HomeMy WebLinkAboutBLOOM FILING FIVE - MA230059 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENT5265 Ronald Reagan Blvd., Suite 210
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970.800.3300 •GallowayUS.com Memorandum
HFH22 - Memorandum F1 Amendment.docx
Page 1 of 2
To:Wes Lamarque, PE
City of Fort Collins
From:Matthew Pepin, PE
Galloway, Inc.
Date:05/10/2023
Re:Bloom Filing 1 Amendment - Drainage Modifications
To Mr. Lamarque,
Bloom Filing 1 required revisions that would include a modified pond, an added pond, and
modifications to associated storm infrastructure. This memorandum is to help provide
information on the changes from the approved Bloom F1 Final Drainage Report and the
amendment.
Pond Modification / Addition
Pond G was initially approved to provide 9.5 ac-ft of volume and release at a rate of 17.6 cfs.
This pond is being split into two separate ponds to allow for increased development within the
piece of land where Pond G initially was planned. Pond G will now be reduced to a volume of
4.8 ac-ft and releasing at 13.5 cfs. A second pond, Pond G1, will be located on the western
part of the site. Pond G1 will provide 5.1 ac-ft of volume and release at 4.4 cfs. This would
increase the amount of total flow existing both ponds from the original by 0.2 cfs. In order to
maintain a maximum of 22.3 cfs releasing into the southern part of the Cooper Slough outfall,
Pond I’s flow will be restricted from 0.35 cfs to 0.15 cfs.
Storm Infrastructure
The associated basin that were tributary to the effected modification storm infrastructure are
labeled as A-G1, A-G2,…A-G6. Inlet calculations were added for these basins as well. An
updated StormCAD output is provided on page 181 of the updated Drainage Report
Amendment. Tailwater conditions were set based on the 100-year WSEL for the major storm
event and a free outfall condition in the minor event. Note: there is HGL surcharging from SD
Inlet L1.5 and SD Inlet L1. The HGL at this location is .27 higher than the RIM at the MH of
SD MH L1.4. This equates to 3.24 inches and would remain within the ROW, not impacting
the lots.
Storm Infrastructure incorporating Bloom F2
In order to take into account LID’s within Bloom F2, there is another modification to the storm
pipe infrastructure. A concern of too much flow entering the LID in the major storm events
would cause damage needed to be mitigated. To prevent this from happening, a manhole
would split flow from outfalling into the LID and by passing downstream to outfall into the EDB
(Pond E). This flow split would have flow entering into the LID at a maximum of 7.46 cfs in the
major storm event. The flow split is achieved by having a weir within the manhole, allowing
Bloom Filing 1
05/08/2023
HFH22 - Memorandum F1 Amendment.docx
Galloway & Company, Inc.Page 2 of 2
for all flow in the minor storm event to enter the LID at a flow rate of 2.80 cfs. These results
can be found on pages 188-196 in the Appendix.
CONCLUSION
The modifications to the site will not change the overall design intent that was originally
approved with Bloom F1 Drainage Report.
Sincerely,
GALLOWAY
Matthew Pepin, PE
Civil Project Engineer
MatthewPepin@Gallowayus.com