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Home My WebLink AboutORCHARD PLACE PUD PRELIMINARY - 40 93 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFOUN DAT 1 O N ENGINEERING Ma6/4-c RARA +� p I I f I II ISY�00�• � i Il f � Oil i - I I - I I , ' 1 �ItOURO ii- I � b■0! I 1 A s I I 6+ � I I zzao I � , ' I rs v� f ns u � y� � �� rsc• } rY I sc[.- nIt[/nloM : — �•e , ,� f e �' l I ,,,t j rs�• I Detail r4 ,F r I live. • I I Ii- BETHEL I ! I I BAPTIST �• UNRAI' PLACE I I l PU.D. i T it o s: Is,10, 64. Delos I ! v� 1 . \ am PUN ST 31. 2 � ` 13 v_ \el "I G I TIf Mie :� I No Text Q100 = (1.25) (. 73) (6.40) (.52) = 3.04 cfs D E T E N T I O N Release at Historic Flow Q = .17 cfs Developed Q = (1.25)(I)(.73)(.52) = .471 Time I Q100 In Volume Q2 Out Volume Volume Min Lin/hrZ cfs (cu.ft) cfs (cu. ft.) (cu.ft.) 10 7.30 3.43 2058 .17 102 1956 20 5.17 2.43 2916 .17 204 2712 30 4.15 1.95 3510 .17 306 3204 40 3.50 1.65 3960 .17 408 3552 50 3.00 1.41 4230 .17 510 3720 60 2.60 1.22 4392 .17 612 3780 70 2.30 1.08 4536 .17 714 3822 80 2.06 0.97 4656 .17 816 3840 90 1.87 '0.88 4752 :17 918 3834 100 1.70 0.80 4800 .17 1020 3780 Detention Required is 3840 cubic feet. DEVE LOPED RUNOFF Flow Path - Developed Site 1. NW corner of site - Overland to east edge of site - 140 feet 2. Swale along east edge of site Slope 1. Backyard at 1% 2. Sideyard at .5% Developed Coefficient of Infiltration Roof & Park Open Street ( 528)(.95) + (.287)(.20) + (.185)(.95) _ .73 1 Time of Coaicentration (TC) 1. Backyard from Figure 3-2 Page 3-6 = 9.0 minutes 2. Sideyard from Urban Drainage (v = 1 foot/sec) = 1.7 minutes Total TC = 10.7 minutes Intensity from Figure 3-1 Page 3-2 I2 = 2.25 inches/hour I100 = 6.40 inches/hour g2 = (1.0)(.73)(2.25)(.52) _ .85 cfs 3. The detention pond, in conjunction with rock filters and silt fences, will provide wind and water erosion protection for the site during construction. 4. Site landscaping will provide the final site erosion control in conjunction with the detention/sedimentation pond. 5. The adjacent street right-of-way is included in the drainage analysis. HI STORI C RUNOFF Historic Run-off Path = 195 feet diagonally across site Slope = .75% Historic Coefficient of Infiltration = 0.2 Time of Concentration (TC) from Figure 3-2, Page 3-6 TC = 24 minutes Intensity from Figure 3-1, Page 3-2 IZ = 1.67 inches/hour 1100 = 4.70 inches/hour Q = Cf C1A QZ = (1.0)(.2)(1.67)(.52) = .17 cfs Q100 = (1.25) (.2) (4.7) (.52) = . 61 cfs EROS ION CONTROL it is anticipated that the erosion potential from this site will be minimal. The site is less than two hundred (200) feet long and is currently surrounded by landscaped areas. Therefore, no improvements are anticipated to control wind erosion. The easterly end of the parking lot will provide the location for a sediment basin to be constructed. Rock filters will provide a filter to further trap sediments and insure protection from water erosion. Silt forming along the south and eastern edging of the site will protect adjacent properties. The sedimentation/detention pond will be the first improvement constructed on the site. Seeding and/or sodding of the site immediately after the units are constructed will provide the permanent erosion control solution. C O N C L U S I O N S 1. The site does not sit in a regulated flood plain and is not subject to severe flooding problems. 2. A detention pond will collect runoff from the site, and an outlet structure will control releases into the existing drainage system. southeast and historically sheet -flow over the street curb into Orchard Place. Flows continued along the north curb and gutter along Orchard Place to a stormwater inlet at the northwest corner of Taft Hill Road and Orchard Place. Historic runoff for the two year storm is .17 cfs. Historic runoff for the one hundred year storm is .61 cfs. (see Calculations in Appendix). PROPOSED DRAINAGE IMPROVEMENTS As per the requirements of the Fort Collins Storm Drainage Design Criteria and Construction Standards, detention is proposed for this site to insure that only historic flows are released into the existing drainage system. Back and sideyard swales will collect offsite flows from the north and onsite runoff from the buildings and convey these flows to a detention pond located in the parking lot. An outlet structure located at the southeast corner of the parking lot will release this runoff at historic rates. The detention pond will be sized to detain the onsite runoff and to allow offsite flows to pass through the site. The two year flows from the developed site are .85 cfs. The one hundred year flows from the developed site are 3.04 cfs. Approximately 3,840 cubic feet of detention will be required in the parking area (see calculations in Appendix). This will require the parking area to pool water approximately eight (8) inches deep. M E T H O D O L O G Y The Rational Method will be used to develop runoff and detention volumes for this project. The Rational Formula is an excellent predictor of flaws in drainage basins less than 200 acres. HI STORIC_ FLOWS Runoff in this area, typically, flows from the northwest to the southeast. Flows are collected by the Orchard Place street curbs and then conveyed by storm sewer to a regional drainage outlet which exists approximately two hundred (200) feet south of Orchard Place (See Figure 2 Photo and Topography). Historical flows have little impact on this site. Areas to the south and east are lower than the proposed project, and these drainage flows run away from the site. The apartment complex to the west constructed berms between these two (2) properties and flows from the apartment complex are diverted to the south, away from the site. The trailer park to the north does discharge runoff to the south through this site; however, these flows will be routed through the site drainage swales. Runoff from the property itself travels from the northwest to the SITE DE SCRIPTION A .42 acre eight-plex project is being developed on a 119' x 155' lot along the north side of Orchard Place, just west of Taft Hill Road. This property is located in the Quarter of Section , Township North, Range West of the Sixth Prime Meridian, Larimer County, Colorado. The site is currently vacant and is covered by native vegetation. Land uses vary around the project. A mobile home park exists to the north, an apartment complex exists to the west, a vacant parcel exists to the south across Orchard Place, and a single family residence exists to the east. The proposed project will have eight (8) units and provide seventeen (17) paved parking spaces. All other areas will be landscaped/open areas. These land use areas are summarized as follows: Area Land Use Square Feet Acres Per Cent Building and Parking 11,955 0.27 52.8 Open Space 6,490 0.15 28.7 Street Right -of -Way 4,185 0.10 18.5 TOTALS 22,630 0.52 100.0 I N T R O D U C T I O N This Drainage and Erosion Control Report is being prepared in conjunction with preliminary site plans for the development of an eight (8) unit complex along Orchard Place. This report has been prepared to meet the requirements of the City of Fort Collins Storm Drainage Design Criteria and Construction Standards as they apply to this project. PRELIMINARY DRAINAGE AND EROSION CONTROL REPORT FOR ORCHARD PLACE EIGHT-PLEX For Lew, Ltd. P.O. Box 271035 Fort Collins, Colorado 80527 June, 1993 Prepared by FOUNDATION ENGINEERING CONSULTING ENGINEERS, LTD. 100 East Third Street Loveland, Colorado 80537