HomeMy WebLinkAboutRIGDEN FARM, 14TH FILING - PDP - 56-98AO - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT1 l� Imo_ -----_-----�------------------------------ --�-- �\ I __ _ _- _------ _--S---
- __—_ // \fit ' Ii
11- _ _ _ __ _ r -___ _ _ _ _ __________
, I
1 1 I
M r I I
I n ri l ' .OB 95 i r i .ts 97 - ,.
mIo -----= =------------------ ------------ 1 I
ii ii' IJ I uff3 I wr! I Im,
u + + +
it
-K-- — — I
,1 uQQI I
IF
r s I I
la
I
�—
"It
91 I a
n L7
I +x2 y I
1
Qg
R
. A3 � A2 I I - ■
At
11 II li �- — — 87 I B3 .83 1 .24 .86
I —
It
lace
it
IIIt
14,
I
It
it
IW
�I
II;
LOT 11
—i—I—,—A�- — — — —I----- t
War
I
IN
±
s�LW;-
I if r,
III
I I Fl___ l "
♦
IL
`
i
_' <�_ - ' --'.
.a1'.
'
III
��
�} WWALIY/VH
.
Ira°I
L
Ile
�--
1! �
III
1II in,'
I
11
Ix. III
II I
�
1� I
PRELIMINARY PLAN
11
11
III III
I11 I11
I
II
NOT FOR CONSTRUCTION
� s
30 75 O 30 60
z
SCALE: 1"= 30' �\ u
\1 �
LEGEND�W oN�E ENE
vR MINORSiR V VT ORBAM R NUMBER
RUNOFF GOEFFlCIEM
ORNNAGE 9ASINAGEA
y PROPosEo ararnoN aF ovEaxNoa-.:
CITY OF FORT COLLINS, COLORADO
UTILITY PLAN APPROVAL
APPROVED: _
OlY ENGINEER
CHECKED BY: _
WRIER L WASN:WATER UMW
CHECKED BY: _
STOIIIWAIEII UxUIY
CHECKED BY: _
PMKS h RECMIXIM
CHECKED BY: _
TRM fNGNEEA
CHECKED BY: _
to
J NLo
Oooto
W LLJ N 0)
W 0InN
pOVN�
IL �Z0N
IO
WW
¢ J-jLd
a IL JpW�
0 >I-0
p �0(L
g aILL
5
a
W
Q
0
PROD. NO. 104603400I
60F6
582
11.5
d'
�-/ 581
49'G7
i1
w
I
ti/ I
J¢ I
I1\
w
c�
S LOCATED GENERALLY IN THE NORTH HALF OF THE SOUTHEAST
TER OF SECTION 29. TOWNSHIP 7 NORTH, RANGE 68 WEST 0
PRINCIPAL MERIDIAN, IN THE CITY Or" TORT COLLINS, LARIMEfi'
XORADO.
POND 212
_Qo27 '
rO
N
r
•
m
NORTH TPJB. STORM SEWER 18 4
- -- -
A •
CULVERT CROSW
SITE AREA IS 308.33 ACRES, INCLUDING R.O.W. Anln rAcr►#r. �c
91-W
Scenario: Base
Combined PipelNode Report
Label
Length
Constructed
Design
Total
Excess
Average
Upstream
Downstream
Hydraulic
Hydraulic
Energy
Energy
Down-
Up-
Downstream
Upstream
Slope
Capacity
Flow
Full
Velocity
Invert
Invert
Grade
Grade
Grade
Grade
stream
stream
Structure
Structure
(ft/ft)
(cfs)
(cfs)
Capacity
(ft/s)
Elevation
Elevation
Line In
Line Out
Line In
Line Out
Cover
Cover
Hydraulic
Hydraulic
(cfs)
(ft)
(ft)
(ft)
(ft)
(ft)
(ft)
(ft)
(ft)
Grade
Grade
(ft)
(ft)
P-1
24.00ft-24inch Concrete
0.012500
25.29
12.30
12.99
3.92
23.00
22.70
27.83
27.76
28.07
27.99
3.50
2.20
27.76
27.20
P-2
100.00ft-24inch Concreti
0.009700
22.28
12.30
9.98
3.92
22.70
21.73
27.57
27.27
27.80
27.51
5.87
3.50
27.27
27.57
P-3
350.00ft-42inch Concret
0.001714
41.65
79.16
-37.51
8.23
21.73
21.13
26.43
23.91
27.48
25.36
1.37
4.37
21.13
26.43
P-4
90.00ft-18inch Concrete
0.011111
11.07
8.30
2.77
4.70
24.93
23.93
29.64
29.08
29.98
29.42
4.07
1.07
29.08
27.50
P-5
144.00ft-18inch Concreti
0.010972
11.00
8.30
2.70
4.70
23.93
22.35
28.81
27.91
29.15
2825
5.85
4.07
27.91
28.81
P-6
55.00ft-24inch Concrete
0.011273
24.02
16.50
7.52
5.25
22.35
21.73
27.56
2727
27.99
27.70
5.87
5.35
27.27
27.56
P-7
24.00ft-18inch Concrete
0.0125001
11.74
8.201
3.541
4.641
22.65
22-351
28.05
27.911
28.391
28.241
5.851
4.551
27.911
28.05
Title: The Center at Rigden Project Engineer. Interwest Consulting Group
x:l..Wesign%storm sewer design 12.14.06.stm Interest Consulting Group Storm CAD v5.5 [5.5005]
12/19/06 09:25-43 AM ®Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Page 1 of 2
Scenario: Base
J-1 P-1 1-1
N
r
l
0
r
a
0-1
Title: The Center at Rigden Project Engineer: Interwest Consulting Group
x:\...\drainage\design\storm sewer design 12.14.06 Interwest Consulting Group Storm CAD v5.5 [5.50051
12/14/06 12:52:27 PM ®Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Page 1 of 1
Inleiwest Consulting Group
1218 West Ash, Suite C
Windsor, Colorado RUNOFF COEFFICIENTS & % IMPERVIOUS
LOCATION: The Center at Rigden Faun
PROJECT NO: I049-034-00
COMPUTATIONS BY: JH
DATE: 12/20/2006
Recommended Runoff Coefficients from Table 3-3 of City of Fort Collins Design Criteria
Recommended % Impervious from Urban Storm Drainage Criteria Manual
Streets, parking lots (asphalt):
Concrete:
Roofs:
Gravel:
Lawns (flat <2%, heavy soil):
Runoff
coefficient
C
%
Impervious
0.95
100
0.95
96
0.95
90
0.50
40
0.20
0
SUBBASIN
DESIGNATION
TOTAL
AREA
(ac.)
TOTAL
AREA
(sq.it)
PAVED
AREA
(sq.ft)
CONCRETE
AREA
(sq.ft)
ROOF
AREA
(sq.ft)
GRAVEL
AREA
(sq.ft)
LANDSCAPE
AREA
(sq.fl)
RUNOFF
COEFF.
(C)
%
Impervious
REMARKS
Al
1.24
54,031
32,563
5,715
9,323
0
6,430
0.86
86
A2
0.83
35,979
24,130
2,174
3,885
0
5,790
0.83
83
A3
0.84
36,568
26,092
5,085
1,561
0
3,830
0.87
89
A4
0.85
37,026
294
2,802
21,067
0
12,863
0.69
59
A5
0.14
6,147
0
1,106
4,875
0
166
0.93
89
A6
0.08
3,454
0
491
2,963
0
0
0.95
91
A7
0.10
4,456
0
609
3,161
1
686
0.83
77
Equations
Calculated C coefficients & % Impervious are area weighted
C=£(CiAi)/At
Ci = runoff coefficient for specific area, Ai
Ai = areas of surface with runoff coefficient of Ci
In = number of different surfaces to consider
At = total area over which C is applicable; the sum of all Ai's
Flow.xls Cval
quality outlet structures and sedimentation forebays. The outlet for Pond 216 will be an
inverted siphon under the Boxelder Ditch, the Fossil Creek Reservoir Inlet Ditch (FCRID)
and the existing Ziegler Road. Pond 216 replaces two temporary detention ponds (Ponds 221
& 222) constructed with Rigden Filing One. The outlet for Pond 269 will be a 8-foot by 4-
foot box culvert under the proposed Ziegler Road into FCRID.
Water Quality Ponds 1, 2, and 3 will store Rigden II runoff for water quality purposes before
releasing it to the Foothills Regional Channel. Pond 1 will be located just west of Rigden
Parkway and Pond 2 will be located just east of Rigden Parkway. Pond 3 will be located just
east of Chase Drive.
Detention Pond 212 was sized in the O.D.P. and will be constructed with Rigden Farm —
Filing Eight. The pond has been designed to match the stage -storage -discharge from the
O.D.P. Detention Pond 212 is located west of Kansas Drive and north of Waukee Drive.
Table 5.2 summarizes the operating parameters for the proposed water quality ponds for
Rigden 11. Appendix G provides the pond sizing calculations.
Table 5.2 Water Qualitv Pond Summary
MAJOR
BASIN
Trib.
area
(acres)
Impervious
Ratio, la
% Impervious
i = la/100
WQCV
(watershed inches)
Design
Volume, Vol.
(ac-ft)
WO Pond 1
5.56
59
0.59
0.23
0.13
WO Pond 2
3.52
1 55
1 0.55
0.22
1 0.08
WO Pond 3
25.25
1 51
1 0.51
0.21
1 0.53
5.4 Detention Pond Outfall Analyses
Major outfall structures are proposed for the two on -site detention ponds. Detention Pond
216 in the northeast comer of the site will have an inverted siphon outlet as specified in the
"Overall Drainage Report for the Rigden Farm O.D.P." Pond 216 has an temporary outlet
that will be utilized until the downstream conveyance facilities are constructed. Detention
Pond 269 in the southern portion of the site will have an 8' by 4' reinforced box culvert
outlet. Both ponds will have inlet boxes with water quality control plates and weirs sized to
control outflows. Trash racks have been designed for both inlet boxes.
Drainage and Erosion Control Report Page 19
Rigden Farm —Filing Six February 8, 2002
7ti
The values recommended by the City of Fort Collins were used for the percent
imperviousness. These values were also close to the estimated values for the Rigden Farm
development. For commercial areas, a percent impervious value of 90% was used and for
multifamily areas, 70% of the area was assumed impervious. For single family residential
sub -basins, 45% of the area was assumed impervious. Basin widths were calculated based
on an average overland flow path length that varies.according to land use. For undeveloped
basins, the overland flow path is estimated to be between 100 ft and 500 ft depending on the
topography. For developed basins, the overland flow path is estimated to be between 50 to
300 ft. The following table summarizes the basin parameters for the Rigden II model..
Table 5.1 - SWMM Subbasin Parameters for Ultimate Development
SWMM
Subbasin
Basin Width
W
(ft)
Area
ac.
Overland flow
Path, L
ft
% Impervious
Slope
Basin Description
58
6000
41.1
298
90%
1.0%
Commercial
581
3450
22.4
283
90%
0.8%
Commercial
582
1700
11.5
295
80%
2.0%
Multi -family & Commercial
583
1 400
2.5
267
70%
2.0%
Multi -family
584
2900
19.7
296
90%
1.5%
Dense multi -family & commercial
65
1200
4.0
145
10%
3.0%
Adjacent to Regional Channel
66
4900
15.1
134
12%
2.0%
Adjacent to Regional Channel
67
10400
99.2
415
45%
2.0%
Single Family
671
2300
8.3
157
19%
10.0%
Adjacent to FCRID
68
2400
25.2
457
45%
2.0%
Single Family
681
640
6.0
408
45%
1.5%
Single Family
682
500
3.5
305
45%
1.5%
Single Family
69
5800
53.5
402
45%
1.9%
le Family
691
1700
3.9
100
31%
10.0%
AdSin jacent to FCRID
total area= 315.9 ac
5.3 Pond Description
Six ponds will be provided for Rigden II. Two primary water quality/detention ponds will be
located in the northeast and southeast corners of the site. Three water quality ponds will be
located south of the Foothills Regional Channel. A detention pond will be located in the
Northwest Roads area.
Water quality/detention Pond 216 will be north and east of the improved Drake and Ziegler
Roads and water quality/detention Pond 269 will be south of Rigden Parkway and west of
Ziegler Road. Both Ponds 216 and 269 will be large wet ponds with detention volume
available above the permanent water surface elevation. The detention ponds will have water
Drainage and Erosion Control Report IPage 18
Rigden Farm - Filing Six February 8, 2002
Fgc)m" FINAL DRAkWP,GE AND EROSION CONTROL REPORT RIDDEN FARM — FILI SIG 51X"
K = headloss coefficient
V = average velocity (ft/s)
g = gravitational constant (32.2 ft/s2)
The storm pipe design was performed for the ultimate build -out of Rigden II in all three
parcels and is included in Appendix E of this report.
.11
5. REGIONAL HYDROLOGY
5.1 Methods and Approach
The hydrology for Rigden II, as in the O.D.P., was evaluated using an integrated
UDSWMM2PC, MODSWMM. The original Master Plan SWMM model was developed by
Resource Consultants Inc. in 1981. An updated Master Plan model was completed by
Faucett Engineering in 1997 using the then -current 100-year rainfall depth (2.89" of rain for
the 100-year, 2-hour storm). An update to the Master Plan SWMM model was completed by
Anderson Consulting Engineers, Inc. (ACE) in July 1999. The "Overall Drainage Report for
the Rigden Farm O.D.P." (Feb. 1999) was developed concurently with the ACE model and
includes Rigden Farms ultimate conditions. The Rigden O.D.P. model was used as a basis for
the SWMM model for this study because it incorporates the most up to date information for
the Foothills Basin and Rigden Farm.
5.2 'Development of SWMM Model
The SWMM model for Rigden II revises the basin parameters to match the proposed
improvements. Minor changes were made to sub -basins 58, 65, 66, 67, 68, 69, 581, 582, 584,
and 681 of the Rigden O.D.P. model. Sub -basins 671, 691, and 682 were added. The
conceptual storage -discharge rating curve for Detention Pond 216 was modified to reflect
proposed grading and Detention Pond 269 was added in Basin 69. The total basin area for
Rigden Farm in the Rigden II model is 315.9 acres, 0.7 acres less than the Filing One model.
This difference is due to changes in basin boundaries along Drake Road and Timberline
Road. A copy of the SWMM Model Sub -basin Delineation is included in Appendix F of this
report.
Drainage and Erosion Control Report Page 17
Rigden Farm — Filing Six February 8, 2002
150:2
5.1
1.0
1
12.
152:5
78.2
3.S
0
37.
153:5
6.8
1.4
4
32.
154:5
5.5
1.4
4
19.
156:5
S7.7
1.8
0
44.
157:2
28.0
.1
3.3:D
3
35.
159:2
8.4
.1
2.7:D
2
2.
162:3
82.6
(D1REC1'
FL04)
0
36.
163:4
09.8
1.0
0
51.
172:2
58.8
.1
6.6:D
1
16.
173:5
53.2
4.1
1
29.
178:9
37.0
4.1
0
51.
184:5
73.3
4.9
0
40.
185:1
84.6
2.0
2
30.
188:1
70.3
3.0
0
46.
193:2
73.3
.1
12.6:D
1
32.
194:1
22.8
7.1
0
55.
201:2
22.9
.1
1.1:D
0
44.
207:2
20.0
.1
9.7:D
2
14.
208:2
20.0
.1
9.5:D
2
6.
209:2
9.0
.1
S.S:D
2
15.
210:2
25.4
.1
1.2:D
0
50.
911.2
9.9
.1
3.1:D
2
3.
214:2
23.3
.1 11.5:D
2
10.
215:2
85.1
�08.3
.1 33.2:D
2
19.
216:2
.1 33.0:D
3
32.
217:2
19.7
.1 2.2:D
1
16.
218:2
09.5
.1 1.6:D
0
39.
244:2
6.0
.8
2
18.
251:2
5.4
.1 .6:D
1
27.
257:1
463.1
3.7
3
33.
269:2
129.7
.1 4.4:D
0
47.
273:3
88.8
(D= FLLW)
0
51.
288:3
22.9
(D= FLOW)
0
41.
303:2
5.6
.1 1.4:D
1
55.
306:2
35.2
.1 .2:D
0
36.
307:5
31.5
2.0
0
39.
313:2
1.7
.1 .6:D
1
37.
338:2
64.1
.1 5.6:D
1
16.
351:3
315.3
(DD2F)✓I' FLOW)
0
36.
361:4
815.3
1.0
0
36.
400:4
60.5
.6
0
40.
401:4
32.5
.8
0
41.
410:2
2.8
.1 2.9:D
2
15.
413:2
1.5
.1 1.9:D
2
7.
444:3
127.1
(D= FLLW)
0
55.
466:3
(DIRWr FLA4)
0
40.
471:3
LL17.2
48.0
(DST FLOE)
0
38.
500:3
10.18.2
(DIPB7r F1LW)
0
S9.
544:3
6.0
(DD= FLOW)
2
14.
562:3
30.0
(D= FLOW)
0
29.
600:4
27.0
1.3
0
36.
644:3
21.1
(DII2FSP FLOW)
0
55.
662:3
52.6
(D= FLOW)
0
36.
849:3
�14.2
(D)RE= FLON)
0
16.
916:3
28.3
(D)72EErP FLLW)
0
41.
au� e:.aa; cu
Rigden Farm- Alternate Outlet -106 YR SWMM output
File: Alt-100.out, 12/05/01
Page 12of12
APPENDIX
PREVIOUS REPORT EXCERPTS
DRAINAGE CALCULATIONS
Mr. Basil Hamdan
December 20, 2006
Page 4 of 4
nuisance that has originated from his operations from damaging crops, orchards, cultivated
fields, and dwellings, or causing naissance to.persons. The Contractor will be held liable for any
damage resulting from dust originating from his operations under these specifications on right-
of-way or elsewhere.
It is unlawful to track or cause to be tracked mud or other debris onto city streets or rights -of -
way. Wherever construction vehicles access routes or intersect paved public roads, previsions
must be made to minimize the transport of sediment by runoff or vehicles tracking onto the
paved surface. Stabilized construction entrances are required with base material consisting of 6"
coarse aggregate. The contractor will be responsible for clearing mud tracked onto city streets
on a daily basis.
All temporary and permanent erosion and sediment control practices must be maintained and
repaired as needed to assure continued performance of their intended function. Silt fence will
require periodic replacement. Maintenance is the responsibility of the contractor. The
Contractor shall obtain and comply with a CDPHE Stormwater Discharge Permit.
All disturbed areas must be seeded and mulched within 30 days of project start. Vegetation shall
not be considered established until a ground cover is achieved which is demonstrated to be
mature enough to control soil erosion to the satisfaction of the City Inspector, the Permit and to
survive severe weather condition.
If you have any questions or comments please contact me at (970) 674-3300.
Sincerely,
Robert Almirall, P.E.
Colorado Professional Engineer 33441
Attachments
Mr. Basil Hamdan
December 20, 2006
Page 3 of 4
side of the basin will enter the flowline on Custer Drive via sidewalk chase drains and sheet flow
across the sidewalk and landscape areas. From the flowline, water will be transported via curb
and gutter into the existing stonn drain system on Custer Drive. The east side of the basin will
also include sidewalk chase drains and sidewalk sheet flow to channel the water into the flowline
on Iowa Drive. Once in the flowline on Iowa Drive, water will be transported via curb and gutter
and street sheet flow to the existing storm drain system on Custer Drive.
Basin A5 and A6 includes half of the roof drainage from Lots 2 and 3 respectively, on -site
sidewalks and landscape areas. Water from the roof drains will enter the flowline on Illinois
Drive via sidewalk chase drains. Water from the sidewalk and landscape areas will sheet now in
to the flowline. Once in the flowline on Illinois Drive, water will be transported via curb and
gutter into existing storm drain inlets included in the storm drain system near the center of the
property.
Basin A7 is comprised of a portion of roof drainage from Lot 10, half of the roof drainage from
Lot 11 and on -site sidewalks. Water from the roof drains will enter the flowline on Iowa Drive
via sidewalk chase drains. Water from the sidewalk will sheet flow in to the flowline. Once
entering the flowline on Iowa Drive, water will be transported via curb and gutter to the existing
storm drain system on Limon Drive.
Filing Six similarly utilized an "Ultimate Development' condition for the basins that make up
the proposed site. All area contained within the site were assumed to be Commercial or Multi -
Family with an imperviousness of 80% used for the middle basin (SWMM Sub basin 582) and
90% for both the north and south basins (SWMM Sub basins 581 and 58). The north and middle
basins flow into the existing storm drain system near the center of the property. The weighted
average site imperviousness for the combined basins is 86%. The combined basin corresponds
to Basins Al, A2, A3, A5 and A6 on the proposed drainage plan. The weighted average site
imperviousness for the five basins on the plan is also 86%. The south basin corresponds to Basin
A4 on the proposed drainage plan. Basin A4 has a 59% impervious, which is well below the
90% impervious called out in the SWMM model. Therefore, it is requested that the site be
deemed in substantial conformance with the previously approved Final Drainage Reports.
EROSION CONTROL (Final Erosion Control Design will be completed at Final
Compliance)
Erosion and sedimentation will be controlled on -site by use of silt fences, area inlet protection, a
gravel construction entrance, and seeding and mulch. The measures are designed to limit the
overall sediment yield increase due to construction as required by the City of Fort Collins.
During overlot and final grading the soil will be roughened and furrowed perpendicular to the
prevailing winds.
During the performance of the work required by these specifications or any operations
appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the contractor
shall furnish all labor, equipment, materials, and means required. The Contractor shall carry out
proper efficient measures wherever and as necessary to reduce dust nuisance, and to prevent dust
Mr. Basil Hamdan
December 20, 2006
Page 2 of 4
PROPOSED DEVELOPMENT
The proposed development will include the construction of eleven commercial buildings, a large
on -site parking area, on -site sidewalks and landscape areas.
BASIN DESCRIPTIONS
The site is divided into seven basins: Al, A2, A3, A4, A5, A6 and AT
Basin Al is comprised of drainage from half of the roofs of Lots 1, 2, 10 and 11, over a third of
the drainage from the parking lot, on -site sidewalks and landscape areas. Water will flow from
the roof drains into sidewalk chase drains and sheet flow over the proposed parking lot into the
proposed drainage inlet. Water from the on -site sidewalks and landscape areas will flow via
sheet flow into the proposed parking lot and into the proposed inlet. From the inlet, water will be
transported via storm drain pipe to the existing storm drain system near the center of the
property.
Basin A2 is comprised of a portion of roof drainage from Lot 3, half of the roof drainage from
Lot 9, about a third of the drainage from the parking lot, on -site sidewalks and landscape areas.
Water will flow from the roof drains into sidewalk chase drains and sheet flow over the proposed
parking lot into the proposed drainage inlet. Water from the on -site sidewalks and landscape
areas will flow via sheet flow into the proposed parking lot and into the proposed inlet. In
addition, water will flow from the proposed driveway entrance on Iowa Drive via curb and gutter
to a transition point in the parking area, then sheet flow into the proposed inlet. From the inlet,
water will be transported via storm drain pipe to the existing storm drain system near the center
of the property.
Basin A3 is comprised of half of the roof drainage from Lot 8, about a third of the parking lot
drainage, on -site sidewalks and landscape areas. Water will flow from the roof drains into
sidewalk chase drains and sheet flow over the proposed parking lot into the proposed drainage
inlet. Water from the on -site sidewalks and landscape areas will flow via sheet flow into the
proposed parking lot and into the proposed inlet. From the inlet, water will be transported via
storm drain pipe to the existing storm drain system near the center of the property.
Hydraulic calculations for sizing the proposed stormwater inlets and pipe discussed in Basins
Al, A2, and A3 were completed using StormCAD hydraulic modeling software. The 100-year
storm was analyzed to insure that the parking lot functions with minimal flooding.
Basin A4 is comprised of roof drainage from Lots 4, 5, 6, 7, a portion of roof drainage from Lots
8, 9, 10; on -site sidewalks, two large landscape areas and a small portion of the access drive off
Iowa Drive. On the west side of the basin, water from the roof drains will enter the flowline on
the Illinois Drive via sidewalk chase drains. Water from the sidewalk will sheet flow into the
flowline. Once entering the flowline on Illinois Drive, water will be transported to existing inlets
via curb and gutter and into the storm drain system along Custer Drive. Drainage from the south
December 20, 2006
INTERWEST - CONSULTING G R O U P
Mr. Basil Hamdan
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, CO 80522
Re: The Center at Rigden Farm — Preliminary Drainage Report
Dear Basil,
Please accept the following letter report on behalf of The Center at Rigden Farm to demonstrate
the site's compliance with the previously approved Final Drainage Report for Rigden Farm
Filing Six, as prepared by JR Engineering.
INTRODUCTION
The site, unplatted, but commonly referred to as Tract P, contains 4.08 acres and is bounded on
all four sides by existing city streets, namely Custer Drive, Illinois Drive, Iowa Drive and Limon
Drive. The site is bisected by a previously constructed storm drainage pipe which outlets in an
existing detention pond which is referred to as Pond 212. The design for this pond was
referenced in the Filing Six report stating that "Pond 212 was sized in the O.D.P. and will be
constructed with Filing Eight". All detention and water quality requirements for this site have
been met by the overall Ridgen Farm development.
Rigden Farm Filing Six updated the basins in the vicinity of this pond based upon anticipated
ultimate development; however, the original pond sizing (stage -storage) was not altered. Filing
Six did update the SWMM model using the updated basin information; however, the EXTRAN
model was not re -run with that Filing. Excerpts from the Filing Six report are attached for
reference. The Filing Six updated SWMM model shows that the peak storage of Pond 212
during a 100-year storm event is 0.8 acre-feet.
EXISTING CONDITIONS
The site is currently vacant and contains dirt, and dry shrubs. The existing site also includes two
existing storm drain pipes. A 36" RCP storm pipe enters the site from the west and connects to
the 42" RCP at an existing manhole near the proposed driveway entrance off Illinois Drive. An
existing 18" RCP with an area inlet entering the manhole from the north will be removed with
the proposed development. The site drains in three distinct directions and the general basin
lines, as proposed in the SWMM model, have been maintained with the proposed development
and in conformance with the Ultimate Development basin delineations as shown in the Rigden
Farm Filing Six Final Drainage Report.
1218 W. ASH, STE. C • WINDSOR, COLORADO 80550
TEL. 970.67A. 3300 • EAx.970.674.3303