HomeMy WebLinkAbout424 WEST OAK PUD FINAL - 40 92B - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage & Erosion Control Report
for
Fort Collins, Colorado
Prepared for:
RICHMOND ASSOCIATES
420 West Oak Street
Fort Collins, CO 80521
Prepared by:
SHEAR ENGINEERING CORPORATION
Project No. 1227-01-92
Date: November, 1992
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334
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APPENDIX 2
CHARTS & FIGURES
TABLE 3-2 RATIONAL METHOD RUNOFF COEFFICIENTS FOR
ZONINGCLASSIFICATIONS
TABLE 3-3 RATIONAL METHOD RUNOFF COEFFICIENTS FOR COMPOSITE
ANALYSIS
FIGURE 602 TRAVEL T AE VELOCITY FOR RATIONAL METHOD
FIGURE 3-1 RAINFALL INTENSITY CURVE FOR FORT COLLINS, COLORADO
FIGURE A CHECKER BLOCK DATA
" 3.1.6 Runoff Coefficients
The runoff coefficients to be used with the Rational Method referred to in Section 3.2
"Analysis Methodology" can be determined based on either zoning classifications or the
types of surfaces on the drainage area. Table 3-2 lists the runoff coefficients for the various
types of zoning along with the zoning definitions. Table 3-3 lists coefficients for the different
kinds of surfaces. Since the Land Development Guidance System for Fort Collins allows land
development to occur which may vary the zoning requirements and produce runoff coeffi-
cients different from those specified in Table 3-2, the runoff coefficients should not be based
solely on the zoning classifications.
The Composite Runoff Coefficient shall be calculated using the following formula:
C = (!CIA,)/At
-t
Where C = Composite Runoff Coefficient
CI = Runoff Coefficient for specific area A,
A, = Area of surface with runoff coefficient of ?;I
n = Number of different surfaces to be considered
A, =Total area over which C is applicable; the sum of all Ai s is equal to At
Table 3-2
RATIONAL METHOD RUNOFF COEFFICIENTS FOR ZONING CLASSIFICATIONS
Description of Area or Zoning
Coeffident
Business: BP, BL.........................................................................................
0.85
Business: BG, HB, C..................................................................................
0.95
Industrial: IL, IP..........................................................................................
0.85
Industrial: IG...............................................................................................
0.95
Residential: RE, RLP..................................................................................
0.45
Residential: RL, ML. RP.............................................................................
0.50
1 Residential: FILM, RMP..............................................................................
0.60
Residential: RM, MM..................................................................................
0.65
Residential: RH..........................................................................................
0.70
Parks, Cemeteries......................................................................................
0.25
Playgrounds...............................................................................................
0.35
Railroad Yard Areas.......................................:...........................................
0.40
Unimproved Areas......................................................................................
0.20
Zoning Definitions
R-E Estate Residential District — a low density residential area primarily in outlying
areas with a minimum lot area of 9,000 square feet.
R-L Low Density, Residential District — low density residential areas located throughout
the City with a minimum lot area of 6,000 square feet.
R-M Medium. Density Residential District — both low and medium density residential
areas with a minimum lot area of 6,000 square feet for one -family or two-family
dwellings and 9,000 square feet for a multiple family dwelling.
R-H High Density Residential District— high density residential areas with a minimum lot
area of 6,000 square feet for one -family or two-family dwellings, 9,000 square feet
for a multiple family dwelling, and 12.000 square feet for other specified uses.
R-P Planned Residential District —designation of areas planned as a unit (PUD) to pro-
vide a variation in use and building placements with a minimum lot area of 6,000
square feet.
R-L-P Low Density Planned Residential District — areas planned as a unit (PUD) to permit
variations in use, density and building placements, with a minumum lot area of 6,000
square feet.
MAY 1984 3-3 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 low 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
Concrete............................................................................................. 0.95
Gravel................................................................................................. 0.50
Roofs .................
....................................................... 0.95
Lawns, Sandy Soil:
Flat<2%.............................................................................................
Average2 to 7%..................................................................................
Steep>7%..........................................................................................
Lawns, Heavy Soil:
Flat<2%.............................................................................................
Average2 to 7%..................................................................................
Steep>7%......... :................................................................................
0.10
0.15
0.20
0.20
0.25
0.35
MAY 1984 3-4 DESIGN CRITERIA
FIGURE 602
d
TRAVEL TIME VELOCITY FOR RATIONAL METHOD
so
30
t- 20
ki
1
MM0111111WA
31111
M
ME11111
M
oil!It■■�
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VELOCITY IN FEET PER SECOND
WRC. EN0. REFERENCE: `Urban
Hydrology.
For Small
Watersheds" Technical
Release
No. 55,
USDA, SCS
Jan. 1975.
3.1.7 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 (1.1 — CC,) D 112
S
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.
3.1.8 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
Frequency Factor
(years)
q
2to 10
1.00
11 to25
1.10
26 to 50
1.20
51 to 100
1.25
Note: The product of C times Cl shall not exceed 1.00
3.2 Analysis Methodology
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 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, cis
A = Total Area of Basin, acres
Cf = Storm Frequency Adjustment Factor (See Section 3.1.8)
C = Runoff Coefficient (See Section 3.1.6)
1 = Rainfall Intensity, inches per hour (See Section 3.1.4)
3.2.2 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 analysis. This procedure is detailed in the Urban Storm Drainage
Criteria Manual, Volume 1, Section 4.
MAY 1984 3-5 DESIGN CRITERIA
No Text
SECTION 3. HYDROLOGY STANDARDS
3.1 General Design Storms
All drainage systems have to take into consideration two separate and distinct drainage problems. The
first is the initial storm which occurs at fairly regular intervals, usually based on the two to ten-year
storm, depending on land use. The runoff from this type of storm is considered the "nuisance flow". The
second is the major storm which is usually based on an infrequent storm, such as the 100-year storm.
In some instances the major storm routing will not be the same as the initial storm. In this case, a
complete set of drainage plans shall be submitted for each storm system.
3.1.1 Initial Storm Provisions
As stated before, the initial storm shall be based on the two to ten-year storm. The objectives
of such drainage system planning are to minimize inconvenience, to protect against recur-
ring minor damage and to reduce maintenance costs in order to create an orderly drainage
system at a reasonable cost for the urban resident. The initial storm drainage system may in-
clude such facilities as curb and gutter, storm sealer and open drainageways, and detention
facilities.
3.1.2 Major Storm Provisions
The major storm shall be considered the 100-year storm. The objectives of the major storm
planning are to eliminate substantial property damage or loss of life. Major drainage systems
may include storm sewers, open drainageways, and detention facilities. The correlation
between the initial and major storm system shall be analyzed to insure a well coordinated
drainage system.
3.1.3 Storm Frequency
The initial and major storm design frequencies shall not be less than those found in the fol-
lowing table:
Table 3-1
DESIGN STORM FREQUENCIES
Design Storm Retum Period
Land Use or Zoning
Initial Storm
Major Storm
Residential:
(RE, RL, RLP, RP, ML, RM, RMP,
FILM, MM, RH)......................................................................
2-year
100-year
Business:
(BG, BL, BP, HB, C, IL, IP, IG)..............................................
10-year
100-year
Public Building Areas...............................................................
10-year
100-year
Parks, Greenbelts, etc..............................................................
2-year
100-year
Open Channels & Drainageways.............................................
—
100-year
Detention Facilities...................................................................
—
100-year
t See Table 3-2 for zoning delinitions.
3.1.4 Rainfall Intensities
The rainfall intensities to be used in the computation of runoff shall be obtained from the
Rainfall Intensity Duration Curves for the City of Fort Collins, included in these specifications
as Figure 3.1.
3.1.5 Runoff Computations
Storm Runoff computations for both the initial and major storm shall comply with the criteria
set forth in Section 3.2 "Analysis Methodology." All runoff calculations made in the design of
both initial and major drainage systems shall be included with the storm drainage plans in the
form of a Drainage Report. Reports submitted for approval should have a typed narrative
with computations and maps in a legible form.
MAY 1984 3-1 DESIGN CRITERIA
May 3, 1993
Project No: 1227-01-92
W. Glenn Schlueter
City of Fort Collins Storm Water Utility
235 Mathews Street
Ft. Collins, Colorado 80524
Re: Drainage analysis for Mountain Oak Neighborhood; Old Town Basin
Ft. Collins, Colorado.
Dear Glenn,
We have completed the revisions to the calculations and clarified the drainage and erosion
control exhibit as you suggested. They are attached for your review and approval. It is
understood that City inspectors may require clean up or some other appropriate measures should
erosion become a problem.
A copy of my November 27, 1992 letter to you is also attached, which states our original
conclusions. The revisions to the calculations and other clarifications still indicate a negligible
increase in runoff and therefore the original conclusion stands.
If you have any questions, please feel free to call me at 226-54334. Thank you for your
sup,gesdons-apd attention in this matter.
Brian W. Shear, PE--'
Shear Engineering Corporation
BWS / jmb
cc: Don Richmond
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334
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CITY OF FORT COLLINS, COLORADO
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November 27, 1992
Project No: 1227-01-92
Mr. Glenn Schlueter
City of Fort Collins Storm Water Utility
235 Mathews Street
Ft. Collins, Colorado 80524
Re: Drainage Analysis for Mountain -Oak Neighborhood; Old Town Basin
Fort Collins, Colorado
Dear Mr. Schlueter,
We have completed a drainage analysis for Mountain - Oak Neighborhood situated in the Old
Town Drainage Basin, Ft. Collins, Colorado. It is our understanding that the proposed
development plan consists of the following:
1. Removal of two (2) out structures.
2. Construction of a 4-car garage behind the existing residence / office located at 420 West
Oak Street.
3. One new residence on the remaining open lot in the block.
4. An addition on to an existing residence / office at 420 West Oak Street.
5. An access drive parking area for the proposed garage constructed using checker blocks.
The purpose of the checker blocks is to provide more pervious surface area in the drive / parking
( lot than a typical paved lot would provide. The blocks also provide a more aesthetically pleasing
parking lot which will help to improve the residential atmosphere of the neighborhood.
Our calculations have shown that there is negligible increase in runoff from the block due to the
proposed improvements. Due to the size of the contributing area studied (2.2 acres), the runoff,
both historical and developed, is minimal and would have absolutely no impact on the Old
Town Basin. Detention facilities would not be justified for this situation.
If you have any questions, please feel rcj a to call at 226-5334
Sincerely,
Brian W. Shear, P.E.
Shear Engineering Corporation
BWS / jmb
cc: Don Richmond
4836 S. College, Suite 12 Fort Collins, CO 80525 (303)226-5334
Summary of Flows
C2,C,o/C„o TC I2,I,d,00 A
Mt-,,- ,.ate
Q2,Q,4/Q,00
Mg
HISTORICAL 0.37/0.47 10 2.5/4.4/7.2 2.2 2.0/3.6/7.4
DEVELOPED 0.40/0.50 10 2.5/4.4/7.2 2.2 2.2/3.9/7.9
APPENDIX 1
HYDROLOGIC CALCULATIONS
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