HomeMy WebLinkAboutHOWES STREET HIDEAWAYS, PHASE II - PDP/FDP - 35-97 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTAppendix V
Stuffer Envelope
Drainage and Erosion Control Plan
PONDING EXHIBIT
NTS
I
a , `7z5f�l
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Sl
LLJ
LLJ
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ly- MULBERRY STREET
It Pi
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I
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X. Ll T t -us-;Ol RG
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Lu X49.
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ry AIII
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AP,- 7 T4
ol
`14 x
L
A.
X49 5.0 MYRTLE STh�ET. X 4994.9 X4993.4
.414
-41.11
X4993.
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1 1 1,
OLD TOWN MASTER
DRAINAGE BASIN PL.*,-N
CITY of FORT COLLINS
drT--
16
Figure 5.15:
PROFILE o REACH 4
OLD TOWN MASTER
DRANAGE BASIN PLAN
CITY of FORT COLL INS
Table 5.1. Flood Frequency Elevation Discharge (continued).
Ref
No
Station
Channel
Elevation
(ft)
Return.FreQuency.;
5-Year
10 Year
25-Year
100-Year
500-Year ,
Overland,}
Flow
(cts}....
WSE.
fft
Ovetland
Flow
(cfsl..... .
W E
(f
;.
0 Flow d'
r...(cfs).::'.
WSE
.. ..
Overland Flow
{cfs)
W S E
Overland
Flow
(c!s) ..
W.S.E.
Reach 4 (continued)
56
9700
4995.0
100
4996.6
180
4996.7
280
4996.8
500
4997.0
700
4997.3
57
9860
4997.0
100
4997.5
180
4997.6
280
4997.7
500
4997.9
700
4998.1
58
9970
4998.1
100
4998.4
180
4998.5
280
4998.6
500
4998.8
700
4998.8
59
10340
4998.1
100
4999.1
180
4999.2
280
4999.3
500
4999.5
700
4999.6
60
10650
4999.7
100
5000.0
180
5000.1
280
5000.2
500
5000.3
700
5000.4
Reach 5
61
0
4965.8
80
4966.1
170
4966.1
250
4966.2
380
4966.3
600
4966.4
62
90
4966.8
1
4967.0
90
4967.1
190
4967.3
260
4967.4
430
4967.5
63
630
4969.0
80
4969.4
170
4969.6
250
4969.7
380
4969.9
500
4969.9
64
1000
4970.1
40
4971.1
90
4971.2
140
4971.3
230
4971.5
330
4971.6
65
1300
4972.9
40
4973.4
90
4976.7
130
4973.9
190
4974.0
260
4974.1
66
1610
4973.9
60
4975.0
130
4975.3
180
4975.5
280
4975.8
390
4976.0
67
1900
4976.8
5o
4977.7
110
4978.0
150
4978.1
220
4978.2
310
4978.4
68
1950
4977.0
50
4977.9
110
4978.2
150
4978.3
220
4978.5
310
4978.6
69
2080
4979.1
8o
4979.8
170
4980.0
240
4980.2
360
4980.3
500
4980.4
70
r2160
4980.0
110
4980.5
240
4980.6
340
4980.7
500
4980.7
690
4980.8
I
3
Table 5.1. Flood Frequency Elevation Discharge (continued).
Pe`
i
�0'
C nn
Ch ^reI
..:i^r
^f`;i
Fe;urii r"reG,.ency _
-5-Yea, I i0-'car
25-Year I 'OOvear
500-Year
C:e
Fl
c`s1
�
l✓SEOv(derfslal nd
cfs
Overlsalrd
w w
cf
W.S.E.
1ft1
OvFelorlwan
.. d
W.S.E....
(ft1
Reach 3 (continued)
41
5690
4983.5
40
4984.7
110
4984.8
250
4984.8
500
4984.9
850
4985.2
42
5860
4984.6
40
I 4984.9
110
4985.0
250
4985.3
500
4985.6
850
4986.0
43
6080
4985.3
40
4986.0
110
498G.1
250
4986.3
500
4986.5
850
4986.7
44
6170
4986.5
40
4986.7
110
4986.8
250
4986.9
500
4987.1
850
4987.2
45
6370
4986.3
40
4987.1
110
4987.3
250
4987.5
530
4987.8
850
4988.1
46
6560
4989.3
40
4989.4
110
4989.5
250
4989.6
530
4989.8
850
4989.9
47
6770
4983.1
40
4989.5
11
44989.6
250
4989.8
530
4990.0
850
4990.2
48
7000
4991.7
1
4991.7'
70
4992.1
250
4992.3
480
4992.4
850
4992.5
Reach 4
49 7820 4990.5 30 4992.7 120 4992.2 280 4992.4 500 4992.6 850 4992.8
50 8080 4991.9 120 4993.1 200 4993.1 300 4993.1 590 4993.2 850 4993.3
51
8340
1 4991.6
100
I 4993.1
180
4993.2
280
4993.3
500
4993.4
700
4993.5
52
8700
4992.4
30
4993.1
60
4993.2
100
4993.3
200
4993.5
300
4993.6
53
8970
4993.5
50
4993.7
90
4993.8
140
4993.9
250
4994.0
350
4994.1
54
9180
4993.0
100
4994.0
180
4994.2
280
4994.3
500
4994.5
700
4994.G
55
9430
4995.7
100
4996.1
180
4996.2
280
4996.3
500
4996.4
700
4996.5
Storage functions were used at elements 203, 204, 205, and 206 in Subbasin 2 to
simulate the ponding of floodwaters behind the various north -south streets with high
crowns. During the 100-year flood, these ponds filled before the peak runoff. Once filled,
the ponds did little to attenuate flood peaks; the inflow rate essentially equaled the outflow
rate. However, this was not the case with the less severe storms.
.Snlitter_functions were used at elements 227-228-22Uand 224 22F U-6to
-distribute_soills from the ponding areas behind College and Mason to ither the AniAinrn ,
—area-or MyU. Street SpIitter functions were used at elements 215-216-217 and 218-
219-220 to direct a portion of the runoff near the intersection of Myrtle and Peterson
Streets into Subbasin 3. Splitter functions were also used at elements 324-325-326 and
327-328-329to determine the amount of water that would be carried under Riverside
through the storm drains and the amount that would be left flowing down Riverside parallel
to the railroad tracts. A splitter function was used at elements 357-358-359to account
for surface returns back to Mulberry along Smith Street.'•'
Runoff in Upper Part of Subbasin 3. In the upper part of Subbasin 3, most of the
flood runoff, which included spills from the Larimer County Canal No. 2, collected along
Elizabeth -Street. The runoff moved across Shields and onto CSU property. Storm drains
diverted some of the runoff to the south and into the Spring Creek drainage, although most
of the runoff flowed across CSU through the intramural field and eventually discharged into
an open reach of the Arthur Ditch. The Arthur Ditch diverted much of the intercepted..
flood runoff into a box culvert that extended under the CSU campus. The culvert, in turn,
carried water out of the Old Town drainage and into the Spring Creek drainage.'.The
capacity of the open reach of the ditch was exceeded during the course of the 100-year
flood, resulting in excess waters spilling into the CSU lagoon located immediately
.downstream of the ditch near the CSU Student Center. -
Routing and storage of floodwaters in the Arthur Ditch and CSU lagoon were
simulated through the use of splitter functions at elements 353-354-355 and 336-337-338
and through the use of the storage•function for element 315.• It was assumed that the
Arthur Ditch was carrying 60 cfs of irrigation water for the duration of the flood. It was
estimated that the ditch could carry an additional 35 cfs before water would overtop the
ditch banks and spill into the CSU lagoon. - Inflows exceeding 35 cfs were routed into the
lagoon using the splitter function for elements 353-354-355. It was further estimated that
releases through the Arthur Ditch box culvert under the CSU campus would increase once
the water elevation in the lagoon reached the top of the open ditch. The dam creating the
CSU lagoon is higher in elevation than the Arthur Ditch.• Estimates for the additional .
surcharged capacity of the box culvert were incorporated into the release rates for the .
storage pond function at element 315. Surface spills, which would result from a complete
filling of the lagoon, were simulated to occur first at the low spot near the intersection of
Pitkin and Center Streets and then over the top of the dam itself near the Student Center.
The splitter function for elements 336-337-338was used to distribute any surface spills.
Surface spillage did not occur from the lagoon for the future condition runs. The.
regional detention pond near Skyline and Elizabeth Streets coupled with improvements to
the Larimer #2 Canal, reduces the current spilling into the Old Town Basin. The future
condition runs assumed those proposed improvements. The simulated spillage from the
lagoon for existing conditions was all to the south, near the intersection of Pitkin and '
Center; no spillage occurred over the top of the dam into the lower part of Subbasin 3.
4.18
C,
Figbre -5.1:
') '�--- --- — - --------- REACH DESIGNATION for
FLOODED AREA MAPPING
1: OLD TOWN
-j MASTER DRAINAGE
BASIN PLAN for the
x.
CITY of FORT COLLINS
REACH I a 76'..*-
7 4 P-n-a"L Ilc
See Figures 5 9 5 RCE V=M:t�
V OEAC C�
=_j
OE
Legend:
FLOODED AREAS YAPPED WITH DETAILED MAPPVC
APPROXUATE UWS of POTENTIAL SHALLOW
CH 8 z FLOODING LESSTHAN IN DEPTH
=REA
ice/1--F; ures5.10&5.20 See rigures.
Scale
I Lj
4dH 5 a 5B -J �--R i
EACH 7-1 See v Igu"s 5.78 5.16'
7'
ee.Figures z REACH
d
REACH i4 7�
ures LJ
. . . . .... *
--REACH.I.EkIB
%C H.
Fig
72
E=f
- :z-
'N
IMM IMM F= I-MF--M IM IM IM im im
Table 4.3. Differences in Impervious Area Percentages for
Existing and Future Conditions.
Subcatchment
Number
Percent Impervious
Existing'r
Future
6
40
70
102
50
70
108
40
60
109
40
60
201
40
60
203
50
70
204
60
70
205
50
70
206
40
60
211
40
60
304
40
60
305
40
60
312
40
50
360
20
40
361
60
100
4.9
Table 4.1. Design Storms for Old Town Basin.
Per16 d
ding
nmi.
Rainfall Intensities.
2 Year.
: ,Year
.. . ... ,. .
lo Year
A 00-Year
5
0.12
0.36
0.48
0.48
0.60
10
0.36
0.60
0.60
0.72
0.96
15
0.48
0.60
0.72
0.96
1.44
20
0.60
0.84
0.96
1.32
1.68
25
0.84
1.56
2.16
2.28
3.00
30
1.80
2.52
3.12
3.72
5.04
35
3.24
4.68
5.64
6.84
9.00
40
1.08
2.04
2.28
2.88
3.72
45
0.84
1.08
1.12
1.56
2.16
50
0.48
0.72
0.84
1.08
1.56
55
0.36
0.48
0.72
0.84
1.20
60
0.36
0.48
0.60
0.72
0.84
65
0.36
0.48
0.60
0.72
0.60
70
0.24
0.36
0.48
0.48
0.48
75
0.24
0.36
0.36
0.36
0.36
80
0.24
0.24
0.24
0.36
0.36
85
0.24
0.24
0.24
0.36
0.24
90
0.12
0.24
0.12
0.36
0.24
95
0.12
0.12
0.12
0.24
0.24
100
0.12
0.12
1 0.12
0.12
0.24
105
0.12
0.12
0.12
0.12
0.24
110
0.12
0.12
0.12
0.12
0.24
115
0.12
0.12
0.12
0.12
0.12
120
0.12
0.12
0.12
0.12
0.12
at hand, recognizing that it is always possible to make additional refinements or revisions
to any model.
4.1.2 Basin Subdivision
As can be seen from Figure 4.1, the Old Town Basin below Larimer County Canal
No. 2 was subdivided into three smaller subbasins numbered 1, 2, and 3. Subbasin 1
encompassed the area in the northern part of the drainage; Subbasin 2 encompassed the
central part, including the downtown area; and Subbasin 3 covered the southern part.
Each of the subbasins was drained by a major storm sewer.
4.3
. 6
-------- j
Figure 3-1:
STORM SEWER SYSTEMS
4
S;.
------- -------
'l-A
OLD TOWN
MASTER DRAINAGE
BASIN PLAN for the
FORT COLLINS
CITY of FOJI
e
7
RCE
Legend:
r7T"
0,
S
DT
DT
STORM SEWER SYSTEM
r\r
a
k.
MS,
1
7.
scale
H
U
r
10
el.
E
LS
I
7q
1;. 7.
�
IF
I
At
$
�u
ED..
;L
J**
f-0
rp
K!x L2
L
T
ri"Fl I
T Colo. Hwv_ 9R7
I
Vine Dr.
HUI
Pro
1
Scale:
1"=1 mi.
Figure 1.1:
GENERAL LOCATION MAP
OLD TOWN
MASTER DRAINAGE
BASIN PLAN for the
CITY of FORT COLLINS
R C E RESOURCE CONSULTANTS i ENGINEERS.
A►cuwaow Mertq C&gompe ly
1.2
APPENDIX IV
Portions of the Old Town Master Drainage Basin Plan
I
� i-
DRAINAGE CRITERIA MANUAL
50
Kia7
F- 2 0
z
w
U
Cr
a 10
z
a I,
O S
U)
w
Cr 3
M
O
U 2
w
Q
1
5
RUNOFF
_-■.�::
1arm
r I
■■ I I
I
��___
I■■■S
,:::1_
NONE
NN
ME
MEME��
.Z .6 .J 1 2 3 5 10 20
VELOCITY IN FEET PER SECOND
FIGURE 3-2. ESTIMATE OF AVERAGE FLOW VELOCITY FOR
USE WITH THE RATIONAL FORMULA.
*MOST FREQUENTLY OCCURRING"UNDEVELOPED"
LAND SURFACES IN THE DENVER REGION.
REFERENCE: "Urban Hydrology For Small Watersheds" Technical
Release No. 55, USDA, SCS Jan. 1975.
5 -1-84
URBAN DRAINAGE & FLOOD CONTROL DISTRICT
DRAINAGE CRITERIA MANUAL
50
30
t- 2 0
z
w
U
w
n' 10
z
w
IL
OJ 5
w
¢ 3
O
U 2
w
Q
's
5
RUNOFF
ME
ON
imi
t z .5 1 2 3 5 10 20
VELOCITY IN FEET PER SECOND
FIGURE 3-2. ESTIMATE OF AVERAGE FLOW VELOCITY FOR
USE WITH THE RATIONAL FORMULA.
*MOST FREQUENTLY OCCURRING "UNDEVELOPED"
LAND SURFACES IN THE DENVER REGION.
REFERENCE: -Urban Hydrology For Small Watersheds" Technical
Release No. 55. USDA, SCS Jan. 1975.
5 -1-84
URBAN DRAINAGE & FLOOD CONTROL DISTRICT
No Text
3.1.7
3.1.8
Time of Concentration
In order to use the Rainfall Intensity Duration Curve, the time of concentration must be
known. This can be determined either by the following equation or the "Overland Time of
Flow Curves" from the Urban Storm Drainage Criteria Manual, included in this report (See
Figure 3-2).
Tc=1.87 (�—CC,) D1/2 51�
Where Tc =Time of Concentration, minutes
S =Slope of Basin, %
C = Rational Method Runoff Coefficient
D = Length of Basin, feet
C, = Frequency Adjustment Factor
Time of concentration calculations should reflect channel and storm sewer velocities as well
as overland flow times.
Adjustment for Infrequent Storms
The preceding variables are based on the initial storm, that is, the two to ten year storms. For
storms with higher intensities an adjustment of the runoff coefficient is required because of
the lessening amount of infiltration, depression retention, and other losses that have a
proportionally smaller effect on storm runoff.
These frequency adjustment factors are found in Table 3-4.
Table 3-4
RATIONAL METHOD FREQUENCY ADJUSTMENT FACTORS
Storm Return Period
(years)
3.2 Analysis Methodology
Frequency Factor
C,
2 to 10 1.00
111o25 1.10
26 to 50 1.20
51 to 100 1.25
Note: The product of C times C, shalt not exceed 1.00
The methods presented in this section will be instituted for use in the determination and/or verification
of runoff at specific design points in the drainage system. These methods are (1), the Rational Method
and (2) the Colorado Urban Hydrograph Procedure (CUHP). Other computer methods, such as
SWMM, STORM, and HEC-1 are allowable if results are not radically different than these two. Where
applicable, drainage systems proposed for construction should provide the minimum protection as
determined by the methodology so mentioned above.
3.2.1
3.2.2
Rational Method
For drainage basins of 200 acres or less, the runoff may be calculated by the Rational
Method, which is essentially the following equation:
Q = C,CIA
Where Q = Flow Quantity, cfs
A = Total Area of Basin, acres
C, = Storm Frequency Adjustment Factor (See Section 3.1.8)
C = Runoff Coefficient (See Section 3.1.6)
1 = Rainfall Intensity, inches per hcur (See Section 3.1.4)
Colorado Urban Hydrograph Procedure
For basins larger than 200 acres, the design storm runoff should be analyzed by deriving
synthetic unit hydrographs. It is recommended that the Colorado Urban Hydrograph
Procedure be used for such ana!ysis. This Procedure is detailed in the Urban Storm Drainage
Criteria Manual, Volume 1, Section 4.
MAY 1984 3-5 DESIGN CRITERIA
R-M-P Medium Density Planned Residential District — designation for medium density
areas planned as a unit (PUD) to provide a variation in use and building placements
with a minimum lot area of 6,000 square feet.
R-L-M Low Density Multiple Family District — areas containing tow density multiple family
units or any other use in the R-L District with a minimum lot area of 6.000 square feet
for one -family or two-family dwellings and•9,000 square feet for multiple -family
dwellings.
M-L Low Density Mobile Home District — designation for areas for mobile home parks
containing independent mobile homes not exceeding 6 units per acre.
M-M Medium Density Mobile Home District — designation for areas of mobile home
parks containing independent mobile homes not exceeding 12 units per acre.
B-G General Business District — district designation for downtown business areas,
including a variety of permitted uses, with minimum lot areas equal to 1/2 of the total
floor area of the building.
B-P Planned Business District — designates areas planned as unit developments to
provide business services while protecting the surrounding residential areas with
minumum lot areas the same as R-M.
H-B Highway Business District — designates an area of automobile -orientated busi-
nesses with a minimum lot area equal to 1 /2 of the total floor area of the building.
B-L Limited. Business District — designates areas for neighborhood convenience
centers, including a variety of community uses with minimum lot areas equal to two
times the total floor area of the building.
C Commercial District —designates areas of commercial, service and storage areas.
I-L Limited Industrial District — designates areas of light industrial uses with a minimum
area of lot equal to two times the total floor area of the building not to be less than
20,000 square feet.
I-P Industrial Park District —designates light industrial park areas containing controlled
industrial uses with minimum lot areas equal to two times the total floor area of the
building not to be less than 20.000 square feet.
I-G General Industrial District — designates areas of major industrial development.
T Transition District — designates areas which are in a transitional stage with regard
to ultimate development.
For current and more explicit definitions of land uses and zoning classifications, refer to the
Code of the City of Fort Collins, Chapters 99 and 118.
Table 3-3
RATIONAL METHOD RUNOFF COEFFICIENTS FOR COMPOSITE ANALYSIS
Character of Surface Runoff Coefficient
Streets, Parking Lots, Drives:
Asphalt................................................................................................ 0.95
95
Concrete............................................................................................. 0.
Gravel................................................................................................. 0.50
Roofs.......................................................................................................... 0.95
Lawns, Sandy Soil:
Flat<2%............................................................................................. 0.10
Average2 to 7%.................................................................................. 0.15
Steep>7%.......................................................................................... 0.20
Lawns, Heavy Soil:
Flat<2%............................................................................................. 0.20
Average2 to 7%.................................................................................. 0.25
Steep>7%.........:................................................................................ 0.35
MAY 1984 3-4 DESIGN CRITERIA
APPENDIX III
Backup Diagrams and Exhibits
Table 3-3; Rational Method Runoff Coefficients for Composite Analysis
Table 3-4; Rational Method Frequency Adjustment Factors
Figure 3-2; Estimate of Average Flow Velocity for Use with the Rational Formula
Figure 3-1; City of Ft. Collins Rainfall Intensity Duration Curve
Howes Street Hideaways
Const Seq
R-Clicnt / Rayline/ Harrison / Erosion / Const Seq.
1536-08-97
Date: 02/28/97
Revised: 04/04/97
CONSTRUCTION SEQUENCE
PROJECT: Howes Street Hideaways II
STANDARD FORM C
SEQUENCE FOR 1998 ONLY COMPLETED BY: MEO / Shear Engineering Corp.
Indicate by use of a bar line or symbols when erosion control measures will be installed. Major
modifications to an approved schedule may require submitting a new schedule for approval by the City
Engineer.
Year 198
Month J F M A M J I A S O N
O VERLOT GRADING
WIND EROSION CONTROL
* Soil Roughening
Perimeter Barrier
Additional Barriers
Vegetative Methods
Soil Sealant
Other
RAINFALL EROSION CONTROL
STRUCTURAL:
Sediment Trap/Basin
Inlet Filters
Straw Barriers
Silt Fence Barriers
Sand Bags
Bare Soil Preparation
Contour Furrows
Terracing
Asphalt/Concrete Paving
Other
VEGETATIVE:
Permanent Seed Planting
Mulching/Sealant
Temporary Seed Planting
Sod Installation
Nettings/Ma ts/B lankets
Other
x**
STRUCTURES: INSTALLED BY: OWNER MAINTAINED BY: OWNER
VEGETATION/MULCHING CONTRACTOR: OWNER
DATE. PREPARED: 12 15 97 DATE SUBMITTED: 12/15/97
APPROVED BY THE CITY OF FORT COLLINS ON:
Vol
December 15, 1997
Project No: 1536-08-97
Re: EROSION CONTROL SECURITY DEPOSIT REQUIREMENTS:
Lot 11, Block 105, Harrison's Addition; Fort Collins, Colorado
A. An erosion control security deposit is required in accordance with City of Fort Collins
policy (Chapter 7, Section C: SECURITY; page 7.23 of the City of Fort Collins
Development Manual). In no instance shall the amount of the security be less than
$ 1000.00.
a. The cost to install the proposed erosion control measures is approximately $ 435.00
Refer to the cost estimate attached in Appendix I. 1.5 times the cost to install the
erosion control measures is $ 652.50
b. Based on current data provided by the City of Fort Collins Stormwater Utility, and
based on an actual anticipated net affected area which will be disturbed by
construction activity (approximately 0.19 acres), we estimate that the cost to re -
vegetate the disturbed area will be $ 120.84 ($ 636.00 per acre x 0.19 acres). 1.5
times the cost to re -vegetate the disturbed area is $ 181.26 The $ 636.00 per acre
for re -seeding sites of less than 5 acres was quoted to us by the City of Fort Collins
Stormwater Utility personnel.
CONCLUSION:
The erosion control security deposit amount required for Lots 11, Block 5, Harrison's
Addition will be S 1,000.00.
4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 FAX (970) 282.031 1
December 15, 1997
Project No: 1536-08-97
Basil Hamdan
City of Fort Collins Stormwater Utility
P.O. Box 580
Ft. Collins, Colorado 80522
Re: Erosion Control Cost Estimate
Howes Street Hideways H
Lot 11, Block 105, Harrison's Addition; Fort Collins, Colorado
Dear Basil,
SHEAR
ENGINEERING
CORPORATION
Attached is the erosion control security deposit estimate for Howes Street Hideaways H
ESTIMATE 1:
145 LF of Silt Fence O $ 3.00 per LF $ 435.00
TOTAL ESTIMATED COST: $ 435.00
x 1.50
$ 652.50
ESTIMATE 2:
re -vegetate the disturbed area of 0.19 acres at $636.00 per acre $ 120.84
TOTAL ESTIMATED COST: $ 120.84
x 1.50
$ 181.26
In no instance shall the amount of the security be less than $1,000.00. Therefore, the total
required erosion control security deposit for Lot 11, Block 5, Harrison's Addition will be $ 1,000.
If you have any questions, please call at 226-5334.
Sincerely,
Mark Oberschmidt
Shear Engineering Corporation
MEO/ meo
cc: Rayline Development Corporation
Jean Pakech; City of Fort Collins Stormwater Utility
4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 FAX (970) 282-031 1
APPENDIX II
Erosion Control Calculations
Erosion Control Sequencing schedule
Erosion Control security deposit estimate
SHEAR ENGINEERING CORPORATION
PAGE 8
CHANNEL CAPACITY
PROJECT NAME: HOWES STREET HIDEAWAYS DATE: 12/15/97
PROJECT NO. : 1536-08-97 BY : MEO
SWALE DESCRIPTION:PAVSD ALLEY WITH INVERTED CROWN
FILE: HSH2CHAN
CAPACITY OF TRIANGULAR OR TRAPEZOIDAL CHANNEL
CHANNEL CONFIGURATION: TRIANGULAR Q100 (cfa) - 3.27
CHANNEL LINING: CONCRETE REFER TO PAGE 6
Da Db Dc Sc n W I
(ft) (ft) (ft) M (ft) (ft)
---- ---- ---- ---- ----- "-- ----
10.00 10.00 0.20 0.500 0.016 0.00 0.05
0.02 = LEFT BANK SLOPE
0.02 - RIGHT BANK SLOPS
DEPTH WIDTH AREA PERIM R 2/3 Sc 1/2 Q V
(£t) (ft) (a.f.) (ft) (A/P) (cfe) (ft/sec)
------- ------- -------------- ------- -------------- -------
0.20 20.00 2.00 20.00 0.22 0.07 2.83 1.41
0.15 15.00 1.13 15.00 0.18 0.07 1.31 1.17
0.10 10.00 0.50 10.00 0.14 0.07 0.45 0.89
0.05 5.00 0.13 5.00 0.09 0.07 0.07 0.56
0.00 0.00 0.00 0.O0 0.00 0.07 0.00 0.00
rrrrrwrrrrrrwrrwrwwwwwwrwwrwwwwwwwwrrrrrrrrrrrrrwwwrwrrrrrrrwrwrrwwwrrrr
DEPTH WIDTH AREA PERIM R 2/3 Sc 1/2 Q V
(ft) (ft) (e.f.) (ft) (A/P) (cfe) (ft/sec)
CONCLUDE:ALLEY CAPACITY IS ADEQUATE BECAUSE SLOPE OF ALLEY INCREASES TO NORTH
SHEAR ENGINEERING CORPORATION
PAGE 7
FLOW TO CONCENTRATION POINT 3
FROM SUBBASIN ROW
PROTECT: HOWES STREET HIDEAWAY II DATE 12/15/97
LOCATION:FORT COLLINS PROJ. NO.1536-08-97
FILE: HSH2RUN BY HBO
NOTE: CP 3 IS AT THE NORTHWEST CORNER OF THE SITE IN THE STREET
AREA (A)- 0.220 ACRES
RUNOFF COEF. (C)
2 YEAR 10 YEAR 100 YEAR
C = 0.78 0.77 0.97
SEE SPREAD SHEET ATTACHED ON PAGE 2
TIME OF CONCENTRATION (TC)
OVERLAND TRAVEL TIME (Ti)
LENGTH 20 FEET SLOPE 2.00 k
2 YEAR 10 YEAR 100 YEAR
C = 0.20 0.20 0.25
Ti (min). 5.99 5.99 5.66
TRAVEL TIME (Tt)-L/(60*V) FLOW TYPE
L (ft) = 190 S (k) 0.5 GUTTER
L (ft) _? S (k) _? 7
L (ft) _? S (k) .? ?
L (ft) _? S (k) =7 7
L (ft) _? S (k) =7 ?
L (ft) _? S (k) _? 7
L (ft) .? S (k) -? ?
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2
TOTAL LENGTH = 210 L/180+10= 11.17 >
Tc -Ti+TOTAL TRAVEL TIME
2 YEAR 10 YEAR 100 YEAR
Tc (min)= 8.10 8.10 8.10
USE Tc - 11 11 11
INTENSITY (I) (iph)
2 YEAR 10 YEAR 100 YEAR
I 2.46 4.31 6.92
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (Q= CIA) (cfs)
2 YEAR 10 YEAR 100 YEAR
Q = 0.42 0.73 1.48
V (fps)
= 1.5
Tt(min)-
2.11
V (fps)
_?
Tt(min)=
0.00
V (fps)
_?
Tt(min)=
0.00
V (fps)
_?
Tt(min)-
0.00
V (fps)
_?
Tt(min)=
0.00
V (fps)
_?
Tt(min)=
0.00
V (fps)
=7
Tt(min)=
0.00
TOTAL TRAVEL TIME
(min)
2.11
8.10
-Ti+Tt
CHOOSE LESSER
CONCLUDE:PEAK FLOW TO NORTWEST CORNER OF PROPERTY IN STREET FROM 1/2 ROW
SHEAR ENGINEERING CORPORATION
FLOW TO CONCENTRATION POINT 2
FROM SUBBASIN As & ALLEY
PROJECT: HOWES STREET HIDEAWAY II DATE 12/15/97
LOCATION:FORT COLLINS PROS. NO.1536-08-97
FILE: HSH2RUN BY MEO
NOTE: CP 2 IS W NB CORNER OF SITE IN ALLEY
AREA (A). 0.480 ACRES
RUNOFF CORP. (C)
2 YEAR 10 YEAR 100 YEAR
C = 0.79 0.79 0.99
SEE SPREAD SHEET ATTACHED ON PAGE 2
TIME OF CONCENTRATION (Tc)
OVERLAND TRAVEL TIME (Ti)
LENGTH 100 FEET SLOPE 0.50 !
2 YEAR 10 YEAR 100 YEAR
C 0.20 0.20 0.25
Ti (min)- 21.16 21.16 19.98
TRAVEL TIME (Tt) .L/(60*V) FLOW TYPE
L (ft) 190 S (4) = 0.5 GUTTER
L (ft) =7 S (t) =7 ?
L (ft) _? S (4) =7 ?
L (ft) =7 S (4) =7 ?
L (ft) _? S (i) =7 ?
L (ft) _? S (4) _? ?
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2
TOTAL LENGTH . 290 L/180+10. 11.61 <
Tc .Ti+TOTAL TRAVEL TIME
2 YEAR 10 YEAR 100 YEAR
Tc (min)- 11.61 11.61 11.61
USE Tc - I1.5 11.5 11.5
INTENSITY (I) (iph)
2 YEAR 10 YEAR 100 YEAR
I = 2.42 4.24 6.82
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (Q= CIA) (cfe)
2 YEAR 10 YEAR 100 YEAR
Q = 0.92 1.61 3.24
CONCLUDE:PRAK FLOW FROM SITE TO ALLEY
MINIMUM SLOPS OF ALLEY = 0.005 FT/FT
CAPACITY OF ALLEY = 2.83 CPS
SEE PAGE 8
PAGE
V (fps)
1.50
Tt(min)-
V (fps)
.?
Tt(min)=
V (fps)
.7
Tt(min)=
V (fps)
.7
Tt(min)=
V (fps)
.?
Tt(min).
V (fps)
.7
Tt(min)-
V (fps)
.7
Tt(min)-
TOTAL TRAVEL TIME
(min) _
22.09
.Ti+Tt
6
2.11
0.00
0.00
0.00
0.00
0.00
0.00
2.11
SHEAR ENGINEERING CORPORATION
PAGE 6
FLOW TO CONCENTRATION POINT 2
FROM SUBBASIN As & ALLEY
PROJECT: HOWES STREET HIDEAWAY II DATE 12/15/97
LOCATION:PORT COLLINS PROJ. NO.1536-08-97
PILE: HSH2RUN BY MEO
NOTE: CP 2 IS ® HE CORNER OF SITE IN ALLEY
AREA (A)- 0.480 ACRES
RUNOFF COEF. (C)
2 YEAR 10 YEAR 100 YEAR
C 0.86 0.86 1.00
SEE SPREAD SHEET ATTACHED ON PAGE 2
TIME OF CONCENTRATION (Tc)
OVERLAND TRAVEL TIME (Ti)
LENGTH = 100 FEET SLOPE - 0.50 4
2 YEAR 10 YEAR 100 YEAR
C = 0.20 0.20 0.25
Ti (min)- 21.16 21.16 19.98
TRAVEL TIME (Tt)-L/(60+V) FLOW TYPE
L (ft) = 190 S (}) = 0.5 GUTTER
L (ft) =7 S (}) _? ?
L (ft) =7 S (}) =7 ?
L (ft) _? S (}) =7 ?
L (ft) _? S (}) _? ?
L (ft) _? S (}) _? ?
L (ft) _? S (4) _? ?
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2
TOTAL LENGTH = 290 L/180+10= 11.61 <
Tc -Ti+TOTAL TRAVEL TIME
2 YEAR 10 YEAR 100 YEAR
Tc (min)= 11.61 11.61 11.61
USE Tc = 11.5 11.5 11.5
INTENSITY (I) (iph)
2 YEAR 10 YEAR 100 YEAR
I 2.42 4.24 6.82
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (Q= CIA) (cfe)
2 YEAR 10 YEAR 100 YEAR
Q 1.00 1.75 3.27
CONCLUDE:PEAK FLOW FROM SITE TO ALLEY
MINIMUM SLOPE OF ALLEY = 0.005 PT/FT
CAPACITY OF ALLEY = 2.83 CPS
SEE PAGE 8
V (fps)
= 1.50
Tt(min)=
V (fps)
=7
Tt(min)=
V (fps)
_?
Tt(min)=
V (fps)
_?
Tt(min)=
V (fps)
=7
Tt(min)=
V (fps)
_?
Tt(min)=
V (fps)
_?
Tt(min)=
TOTAL TRAVEL TIME
(min) _
22.09
=Ti+Tt
2.11
0.00
0.00
0.00
0.00
0.00
0.00
2.11
SHEAR ENGINEERING CORPORATION
PAGE 5
FLOW TO CONCENTRATION POINT 1
FROM SUBBASIN Aw
PROJECT: HOWBS STREET HIDEAWAY II DATE 12/15/97
LOCATION:FORT COLLINS PROJ. NO.1536-08-97
FILE: HSH2RUN BY MEO
NOTE: CP 1 IS NEAR THE CENTER OF THE SITE AT THE NORTH PROPERTY LINE
AREA (A). 0.440 ACRES
RUNOFF COEF. (C)
2 YEAR 10 YEAR 100 YEAR
C - 0.42 0.42 0.53
SSE SPREAD SHEET ATTACHED ON PAGE 2
TIME OF CONCENTRATION (Tc)
OVERLAND TRAVEL TIME (Ti)
LENGTH = 85 FEET SLOPE = 0.70 4
2 YEAR 10 YEAR 100 YEAR
C = 0.20 0.20 0.25
Ti (min). 17.45 17.45 16.48
TRAVEL TIME (Tt)=L/(60+V) FLOW TYPE
L (ft) 190 S (4) = 1 SWALE
L (ft) =7 S (4I _? ?
L (ft) _? S (4) _? ?
L (ft) =? S (4) .? ?
L (ft) =7 S (t) _? ?
L (ft) _? S (4) .7 7
L (ft) =? S (4) .7 7
NOTE: ALL VELOCITIES TAKEN FROM FIGURE 3-2
TOTAL LENGTH . 275 L/180+10- 11.53 <
Tc .Ti+TOTAL TRAVEL TIME
2 YEAR 10 YEAR 100 YEAR
Tc (min). 11.53 11.53 11.53
USE Tc . 11.6 11.5 11.5
INTENSITY (I) (iph)
2 YEAR 10 YEAR 100 YEAR
I = 2.42 4.24 6.82
NOTE: INTENSITIES TAKEN FROM FIGURE 3-1
RUNOFF (Q- CIA) (cfe)
2 YEAR 10 YEAR 100 YEAR
Q = 0.45 0.78 1.59
V (fps) = 1.58 Tt(min)= 2.00
V (fps) _? Tt(min)= 0.00
V (fps) =? Tt(min)= 0.00
V (fps) =? Tt(min)= 0.00
V (fps) =? Tt(min)= 0.00
V (fps) =? Tt(min)= 0.00
V (fps) _? Tt(min)- 0.00
TOTAL TRAVEL TIME (min) 2.00
19.46 .Ti+Tt CHOOSE LESSER
CONCLUDE:PEAK FLOW FROM WESTERN PORTION OF SITE AFTER DEVELOPMENT TO LOT 10
SURFACE
CHARACTERISTICS
STREETS
ASPHALT
CONCRETE
GRAVEL
:Z•�3;T
LAWNS SANDY SOIL
FLAT < 2i
AVERAGE 2 - 74
STEEP > 7%
LAWNS HEAVY SOIL
SHEAR ENGINEERING CORPORATION
SUB -BASIN BREAKDOWN FOR HOWES STREET HIDEAWAYS
DEVELOPED CONDITIONS
PROJECT :HOWES STREET HIDEAWAYS
PROJ.NO. :1536-08-97 DATE: 12/15/97
LOCATION :OLD TOWN BY: HBO
FILE :HSH2BASIN
NOTES :SITE ONLY
RUNOFF
COEF.
AREA C C*A L
(acres) IMPERVIOUS
0.090 0.950 0.085 100.00t 0.0900
0.040 0.950 0.038 100.00% 0.0400
0.000 0.500 0.000 50.00t 0.0000
0.290 0.950 0.275 100.00% 0.2900
0.000 0.100 0.000 0.00t 0.0000
0.000 0.1s0 0.000 0.00% 0.0000
0.000 0.200 0.000 0.00% 0.0000
FLAT < 24
0.410
0.200
0.082
AVERAGE 2 - 74
0.000
0.250
0.000
STEEP > 7•
0.000
0.350
0.000
TOTAL AREA
0.830
0.481
C2
CIO
C100
COMPOSITE C VALUE
0.580
0.580
0.724
% IMPERVIOUS
50.60%
SITE ONLY
0.00% 0.0000
0.00% 0.0000
0.00% 0.0000
0.4200
PAGE 4
SURFACE
CHARACTERISTICS
STREETS
ASPHALT
CONCRETE
GRAVEL
TZ7�E?
LAWNS SANDY SOIL
FLAT < 2%
AVERAGE 2 - 7%
STEEP > 7%
LAWNS HEAVY SOIL
SHEAR ENGINEERING CORPORATION
SUB -BASIN BREAKDOWN FOR HOWES STREET HIDEAWAYS II
EXISTING CONDITIONS
PROJECT :HOWES STREET HIDEAWAYS II
PROJ.NO. :1536-08-97 DATE: 12/15/97
LOCATION :OLD TOWN BY: HBO
FILE :HSH2BASIN
NOTES :SITS ONLY
RUNOFF
COEF.
AREA
C
C-A
6
(acres)
IMPERVIOUS
0.060
0.950
0.057
100.00%
0.0600
0.030
0.950
0.028
100.00%
0.0300
0.000
0.500
0.000
50.00%
0.0000
0.260
0.950
0.247
100.004
0.2600
0.000
0.100
0.000
0.00%
0.0000
0.000
0.150
0.000
0.00%
0.0000
0.000
0.200
0.000
0.00%
0.0000
FLAT < 2i
0.480
0.200
0.096
AVERAGE 2 - 74
0.000
0.250
0.000
STEEP > 74
0.000
0.350
0.000
TOTAL AREA
O.B30
0.429
C2
C10
C100
COMPOSITE C VALUE
0.516
0.516
0.645
4 IMPERVIOUS
42.17%
SITE ONLY
0.004 0.0000
0.00► 0.0000
0.00% 0.0000
0.3500
PAGE 3
SHEAR ENGINEERING
CORPORATION
PAGE 2
SUMMARY OF
SUBBASIN BREAKDOWN
PROJECT: HOWES STREET HIDEAWAYS II
DATE: 12/15/97
PROJ NO :1536-06-97
BY HBO
FILE: HSH2BASIN
PLATTED AREA
HOWES STREET HIDEAWAYS II
0.83
ACRES
ROW
0.22
ACRES
ALLEY
0.09
ACRES
TOTAL
1.14
ACRES
DEVELOPED CONDITIONS
IMPERVIOUS PERVIOUS
SUB-
GRAVEL
ASPHALT
ROOF/ LAWN C2
C100
BASIN
CONCRETE
DRIVES
Cfactor
0.50
0.95
0.95 0.20
i IMPERVIOUS
13.00i
100.00% 100.001, 0.001,
ACRES
ACRES
ACRES
ACRES ACRES
rrr++++++r++r+rrrrr+r
rrrrr rrrrrrrwwwwwwww+++++++++r++rrrrrrrrrrrrrrrr•rr
SITE 0.83
0.00
0.13
0.29 0.41 0.58
0.72
1/2 ROW 0.22
0.00
0.17
0.00 0.05 0.78
0.97
ALLEY 0.09
0.00
0.09
0.00 0.00 0.95
1.00
TOTAL 1.14
0.00
0.39
0.29 0.46 0.65
0.81
Aw 0.44
0.00
0.03
0.10 0.31 0.42
0.53
Ae 0.39
0.00
0.10
0.19 0.10 0.76
0.95
Ae&ALLBY 0.48
0.00
0.19
0.19 0.10 0.79
0.99
i IMPERVIOUS a
59.654
- INCLUDES 1/2 ROW AND ALLEY AND DEVELOPED SITE
i IMPERVIOUS .
50.60%
- SITE
ONLY- DEVELOPED CONDITIONS
i IMPERVIOUS .
42.17i
- SITE
ONLY- EXISTING CONDITIONS
FLOW SUMMARY FOR HOWBS STREET HIDEAWAY II PAGE 1
DATE: 12/15/97
DESIGN CONTRIBUTING AREA C2 C10 C100 Tc Tc I2 I10 I100 Q2 Q10 Q100 PAGE
POINT SUB 2,10 100
BASINS) ac. min. min iph iph iph cfe cfe cfe
r rrrxrrrrrrrrrr rrrrrvvrrrrrrrrr rrrr•rr rrrvrvrrrrrrrrrxrirrrrrrrrerrtr:vrxrrrtrrvrrrrrrrrrrrrrxxrxrrrrx
1 Aw 0.44 0.42 0.42 0.53 11.50 11.50 2.42 4.24 6.82 0.45 0.78 1.59 5
2 Ae & ALLEY 0.48 0.79 0.79 0.99 11.50 11.50 2.42 4.24 6.82 0.92 1.61 3.24 6
3 ROW 0.22 0.78 0.77 0.97 11.00 11.00 2.46 4.31 6.92 0.42 0.73 1.48 7
APPENDIX I
Storm Drainage Calculations
PAGE 7
Project No. 1536-08-97
Final Drainage and Erosion Control Report
Howes Street Hideaways H
1. Fort Collins Storm Drainage Criteria Manual
2. Urban Drainage and Flood Control District Drainage Criteria Manual
3. Fort Collins Storm Erosion Control Reference Manual
4. Old Town Master Drainage Basin Plan; Prepared by Resource Consultants &
Engineers, Inc.; Dated January 7, 1993
5. Final Drainage and Erosion Control Report for Mulberry Green; prepared by Shear
Engineering Corporation ; Project No: 1151-24-95; Dated: June, 1996
6. Final Drainage and Erosion Control Report for Howes Street Hideaways; prepared by
Shear Engineering Corporation; Project No: 1536-08-97; Dated: April, 1997
PAGE 6
Project No. 1536-08-97
Final Drainage and Erosion Control Report
Howes Street Hideaways II
V. EROSION CONTROL:
A. General Concept
1. Erosion control measures will be as identified on the Final Grading, Drainage and
Erosion Control Plan.
2. An erosion control security deposit is required in accordance with City of Fort Collins
policy (Chapter 7, Section C: SECURITY; page 7.23 of the City of Fort Collins
Development Manual). In no instance shall the amount of the security be less than
$1,000.00.
3. Refer to the Erosion Control Security Document located in Appendix II for the
amount of the deposit.
VI. VARIANCE REQUEST:
A. Variance from City of Fort Collins Requirements
1. There will be no requests for any variances from the City of Fort Collins Storm
Drainage Criteria for The Howes Street Hideaways.
VII. CONCLUSIONS:
A. Compliance with Standards
1. All drainage analysis has been performed according to the requirements of the City of
Fort Collins Storm Drainage Criteria Manual, the City of Fort Collins policy, and the
Old Town Master Drainage Basin Plan.
2. All Erosion Control design complies with the City of Fort Collins Erosion Control
Reference Manual and generally accepted practices.
B. Drainage Concept
1. The drainage design for The Howes Street Hideaways and Howes Street Hideaways
II is in accordance with the City of Fort Collins requirements and the
recommendations of the Master Drainage Basin Plan for Old Town Basin.
2. There will be no adverse downstream effects due to the development of the site.
PAGE 5
Project No. 1536-08-97
Final Drainage and Erosion Control Report
Howes Street Hideaways H
IV. DRAINAGE FACILITY DESIGN:
B. Specific Details
2. The following table summarizes the land cover and the appropriate imperviousness
on the developed site:
Area
Impervious
Runoff Coefficient
(acres)
%
"C"
Lawn
-----------
0.41
---------------
0.00
----------------------
0.20
Roof
0.29
100.00
0.95
Concrete
0.04
100.00
0.95
Asphalt
0.09
100.00
0.95
Total 0.83
The resultant imperviousness of the developed site is 50.60%. This does not include
the alley or the 1/2 right-of-way which fronts on the property. The imperviousness
percentages are taken from Table 3-1 in the Urban Storm Drainage Criteria Manual -
Volume 1. The Runoff Coefficient is taken from the City of Fort Collins Drainage
Criteria Manual.
3. The proposed development results in an increase from 42.17% impervious to 50.60%
impervious. Detention is not required because the site is less than 70% impervious.
4. The overall imperviousness of the developed site, the alley and the 1/2 right-of-way
of Howes Street is 59.65 percent.
5. Retaining walls will be constructed along the north property line because the grading
around the new building will be higher than existing grade at the property line.
6. The alley has a minimum slope of 0.50% Concrete will be used in the alley and
parking lot. The alley will act as a channel for the runoff from the site.
a. The capacity of the alley at the minimum slope is 2.83 cfs.
b. Grading constraints do not allow an increase in the minimum slope of the alley
without adversely affecting the adjoining properties.
PAGE 4
Project No. 1536-08-97
Final Drainage and Erosion Control Report
Howes Street Hideaways H
III. DRAINAGE AND EROSION CONTROL DESIGN CRITERIA:
D. Hydraulic Criteria
1. Storm sewer and drainage channel capacities were based on the Mannings Equation.
The Mannings coefficients are as suggested by the City of Fort Collins Storm
Drainage Criteria Manual.
IV. DRAINAGE FACILITY DESIGN:
A. General Concept
1. Stormwater is conveyed to West Mulberry Street by a combination of overland and
gutter flow.
2. The alley has been graded with an inverted crown to facilitate conveyance of
stormwater into Mulberry West Street.
3. Detention is not required because the imperviousness of the developed site does not
exceed 70%.
B. Specific Details
1. The following table summarizes the land cover and the appropriate percent
imperviousness on the existing site.
Area
Impervious
Runoff Coefficient
(acres)
%
"C"
Lawn
----------
0.48
-------------
0.00
----------------------
0.20
Roof
0.26
100.00
0.95
Concrete
0.03
100.00
0.95
Asphalt
0.06
100.00
0.95
Total 0.83
The imperviousness of the existing site is 42.17%. This does not include the alley or
the 1/2 right-of-way which fronts on the property. The imperviousness percentages
are taken from Table 3-1 in the Urban Storm Drainage Criteria Manual - Volume 1.
The Runoff Coefficient is taken from the City of Fort Collins Drainage Criteria
Manual.
PAGE 3
Project No. 1536-08-97
Final Drainage and Erosion Control Report
Howes Street Hideaways H
M. DRAINAGE AND EROSION CONTROL DESIGN CRITERIA:
A. Regulations (continued)
2. Recommendations made in the Old Town Master Drainage Basin Plan prepared by
Resource Consultants & Engineers, Inc. were also considered.
a. Flood elevations noted in the Old Town Master Drainage Basin Plan were utilized
to establish the minimum allowable Finished Floor Elevations of the proposed
single family residence.
3. All erosion control design criteria from the City of Fort Collins Erosion Control
Reference Manual was considered.
B. Development Criteria Reference and Constraints
1. All grading design must match the existing elevations at the property line due to fully
developed properties adjacent to the site.
2. The nearby intersection of Mason Street and West Mulberry Street is subject to
flooding due to insufficient capacity of the existing storm sewer.
a. According to the Old Town Master Drainage Basin Plan, the 100-year flood
elevation on Mulberry Street in the area of Howes Street Hideaways is
approximately 4993.5 feet. Refer to figure 5.6 in the Old Town Master Drainage
Basin Plan attached in Appendix IV.
b. The lowest existing elevation on the site based on survey information is 4993.93
feet.
3. Minimum Allowable finished floor elevations shall be 4995.0 feet in order to
provided the minimum 1.5 feet separation above the defined 100-year water surface
elevation. A note stating this is provided on the Master Grading, and the Drainage
and Erosion Control Plan.
4. Detention is required if the imperviousness of the site exceeds seventy percent
(70.0%). This is in accordance with the assumptions of the Stormwater Management
Model (SWMM) for subcatchment 205 in the Old Town Basin.
C. Hydrological Criteria
1. The Rational Method (Q = CIA) was used to determine the pre -developed and/or
post development peak flows for the 2, 10 and 100-year storm events at critical
points.
PAGE 2
Project No. 1536-08-97
Final Drainage and Erosion Control Report
Howes Street Hideaways H
H. DRAINAGE BASINS AND SUB -BASINS:
A. Major Basin Description (continued)
2. The approximate limits of ponding in the area of Mason and Mulberry are shown on
fig 5.1 of the Old Town Report in appendix IV and the ponding exhibit on the
Drainage and Erosion Control plan.
3. Stormwater from the site drains to conveyance element 205 as delineated on figure
4.1 of the Old Town Master Drainage Basin Plan.
a. According to the Old Town Master Drainage Basin Plan, stormwater flows in
conveyance element 205 are split at the intersection of Mason Street and
Mulberry Street.
b. Some of the flows are conveyed east in the existing storm sewer while others are
conveyed north on Mason when the storm sewer capacity is reached.
B. Sub -Basin Description
1. The site is extremely flat. The site was surveyed to determine if there was a defined
flow path. Slopes across the entire Howes Street Hideaways site ranges from 0.5% to
0.70% from west to east and from south to north. The site slopes from the back of
walk along South Howes to the east between the existing houses. At the rear of the
existing houses the site begins to slope to the north towards lot 10. Runoff then flows
in a northeasterly direction across lots 11 and 10 to the alley. There is a high point
approximately 60 feet east of the alley which breaks the Howes Street Hideaways site
into two sub -basins which we have designated Ae and Aw.
a. Existing spot elevations are shown on the grading plan.
2. Development of the site will increase the area in basin Ae because this area will be
developed and therefore it is deemed better to convey as much of of the runoff from
sub -basin Ae to the alley.
III. DRAINAGE AND EROSION CONTROL DESIGN CRITERIA:
A. Regulations
1. All storm drainage design criteria from the City of Fort Collins Drainage Criteria
Manual was considered.
PAGE 1
Project No 1536-08-97
Final Drainage and Erosion Control Report
Howes Street Hideaways II
L GENERAL LOCATION AND DESCRIPTION:
A. Location
1. The project site is located in the Northeast One Quarter (1/4) of Section 14, UN,
Range 69 West of the 6th P.M., Ft. Collins, Colorado. The site is Lot 11, Block 105,
Harrison's Addition.
2. More specifically, the project site is located between West Mulberry Street and
Myrtle street nearest the north end of the westernmost lots of Block 105 (See
Vicinity Map).
3. The site is a part of Old Town Fort Collins and is developed. The proposed duplex
. will be constructed along the existing alley at the rear of the existing lot.
B. Description of Property
1. There is currently a single family residence on this lot. The existing house fronts on
South Howes Street.
2. The site area is approximately 0.20 acres.
3. Development of the site will consist of the construction of 1 single family residence at
the rear of the existing lot along the alley.
4. An existing paved alley borders the site on the east side.
a. The alley was paved with the Mulberry Green and the Howes Street Hideaways
projects.
b. The alley has an inverted crown section to assist in the conveyance of stormwater
to West Mulberry Street.
5. There are no major drainageways located on or within 150' feet the project site. See
Drainage and Erosion Control Plan in stuffer envelope.
II. DRAINAGE BASINS AND SUB -BASINS:
A. Major Basin Description
1. The site is situated within the Old Town Drainage Basin as designated on the City of
Fort Collins Stormwater Basin Map.
a. according to the conceptual review summary letter dated October 27, 1997, the
drainage basin fee associated with grid #71 in the Old Town Basin, is $4,150.00
per acre.
December 15, 1997
Project No: 1536-08-97
Basil Harridan
City of Ft. Collins Stormwater Utility
P.O. Box 580
Ft. Collins, Colorado 80524
Re: Howes Street Hideaways H
Previously Known as
Lot 11, Block 105, Harrison's Addition; Fort Collins, Colorado
Dear Basil,
Enclosed, please find the Final Drainage and Erosion Control Report for Lot 11, Block 105,
Harrison's Addition. The hydrology data and the hydraulic analysis presented in this report
complies with the requirements of the City of Fort Collins Storm Drainage Criteria Manual;
dated March, 1984, the City of Fort Collins Erosion Control Reference Manual and the Old
Town Master Drainage Basin Plan for the City of Fort Collins.
Please note that this project consists of the construction of 1 single family home and parking
adjacent to the existing alley which was improved with Howes Street Hideaways (Lots 12-14,
Block 105, Harrison's Addition). This report has been prepared as an amendment to the
approved Final Drainage and Erosion Control Report for Howes Street Hideaways (Lots 12-14,
Block 105, Harrison's Addition) since the product is exactly the same as that constructed with the
original Howes Street Hideaways.
If you have questions, or require further information on any item, please call at (970) 226-5334.
Shear Engineering Corporation
BWS / mb
cc: Rayline Development Corporation
4836 s. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 FAX (970) 282-031 1
Final Drainage and Erosion Control Report
for
The Howes Street Hideaways II
Amendment to The Howes Street Hideaways (approved 05/27/97)
Fort Collins, Colorado
Previously known as
Lot 11, Block 105, Harrison's Addition
Prepared for:
RAYLINE DEVELOPMENT CORPORATION
3600 South College Avenue #204
Ft. Collins, Colorado 80525
Phone: (970) 204-0306
INITIALdate . MITTAL
Prepared by:
SHEAR ENGINEERING CORPORATION
Project No: 1536-08-97
DATE: December, 1997
4836 S. College, Suite 12 Ft. Collins, CO 80525 (970) 226-5334 FAX (970) 282-0311