The URL can be used to link to this page

Home My WebLink AboutLANDINGS OFFICE PARK P.U.D. - FINAL - 10-95A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTLandings Office Park P.U.D. May 22, 1995 Final Drainage Report Page 8 APPENDIX PAGE HistoricDrainage.......................................................................... 1 - 4 Developed Drainage................................................................... 5 - 17 Developed Detention.................................................................. 18- 30 Design of Inlets, Sewers and Culverts ....................................... 31- 40 Off -site Swale Design.................................................................. 41- 45 Erosion Control Calculations....................................................... 46- 53 Heart Special Improvement District Final Drainage Report.......... 54- 58 ShopKo P.U.D. Letter Addenum................................................... 59- 62 Final Drainage Report for High Pointe P.U.D ............................... 63- 65 Landings Office Park P.U.D. Final Drainage Report REFERENCES May 22, 1995 Page 7 1. Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. 2. Final Drainage Report for Heart Special Improvement District, Engineering Professionals, Inc., December, 1984, Revised: January, 1985. 3. Shor)Ko P.U.D. Addendum to the Final Drainage Report, TST, Inc., August 10, 1993. 4. Final Drainage Report for High Pointe P.U.D., Parsons & Associates, Revised August 22, 1989. 5. Drainage Criteria Maunal, Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. Landings Office Park P.U.D. May 22, 1995 Final Drainage Report Page 6 V. CONCLUSIONS Compliance with Standards All drainage analyses have been performed according to the City of Fort Collins Storm Drainage Design Criteria Manual (SDDCM) and the Urban Drainage and Flood Control District's Drainage Criteria Manual. A variance is requested for the required 0.87 cfs/acre maximum release rate as stated in the "Final Drainage Report for Heart Special Improvement District". This is requested due to the inability to detain all developed runoff from the site due to topography. Summary of Drainage Concept Measures have been taken to ensure adequate drainage facilities have been provided with attention given to water quality and, public health and safety of persons using the Landings Office Park facilities. The hydraulic and hydrologic analyses conducted for this study have been performed in a manner consistent with standard practice and principles of civil engineering. All known available information has been referenced where applicable to this study. Impacts to the Larimer County #2 Canal in relation to existing conditions shall be improved upon development of the site. Developed release rates are lower than historic at all discharge locations. Landings Office Park P.U.D. May 22, 1995 Final Drainage Report Page 5 ISpecific Details, con't Boardwalk. From the inlet stormwater will be conveyed through an existing 15 inch RCP which daylights onto a vacant City of Fort Collins S.I.D. property at the southeast corner of the intersection. Stormwater will be conveyed from the pipe outlet to the Larimer #2 Canal via an open grass -lined swale. This channel will require a 10' drainage easement through the City of Fort Collins S.I.D. property. The size of the orifice controlling the release from Pond D1 has arbitrarily been set at 3-inch diameter which allows for a minimum release rate at a minimum practical diameter to minimize clogging. Runoff from Basin D6 will be undetained and will collect at the existing 4' curb inlet located at the northwest corner of Landings and Boardwalk. From the inlet stormwater will be routed through the same conveyance elements as the release from Pond D1 to the Larimer #2 Canal. We attempted to direct this water to Pond D1 through the existing 4' curb inlet but due to the anticipated 100-year water surface elevation of 5042.38 in the pond, and the fact that the pond and street would then be hydraulically connected, water from the pond would back up into Landings Drive due to the existing flowline elevation of 5041.82 at the inlet. Detention Pond D4, located in the northeast corner of the site, will detain developed runoff from Basin D4 and will have a maximum release rate of 0.289 cfs through a 3" diameter control orifice. This parking lot detention pond will discharge into the flowline of Landings Drive, combine with flow from Basin D2 and continue north down Landings to an existing curb inlet and eventually into the Larimer County Canal #2. IV. EROSION CONTROL Temporary sediment control will be provided at the inlet end of both the detention pond outlets. Permanent vegetative erosion control will be used in conjunction with landscaping in areas surrounding the building and parking areas and, in the parking islands. The proposed grassed detention facility and off -site swale shall be covered with topsoil and revegetated with grass according to criteria given in Section 704.2(7). Permanent Type L riprap will be provided at the outlet of the existing 15" RCP on the city's S.I.D. property and grouted riprap at the end of the proposed off -site swale. Permanent riprap will be placed at the outlets of all storm sewers. Landings Office Park P.U.D. May 22, 1995 Final Drainage Report Page 4 Specific Details, con't The release rate specified by the Heart Special Improvement District report is not the only criteria to be met in discharging stormwater from the site, there are two additional requirements. First, the release rate from Basins' D2 (undetained) and D4 (detained) combined should not exceed 2.75 cfs at an existing inlet located approximately 170 feet north of the site in the west flowline of Landings Drive. Shear Engineering calculated this (historic) flow as part of the Jetty P.U.D. in 1986. The same site was developed as High Pointe P.U.D. in 1989 (See excerpts from High Pointe Drainage Report in Appendix). The developed 100-year flow from these basins (D2 and D4) at Design Point D10 is 3.1 cfs which exceeds 2.75 cfs but is not excessive and is anticipated to have minimal impact on street and inlet capacities. It is not possible to capture any additional runoff from these basins, in addition, a transverse inlet is proposed across the drive entrance off of Landings Drive to intercept any last runoff prior to leaving the site. , Secondly, the release rate from Basin D3 must not exceed 2.76 cfs at an existing 15' curb inlet located at the northeast comer of JFK Parkway and Boardwalk Drive. The inlet was installed as part of the ShopKo P.U.D. (JFK Parkway Improvements) and designed by TST, Inc, Consulting Engineers in 1993 (See letter dated August 10, 1993 in Appendix). Runoff entering the inlet is conveyed to the East Detention Pond of ShopKo. The developed 100-year flow calculated at Design Point D3 from the Landings site is 2.3 cfs and therefore is below the anticipated flow calculated by TST. The Landings site is divided into three release points discharging stormwater into three separate directions all of which are conveyed to the Larimer County #2 Canal. As previously mentioned, runoff from Basin D3 will be conveyed to the ShopKo P.U.D. due to the presence of an existing curb inlet. Runoff from Basins' D2 and D4 is conveyed north down Landings Drive to an existing curb inlet and then through Pond 'A' of High Pointe P.U.D. to the Larimer #2 Canal. Runoff from Basins' D1, D5, D7,D8 and D9 will be routed to the proposed Detention Pond D1 located in the southeast corner of the site. The pond will release into an existing 4' curb inlet 6 located at the northwest corner of Landings and Landings Office Park P.U.D. May 22, 1995 Final Drainage Report Page 3 I ' III. DEVELOPED DRAINAGE con't Hydrologic Criteria The Rational Method was used to estimate peak stormwater runoff from the proposed development site. An initial 2-year design storm and major 100-year design storm was used to evaluate the proposed drainage system. The culvert under the Boardwalk drive entrance has been sized for the 10-year storm. Rainfall intensity data for the Rational Method was taken from Figure 3-1 of SDDCM. Hydraulic Criteria The City of Fort Collins Storm Drainage Design Criteria has been used for all hydraulic calculations. General Drainage Concept The majority of on -site developed stormwater runoff will be conveyed through the Landings Office Park site by overland flow, vertical curb and gutter, sidewalk chases and a drainage culvert to two (2) proposed detention facilities located in the northeast and southeast corners of the site. From the detention facilities, stormwater will be conveyed to the Larimer County #2 Canal via either off -site swale or curb and gutter. Specific Details According to the Heart Special Improvement District Drainage Report, a total of 98 acres above the Larimer Canal drains to the irrigation/stormwater ditch. The staff at the City of Fort Collins Stormwater Utility Department recommended the canal convey a total discharge of 240 cfs, 155 cfs of irrigation flow and 85 cfs of stormwater flow. The 0.87 cfs/acre maximum release rate was calculated using these factors (85 cfs/ 98acres). The Landings site is part of the 98 acres tributary to the Larimer Canal and therefore would require detention of stormwater to the required rates. Due to the topography of the site, it will not be feasible to route runoff from the entire site and adjacent streets to detention facilities to be released at the allowable rate of 0.87 cfs/acre. II� ' Landings Office Park P.U.D. May 22, 1995 Final Drainage Report Page 2 II. HISTORIC DRAINAGE. con't Historic Drainage Patterns A ridge traversing east -west divides the site, with the majority of stormwater runoff flowing to the south-southeast to Boardwalk Drive. The historic drainage pattern of the site is from, north to south-southeast and, south to northeast (as predicated by the ridge) by overland flow at slopes ranging from 3.2% to 4.9%. There is no off -site runoff entering the site due to the ridge and street boundaries. ' There is an existing 4' Type R Curb Inlet located at the northwest corner of Boardwalk and Landings Drives. A 15" diameter pipe extends from the inlet, southeast under Boardwalk and daylights into a vacant lot east of the U.S. Post Office. A 15' Type R Curb Inlet is located at the northeast corner of JFK Parkway and Boardwalk. Stormwater flows from this inlet west, under JFK Parkway to another 15' Curb Inlet and continues north to the East Detention Pond of ShopKo P.U.D.. There are no existing drainage structures or irrigation laterals on the site. Ill. DEVELOPED DRAINAGE Developed Conditions The proposed development of the site includes 8 commercial buildings with a central parking area and includes all utilities. Three (3) drive entrances will serve the site off of JFK Parkway, Boardwalk Drive and Landings Drive. Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual.(SDDCM) and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been used for this Preliminary Drainage Study. The "Final Drainage Report for Heart Special Improvement District" by Engineering Professionals, Inc. has also been referenced. I Final Drainage Report for Landings Office Park P.U.D. I. GENERAL LOCATION SITE DESCRIPTION General Location This report summarizes the results of a storm drainage investigation for the proposed Landings Office Park P.U.D. site. The project is located in the NW Quarter of Section 36, Township 7 North, Range 69 West of the 6th Principal Meridian in Fort Collins, Colorado. The project is bounded by Horsetooth Road to the north, Boardwalk Drive on the south, Landings Drive on the east, and JFK Parkway to the west: (See Vicinity Map). Site Description The 3.19 acre site is located in southeast Fort Collins, is currently residential and vegetated with native grasses and weeds. The surrounding land use patterns are residential (The Landings P.U.D. and High Point P.U.D.) to the east, commercial to the south (U.S. Post Office) and west (ShopKo P.U.D.) and currently undeveloped land to I the north. The site is in the vicinity of the Larimer County Canal No.2 to the north, south and east. II. HISTORIC DRAINAGE Major Basin Description The project is located in the McClellands/Mail Creek Drainage Basin. The Iproposed site drains to the Larimer County Canal No. 2 according to the "Final Drainage Report for Heart Special Improvement District', dated December, 1984, revised January, 1985 by Engineering Professionals, Inc.. The report gives a maximum allowable release rate for the site of 0.87 cfs/acre. PROJECT SITE -moft mud s ua• u.wma a � M ti �M• At x• : s i . ° . � aYnmr 3 S 111 m ,mgs m. d Li -n C Mai «rn nrn noFY LAKE Tj H ,■ I W.W.T�} �• l NORTHERN ENGINEERING SERVICES " 1 k. MumWW" BOAR7D/WAII.}H�riCOIO[RRCIAL m MOM mm Ri ML R coum CO,iL,D° ma 11�/11�11 1 DlL'lr Northern Engineering Services, Inc. . May 22, 1995 City of Fort Collins Stormwater Utility 235 Mathews Fort Collins, Colorado 80522 RE: Landings Office Park P.U.D. Fort Collins, Colorado Project Number: 9516.00 Dear Staff: Northern Engineering is pleased to submit this Final Drainage Report for the Landings Office Park P.U.D. for your review. We have addressed the comments contained on the Project Comment Sheet dated April 17, 1995. This report was prepared in compliance with technical criteria set forth in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual. If you should have any questions or comments as you review this revised report, please feel free to contact me at your convenience. Sincerely, NORTHERN ENGII Mary B. Wohnrade, ES, INC. 420 S. Howes, Suite 202 • Fort Collins, Colorado 80521 • (970) 221-4158 • Fax (970) 221-4159 Final Drainage Report for Landings Office Park P.U.D. City of Fort Collins, Colorado May 22, 1995 Prepared For: Lagunitas Company Prepared By: Northern Engineering Services, Inc. 420 South Howes, Suite 202 Fort Collins, Colorado 80521 (970)221-4158 Fax (970)221-4159 Project Number: 9516.00