HomeMy WebLinkAbout59 Development 587 KW Brown Expansion~i lCWBrovvn
Spencer G. Thompson, Jr.
Project Manager
409·690·9280
sthompson@kwbes.com
January 26, 1999
City of College Station
Development Services
1101 S . Texas Ave.
College Station, TX 77845
KW Brown & Associates, Inc.
50 I Graham Road
College Station, Texas 77845
Fax: 409·690·7310
www.kwbes.com
E lEWED FOR
COMPLtANCE
FEB 0 3 1999
COLLt:.UC \.) 11"\l iON
ENGINEERING
~f.{f
Re: Stormwater Management Plan for KW Brown & Associates, Inc., South Graham Road,
College Station, TX
This letter introduces a stormwater management plan proposed by KW Brown & Associates, Inc .
(KW Brown) to address the increased stormwater drainage, due to construction, from the property of
Dr. Kirk W. Brown (Dr. Brown) located at 501 South Graham Road . Dr. Brown has constructed a
metal building and associated paving on his property (Building Permit No. 9899017) to house the
KW Brown geotechnical laboratory. The new construction will alter the existing stormwater
drainage characteristics of the property by increasing stormwater runoff.
We understand from Dr. Brown that a meeting was held at the site in late July to discuss possible
options for handling the increased stormwater runoff. We also understand that the meeting was
attended by Dr. Brown and Rusty Etheridge, the builder hired by Dr. Brown, Mr. Joel Mitchell, P .E.
of McClure Engineering, the engineer retained by Dr. Brown to provide drainage consultation, and
Ms . Veronica Morgan, P .E., of the City of College Station. Two options were discussed at the
meeting and are briefly outlined in the following paragraphs .
The first option involves utilization of the existing drainage channel which runs, approximately, in a
west to east direction along the base of the southern berm of the Edelweiss Detention Basin (EDB).
In the past the drainage from the rear portion of the Brown property and other properties along South
Graham Road flowed to the north and northeast. However, the construction of the EDB in the early
1990s altered the natural drainage pattern. A high earthen berm was constructed along the southern
border of the EDB and prevented direct flows from the Brown property and other South Graham
Road properties from directly entering the EDB. Rather, an earthen channel formed along the base of
the berm to carry surface water runoff from the referenced properties to an inlet drop box located at
the southern comer of the EDB. The stormwater then enters the EDB through the inlet drop box
structure . The drainage option considered for the Brown property involved improvement of the
drainage characteristics of the channel by widening and deepening it between the Brown property
and the inlet drop box. Improvement of this channel would be done at the expense of Dr. Brown and
would need to include flows from properties located both west and east of the Brown property.
Implementation of this first option may be difficult due to space limitations associated with both the
Scientists • Engineers • Planners
Burbank • College Station • Houston • Victoria • Phoenix • Logan • Mexico City
ii&1cws
City of College Station
Development Services
January 26, 1999
existing earthen berms comprising the southern boundary of the EBO and the inlet box structure . The
increased width associated with the planned channel drainage improvements will "cut" into the
existing berm and require removal of a portion of the berm where some existing trees are located,
thereby resulting in the loss of several trees and possibly the stability of the earthen berm . In
addition, an existing electrical transformer is located adjacent to the inlet drop box and will have to
be relocated if changes to the previously discussed channel are made .
We understand that the second option discussed at the meeting was to route the increased drainage
from the Brown property directly into the EDB . This direct routing option would involve
construction of three drainage features : a surface inlet box on the Brown property; a storm sewer
outlet pipe from the inlet structure to the interior of the earthen berm comprising the southern
boundary of the EDB; and a concrete outlet structure below the inside slope of the earthen berm of
EDB.
The second option is attractive for the following reasons :
• lower construction and maintenance costs;
• less disturbance to existing structures, such as the earthen berm along the EDB and the
electrical transformer, and no destruction of the trees along the embankment;
• the drop inlet on the Brown property will act as a sediment trap, thereby reducing soil
loading to the EDB ; and
• more efficient routing of the stormwater from the Brown property to the EDB .
Dr. Brown has chosen the second option . The recommended implementation of this second option is
discussed in the attached report (Attachment A).
As you know, we previously submitted a set of plans for preliminary review . An energy dissipation
channel constructed on the side of the EDB berm was turned down . We have subsequently designed
a storm sewer to accommodate the increased stormwater as a result of the new construction that is
less obtrusive . We hope you will find this design more appealing as well as functional.
Kindest regards ,
~~b~
Spencer G . Thompson, Jr.
Project Manager
cc: John P .(Pat) Lee. P .E.
SGT/JPL:le
Attachments : Design Report for Stormwater Drainage from KW Brown & Associates', Inc .
Property and Figures
File : 7000-230
Via Hand Delivery
2
ATTACHMENT A
Design Report for Stormwater Drainage from KW Brown & Associates ', Inc . Property
DESIGN REPORT FOR STORMWATER DRAINAGE FROM KW
BROWN & ASSOCIATES', INC. PROPERTY
1.0 KW BROWN ENVIRONMENTAL SERVICES PROPERTY
KW Brown & Associates, Inc . (KW Brown) is located at 501 Graham Road on
approximately 1.6 acres (Figure 1, Appendix A). The property houses the KW Brown office
building, several document storage sheds, a mobile home, and parking lot. The new construction
consists of a laboratory building, approximately 5000 square feet (sq ft), and parking renovations,
approximately 500 sq ft (Figure 2, Appendix A). The property lies entirely in the Lick Creek
Drainage Basin.
1.1 Drainage Characteristics
A topographical survey of the KW Brown property shows the front, one-half of the
property (Graham Road side), approximately 0.8 acres, drains to the ditch along Graham Road .
This ditch flows northeastward and runs adjacent to Graham Road. It turns to flow along Shaffer
Road and empties into the North Fork of Lick Creek.
The remaining back half of the KW Brown property drains to the rear, northeastern
property corner (Figure 2, Appendix A). Drainage along the northeastern property line , between
KW Brown and International Supply, is aided by a dug channel permitting water to flow both to
the front and to the rear of the property.
The construction of the new lab building will increase the impervious area of the back
one-half of the property and subsequently increase the storm water runoff by 2.4 cfs for a 100-year
rainfall event. KW Brown will design and install a storm drainage system to accommodate the
increased runoff (2.4 cfs) from a 100-year rainfall event due to the new construction on the
property .
The front half of the property will be nominally affected by the improvements ; a small
parking area has been changed from crushed-rock to pavement. One-half of the back area (0.4
acres) has changed from a landscaped area to an impervious area which consists of buildings ,
pavement, and a compacted driveway . The remaining back area (0.4 acres) remains landscaped
and has not been altered by the improvements .
1.2 Area Drainage Conditions
Presently, rainfall runoff from the rear area of the KW Brown property flows to the rear
(northeast) property comer and eventually into the Edelweiss detention basin (EDB). However,
rainfall runoff is diverted into the detention basin by having to travel around a constructed berm
surrounding the EDB along the basin 's southeast side . The berm diverts stormwater runoff from
the KW Brown property, as well as those properties up-slope and down-slope , to Victoria
A venue. This berm has created drainage difficulties for these property owners and erosional
conditions at the culvert at Victoria Avenue. In addition , a concrete pad and electrical transformer
located near the culvert have experienced erosional undercutting and the increased flows have
only worsened the situation. Some modification of this situation will eventually be necessary . A
constructed channel between the berm and property owners, as discussed by the City of College
Station and KW Brown , is not a cure-all for this problem . Considerable earthwork would need to
be done to obtain the necessary drainage characteristics for the channel. This earthwork would
result in the loss of trees that act as a visual barrier between the residential and commercial areas .
It is our opinion these trees should not be uprooted or disturbed. Suggestions have been made that
more trees be planted along this row to further veil the commercial activities of the Graham Road
establishments from the residential neighborhoods to the north.
1.3 Drainage Solutions and Recommended Options
KW Brown is proposing a storm drain system for the Graham Road property that will
direct stormwater runoff to the detention basin by way of a drop inlet box, storm sewer, and outlet
structure (Figure 2 , Appendix A). If this can be done in an effective and attractive manner, it is
our opinion it wou ld be the best solution to the present dilemma. Stormwater would enter the
detention basin directly and more rapidly through the berm , rather than having to flow around
(Figure 1, Appendix A). A study by McClure Engi neerin g, Inc. (McClure, Oct. 5, 1998 , attached)
has determined that the additional flow from the new construction at KW Brown will not
significantly impact the detention basin . While the McClure study calculates the runoff going into
the headwaters of the present drainage pathway between KW Brown and the detention basin
berm , we have based our calculations on the excess runoff from the KW Brown property due to
the new construction. Stormwater runoff in excess of the capacity of the storm sewer will
continue to flow on its present course .
2.0 DESIGN CRITERIA
Our design considerations have employed established engineering practices and utilized
the methods adopted by the City of College Station in the Drainage Policy and Design Standards
(DP&DS) manual.
2.1 Design Description
2.1.1 Drop Inlet
KW Brown has designed a drop inlet box which will be located at the rear, northeast
corner of the property (Figure 3 , Appendix A ) in order to accommodate peak stormwater runoff.
The drop inlet box will collect stormwater runoff from the KW Brown property and convey it to
the detention basin via an 8 in PVC pipe and 12 in reinforced concrete pipe (RCP). The drop inlet
will include an inlet grate with the necessary 0 .77 sq ft minimum open area. The invert of the
storm sewer at the inlet box is expected to be 2 ft below surface grade elevation at an elevation of
311 . 79 ft. The pipe invert will be set approximately 6 in above the bottom of the drop inlet box to
allow for trapping of sediment and fluid energy dissipation .
2.1.2 Storm Sewer
The 8 in PVC storm sewer will convey storm water runoff to the outlet structure (Figure
5 , Appendix A). This section of pipe will be approximately 65 ft in length and set at an 1 1 %
grade .
2.1. 3 Outlet Structure
The outlet structure shall consist of 30 ft of 12 in RCP set at a 1 % slope (Figure 5,
Appendix A). The pipe-end shall include a 45° angled fitting to convey the flow in the
downstream direction of the trickle channel. The 45° fitting shall be cut to match the berm rather
than protrude. A concrete apron will be installed at the base of the pipe adjacent to and on either
side of the EDB trickle channel (Figure 4 , Appendix A). Each side of the concrete apron shall be
2 ft wide by 4 ft long by 2 in thick. The finish of the concrete apron shall be rough. This extended
concrete apron will allow the storrnwater outflow to converge with th e basin stream without
scouring the basin channel bottom. All apron specifications w ill conform to specifications where
applicable in§ VII of the DP&DS.
This outlet structure is designed to reduce the storrnwater velocity before entering the
detention basin channel. This velocity reduction and concrete apron will minimize scour and
erosion by the stormwater discharged from the KW Brown property. The detention basin trickle
channel flows below the berm to the Victoria Avenue culvert where it joins the main basin stream
and crosses under Victoria Avenue. The main basin stream flows into the North Fork of Lick
Creek and subsequently into Lick Creek.
2.2 Calcul ation s
Calculations are shown in the following sections for the peak runoff flows , the inlet
grating capacity, flow capacity of the drop box ou tl et pipe, and the flow capacity of the outlet
structure.
2.2.1 Peak Rainfall Runoff
Considering the relatively small area of the proposed improvements ( < 1 acre), we have
utilized the Rational Method to compute runoff flows .
Rational Formula:
Q = C*I* A, where:
• Q = Flow from rainfall runoff in cubic ft per second
• C = Rational formula runoff coefficient<2l
• I = Rainfall intensity in inches per hour<3•4l
• A = Area under consideration in acres
<2l From Table III-1; DP&DS
<3l From Figure III-1; DP&DS; for a 100 year event, for minim um time of concentration of 10
minutes .
<
4ltc determined as mi n imum (10 min.), DP&DS ; §III, B , 3, C , (3).
Table 1. Pre-development Conditions
Area, A Runoff Rainfall Flow,Q Description of Area (acres) Coefficient C Intensity, I (cfs) dimensionless (in/hr)
Total KW Brown Property 1.6 Area
Front half 0.8
Back half 0.8
One-half of back 0.8 acres 0.4 0.35 10.75 1.5 Landscaped
One-half of back 0.8 acres 0.4 0.35 10.75 1.5 Landscaped
Total 3.0
Table 2. Post-development
Area, A Runoff Rainfall Flow,Q Description of Area (acres) Coefficient C Intensity, I (cfs) dimensionless (in/hr)
Total KW Brown Property 1.6
Area
Front half 0.8
Back half 0.8
One-half of back 0.8 acres 0.4 0.90 10.75 3.9 Impervious
One-half of back 0.8 acres 0.4 0.35 10.75 1.5 Landscaped
Total 5.4
Using the City of College Station DP&DS and the recommended Rational Method , the
calculated peak rainfall runoff from the KW Brown property (rear) in a 100-year storm event
would be 3.0 cfs, pre-development and 5.4 cfs , post-development. The difference between the
pre-development, and post-development flows , for which our storm drain design will be based on ,
is 2.4 cfs.
2.2.2 Inlet Grate Calculations
The required open area of the grate inlet shall be calcu lated using the following equation :
1
Q =4.82 * Ag * y 2 , where:
• Q = flow capacity in cfs, shall be reduced by 25% for design purposes<5
)
• A g = Open area of grate
• y = depth of water over grate
<5>From § V .D .1.b ; DP&DS
Estimating 2.4 cfs rainfall runoff and 5 .75 fps <6>, the estimated depth of flow , (y), would be 0.42
ft .
<6> From Table III -2, averaged ; DP&DS
A g= Open Area of Grate = 0.77 sq ft (111 sq in ).
2. 2. 3 Stormwater conduit calculation s
Design of the outlet pipe for the drop inlet box is based upon application of the continuity
equation and Manning 's Equation(§ VI.C. l)
Manning's Equation:
2
Q = 1.49 * A * (__i_J3 * S ~ n W J , where :
p
• Q =Pipe flow in cubic ft per second (cfs)
• n =Manning 's roughness coefficient, dimensionless
• A = Area of conduit in square feet (sq. ft .);= 0 .2 5 * n *D2
• WP = Wetted perimeter = n*D
• S =Conduit slope or friction slope of conduit in ft/ft
However, § VI , B , 2 states, "Conduits of 24 or less shall have a 25% reduced cross-
sectional area for design purposes". Thus , the equation shall read :
Q ~ 1.:9 •( 0·75 *411:* D') * (0 .75 * 0 .25* D)~ * s)
Solving for Dusing n = 0.0008(7) for PVC pipe and S= 0.11 yi elds
2.4 cfs = l.49 * (0 ·75 * :r * D
2 J * ( 0.75* 0.25 * D)f * (0.11)~
0.008 4
C7l From § VI, B , 2; DP&DS
therefore D = 0.55 ft= 6 .6 in Use next size pipe= 8 in pipe
For 8 in. PVC pipe flowing at 2.4 cfs with 11 % slope; based on Manning's Equation :
Flow Depth = 3 in
Flow velocity = 17 fps
For the second section of pipe being RCP, the slope is changed to 1 %.
using the above equation and substituting S = 1 % and n = 0 .014:
D = 1 ft = 12 in pipe.
For 12 in RCP flowing at 2.4 cfs ; based on Manning 's Equation:
Flow Depth = 8 in
Flow velocity = 5 fps
3.0 CONCLUSION
This engineered stormwater drainage system is considered the most effective control
measure to provide for the additional drainage needs of the KW Brown property as a result of the
construction project. The new storm sewer is designed to convey stormwater directl y to the
Edelweiss detention basin (Figures 2 and 4 , Appendix A), preventing the need for the
construction of a proposed drainage channel. This design provides for stormwater conveyance,
velocity reduction , scour prevention , and is easily maintained . KW Brown hopes The City will
find the design satisfactory and welcomes your comments.
ENGINEER'S CERTIFICATION
"I hereby certify that this report (plan) for the drainage design of KW Brown &
Associates', Inc. Property was prepared by me (or under my supervision) in accordance with the
provisions of the City of College Station Drainage Policy and Design Standards for the owners
thereof."
Registered Professional Engineer
State of Texas No. ----"b-=-g..._4~-'-g,.,__ ____ _
(Affix Seal)
APPENDIX A
Figure s I throu gh 4
Final Grade Final Grade
Concrete N
Inlet
Box
1 8"PVC
Co
T
2'
~ ~~
... / \
'
Inlet Grating
... \ J
~~ ~~
JFigure 3 D rop ][nlet Box D esign
KWBES i distance
Property ft . 10 20
315 .5-
315-
314 .5-
314-
313 .5-
313-
312.5-
312-
311 .5 -
311-
310 .5 -
310-
309 .5-
309-
308.5-
308-
307.5 -
307-
306 .5-
306 -
305 .5-
305-
304 .5-
Figure 4
30 40
Present storm
water runoff
pathway to
Victoria Ave .
Edelweiss
\ detention basin
berm
8" PVC from drop inlet box
11% slope
50 60
25% Benn
Slope
70 80 90
Tie-in to EEDB trickle
channel
12 " RCP and 45o
bend
12" RCP and 45° bend
1% slope
100
I
i
i
fi>roposed
!Apron
~ddition
iowflow
i side
i
trickle
channel
4'
110 120
+----2'-.
Proposed
Apron
Addition
high flow
side
Edelweiss
detention basin
trickle channel
Profile View of Berm
S~l
COLLEGE STATION
P. 0 . Box 996 0 1101 Te xas Avenue
Tel : 409 764 3500
College Statio n , T X 77 842
KW Brown November 20 ,1998
501 Graham Road
College Station, Texas 77845
Attn: Spencer G . Thompson, Jr.
Dear Mr. Thompson:
Attached you will find our review comments for the KWBrown drainage design. If you have any
questions, please call. I can be reached at 764-3570.
Veronica J.B . rgan, . .
Asst. City Engineer
VJr~~~~Wf~
Home of Texas A&M University
October 5, 1998
Veronica Morgan, P .E .
Assistant City Engineer
City of College Station
P .O . Box 9960
College Station, TX 77842-9960
RE: K.W. Brown Expansion Project
Dear Veronica:
~l
·~~{~ . ., ..
~vu-~~
We have been asked to review and comment on the drainagk design of the above refere ed proje~t~ •T he
grading plan provided by the owner shows a negligible amount of increase in the impervious area of the site (0.12
acres.) Additionally, the plan does not call for any flow to be diverted from existing watercourses, which means
this development is not hydraulically connected to the improved storm drain system on Victoria Drive.
The site being proposed for development by K.W. Brown was included in the analysis of the Edelweiss
Estates Subdivision Drainage Study. It is included as Drainage Area #4 of Exhibit D-2 in that report and constitutes
Jess than one percent of the total drainage basin. Runoff from the site was estimated using a conservative CN
value of 84. The storm drainage system and stormwater detention pond built with Edelweiss Estates was designed
to compensate for fully developed conditions at the K.W. Brown site without additional detention.
The rational drainage area used for flow computations for the K.W. Brown site is referred to as Area 40B in
the above referenced report. Analysis of Area 40B shows that:
Q 2s = 15 cfs
Qs/3 = 4 cfs
Based on these flows, a grassed-lined, trapezoidal channel (n=0.030) on a 1.3% slope that is 1.3 ' deep and
two feet (2 ') wide (bottom width) with 4 :1 side slopes is capable of carrying the runoff at non-erosive velocities.
This cross-section produces the following flow characteristics:
Flowrate
Qis 15 cfs
Qs/3 4
Flow depth
0.80 ft.
0.42
Velocity ·
3.6 fps
2 .5
Note that these velocity and depth parameters meet the requirements of the City of College Station
Drainage Policy. Should you have any questions regarding my analysis, please do not hesitate to call.
Sincerely,
itchell, P.E .
C efDesign Engineer
xc. Rusty Ethridge, K.W. Brown.
1722 Broadmoor, Suite 21 O • Bryan , Texas 77802 • (409) 776 -6700 • FAX (409) 776-6699
DEVELOPMENT PERMIT
PERMIT N0.587
KW BROWN EXPANSION
FOR AREAS OUTSIDE THE SPECIAL FLOOD HAZARD AREA
RE: CHAPTER 13 OF THE COLLEGE STATION CITY CODE
SITE LEGAL DESCRIPTION:
Lot 1, Block 1 of the Brown Addition
OWNER:
KW Brown
Environmental Science & Engineering
501 Graham Road, College Station 77845
690-9280
DRAINAGE BASIN:
Lick Creek
TYPE OF DEVELOPMENT:
This pennit is valid for all site construction per the approved plans.
SITE ADDRESS:
501 Graham Road
The Contractor shall take all necessary precautions to prevent silt and debris from leaving the immediate
construction site in accordance with the approved erosion control plan as well as the City of College
Station Drainage Policy and Design Criteria. The Owner and/or Contractor shall assure that all disturbed
areas are sodden and establishment of vegetation occurs prior to removal of any silt fencing or hay bales
used for temporary erosion control. The Owner and/or Contractor shall also insure that any disturbed
vegetation be returned to its original condition, placement and state. The Owner and/or Contractor shall
be responsible for any damage to adjacent properties, city streets or infrastructure due to heavy machinery
and/or equipment as well as erosion, siltation or sedimentation resulting from the pennitted work.
Any trees required to be protected by ordinance or as part of the landscape plan must be completely fenced
before any operations of this pennit can begin.
In accordance with Chapter 13 of the Code of Ordinances of the City of College Station, measures shall be
taken to insure that debris from construction, erosion, and sedimentation shall not be deposited in city
streets, or existing drainage facilities .
Contractor Date
I
)
TO:
COLLEGE STATION
P. 0 . Bo x 9960 1101 Texas Avenue
Tel : 409 764 3500
MEMORANDUM
College Station , TX 77842
FROM:
Kirk Brown, K. W . Brown Environmental Science
Natalie Ruiz, Assistant Development Coordina 0
July 6, 1998 DATE :
RE : K. W . Brown Office Building Addition on Graham Road.
Attached are the applications that need to be completed before the building pennit can be issued .
I've also put together the following list of items and/or fees that must also be taken care of prior
to permit issuance:
· Water and sewer tap fees:
_ 4" Sanitary Sewer Tap -$350
_ Based ·on the domestic water demands provided on the site plan, a I 1/2" water
meter is required. You have the following two options : I) Replace the existing I"
water meter with a I 1/2" water meter ($800 tap fee), or; 2) Add a I" water meter
($500 tap fee) to the site .
_ Sanitary sewer impact fees in the amount of $724.43 . (This fee remains the same
regardless of the water meter size.)
_ Completed application for building pennit (see attached).
__ Building pennit fees. (Staff will calculate the amount once the applicatinn is returned .)
_ Completed application for Contractor's License (see attached).
_ $54 Contractor's License application and processing fee .
_ Completed application for a Development Pennit (see attached). Once we receive the
completed application, staff will prepare a development pennit for your signature.
_ Development Pennit & infrastructure inspection fees in the amount of $400 .
Home of Texas A&M University
Memo to K. W Brown
July 6, 1998
Case # 98-411
Page 2 o/2
All of the above fees will be collected at the Building Department and may be paid by one check
for your convenience.
From what I understand, your civil engineer is currently working with City Staff to resolve the
drainage issues associated with the site . In an effort to expedite your expansion, City Staff has
agreed to proceed with the issuance of a building permit. However, there will be a condition
placed on the building permit that a Certificate of Occupancy will not be issued until the drainage
along the rear of the property is resolved .
If you have any questions about the items listed above or need additional information pertaining to
issuance of a building permit, please contact me at (409) 764-3570 or e-mail me at
"nruiz@ci . college-station . tx . us". Thank you.
cc : Lance Simms, Building Official
Case file #98-411
• McCLURE ENGINEERING, INC.------~
June 10, 1998
Paul Kaspar
City of College Station
P.O. Box 9960
College Station, TX 77842-9960
RE: K.W. Brown Expansion Project
Dear Paul:
We have been asked to review the drainage design of the above referenced
project. The grading plan provided to me by the owner shows a negligible amount of
increase in the impervious area of the site (roughly 0.12 acres.) Additionally, this area is
not hydraulically connected to the improved storm drain system. The proposed grading
also does not divert any flow from the existing watercourses.
The proposed improvements constitute less than one percent of the area of the
drainage basin. The area was modeled in the Edelweiss Estates Subdivision Storm
Drainage Analysis using an assumed curve number of 84 for this area (called area #4 in
the HEC-1 modeling. This assumption is more conservative than the proposed
development. Hence, the storm drain system and storm water detention pond built with
Edelweiss Estates is adequately sized so that no detention is required for this expansion.
Should you have any questions or require my assistance, please do not hesitate to
call.
Sincerely,
i!ttc!:::
Chief Design Engineer
1722 Broadmoor, Suite 210 • Bryan, Texas 77802 • (409) 776-6700 • FAX (409) 776-6699