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HomeMy WebLinkAboutEAST VINE DRIVE STREETS FACILITY PUD PRELIMINARY - 30 91A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT?RELIMINARY DRAINAGE. EROSION AND STORM WATER QUALITY STUDY FOR THE ;T VINE STREETS FACILITY P.U.D. CITY OF FORT COLLINS % transported underground. The storm sewer pipe connecting the proposed 5' curb inlet to the outfall line is shown as 12" due to available depth in the curb inlet and cover in the driveway. If this inlet remains in the location preliminarily shown, during the final design phase of this project a variance will need to be requested from the City Stormwater Utility to use a 12" pipe rather than their minimum 15" pipe. Storm events in Basin 1 larger than the 2 year storm event are designed to be transported overland via either concrete, asphalt, or grass water ways, easterly to the storm water detention ponds. Calculations within the appendix indicate that storm water runoff from the 100 year storm can be conveyed easterly within Basin 1 to the storm water detention ponds. Only the developed drainage for Basin 1 has been addressed at this time, as Basin 1 is currently planned as a three phase project for the new Streets Facility. It is anticipated that Basin 2 will be developed by another entity at some future date. For the development of Basin 2, an internal storm sewer system may be required in the future, and both the areas of storm water detention and storm water quality detention will need to be addressed as they are done here for Basin 1. The on -site storm water detention system should be sized to release at the 2 year historic rate during the 100 year developed runoff event unless downstream off -site hydraulics are evaluated. For this study, the downstream off -site hydraulics are not evaluated any further than the existing 15" culvert under Buckingham Street at 9th Avenue. The 15" culvert at this location cannot pass the 2 year historic event from this site without overtopping the intersection. For this study, we have preliminarily designed the storm water detention pond within Basin 1 to detain-up.-to_the 100 year -developed runoff and release all flows at not larger than the 2 year historic release rate. As Basin 2 is developed, the site must be planned for future on -site detention. The release rate from this detention pond.must be limited to the 2 year historic event during the 100 year developed runoff event. Use of a higher release rate must consider the downstream hydraulic capacities .to verify the capacities to the Cache La Poudre River. 5 0 V. STORM WATER QUALITY A. General Concert Beginning in 1992, the water quality of storm water runoff will need to be addressed on all final design utility plans. The East Vine Streets Facility is anticipating construction beginning in 1992. Therefore for this study, we have sought to find various Best Management Practices for the treatment of storm water runoff at this preliminary design phase which could be implemented in the final design process. B. Specific Details It is our understanding at this preliminary phase, that the concept of storm water quality should address the treatment of the initial first flush (2 year storm) runoff. By capturing the initial flush in either a water quality pond, infiltration device, dry wells or other devices, the pollutants can be filtered out of the storm water runoff. Included in the appendix are two exhibits of water quality pond configurations. The water quality ponds should be designed to release the storm water runoff over a 24 to 40 hour period in order to filter out pollutants. At this preliminary phase, only concepts have been presented here for the water quality ponds. As storm water quality evolves, additional concepts will become available. Water quality ponds A and B have been shown on the Preliminary Grading and Drainage Plan, and these ponds have been graded to enable each pond to contain the entire 2 year storm water runoff from its respective runoff basins. During final design, overflow weirs for runoff events greater than the 2 year storm event, as well as perforated riser outlets to limit the drain time to between 24 and 40 hours, will need to be designed for each water quality pond. I Included in the appendix is an exhibit on infiltration devices. The water quality concept is to infiltrate the I storm water runoff to the groundwater and use the soil as a filter for pollutants. The inlets and trench drain will be designed with a bottom some distance below the invert of the outlet pipe. The depressed bottom can then collect sediment and other pollutants. Weep holes in the base of each structure will enable the storm water to filter out into the ground water. Sediment and pollutants must be removed regularly from the base of each structure. �` 6 14 An exhibit on dry wells is included in the appendix. Dry wells are designed to accept rooftop runoff and filter out the pollutants in the gravel medium and allow the cleaned water to filter into the ground water. During final design of the subject site, each rooftop drain could drain into a dry well and the overflow pipe could connect into the storm sewer system. VI. EROSION CONTROL A. General Concept The East -Vine Streets Facility lies within the Moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. Due to the existing site slopes of 0.5%, the potential exists for minor erosion problems during and after the construction phases of the project. Due to the uncertainty of the development time frame for the new improvements, the site will probably be subjected to both wind and rainfall erosion before the new vegetation has taken hold. Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites and the related calculation in the appendix, the erosion control performance standard for the subject site is 72.4%. From the calculations in the appendix, the effectiveness of the proposed erosion control plan is 97.6%. Therefore the erosion control plan as specifically detailed below, meets and exceeds the City of Fort Collins requirements. B. Specific Details Basin 1 currently consists of native vegetation on the eastern one third, gravel and asphalt in the middle one third, and gravel and concrete on the western one third. The-eastern_one third is proposed for the detention pond system. From the Erosion Control Reference -Manual, —it states "All disturbed areas seeded with permanent grasses will be mulched immediately after seeding". Therefore after overlot grading in the detention pond system, a seed and mulch combination should be immediately applied ' to this area in order to begin the revegetation process. After the seed is applied, a hay or straw mulch should be applied over the seed at a rate of 2 tons/acre (minimum) and the mulch should be adequately anchored, tacked, or crimped into the soil. The mulch should reduce both wind and rainfall erosion. ' The majority of the remainder of Basin 1 is proposed for the development of asphalt and concrete impervious �' 7 r� r surfaces. After overlot grading and prior to construction of the concrete and asphalt pavement structures, all bare ground should have straw bale barriers installed on alternating sides of the drives, parking lots, storage lots, etc., perpendicular to the direction of rainfall runoff per the grading concepts, extending 1/2 way across the disturbed areas at 150 foot intervals. After installation of the pavement structures and inlets, the inlets should be filtered with a combination of concrete blocks, wire screen and coarse gravel. VII. CONCLUSIONS A. Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria and the Erosion Control Reference Manual for Construction Sites. B. Drainage Concept The proposed drainage concepts adequately provide the detention of developed on -site flows within Basin 1 of the subject site. The proposed storm sewer system will remove nuisance and snowmelt flows from the impervious surfaces and up to the 2 year storm water runofff. The proposed grading concepts will adequately transport storm water runoff to the discharge locations. As Basin 2 develops, drainage concepts as used in Basin 1 will need to be applied in order to convey, detain and release storm water runoff. C. Storm Water Oualit As storm water quality treatment becomes required in -- - 1992,--the—site- -will need to address .this_storm water _ aspect. The proposed grading concepts in Basin 1 provide for two storm water quality ponds (A and B) which are preliminarily sized to contain the storm water runoff from a 2 year storm event. The storm water quality ponds will need to release the 2 year storm water runoff over a period of up to 40 hours in order for the pollutants to settle out of the runoff. The inlets should be constructed with the bottoms some distance lower than the out going pipe inverts in order to filter out some pollutants and sediment. The roof drains should be run through some kind of a dry well to remove pollutants, with overflows which connect into the on -site storm sewer system. As Basin 2 develops, storm water quality concepts, as used in Basin 1, will need to be applied in a order to improve the water quality before the runoff enters Linden Street. D. Erosion Control Concept The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from Basin 1 of the site. Through the construction of the proposed erosion control concepts, the City of Fort Collins performance standards will be met. As Basin 2 develops, erosion control concepts, as used in Basin 1, will need to be applied in order to prevent erosion of the basin onto Linden Street. REFERENCES 1. Storm Drainage Design criteria and Construction standards by i the City of Fort Collins, Colorado, May 1984. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. 3. Dry Creek Drainageway Planning for the City of Fort Collins, Larimer County Colorado by Gingery Associates, Inc., January 1980. 4. Flood Plain Information Cache La Poudre River Colorado Volume .1 Fort Collins, Larimer County, prepared for the Larimer-Weld Regional Planning Commission by the Department of the Army, October 1973. 5. 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. 9 PRELIMINARY DRAINAGE, EROSION AND STORM WATER QUALITY STUDY FOR THE EAST VINE STREETS FACILITY P.U.D. CITY OF FORT COLLINS June 3, 1991 Prepared for: Client: Vaught*Frye Architects, P.C. 2900 S. College Avenue Fort Collins, Colorado 80525 Owner: City of Fort Collins - -- —_ Streets Department 700 Wood Street Fort Collins, Colorado 80522 Prepared by: RBD, Inc. Engineering Consultants 2900 South College.Avenue Fort Collins, Colorado 80525 (303) 226-4955 RBD Job No. 183-012 n NC. A ' Engineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 i 303/226-4955 FAX:303/226-4971 A I June 3, 1991 Ms. Susan Hayes City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 A ' RE: Preliminary Drainage, Erosion and Storm Water Quality Study for the 3 East Vine Streets Facility P.U.D. RBD Inc. Job No. 183-012 Dear Susan: We are pleased to submit to you, for your review and approval, this Preliminary Drainage, Erosion and Storm Water Quality Study for the East Vine Streets Facility P.U.D.. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. Thank you for meeting with us on this project during the .preliminary design phase and thank you for supplying the information on Dry Creek and the Cache La Poudre River. We -appreciate your time and consideration in reviewing this submittal. Please call if yotf have -any questions. - Respectfully, RBD nr---­Pngineering onsultants Q� .oQO.O ,RE Ted A. Borstad, P.E. Project Manager Kevin W. Gingery,. P.E. Project Engineer 24766 moo41, . CC: Mr. Joe Frye - Vaught*Frye Architects, P.C. Other offices: Denver 303/778-7338 • Vail 303/476-6340 • Colorado Springs 719/598-4107 - Longmont 303/678-9584 PROJECT PERSONNEL EAST VINE STREETS FACILITY P.U.D. City of Fort Collins Jack Gianola Susan Hayes Vaught*Frye Architects, P.C. Joe Frye RBD, Inc. Ted Borstad, P.E. Kevin Gingery, P.E. Steve Birdsall, E.I.T. Terry Everitt, P.L.S. Kelly Priest Keith Smith Jim Anderson, S.I.T. Project Manager Stormwater Utility Project Manager Project Manager Project Engineer Design Engineer CADD CADD Surveying Surveying a� TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION 1 A. LOCATION 1 B. DESCRIPTION OF PROPERTY 1 II. DRAINAGE BASINS AND SUB -BASINS 1 A. MAJOR BASIN DESCRIPTION 1 B. SUB -BASIN DESCRIPTION 2 III. DRAINAGE DESIGN CRITERIA 2 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 3 B. SPECIFIC DETAILS 4 V. STORM WATER QUALITY 6 A. GENERAL CONCEPT 6 B. SPECIFIC DETAILS 6 i 1 VI. EROSION CONTROL 7 A. GENERAL CONCEPT 7 B. SPECIFIC DETAILS 7 VII. CONCLUSIONS 8 A. COMPLIANCE WITH STANDARDS 8 B. DRAINAGE CONCEPT 8 C. STORM WATER QUALITY 8 D. EROSION CONTROL CONCEPT 9 t 9 APPENDIX VICINITY MAP 1 HYDROLOGY 2 WATER QUALITY AND STORMWATER DETENTION 11 DESIGN OF INLETS, STORM SEWER AND ANALYSIS OF THE OFFSITE ROADSIDE DITCH 18 RIPRAP DESIGN 25 EROSION CONTROL 27 WATER QUALITY 31 CHARTS, TABLES AND FIGURES 40 111 PRELIMINARY DRAINAGE, EROSION AND STORM WATER QUALITY STUDY FOR THE EAST VINE STREETS FACILITY P.U.D. CITY OF FORT COLLINS I. GENERAL LOCATION AND DESCRIPTION A. Location The East Vine Streets Facility P.U.D. is located on the old Great Western Sugar Factory site and is bounded on the north by the Burlington Northern Railroad, bounded on the east by 9th Avenue ,bounded on the west by Linden Street and on the south by undeveloped land. The site is shown on the Vicinity Map in the Appendix. More particularly, the site is situated in the North half of Section 12, Township 7 North, Range 69 West of the 6th P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property The East Vine Streets Facility P.U.D. entire site contains 32.8 acres more or less. Currently the site contains existing buildings and storage areas being used by Platte Valley, ADS Pipe, and Centennial Lumber companies. Some of the existing buildings were previously used by the Great Western Sugar Company. The site contains numerous stockpiles of plastic pipe and lumber. The property is being proposed for the City of Fort Collins Streets Facility. The existing site contains large quantities of asphalt, concrete and gravel --- - --parking- and -storage areas per the Existing_Site-Condition Drainage Plan included in the back pocket of this report and the calculations within the appendix. A portion of the site contains natural Colorado grasses. Topography at the site is generally sloping from west to east at approximately 0.5%. II. DRAINAGE BASINS AND SUB -BASINS A. Major Basin Description No major drainageway exists within the subject site. The East Vine Streets Facility P.U.D. does lie within the Dry Creek Basin per the Dry Creek Drainageway Planning report by Gingery Associates, Inc. dated January 1980. The 1 majority of the site drains eventually to Dry Creek. On the existing site drainage plan, the flood plains for the Dry Creek Basin and the Cache La Poudre River are delineated and indicate that the site does not lie within the 100 year flood plain of either waterway as discussed later within this report. B. sub -Basin Description Historic drainage patterns for 28.9 acres of the site are easterly across the site towards 9th Avenue. Once storm water runoff reaches 9th Avenue, the runoff is collected in a roadside ditch and directed southerly and then easterly to eventually reach Dry Creek. Approximately 3.9 acres of the site drains southwesterly towards Linden Street. Once storm water runoff reaches Linden Street, the runoff travels along the shoulder of Linden Street and eventually reaches the Cache La Poudre River, if not intercepted by the, existing irrigation lateral. Two small off -site areas totalling 1.25 acres currently drain onto the subject site along the northern property line. These two small off -site areas are the Burlington Northern Railroad fill areas for the tracks. The off -site flows meander along the northern property line and eventually reach the roadside ditch along 9th Avenue. III. 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 The subject site is in the Dry Creek Basin. The Dry -�— Creek Master Plan does not require on -site detention. However, the City of Fort Collins Stormwater—U•tl--ity _ requires that the developer analyze and improve, if necessary, the drainage system from this site downstream to Dry Creek to adequately carry the 100 year developed storm water runoff. If the downstream system is not ' adequate, then on -site detention will be required. Per the City Stormwater Utility, if an on -site detention i system is used, the release rate from the detention pond must be limited to the 2 year historic event during the 100 year developed runoff event. Use of a higher release rate must consider downstream limitations and an off -site analysis must be performed from the subject site to Dry Creek to verify the capacity of the off -site hydraulic 2 A .1 structures. The western portion of the subject site must be planned for future on -site detention. The release rate from this detention pond must again be limited to the 2 year historic event during the 100 year developed runoff event. Use of a higher release rate must consider downstream limitations and an off -site analysis must be performed from the subject site to the Cache La Poudre River to verify the capacity of Linden Street and the off -site hydraulic structures. The City of Fort Collins Stormwater Utility has indicated that the existing conditions of the subject site as of May 16, 1991 can be used for calculating.the historic "C" value. C. Hydrological Criteria The rational method was used to determine runoff peak flows from the site. The 2, 10 and 100 year rainfall criteria, which was 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 Drainage Criteria. E. Variances from Criteria No variances are being sought for the proposed project site. IV. DRAINAGE FACILITY DESIGN A. General Concept As development occurs within the subject site, all on - site fully developed flows will either flow easterly and eventually into a storm water detention pond near 9th Avenue or westerly and into a storm water detention pond near Linden Street. Included in the back pocket of this report is the East Vine Streets Facility P.U.D. Preliminary Grading & Drainage Plan. The Preliminary Grading & Drainage Plan also addresses erosion control and storm water quality issues. 3 B. Specific Details In preparing the Existing Site Condition Drainage Plan, the flood fringe line separating the Intermediate Regional Flood and the Standard Project Flood for the Cache La Poudre River required some special attention. From the report "Flood Plain Information Cache La Poudre River Colorado" dated October 1973, the flood fringe line shown on the drawings indicated the flood fringe line encroached onto the subject site. A careful examination was performed in the area where the flood fringe line encroached onto the subject site. By comparing the Intermediate Regional Flood Elevations between sections 68 and 69 with the existing site topo and the City of Fort Collins Engineering Division aerial photographs by Arix dated 1974, we determined that the flood fringe line does not encroach onto the subject site. Additionally, the City of Fort Collins Stormwater Utility provided RBD Inc. with two preliminary Poudre River Floodplain maps for the North half of section 12, T7N, R69W which are not currently being used for enforcement purposes. These preliminary drawings also indicate that the flood fringe line does not lie within the subject site. The East Vine Streets Facility P.U.D. soils report indicates that ground water lies approximately 5 feet below the existing surface. If groundwater is encountered during construction, a Colorado Department of Health Construction Dewatering Permit would be required. During the course of preparing the proposed preliminary drainage plan for the subject site, the lack of available I fall in elevation across the subject site governed the establishment of the proposed contours in Basin 1. A storm sewer system was designed to collect the two year storm water runoff from sub -basins A-G and transport this I runoff easterly toward storm water quality Pond A. Only a small "portion-of-the--2 year runoff. -from the easterly parking lot passes the curb inlet and is conveyed to I water quality pond A by the road system due to the proximity of the parking lot to the pond. Storm water quality ponds are discussed later within this study. I Through the use of area inlets, a trench drain, and a 5' inlet, the 2 year storm water runoff is collected by the storm sewer system. Storm water runoff from sub -basin H is collected in either a concrete trickle channel I immediately north of the buildings or in a grass swale along the. north property line of the subject site. Runoff from sub -basin H drains easterly and into storm water quality Pond B. Through the storm sewer system and trickle channel, runoff from the minor 2 year storm event and nuisance flows will be removed from the surface and n