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DRAINAGE REPORT FOR
KOREAN MISSION CHURCH OF TEXAS A&M
WORSHIP CENTER BUILDING F LE
COLLEGE STATION, TEXAS
Prepared for
Mike Lane Custom Builder
P.O. Box 9905
College Station, Texas 77842
Submitted to
City of College Station
Development Services
1101 Texas Avenue
College Station, Texas 77842
Prepared by
CSC Engineering & Environmental Consultants, Inc.
3407 Tabor Road
Bryan, Texas 77808
December, 2002
William R. Cullen, P .E.
Senior Engineer
COLLEGE STATION
ENGINEERING
CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
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Report of Drainage Study for Korean Mission Church of Texas A&M
TABLE OF CONTENTS
Page
1.0 GENERAL DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT ............................ 3
2.0 PRE-DEVELOPMENT DRAINAGE PATTERNS AND MAJOR DRAINAGE BASINS ......... 4
3.0 SCOPE OF REPORT AND DRAINAGE DESIGN CRITERIA ................................................. 5
4.0 STORM WATER RUNOFF COMPUTATIONS ....................................................................... 5
4.1 USE OF THE RATIONAL FORMULA ........................................................................... 5
4.2 RUNOFF COEFFICIENTS (C) ........................................................................................ 6
4.3 TIME OF CONCENTRATION (Tc) ............................................................................... 7
4.4 RAINFALL INTENSITY (1) ............................................................................................ 8
4.5 AREA OF SITE (A) ......................................................................................................... 9
4.6 STORM WATER RUNOFF QUANTITIES ..................................................................... 9
5.0 STORM WATER DETENTION COMPUTATIONS ................................................................ 9
5.1 REQUIRED MINIMUM DETENTION STORAGE VOLUME ....................................... 9
5.2 DETENTION BASIN STORAGE AREA ........................................................................ 10
5.3 DETENTION BASIN OUTLET STRUCTURE ............................................................... 11
6.0 STORMWATERROUTINGCOMPUTATIONS ...................................................................... 12
6.1 METHODOLOGY .......................................................................................................... 12
6.2 ROUTING COMPUTATIONS AND CONCLUSIONS ................................................... 12
7.0 EROSION CONTROL MEASURES ......................................................................................... 13
7.1 GENERAL CONSIDERATIONS .................................................................................... 13
8.0 CERTIFICATION ..................................................................................................................... 13
9.0 REFERENCES ......................................................................................................................... 14
LIST OF TABLES
Table l. Summary of Determination of Runoff Coefficient (C) Values for Post-Development
Conditions for Entire Site ................................................................................................. 7
Table 2. Computed Rainfall Intensity Values for Defined Storm Return Period .............................. 8
Table 3. Calculation of Pre-and Post-Development Stonn Water Runoff Quantities Using the
Rational Method .............................................................................................................. 9
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CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Report of Drainage Study for Korean Mission Church of Texas A&M
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
LIST OF FIGURES
General Site Vicinity Map
Lick Creek Drainage Basin
General Site Map and Currently Planned Development Scheme
Pre-Development Surface Storm Water Runoff Flow Patterns
Post-Development Site Grading Plan and Surface Storm Water Runoff Flow
Patterns
Post-Development Site Drainage Basin and Sub-basin Boundaries
Types of Site Cover Materials
Pre-and Post-Development Hydrographs -25 Year Event (for Determining
Minimum Requi red Volume of Detention Basin)
Storm Water Detention Basin Storage Depth versus Storage Volume
Cumulative Outflow (Discharge) versus Depth of Storage
Inflow and Outflow Hydrographs Illustrating Routing for 25 -Year Storm Event
Inflow and Outflow Hydrographs Illustrating Routing for 100-Year Storm Event
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Report of Drainage Study for Korean Mission Church of Texas A&M
1.0 GENERAL DESCRIPTION OF SITE AND PROPOSED DEVELOPMENT
Information concerning the proj ect was provided by Mr. Chad Grauke, AJA of Mike Lane
Custom Builder.
The site of the proposed church that is the subject of this report is located in the southern portion
of College Station, Texas. The site is located on the western si de of the State Highway 6 access road,
approximately Yz mile south of the intersection with Southern Plantation Drive. The general location of
the site is illustrated on Figure 1 of this report. The site is situated within the Spring Creek segment of the
Lick Creek Drainage Basin (Figure 2).
The subject tract of land is approximately 2.17 acres in area and is part of a larger 10.674 acres
tract that has been referred to as Lot 1, Block 1 of the K.T.H. Commercial Addition Robert Stevenson
League, A-54 (Figure 3). The small er tract that is the subj ect of this report is the only portion of the
10.764-acre tract that is presently plaimed fo r development.
The subject tract is roughly rectangular is shape and oriented in a northeastern-southwestern
direction. The subj ect tract has approximate plan dimensions of 150 ft by 530 ft . However, a small
access corridor within the adjacent lot along State Highway 6 is al so part of the planned development
(Figure 3). We understand that the Texas Department of Transportation (TxDOT) would not permit
direct access of vehicles from State Highway 6 to the portion of the property planned for current
development, and therefore, the referenced access corridor was a necessary addition to the proposed
development. This corridor will provide access to State Highway 6 at a location acceptable to TxDOT.
The proposed access corridor is aligned parallel to State Highway 6 and has approximately plan
dimensions of 50 ft by 250 ft . Consequently, the entire tract of land planned for current development is
roughly "L-shaped" (Figure 3) and e:-..1ends over an area of approximately 2.17-acres.
The site is bordered on the northeastern side by the access or service road of State Highway 6 and
the Texas Department of Transportation's right-of-way for State Highway 6. The long southeastern
boundary of the subj ect site is bordered by an approximately 14.28-acre tract of land owned by the K.S .
Moss Capital Corp oration. The short southwestern boundary of the subject property is bordered by a 40-
ft-wide drainage easement a11d smaller natural drainage channel that is a tributary of Spring Creek. The
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Report of Drainage Study for Korean Mission Church of Texas A&M
general flow of the channel is toward Spring Creek to the northeast. The long northwestern boundary of
the site borders the western portion of Lots l and 2 of the referenced commercial addition.
The subject site is situated on a relatively heavily wooded tract of land. Some clearing of the land
has been performed by others in the area of the proposed building location and the proposed parking lot
in front of the building. The portion of the property adjacent to State Highwa 6, which is the area of
interest for the present study, has a relative ly gentle slope from the higher elevations in the north and
northeastern portions of the site to the lower elevations along the existing Spring Creek tributary that
forms the southwestern boundary of the site (Figure 4). Existing ground surface elevations range from
approximately El. 29 1 near the northwestern corner of the property to approximately El. 278 near the
previously referenced tributary. The average surface grade across the site is approximately 2.5 percent,
wi th slightly steeper grades being present in the northwestern comer of the site and shallower grades near
th e creek tributary. There do not appear to be any other significant surface features across the site.
We understand that the proposed new worship center building wi ll be a single-story structure and
wi ll have a footprint or ground floor area of approximately 15 ,000 square feet. We anticipate that the
structure will be situated in the southwestern portion of the previously described property and northeast of
the tributary creek that forms the southwestern boundary of the site. We further anticipate that the
proposed development will have two parking areas, with one area along the previously described access
corridor and the second area in front of the proposed building (Figure 1). We believe that the parking in
the access corridor wi ll accornn1odate approximately 19 vehicles and that the parking area in front of the
church will have approxi mately 99 spaces. We anticipate that the paved dri ve and parking areas·
associated with the new building will be constructed of a rigid pavement system with a Portland cement
concrete (PCC) surface. Landscaping of the site will be done in the areas around the church building,
behind the church, and the islands and areas bordering the parking lots.
2.0 PRE-DEVELOPMENT DRAINAGE PATTERNS AND MAJOR
DRAINAGE BASINS
As previously discussed, the subject 2.17-acre site is located in the Spring Creek sub-basin of the
Lick Creek drainage basin. The subject site is situated near the sub-basin drainage divide between Spring
Creek and the upper reaches of the south fork of Lick Creek as illustrated on Figure 2.
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Report of Drainage Study for Korean Mission Church of Texas A&M
There are no distinct drainage channels across the existing site. The major portion of current
storm water nmoff from the site appears to be by sheet-flow in a southerly or southwesterly direction
towards the previously described existing tributary of Spring Creek (Figure 4). No portion of the 2.17-
acre site appears to lie within the 100-year floodplain of Spring Creek or Lick Creek.
3.0 SCOPE OF REPORT AND DRAINAGE DESIGN CRITERIA
This report addresses the need for retention of drainage from the subject site following the
planned development of the church. The site and proposed development were evaluated in accordance
with the criteria outlined in the "Drainage Policy and Design Standards (DPDS)" manual of the City of
College Station, Texas. The DPDS manual is undated but contains a chapter on "Flood Hazard
Protection" that has a revision date of October 1, 1990. This report also discusses specific drainage
control structures related to the detention of storm water runoff from the new facility and general erosion
control measures.
4.0 STORM WATER RUNOFF COMPUTATIONS
4.1 USE OF THE RATIONAL FORMULA
The Rational Formula was used to compute the volume of storm water runoff prior to and
following the planned development. Calculations based upon the Rational Formula were employed to
assess the quantity of stom1 \Vater that must be detained to "offset" the increased runoff associated with
the new development. The generalized grading plan for the proposed development, the patterns of post-
development storm water runoff flows, and the location and approximately area of the proposed detention
basin are illustrated on the accompanying Figure 5. The approximate drainage basin and sub-basin
boundaries of the drainage areas associated with post-development flow patterns across the site are
illustrated on Figure 6.
Use of the Rational Formula is reasonable for this project since the contributory area of runoff is
less than 50 acres, an area sometimes referenced in the literature as an upper limit for use of the Rational
Formula. In addition, the subject site is located within a Secondary Drainage System and not within a
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Report of Drainage Study for Korean Mission Church of Texas A&M
Primary Drainage System. The Rational Formula is not recommended for use within a Primary Drainage
System. Therefore, the Rational Formula was used to determine the peak discharge for both pre-and post-
development conditions.
The general equation for the Rational Formula is well known:
Q =CIA
where
Q =discharge of storm water in units of cubic feet per second (cfs)
C = coefficient that represents the average runoff characteristics of the land cover within the
drainage area of interest, i.e., the runoff coefficient, which is dimensionless
I = rainfall intensity in units of inches per hour (in/hr), and
A = area of the site that contributes to the storm water runoff in units of acres
The numbers for each of the values used to compute the storm water runoff at the subject site are
discussed in the following sections.
4.2 RUNOFF COEFFICIENTS (C)
The runoff coefficients or "C" values were computed for both pre-and post-development
conditions. Coefficients for the different types of surface covers were determined from Table 111-1 of the
DPDS manual.
The coefficient for the pre-development condition was determined based upon the land cover
category listed in Table III-1 as a combination of "Natural Woodlands" and "Natural Grasslands" for
slopes in the range of 1 % to 3. 5 %. A range of C-values of 0 .18 to 0 .25 was listed in the referenced table
for the "Natural Woodlands" and a range of C-values of 0.35 to 0.45 was given for ''Natural Grasslands"
for the cited topographic conditions. Therefore, a conservative value of 0.4 was selected for use for pre-
development cover of the entire 2.17-acre site.
The post-development side grading plan and surface storm water runoff flow patterns are
illustrated in Figure 5. As can be seen from Figure 5, the area incorporated in our analyses for post-
development included the access corridor along the State Highway 6 service road as well as the site that is
actually being developed for the church building. However, as indicated by the specific site drainage
basin and sub-basin boundaries associated with development (Figure 6), not all of the developed site will
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Report of Drainage Study for Korean Mission Church of Texas A&M
be draining directly to the planned detention basin. 1l1e portion of the paved area comprising the access
corridor will drain onto the adjoining property owned by the developer through openings between the
wheel stop structures that border the paved access corridor on the southwest.
The post-development C-values were determined from the referenced table for the specific types
of site cover associated with post-developed site conditions (Figure 7). The specific types of post-
development cover materials illustrated in Figure 7 and the corresponding C-values from Table III-1 of
the DPDS manual were used in the analysis listed in Table 1 to compute an average C-value for the post-
developed site .. In general, a C-valu e of 0.9 was used for building roof and concrete covered pavements
and sidewalks and a C-value of 0.5 was used for the landscaped or grassed areas.
Table 1. Summary of Determination of Runoff Coefficient (C) Values for Post-Development
Conditions for Entire Site
Type of Ground Cover
Concrete (sidewalks, streets, etc.)
Building roof
Grassed or landscaped areas
Summation
Area of Coverage,
Square Feet
14,500
44,969
36,309
95,778
Typical
C-Values
0.90
0.90
0.50
Extended Multiplication of
C-Values X Area
13,050
40,472
18,154
71,676
Therefore, the average C-value across the site can be determined by dividing the summation of
the product of the individual areas times the respective C-values and dividing that summation by the
overall area:
Average C-value = 71 ,676 C-square feet/95 ,778 square feet= 0.75
4.3 TIME OF CONCENTRATION (Tc)
The time of concentration at a site is used to determine the intensity of the rainfall event used for
computing storm water flows and required detention volumes. The time of concentration is defined as
''the time required for the runoff to be established and flow from the most remote part of the drainage area
to the point under design." For pre-development conditions the time of concentration for the subject site
was calculated based upon the elevation difference and the flow distance from the higher elevations in the
northeastern portion of the property to the lower elevations where the storm water detention basin outlet
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Report of Drainage Study for Korean Mission Church of Texas A&M
structure is to be located. The referenced change in elevation is 9 ft and the referenced distance is
approximately 460 ft which produces a slope of approximately 2% for pre-development conditions. The
slope for post-development conditions was determined from the proposed site grading plan and drainage
patterns as illu strated in Figure 5. The surface slopes or grades and the velocities presented in Table III-2
of th e DPDS manual were utilized to determine the appropriate storm water runoff velocity.
For overland or sheet-flow over land with slopes in the range of 0 to 3 percent, such as at the
subject site, velocities of runoff flow are listed to be in the range of 0 to 1.5 feet per second (fps) for
natural woodlands and in the range of 0 to 2.5 fps for natural grasslands . An average velocity of 1 fps was
conservatively selected fo r pre-development conditions. Thus, time of travel between the location of the
higher elevations of the site and the proposed detention basin outlet structure location was calculated to be
approximately 460 seconds (460 ft distance/l fp s velocity) or approximately 7.7 minutes for pre-
development conditions. The post-development time of concentration was calculated over the paved areas
of the site without consideration of any detention and was determined to be a shorter time period.
Therefore, a minimum time of concentration of 10 minutes (as specified in the DPDS manual) was us ed
in the calculations for both pre-and post-development conditions.
4.4 RAINFALL INTENSITY (I)
The rainfall intensity values were computed for the minimum 10-minute time of concentration
previously discussed using the intensity-du ration-frequency curves develop ed by the Texas Department of
Transportation. The computed intensities calculated for storn1 events with "return periods" of 5, 10, 25,
50, and 100 years are indicated in Table 2.
Table 2. Computed Rainfall Intensity Values for Defined Stom1 Return Period
Storm Return Period
(Years)
5
10
25
50
100
8
Rainfall Intensity
(Inches/Hour)
7.7
8.6
9.9
11.1
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Report of Drainage Study for Korean Mission Church of Texas A&M
4.5 AREA OF SITE (A)
The area of the site used in the computation of storm water runoff is the original site area of 2 .17
acres .
4.6 STORM WATER RUNOFF QUANTITIES
Storm water runoff quantities were calculated using the Rational Formula. Runoff quantities were
calculated for both pre-and post-development conditions for the 2.1 7-acre site and are presented in Table
..,
.) .
Table 3. Calculation of Pre-and Post-Development Storm Water Runoff Quantities Using the Rational
Method
PRE-
Storm Area_ Intensity< DEVELOPMENT
Event (acres) (inches
(year) /hr) Cprea Qpre
(dlessb) (cfs)
5 2.17 7.7 0.40 6.7
10 2.17 8.6 0.40 7.5
25 2.17 9.9 0.40 8.6
50 2.17 11 . l 0.40 9.7
100 2.17 12.3 0.40 10.7
•Average values ofC were obtained from Table III-I of the DPDS Manual
b dless = dimensionless
c Values obtained from Table 2 of th.is report
POST-DIFFERENCE
DEVELOPMENT
Cpost3 Qpost Qo
(dlessb) (cfs) (cfs)
0.75 12.5 5.8
0.75 14 .1 6.6
0.75 16.0 7.5
0.75 18.1 8.5
0.75 20.0 9.3
5.0 STORM WATER DETENTION COMPUTATIONS
5.1 REQUIRED MINIMUM DETENTION STORAGE VOLUME
The storage volume of the detention area was calculated such that the peak discharge of the
ultimate development hydrographs for the 25-year design storm was limited to a discharge less than a
defined target discharge. The defined target discharge was characterized by the DPDS manual to be the
peak discharge of the pre-development hydrograph for the 25-year storm event. Since the entire 2.17-acre
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Report of Drainage Study for Korean Mission Church of Texas A&M
site is being developed at the present time, the current developed condition and the ultimate developed
condition were assumed to be the same.
The required detention storage volume was determined as the difference in area between the pre-
and post-development hydrographs, as depicted on Figure 8. The Triangular Approxi mation method was
used to determine the hydrographs. The hydrographs were constructed by assuming that the peak
discharge, as calculated from the Rational Formula, occurs at a time equal to the time of concentration
and that one-third of the flow volume occurs before the peak discharge is reached and two-thirds occur
following the peak discharge. The Triangular Approximation method of developing hydrographs is
generally considered to be acceptable for analysis of Secondary Drainage Systems with an area of less
than 50 acres, which is applicable to the drainage basin addressed in this report.
The difference in area between the two hydrographs, or the required minimum volume of the
detention storage area, was calculated to be approximately 6, 740 ft3 for the 25-year event.
5.2 DETENTION BASIN STORAGE AREA
We propose to construction the required detention basin on the southwestern side of the proposed
building and adjacent to th e existing Spring Creek tributary as depicted in Figure 5.
The proposed detention basin will be an earthen structure that is created by a combination of
excavation below the existing surface grades and construction of above-grade earthen berms to provide
the required volume for stom1 water detention. The proposed detention basin will be roughly triangular in
shape to conform to the space between the back of the building and the site boundaries along tributary
creek. The detention basin will have an approximate length of 120 ft and a base width of approximately
45 ft as indicated in Fi gure 5. The total depth of the basin will be approximately 3 ft from the base of
the structure to the bottom of the emergency overflow structure that will be built into the perimeter levee
or embankment. The embankments for the detention basin will be formed with compacted clay soils,
excavated as part of the proposed building developm ent. The embankments will have side slope with
inclinations of 4: 1 (horizontal to vertical dimension) with a minimum crest or top width of 1 ft to provide
resistance to erosion or damage from mowing equipmentThe slopes of the embankment will be sodded
with grass follov.·ing construction to minimize erosion of the embankment soils.
The approximate volume provided by the proposed detention basin is illustrated on Figure 9. As
can be seen from Figure 9, the full basin depth below the emergency overflow spillwau elevation would
provide a potential storage volume of approximately 7,3 60 cu ft. With the addition of the 0.75 ft of
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CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Report of Drainage Study for Korean Mission Church of Texas A&M
freeboard to the crest of the embankment, the proposed detention basin would have a storage volume of
approximately 10,071 cu . ft. As previously stated, the required minimum storage volume of the detention
basin would be approximately 6,740 cu ft in order to detain the difference between the 25-year event
stom1 water runoff for pre-and post-development conditions. The minimum required volume of 6, 740 cu
ft is within the available storage capacity of the proposed basin.
5.3 DETENTION BASIN OUTLET STRUCTURE
The outlet strnctures for the detention basin are composed of tow separate structures. A 8 in.
diameter high density polyethylene (HDPE) pipe through the embankment will serves to drain the
detention for '·normal" discharges corresponding to a 25-year event. A 8-ft-wide concrete weir structure
that is cut into the top of the detention basin embankment will provide for "emergency overflow"
discharges for the l 00-year event. The discharges from both structures will be routed to the previously
referenced tributary of Spring Creek
The dian1eter and slope of the HDPE outlet pipe was established to provide discharges from the
detention basin during the 25 -year storm event that were less than or equal to the 8.6 cfs rnnoff flows that
\\'ere associated with the pre-development site conditions. As indicated by the graphical presentation of
detention basin discharge versus depth illustrated on Figure 10, the planned pipe size and pipe grade
provides for a discharge of approximately 3 .5 cfs, from the detention basin with 3 ft depth of storm water
detention, which is a flow that is less than the 8.6 cfs pre-development flow for the predevelopment 25-
year stom1 event. The detention basin outlet pipe will discharge through the earthen side slope of the
tributary stream and not at the base of the stream where the pipe outlet might become inundated for even
common rainfall events. Erosion of the earthen side slopes of the "receiving" tributary creek from
detention basin discharges will be minimized by providing rock-rip along the slope at the discharge point.
The emergency overflow concrete wier was sized to pass the outflow from a l 00-year event. The
length of the weir opening were calculated based upon the Francis fommla for weirs :
Q = 3.33 (L -0.2 H) H15
where
Q = flow rate through rectangular weir opening in cfs
L = length of rectangular opening in feet
H = head of water at a defined distance behind the wall in fe et
11
CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
t--''"'"'"f~.;;:,-:.;:;:,.;-:.-:..;.;:.,..,-:.,.;;:..;,.;,,.;.%'Wf.~f\"'>"'.;;:...:,.;,.;.;§"'"'"#.;'&.:i>-:...''' .. .;.;-:..;.;-:.;:,-:.:.:.: .. ;>.:.:.;'''-:-:.;&%'fn«-:..:gx;>.:'{·*'''"';>.:.;.:,.;lf&''&'-''';;.,'''"';:.,"":>'"&"-'.;&-:,.;.-:.;:.·:;:...'>'h";).:..:.''".;".;'.;'*''".;'*''«5 . .;.''"-;}''-\"'§':..;S"h"l'\'h':.:.;:.,:.:.;.;.:.:..;.;:.:..;.;;:,,:.:..;..;;;,;.,..;.;:.)">';)';:,,'if""'''"""'s.'.;*
Report of Drainage Study for Korean Mission Church of Texas A&M
A wier length of 8 feet was selected so that the cumulative flows from the emergency spillway
and the outlet pipe of the detention basin exceeds the I 00-year post-development in-flow of 20 cfs.
6.0 STORMW ATER ROUTING COMPUTATIONS
6.1 METHODOLOGY
The proposed detenti on basin in the southwestern portion of the project site was analyzed for
fl ow routing through the areas under different storm events. The purpose of the routing analysis was to
simulate the performance of the detention basins in the form of inflow and outflow hydrographs.
The storage-routing analysis was performed based upon the Puls Method. The Puls Method is a
procedure fo r graphically solving the continuity equation for storage reservoirs using the characteristic
height-storage and height-discharge curves. As previously discussed, the depth-volume storage curve for
the detention basin was developed graphically from the final grading plan and is graphically depicted on
Figure 9. A height-discharge or discharge versus depth of storage curve was also developed and is
illustrated in Figure 10. The routing time interval was selected to be slightly less than 10 percent of the
time to peak of the inflow hydrograph to ensure that th e numerical averaging procedures of the Puls
Method does not diminish the impact of the peak flow.
6.2 ROUTING COMPUTATIONS AND CONCLUSIONS
Routing analysis was performed for two storm events: the 25-year event, which represents the
des ign storm; and the 100-year event called for in the DPDS . The results of th e routing analyses are
presented graphically on Figures 11 and 12 in the form in inflow and outflow hydrographs, the difference
between the two curves being the volume that must be stored.
A review of Figure 9 for the 25-year event indicates that the basin has the capacity to store the
difference between the inflow and outflow quantities without overtopping. The maximum calculated
height of the stored water in the detention basin during the 25-year storm event is approximately 2.9 ft.
Therefore, it can be stated that the detention basis has the capacity to store the excess volume of storm
water associated with the planned development of the site and [to] discharge the stored water at a rate that
12
CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Report of Drainage Study for Korean Mission Church of Texas A&M
is '·equal to or less than the peak discharges of the pre-development hydrographs for the design [2 5-year]
storm" as called for in the DPDS.
As can be seen from Figure 12 for the 100-year event, the basin will contain a portion of the
mnoff associated with the 100-year storm event but without any freeboard for the stored storm water.
The remainder of the 100-year event flows will be routed via the previously discussed concrete spillway
through the embankment to the tributary to Spring Creek. The detention basin should not be damaged at
the point of overtopping due to the flume paving over the earthen slope.
7.0 EROSION CONTROL MEASURES
7.1 GENERAL CONSIDERATIONS
The erosion control measures proposed at the site will consist of a combination of silt fences, hay
bale barriers, and sedimentation traps. The locations of the proposed erosion control measures are
depicted on Sheet C 4 of the plans .
8.0 CERTIFICATION
"I hereby certify that this report for drainage design of the storm water detention basin at the 2 .17-acre
site of the proposed Korean Mission Church of Texas A&M located on the western side of the State
Highway 6 service road south of Southern Plantation Drive in College Station, Texas, was prepared under
my supervision in accordance with the previsions of the City of College Station "Drainage Policy and
Design Standards (1 990)" for the owners th ereof."
m. ai /)p~ :&~1~
M. Frederick Conlin, Jr., P.E.
Registered Professional Engineer
State of Texas P.E. Number 44481
13
CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC.
Report of Drainage Study for Korean Mission Church of Texas A&M
9.0 REFERENCES
Chow, Ven T., Maidment, David R., and Mays, Larry W. 1988. Applied Hydrology. McGraw-Hill Book
Company. New York, NY. 1988.
City of College Station, Texas. 1990. "Drainage Policy and Design Standards," part of the Stormwater
Management Plan for the City of College Station. October, 1, 1990.
Davis, Victor D., and Sorensen, Kenneth E. 1969. Handbook of Applied Hydraulics. McGraw-Hill Book
Company. New York, NY. 1969.
Harm, C. T., Barfield, B. J., and Hayes, C. J. 1994. Design Hydrologv and Sedimentology for Small
Catchments. Academic Press, Inc. San Diego, CA. 1994.
Mason, John M. and Rhombrerg, Edward L. 1980. On-Site Detention. Prepared for Texas Engineering
E>..iension Service, Texas A& M University. College Station, TX. 1980. Publication No. PWP: 03355-01.
McCuen, Richard H. A Guide to Hydrologic Analysis Using SCS Methods. Prentice-Hall, Inc.
Englewood Cliffs, NJ. 1982.
United States Department of Agriculture. 1975. Urban Hydrologv for Small Watersheds. Technical
Release No. 55 . Engineering Division, Soils Conservation Service, U.S. Department of Agriculture.
January 1975.
Wanielista, Martin P. 1978. Storm water Mar1agement Quar1tity and Quality. Ann Arbor Science. Ann
Arbor, MI. 1978.
Westaway, C.R. and Loomis, A. W. 1979. Carneron Hvdraulic Data. (l61h Edition). Ingersoll-Rand.
Woodcliff Lake, NJ. 1979.
14
FIGURES
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KOREAN MISSION CHURCH OF TEXAS A&M
COLLEGE STATION, TEXAS
repa or. PROJECT: KOREAN MISSION CHURCH
LOCATION: COLLEGE STATION, TEXAS
APPR: MFC REV. DATE:
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25
20
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Q POST • 16.1 cfa
Pre-Development
HydrO<;Jroph
5 10
(600 sec.)
PRE AND POST DEVELOPMENT
HYDROGRAPHS FOR 25-YEAR STORM EVENT
KOREAN MISSION CHURCH OF TEXAS A & M
15
TIME
Minumum Volume of Detention Storoge Baain •
Difference In Areas Between Pre and Poat
Development Hydf09ropha
20
(1200 sec.)
25
PROJECT: KOREAN MISSION CHURCH
LOCATION: COLLEGE STATION TEXAS
30 min.
(1800 sec.)
APPR: MFC REV. DATE:
DRAWN BY: DWA SCALE: ASSHO'Ml
DATE: 12/16/02 FIGURE NO.: 8
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Depth, feet
(Elevation)
STORM WATER DETENTION BASIN
DEPTH VS. STORAGE VOLUME
KOREAN MISSION CURCH OF TEXAS A & M
PROJECT: KOREAN MISSION CHURCH
LOCATION: COLLEGE STATION TEXAS
APPR: MFC REV. DATE:
DRAWN BY: DWA SCALE: ASSHOIM'J
DATE: 12/1&12 FIGURE NO.: 9
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STORED WATERE HEIGHT IN
DETENTION BASIN, FT.
CUMULATIVE OUTFLOWS VS.
DEPTH OF STORAGE
KOREAN MISSION CURCH OF TEXAS A& M
3.0 3.5 4.0
PROJECT: KOREAN MISSION CHURCH
LOCATION: COLLEGE 5rATION TEXAS
APPR: MFC REV. DATE:
DRAVVN BY: DWA SCALE: ASSHO\M>J
DATE: 12/1002 FIGURE NO.: 10
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6
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0 5 10
INFLOW AND OUTFLOW HYDROGRAPHS
ILLUSTRATING ROUTING FOR 25-YEAR EVENT
INFLOW
OUTFLOW
15 20 25 30
TIME (minutes)
PROJECT: KOREAN MISSION CHURCH
LOCATION: COLLEGE STATION TEXAS
APPR: MFC REV. DATE:
DRAWN BY: JBF SCALE: ASSHO'M'l
DATE: 12/1!W2 FIGURE NO.: 11
Y:\Graphics\Korean Mission Church\dwg\DRAINAGE REPOR'l\Figurel J.dwg, 1211912002 10:42:26 AM
20
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INFLOW
OUTFLOW
5 10 15
TIME (minutes)
INFLOW AND OUTFLOW HYDROGRAPHS
ILLUSTRATING ROUTING FOR 100-YEAR EVENT
20 25 30
PROJECT: KOREAN MISSION CHURCH
LOCATION: COLLEGE STATION TEXAS
APPR: MFC REV. DATE:
DRAWN BY: JBF SCALE: ASSHO'M-4
DATE: 1211002 FIGURE NO.: 12
Y:\Graphics\Korean Mission Churchldwg\DRAINAGE REPOR1\Figurel2.dwg, 1211912002 10:42:37 AM