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HomeMy WebLinkAboutCOURTYARD COMMONS - PDP - 38-98 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTVICINITY MAP 1 "= 2000' APPENDIX REFERENCES 1. Storm Drainage Design Criteria and Construction Standards. City of Fort Collins, Colorado, May, 1984. 2. Drainage Criteria Manual. Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. 3. Final Drainage and Erosion Control Study for JFK Parkway, by Parsons & Associates, dated May 19, 1992 4. Final Drainage and Erosion Control Study for Shopko. by TST 5. Final Drainage and Erosion Control Study for the Landings, by Northern Engineering Services I I 1 1 I 1 1 I L 1 .1 I 1 I Drainage Conceit The proposed drainage concepts presented in this study and shown on the grading and drainage plans adequately provide for the conveyance and detention of developed runoff from the proposed development. If groundwater is encountered during construction, and dewatering is used to install utilities, a State of Colorado Construction Dewatering Wastewater Discharge Permit will be required. Stormwater OualitX Because water quality is important to this developer, water quality mechanism will be incorporated into all aspects of final design of drainage systems. Erosion Control Concepts Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, at the time of Final Design, the erosion control performance standard will need to be calculated and appropriate measures taken to control rain and wind erosion from the site 1 I I constructed as a part of this project, to direct emergency spills to the Latimer No. 2. Since construction, the existing pond has been revegetated and will provide a significant water quality component to this project, as well as the other developed flows entering the pond. It is therefore our opinion, that this pond should not be disturbed for the addition of temp siltation pond. IV. EROSION CONTROL General Conceut Courtyard Commons lies within the Moderate Rainfall Erodibility Zone, and the Moderate Wind Erodibility Zone, per the City of Fort Collins zone maps. The desired effectiveness goal for this site was estimated to be approximately 85% The intent ofthe erosion control plan for the site include the following guidelines. As these measures can vary depending on the time of year construction activities take place, as well as the construction window involved, we would look to the contractor to work closely with the City to insure the intent of the plan is generally complied with. It is the intent of the owner to move quickly ahead with development once overlot grading `takes place. It is anticipated that overlot grading would start sometime around January, 1999, or sooner if possible. Therefore, once overlot grading and utilities have been completed, the owner would like to restabilize all disturbed areas, either with vegetative means, or by hard surfaces. In no cases shall restabilization occur more than 30 days after disturbance. In addition; silt fence will be provided around most of the exterior of the disturbed areas; gravel inlet filters will be installed at all curb inlets, curb openings, and pipe entrances. Straw bale check dams will be placed in all open channels, at a minimum of 250' intervals. Temporary vehicle wash pads will be located at the anticipated construction traffic entrances to the site. All construction activities must also comply with the State of Colorado permitting process for Stormwater Discharges associated with construction activities. A Colorado Department of Health NPDES discharge permit will be required before any construction grading can begin. V. CONCLUSIONS Compliance with Standards 11 All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. I Developed flows from subbasins .C-9 and 10 will be directed towards the south, and will be intercepted by area inlets, and directed to the existing detention pond, detained, and released into the Larimer No. 2 Subbasins C-11 and C-12 represent those area adjacent or including the detention pond. Developed flows from these subbasins will be directed via surface flows to the pond, where storage capacity has been verified, and ultimately in to Latimer No. 2. Subbasin LC-1 represents that portion of the site, which is adjacent to and includes the Larimer No. 2. This area will not be disturbed, and will be allowed to continue to sheet flow to the canal. Peak runoff was calculated to be approximately 4.3 cfs. These flows were subtracted from the allowable release rate for the site identified by the JFK Parkway drainage study by Parsons & Associates, approved by the City Subbasins D2 and D3 correspond to the subbasins identified in the Landings drainage study by Northern Engineering. Developed runoff from Subbasin D2 (Landings Drive), including portions of the Landings project, will be conveyed to the north via curb and gutter to an existing inlet located at the proposed driveway section for Courtyard Commons. This is currently a Type R inlet, which will be reconstructed as am area inlet, will still intercept these flows, convey them through the High Pointe detention facility, and ultimately to the Larimer No. 2. Developed flows from subbasin D3 (JFK Parkway) are conveyed to the south via curb and gutter to an existing 15' curb inlet located at the comer of JFK and Boardwalk. This project does not significantly increase the flows to this inlet. A subbasin has been identified on our plan as subbasin LD2, which represents that portion of Landings Drive, currently existing, which is not intercepted by the curb inlet, and which currently is conveyed to the north via curb and gutter. This project does not significantly affect the performance or nature of these flows. Subbasins JFK 19 2 and 3 represent basins associated with JFK Parkway and roughly approximate basins A, E, and F identified in the Parsons study for JFK Parkway. Detention for these basins is being provided in the existing detention pond. A new curb inlet (32.5' Type R) will be constructed at the northerly boundary of basin JFK1, and will intercept the majority of the flows from JFK1, as well as C-1,2,3. The remainder will continue north to an existing curb inlet located at the Latimer No. 2. All of the developed flows will be conveyed to the existing pond, and released into the Latimer No. 2. The existing pond, referred to in the Parsons study as pond B, has been certified as a part of the Shopko project, and volume has again been checked as a part of this study. The allowable release rate from the pond was identified to be 12.54 cfs. The Shopko project will be allowed to bypass approximately 5.02 cfs through the pond. Subbasin LC 1 is free releasing into the canal. This results in an allowable release from our site of 3.22 cfs, which was the basis of our volume verification. The 100 year WSEL was determined to be approximately 30.51. The pond would currently overflow at approximate elevation 30.85. Detention storage provided to elevation 30.51 was calculated to be approximately 1.192 acre feet. An emergency overflow weir will be M. DEVELOPED DRAINAGE Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual. and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District have been used for this,Drainage Study. Hydrologic Criteria The Rational Method was used to estimate peak stormwater runoff from the proposed site. The 10 year storm event and the 100 year storm event was used to evaluate the proposed drainage system. Rainfall intensity data for the Rational method was taken from the City of Fort Collins Stormwater Utility Intensity curves (Figure 3-1). Hydraulic Criteria City of Fort Collins Storm Drainage Criteria has been used for all hydraulic calculations. In addition, the detention volumes required for this development have been verified using the FAA method for detention ponds developed by the UDFCD was used. Drainage Concepts The site has been broken down into 12 smaller subbasins onsite, as well as 6 subbasins adjacent to the site. Subbasins C-1, 2, and 3 represent the majority of the office park portion of the project. Developed runoff from these basins will be directed towards the center of the parking area, and conveyed'via concrete pans, curb openings, and sidewalk culverts to JFK Parkway. At JFK, these flows will combine with the developed flows from JFK1, and be conveyed north to a proposed 32.5' type R curb inlet to be constructed at the northernmost limits of the new curb and gutter being installed with this project. Ultimately, detention is being provided in the existing pond, and the detained flows from these basins, as well as JFK 1, will be released into the Larimer No. 2. Developed flows from subbasins C-4 and 5 will be conveyed via curb and gutter towards the center of the site and will be intercepted by a proposed Type C area inlet. Flows from the area inlet will be piped to the existing detention pond, detained, and released into the Larimer No. 2. Developed flows from subbasins C-6, 7 and 8 will be conveyed towards the center of the site via curb and gutter, and intercepted in a proposed 15' Type R curb inlet. Along with the developed flows from C-4 and 5, these flows will be conveyed to the existing detention pond, detained, and released into the Larimer No. 2 Final Drainage Report for the Courtyard Commons PUD I. GENERAL. LOCATION AND SITE DESCRIPTION The Courtyard Commons PUD project is located North of the Landings project, North of Boardwalk Drive, East of JFK Parkway, and west of Landings Drive. The site is also bounded on the north by the Larimer Canal No. 2. The site can also be described as a portion of Section 36, Township 7 North, Range 69 West of the 6th PM, City of Fort Collins, Larimer County, Colorado. A vicinity map of the site is included in the appendix of this report. This site includes approximately 6.32 acres, including the adjacent roadways. The site is presently undeveloped, and consist mainly of native grasses. As mentioned above, the Landings Office Park is currently being constructed on the south side of this site. The site generally slopes from the south to the north at slopes less than 4%. There is also an existing detention pond located on the site which was constructed with the Shopko project. This pond is referred to in the Parsons study as Pond B. Plans for this site include multi -family residential buildings, with associated parking and garages, and 5 additional office buildings, similar to the product currently being constructed in the Landings. H. IUSTORIC DRAINAGE As mentioned above, the site is presently undeveloped, and consists mainly of native grasses and vegetation. JFK Parkway has been fully developed on the west side of the site, and will be widened with this project. Landings Drive has also been fully developed, and will remain essentially in tact as a result of this project. The Landings is currently being constructed on the south side of this project. Currently, runoff will be conveyed to the existing Larimer Canal No. 2, and to the existing pond constructed with Shopko. Runoff from Landings Drive, to the approximate new driveway to Courtyard Commons will be intercepted by an existing curb inlet, and routed through the High Pointe detention pond to Larimer Canal No. 2. The remainder of Landings Drive, approximated by LD2 continues to flow north across the Larimer No. 2 to the north. Flows from JFK Parkway flows to the north to an existing curb inlet at the Larimer No. 2, through the existing pond, and to the Larimer No. 2. August 7, 1998 Mr. Glen Schlueter City of Fort Collins Stormwater Utility I 700 Wood Street Fort Collins, Colorado 80522 RE: Courtyard Commons P.U.D. Fort Collins, Colorado ' Project Number: 9837.00 1 Dear Glen: Northern Engineering is absolutely ecstatic to submit this Final Drainage Report ' for the Courtyard Commons for your review. It represents a study of existing and proposed stormwater characteristics of the project site. 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 report, please feel free to contact me at your convenience. 1 Sincerely, NORTHERN ENGINEERING SERVICES, INC. Roger A. Curtiss, P.E. cc: Jon Prouty 420 SOUTH HOWES, SUITE 202, FORT (OLLINS, (OLORADO 80521, (970) 221-4158, FAX (970) 221-4159 Final Drainage Report for Courtyard Commons P.U.D. Fort Collins, Colorado August 5, 1998 Prepared For: Lagunitas Companies 3307 South College Ave Suite 200 Fort Collins, Colorado 80525 Prepared By: Northern Engineering Services, Inc. 420 South Howes, Suite 202 Fort Collins, Colorado 80521 (970)221-4158 Fax(970)221-4159 Project Number: 9837.00 1st Submittal Final Drainage Report for Courtyard Commons P.U.D. j Fort Collins, Colorado August 5, 1998 0 ENGINEERING