HomeMy WebLinkAboutDrainage Reports - 10/29/2013April 24, 2013
Mr. Glen Schlueter & Mr. Wes Lamarque
Storm Water Department
City of Fort Collins
700 Wood Street
Fort Collins, Colorado 80521
RE: Rigden Farm — Filing 17 Drainage
Dear Mr. Schlueter & Mr. Lamarque,
C trof fit. Col ins A prov Plans
Approved By.
Date 1 a 0) -1-3
J•R ENGINEERING
A Weslrian Company
Rigden Farm, Filing 17 is a partial replat of Rigden Farm, Filing 6. Specifically, this PDP deals with
three blocks of lots, formerly shown as Rigden Farm, Filing 6 lots 220-231, 259-298 and Tracts
AQ, AR, AV & AW. Within this PDP replat, these areas are renamed as Blocks 1, 2 & 3, and for
purposes of conciseness, we shall refer to the areas in this way. Block (former lots 220-231) is
located adjacent to and north of William Neal Parkway and is encompassed by Bryce Drive,
Haflinger Drive and Cobb Drive. Block 2 (former lots 268-298), is flanked on the west by Bryce
Drive and on the east by Anika Drive. Block 3 (former lots 259-267), is located on the south
side of Percheron Drive, immediately west of Ziegler Road.
There are slight changes being made to each block, but the use is remaining single-family in all
cases and the original drainage basins are unchanged as shown on the attached Rigden,Filing 6
Drainage sheets. On Block I, the original alley that was designed to run in the back of the rear
loaded lots is being removed. Alternatively, a shared driveway will be added for the six
southerly lots, so that the realigned front -loaded driveways do not take access directly from
William Neal Parkway. With this change, a double Type 13 inlet is added at the east end of the
shared driveway to prevent storm water from passing over the sidewalk, and the eliminated
alley inlets are replaced by a double curb inlet on the west side of Cobb Drive. These changes
do not alter the original drainage basin design point and by adding the proposed inlets, the
storm water is introduced to the drainage system in a way that alleviates the inlets at the
intersection of Cobb Drive and William Neal Parkway. Similarly, Block 2 will eliminate a
longitudinal, north to south alley drive. This alley provided rear -loading for all of the Block 2
houses. The drainage paths for this Block are remaining exactly the same, except in place of the
20' impervious asphalt shared drive, there will now be a 3' trickle pan centered in the open
space tract at the rear yards. No storm drain changes have been made for Block 2. Block 2
drainage basins remain exactly the same. Block 3 will encompass the same area as former lots
259 through 267, but will reduce the average size of the parcels by adding 5 more lots. Block 3
lots are graded the same as the previous plan, staying with type A drainage patterns. We find
that the rooftop area does not increase because the proposed smaller lots utilize 2-story
houses, while the former larger lots had expanded ranch footprints. There will be 5 more
driveways, but we find the addition of this minor impervious area to be negligible.
2900 South College Avenue, Suite 3D
Fort Collins, Colorado 80525
Using a more specific drainage basin approach, Block I is comprised of a portion of basins 136,
137 and 138. Replacement of the alley with a shared driveway access for the south lots, reduces
overall impervious area and the addition of on -site inlets remove storm flows prior to
conveyance into the right-of-way. Basins 136, 137 and 138 are essentially unchanged, and flow
to the same design points as originally approved. Block 2 drainage paths include basins 152, 156,
157, 160, 162 and 166. These basins remain unchanged by this PDP, impervious area is lessened
and the design points are identical to those originally approved. Block 3 drainage basins include
basins 167 and 170. As with the other two blocks, the basin areas and the design points remain
the same, with a slight increase of impervious area attributed to 5 additional driveways.
In all, due to the fact that the changes being proposed by Rigden Farm, Filing 17 are minor in
character and nature, and in most cases, impervious area has been lessened, we find the storm
water impacts by this PDP to be negligible and thus have provided this letter in lieu of a drainage
report. We ask that you accept this letter as a record drainage document, to be kept on file for
future reference. If you have any questions or concerns, please do not hesitate to contact me at
970.817. 10 10 or by email at talopoff@jrengineering.com.
Sincerely,
JR Engineering, LLC
Tim Halopoff, PE
Project Manager
Enclosure
Cc: File
2900 South College Avenue, Suite 3D
Fort Collins, Colorado 80525
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