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Home My WebLink AboutPARK SOUTH PUD, 3RD REPLAT - PRELIMINARY & FINAL - 46-88G - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE REPORT FOR PARK SOUTH P.U.D. THIRD REPLAT LOCATED IN THE MCCLELLANDS AND MAIL CREEK DRAINAGE BASINS PREPARED FOR MARC MIDDEL April 22, 1996 PREPARED BY PHILLIP L ROBINSON STEWART & ASSOCIATES, INC. 103 SOUTH MELDRUM STREET FORT COLLINS, COLORADO 80521 970/482-9331 STEWART&ASSOCWES Consulting Engineers and Surveyors April22, 1996 Mr. Basil Hamdan Storm Water Utility City of Fort Collins P.O. Box 580 Fort Collins, CO 80522 Dear Basil, Mr. Marc Middel is planning to develop the remainder of the Park South area as Park South P.U.D. Third Replat. This site contains 13.34 net acres and is located south of West Horsetooth Road and west of Manhattan Avenue. This site was originally to be developed as commercial and office sites, but is now being planned as 75 single family residential lots. The existing Park South -South Glen detention pond which was designed and constructed in 1980, provides detention for this remaining Park South area. The pond was sized for the original Park South P.U.D. which was all single family residential, and since this remaining area also is being developed as single family residential, the required detention is provided in this pond. There is an existing 36 inch storm drain running south along the west side of Manhattan Avenue, and we propose to tie into this existing drain pipe with new pipes and catch basins. The proposed storm drainage facilities in Park South Third Replat are designed in compliance with City of Fort Collins Storm Drainage criteria. Sincerely, Phillip I. Robinson P.E. & L.S. rrC � � i `ft� CQ '• rir. • 4502 i.•. 7••a � �- ••r "+'� James H. Stewart and Associates, Inc. 103 S. Meldrum Street P.O. Box 429 Ft. Collins, CO 80522 303/482-9331 Fax .103/482-9382 TABLE OF CONTENTS PAGE 1 and 2 Text of report 3 Vicinity Map 4 McClellands and Mail Creek Basin map 5 Historic Site Runoff 6 Developed Site Runoff 7 - 13 Subbasin Calculations 14 - 18 Concentration points 19 Pipe flows 20 Existing 36 inch pipe 21 Overflow between Lots 117 and 118 22 Overflow along Manhattan Avenue 23 - 25 Erosion Control Calculations 26 Erosions Control Collateral 27 Kutter's Chart for pipe flow 28 Figure 3 - 2 (flow velocity) 29 Figure 5 - 5 (curb inlet on grade) 30 Figure 5 - 2 (curb inlet sump condition) 31 Calc. curb inlet in sump conditions 32 Allowable flow in gutter - 2 year storm 33 Allowable flow in local street - 100 year storm Pocket Grading, Drainage and Erosion Control Plan (Design Plan) FINAL STORM DRAINAGE AND EROSION CONTROL REPORT FOR PARK SOUTH THIRD REPLAT EXISTING SITE LOCATION AND DESCRIPTION Park South P.U.D. Third Replat is located adjacent to the south line of West Horsetooth Road and to the west line of Manhattan Avenue. It is bounded on the south by Park South P.U.D. Second Replat and on the west by the Four Seasons Townhomes. The site is within the Mail Creek basin portion on the McClellands and Mail Creek master drainage basin. The net area of the site is 13.34 acres, not including the south half of Horsetooth or the west half of Manhattan, both of which are developed streets with drainage facilities in place. The site is a field with sparse vegetation. The historic drainage is from west to east on approximately a 1% slope. There is an existing 36 inch RCP located along the west lime of Manhattan Avenue. This pipe was installed by the City when Horsetooth Road was improved. This pipe is the outlet from an existing 15 foot curb inlet at the southwest intersection of Horsetooth and Manhattan. The pipe drains south from the curb inlet, along the west side of Manhattan, then turns east under Manhattan to the existing Park South -South Glen detention pond. This pond was constructed in 1980. This pond, which has a volume of 11.6 acre feet, provides detention for single family residential lot development on all of the original Park South P.U.D. Park South P.U.D. Third Replat is the remaining undeveloped portion of the original Park South P.U.D. PROPOSED DRAINAGE DEVELOPMENT A storm drainage pipe line will be constructed from the existing 36 inch RCP on the west side of Manhattan to the west side of Rockaway Street. Inlets will be placed at the intersections of Haven Court, Mayflower Court and Rockaway Street which will intercept all of the 2 year developed flow and a portion of the 10 year developed flow. The proposed maximum piped flow from the Park South Third Replat into the existing 36 inch pipe is 24 cfs. Larger flows will be carried by the street gutters to the southeast corner of Haven Drive and Haven Court. At this location, surface overflows will top the walk and flow southeast between Lots 117 and 118 to the west gutter swale of Manhattan Avenue. The west swale of Manhattan Avenue drains south to the Park South -South Glen detention area. OFFSITE FLOWS The rear portion of the Four Seasons Townhomes flows onto the west side of Park South Third Replat. This flow will be carried east along the side lines of Lots 131 through 140 to the west gutter of Rockaway Street. The rear yards of Lots 59 through 73 of Park South Second Replat drain to the existing 2 foot concrete pan which drains east along the rear line of Lots 118 through 129. This plan flows directly to the west gutter Swale of Manhattan Avenue. The maximum allowable street capacity for 100 year storms will not be exceeded at any location in the Park South P.U.D. Third Filing. Following in this report are calculation sheets for runoff from the subbasins and for flows at concentration points. Included in the pocket is a copy of the Grading, Drainage and Erosion Control Design Plan. EROSION CONTROL Park South P.U.D. Third Replat is located in a low wind erodibility zone and in a moderate rainfall erodibility zone. During the overlot grading process, sediment will be controlled by installing a silt fence along the west line of Manhattan Avenue. Gravel filters will be place at catch basins to prevent sediment from entering the pipe system After grading, a temporary crop of annual rye is proposed on the rear 50 feet of all lots to eliminate bare soil. Wind erosion barriers will be provided by the installation of curbs and by the rainfall erosion control procedures. 2 VICINITY MAP SCALE - 1 "=1000' \ Monroq eAvenue qWestorsetooth Rood Arbor Avenue o c a 4\ CIO lbv � �c o t (n Denniso Av+en c P \ o BoordaJA Drive � Lopez O r 7 m Elementary hoc o Butfe Pass Drive go, \ � c ° go Troutman Parkway I t