HomeMy WebLinkAboutDrainage ReportDrainage Report
FOR
INDIAN L4KES; PHASES N & VI
COLLEGE
STATION
u
c
� tam e
Phase
NILUCAN
Location Map
NTS
MAY, 2004
Prepared By:
McClure do Browne Engineering /Surveying, Inc.
1008 Woodcreek Drive, Suite 103
College Station, Texas 77845
(979) 693 -3838
1n
Drainage Report
FOR
INDIAN L4AT$ PHASES IV & VI
Location Mop
NTS
MAY, 2004
rr
Prepared By:
McClure do Browne Engineering /Surveying, Inc.
1008 Woodereek Drive, Suite 103
College Station, Texas 77845
(979) 693 -3838
a
CERTIFICATION
I, Kent M. Laza, Registered Professional Engineer No. 65923, State of Texas, certify that the
Drainage Report for the INDIAN LAKES SUBDIVISION, PHASES IV & VI, was prepared by me
in accordance with the provisions of the City of College Station Drainage Policy and Design
Standards for the owners thereof.
Kent M. Laza, P.E. No. 65923
DRAINAGE REPORT
TABLE OF CONTENTS
INDIAN LAKES SUBDIVISION, PHASES IV & VI
INTRODUCTION 1
GENERAL LOCATION AND DESCRIPTION 1
FLOOD HAZARD INFORMATION 1
PRIMARY DRAINAGE SYSTEM DESCRIPTION 1
DRAINAGE DESIGN CRITERIA 1
DETENTION DESIGN 2
CONCLUSION 3
EXHIBITS
FEMA FLOOD INSURANCE RATE MAP EXCERPT
A
DRAINAGE AREA MAP - PROPOSED CONDITIONS
B
RATIONAL FORMULAS DRAINAGE AREA CALCULATIONS
C -1
CULVERT ANALYSIS: CULVERT 1
C -2
CULVERT ANALYSIS: CULVERT 2
C -3
CULVERT ANALYSIS: CULVERT 5
C -4
DRAINAGE REPORT
INDIAN LAKES SUBDIVISION, PHASES IV & VI
STORM DRAINAGE REPORT
INDIAN LAKES SUBDIVISION, PHASES IV & VI
INTRODUCTION:
This storm drainage report is intended to analyze the drainage infrastructure proposed for the
development of the Indian Lakes Subdivision, Phases IV & VI. The existing and proposed conditions are
included to show how the design will achieve the desired drainage objectives of Brazos County and the City
of College Station.
GENERAL LOCATION AND DESCRIPTION:
Indian Lakes Subdivision is located in the southern portion of the extra territorial jurisdiction of
College Station in Brazos County. The site is bounded by property owned by Bewley Trust to the North
and Indian Lakes Subdivision, Phase 1, to the South and West. Property to the East is owned by Smiling
Mallard Development, LTD. and is planned as future phases of the Indian Lakes Subdivision.
FLOOD HAZARD INFORMATION:
No portion of the site is shown to be within the 100 -year floodplain on the FEMA Flood Insurance
Rate Maps (FIRM) for Brazos County, Texas and Incorporated Areas, Map Number 48041CO215C,
effective July 2, 1992. As such, this site is not currently regulated under the National Flood Insurance
Program An excerpt from the FIRM panel is shown in Exhibit A.
PRIMARY DRAINAGE SYSTEM DESCRIPTION:
Exhibit B is a drainage area map that shows contours and proposed drainage areas for the site. The
proposed streets will have either a 24' or 30' wide paved surface with ditches. Storm water from the site will
be captured in the ditches along the roads and conveyed to the natural streams on the site. Corrugated
metal pipe culverts will be used at the street crossings.
DRAINAGE DESIGN CRITERIA:
Since this project falls within the ETJ of College Station, the drainage system for Indian Lakes was
designed using the criteria in College Station's Drainage Policy and Design Standards. The design storm is
a 10 -year rainfall event for ditch line culverts and a 25 -year rainfall event for all stream crossing drainage
STORM DRAINAGE REPORT PAGE 1
INDIAN LAKES SUBDIVISION, PHASE IV & VI
structures that are "non- trapped" and 100 -year event for "trapped" conditions. Flow calculations for
culverts "1" & "2" are based on the Rational Method (Exhibit C -1). Flow for culvert "3" (emergency
spillway crossing) is taken from the Engineering Report for Lake Arapaho prepared by East Texas
Engineers, Inc. The 100 year flow was determined to be 100 cfs. Pipe sizes were determined by analyzing
culvert capacity under inlet and outlet control. All proposed culverts meet requirements for freeboard and
road overtopping.
Exhibit C -2 describes the peak runoff calculations for the post - development conditions of the
culverts shown in Exhibit B. A summary of these results is shown below:
Flowrates (efs) from Culverts
In Indian Lakes Subdivision, Phase IV & VI
Culvert 1 5 year 10 year 25 year 50 year 100 year
1 31.4 35.3 40.3 45.5 51.2
2 29.6 33.2 38.0 42.9 48.2
These runoff rates were used to design the roadway crossings shown in Exhibits D -1 through D -8.
The resulting culvert sizes are as follows:
Culvert Sizes
Culvert
Culvert Size
1
2 -24" Corrugated Metal Pipes
2
( 2 -24" Corrugated Metal Pipes
3
3 -30" Corrugated Metal Pipe
DETENTION DESIGN:
Detention for Phase IV & VI of Indian Lakes Subdivision is provided by Lake Arapaho, which was
constructed with Phase I ofthe subdivision. The lake and its accompanying outlet works were designed to
capture and store runoff from the 390 -acre drainage basin above the dam. The table that follows is an
excerpt from the Engineering Report for Lake Arapaho prepared by East Texas Engineers, Inc. in
September 2002. The Peak Inflow figures are based on post - development runoff rates. It shows that all
rainfall events have been analyzed during the design of the lake and provisions made to store and release
STORM DRAINAGE REPORT PAGE 2
INDIAN LAKES SUBDIVISION, PHASE IV & VI
water at a significantly reduced rate.
Flood Event
j Peak Inflow
Peak Outflow Max. Lake Level
(CA)
(cfs) (feet msl)
PMF
7794
3113 264.9
48.1 %PMF
3750
958 262.2
100 -yr
1536
201 260.0
50 -yr
i
1305
i 153 259.7
25 -yr
( 1100
114 259.4
10 -yr
877
113 259.0
5 -yr
660
94 258.6
2 -yr
429
57
258.3
Note that for the standard design storms (2 -yr through 100 -yr) the peak outflows are approximately
10 -15% of the peak inflow. No pre - development runoffrates were computed with the analysis ofthe lake,
but the report indicates that a SCS Curve number of 82 was assumed for these post- development
computations. The large, rural estate lots that are planned with this development have a very small
percentage of impervious cover associated with them, so the SCS Curve number for the pre - development
condition would have been only slightly less than the post - development number. This implies that only
small increases in runoff rates would be expected between the pre- and post - development scenarios. The
high capacity for storage that the lake offers will easily offset any small increases in runoff rates due to the
development surrounding it.
CONCLUSION:
Indian Lakes Subdivision, Phase IV & VI is a rural subdivision for single family residences on lots
that are approximately 1 acre in size or larger. The small change in impervious area from the development
of this subdivision is small and has minima effects on the existing drainage system.
Proposed improvements at the street crossings are designed using guidelines in the City of College
Station's Drainage Policy and Design Standards. Exhibits D -1 through D -8 shows that all drainage
structures in the Indian Lakes Subdivision, Phase IV & VI are capable of passing the design rainfall event
with one foot of freeboard.
STORM DRAINAGE REPORT PAGE 3
INDIAN LAKES SUBDIVISION, PHASE IV & VI
EXHIBIT C -1
Rational Formula Drainage Area Calculations
Indian Lakes Phase IV & VI
5/19/04
0408- ph4- dre.)ds
Exhibit C -1
EXHIBIT C•2
CULVERT ANALYSIS
INDIAN LAKES PHASE FOUR
CULVERT #1
Dual 24" RCP
Culvert Donlon Criteria
Circular
Lt. Side
Rt, Side
Bottom
Invert
Outlet
Culvert
Slope
Top
Pipe
ft/ft
No.
9:1
Elev. (ELI)
Elev, (ELo)
1
Length
Slope
of
Die. ft.
0.024
pipes
n
ft.
ft.
fL
ft/ft
Road
2.00
2
0.014
1 283.00
259.00
133.50
1 0.0300
270.45
ELM - T�offta d E Lho
=W1 �_ H
D
r r r - - _ _ _ � TW
ELI Proposed Culvert i7 R\
`- ELo
ke
0.5Q
Outfail Channel Design Criteria
Culvert Analvals Calculations
Design
Storm
Lt. Side
Rt, Side
Bottom
Normal
Depth
ft.
Slope
Slope
Slope
Width
n
ft/ft
7:1
9:1
ft.
I HWI
0.0100
4.00
4.00
0.00
0.024
Design
Storm
Total
Flow
cfs )
Flow per
Pipe
(Cfs)
Critical
Depth(ft.)
do
Normal
Depth
ft.
HEADWATER CALCULATIONS
Control
HW
Elev.
Type
of
Control
Outlet
Velocity
Me)
Freeboard
ft.
INLET CONTROL
OUTLET CONTROL
HWI /D
I HWI
ELhI
TW
do
do + D)/2
ho
H
ELho
5
31.40
15.70
1.45
0.92
1.13
1 2.26
265.26
0.95
1.45
1.73
1.73
1.32
282.05
265.26
Inlet
11.19
5.19
10
35.30
17.85
1.53
0.98
1.24
1 2.47
265.47
1.01
1.53
1.77
1.77
1.87
282.44
265.47
Inlet
11.52
4.98
25
40.30
20.15
1.60
1.06
1.33
2.85
265.65
1.09
1.60
1.80
1.80
2.18
262.98
265.85
inlet
11.90
4.80
50
45.50
22.75
1.73
1.14
1.49
2.98
265.98
1.18
1.73
1.87
1.87
2.78
263.84
265.98
1 inlet
12.24
4.47
100
1 51.201
25.80
1 1.80
1 1.24
1.70
1 3.39
288.39
1,19
1.80
1.90
1.90
3.52
264.42
266.39
1 Inlet
1 12.56
1 4.06
ELhi = Hwl + ELi H - ( 1+ ke +((2V(M2)*LYR
ho - 7W or (dc + D)t2 (Whichever is Greeter) El-ho - ELo + H + ho
5/19/04
0402- cul- ph4- 01.)ds
Exhibit C -2
EXHIBIT C -3
CULVERT ANALYSIS
INDIAN LAKES PHASE FOUR
CULVERT #2
Culvert Deslan Criteria
Circular
Lt. Side
Rt. Side
Bottom
Invert
Outlet
Culvert
Slope
Top
Pipe
ft/ft
No.
0:1
Elev. (ELI)
Elev. (ELo)
Length
Slope
1
of
Dia. ft.
0.024
Pipes
n
ft.
ft.
ft.
ft/ft
Road
2.00
2
0.014
1 255.00
252.00
104.00
0.0288
259.98
ELM -�
Top of Road ELho
�
EH HWI �.��.�����- - -�
ELI Proposed Culvert
ELo
ke
0.50
Outfall Channel Desl n Criteria
Dual 24" RCP
Cot wart Anal-isle Cwlrad Minns
Design
Storm
Lt. Side
Rt. Side
Bottom
Normal
Depth
(ft)
Slope
Slope
Slope
Width
n
ft/ft
7:1
0:1
ft.
I HWI
0.0100
4.00
4.00
0.00
0.024
Design
Storm
Total
Flow
(cla)
Flow per
Pipe
(cis
Critical
Depth(ft.)
do
Normal
Depth
(ft)
HEADWATER CALCULATIONS
Control
HW
Elev.
Type
of
Control
Outlet
Velocity
(fps)
Freeboard
ft.
INLET CONTROL
OUTLET CONTROL
HWi /D
I HWI
Uhl
TW
do
do + M/2
ho
H
ELho
5
10
25
29.60
33.20
38.00
14.80
16.60
19.00
1.40
1.50
1.55
0.90
0.96
1.04
1.08
1.18
1.26
2.16
2.36
2.52
257.16
257.36
257.52
0.95
1.00
1.06
1.40
1.50
1.55
1.70
1.75
1.78
1.70
1.75
1.78
1.03
1.30
1.70
254.73
255.05
255.47
257.16
257.36
257.52
Inlet
Inlet
Inlet
10.87
11.19
11.56
2.80
2.60
2.44
50
42.90
21.45
1 .85
1.12
1.41
2.81
257.81
1.12
1.85
1.83
1.83
2.18
255.99
257.81
Inlet
11.90
2.15
100
48. 20
24.10
1.75
1.20
1.59
3.17
258.17
1.18
1.75
1.88
1.88
2.73
256.81
258.17
Inlet
12.21
1.79
ELhi - Hwi + ELI H = (1 +ke +((29 (rt^2)'LyWl - 33))•((` 12 y 2 9)
ho = TW or (dc + D)12 (Whichever is Greeter) ELho - ELo + H + ho
5/19/04
0402- cul- ph4.02.)1s
Exhibit C -3
SPILLWAY CULVERT
Triple 30" CMP
EXHIBIT C-4
CULVERT ANALYSIS
INDIAN LAKES PHASES VI
Culvert Desian Criteria
Circular
Lt. Side
Rt. Side
Bottom
Invert
Outlet
Culvert
Slope
Top
Pipe
ft/ft
No.
?:1
Bev. (ELI)
Elev. (ELo)
Length
Slope
of
Die. ft.
0.024
PI s
n
ft.
ft.
ft.
ft/ft
Road
2.50
3
0.020
253.85
253.38
70.00
0.0070
258.00
Culvert Anelvele Cwlculatinne
El-hl Top of Road ELho
�.. - -- H
—
HWi D ���..�..
��� TW
ELI --X Proposed Culvert �- ,
`-- ELo
ke
0.50
Outfall Channel Desian Criteria
Design
Storm
Lt. Side
Rt. Side
Bottom
Normal
Depth
ft
Slope
Slope
Slope
Width
n
ft/ft
?:1
?:1
ft.
I do
0.0080
4.00
4.00
0.00
0.024
Design
Storm
Total
Flow
cfs
Flow per
Pipe
cfs
Cticl
D
do
Normal
Depth
ft
HEADWATER CALCULATIONS
INLET CONTROL I OUTLET CONTROL
Control
HW
Elev.
Type
of
I Control
Outlet
Velocity
(f D
Freeboard
ft.
HWUD
I HWI I
ELM
I TW
I do
do + D)/21
ho I
H j
ELho
10
1100.001
33.33
1 1.98
1 2.50
1 1.80
1 4.00
1 257.85
1 1.47
1 1.98
1 2.24
1 2.24 1
2.18
1 257.78
1 257.85
1 Inlet
8.79
1 0.15
ELhi = Hwi + ELI H = ( 1+ ke+( (29'(n "2)'LpR^1.33))•((v
ho -TW or (dc + Dy2 (Whichever is Greater) ELho = ELo + H + ho
5/19/04
0408- cul- phe- 03.>1s
Exhibit C-4
I it " INDIAN LAKES
PHASE /V
lift 1 �
EX
I 1
oil
INDIAN LAKES °
PHASE V/ 1
== PEACH CREEK
EXHIBIT A
Flood Insurance Rate Map Excerpt
Brazos County, Texas
and Incorporated Areas
Map Numbers: 48041 CO215C
N.T.S.
Effective Date: July 2, 1992
j ��•_ _._... �_ _.._ mot-.^_ .._.. _...... -._.. �
It N
Z 62
_.._ 264 — - ' � � f
� — of
Lot 21 — Lo #._2Q._ 266— 1,04_.._19- o
—268 J ✓�' j1, r Scale: 1" 200' (Horiz.)
-- 270 _ — z `'' SC - ' l � / !!� / f / ! 1 �K / , At I A i
-272 � t i ay I / !
haco Canyon D
?6;9 •270 \ ! / ` � J t i t i f
_ z 6k
I 24" c�lY� — �J / l 'J / / O a li /
f �� i l� I 'Lot 33� Lit" 35
a j
Lod 6
2 48_ ! \ `8lo��fc. e ; l I 9.6 6 a C
. - 252 / `
254 -- _ ,/ / m V .._ ......
— 256 - ..� � � �,.. J N w f / I
ry ,�� f , ` � ! , t \ 'ti ,� \ .. -' \ ��\ � \ \ �, 4 � � �• ,�-' �' � _._ J --
26 - i ro CV ti ! \ \ \^ \ \J \ _
CY
256 1 ;�
" ~ �p \ S\ �, \
k
Legend
- Drainage Area Number
0 oc - Acreage
- -xxx- - - Existing Ground Contours
- Drainage Flow
DRAINAGE AREA MAP
PROPOSED CONDITION
EXHIBIT B