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HomeMy WebLinkAboutINTERSTATE LAND PUD, 1ST FILING (HARLEY DAVIDSON) - FINAL - 34-88C - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL REPORT FOR INTERSTATE LAND P.U.D. FIRST FILING FORT COLLINS, COLORADO FINAL DRAINAGE AND EROSION CONTROL REPORT FOR INTERSTATE LAND P.U.D. FIRST FILING FORT COLLINS, COLORADO October 16, 1995 Prepared for: R.C. Heath Construction Co. 145 Racquette Drive Fort Collins, Colorado 80524 Prepared by: RBD, Inc. Engineering Consultants 209 South Meldrum Fort Collins, Colorado 80521 (970) 482-5922 RBD Job No. 247-011 INC. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 3031482-5922 FAX: 303/482-6368 October 16, 1995 Mr. Glen Schlueter City of Fort Collins Utility Services Stormwater 235 Mathews Street Fort Collins, Colorado 80522 RE: Final Drainage and Erosion Control Report for the Interstate Land P.U.D. First Filing - Dear Mr. Schlueter: We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Report for the above referenced development. 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. Respectfully, RBD Inc. Engineering Consultants Prepared by: Ile" • 9 David K. Delaney, P.E:'``~~ Project Manager �,�1 RE ,I cc: File 28324 FSS��NAL i '' Reviewed by: Kevin W. Gingery, P.E. Water Resources Project Manager Denver 3031458-5526 DESCRIPTION I. GENERAL LOCATION AND DESCRIPTION PAGE 1 II. DRAINAGE BASINS I III. DRAINAGE DESIGN CRITERIA 2 IV. DRAINAGE FACILITY DESIGN 3 V. STORM WATER QUALITY 6 VI. EROSION CONTROL 7 VII. CONCLUSIONS 8 9 REFERENCES APPENDIXA A2 VICINITY MAP A3 HYDROLOGY A 13 DETENTION DESIGN OF INLETS, STORM DRAIN, AND SWALES A 17 A24 RIP -RAP DESIGN A30 EROSION CONTROL EXCERPTS FROM BOXELDER CREEK FLOOD STUDY EXISTING AND FUTURE CONDITIONS A39 CHARTS, TABLES, AND FIGURES A46 Total Appendix A pages 53 a a FINAL DRAINAGE STUDY FOR INTERSTATE LAND P.U.D., FIRST FILING ■ FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location The Interstate Land P.U.D., First Filing is bound by the I-25 Frontage Road on Poudre the east and south, Boxelder Creek on the west, and the Cache La Reservoir Inlet on the north. The site location can also be described as situated in the Southeast 1/4 of Section 16, Township 7 North, Range 68 West of the 6th P.M., City of Fort Collins, ■ L.arimer County, Colorado. The site location can be seen on page 2 of Appendix A. B. Description of Property The Interstate Land P.U.D., First Filing will contain approximately 4 acres of land Prospect Road. Presently, the property located at the northwest corner of I-25 and is undeveloped. A portion of the area was previously farmland and the remainder ■ in the floodplain of Boxelder Creek. The topography of the site generally slopes from the east to the west at approximately 2 percent. N II. DRAINAGE BASINS A. Major Basin Description The proposed development lies within the Boxelder Creek Basin. Natural drainageways run along the south and east boundaries of the development. Boxelder Creek roughly parallels the west boundary of the development. B. Sub -Basin Description The Interstate Land First Filing has been broken into 6 sub -basins. Sub -basins 1-3 will be developed with commercial buildings including the proposed John's Harley Davidson dealership. Sub -basin 4 contains the portion of the I-25 Frontage Road which fronts the site. Sub -basin 5 includes a small section of the Frontage Road and the proposed water quality capture pond for this development. Sub -basin 6 contains the portion of the site which includes Boxelder Creek and will have very little disturbance. These sub -basins are shown on the Drainage and Erosion Control Plan in the back of this report. 1 � I I M. DRAINAGE DESIGN CRITERIA A. Regulations ' The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. B. Development Criteria Reference and Constraints Runoff from the 10-year storm event is routed via curb flow, an area inlet and piping to the water quality capture pond located in the southwest corner of the development. The runoff from the 100-year storm is also routed to the water quality pond via parking lot and overland flow which then overflows to Boxelder Creek located to the west of the development. C. Hydrological Criteria The Rational Method was used to determine surface runoff for the project site. The 10-year and 100-year storm event criteria, obtained by the City of Fort Collins, were used in calculating runoff values. These calculations and criteria are included in the Appendix A of this report. D. Hydraulic Criteria All hydraulic calculations within this report have been prepared in accordance with the City of Fort Collins Drainage Criteria, and are also included in the Appendix A. E. Variances from Criteria No variances are being sought for the proposed project site. Pa M IV. DRAINAGE FACILITY DESIGN MA. General Concept Drainage sub -basins 1 - 5 are designed to flow through the water quality capture pond located in the southwest corner of the development. The 10-year storm as well as the 100-year storm will be routed to the pond. Because the volume of the 10-year storm event runoff is greater than the volume of the water quality pond, the 10-year storm event runoff will overflow the water quality ponds and sheet flow directly into Boxelder Creek. The water quality capture ponds were designed using the Urban Drainage and Flood Control District of Denver and the City of _ Fort Collins Drainage guidelines in order to capture the first flush of stormwater and release it over a 40-hour drain time. Sub -basin 6 will remain undisturbed and drains directly into Boxelder Creek. Reference the Drainage and Erosion Control Plan in the back of this report for sub -basin delineation. Flow from Sub -basin 1, which consists entirely of roof area, will be collected in the roof gutter system and connected to the storm drain pipe running to the water quality pond. Runoff from Sub -basin 2 will enter an area inlet located at the loading dock and be carried in a pipe to the water quality pond. Sub -basin 3 will — sheet flow and curb and gutter flow to a curb cut located at the southwesterly corner of the parking lot. The runoff will then outfall to the water quality pond in a swale down the side of the pond. Stormwaters from Sub -basin 4 will be carried by the proposed curb and gutter along the Frontage Road to a swale which runs into the water quality pond. Sub -basin 5 will flow directly into the water quality pond, and Sub -basin 6 will drain directly into Boxelder Creek. B. Specific Details The 10-year storm event runoff from Sub -basin 1 was determined to be 1.1 cfs, _ and will be collected by the roof drain system of the Harley Davidson Dealership building. The gutter system and roof drain pipes will need to carry the 10-year flow. To pass the first flush of the roof runoff through the water quality capture pond, the roof drain system will be connected to the stormdrain pipe from Sub - basin 2. The 100-year runoff from Sub -basin 1 was determined to be 2.2 cfs and will overflow the gutter system and flow directly into Boxelder Creek. Sub -basin 2 includes the loading dock area. The 10-year and 100-year runoff for ■ this basin were determined to be 2.2 cfs and 4.4 cfs, respectively. To drain the loading dock pit and pass the runoff through the water quality capture pond, an area inlet was placed in a sump at the base of the loading dock and connected to . a pipe running to the pond. The roof drains along this section of the building can 3 . M 0 • outlet onto the dock ramp which will then carry the flow the area inlet. The area inlet needs to handle the 100-year flows since flow over topping the gutters along this section of the building will still run down the ramp to the loading dock. For the grate selected, with 2.2 sf opening and 1 ft head, capacity is 5.3 cfs. The inlet is connected to a 15" pipe running into the water quality pond. The stormdrain pipe from the area inlet was designed to carry the 10- ear flow PP g riY Y from Sub -basin 1, 1.1 cfs, combined with the 100-year runoff from Sub -basin 2, 4.4 cfs, for a total of 5.4 cfs. With a slope of 1 %, a 15" pipe will carry the discharge under gravity flow. Flow from Sub -basin 3 will overland flow to the parking lot, then be conveyed by curb and gutter to a curb cut in the southwest corner of the parking lot. The 10- year discharge was computed to be 8.1 cfs. Using the weir formula and a maximum depth of 6", an 8 ft. long curb cut is required to pass the 10-year flow. The curb cut outfalls to a swale which runs down into the water quality capture pond. The 100-year flow for this sub -basin of 16.3 cfs will overtop the curb along the west side of the parking lot and flow directly into Boxelder Creek. The property fronts onto the I-25 Frontage Road. Curb and gutter will be constructed along the property frontage. Sub -basin 4 will flow along the proposed curb and gutter. The 10-year flow was determined to be 4.3 cfs which is also the gutter capacity at 0.4 % slope under a minor event (see calculations in Appendix A). The 100-year runoff was computed to be 8.6 cfs. The curb and gutter ends at the water quality pond where the flow will enter a swale which outfalls into the pond. Sub -basin 5 encompasses the water quality capture pond and a small section of the frontage road. The 10-year and 100-year runoff generated by this basin are 1.1 cfs and 2.4 cfs, respectively. Without accounting for the minor effect that lagging the runoff from the individual basins would have on the peak discharge entering the water quality pond, the total 100-year discharge passing through the pond from the site is 32.5 cfs. For a maximum depth of 6" over the overflow weir exiting the water quality pond, a 32 ft. wide weir is needed. The 100-yr historic runoff was computed to be 7.7 cfs. entering Boxelder Creek from this site. Because of the sites proximity to Boxelder Creek, the peak discharge from the developed site will enter Boxelder Creek and pass downstream long before the 100-year flood peak reaches the site. Therefore, the development of this site will not impact the 100-year floodplain of Boxelder Creek; thus, detention is not necessary. Included in the Appendix of this report is a copy of the flood hydrograph for Boxelder Creek at a point approximately 1/2 mile upstream from this site as generated by Simon, Li, & Associates, 1981. I! C. Boxelder Creek Floodplain Boxelder Creek borders the west side of the Interstate Land First Filing. A study performed by Simons, Li & Associates, Inc., 1981, (SLA 1981) was used as the basis for the current Federal Emergency Management Agency Flood Insurance Rate Maps (FEMA FIRM) for this reach of Boxelder Creek. CA Existing Floodplain/Floodway The original study by SLA 1981 did not determine the bounds of the 100 year floodway along this section of Boxelder Creek. It appears the floodway was not determined downstream of the Boxelder Creek/Interstate 25 crossing, which is just upstream from this site, because flow patterns are complicated by inflow from irrigation ditches immediately west of I-25 and split flows and cross -over flows from the Cooper Slough are encountered south of Prospect Road. However; the portion of Boxelder Creek which borders the proposed project is below the irrigation ditches and north of Prospect Road. It was determined, in a meeting with the City of Fort Collins Stormwater Utility, the floodway was definable for this portion of Boxelder Creek. Since no computer files of the original study were known to exist, the model had to be recreated and verified against a hard copy secured by RBD, Inc., before floodway computations could be performed. At the time of preliminary P&Z approval for the Interstate Land ODP, a HEC-II model which consisted of cross -sections 11 through 18 of the SLA 1981 study was generated and analysis results checked against the original study. Once consistent results were obtained, Method 4 of the floodway encroachment routines was used with a target maximum increase in water surface elevation of 0.5 ft. Included in the appendix of the Preliminary Drainage and Erosion Control report for the Interstate Land Development are the results of this study including floodway encroachment computations. Cross sections 16 & 17 of the above study were used to delineate the extent of the floodplain through the Interstate Land First Filing. The extent of the FEMA Floodplain and the Base Flood Elevation for Cross- section 17 are shown of the Drainage and Erosion Control plan included with this report. C.2 Future Condition Floodplain As part of the flood study of Boxelder Creek for the Interstate Land ODP/Preliminary, the affect on the base flood elevations, resulting from possible improvements to the structure carrying Boxelder Creek under I-25, was investigated. The floodplain elevation at the same FEMA Cross- section 17, under future conditions, was determined to be 4908.5. The 5 a( 0 Ll minimum building finished floor elevation in the Interstate Land First Filing is set at 4912.4, which is greater than 18" above the anticipated maximum flood elevation. V. STORM WATER QUALITY A. General Concept Beginning in October 1992, the water quality of storm water runoff was required to be addressed on all final design utility plans. Since the construction of the Interstate Lands development will begin after October 1992, we have sought to find various Best Management Practices for the treatment of storm water runoff. The Interstate Land P.U.D. First Filing will provide a water quality pond to help improve the runoff water quality by settling out pollutants before it flows into Boxelder Creek. B. Specific Details The bottom 2 feet of the water quality pond constitute the available Water Quality Capture Volume. Water within this volume will drain out of the pond over a 40- hour time frame via the outlet structure. The outlet structure is buried beneath a gravel filter to further remove pollutants before being released downstream. Water above the two foot depth outflows over the overflow weir into Boxelder Creek. During construction, a silt fence will be installed around the perimeter of the pond to prevent or minimize construction debris from leaving the site. 2 VI. EROSION CONTROL A. General Concept This development lies within the Moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. It is anticipated that the project site improvements will be subject to minor erosion before the building is constructed. The Erosion Control Performance Standard (PS) after construction for this project was computed to be 95.9 percent per the criteria in the City of Fort Collins Erosion Control Reference Manual for Construction Sites. The Effectiveness (EFF) of the proposed erosion control plan was calculated to be 99.4 percent. Therefore, the erosion control plan below meets the City of Fort Collins' requirements. A copy of the calculations has been included in the Appendix. An erosion control escrow cost estimate of $5,999 is also included in the Erosion Control section of the Appendix. All construction activities for this site must comply with the State of Colorado permitting process for Stormwater Discharges Associated with Construction Activity. A Colorado Department of Health NPDES Permit will be required before any construction grading can begin. I B. Specific Details Before commencing overlot grading, silt fence shall be installed along all downwind and downstream perimeters of the site, as well as surrounding the proposed water quality capture pond. Access roads, parking lots, and staging yards that are to be paved as part of this development must have a 1-inch layer of gravel mulch ('/a-1'/z gravel) applied at a mstru structure shall be appliedlasely soonter as overlot grading is completed. The pavement . possible after the utilities have been installed. All disturbed areas not in a roadway, parking lot, or greenbelt area shall have temporary vegetation seed applied. After seeding, a hay or straw mulch shall be applied over the seed at a rate of 2 tons/acre minimum, and the mulch shall be adequately anchored, tacked, or crimped into the soil. If the disturbed areas will not be built on within one growing season, a permanent seed shall be applied. After seeding, a hay or straw and themulch shallmulch shall bepadlied over equ adequately the seed at a minimum rate of 2 tons/acre, ?, anchored, tacked or crimped into the soil• In structed for an extended period of e event a portion of the roadway pavement surface and utilities will not be con 7 I! time after overlot grading, a temporary vegetation seed and mulch shall also be applied to the roadway areas as discussed above. VIL CONCLUSIONS A. Compliance with Standards All computations that have been completed within this report are in compliance with the City of Fort Collins Erosion Control Reference Manual for Construction Sites and the Storm Drainage Design Criteria Manual. In addition, all computations are in compliance with the Preliminary Drainage and Erosion Control Report for the Interstate Lands Development, prepared by RBD, Inc. B. Drainage Concept The proposed drainage concepts presented in this report and on the construction plans adequately provide for the transmission of the developed on -site runoff to Boxelder Creek located on the west edge of the development. The combination of on -site capacities in the curb and gutter, and the on -site storm sewer system will provide for the 10-year, and the 100-year developed flows to reach the water quality pond and Boxelder Creek. Due to localized stormwater runoff reaching Boxelder Creek long before the peak basin runoff in Boxelder Creek, no onsite detention of localized stormwater runoff is required for this development. C. Storm Water Quality Concept Because storm water quality has become a requirement, the site has addressed this storm water aspect. A water quality pond will be constructed to help improve the stormwater runoff quality before it reaches Boxelder Creek. D. Erosion Control Concept The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from the site. Through the construction of the proposed erosion control concepts, the City of Fort Collins performance standard will be met. All construction activities will comply with the State of Colorado permitting process for Stormwater Discharges Associated with Construction Activity. A Colorado Department of Health NPDES Permit will be required before any construction grading begins. REFERENCES 1. 2. 3. 4. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984, Revised January 1991. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. RBD, Inc., Preliminary Drainage and Erosion Control Report for Interstate Lands Development, Fort Collins, Colorado, August 1985. Simons, Li, & Associates, Inc., Cooper Slough Boxelder Creek Master Drainageway Planning Study, August 1981. w a ■ L VICINITY MAP MULBERRY (HWY 14 z � CRC a Fq y � J PROJECT C"aJE �o PROSPECT CO SITE 44E RESERVOIR INLET �F 1 CgNq� o l� R"T L SCALE 1 "=2000'