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HomeMy WebLinkAboutSPRADLEY BARR DEALERSHIP PRELIMINARY PUD - 64 93B - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTHORSETOOTH ROAD w 0 0 N HARMONY ROAD i� LI 1.1 IC N n b CND J � T PROJECT SITE L�ui w L 11 l LI U JW J n U N VICINITY MAP SCALE: 1"=1000' APPENDIX continue to do so. C. Storm Water Quality For this preliminary study, we are aware that the stormwater quality will be affected by most of the grass areas being converted to pavement. Stormwater quality will be maintained to the maximum degree possible. D. Erosion Control Concept At the time of final design, the erosion control performance standard will be calculated, and appropriate measures will be taken to control erosion from the site. The erosion control measures will be consistent with the City of Fort Collins Erosion Control Reference Manual for Construction Sites. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards, by the City of Fort Collins, Colorado, May 1991. 2. Erosion Control Reference Manual for Construction Sites, by the City,of Fort _ Collins, Colorado, January 1991. 3. Urban Stormwater Quality Management Guidelines, prepared for the American Society of Civil Engineers, prepared by Wright Water Engineers, Inc., Denver, Colorado and Camp Dresser McKee, Orlando, Florida, 1991. I1- Ii i 0 11 V. STORMWATER QUALITY A. General Concept In late 1993 or in 1994, it is anticipated that the water quality of stormwater runoff will be required to be addressed on all final design utility plans. For this preliminary study, we are aware that the stormwater quality will be affected by most of the grass areas being converted to pavement. One possible way of improving stormwater quality is to construct the area inlets with a sump in the bottom of the inlet, for sediment collection. Some of the developed flows will still be directed toward the grass area along the south side of the site, which provides an area for pollutants to settle out. VI. EROSION CONTROL. A. General Concept The Spradley Barr Dealership lies on the edge of a High Rainfall Erodibility Zone, and within a Moderate Wind Erodibility Zone, per the City zone maps. Since existing site slopes are generally around 3%, the potential exists for some erosion problems during the construction phases of the project. Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites, at the time of final design of the site, the erosion control performance standard will be calculated, and appropriate measures will be taken to control erosion from the site. VII. CONCLUSIONS A. Compliance �01h Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. B. Drainage Concept The proposed drainage concepts adequately provide for the conveyance and release of developed on -site flows into Highway 287. The developed condition is very similar to the historic, except for the east portion of the site. A detention area on the east side will detain runoff and release stormwater at the current historic rate. Off -site flows which presently enter the site will 5 w the change in use. The result is that there will be no change in the amount of stormwater runoff which reaches the nursery property on the south, or which reaches the state highway on the east. The Preliminary Grading and Drainage Plan identifies this area as being excluded from the analysis. In the one proposed basin, the very northwest corner of the site is included. The rationale for this inclusion is because of a planned increase in the impervious condition. This corner is presently paved with gravel, but will be paved with asphalt. Although this corner now drains toward the south, the flows will be intercepted by a pan and transported to the east. Therefore, there will be no increase, and even a decrease, in the amount of stormwater draining toward the nursery due to a change in surface imperviousness or in overall slopes. The areas to the north and east of the building which are currently covered with grass will become paved, for the display of vehicles. This increase in surface imperviousness will be accommodated by providing for a detention area in the newly paved area east of the building. Preliminary calculations in the appendix show the detention requirements based on 100-year subbasin A developed flows (34.1 cfs) versus the 2-year subbasin E3 historic runoff (0.5 cfs) plus the 100-year existing flows from subbasin E2 (6.8 cfs). The rationale for adding the 100-year flows from E2 to the outlet rate is because E2 will no longer release flows onto the highway to be intercepted by the curb inlet and thence the 18" pipe. These historic flows will instead be intercepted by the area inlets in the detention area. Survey data of this culvert shows an 18" CMP, at approximately 1.8% slope, which affords a 7.7 cfs capacity with Manning's n = 0.024. A proposed pipe and area inlet system in the detention area will convey the flows into the existing 18" pipe. The flows which reach the culvert will be limited to 7.3 cfs by installing an orifice plate at the last area inlet. At the time of final design, the orifice plate will be sized. Existing Inlet The existing 5' curb inlet on Highway 287, near the southeast corner of the site will remain in place. The functioning of the curb inlet is directly affected by the flows entering the 18" culvert, previously mentioned. The 18" culvert drains into the back of the inlet, and then a separate 18" pipe section carries the water underneath the highway. 11 11 4 11 11 s C. Hydrological Criteria The rational method was used to determine runoff peak flows from the site. The 10 and 100 year rainfall criteria, obtained from the City of Fort Collins, is the criteria which was utilized. This criteria is included in the Appendix. D. Hydraulic Criteria All calculations within this report have been prepared in accordance with the City of Fort Collins Storm Drainage Criteria. E. Variances from Criteria No variance from City of Fort Collins Storm Drainage Criteria is being sought. IIV. DRAINAGE FACILITY DESIGN A. General Concept When the improvements are complete for the subject site, all on -site fully developed flows will flow either directly or indirectly onto Highway 287, or into the existing culvert under the highway. The drainage patterns generally will be unchanged by the change in site use. No additional flows will be directed toward the south nor toward Highway 287. The additional runoff created by replacing grass areas with asphalt, pavement will be detained on - site before exiting via the existing culvert under the highway. Off -site flows which presently enter the site from the west will continue to do SO. Included in the back pocket of this report is the Spradley Barr Dealership Preliminary Grading & Drainage Plan. B. Specific Details Subbasin Design Only one developed subbasin was analyzed for the proposed condition. Please refer to the Preliminary Grading and Drainage Plan for the location of this basin. All areas outside of the one analyzed subbasin are essentially unaffected by 3 IN Sub -Basin Description Historic drainage patterns for the site direct runoff toward the south and east. The areas west and south of the body shop produce sheet flow across the paved lot to a point along the south side of the site, near the fire hydrant. From this spot, the runoff either continues to flow in a southeasterly direction across the nursery property, or turns toward the east and runs along a grassy swale parallel to the driveway. By either flow path, these flows are eventually released into Highway 287. A portion of the building roof plus the front driveway area contribute flows which follow the south driveway and are directed to Highway 287. Since there is an asphalt curb along the south side of this driveway, the flows stay within the driveway until they reach the highway. Another portion of the building roof, the north driveway, and the grass areas on the north side of the site reach the highway via the north driveway. The front lawn, east of the building, drains to a low spot and enters a culvert. This culvert also takes flows from Highway 287 via a 5 foot Type R inlet. The culvert outlets into a concrete -lined channel on the east side of Highway 287. This concrete channel runs parallel to the highway, and eventually delivers flows to Fossil Creek. The off -site flow contribution from the north is controlled by a curb line adjacent to the property line. Offsite flows are limited on the east side by the curb and gutter. along the highway. There will be no change on these sides of the site. On the west side of the property, the railroad right-of-way slopes toward the subject site. This will remain as is. I1I. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. Development Criteria Reference and Constraints The subject site is within the Fossil Creek Basin. 2 I. II PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY SPRADLEY BARR DEALERSHIP CITY OF FORT COLLINS GENERAL LOCATION AND DESCRIPTION A. Location The proposed location for the Spradley Barr Dealership is located south of the intersection of South College Avenue and Harmony Road in Fort Collins. The site is presently owned and occupied by Poudre Valley REA. The site is bounded on the north by Pizza Hut and Walmart, on the south by Fossil Creek Nursery, on the west by railroad tracks, and on the east by U.S. Highway 287. The site is shown on the Vicinity Map in the Appendix. More particularly, the site is situated in the northeast quarter of Section 2, Township 6 North, Range 69 West of the 6th P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property The proposed Spradley Barr site contains 9.3 acres, more or less. Currently, the site contains the administrative, vehicular, and utility operations for Poudre Valley REA. The western portion of the site is mostly paved, with slopes averaging 3%. This area is fenced off for use as storage. North and east of the building, the ground is covered with grass and numerous trees. The existing ground in front of the building slopes at roughly 2.7%. A line of trees marks the south property line, along with a grass strip between the trees and the south edge of pavement. The entire site slopes toward the southeast, with drainage eventually reaching Highway 287, or entering an 18" culvert which crosses under Highway 287. DRAINAGE BASINS AND SUB -BASINS A. Major Basin Description The Spradley Barr Dealership lies within the Fossil Creek Basin. No major drainageway crosses the subject site. 1 APPENDIX VICINITY MAP 1 HYDROLOGY .2 DETENTION 7 DESIGN OF INLETS & STORM DRAINS 12 CHARTS, TABLES, & FIGURES .15 1 TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION A. LOCATION 1 B. DESCRIPTION OF PROPERTY 1 II. DRAINAGE BASINS AND SUB -BASINS A. MAJOR BASIN DESCRIPTION 1 B. SUB -BASIN DESCRIPTION 2 III. DRAINAGE DESIGN CRITERIA A. REGULATIONS 2 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 2 C. HYDROLOGICAL CRITERIA 3 D. HYDRAULIC CRITERIA 3 E. VARIANCES FROM CRITERIA 3 IV. DRAINAGE FACILITY DESIGN A. GENERAL CONCEPT 4 B. SPECIFIC DETAILS 4 V. STORM WATER QUALITY A. GENERAL CONCEPT 5 VI. EROSION CONTROL A. GENERAL CONCEPT 5 VII. CONCLUSIONS A. COMPLIANCE WITH STANDARDS .5 B. DRAINAGE CONCEPT 5 C. STORM WATER QUALITY 6 D. EROSION CONTROL CONCEPT 6 REFERENCES 6 INC. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 303/482-5922 FAX:303/482-6368 October 25, 1993 Mr. Glen Schlueter City of Fort Collins Utility Services Stormwater 235 Mathews Street Port Collins, Colorado 50522 RE: Preliminary Drainage and Erosion Control Study for Spradley Barr Dealership Dear Glen: We are pleased to submit to you, for your review and approval, this Preliminary Drainage and Erosion Control Study for the Spradley Barr Dealership. 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 C nsuItants J nelle K. Ohms, P.E. roject Engineer Kevin W. Gingery, P.E. cc: Mr. Kriss Spradley Mr. Bill Barr file 593-001 Other Offices: Denver 303/458-5526 • Vail 303/476-6340 � ` 6 25485 L PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY SPRADLEY BARR DEALERSHIP CITY OF FORT COLLINS October 25, 1993 Prepared for: Spradley Barr 2601 South College Avenue Fort Collins, Colorado 80525 Prepared by: RBD, Inc. Engineering Consultants 209 South Meldrum Street Fort Collins, Colorado 80521 (303) 482-5922 RBD Job No. 598-001 i 0 PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY SPRADLEY BARR DEALERSHIP CITY OF FORT COLLINS