aerial maps, and utilizing the NRCS Web
Soil Survey web-based program. The associated sectional maps and Hydrologic Soil
Group Data figures and tables which substantiate the selection of these CNs are contained
in the "Attachment -Appendix C" section of the Drainage Study. Calculations for the
composite runoff CNs are illustrated below in Table #2-"Composite Curve Number" and
the resulting Composite CN of 82 will be utilized.
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Creek Meadows Subdivision
Limited Flood Study
Drainage Area l.D.
Peach Creek S. 16.4.3
TABLE#2
Composite Curve Number (CNwtd)
TypeC TypeD
Open Space Pasture
Fair Fair Woods Good Rural
Condition Condition Condition Residential
CN=77 CN=84 CN=77 CN=80
4.5% 2.0% 20.4% 53 .7%
3.4 Time of Concentration & Lag:
RME Consulting Engineers
March 27, 2015
High Density
w/Detention Composite
CN=85 CNwtd
19.4% 82
The Time-of-Concentration (Tc), for each watershed, is used to determine the intensity of
the rainfall event for the corresponding drainage basin. Time-of-Concentration is defined
as the time required for the surface runoff to flow from the most hydraulically remote
point in a watershed to the point of analysis. The Tc is the summation of the flow time for
overland sheet flow plus shallow overland flow and/or concentrated flow to the lower reach
of the watershed. Overland sheet flow is a method developed by Overton and Meadows
and is typically used for flow distances of 300 feet or less. Concentrated flows are
estimated by velocities determined by use of the Manning's Equation. These two types of
flow time calculations are further explained as follows.
Overland Sheet Flow, Tt = {0.0197 (n L)0·8} I {Pi112 s0·4} where,
Tt = travel time (hours);
n =Manning's roughness coefficient -This represents the flow-ability of runoff
across a particular surface type and is a dimensionless coefficient. These
coefficients are obtained from Table C-5 of the USDG;
Pi = ith-year recurrence interval for the 24-hour rainfall depth (inches) -Rainfall
depths are obtained from Table C-6 of the USDG;
S =land slope (feet/foot)
Shallow Concentrated Flow, Tt = D/(60V) where,
Tt =Travel time (minutes);
D =Flow distance (feet);
V = Average velocity of runoff (ft/sec) -These values are determined from
interpolation velocities recorded in Table C-4 of the USDG;
Table #3 -"Tu-Overland Sheet Flow" and Table #4 -"Tt2-Shallow Concentrated Flow"
illustrates the flow travel times for each segment of the sub-drainage basin in respect to the
condition of the flow. The Tc's for each sub-drainage basin where then computed and are
summarized below in Table #5 -"Tc Summary" which also includes the Basin Lag Time
(TL). Basin lag is the time from the center of mass of rainfall excess to the hydro graph
peak. Steep slopes, compact shape, and an efficient drainage network tend to make lag
time short and peaks high. Flat slopes, elongated shape, and an inefficient drainage network
tend to make lag time long and peaks low. The TL can be calculated using the Tc of the
sub-drainage basin with the following equation.
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Creek Meadows Subdivision
Limited Flood Study
RME Consulting Engineers
March 27, 2015
Basin Lag Time, TL= (0.60) Tc where,
Tc = Time of Concentration (minutes);
TABLE#3
Ttl -Overland Sheet Flow
Overland Average
Flow Land Travel
Drainage Area Manning's Distance Pi Slope Time
I.D. "n" (L) (100-vear) (S) (Tc)
PC 0.03 150 11.0 0.0075 0.050
TABLE#4
Tt2 -Shallow and/or Concentrated Flow
Shallow Creek Flow (1)
Flow Average Flow Average
Drainage Area Distance Velocity Distance Velocity
I.D. (DI) (VI) (D2) (V2)
PC 730 2.2 760 4.1
TABLE#4
Tt2 -Shallow and/or Concentrated Flow
Branch Flow (1) Branch Flow (2)
Flow Average Flow Average
Drainage Area Distance Velocity Distance Velocity
I.D. (D2) (V2) (D2) (V2)
PC 4126 3.8 5190 3.4
1) Shallow Flow average velocities were estimated using the following
equation V = 16.13 5 *S05 where,
V =fj:>s
S = average slope
Assumptions -Manning's N = 0.05 & Hydraulic radius = 0.4 ft
Time
(Tc)
8.62
Time
(Tc)
43 .54
2) Channel Flow average velocities were estimated using the following equation V
= 20.328*S05 where,
V = fj:>s
S = average slope
Assumptions -Manning's N = 0.025 & Hydraulic radius = 0.2 ft
3) Creek Flow average velocities were approximated from estimated 25-
year flows inputted into the HEC-RAS model;
TABLE#5
Tc SUMMARY
Combined Drainage LagTime
Drainage Area Overland Concentrated Basin "Tc" (0.6*Tc)
I.D. Flow Time Flow Time (min) (min)
PC 0.050 52.16 55.2 33 .1
An alternative method of determining the Basin Lag Time (TL) is by the SCS Lag Time
Equation which is as follows. Using this equation the TL'S for each sub-drainage basin
were then computed and are summarized below in Table #6-"SCS TL Summary".
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Creek Meadows Subdivision
Limited Flood Study
RME Consulting Engineers
March 27, 2015
SCS Lag Time, TL= Lo.s [(S+t)0•7 I1900*Yo5]
TL= basin lag time (hours);
L =hydraulic length of the watershed (feet);
Y =watershed slope(%);
where,
S =maximum retention in the watershed (in); where,
S = (1000/CN)-10
CN = SCS composite curve number for the sub-drainage basin;
TABLE#6
SCS TL -Summary
Basin scs
Hydraulic Watershed Curve Basin Lag
Drainage Length Slope Number Retention Time
Area l.D. (L) (Y) (CN) (S) (min)
Thompson Creek 8,565 0.80 82 2.20 111.5
Note: The hydraulic length for each drainage basin was reduced by
15% to illustrate a "valley" length in lieu of the actual creek flow line
length;
As illustrated the SCS equation TL'S yielded flow times that were near the magnitude of
two-times greater than those calculated by segment analysis. Therefore, since the Basin
Lag Times, generated by the segment analysis equations, would generate more
conservative hydrologic output/runoff the TL = 33.1 minutes will be utilized.
4.0 HEC-HMS COMPUTATIONS & RESULTS
All runoff calculations for this Drainage Study will utilize the Hydrologic Modeling System
(HEC-HMS) program. This program is a product of the US Army Corps of Engineers'
(USACE) research and development program, and is produced by the Hydrologic Engineering
Center (HEC). The program simulates precipitation-runoff and routing processes, both natural
and controlled. The program is the successor to and replacement for the Flood Hydrograph
Package HEC-1 DOS based program.
4.1 Basin Model Summary:
The first step in the hydrologic program process of the HEC-HMS program was to create
a "skeleton" or schematic layout of the Peach Creek South-Tributary 16.4.3 watershed
with its sub-drainage basins as described in Section 2.1. The schematic layout will
generally consist of three (3) basic components (Sub-basins, Reaches, and Junctions).
The modeling of the Thompson Creek watershed, for the purposes of this report, is a
simplified approach therefore there will only be "Sub-Basin" component of the HEC-
HMS model. The assumptions for this is identified and summarized as follows.
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Limited Flood Study
SUB-BASINS:
RME Consulting Engineers
March 27, 2015
The Thompson Creek watershed is outlined in Section 2.3 of this report. Losses utilized
for the drainage area is computed and reported in Section 3 .3 and the transform component
of Time Lag (TL) is illustrated and explained in Section 3.4. Other basic modeling
methods and assumptions are as follows:
• Loss Method: SCS Curve Number;
• Transform Method: SCS Unit Hydrograph;
• Initial Abstraction = 0
• Impervious = 0%
• Transform Graphing Type: Standard;
REACHES:
There are no reaches for this HEC-HMS model.
JUNCTIONS:
There are no junctions for this HEC-HMS model.
4.2 Meteorological Model Summary:
The Meteorological Model portion of the HEC-HMS program is the component that
"controls" the rainfall aspect of the watershed simulation. With the SCS Storm method
the rainfall depth data reported in Table #1 will be utilized. Other standard assumptions
for meteorological conditions are as summarized below.
• Precipitation: SCS Storm;
• Duration: 24 hours;
• Storm Type: Type III;
4.3 Control Specification Summary:
The Control Specification aspect of the HEC-HMS program is simply the input data for
the length that the program will simulate the rainfall event. Therefore the "start time" to
"end time" will be the equivalent of the storm duration reported in Section 4.2.
As reported in the Technical Reference Manual for the HEC-HMS program the
computational interval, Lit, must be less than 29% of TL so that adequate definition of the
ordinates on the rising limb of the SCS Unit Hydrograph can be generated (see Figure 1).
Therefore, in this case a 6 minute time interval was selected.
Lit= 29%TL = 0.29 * 33.1 min = 9.6 minutes
where, TL is from Table #5
4.4 Stormwater Runoff Quantities:
Stormwater runoff quantities were calculated, using the SCS-TC 20 formula with the
assistance of the Hydrologic stormwater modeling program HEC-HMS. Runoff values for
the analyzed studied points (Junctions) are summarized below in Table #9 -"Routed
Runoff Quantities". 2-YR, 5-YR, 10-YR, 25-YR, 50-YR, 100-YR & 500-YR Simulation
Runs and their supporting data/hydrographs are contained "Attachment -Appendix D"
section of the report.
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Limited Flood Study
TABLE#7
ROUTED RUNOFF
QUANTITIES
Study Pomt of
Rainfall Peach Creek South
Event Trib 16.4.3
50% 422
20% 666
10% 840
4% 985
2% 1, 188
1% 1,362
0.20% 2,104
RME Consulting Engineers
March 27, 2015
CONSIDERATION & CALIBRATION: The studied portion of Peach Creek South -
Tributary 16.4.3 has not been "officially" studied in the past and therefore there is no
comparable data for hydrologic output information. Also this creek has no historical
measured data (rainfall and/or timing information) therefore very little, in the means of
program calibration, can be accomplished. However, the above reported runoff rates do
seem reasonable for this watershed and will be utilized for this Limited Flood Study.
5.0 HYDRAULIC MODELING
5.1 HEC-RAS Modeling & Methodology
The computation of water surface elevations along a stream/creek is called the hydraulic
analysis. These water surface elevations are computed using an iterative application of the
Manning's Equation called the standard step. The accepted and well-used computer
program, for this type of computation, is the HEC-2 and more recently its modem version,
HEC-RAS. HEC-RAS uses the same theoretical computational methods as HEC-2, but
this program is a Windows based software, therefore providing a more user-friendly
approach. Since the HEC-RAS program is a more flexible tool, offers more powerful
modeling options, and no precedence has been established for this section of Thompson
Creek, HEC-RAS will be utilized.
The hydraulic analysis is divided into the four (4) following master components
(Geometric Data, Manning's "N", Flow Data, and Plan Data) which are detailed below.
5.2 Geometric Data
The geometry data, for HEC-RAS, contains all of the geometric data for the river system
being analyzed. The geometric data consist of: cross section information; hydraulic
structures data (e.g., bridges and culverts); roughness coefficients; and modeling approach
information.
There will be two (2) geometric model contained within this hydraulic study. They are
labeled as stated and described for the following purposes.
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Creek Meadows Subdivision
Limited Flood Study
RME Consulting Engineers
March 27, 2015
Existing Conditions -This model contains geometric data for Peach Creek South -
Tributary 16.4.3 at existing/current conditions. Data used to develop this geometrical
layout and cross-sections was a combination of the following information. This
geometrical data is further illustrated on the GP-01: Site Grading & Drainage Plan which
is contained "Attachment-Appendix E" section of the report.
(1) Within the creek banks(+/-200' either side of the bank) an on-the-ground survey data
was performed by Vannoy Surveying at the proposed channel realignment location.
This on-the-ground survey utilized CoCS Monuments (NA VD 29) for both horizontal
and vertical control;
(2) Cross-sectional data for overland areas utilized the CoCS topographical maps. This
data was considered accurate since very little development has occurred within the
overland flow areas of Peach Creek South-Tributary 16.4.3;
Proposed Conditions -This model contains geometric data for Peach Creek South -
Tributary 16.4.3 at existing/current conditions and integrates the proposed channel
realignment information. Data used to develop this geometrical layout and cross-sections
will be compared to the existing conditions Water Surface Elevations (WSE) to measure
impacts of the proposed improvements. This geometrical data is further illustrated on the
GP-01: Site & Grading & Drainage Plan which is contained "Attachment -Appendix E"
section of the report.
5.3 Manning's "N" Coefficient
Roughness coefficients are one of the main variables used in calibrating a hydraulic model.
Generally, for a free flowing stream, creek or river, roughness decreases with increased
stage and flow. However, if the banks of a river are rougher than the channel bottom, due
to trees and brush, then the composite ''N" value will increase with increased stage.
Sediment and debris can also play an important role in changing the roughness. More
sediment and debris in a river will require the modeler to use higher ''N" values in order to
match observed water surfaces.
Manning's ''N"s for the described geometrical scenarios in Section 5.2 was made from
field reconnaissance along the studied portion of Peach Creek South -Tributary 16.4.3 .
Roughness coefficients were determined by comparison with accepted standards and the
current FIS. Typical values for stream over-bank, along natural channels, range from 0.07
to 0.09 (0.060-0.090 FIS), and typical values for natural stream channels range from 0.03
to 0.06 (0.014 -0.065 FIS). The U.S. Geological Survey has published a book, dated 1987,
and entitled "Roughness Characteristics of Natural Channels".
Field reconnaissance was made during the spring of 2015 (high growth season).
Vegetation was at medium to high levels, therefore, the ''N"s utilized are considered to be
conservative for flow resistance levels. These roughness coefficients should yield
conservative Water Surface Profiles (WSP).
260-0551 Flood Study.docx Page-11
Creek Meadows Subdivision
Limited Flood Study
5.4 Flow Data
RME Consulting Engineers
March 27, 2015
Flow data for the HEC-RAS modeling will utilize the hydrologic runoff values reported in
Section 4.4 (Table #7) and the upstream boundary cross-section stated in that table. Flow
data was entered into the HEC-RAS model as a "steady state" flow condition.
Also in the "Flow Data" component of HEC-RAS is the inputting of the starting Water
Surface Elevation (WSE). This starting WSE can be defined by several different methods.
When the hydraulic model is not starting at a previously studied location and the starting
WSE is unknown, then the most common method of establishing a starting WSE is by the
Normal Depth method and equation. Otherwise it is best utilize a starting WSE. Since the
FIS has calculated WSE for Peach Creek South -Tributary 16.4.3, immediately
downstream, this information will be utilized.
5.5 Plan Data
A "Plan" in HEC-RAS is the combination of the various Geometric Data and Flow Data to
develop the desired WSPs. For this hydraulic analysis, there were two (2) Plans created
for computation, review, and comparison. These Plans are as identified below.
EX-FP -Floodplain model with existing geometrical data and flow schemes generated
with the methods described in Section 4.0 ofthis report for all analyzed rainfall
events;
PR-FP -Floodplain model with proposed geometrical data and flow schemes generated
with the methods described in Section 4.0 ofthis report for all analyzed rainfall
events. This floodplain model will include the proposed channel realignment;
6.0 HEC-RAS COMPUTATIONS & RESULTS
6.1 Existing Floodplain Model
This section will contain the hydraulic modeling results for the first "Plan" that was listed
under Section 5.5 of this report. This Plan is reiterated and more fully described below.
EX-FP -This hydraulic floodplain model utilized the "original" existing geometrical data
and flow schemes generated with the methods described in Section 4.0 of this report for all
analyzed rainfall events.
The hydraulic model consisted of "original" existing geometric conditions as described in
Section 5.2, flow data as summarized in Section 5.4, and special considerations needed for
the generation of the hydraulic models.
6.2 Proposed Floodplain Model
This section will contain the hydraulic modeling results for the second "Plan" that was
listed under Section 5.5 of this report. This Plan is reiterated and more fully described
below.
260-0551 Flood Study.docx Page -12
Creek Meadows Subdivision
Limited Flood Study
RME Consulting Engineers
March 27, 2015
PR-FP -This hydraulic floodplain model utilized the "original" existing geometrical data,
where applicable, and flow schemes generated with the methods described in Section 4.0
of this report for all analyzed rainfall events. Also the proposed channel realignment is
modeled in the geometric data. This channel cross-section is further described below and
is also illustrated on GP-01: Site & Grading & Drainage Plan which is contained
"Attachment-Appendix F" section of the report.
The hydraulic model consisted of"proposed" geometric conditions as described in Section
5.2, flow data as summarized in Section 5.4, and special considerations needed for the
generation of the hydraulic models. These special considerations are briefly summarized
as follows.
SPECIAL CONSIDERATIONS:
1. At RS 3+86 & RS 5+24 the proposed channel realignment cross-section and Manning's
"N" will be integrated into the creek data;
2. At RS 3+86 & RS 5+24 proposed fill will be placed to elevate the proposed lots above
the 100-year floodplain elevation;
3. RS 3+86 & RS 5+24, the flow conveyed by the tributary will experience a noticeable
change in flow regime due to the proposed fill. Therefore the contraction and
expansion coefficients were changed from typical values of 0.1 and 0.3 to 0.3 and 0.5,
respectively;
Based on the above mentioned geometric, flow data, and special considerations, the
following results are reported for the "Existing Conditions" and "Proposed Conditions"
floodplain hydraulic model. This data is summarized in Table #8 -"Existing vs. Proposed
Conditions Floodplain Comparison". Output data for additional analyzed rainfall events
are contained in Existing & Proposed Conditions HEC-RAS Model Output Data which is
in the "Attachment -Appendix F" section of the report.
TABLE#8
EXISTING vs. PROPOSED
CONDITIONS FLOODPLAIN
Existing Proposed
River Station 1% Freq. 1% Freq. Di ff.
(RS) (ft) (ft) (ft)
151 288.18 288.18 0.00
386 288.75 288.69 -0.06
524 288.65 288.17 -0.48
755 290.45 290.25 -0.20
989 290.94 290.82 -0.12
As illustrated in Table #8 the Vehicular Bridge No. 1 improvements have an impact on the
floodplain elevations by less than two-inches. Therefore this will be considered a
negligible influence.
260-0551 Flood Study.docx Page -13
Creek Meadows Subdivision
Limited Flood Study
7.0 CERTIFICATION
260-0551 Flood Study.docx
Rabon Metcalf, P .E.
State of Texas P.E. No. 88583
RME Consulting Engineers
March 27, 2015
Page -14
Appendix A
GENERAL INFORMATION
CREEK MEADOWS:
SECTION 7, PH. 1
VICINITY MAP
NOT TO SCALE
N
NOTTO
SCALE
Appendix B
WATERSHEDS & SUB-DRAINAGE BASINS
Appendix C
HYDROLOGIC MODELING
GLO Location "13" Parameter Map
U> ~ co~ ~ §
(.) 0 I-(.)
GLO Scale "a" Parameter Map
GLO Shape "µ" Parameter Map
»' 32'46"N
»' 31'21"N
759200
:;;::
&l
~ N
A
Hydrologic Soil Group-Brazos County, Texas
(Peach Creek South Trib 16.4.3)
759500 7fi0400
Map Scale: 1:12,700 if prinlEd on A portrait (8.5" x 11") sheet ------<=====-------------===========Meiers 0 150 300 600 900 -------======-------------============f€ft 0 500 1000 2000 3000
Map projection: Web Mertator Comerandin<tes: WGS84 Edge tics: UTM Zone 14N WGS84
USDA Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
760700 761000
3/3/2015
Page 1 of4
»' 32'46"N
Hydrologic Soil Group-Brazos County, Texas
(Peach Creek South Trib 16.4.3)
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
D Area of Interest (AOI)
Soils
Soll Rating Polygons
D A
D AID
DB
D B/D
D c
D C/D
D D
D Not rated or not available
Soll Rating Lines
A
AID
,_,. B
,_,. B/D
c
CID
D
-; Not rated or not available
Soll Rating Points
A
AID
• B
• B/D
Natural Resources
Conservation Service
c
CID
D
C Not rated or not available
Water Features
Streams and Canals
Transportation
H-t Rails
""""' Interstate Highways
f/lllWllJ US Routes
Major Roads
Local Roads
Background
• Aerial Photography
Web Soil Survey
National Cooperative Soil Survey
The soil surveys that comprise your AOI were mapped at 1 :20,000.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more accurate
calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as of
the version date(s) listed below.
Soil Survey Area:
Survey Area Data:
Brazos County, Texas
Version 12, Sep 29, 2014
Soil map units are labeled (as space allows) for map scales 1 :50,000
or larger.
Date(s) aerial images were photographed: Jan 27, 2011-May
16,2011
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor shifting
of map unit boundaries may be evident.
3/3/2015
Page 2 of 4
Hydrologic Soil Group-Brazos County, Texas
Hydrologic Soil Group
Hydrologic Soll Group-Summary by Map Unit-Brazos County, Texas (TX041)
Map unit symbol Map unit name Rating
BwC Burlewash fine sandy D
loam, 1 to 5 percent
slopes
ChC Chazos loamy fine sand, c
1 to 5 percent slopes
GrC Gredge fine sandy loam, D
1 to 5 percent slopes
KrD Koether-Rock outcrop D
complex, 3 to 12
percent slopes
MaA Mabank loam, 0 to 1 D
percent slopes
SkB Shiro loamy fine sand, 1 D
to 3 percent slopes
SnB Singleton fine sandy D
loam, 1 to 3 percent
slopes
TaA Tabor fine sandy loam, 0 D
to 2 percent slopes
Totals for Area of Interest
USDA Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
Acres inAOI
10.8
13.7
31 .3
2.9
13.8
3.1
210.9
21 .0
307.4
Peach Creek South Trib 16.4.3
Percent of AOI
3.5%
4.5%
10.2%
0.9%
4.5%
1.0%
68.6%
6.8%
100.0%
3/3/2015
Page 3 of 4
Hydrologic Soil Group-Brazos County, Texas Peach Creek South Trib 16.4.3
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive precipitation
from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (ND, B/D, and CID). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly
wet. These consist mainly of deep, well drained to excessively drained sands or
gravelly sands. These soils have a high rate of water transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well drained
soils that have moderately fine texture to moderately coarse texture. These soils
have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of water
transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay layer
at or near the surface, and soils that are shallow over nearly impervious material.
These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (ND, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in their
natural condition are in group D are assigned to dual classes.
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
USDA Natural Resources
aiii Conservation Service
Web Soil Survey
National Cooperative Soil Survey
3/3/2015
Page 4 of 4
Appendix D
HEC-HMS COMPUTATIONS & RESULTS
Project: 0551 HEC-HMS-R1 Simulation Run: 2YR
Start of Run: 01Jan2015, 12:00 Basin Model: Peach Creek S
End of Run: 02Jan2015, 12:06 Meteorologic Model: 2-YR
Compute Time:03Mar2015, 21 :54:15 Control Specifications:Peach Creek
Hydrologic Drainage Area Peak Dischar~ eTime of Peak Volume
Element (Ml2) (CFS) (IN)
PC 0.512 422.5 02Jan2015, 00:36 2.61
Subbasin "PC" Results for Run "2YR"
0.00 ,-----:-----:---111111!111---
a 0.20 --1
~ 0.30
0.40---~~---~~~~~~~~~~~~~~~~~~~~
400 -1 -E-: 300 ......... JQ 200 + + -(.) "-"
~ 100 0 L-----1---LL 0
--r--f
12:00 15:00 18:00
01Jan2015
21:00 00:00
I
03:00 06:00 09:00 12:00
02Jan2015
Run :2YR Element:PC Result:Precipitation
Run:2YR Element:PC Result:Precipitation Loss
--Run:2YR Element:PC Result:Outflow
Run:2YR Element:PC Result:Baseflow
Project: 0551 HEC-HMS-R1 Simulation Run: 5 YR
Start of Run : 01Jan2015, 12:00 Basin Model: Peach Creek S
End of Run: 02Jan2015, 12:06 Meteorologic Model: 5-YR
Compute Time:03Mar2015, 21 :54:33 Control Specifications:Peach Creek
Hydrologic Drainage Area Peak Discharg eTime of Peak Volume
Element (Ml2) (CFS) (IN)
PC 0.512 666.1 02Jan2015, 00:36 4.14
Subbasin "PC" Results for Run "5 YR"
0.0 I
......... -+. c -0.2 ..c -a. 0.4 Q)
0
600 --i---t---+----
~ 400 --F-r
~ 200 -I I ~-
~ o.l--_JL-_ _j. ____ ~::::::::==-l--_JL-=:=:::::!:::::====~=====;1
12:00 15:00 18:00 21 :00 00:00 03:00 06:00
01Jan2015 I
--Run:5 YR Element:PC Result:Precipitation
--Run:5 YR Element:PC Result:Precipitation Loss
Run :5 YR Element:PC Result:Outflow
Run :5 YR Element:PC Result:Baseflow
09:00 12:00
02Jan2015
Project: 0551HEC-HMS-R1 Simulation Run: 10 YR
Start of Run: 01Jan2015, 12:00 Basin Model: Peach Creek S
End of Run : 02Jan2015, 12:06 Meteorologic Model: 10-YR
Compute Time:03Mar2015, 21:49:50 Control Specifications:Peach Creek
Hydrologic Drainage Area Peak Dischar~ eTime of Peak Volume
Element (Ml2) (CFS) (IN)
PC 0.512 840.1 02Jan2015, 00:36 5.25
Subbasin "PC" Results for Run "10 YR"
0.0.------.----:---,.....-
~ -
0. 0.4 -------------------------.----......---,
ID _,__ -+---~~----+
0 0.6-
-(/)
800
600
't5 400 -~ 200 0
LL 0
-
-
-----<
I
--,____ -
-1
I I
A ; I\ J
I \ ~
_ _:
l
k_ ~ -,__.
I I
I
I I I I I
12:00 15:00 18:00 21 :00 00:00 03:00 06:00 09:00 12:00
01Jan2015 I 02Jan2015
Run: 10 YR Element: PC Result: Precipitation
Run:10 YR Element:PC Result:Precipitation Loss
Run:10 YR Element:PC Result:Outflow
Run:10 YR Element:PC Result:Baseflow
Project: 0551 HEC-HMS-R1 Simulation Run: 25 YR
Start of Run: 01Jan2015, 12:00 Basin Model: Peach Creek S
End of Run: 02Jan2015, 12:06 Meteorologic Model: 25-YR
Compute Time:03Mar2015, 21 :54:30 Control Specifications:Peach Creek
Hydro logic Drainage Area Peak Dischar~ eTime of Peak Volume
Element (Ml2) (CFS) (IN)
PC 0.512 985.4 02Jan2015, 00:36 6.20
0.0
.........
c: 0.2 -£ 0.4 a. Q)
0 0.6
:§'
(.) -
0.8
1,000
800
600
400
200
-0
-------
---
--
-
Subbasin "PC" Results for Run "25 YR"
.
I
I
I --1 I -----t---r--- -=----1
f-I
I I I
Pr-I
I -+----\
~ -·~ -I
--+-~ "'----
I I I I I I
12:00 15:00 18:00 21 :00 00:00 03:00 06:00 09:00 12:00
01Jan2015 I 02Jan2015
--Run:25 YR Element:PC Result:Precipitation
--Run:25 YR Element:PC Result:Precipitation Loss
--Run:25 YR Element:PC Result:Outflow
Run:25 YR Element:PC Result:Baseflow
Project: 0551 HEC-HMS-R1 Simulation Run: 50 YR
Start of Run : 01Jan2015, 12:00 Basin Model: Peach Creek S
End of Run: 02Jan2015, 12:06 Meteorologic Model: 50-YR
Compute Time:03Mar2015, 21:54:37 Control Specifications:Peach Creek
Hydrologic Drainage Area Peak Dischar~ ~Time of Peak Volume
Element (Ml2) (CFS) (IN)
PC 0.512 1188.4 02Jan2015, 00:36 7.53
-c: ..._..
.I::. -Q.
<l> 0
0.0
0.2
0.4
0.6
0.8
1,200
800
400
0
-
-
--
Subbasin "PC" Results for Run "50 YR"
-----
I
--~~\] ---------.... -~ -t----
I I I I I I I
12:00 15:00 18:00 21 :00 00:00 03:00 06:00 09 :00 12:00
01Jan2015 I 02Jan2015
--Run:50 YR Element:PC Result:Precipitation
Run:50 YR Element:PC Result:Precipitation Loss
Run :50 YR Element:PC Result:Outflow
Run :50 YR Element:PC Result:Baseflow
Project: 0551 HEC-HMS-R1 Simulation Run: 100 YR
Start of Run: 01Jan2015, 12:00
End of Run: 02Jan2015, 12:06
Compute Time:03Mar2015, 21 :56:12
Basin Model: Peach Creek S
Meteorologic Model: 100-YR
Control Specifications:Peach Creek
Hydrologic Drainage Area Peak Discharg eTime of Peak Volume
Element (Ml2) (CFS) (IN)
PC 0.512 1362.0 02Jan2015, 00:36 8.68
-c -..c. ... 0.
Q)
0
Subbasin "PC" Results for Run "100 YR"
0.0 -
0.3 I
I -
0.6 ---
0.9
1,200 _, __________ ,__ __
800
400~---+---+---l---
o
,____
--.
I
I
!
- + -
""
12:00 15:00 18:00 21 :00 00:00 03:00 06:00 09:00 12:00
01Jan2015 I 02Jan2015
--Run:100 YR Element:PC Result:Precipitation
--Run:100 YR Element:PC Result:Precipitation Loss
--Run:100 YR Element:PC Result:Outflow
Run: 100 YR Element: PC Result: Baseflow
Project: 0551HEC-HMS-R1 Simulation Run: 500 YR
Start of Run : 01Jan2015, 12:00
End of Run: 02Jan2015, 12:06
Compute Time:03Mar2015, 21 :54:41
Basin Model: Peach Creek S
Meteorologic Model: 500-YR
Control Specifications:Peach Creek
Hydro logic Drainage Area Peak Dischar~ 1emme of Peak Volume
Element (Ml2) (CFS) (IN)
PC 0.512 2103.6 02Jan2015, 00:36 13.71
Subbasin "PC" Results for Run "500 YR"
0.0 -c 0.4 -..c. ...... 0.8 c..
Q)
0 1.2
2,000
1,500 ~ u 1,000 -
~ --------
-··-r--
500-1----t---+---
o -!---~~--..-:;====:::::::=----T--~--!.-===~::::::==;:::=====;!
12:00 15:00
01Jan2015
18:00 21 :00 00:00 03:00 06:00 09:00 12 :00
I 02Jan2015
Run:500 YR Element:PC Result:Precipitation
Run:500 YR Element:PC Result:Precipitation Loss
Run:500 YR Element:PC Result:Outflow
- - -Run:500 YR Element: PC Result:Baseflow
Appendix E
HYDRAULIC MODELING
Appendix F
HEC-RAS COMPUTATIONS & RESULTS
HEC-RAS Plan: EX-FP1 River: Peach Creek Reach: PC
Reach River Sta Profile a Total Min Ch El W.S. Elev CritW.S. E.G. Elev E.G. Slope Vet Chnl Flow Area Top Width Froude# Chi
(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)
PC 151 50% 422.00 281 .20 286.29 285.33 286.47 0.003001 4.06 140.31 86.88 0.36
PC 151 20% 666.00 281 .20 286.95 285.92 287.16 0.003003 4.49 206.36 112.10 0.37
PC 151 10% 840.00 281 .20 287.32 286.20 287.54 0.003003 4.73 250.84 126.29 0.37
PC 151 4% 985.00 281 .20 287.60 286.43 287.83 0.003001 4.90 287.53 155.71 0.37
PC 151 2% 1188.00 281 .20 287.92 286.69 288.15 0.003000 5.09 349.51 231 .84 0.38
PC 151 1% 1362.00 281 .20 288.18 286.87 288.41 0.003001 5.25 420.13 314.79 0.38
PC 151 0.2% 2104.00 281.20 288.97 287.73 289.18 0.003003 5.71 818.08 689.37 0.39
PC 386 50% 422.00 281 .90 286.85 286.89 0.001174 2.27 336.30 232.64 0.23
PC 386 20% 666.00 281 .90 287.51 287.56 0.001025 2.42 496.52 254.04 0.22
PC 386 10% 840.00 281.90 287.89 287.94 0.000999 2.55 595.29 266.37 0.22
PC 386 4% 985.00 281 .90 288.17 288.22 0.001002 2.66 672.85 295.13 0.22
PC 386 2% 1188.00 281 .90 288.49 288.56 0.001045 2.86 777.03 343.72 0.23
PC 386 1% 1362.00 281 .90 288.75 288.82 0.001078 3.00 869.75 381.80 0.24
PC 386 0.2% 2104.00 281.90 289.54 289.64 0.001323 3.67 1216.55 499.12 0.27
PC 524 50% 422.00 282.30 286.87 287.33 0.005918 5.51 130.83 97.46 0.53
PC 524 20% 666.00 282.30 287.25 286.63 288.13 0.010012 7.70 173.35 130.43 0.70
PC 524 10% 840.00 282.30 287.38 287.26 288.66 0.013969 9.30 191 .20 143.72 0.83
PC 524 4% 985.00 282.30 287.88 287.88 289.06 0.011539 9.16 276.63 195.15 0.77
PC 524 2% 1188.00 282.30 288.35 288.35 289.49 0.010423 9.31 377.50 236.53 0.74
PC 524 1% 1362.00 282.30 288.65 288.65 289.79 0.010152 9.56 452.06 261 .82 0.74
PC 524 0.2% 2104.00 282.30 289.63 289.63 290.80 0.009702 10.49 755.02 366.83 0.75
PC 755 50% 422.00 283.00 287.85 288.00 0.001608 3.17 191.19 101.61 0.29
PC 755 20% 666.00 283.00 288.79 289.01 0.001778 3.87 320.60 180.07 0.31
PC 755 10% 840.00 283.00 289.40 289.63 0.001709 4.11 445.54 235.40 0.31
PC 755 4% 985.00 283.00 289.75 290.00 0.001764 4.35 533.38 267.54 0.32
PC 755 2% 1188.00 283.00 290.14 290.42 0.001866 4.68 647.54 305.05 0.33
PC 755 1% 1362.00 283.00 290.45 290.75 0.001940 4.93 744.07 334.48 0.34
PC 755 0.2% 2104.00 283.00 291.44 291 .78 0.002068 5.61 1117.70 391.83 0.36
PC 989 50% 422.00 283.70 288.31 288.66 0.004624 4.76 119.26 86.46 0.47
PC 989 20% 666.00 283.70 289.26 289.69 0.004313 5.46 239.02 165.04 0.47
PC 989 10% 840.00 283.70 289.83 290.27 0.003912 5.66 347.10 212.30 0.46
PC 989 4% 985.00 283.70 290.19 290.64 0.003844 5.89 429.12 246.38 0.46
PC 989 2% 1188.00 283.70 290.62 291 .08 0.003802 6.18 542.94 291 .07 0.46
PC 989 1% 1362.00 283.70 290.94 291.41 0.003744 6.36 642.02 325.00 0.46
HEC-RAS Plan: EX-FP1 River: Peach Creek Reach: PC (Continued)
Reach River Sta Profile Q Total Min Ch El W.S. Elev CritW.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude #Chi
(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)
PC 989 0.2% 2104.00 283.70 291.98 292.43 0.003438 6.80 1001 .97 364.22 0.46
HEC-RAS River: Peach Creek Reach: PC
Reach River Sta Profile Pian QTotal Min Ch El W.S. Elev CritW.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude#Chl
(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)
PC 151 50% PRFP 422.00 281 .20 286.29 285.33 286.47 0.003003 4.06 140.26 86.85 0.36
PC 151 20% PRFP 666.00 281 .20 286.95 285.92 287.16 0.003003 4.49 206.35 112.10 0.37
PC 151 10% PRFP 840.00 281 .20 287.32 286.20 287.54 0.003002 4.73 250.88 126.30 0.37
PC 151 4% PRFP 985.00 281 .20 287.59 286.43 287.83 0.003005 4.90 287.38 155.49 0.37
PC 151 2% PRFP 1188.00 281 .20 287.91 286.69 288.15 0.003004 5.09 349.26 231.58 0.38
PC 151 1% PRFP 1362.00 281 .20 288.18 286.87 288.41 0.003000 5.24 420.22 314.90 0.38
PC 151 0.2% PRFP 2104.00 281 .20 288.97 287.73 289.18 0.003003 5.71 792.17 583.09 0.39
PC 386 50% PRFP 422.00 281 .90 286.76 286.82 0.000865 2.57 320.83 209.55 0.23
PC 386 20% PRFP 666.00 281 .90 287.44 287.50 0.000832 2.82 466.41 218.86 0.24
PC 386 10% PRFP 840.00 281 .90 287.82 287.90 0.000841 3.00 552.20 224.17 0.24
PC 386 4% PRFP 985.00 281 .90 288.10 288.19 0.000861 3.15 616.11 228.98 0.25
PC 386 2% PRFP 1188.00 281 .90 288.43 288.52 0.000919 3.39 692.32 236.42 0.26
PC 386 1% PRFP 1362.00 281 .90 288.69 288.79 0.000962 3.58 753.80 242.25 0.27
PC 386 0.2% PRFP 2104.00 281 .90 289.47 289.61 0.001239 4.43 949.72 259.96 0.31
PC 524 50% PRFP 422.00 282.30 286.76 287.10 0.003378 4.67 107.62 52.23 0.45
PC 524 20% PRFP 666.00 282.30 287.28 287.88 0.005081 6.31 139.25 77.71 0.57
PC 524 10% PRFP 840.00 282.30 287.53 286.61 288.35 0.006354 7.37 161 .75 97.02 0.64
PC 524 4% PRFP 985.00 282.30 287.70 286.96 288.71 0.007458 8.21 179.45 109.86 0.70
PC 524 2% PRFP 1188.00 282.30 287.84 287.65 289.17 0.009614 9.51 194.55 119.73 0.80
PC 524 1% PRFP 1362.00 282.30 288.17 288.17 289.55 0.009262 9.81 239.04 141.69 0.80
PC 524 0.2% PRFP 2104.00 282.30 289.50 289.50 290.75 0.007048 10.10 536.53 352.03 0.72
PC 755 50% PRFP 422.00 283.00 287.55 287.73 0.002173 3.48 161.79 90.43 0.33
PC 755 20% PRFP 666.00 283.00 288.43 288.70 0.002430 4.28 260.80 146.36 0.36
PC 755 10% PRFP 840.00 283.00 288.96 289.27 0.002470 4.66 350.78 194.88 0.37
PC 755 4% PRFP 985.00 283.00 289.36 289.68 0.002429 4.87 436.25 231 .74 0.37
PC 755 2% PRFP 1188.00 283.00 289.89 287.49 290.22 0.002282 5.03 573.06 280.85 0.37
PC 755 1% PRFP 1362.00 283.00 290.25 287.82 290.59 0.002266 5.22 679.20 315.01 0.37
PC 755 0.2% PRFP 2104.00 283.00 291.33 291 .70 0.002273 5.82 1073.02 390.98 0.38
PC 989 50% PRFP 422.00 283.70 288.17 288.55 0.005399 5.00 107.78 74.71 0.50
PC 989 20% PRFP 666.00 283.70 289.07 289.57 0.005218 5.83 209.20 149.39 0.51
PC 989 10% PRFP 840.00 283.70 289.60 290.12 0.004924 6.14 299.04 192.72 0.51
PC 989 4% PRFP 985.00 283.70 289.98 290.51 0.004669 6.31 379.39 224.49 0.50
PC 989 2% PRFP 1188.00 283.70 290.47 291.00 0.004336 6.48 501.87 275.78 0.49
PC 989 1% PRFP 1362.00 283.70 290.82 291 .34 0.004147 6.61 605.55 312.94 0.49
PC 989 0.2% PRFP 2104.00 283.70 291.92 292.39 0.003613 6.93 980.52 362.24 0.47