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FORT COLLINS | GREELEY
FINAL DRAINAGE REPORT: IMPALA REDEVELOPMENT
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Sub-Basin 101
Sub-Basin 101 is composed of existing duplexes, landscaped area, Rain Garden 1, and modified
Detention Pond 1. Flows travel via overland flow to Detention Pond 1.
Sub-Basin 102
Sub-Basin 102 is comprised of existing duplexes, paved drives and parking, and landscaped area.
The flows from this basin are conveyed via overland flow, curb and gutter flow, and concrete pan to
Detention Pond 1.
Sub-Basin 200
Sub-Basin 200 is comprised of existing duplexes, asphalt drives and parking, landscaped areas, and
proposed multi-family. Sub-Basin 200 contains Detention Pond 2. Detention Pond 2 was previously
proposed with Hill Crest P.U.D but is being modified to better suit the needs of the proposed site
including adding a water quality headwall with a proposed water quality plate.
Sub-Basin OS1
Sub-Basin OS1 is composed of multi-family buildings, concrete walks, and landscaped areas. The
flows from this basin travel via overland flow directly offsite and are not treated for water quality or
captured. This follows historic patterns and will still allow for 75% of the modified site area to be
treated with LID.
Sub-Basin OS2
Sub-Basin OS2 Is comprised of existing off-site soccer and baseball fields whose flow is accounted
for in Detention Pond 1’s sizing. Overland flow is the primary method in which these flows travel to
Detention Pond 1. These flows are not treated by LID.
Sub-Basins OS3 and OS4
Sub-Basins OS3 and OS4 are composed of existing and proposed buildings, landscaped area, and
paved roadways. Flows from these basins travel via overland flow and curb and gutter flow to W
Mulberry Street. These flows are not captured nor were they planned to be captured with Hill Crest
P.U.D.
Sub-Basins OS5
Sub-Basin OS5 is composed of a small portion of proposed roadway and sidewalk. These flows
travel directly offsite and are not captured or treated.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report.
B. SPECIFIC DETAILS
1. There are 2 existing detention ponds on the project site, both of which are being modified to
accommodate the additional impervious area being added to the existing site. These ponds will
detain up to the 100-yr storm event and release at or below the previously calculated release rates.
See Table 2 for detention summary.
Table 2 - Detention Summary
XSSTTTTVAULT
F.O
.XXXXXXXXXSX
SIRR
IRRIRR SSSFODSSDSTSTSTSTXXXX
T T
POND 1WHWHWHWHUPXXOS1102OS2101OS3OS4101OS1102OS3OS4OS2200200DETENTIONPOND 2100100RAIN GARDEN 1RAIN GARDEN 2OS5OS5DRAWN BY:SCALE:ISSUED:IMPALAREDEVELOPMENTSHEET NO:FORT COLLINS: 301 North Howes Street, Suite 100, 80521GREELEY: 820 8th Street, 80631ENGINEERNGIEHTRONRN970.221.4158northernengineering.comLID EXHIBITC. Ungerman1in=120ft01/11/23PROPOSED STORM SEWERPROPOSED CURB & GUTTERPROPERTY BOUNDARYPROPOSED INLETADESIGN POINTDRAINAGE BASIN LABELDRAINAGE BASIN BOUNDARYALEGEND:( IN FEET )1 inch = ft.Feet0120120120RAIN GARDEN LIMITSSTORMTECH CHAMBERSFOR DRAINAGE REVIEW ONLYNOT FOR CONSTRUCTIONTotal Area of Current Development168,153ft2Total Impervious Area92,745ft2Total Impervious Area without LID Treatment10,584ft2O1-O775% Requried Minimum Area to be Treated69,559ft2Total Treated Area71,493ft2Percent Impervious Treated by LID77.09%