HomeMy WebLinkAboutDrainage Reports - 12/18/2015 (4)r77QUALITY
~ ENGINEERING
December 18 , 2015
Mr. Shane Boyle & Mr. Dan Magen
City of Fort Collins Engineering Department
281 N College A venue
Fort Collins, Colorado 80524
WWW.QUALITY-ENGINEERING.COM
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RE: Drainage Memo -615 E. Plum Street Addition
615 E. Plum Street, Fort Collins (Larimer County), Colorado 80525
QE Project No. 6270-01
Mr. Boyle & Mr. Mogen:
The purpose of this letter is to address drainage impacts to the existing 0.21 acre property located at 615
E. Plum Street due to the proposed building addition and garage. The site is situated in Lot 5 , Block
178, City of Fort Collins, County of Larimer, State of Colorado. Specifically, the property is located
midway between Smith Street and Stover Street and bound by East Plum Street to the north and a
common alley access-Way to the south. The subject property is surrounded by residential properties to
the west, east, across the alley to south, as well as across Plum Street to the north.
The existing property currently consists of a house , sidewalks, a storage/shop building, and mature
landscaping. The existing site currently drains to a low-point in the lawn area of the southwest corner of
the lot. The existing shop/shed located south of the house will be removed and replace with the
proposed building addition footprint. The proposed work shall consist of an approximately 1,600 square
foot addition onto the existing home enlarging the building footprint , as well as the addition of a
proposed 24-ft x 24-ft detached 2-car garage in the southeast corner of the property.
The proposed grading plan for the site follows historical patterns as closely as possibly, while making an
effort to improve drainage and water quality issues that currently exist on the site. An existing high-
point, located within the northern third of the lot, splits the proposed runoff into north and south basins,
respectively.
The developed flows from the north basin shall continue to sheet flow north, as they do historically, to
the curb and gutter of East Plum Street. Runoff from the south basin will be routed into natural
flowlines conveying the flows into a proposed on-site runoff storage depression constructed with a 'Dry-
Well' at the depression's low point. Due to this unique, historical, city drainage basin not having an
outlet, as it is the local low-point, the proposed depression and Dry-Well cannot have an underdrain
outlet. Therefore, the Dry-Well shall be considered as a point of infiltration to mitigate developed storm
water runoff.
QUALITY ENGINEERING, LLC (970) 416 -7891 2637 MIDPOINT DRIVE, SUITE E FORT COLLINS, COLORADO
Page2
Drainage calculations are provided for this project due to the increase of impervious area on the exiting
subject lot and to verify that increased flows will not adversely impact adjacent properties. Since the
existing lot does not have any adverse impact to adjacent properties , a design is proposed to increase the
site's infiltration with the addition of the Dry-Well , in addition to detaining the difference in volume of
runoff due to the site's increased imperviousness. This design was also chosen based on the survey data
provided to the designer being limited to only the subject property , therefore limiting existing versus
proposed drainage conditions analysis.
For a comparison of the existing and proposed sites, the existing 2-year historical flow shall be used for
a baseline for the southern drainage basin . The 100-year, existing flow rate is 0.5 cfs/acre for the subject
property (See calculations in Appendix). Using this flow rate as the allowed release rate for the
proposed development , the site produces a mnoff detention volume of 149 cubic feet of more storage
capacity than the existing site due to the proposed building/sidewalk additions .
The rear (south) yard area of the lot was selected as the location for the depression and Dry-Well to
follow existing drainage patterns as closely as possible as well a s maintain as much distance as possible
to the surrounding adjacent homes . On December 10 , 2015 , Soilogic performed a borehole te st in the
area of the proposed Dry-Well to detern1ine the existing depth of the clay soil layer. The depth of clay
on-site is approximately 14-feet deep , and therefore the proposed Dry-Well shall also be a depth of 14-
feet , to allow maximum infiltration to the sand layer beneath the clay. Because the Dry-Well is being
extended to the depth of the sand soil layer, it is anticipated that the proposed release rate will be
increased from 0.5 cfs/acre to 0.8 cfs/acre. This difference of 0.3 cfs is accounted for by dividing said
flow by the area of the manhole base (pi *R'''2 = 12.56 sf), leaving 0.024 vertical feet of drop in the
manhole per second. This is also equal to 1.4 vertical feet per minute of infiltration.
Per the proposed grading design , th e volum e capacity of the earthen depression is 128 cubic feet , leaving
21 cubic feet of storage un-accounted for. However, it is also proposed that the Dry-Well be constmcted
of a typical 4-foot diameter manhole to a depth of 14-feet. The Dry-Well shall be built with 2.5 -feet of
(+/-)9-inch Rip Rap at the bottom of the structure. The top 11.5-feet of the Dry-Well shall be left as
pure storage volume, providing 144 additional cubic feet for a total of 272 cubic feet , which is well over
the 149 cubic foot difference of developed storm water runoff. The development of the lot as proposed,
along with the depression and Dry-Well feature will enhance and improve the drainage on this site, as
well as the entire block , as the back yard of this lot appears to be the local low-point within the area.
The City of Fort Collins Stormwater manual amending the Urban Storm Drainage and Flood Control
District (USDFCD) has been used for drainage design guidance.
Please see the attached hydrologic basin parameters, 2-year and 100-year existing & developed flow rates.
In summary, the grading and drainage design for the proposed home addition and garage at 615 East Plum
Street complies with the requirements of Urban Storm Drainage and Flood Control District as well as the
City of Fort Collins' Storm Drainage Criteria. The proposed changes have nearly negligible effects on
the historic drainage system of the lot. Please see the attached grading plan and drainage plan. If you
have any questions or require additional information, please call at (970) 416-7891.
Page3
Sincerely,
QUALITY ENGINEERING , LLC Reviewed by ,
Mark Morrison, EI
Project Manager
Attachments -
Principal Engineer
Appendix A
-Existing and Proposed composite 'C ' values
-Existing and Proposed flows (cfs)
-Existing Detention Required (cubic feet)
-Proposed Detention Required (cubic feet)
-Grading/Drainage Plan
Appendix A
-Existing and Proposed composite 'C ' values
-Existing and Proposed flows (cfs)
-Fort Collins Existing Detention Spreadsheet
-Fort Collins Proposed Detention Spreadsheet
-Grading Plan (24x36)
Design Point Basin(s) Asphalt Area (acres) (C=0.95) Pl El 0.00 E2 0.000 D1 Bl 0.000 D2 82 0.000 Notes: Composite C values obtained from Table R0-11 Major Storm Runoff factored per Table R0-12 MAP Concrete Area (acres) (C=0.95) 0.001 0.009 0.003 0.024 Composite C Values 615 PLUM Gravel (acres) Roofs (acres) (C=0.50) (C=0.95) Existing 0.005 0.00 0.0000 0.0200 Developed 0.000 0.010 0.000 0.060 Lawns (acres) (C=0.15) 0.024 0.1560 0.036 0.089 PLUM_City of Fort Collins Rational Method.xlsx Total Area Minor (2-YR) Major (100-YR) (acres) Composite "C' Composite "C" (Cfx C) 0.03 0.24 0.29 0.19 0.28 0.34 0.05 0.36 0.45 0.17 0.54 0.67 12/17/2015
Arn Minor Dcsicn Basin (s) Major lnltuil/OVortand rune Basin Flow Calculati<m~ 615 PLUM TraveJTime Minort_ Majort., Channel Point Slope (acres} Composite "C" Compo51te "C" lfflcth (ft) Slop•(") (min)' (min)' ~ncth (ft) l"l Type Pl El 0.0300 I 0.24 I 0.29 I 28 I 0.% I 8.68 8.09 I E2 0.1850 I 0.28 I 0.34 I 65 I 1.00 I 12.43 11.39 I I I I I I D1 Bl 0.0490 0.36 0.45 45 1.,1 8.14 7.14 D2 B2 0.1730 0.54 0.67 65 1.50 7.40 5.62 Not~s: , _ l.87(1.l-CC1)D'" t_-S"l •ttM $ Heavv Meadow. TF • Tillaet!/field, Pl• Short pasture a:id lawns, BG• Ne~rtr bMe cround, GW • Gus.sed \Vatervny, PA• Paved Area. 'Velocsty a!ues from Fi&ure 3-3/Tab!e R0-2 EsUINllt of Aver.gt Flow Velocity fot use with the Ro1ti0nal Methot Exlstinl 0 2.00 I Pt. I 60 2.00 I PL I I I Developed 2.00 PL 86 2.00 PL Volo<ity (fps)' 0.99 0.99 0.99 0.99 CAG PLUM_City of Fort Collins R•tional Method.xlsx AnalT, Intensity (in/hr) ea.in Flows (cfs) MinorT, t,(min) (min) MajorT, (min) 2-yr 111-yr 100-yr 2-yr 10-yr 100-yr I o.oo I 8.68 8.09 I 2.35 I 4.02 I 8.38 I 0.02 I 0.03 I 0.07 I 1.01 I 13.44 12.40 I 1.95 I 3.34 I 7.04 I 0.10 I 0.17 I 0.45 I I 0.0000 8.14 7.14 2.40 4.10 8.80 0.04 0.07 0.20 1.4479 8.84 7.07 2.30 3.93 8.80 0.21 0.37 1.02 12/3/2015
615 E . Plum Stre et -Exi stin g D ra in age Conditi ons
Eguations :
Q 0 =CiA
Vi = T *CiA = T *Q 0
V0 =m*Q1'0 *(60*T)
S=Vi -Vo
Rainfall intensity from Larimer County Area I IDF Curve
Storm Rainfall
Duration , T Intensity, i
(min) (in/hr)
5 9.95
10 7 .72
20 5 .60
30 4 .52
40 3 .74
so 3 .23
60 2 .86
70 2 .62
80 2.38
90 2.22
100 2 .05
IJO 1.93
120 1.80
130 1.60
140 1.40
t 150 1.20
160 1.15
170 1.10
180 I.OS
Required Storage Volume:
QI)
(cfs)
0.6
0.5
0.4
0.3
0 .2
0 .2
0.2
0 .2
0.2
0 .1
0 .1
0 .1
0.1
0.1
0 .1
0 .1
0 .1
0.1
0.1
43
0.001
Vol .In
v,
(ft3)
193
299
434
526
580
626
665
711
738
774
795
823
837
806
760
698
713
725
733
ft3
acre-ft
A trib. To pond = 0.19 acre
C rno = 0.34
De ve lope d C * A = 0 .06 acre
Oro = 0 .50 cfs
tc = 7 .07 min
Outflow Vol.Out Storage Storage
Adjustment v. s s
Factor, m (ft3) (ft3) (ac-ft)
1.00 150 43 0 .001
0 .85 256 43 0 .001
0.68 406 28 0 .001
0.62 556 -30 -0.001
0 .59 706 -126 -0.003
0.57 856 -230 -0.005
0.56 1006 -341 -0.008
0.55 1156 -445 -0.010
0 .54 1306 -568 -0.013
0 .54 1456 -682 -0.016
0 .54 1606 -811 -0.019
0 .53 1756 -933 -0 .021
0.53 1906 -1069 -0.025
0.53 2056 -1250 -0 .029
0 .53 2206 -1446 -0.0'.B
0.52 I 2356 -1658 -0 .038
0 .52 2506 -1793 -0.041
0.52 2656 -1931 -0.044
0.52 2806 -2073 -0.048
615 E. Plum Street -Propos ed Drainage Conditions
Equations:
Q0 =CiA
V; = T*CiA = T*Q 0
Vo =m *Oro*( 60 *T)
S = V; -V0
Rainfall intensity from Larim er County Area 1 IDF Curve
Storm Rainfall Qo Vol. In
Duration, T Intensity, i (cfs) V1
(min) (in/hr) (ft3)
5 9 .95 1.2 374
10 7.72 1.0 580
20 S.60 0.7 842
30 4.52 0.6 1019
40 3.74 0.5 1125
50 3.23 0.4 1214
60 2.86 0.4 1290
70 2.62 0.3 1379
80 2.38 0.3 1431
90 2.22 0.3 1502
100 2 .05 0.3 1541
110 1.93 0.2 1596
120 1.80 0.2 1624
130 1.60 0.2 1564
140 1.40 I 0.2 1473
150 1.20 0 .2 1353
160 I.IS 0.1 1383
170 1.10 0.1 1406
180 1.05 0.1 1421
Required Storage Volume: 192 rt3
0.004 acre-ft
A trib . To pond = 0.19 acre
C100 = 0.67
Developed C* A = 0.13 acre
Oro = 0.80 cfs
tc = 7.07 mi n
Outflow Vol. Out Storage Storage
Adjustment Vo s s
Factor, m (ft3) (ft3) (ac-ft)
1.00 240 134 0.003
0 .85 410 171 0.004
0.68 650 192 0.004
0 .62 890 130 0.003
0.59 1130 -5 0 .000
0.57 1370 -156 -0.004
0.56 1610 -320 -0.007
0.55 1850 -471 -0.01 I
0.54 2090 -658 -0.015
0.54 2330 -828 -0.019
0.54 2570 -1029 -0.024
0.53 2810 -1214 -0.028
0.53 3050 -1426 -0 .033
0.53 3290 -1726 -0.040
0.53 3530 -2056 I -0.047
0.52 3770 -2417 -0.055
0 .52 4010 -2626 -0.060
0.52 4250 -2844 -0.065
0.52 4490 -3069 -0.070
• :l' .. ! .. ~--~-..,_,_ ' i,-K . )} "' C ~•,-.., ~ " !! .. ---~~---""""::':;OCATEDTELEPHONE, ► ~ .,_ _____ ,, .. ~!!:i!=""..,;:e~==-~~~...e&:=~~~:,11.----------.1........ ' -~-. . ~ tr· ·-4 "" '7 .;;_\(~SDEW~~l~-------,.w---:..-_-~l:-.-~r1~ -I "i,~~~ .. ~-=\""' '~74.15 RELOCATED _SED...,..GE • O ' -" ,~ I •·=--• "'\ 1 @ ,~(r i ---.-,~:!~-;-c· -.,.......,_______ 7 ~-~ I -~;-· I ". · .. , ! I ' . -• ----------,1 ·~ I I L__ ~si=:=~:!i!!f.\~;.::_='-!Q\l•tt--~(" -----~ ~DRYWElL ! ~=-1 =---,,, :r:r ~-\~OETAL ~ . o~,. ..... I '-'-"""':------.. _ @-~· I~ L ~ a \ ~ 385% --h . .------=-""CONCRETE,...~-.,---""'~-.1rl'l-J~ i· 1 ....--• o.,s8~" __l,.. ~ ~ \___----+ ~ " ~ "' PROPOSED ' I r-111 --=--=±:::'"""':+l=~"'=l=!!;:]=ti::'.:::~~ ~L . i3. ~ N 'l ~~==~-;; :.• ----,........---, 'L~-~;1 ----~· ---~ -11 .,, ..,__ i::__.,.~ J ·~ ii """"'l'i'li~➔==F~-~ ,,-. ..__ ...._g,~ PERCOLATION AREA INLET MANHOLE FOR ON-SITE PERMANENT WATER QUALITY (NOT TO SCALE) NOTES 1 1. MANHOLE CONSTRUCTION SHALL CONFORM EXACTLY TO THE STORM MANHOLE DETAIL PER CITY OF FORT COL.UN$. AN INLET GRATE SHALL BE USED IN LIEU OF TYPICAL MANHOLE LIO. <( DRAINAGE LEGEND ~BASIN NAME s PERCENT IMPERVIOUS p AREA (ACRES) A DESIGN POINT ----BASIN BOUNDARY '' PROPOSED FLOW DIRECTION A A DRAINAGE SECTION ' ' 2. INLET SHALL BE CONSTRUCTED \NITHOUT A SOLID CONCRETE BOTTOM ANO FILLED \IVITH 9" MIN RIP RAP TO A DEPTH OF 30". f-----------5.8'------------I t------------16.0'-------------I v-··"'-PROPOSED GROUND ► ► ► I ~ PROPOSED LANDSCAPING WALL MAX HEIGHT • 1.0' SECTION A-A NTS PROPOSED HOUSE I I NTS PROPOSED GROUND -·-1 ~ PROPOSED LANDSCAPING WALL MAX HEIGHT • 1.0' SECTION 8-8 ► '> ► I (t 10' 20' SCALE: 1" :o: 10' 'il·~~~~,u;~~r:!i'.:~r~ BEFORE YOU DIG ~ (Ollc~~~11 p UTILITY NOTIACATION CENTER Of COLORADO (LNCC) WWW.UNCCORG "' -0 0 U ~~~ ~~~ ~ 8s~->-.u.1cn ::EVI I CD -~~~'t >-ffi~s~; I-I.LI olr~R° ::; Z ~f?:.e ~~ ~I.LI ~ ~ ~ 8 ~~ ~g 1-,0 Cl)U <t r,j UJ :z: ~::i "' .... 0 u ... ~ C: ~ ~ ~ ~ i <:( C> ~ Q ffi CHECKED BY: CAG DESIGN[O BY: RJP DRAWN BY: R..JP CATE: 11/24/2015 SCAl£: ,· • 10· PROJECT NO.: 6270-001 ~ /;; ~ ~ ~