HomeMy WebLinkAboutDrainage Reports - 07/11/2017February 17, 2017
Mr. Wes Lamarque
City of Fort Collins
Storm Water Utility
700 Wood Street
Fort Collins, CO 80522
Re: Maple Hill Park
ICG Project No. 1165-012-89
Dear Wes,
City of Ft. Colfi~~s
Approved By . ~
Date 7-JJ-. l7-•
Please accept the following letter report on behalf of The City of Fort Collins Park Planning and
Development to demonstrate the site's compliance with the previously approved Final Drainage
Report for Maple Hill Subdivision , as prepared by TST Consulting Engineers, dated March 26,
2003.
INTRODUCTION
The proposed park is legally known as Tract I of Maple Hill Subdivision and is 7 .14 acres. The
park is bounded on the north by Maple Hill Drive, the east by Bar Harbor Drive, and existing
single family homes on the west and south. The majority of the park currently drains to an
existing low point located near the eastern property line. The original runoff coefficient
calculations and stage-storage table are attached for reference and all detention and water quality
requirements for this site have been met by the overall Maple Hill development.
EXISTING CONDITIONS
The site is currently vacant and contains a stand of natural grasses. The Overall Drainage Plan
that was included in the previously approved Final Utility Plans for Maple Hill designates the
park area and the back yards of the surrounding single family homes that are tributary to the park
as Basin B 13. This basin drains to a low point on the park property where it is collected by an
area inlet. The area inlet is connected to the storm system that discharges into the existing water
quality and detention pond located just east of Bar Harbor Drive. The northeast and southeast
comers of the park property are designated as portions of Basin B9 and B 14, respectively. These
areas sheet flow directly onto Bar Harbor Drive and are collected by the existing storm system
which discharges into the existing pond. Basin B 13 has a minor storm runoff coefficient of
0.28.
Mr. Wes Lamarque
February 17, 2017
Page 2 of 2
PROPOSED DEVELOPMENT
The proposed park primarily follows the original drainage patterns described in the original
plans. Basin 1, 2 and 3 make up the park property. Basin OS accounts for the off-site tributary
area that was originally included with Basin B13 from the approved plans. Basin 1 and 3
continue to sheet flow directly on to Bar Harbor Drive as initially intended; however, these basin
areas are slightly increased. Basin 2 and Basin OS drain to a low point in the park which is the
proposed irrigation pond. This pond will be fed by a proposed raw water connection from the
existing irrigation main located off-site. All stormwater runoff from Basin 2 and Basin OS will
sheet flow directly into this pond. A Type C inlet structure will be placed 6 inches below the top
bank of the pond setting the permanent water surface elevation to 5009.50. This inlet will be
connected to the existing area inlet (which will be replaced with a proposed manhole) and be
conveyed to the existing storm system which outfalls to the existing pond constructed with the
subdivision.
Basin 1, 2, 3 and OS have a combined minor storm Runoff Coefficient of 0.23 which is less than
the Runoff Coefficient for Basin B13 (0.28) from the approved plan. Therefore, it is requested
that the site be deemed in substantial conformance with the previously approved Final Drainage
Report. Please see the attached excerpts from the Maple Hill Subdivision Final Drainage Report
detailing the assumptions and original flow calculations for the park area.
LOW IMPACT DEVELOPMENT REQUIREMENTS
Runoff reduction practices (LID techniques) are also required. No less than seventy-five percent
of any newly added impervious area must be treated using one or a combination of LID
techniques. The development of the park adds 28,857 sf of new impervious area. Approximately
81 % of that area (23,303 sf) will sheet flow over a grass buffer prior to entering the irrigation
pond. City Stormwater has confirmed that the LID requirements are met with the grass buffers
and the wet irrigation pond. The new impervious area and turf areas will be treated with these
two methods.
It is also important to note that there is no pavement or pollution producing impervious area
associated with this project. Additionally, any suspended solids associated with the runoff from
the park will be captured in the irrigation pond prior to exiting the site via the proposed Type C
inlet.
If you have any questions or comments please contact me at (970) 460-1091.
Sincerely,
5/t!:!:::::
Colorado Professional Engineer 44248
\ \
\ \ I
\ \ II ---c \ \ I I f, --
1 !1..!
w -----w w ----w ----W --f---W -----W ----;------;,'------;;-W --_W--W ----->~----; ~ W :,::
£X76'RO W MAPLEHILLDRIVE -~=~-d ~ £X8/'RO W ~s s ~~-~=,:r,=====~ss=~f="i===-s s s s s s----~~ ..:--=---=-=--=~-~=--=-=------~--=~~~_..,-----... ---=-=-------cl --= ~----
' I -~ 2
I ?,; '"
I j
I I I
I I
I I I
I
--I '
-----, -~ • • cl+r
~1' 1 ~
I
1H
~
ii:
Cl
9:: 3
~
Q:
~
II:
~ 3
JO R!I H I
I I I I
I I I I
11-:i
I
i1f_/
£Xts,1NG WATE:R OUAL/Ty
& OP:,E:N,10N PONo
LocA ,e:o IN iRA c , AA --.. ·-------.
I
I
I
I I 1
S_)
~'
~
.. ' TRACT I H'I
--@ PUBLIC NEIGHBORHOOD PARK
A CC ESS, DRAINAGE & UTILl1Y EASEM E NT
PER PLAT OF MAPL E H ILL
I I I
H
i : I
I
I
I I I
I I
Ui
fi/--1 1 I I I
,,.~ Construction Sequence
"' , Cleor,Smp,
y_
(Cons tructio n Ph ases) M ob ilization Grode I Sub9rode Paving
--1
Best Mana2ement Practices (BMPs)
----Struct ura, NlnstaUa t ionN
Compactl!d ~m •
Contour Furrows (Ri ppi n&/ O1sk1ng) I
Sediment Trap / Filter I I
Vehicle Track i ne Pad •
Concrete Wa shou r I I
Flow Barri en (Wattles)• I I
Stream Flow D1vers10n•
Ri p Rap
•AJ t BMPs 10 be Remove-d once
Construction is Complete.
Vece t atlve
Temporary Seedi ng Ph1 nti ng An y tim e th e sit e wil l si t d orm e nt lomle rth an 30 Days
Mu lc h ing/Sea lan t An y t i me th e site w il l si t d o rm e nt lonR.er t han 30 Davs
Per ma nrnt Seeding Pl1ntt ng I
Rolttt! Products : Netting/Blankets/Mats An y t i me the site wil l sit d o rm e nt lom1.e rt han 30 Days
I I
I
I
londsca,pe Demobiliza tion •• ---
I
I
I
I
/~,
FO
3
3
I I l
., • I r,. I I ·i Ii I I ,, I :~ I ' I ______ , I I I ·.1· '-b~i I
I I I I I f j " I
___ [i:!--=1:-1~-__ J 1 1 • I
t_; ------j \___
,,
SU!BASIN TOTAL TOTAL RJCF At.YEO snwALK LA'°9CARe IUCfF ..
ce;rJN< l1CJ'I ·-AIEA ·-·-AIEA ·-CCEff --,_RKS
(at .) (sq.ft) (sq ff ) (sqff) (sq.ff) (sq.ft) (q
1 1.02 44,.fgs 0 0 570 43,925 0.11 1
2 5.88 256,1" 0 0 27,271 228,873 0.19 10
3 0.24 10,.,.,8 0 0 1,0ffJ 9,432 0.18 •
FMi;ToCal 7.14 311.087 0 0 28,857 282,230 0.18 •
OS 170 14,218 3().800 0 0 "3.41 8 0.-45 37 ASSlJ'll ed Roof Area for Ex homes
TOTAL U5 315,306 ...... 0 21,157 325,8'1 023 10
40 20
~
@
~
0
0 4 0
SCAL E: 1 " = 40'
LEGEND
PROPOSED DIRECTIO N
OF OVERLAN D Fl.O W
VEHICLE TRAC K ING C ONTROL
(CON STRUCTIO N ENTRANCE)
CO NCRETE WASH OUT
--•--SILT FENCE
0
e )
(v ii'.:s1:S'i!
®~ ----
1Nl.ET PROTECTION (TYPE 0
w•TTI..E
GRAVEL BAG
PROPOSED D RAINAG E
BASIN DIVIDE LINE
80
~ DRAIN AG E BASIN N U M BER
M IN OR STORM RUNO F F CO EFF ICIENT
DRAINAG E BASIN AREA
---
NOTES:
PROPOSED DIRECTION OF
OVERLAN D FLOW
1 . CO NTRACTOR T O PROV IDE AND MAINTAIN ALL
N ECESSARY EROSION CO NTRO L MEASURES PRIOR T O
AND THROUGHOUT CONSTRUCTIO N . PLACE EROSIO N
C O NTROL PRO TECTIO N AT ALL EXISTING INLErS
DOWNSTREAM FRO M THE CONSTRUCTION AREA.
EROSION C ONTROL PROTECTION SHALL REMAIN IN
PLACE UNTIL CONSTRU CTION IS C OMPLETE AND ALL
DISTIJRBED GROUND IS ADEQUATELY VEGETATED WITH
OWNER 'S APPROVAL FOR REMOVAL
2. THE EXTENT OF EROSIO N C ONTROL PROTECTION
SHALL BE OBSERVED AND ADJUSTED AS NEEDED
DURING CONSTRUCTION BASED ON SITE CONDmONS
AND THE PERFORMANCE O F THE EROSI ON CONTROL
CONTROL MEASURES SHOWN . T O SUPPLY SUFFICI ENT
EROSION C ONTROL AND MINIMIZE DOWNSTREAM
WATER'WAYPOLLUTION.
CALL UTILITY NOTIFICATION
CENTER OF COLORADO
811 ~ 2-BUSINESS DAYS IN ADVANCE
BEFORE YOU DIG, GRADE, OR EXCAVA TE
FOR THE MARKING OF UNDERGROUND
UEMB ER UTI LI TIES.
CITY OF FORT COLLINS, COLORADO
UTILITY PLAN APPROVAL
APPROVED:
CITY ENGINEER ~
CH ECKED BY:
WATER & WASTEWATER UTILITY ~
CHECKED BY:
STORM WATER UTILITY ~
0::
~
C
Ill
0::
~
Ill
0::
II.
Ill
l: < z
t
Ill a
0::
II.
" ' " ' N
0
iii
~
0
I ~ ~ ~r~ ~
j ~~-0
HH
0
0
z
0 u
" . . -. .
" •
N
N
l!l
Ill~ g z w 0 -0::0(0(0
.J 1-0<"loo
.J (/)~l()l!l o z 0 -<0 UQ_JN.,'..
I-If) 0 C\l N
0:: "-QN 0 :;EUr--cj
IL I<JiOlr--
lL 1-zwoi 00:::JZ ..
> oz_Jo~ I-QIIJ.. -mua.. u -I-
N 0::
::.::
0::
<(
a.
.J
.J -:c
w
.J
a.
<(
~
o ..,
JI
;
..
.J < u
"'
0
lJ..
<
' z
~ ..
.J < u
"'
CD
Ul
► m
0 .. z
" iii ..
0
z
~
D.
.J
0
l:t: ~ z
0 u
z
0
iii
0
l:t:
Lt.I
dS
Lt.I
t!)
<( z
~
C
0
~
► m
0 ..
" u ..
:c u
CHE CK ED BY:
PARKS & RECREATION ~ I PROJ. N0 .1 1 165-0 12-6'
CHE CK ED BY:
TRAFFIC ENGI NEER ~ 60F 10
CH ECKED BY: ~
LOCATION :
PROJECT NO :
COMPUTATIONS BY:
DATE:
RUNOFF COEFFICIENTS & % IMPERVIOUS
M aple Hill Park
I 165 -0/2 -6 9
sb
//101201 7
Recommended Runoff Coefficients from Table RO-11 of City of Fort Collins Stormwater Code , Volume I
Recommended% Impervious from Table RO-3 Urban Storm Drainage Criteria Manual , Volume I
Type B Soils
SUBBASIN TOTAL
DESIGNATION AREA
(ac.)
1 1.02
2 5.88
3 0.24
Park Total 7.14
OS 1.70
TOTAL 8.85
Equations
Streets , parking lots (asphalt)
Sidewalks (concrete)
Roofs
Gravel or Pavers
Lawns, sandy soil (Flat <2%)
TOTAL ROOF
AREA AREA
(sq.ft) (sq .ft)
44,495 0
256,144 0
10,448 0
311 ,087 0
74,218 30,800
385,305 30,800
Runoff %
coefficient Impervious
C
: 0.95 100
: 0 .95 96
0.95 90
0.50 40
: 0 .10 0
PAVED SIDEWALK
AREA AREA
(sq.ft) (sq.ft}
0 570
0 27,271
0 1,016
0 28,857
0 0
0 28,857
-Calculated C coefficients & % Impervious are area weighted
C = E (Ci Ai) / At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
n = number of different surfaces to consider
LANDSCAPE
AREA
(sq .ft)
43,925
228,873
9,432
282,230
43,418
325,648
At= total area over which C is applicable ; the sum of all Ai's
Final FLOW(0H0-17).xls
RUNOFF
COEFF.
(C)
0.11
0.19
0.18
0.18
0 .45
0.23
lnterwest Consulting Group
%
Impervious REMARKS
1
10
9
9
37 Assumed Roof Area for Ex homes
10
"' I
C,.)
', ',
~ o _
l b
;0
a \ o<-
'' \
, C
?
' \ \ \
/:\.;1Q 'W I,
Jo ·,· 11
1
'
,.. 0 1 •• o ,1
50
1 , o .\,
/ I '~ -0 .c,'
/0 c§)> . r.
--~--0 '
----~6
.• --0
·,' ., ) '
jV')
--~//,.. \ " • ----~
-1
(
,,.
/
/
rtOIO lll'ICCl'°"' -SIO!IV5£WCIII
rn~.:Csnir1t =D
'"""' "'"''"' '"""' "'"''"'
~
@ '""'"'-"'I I @) D(SGftlONI'
ror .. 1 .. ~o ~~ 1\.(1()111 •
·•-11,t1·
......... / ---
\
Ci ly o f F l. Coll in s, Co l o r a d o
UTILITY PLA N CR OVAL
APPRO\of'.0: c~ -,,.~)a,.. Cll,»,ceu ~
CHECKED BY: ~~~~~~
Waler -~•-;i;-.;;;;.lllJ
~EO<E0 BY: AL : ~ ... lertil1llly
~
Z:..l.:.Af Do<a
CHEO<[D BY: b pfu -
Park• 4t Reere•Uon 7-t;:l:--J -~ ~ Do<a
C-3
:I
:i:
-"'
C:
::
,
0 91
("
)
a
8 ~ ~ e;
0
.
0 ~
::
,
[ g_
0
::
,
...
.
=-Co.
)
0
,:
.
,
0 U
l
::
;
"
0 3
5-
(>
D.
'<
0
...
.
,
ci1
;
l
~
~-
-0
C:
2:
;;
·
~
~
0 a.
"'
t g-~-
::
:
,
-
-6
:::
:
:
("
)
i g
"'
;:,
,
°8
:<
-
('
)
'
0 3 .
'
-
-
TS
T
.
I
N
C
.
CO
N
S
U
L
I
D
I
G
EN
O
I
N
E
E
R
S
-
-
-
-
--
-
-
-
-
-
-
-
TA
B
L
E
1.
HY
D
R
O
L
O
G
I
C
CA
L
C
U
L
A
T
I
O
N
S
WO
R
K
S
H
E
E
T
BA
S
I
N
A B C
5
T
S
T
,
I
N
C
C
-
l
l
i
q
E
l
l
,
u
u
,
e
r
,
74
1
W
u
J
a
,
Wt
t
1
-
lh
a
l
l
d
i
a
l
D
Fo
r
t
Co
l
l
i
m
,
CO
I0
$
2
S
Pl
l
a
a
c
(9
7
0
)
22
6
om
Fu
:
(9
7
0
)
22
6
-
0
l
l
M
R.
1
/
N
O
f
f
SU
B
Dl
:
S
J
C
N
Al
l
.
E
A
C
O
U
P
,
11
.
U
I
N
PO
I
N
T
(A
&
.
)
C
A
l
I
1.
6
0
0.11
AZ
l
0.
1
1
0.11
A
l
l
0.
2
1
0.81
A◄
l
o.
s
o
0.11
A.
5
4
o.◄s
0.
6
4
A6
4
l.
S
O
0.5◄
A7
s
2.
4
1
0.61
A
l
s
0.
3
1
Cl
.
I
I
A9
I
0.64
0.
1
1
AI
D
a
I.(
)
◄
0.
1
1
A
l
l
6
l
.46
Q.
S
7
A
l
1
7
l.
1
9
tl
.
5
2
A
l
l
9
0.42
0.
1
1
A
l
4
14
0
.42
o.
&
l
AI
S
10
l.
J
.
4
O.
S
9
Al
6
IS
3.
3
0
0.
S
0
Al
7
II
0.
7
9
0.
1
1
A
l
l
12
0.
2
7
0.
1
1
Al
9
13
0.
3
2
0.
1
1
Bl
16
0.76
0.11
82
16
4.
6
4
0.
5
4
B
l
16
I.
G
6
0.70
84
I
I
7.
.
0
7
0.70
BS
I
I
l.
2
1
0.
6
0
86
I
I
0.6s
0.
7
4
87
17
1.
2
6
O.S
9
81
19
1.
2
5
O.
S
I
B9
21
1.
76
0.64
BI
O
20
1.
3
6
0-
'
1
81
1
20
8.40
0.
7
0
81
2
20
I.IS
0.11
►
B
i
l
22
U
6
0.21
81
4
2l
3.72
0.
6
4
BI
S
2l
2.77
G.
5
9
Cl
l
6
1.
2
0
0.
1
1
C2
l
7
0.
9
4
0.
1
1
C
l
-
I
37
0.
9
S
0.
2
1
C
l
31
J.
6
7
0.
6
0
C4
39
0.
6
4
0.
5
4
cs
39
2.
l
S
0.
6
1
C6
40
0.
1
6
0.
6
6
C7
40
2.
5
3
Q.
S
6
Cl
41
2.
6
1
o.
s
◄
--
OV
D
L
A
N
D
AV
E
R
A
.
C
E
o
~
D
T
I
I
A
l
V
E
L
T
;
u
P
U
Q
U
D
I
C
Y
C
O
D
I
'
.
PL
O
W
OV
U
L
A
H
I
>
er
I
a
U
N
G
T
I
I
SL
O
P
E
2-
y
r
10
1
)
.
y
r
J.
:
,
,
1
-
(f
t
)
(%
)
(m
l
l
)
(111
1
■)
1.00
l.
l
S
S7
S.
2
0
2.
3
1
0.72
I.
I
I
O
1.
2
.
5
.
24
4
0.40
11
.46
3.
9
5
I.
I
I
O
1.
2
5
22
uo
1.
5
5
0.47
1.
0
0
1
-
"
21
l
.60
1.
8
6
0.'6
1.
0
0
1.
2
.
5
22
0
1.
4
0
11
.
3
7
7.
3
1
UI
O
J.
2
5
19
9
uo
10
.
1
4
1.19
I.
I
I
O
1.
2
5
25
3
:u
o
10
.44
7
.
l
l
t
.00
1.
2
.
5
l
l
2.
6
0
2.
4
4
0.
1
◄
1.00
u
s
1
6
'
0.
6
0
1.
2
5
2.
"
9
1.
0
0
1.
2
5
.
16
2
Q.
6
0
1.17
2.
4
7
1.
0
0
1.
2
5
21
0
4.
3
0
1.
9
6
6.
5
9
1.
0
0
1.
2
5
19
1
S.00
1.
9
3
6.
9
0
1.
0
0
1.
2
5
27
l
.70
I.
J
4
0.56
1.00
1.
2
5
19
3.
S
O
l.
l
l
l
O.
S
I
1.
0
0
1.
2
5
20
6
S.
3
0
7.
9
6
S.69
1.
0
0
1.
2
5
20
0
4.
0
0
10
.
.
0
1
7.91
1.
0
0
1.
2
5
14
0
0.70
7.
2
2
2.
1
1
1.
0
0
1.
2
5
31
3.
2
0
2.
1
1
6
0.62
1.
0
0
1.
2
5
32
3.
1
0
2.
1
1
0.64
1.
0
0
1.
2
5
46
2.
2
0
2.
1
2
o.a
s
1.
0
0
l.
l
S
30
0
S.
0
0
10
.72
1.
1
6
1.00
1.
2
5
11
7
1.
7
0
6.1
1
2
l
.16
t.
0
0
l.
2
S
30
0
l
.00
9.
0
6
S.13
1.00
1.
2
5
13
6
3.
1
0
7.02
4.9
1
1.
0
0
1.
2
5
10
1
3.70
4.
5
4
U
I
1.00
1.
2
.
5
10
6
1.
9
0
7.1
1
8
s.sa
1.
0
0
1.
2
5
11
7
1.70
1.85
6.
3
9
1.00
1.
2
5
12
1
1.70
1.03
S.
2
9
1.00
1.
2
5
IO
S
1.90
I
.OI
5.
1
3
1.00
1.
2
5
30
0
2.
7
0
9.
3
1
S.
l
l
1.
.
0
0
1.
2
5
21
3.60
1.
1
7
0.56
1.
0
0
-
1.
2
5
-
11
7
-
-
7.
S
O
-
-
10
.12
-
-
9.91
-
-
-
-
-
-
-
-
1.
.
0
0
1.
2
5
27
3.10
2.
1
4
1.
1
4
1.
0
0
1.
2
5
12
.
S
4.
I
O
6.
3
1
4.46
1.
0
0
1.
2
5
51
1.
9
6
3.
1
0
0.94
1.00
l.
l
S
27
3.60
1.
1
6
0.
56
1.
00
1.
2
5
54
12
.
9
6
u
s
4.44
1.00
1.
.
2
.
5
20
9
4.
1
1
1
8.
0
6
S.64
1.00
l.
l
S
94
S.16
U
4
4.
5
2
I.
I
I
O
1.
2
5
1!
1
0
S.
2
6
7.
3
5
S.09
1.
0
0
l.
l
S
S9
S.00
l
.75
2.
3
6
1.00
1.
2
5
24
6
4.10
9.
9
9
7.42
1.
0
0
1.
l
S
:w
◄.9
0
9.
l
S
7.12
-G
l
l
1
T
I
R
no
w
LE
N
G
T
H
(r
t
)
66
4
106
17
.
S
44
7
0
62
0
21
3
22
l
ID
S
26
7
24
4
24
1
23
2
19
'
lO
l
30
4
60
172
20
7
74
7
53
9
23
1
65
1
46
2
23
2
42
.
S
46
4
20
1
28
7
70
3
71
1
-
-
so
-
~
78
0
2
9
l
Sl
7
73
1
39
3
41
7
2)
4
l6
1
21
1
34
0
33
S
11
1
1
1
1
1
1
!
1
-1/
2
8
/
0
3
Hy
d
r
o
m
a
s
.
x
l
s
-