The URL can be used to link to this page

Home My WebLink AboutINTERSTATE LAND - ODP - 49-02A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTTlktf� ;-ULA oo�vtz lo" T-tAq- MA m 6 coUee.- A&V I 1 1 1200 600 0 1200 2400 SCALE: 1" = 1200' VICINITY MAP INTERSTATE LAND JOB NO. 39177.20 B-07-03 FIGURE 1 J•R ENGINEERING A"I"m� rawa asap Fal ftped Fla4 sk W-Fce cft co eon am-�-eeae��c ero-�aE:esea�w�ia�r�room� APPENDIX A FIGURES 6. REFERENCES "Storm Drainage Design Criteria and Construction Standards (SDDCCS)", Revised January 1997, City of Fort Collins. ' "Technical Documentation for the Hydrologic Modeling of the Boxelder Creek/Cooper Slough Basin, Volume 1, Hydrologic Evaluation for Existing Drainage Facilities, ' Technical Appendix A, B", January 25, 2002, Anderson Consulting Engineers, Inc. ' "Technical Documentation for the Half -Foot Floodway Hydraulic Analysis of the Boxelder/Cooper Slough Basin", Revised March 17, 2003, Anderson Consulting ' Engineers, Inc. Urban Drainage and Flood Control District, "Urban Storm Drainage Criteria Manual", Volumes 1-3, Revised June 2001. I ' 8 i 4. EROSION CONTROL ' Erosion control will be provided as required by the City of Fort Collins. Erosion control ' measures will include the use of inlet filters, silt fences, straw bale barriers, sediment traps and gravel construction entrances. Final design of the erosion control measures will be included with Final Development Plans for the site. 5. CONCLUSION This report complies with the City of Fort Collins "Storm Drainage Design Criteria and Construction Standards" and the Urban Drainage and Flood Control District's "Urban Storm Drainage Criteria Manual". Storm runoff.will be conveyed to historical drainage paths through a system of curb & gutters, cross -pans, sidewalk chases, inlets & storm I! drain pipe lines and detention ponds that will reduce the runoff discharge to historical 10 and 100-year discharge rates and provide water quality facilities, effectively controlling runoff from the site and avoiding significant adverse impacts to downstream properties due to the development of this site. ill quality features included in its design and this pond will discharge east into Boxelder Creek in the southern end of the site. The Historic Basin H2 is subdivided into Sub -basins B 1 and BOS. Sub -basin BOS is that potion of the Historic Basin H2 that will continue to naturally runoff into Cooper Slough. The 100-year historic discharge from Historic Basin H2 (21.7 cfs) will be reduced by the amount Sub -basin BOS contributes (9.1 cfs) and the remainder (12.6 cfs) will be the discharge for Detention Pond 6. All runoff from Sub -basin B1 will be collected and discharged into Detention Pond 6. Detention Pond 6 will have water quality features included in its design and this pond will discharge southwest into the Cooper Slough approximately in the middle of the site. The Historic Basin H3 is the developed Sub -basin C1. The 100-year historic discharge from Historic Basin H3 (26.4 cfs) will be the discharge for Detention Pond 7. All runoff from Sub -basin Cl will be collected and discharged into Detention Pond 7. Detention Pond 7 will have water quality features included in its design and this pond will discharge southeast into Boxelder Creek in the southern end of the site. Portions of the proposed development are within the City and/or FEMA regulated floodplains. An access street is proposed to cross the Boxelder Creek floodplain from the existing I-25 Frontage Road to the proposed developed portion of the site. It is expected that the crossing of the floodplain will be accomplished with a proposed earthen embankment and bridge designed to pass the City's future condition flow rate of 4180cfs. Areas proposed for development within the floodplain located adjacent to and upstream of the proposed access street will be elevated above the floodplain by filling prior to development in accordance with the applicable City and FEMA regulations. The floodplain area located east of the Frontage Road will be filled in accordance with applicable regulations. Development of land within the floodplain caused by the backup of storm water at Prospect Road should either be delayed until adequate storm water conveyances under Prospect Road are constructed for Boxelder Creek and Cooper Slough or be done in a manner that minimizes negative impacts to the floodplain. The proposed development areas located within the backwater floodplain are expected to require fill in addition to the conveyance improvements to eliminate the floodplain from these areas. 2 iI ' directly into existing natural drainage ways will have water quality features included in their design. As mentioned previously, there is an historic separation of storm runoff that discharge into the Cooper Slough versus the Boxelder Creek. This historic separation will be _ maintained as closely as possible. The site has been divided into three primary basins (Basins A, B and C) along the lines of the previously mentioned three Historic Basins. Basin A will discharge east into Boxelder Creek per Historic Basin H1. Basin B will discharge west into Cooper Slough per Historic Basin H2. Basin C will discharge west into Boxelder Creek per Historic Basin H3. 3.2 Specific Details The Interstate Land development contains approximately 111 developed acres divided between the three primary basins A, B and C for Rational Method runoff analysis. Sub - basins Al, A2, A3, A4 and A5 will discharge east into Boxelder Creek via Detention Ponds 1 through 5. Sub -basin B1 will discharge west into Cooper Slough via Detention Pond 6. Sub -basin C1 will discharge west into Boxelder Creek via Detention Pond 7. The Historic Basin HI is subdivided into Sub -basins Al through A5 and AOS. Sub -basin AOS is that portion of the Historic Basin Hl that will continue to naturally runoff into Boxelder Creek (see Overall Drainage Plan in Appendix). The 100-year historic discharge rate from Historic Basin Hl (80.1 cfs) will be reduced by the amount Sub -basin AOS contributes (16.3 cfs) and the remainder (63.8 cfs) divided between Detention Ponds 1 1 through 5. Sub -basin Al runoff will be collected and discharged into Detention Pond 1. Detention Pond 1 will discharge east into Detention Pond 2 without any water quality enhancement. ' Sub -basin A2 runoff will be collected and discharged into Detention Pond 2. Runoff from Sub -basin A3 will be collected and discharged into Detention Pond 3. Detention Ponds 2 and 3 will have water quality features included in their design and the discharge tfrom these two ponds will be combined just prior to discharging east into Boxelder Creek in approximately the middle of the site. Runoff from Sub -basin A4 will be collected and discharged into Detention Pond 4. Detention Pond 4 will discharge east into Detention Pond 5 without any water quality enhancement. Runoff from Sub -basin A5 will be tcollected and discharged into Detention Pond 5. Detention Pond 5 will have water 1 5 I The existing Boxelder Creek and Cooper Slough conveyance structures under Prospect Road are inadequate to convey the existing condition runoff produced by larger ' infrequent storms. Thus, in large runoff events, runoff conveyed to Prospect Road by the Cooper Slough and Boxelder Creek, as well as runoff from the site, backs up behind and overtops Prospect Road. According to the ACE Report, this overtopping diverts a significant portion of the flow in Boxelder Creek from the creek and toward the Cache la Poudre River floodplain located downstream of Prospect Road. tBoth City of Fort Collins and FEMA regulated floodplains have been mapped on the Interstate Land site. These floodplains are associated with the Cooper Slough, Boxelder Creek and the backwater condition described above at Prospect Road. The City regulated I floodplain is based on a larger flow rate than the FEMA floodplain and thus is more restrictive. A floodway associated with Boxelder Creek has been defined by Anderson Consulting Engineers for the City. The adoption of this floodway is currently under consideration by the City. The boundaries of the proposed City Floodway and the City 100 year Floodplain are shown on the Overall Drainage Plan Exhibit contained in the appendix of this report. 3. PROPOSED DRAINAGE PLAN ' 3.1 General Concept The ACE report recommends that the site discharge the 2-year historic discharge for the 100-year developed condition. Due to the hydrograph timing, it appears from the hydrological output data contained in the ACE report that undetained discharge from the ' Interstate Land site does not have a significant impact on the peak flow in Boxelder Creek. The City has expressed concerns about stability issues within Boxelder Creek should developed flows be discharged undetained into the creek. The City has indicated that providing on -site detention of developed condition runoff from the site with peak 10 and 100-year release rates not to exceed the existing historical rates for those events ' would be an acceptable method to address this concern. Therefore, on -site runoff produced by the developed portions of the proposed Interstate Land development will be ' routed to one of seven proposed detention ponds via curb & gutters, cross -pans, sidewalk chases, inlets and storm drain pipe lines. These detention ponds will be designed to discharge the 10 and 100-year developed flows at or below the predeveloped condition (historical) peak rates for the respective storms. All the detention ponds discharging 1 4 Creek/Cooper Slough Basin, Volume 1, Hydrologic Evaluation for Existing Drainage Facilities, Technical Appendix A, B", by Anderson Consulting Engineers, Inc. (ACE), January 25, 2002 was consulted during preparation of this report. This report incorporates the revised 3.67" rainfall amount for the 100-year, 2-hour storm in the SWMM and HEC models for the drainage basin while revising the 100-year floodplain boundary for Boxelder Creek and Cooper Slough. 1.4 Purpose and Scope of Report This report defines the proposed overall drainage plan for the Overall Development of the Interstate Land site and includes consideration of all on -site and tributary off -site runoff. Included in this drainage report are preliminary design requirements for major detention facilities. The final design of all drainage structures, including any temporary detention and water quality facilities, required for this development will be completed with final project development plans. 1.5 Design Criteria This report and associated calculations were prepared to meet requirements established in the City of Fort Collins "Storm Drainage Design Criteria and Construction Standards" (SDDCCS), revised January 1997. Where applicable, the criteria established in the "Urban Storm Drainage Criteria Manual" (UDFCD), revised June 2001, developed by the Denver Regional Council of Governments, was also used. 2. HISTORIC DRAINAGE & FLOODING Generally, the Interstate Land site drains in a southerly direction. Slopes are generally less than 1.0% but greater than 0.5% across the site. Storm runoff is intercepted primarily by Boxelder Creek, however there are those areas where storm runoff is intercepted by ' the Cooper Slough. Runoff from the western side of the site, Historic basin H2, flows southwest into the Cooper Slough (see Figure 2 in the Appendix). Runoff from the majority of the larger section, Historic Basin HI, flows southeast into Boxelder Creek. ' The remainder of the runoff from Historic Basin H1 flows to a low point on the north side of Prospect Road where the runoff is then directed east to Boxelder Creek via a roadside ' ditch. Runoff from the primary proposed commercial site (southeast of the Frontage Road), Historic Basin H3, flows to a low point on the north side of Prospect Road where the runoff is then directed west to Boxelder Creek via a roadside ditch. 1 3 1. INTRODUCTION • 1.1 Project Description The Interstate Land project site is a proposed multi -use development that consists of single family & multi -family residential, commercial & office space, and park & open space areas. The Interstate Land site is located at the northwest corner of the intersection of Prospect Road and Interstate 25 in the southeast corner of Section 16, Township 7 North, Range 68 West of the Sixth Principal Meridian in the City of Ft. Collins, Larimer County, Colorado. The site is bounded by the Lake Canal and Crossroads East Business . Center on the north, Sunrise Acres, Boxelder Family Estates and the Cooper Slough on the west, Prospect Road to the south and Interstate 25 to the east (see Figure 1 in the Appendix). 1.2 Existing Site Characteristics The Interstate Land project site includes approximately 179 acres of land. The majority of the site (area west of Boxelder Creek and south of the Cache La Poudre Ditch) is being cultivated and the remainder is covered with grasses. As previously mentioned, the Lake Canal crosses the site from west to east along the northern property line then turns south along the west side of Interstate 25 crossing Boxelder Creek then joining with the Cache La Poudre Ditch to pass east under Interstate 25. The Cache La Poudre Ditch crosses the site from west to east just south of the Lake Canal crossing Boxelder Creek and passing under Interstate 25 to continue easterly. Boxelder Creek meanders southwesterly through the site from the northeast comer to its crossing under Prospect Road just west of the Frontage Road. The Frontage Road bisects the southern boundary of the property and swings east until it adjoins the west side of Interstate 25 and continues north paralleling the interstate. The Cooper Slough crosses the site from north to south along the western property line (see the Overall Drainage Plan in the Appendix). The site lies within the Moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. ILI 1.3 Master Drainage Basin & Other Drainage Reports The Interstate Land site lies within the Boxelder Creek/Cooper Slough Drainage Basin. This drainage basin continues southward where it terminates at the Cache La Poudre River. The "Technical Documentation for the Hydraulic Modeling of the Boxelder 1 2 1J 1 1 11 [J I 1 TABLE OF CONTENTS PAGE TABLEOF CONTENTS............................................................. :................................................ 1 1. INTRODUCTION................................................................................................................. 2 1.1 Project Description..................................................................................................... 2 1.2 Existing Site Characteristics...................................................................................... 2 1.3 Master Drainage Basin & Other Drainage Reports .................................................... 2 1.4 Purpose and Scope of Report ..................................................................................... 3 1.5 Design Criteria........................................................................................................... 3 2. HISTORIC DRAINAGE & FLOODING.............................................................................. 3 3. PROPOSED DRAINAGE PLAN..............................................:........................................... 4 3.1 General Concept......................................................................................................... 4 3.2 Specific Details...........................................................:.............................................. 5 4. EROSION CONTROL.......................................................................................................... 7 5. CONCLUSION......................................................................................................................7 6. REFERENCES...................................................................................................................... 8 APPENDIX A - FIGURES APPENDIX B - HYDROLOGIC AND HYDRAULIC COMPUTATIONS APPENDIX C - TABLES AND FIGURES MAP POCKET - OVERALL DRAINAGE PLAN I 1 I 1 ' August 7, 2003 ' Mr. Glen Schlueter City of Fort Collins Stormwater Utility ' 700 Wood Street Fort Collins, CO 80521 ' RE: Drainage Plan for the Interstate Land O.D.P. Dear Glen, ' We are pleased to submit to you for your review and approval, this Overall Drainage Plan for the ' Interstate Land O.D.P. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. ' We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. ISincerely, JR ENGINEERING ' Prepared by, Frank Feero, E.I. Project Engineer I I [1 I Reviewed y, cha 1 rake, P.E., L.S. Director of Operations 1 I I I 1 1 I I I I I I I 1 OVERALL DRAINAGE PLAN FOR THE INTERSTATE LAND O.D.P. Prepared by JR ENGINEERING 2620 E. Prospect Rd., Suite 190 Fort Collins, Colorado 80525 (970) 491-9888 Preparedfor Western VII Investment, I -LC 11859 Pecos Street, Suite 300 Westminster, Colorado 80234 (303) 469-4200 August 7, 2003 Job Number 39177.20 X:\3910000.all\3917720\Word\Reports\ODP Drainage Report.Doc r OVERALL DRAINAGE PLAN FOR THE INTERSTATE LAND O.D.P. J-R ENGINEERING A Subsidiary of Westrien