The URL can be used to link to this page

Home My WebLink AboutRIGDEN FARM, 15TH FILING - PDP - 11-09 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTCONCLUSION Compliance with Standards The proposed drainage system Rigden Farms Tract A was designed to meet the City of Fort Collins Storm Drainage Design Criteria and Construction Standards. The site does not include any F.E.M.A. mapped floodplains. The existing Flood Insurance Rate Map (F.I.R.M) is not presented in Appendix A as the new map has not been released by F.E.M.A. and shows no portion of the site to be in a flood hazard area. Therefore, no map revisions are required as part of this development. Drainage Concept The drainage system for Rigden Farms Tract A was designed to allow storm water to be safely conveyed through and away from the site without negatively impacting downstream or upstream properties (regionally) beyond that imposed by the historic condition. The drainage concepts proposed for this site are in accordance with those presented in previous reports. Sediment and Erosion Control Concept The construction BMP's proposed for this site follow the requirements of the City of Fort Collins. Attention to proper installation and maintenance are essential for the sediment and erosion control practices to function properly. In Page 5 Water Quality and Detention Water Quality is being provided by the existing Water Quality Pond #2 as provided for in the Master Report. Runoff from the proposed site will be detained by the existing Fossil Creek Reservoir as directed by the Master Report. Storm Sewer and Culverts As the lots are developed the storm sewer piping should generally be designed to accommodate the 100-year storm event. In all cases, pipe velocities at the outlet should be kept below 12 fps to minimize the need for energy dissipation or reinforcement at bends. Pipe velocities greater than 3 fps during a 2-year event are desirable to keep the pipe free of debris. To determine required pipe sizes, pipe networks should be modeled using StormCAD a Haestad Methods product. There is one culvert proposed for the site. ENVIRONMENTAL PROTECTION CRITERIA General There are no wetland areas on the site nor are there any threatened or endangered species. Sedimentation and Erosion Control Measures _ During construction, silt fence, inlet/outlet protection and vehicle tracking pads will be utilized to prevent sediment entering the storm sewer system or sediment leaving the site. The lots will be seeded to prevent soil erosion. Temporary sediment basins will be utilized to offer initial water quality. Calculations for the temporary sediment basins can be found in Appendix C. As the lots are developed any and all open space areas will be landscaped. The erosion control plan is part of the Final Construction Plans. All erosion and sediment control methods shall be maintained and repaired by the owner during construction and shall be inspected after each heavy precipitation event. ® Page 4 Hydraulic Criteria The following criteria were utilized in determining allowable street flow. Initial Storm Local Street- No curb overtopping and flow may spread to crown of street. Major Storm (100-yr) Local Street — Buildings shall not be inundated at the ground line unless flood proofed. The depth"of;water over the crown shall not exceed 6-inches. Street capacities were determineduusing STANDARDS Table 4-1 for Initial Storm -- Street Runoff Encroachment and STANDARDS Table 4-2 for Major Storm — Street Runoff Encroachment. r' -..ES..... •._ DRAINAGE FACILITY DIGNN' General Concept All runoff from the site will be conveyed to either the existing inlet at the northeast corner of the property or the drainage swale along the southern property boundary. Runoff is directed to Water Qualify Pond` #2' The 'drainage 'patterns outlined in'the ` Rigden `Farm, Filing One, Drainage Report" October 1999 prepared by JR Engineering are maintained. Rational calculations are included in Appendix 8. Specific Details The proposed development has been divided into 'two major basins: Basin A and Basin B, representing lots 1-3. A drainage map, presenting the drainage basin delineations as well as existing and proposed drainage facilities, can be found in the back of this report. The following text generally, describes basin conveyance to design points. Hydrologic calculations for each sub -basin are presented in the rational method SF-3 forms in Appendix B of this report. Basin A, 1.72 acres, is located along the west and south portion of the site and is comprised of a potential bank, drive aisles, parking lot, and landscape areas. Basin flow is directed to the existing drainage swale that runs the length of the southern boundary. As the lots are developed the intent is to direct runoff to the swale, Design Point 1, by curb cuts and/or with a storm sewer ;y pipe system. rr Basin B, 1.58 acres, is located along the north and east portion of the site and is comprised of two drive aisles with the remainder of the lots to be over -lot graded and seeded with native grasses. The basin flow is to be directed to the existing inlets located at the northeast corner of the property. As the lots are developed the intent is to direct runoff to the existing inlet, Design Point 2. Flows from the existing inlet and the existing drainage swale are then routed to the existing r, Water Quality Pond #2. The runoff is then directed from the water quality pond to the Foothills Regional Channel to the Fossil Creek Reservoir ditch to finally outfall to the Fossil Creek Reservoir. r: r Page 3 r. In order to maintain the overall drainage patterns from the Master Report, Tract A was divided into two basins. The northerly half of the basin, Basin B, will drain to the existing inlets at the northeasterly corner of the property. The Basin A will drain to the existing drainage swale along the southern property boundary. The basins were sized anticipating final build -out in which the flows entering the swale or the inlets would be less than or equal to the 2-yr and 100-yr flows as given in the Master Report. An interim phase has also been included in the Appendix. It is anticipated that phase 1 could be a drive through bank on Lot 1. The interim calculations show a typical layout for a commercial bank with the remaining two lots being .overlot graded with the driveways installed. This condition gives the interim flows for both basins. Note that Basin A is calculated to be at full build -out in both conditions. DRAINAGE DESIGN CRITERIA Hydrology Criteria City of Fort Collins Storm Drainage Design Criteria and Construction Standards (STANDARDS). The following criteria were utilized in developing the proposed drainage system. • The proposed drainage system is designed to match, as best as possible, the historic drainage patterns occurring at the site. • The proposed drainage system attempts to limit the diversion of storm runoff from one basin to another (basin transfer). !■ • Runoff generated from drainage sub -basins is conveyed either directly or via storm sewer systems or channels to outfall locations into a regional water quality pond then to the regional detention pond. Design Rainfall: City of Fort Collins rainfall data is used to determine peak runoff values. The 2-year and 100-year frequency storms are used as the initial and major design storms respectively. Runoff Calculation: Peak storm runoff is determined using the rational formula, Q = CIA: Q = storm runoff in CFS; C = runoff coefficient based on surface impermeability; I = rainfall intensity in inches per hour; and A = drainage basin area in acres. City of Fort Collins runoff coefficients for composite analysis (Table 3-3) are used to develop basin runoff coefficients. The runoff coefficients are weighted for each applicable sub -basin to more accurately reflect the runoff characteristics of the site. Time of Concentration is determined using STANDARDS in Sections 3.1.7. Rainfall intensities are determined using STANDARDS Point Rainfall data and Intensity - Duration curves. The recurrence intervals used for this study were based on a commercial land use. The minor drainage system is designed for a 2-year recurrence interval and the major drainage system is designed for a 100-year recurrence interval. 14 Page 2 GENERAL LOCATION AND DESCRIPTION This report presents the Rigden Farms Tract A preliminary drainage study. The design and analysis of this site has been performed in accordance with the City of Fort Collins Storm Drainage Design Criteria and Construction Standards. Drawings, tables, and design calculations are included in the appendix of this report. Site Location The site is Tract A, Rigden Farms Filing Number One, located in Northwest Quarter of Section 29, Township 7 North, Range 68 West of the 6`h Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. More specifically it is located south of Custer Drive; west of Timberline Road and east of Illinois Drive. Adjacent developments include a commercial shoppingcenter to the north, a day care facility to the east, a church to the south and a residential subdivision to the west. Site Description The site is approximately 2.69 acres in size. The topography for the site generally slopes southeasterly at slopes ranging from 0.5% to 2.0%. The soils within the site are Nunn clay loam and fall into Hydrologic soils group Type C. The vegetation is native grasses and weeds. Proposed Project Description The project consists of three lots. The intention at this point is to prepare the property for three potential tenants/buyers. Water and sanitary sewer will be installed and stubbed for each lot. The main driveways will be constructed with this initial phase. Each lot as it is leased/purchased will be required to present to the City of Fort Collins. This will include the development process, individual utility, drainage, erosion control reports and plans as well as construction documents. DRAINAGE BASINS AND SUB -BASINS Major Basin Description The site is located within the limits of the "Rigden Farm, Filing One Drainage Report" (Master), October 1999 prepared by JR Engineering, shown as Basins 108a, 108e and 108b1. Drainage patterns for the site established in the Master report are maintained. The site is divided into two major basins, which drain to the existing Water Quality Pond #2. Flows from this pond are routed to the Foothills Regional Channel then to the Fossil Creek Reservoir Channel and outfalling to the Fossil Creek Reservoir. The site is assumed to be located outside the 100-yr floodplain. The Flood Insurance Rate Map Community -Panel Number 08069C1000 F, unknown date, for Larimer County, Colorado is no longer available. The map has been revised but has yet to be released by FEMA. A copy of the Fort Collins' Floodplain Map is shown in Appendix A. Site Sub -Basin Description Offsite flows to the site from the west will be routed through proposed storm sewer system for Lot 1 to outfall to the existing drainage swale on the south side of the site. Since the off -site area is insignificant the area has been included within the Basin A calculations. Page 1 r `4 Index of Figures "n All figures are presented in the appendices Appendix A Vicinity Map City of Fort Collins Floodplain Map Soils Map City of Fort Collins Rainfall Intensity -Duration -Frequency Table (Rational Method) Appendix B Weighted C Coefficient ` Standard SF-2 Form (Time of Concentration Calculations) Standard SF-3 Form (Rational Method Calculations) Appendix C -i A portion of the Drainage Map•and Drainage Summary Table from "Rigden Farms Filing One F Drainage Plan" prepared by JR Engineering, Inc. ® Page 11 TABLE OF CONTENTS GENERAL LOCATION AND DESCRIPTION a� Site Location...........................................................................................................................1 SiteDescription.......................................................................................................................1 ProposedProject Description..................................................................................................1 DRAINAGE BASINS AND SUB -BASINS ............. ...........:...... ...................1 MajorBasin Description.................................................................................:........................1 SiteSub -Basin Description.....................................................................................................1 DRAINAGE DESIGN CRITERIA................................................................ 2 HydrologyCriteria...................................................................................................................2 - Hydraulic Criteria............................:.......................................................................................3 .Wi DRAINAGE FACILITY DESIGN................................................................. 3 GeneralConcept.....................................................................................................................3 SpecificDetails.......................................................................................................................3 WaterQuality and Detention...................................................................................................4 StormSewer and Culverts....................................................................................................:.4 ENVIRONMENTAL PROTECTION CRITERIA..........................................4 General............................................................................................................:......................4 Sedimentation and Erosion Control Measures........................................................................4 CONCLUSION........................................................................................... 5 Compliancewith Standards....................................................................................................5 DrainageConcept...................................................................................................................5 Sediment and Erosion Control Concept..................................................................................5 REFERENCES........................................................................................... 6 Page I 777774 F ,tz.......y1x'f jyv7 WSY'$s$�iYfl ENGINEER'S STATEMENT This report for the final design of Rigden Farms Tract A was prepared by me or under my direct supervision in accordance with the provisions of the City of Fort Collin's Storm Drainage Design Criteria and Construction Standards. I understand that the City of Fort Collins and its designated town authority do not and will not assume liability for drainage facilities designed by others. Daniel J. Madruga P.E. # 36834 State of Colorado Date January 30, 2009 Prepared for: Armstrong Development Properties, Inc. 999 Eighteenth Street, Ste. 2700 Denver, CO 80202 Phone: 303.352.4600 Prepared by: CLC Associates, Inc. 8480 E. Orchard Road, Ste. 2000 Greenwood Village, CO 80111 Phone: 303.770.5600 CLC Job No. 09-0010 FA2009\09-0010 Rigden Farms Tract X3.0 Design Development\i - Reports\Drainage\09-0010 Prelim Drainage Report.doc CLC ASSOCIATES c PRELIMINARY DRAINAGE STUDY FOR RIGDEN FARMS TRACT A CITY OF FORT COLLINS, COLORADO