HomeMy WebLinkAboutDrainage Reports - 04/21/2003FINAL
DRAINAGE
AND
EROSION CONTROL REPORT
for
Lot 9, Tefft Acres
(3209 Moore Lane, Fort Collins, Colorado 80526)
March 1, 2003
Prepared for:
Mr. Richard Pitner
3209 Moore Lane
Fort Collins, CO 80526
(970)282-8088
Prepared by:
Jeffrey W. Couch, P.E.
TEAM Engineering
3468 Shallow Pond Drive
Fort Collins, CO 80528.7002
(970)231-9937
Project Number: 791.0201
Flna�,Approved Report
i�
Jeffrey W. Couch, P.E.
TEAM Engineering
3468 Shallow Pond Drive
Fort Collins, CO 80528-7002
(970) 231-9937
March 1, 2003
Mr. Basil Hamden
City of Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80521
RE: Lot 9, Tefft Acres (3209 Moore Lane)
Minor Subdivision
Dear Basil:
Attached is a drainage report for Lot 9, Tefft Acres. Lot 9 is a 7.079 acre lot located in southwest
Fort Collins, Colorado. This property has recently been annexed into the City of Fort Collins as
part of a voluntary enclave annexation.
One single family structure is currently located on Lot 9. The owner would like to split this tract into
two parcels to create one additional building site. Due to the size of the parcels, we have
determined that the addition of another residential structure would have NO impact to existing
drainage patterns in this area.
Please review this information at your earliest convenience and contact me at (970) 231-9937 if
you have additional questions.
Cc: Richard Pitner, 3209 Moore Lane, Fort Collins, CO 80526
Jeffrey W. Couch, P.E.
TEAM Engineering
3468 Shallow Pond Drive
Fort Collins, CO 80528-7002
(970) 231-9937
March 1, 2003
Mr. Basil Hamden
City of Fort Collins Utilities
700 Wood Street
Fort Collins, CO 80521
RE: Lot 9, Tefft Acres (3209 Moore Lane)
Erosion Control I Estimate
Dear Basil:
This letter is to summarize the erosion control improvements needed for the minor subdivision
proposed for Lot 9 of Tefft Acres. The minor subdivision is intended to subdivide the existing 7.079
acre parcel into a 2.371 acre parcel and a 4.708 acre parcel as a future building site.
We are proposing that NO erosion control escrow account be established as part of the project.
We have based this request on the following information:
1. There are no public improvements proposed as part of this subdivision.
A. Moore Lane is a paved existing roadway.
B. Water main is located on the west side of Moore Lane. Only a service tap is required
for the new lot.
C. All dry utilities (gas, electrical and telephone) are existing in Moore Lane.
D. An on -site septic system will provide sanitary facilities for the project.
E. No storm drainage facilities are proposed.
2. The site is currently covered with irrigated, native grasses. No disruption of the site via
overlot grading is proposed as part of this project.
Please feel free to call me at (970) 231-9937 if you have additional questions.
Cc: Richard Pitner
CERTIFICATIONS
OWNER
Richard Pitner hereby certifies that the drainage facilities for the proposed Lot 9, Tefft Acres shall
be constructed according to the design presented in this report I understand that the City of Fort
Collins does not and will not assume liability for the drainage facilities designed and/or certified by
my Engineer. I understand that the City of Fort Collins reviews drainage plans pursuant to
Colorado Revised Statutes Title 30, Article 28; but cannot, on behalf of myself, guarantee that final
drainage design review will absolve Lot 9, Tefft Acres and/or their successors and/or assigns of
future liability for improper design. I further understand that approval of the Final Plat and/or Final
Development Plan does not imply approval of my Engineer's design.
Lot 9, Tefft Acres
ENGINEER
I hereby certify that this report for the Final Drainage and Erosion Control Report for Lot 9, Tefft
Acres was prepared by me in accordance with the provisions of the City of Fort Collins STORM
DRAINAGE DESIGN CRITERIA and CONSTRUCTION STANDARDS for the owner thereof. I
understand that the City of Fort Collins does not and will not assume liability for drainage facilities
designed by others. h k
Respectfully Submitted,
Jeffrey W. Couch, P.E.
Colorado Professional Engineer No.16584
For and on Behalf of Team Engineering
FINAL
DRAINAGE
AND
EROSION CONTROL REPORT
for
Lot 9, Tefft Acres
(3209 Moore Lane, Fort Collins, CO)
INTRODUCTION
This report has been prepared to identify existing drainage patterns and issues for Lot 9,
Tefft Acres. Once these patterns and issues are identified, a plan will be created to mitigate any
impacts which may be created by the proposed subdivision. All information will be prepared to be
in conformance with the criteria established by the °City of Fort Collins Storm Drainage Criteria
Manual°.
Lot 9 of Tefft Acres is a 7.079 parcel which was created as part of a Larimer County rural
subdivision in 1961. The site is located in the Southeast Quarter of Section 28, Township 7 North,
Range 69 West of the 6'h Principal Meridian in Larimer County. The site was developed as a large
lot subdivision for large residential structures with large animal facilities.
Irrigation laterals surround the existing lots which allows the area to be irrigated with native
water. Streets are rural sections without curbs and sidewalks. The existing landscaping features
native grasses and open split rail fences.
The intent of this project is to split the 7.079 parcel into two pieces. The northerly piece
will be 2.371 acres and includes the existing residential structure. The southerly lot will be a vacant
4.708 acre parcel which is intended for the addition of one residential structure.
ADJACENT LAND USES
Large lot residential structures surround Lot 9 of Tefft Acres to the north, east and south.
City of Fort Collins open space is adjacent to the west boundary of the existing lot. All surrounding
areas are covered with native grasses supported by native water supplies transported by a series
of private irrigation laterals.
DRAINAGE MASTER PLAN
This project is located within the Spring Creek Drainage Basin located west of Taft Hill
Road. This area has no existing major storm drainage improvements and no major storm drainage
improvements are anticipated.
Six hundred feet (600') south of this site, at the end of Moore Lane, a subbasin divide
directs flow from the Silver Oaks Subdivision to the east — away from this site. A map of the area
topography based on City of Fort Collins Quarter Section Maps is attached. Water from the east of
this site is diverted by the easterly roadside ditch along Moore Lane to the north. Flows from the
west and north historically flow to the north and have no impact on the project. Runoff from the
south 10± acres sheet flows northerly and is intercepted by irrigation laterals and diverted westerly
around the project.
HISTORIC FLOWS
Off -site Areas
Historic runoff flows from south to north through the area. Flows start approximately 600
feet south of Lot 9 and because of the rural density of the area do not develop into large
concentrated flows. All flows are intercepted by an irrigation lateral which runs from south to north
on City of Fort Collins Open Space.
9
On -site Areas
The existing site flows from southeast to northwest. A residence at the northeast corner of
the site creates the only impervious area. All runoff is established as sheet flow and eventually
discharges into Spring Creek. An irrigation lateral along the east boundary of Lot 9 will remain
unchanged and conveys water to lots north of this site.
DESIGN CRITERIA
The Rational Formula has been used to develop flow quantities for this project. The
Rational Method of determining stormwater quantities is an acceptable method of analysis for
drainage areas less than 200 acres.
PROPOSED DRAINAGE
The existing site has a coefficient of infiltration of 0.216 (see Calculations in Appendix).
This is based on one residential area with a footprint of approximately 6,375 square feet. Splitting
the existing lot and adding one additional residential campus of the same area will increase the
coefficient of infiltration from 0.216 to 0.231 (see Calculations in Appendix).
This increases runoff in the minor (Two Year) and major (100 Year) events as follows:
Historic
(One Residence)
2 Year 1.80 cis
100 Year 7.87 cis
Developed
(Two Residences) Increase
1.93 cis 0.13 cfs
8.42 cfs 0.55 cis
Based on this information, we do not propose the installation of additional storm drainage
improvements. The small increase in runoff will not impact adjacent downstream properties as
follows:
3
1. The existing ground cover represents 6.923 acres of the total 7.079 acre site (97.9%),
2. Offsite flows are diverted around this site.
3. On -site flows are spread out across the entire 7.079 acres and do not create a concentrated
discharge at any location.
4. A field review of the area indicates that there are no indications of negative drainage impacts
either by inundation or erosion.
5. The existing irrigation lateral system serves as an adequate informal conveyance system for
the entire area. The outfall to Spring Creek runs from north to south on City of Fort Collins
Open Space.
6. There are no Public Improvements proposed as part of this project.
7. There are no areas subject to flooding within the limits of this project.
8. There are no flood plains or floodways located within the limits of this project.
EROSION CONTROL
The subdivision being proposed will not involve disruption of the existing site. There are
no utilities, grading, drainage, landscaping or street improvements required as part of this
subdivision.
CONCLUSION
The creation of an additional building site in an existing large lot rural subdivision will result
in minor increases in runoff. This increase does not pose a problem to downstream properties or
downstream improvements.
4
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CITY OF FORT COLLINS
STORMWATER CRITERIA MANUAL
TABLE 306
RAINFALL INTENSITY DISTRIBUTION FOR UDSWM2-PC
2-YEAR 5-YEAR 10-YEAR 25-YEAR 50-YEAR 100-YEAR
TIME I INTENSITY INTENSITY INTENSITY INTENSITY INTENSITY INTENSITY
5
0.29
0.40
0.49
0.63
0.79
1.00
10
0.33
0.45
0.56
0.72
0.90
1.14
15
0.38
0.53
0.65
0.84
.1.05
1.33
20
0.64
0.89
1.09
1.41
1.77
2.23
25
0.81
1.13
1.39
1.80
2.25
2.84
30
1.57
2.19
2.69
3.48
4.36
5.49
35
2.85
3.97
4.87
6.30
7.90
9.95
40
1.18_
1.64
2.02
2.61
3.27
4.12
45
0.71
0.99
1.21
1.57
1.97
2.48
50
0.42
0.58
0.71
0.92
1.16
1.46
55
0.35
0:49
0.60
0.77
0.97
1.22
60
0.30
0.42
0.52
0.67
0.84
1.06
65
0.20
0.28
0.39
0.62
0.79
1.00
70
0.19
0.27
0.37
0.59
0.75
0.95
75
0.18
0.25
0.35
0.56
0.72
0.91
80
0.17
0.24
0.34
0.54
0.69
0.87
85
0.17
0.23
0.32
0.52
0.66
0.84
90
0.16
0.22
0.31
0.50
0.64
0.81
95
0.15
0.21
0.30
0.48
0.62
0.78
100
0.15
0.20
0.29
0.47
0.60
0.75
105
0.14
0.19
0.28
0.45
0.58
0.73
110
0.14
0.19
0.27
0.44
0.56
0.71
115
0.13
0.18
0.26
0.42
0.54
0.69
120
0.13
0.18
0.25
0.41
0.53
0.67
303.2 Surface Storage and Infiltration
Table 307 gives those values for surface storage for pervious and impervious surfaces. Table 308
gives the infiltration rates to be used with UDSWM2-PC.
TABLE 307
SURFACE STORAGE
TYPE OF SURFACE
DEPTH OF STORAGE
(inches)
ervious Areas
0.1
Pervious Areas
0.3
Hydrology Standards 1 309
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