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HomeMy WebLinkAboutTHE GATES AT WOODRIDGE PUD, 2ND FILING - FINAL - 55-87F - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT ORA IMGE AND EROSION CONTROL STUDY FOR TEE GATES AT WOODRIDGE SECOND FILING AND TEE OVERLOOK AT WOODRIDGE SECOND FILING 111133 INC. Engineering Consultants r NO I FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE GATES AT WOODRIDGE SECOND FILING AND THE OVERLOOK AT WOODRIDGE SECOND FILING U February 3 , 1992 I Prepared for: Woodcraft Homes Ill 1501 N. Cleveland Ave. Loveland, Co. 80538 I III • Prepared by: RBD, Inc. Engineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 (303) 226-4955 I III I RBD Job No. 434-005 I I Se j 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. HYDROLOGIC CRITERIA 3 D. HYDRAULIC CRITERIA 3 E. VARIANCES FROM CRITERIA 3 IV. DRAINAGE FACILITY DESIGN 3 A. GENERAL CONCEPTS 3 B. SPECIFIC DETAILS 3 !Ill V. EROSION CONTROL 5 A. GENERAL CONCEPTS 5 !II B. SPECIFIC DETAILS 5 VI . CONCLUSIONS 6 A. COMPLIANCE WITH STANDARDS 6 III B. DRAINAGE CONCEPT 6 C. EROSION CONTROL CONCEPT 7 REFERENCES 8 III APPENDIX IIIVICINITY MAP 1 SECOND FILING HYDROLOGY 2 DETENTION 5 III DESIGN OF INLETS, STORM SEWER AND SWALES 7 RIPRAP DESIGN 15 EROSION CONTROL 17 IIICHARTS, TABLES AND FIGURES 20 III 1 III N mi 3DNC. Engineering Consultants 2900 South College Avenue 1 Fort Collins,Colorado 80525 U 303/226-4955 FAX:303/226-4971 February 3 , 1992 Ms. Susan Hayes Stormwater Utility Department City of Fort Collins 235 Mathews Street Fort Collins, CO 80522 RE: Final Drainage and Erosion Control Study for The Gates At Woodridge Second Filing and The Overlook At Woodridge Second Filing RBD Job No. 434-005 Dear Susan: II] We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Study for The Gates at Woodridge Second Filing and The Overlook at Woodridge Second Filing. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage 'Design Criteria. Thank you for your time and consideration of this submittal. Please call if you have any questions. Respectfully, RBD Inc. Engineering Consultants Stan A. Myers, P.E. Project Manager a/-4;777 Kevin W. Gingery, P.E. g Y� Project Engineer cc: Mr. Gary Berger Mr. John Hutchinson U Other offices:Denver 303/778-7338•Vail 303/476-6340•Longmont 303/678-9584 J FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE GATES AT WOODRIDGE SECOND FILING AND THE OVERLOOK AT WOODRIDGE SECOND FILING I. GENERAL LOCATION AND DESCRIPTION A. Location The Gates and The Overlook at Woodridge P.U.D. ' s are located east of Taft Hill Road (County Road 19) and north of the existing Harmony Road. The development is bounded by Webber Junior High School and Regency Park PUD to the east and open space (proposed future filings) and Imperial Estates to the north. The site location can also be described as situated in the Southwest 1/4 of Section 34 , Township 7 North, Range 69 West of the 6th P.M. , City of Fort Collins, Larimer County, Colorado. The site location can be seen on Exhibit 1 in the Appendix. B. Description of Property The Second Filing of The Gates and The Second Filing of The Overlook at Woodridge together contain 17 . 1 acres more or less. Presently, the property is undeveloped. The property is being proposed for planned unit development within the City of Fort Collins Zoning District PUD. Native Colorado grasses cover the property presently. The topography of the site generally slopes from the west to the east at approximately 1. 5 percent. II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Characteristics The proposed developments lie within Basins 75 and 80 of the McClellands and Mail Creek Major Drainageway Plan prepared by Cornell Consulting Company. A natural drainageway runs west to east along the northern edge of The Gates at Woodridge Second Filing boundary within Basin 80. Runoff from Basin 80 is routed by open channels and culverts along the north side of Seneca Street past Webber Junior High School and then along the east side of Regency Drive to the existing Regional Detention Pond. The Overlook at Woodridge development lies in both Basins 75 and 80. Runoff from Basin 75 is routed through the Regency Park development (east of the Woodridge property) in an open channel along the north U 1 U 111 -A 111 side of Harmony Road and eventually into the existing Regional Detention Pond. B. Sub-Basin Description The project site has been divided into four sub-basins of which three were assumed to be developed and the other one was off-site undeveloped. The three developed sub- basins incorporated the proposed building lots and most of the street improvements. The one undeveloped sub- basin consisted of natural ground cover and portions of Harmony Road improvements. These sub-basins are shown on the Drainage and Erosion Control Plan in the back pocket of this report. 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 From The Final Drainage Report for Regency Park P.U.D. , 100 year developed runoff from Basin 75 will be routed through the Regency Park subdivision in an open channel along the north side of Harmony Road. A 42 inch culvert lies under Regency Drive. A newly constructed open channel along the east side of Regency Drive transports storm water runoff from the 42" culvert, north to the existing Regional Detention Pond near Wake Robin Lane. From the Preliminary Drainage Report for the 1990 Junior High School, the channel and culvert system along the north side of Seneca Street and the east side of Regency Drive was sized for undetained on-site as well as undetained off-site 100 year developed runoff from Basins 79 , 80, and 85. A current SWMM model analysis for Basins 79, 80, as recently obtained by the City of Fort Collins, has determined that the existing channel, culverts and Seneca Street (downstream of the subject site) will receive greater 100 year developed runoff than was originally anticipated. The City of Fort Collins is currently reviewing this matter and has indicated that the downstream existing improvements may not be adequate to transport the entire 100 year developed runoff (318 cfs) that could be produced from the Woodridge property at Seneca Street and the east property line. The City is considering acquiring a portion of the Woodridge property for another regional detention pond. 2 J IIIC. Hydrologic Criteria III The Rational Method for determining surface runoff was used for the project site. The 2 and 100 year storm event criteria, obtained by the City of Fort Collins, was utilized in calculating runoff values. These IIIcalculations and criteria are included in the Appendix. D. Hydraulic Criteria IIIAll 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. III E. Variances from Criteria III No variances are being sought for the proposed project site. IIIIV. DRAINAGE FACILITY DESIGN A. General Concept III All on-site runoff produced by the proposed development of The Gates and The Overlook - Second Filings will flow easterly to the existing drainageway along the east side III of Seneca Street and eventually arrive at the Regional Detention Pond. Included in the back pocket of this report are the proposed drainage and grading plans. IIIB. Specific Details The Second Filing of The Overlook at Woodridge was III combined with the First Filing of The Overlook at Woodridge for the basin delineations. This combination and the basin numbers used relate directly to the III recently approved Preliminary/Master Drainage Study for the Woodridge Development. Runoff from basin 7A is to combine with runoff from basin ;1: 0-3 and be transported to the existing off-site regional detention pond by a series of streets, culverts, roadside ditches, and open channels. From the calculations in the appendix, the existing 21" pipe under the temporary access road to Harmony Road can convey the runoff from the developed basin 7A and the undeveloped basin 0-3 . Thus no further storm sewer systems are required for IIIbasins 7A and 0-3 . Runoff from basin 9 is to be redirected at Harmony Road III and head northerly in a temporary swale. The temporary swale is proposed to day light to match the existing III 3 III j j IIIground north of Overlook Drive and Harmony Road. The concept being utilized will let the runoff spread in a III sheet flow manner once the swale day lights so the runoff can be distributed over the existing ground and not remain in a concentrated manner. Due to the existing Fort Collins-Loveland Water District Water Line running III north south along Overlook Drive, and the desire to not lower the water line in the area of the regional channel crossing at this time, the ground over the water line can III not be lower. A temporary swale is being proposed around the northwest corner of the Gates at Woodridge Second Filing to convey runoff around the developed lots and over the District water line. Thus we are proposing to III let the runoff from basin 9 combine with the historic off-site runoff and be collected and redirected around the northwesterly lots of the Gates at Woodridge Second III Filing and over the District water line at the existing water line ground elevation. III Runoff from basin 18 is to be directed northerly to the intersection of Silvergate Road and Overlook Drive. At this point a sump condition was created in the streets to convey the runoff northerly through the open space and III into the regional channel north of the Gates at Woodridge Second Filing. Due to extremely tight street working elevations, the inlets and storm sewer system from this III sump location to the regional channel were modified to collect the 100 year storm water runoff rather than only the 2 year runoff. In the event the inlets become plugged, water will pond up, cross the crown of III Silvergate Road and proceed northerly through the open space. The water will also begin to flow easterly along Silvergate Road after ponding some 0.20 feet above the III crown of Silvergate Road. Thus if the inlets become plugged, storm water runoff will have two relief points to drain and thus no damage should occur to the residential homes. IIIA portion of the regional channel was build during the First Filing work in the summer of 1991. Therefore we Ill are planning to continue the regional channel westerly to a point immediately downstream of the Fort Collins- Loveland Water District water line. Storm water runoff from basins 9, 18, and off-site areas will be collected IIIin the regional channel and directly easterly to the existing 42 inch culverts immediately north of Seneca Street. , Ill water runoff exiting g by the existing 42 inch culverts (at the east property line immediately north of III Seneca Street) travels east via 42" culverts and open channels, and eventually reaches the Regional Detention III 4 , III 'III ' Pond at Wake Robin Lane and Regency Drive. The City of Fort Collins is currently studying the possible III reconfiguration of these two existing 42 inch culverts to provide a more efficient transmission of storm water to the east. For the subject developments, the developed runoff is proposed to be directed to the existing 42 inch III culverts by the above described storm sewer system and temporary swales. The existing 42 inch culverts have a combined capacity of approximately 114 cfs. As the City III of Fort Collins completes their study of the existing 42 inch culverts, their possible reconfiguration future use in the main drainageway of this development will be incorporated with future filings of the Woodridge III development. V. EROSION CONTROL IIIA. General Concepts III Both developments, The Gates and The Overlook Second Filings, lie within the High Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. The potential exists for III moderate erosion problems after completing the Second Filing improvements, due to the existing and proposed site slopes of 2 . 0 % more or less. It is also anticipated that the project site improvements will be 1 III constructed during the spring and summer of 1992 . Thus, the new improvements will be subject to both wind and 101 rainfall erosion before new vegetation can take hold or before the new residential lots are developed. The Erosion Control Performance Standard (PS) for both III sites was computed to be 79 . 8% per the criteria in the City of Fort Collins Erosion Control Reference Manual for Construction Sites. The Effectiveness (EFF) of the III proposed erosion control plan was calculated to be 95 . 45%. Therefore, the erosion control plan as detailed below meets the City of Fort Collins ' requirements. IIIB. Specific Details Sub-basins 7A and 9 incorporate The Overlook at Woodridge III Second Filing. After the overlot grading has been completed, all disturbed areas, not in a roadway, should have temporary vegetation seed applied. After seeding, III a hay or straw mulch should be applied over the seed at a rate of 2 tons/acre (min. ) and the mulch should be adequately anchored, tacked, or crimped into the soil. After the utilities have been installed, the roadway IIIsurfaces should receive the pavement structure. III 5 III Sub-basin 18 incorporates The Gates at Woodridge Second Filing. After the overlot grading has been completed, III all disturbed areas, not in a roadway, should have temporary vegetation seed applied. After seeding, a hay or straw mulch should be applied over the seed at a rate of 2 tons/acre (min. ) and the mulch should be adequately III anchored, tacked, or crimped into the soil. After the utilities have been installed, the roadway surfaces should receive the pavement structure. After III installation of the curb inlets, the inlets should be filtered with a combination of concrete blocks, 1/2" wire screen and coarse gravel (3/4") . III All other disturbed areas should have temporary vegetation seed applied. After seeding, a hay or straw mulch should be applied over the seed at a rate of 2 III tons/acre (min. ) and the mulch should be adequately anchored, tacked, or crimped into the soil. In the event a portion of a roadway pavement surface and utilities III will not be constructed for an extended period of time after overlot grading, the temporary vegetation seed and mulch should also be applied to the roadway areas as I discussed above. III VI. CONCLUSIONS IIIA. Compliance with Standards All computations that have been completed within this report are in compliance with the City of Fort Collins III Erosion Control Reference Manual for Construction Sites and Storm Drainage Design Criteria Manual. In addition, all computations are in compliance with the III Preliminary/Master Drainage Study for Woodridge prepared by RBD in December 1991. III B. Drainage Concepts The proposed drainage concepts adequately provide for the transmission of developed on-site runoff to the existing III drainage devices at the eastern property line of the subject site. The proposed storm sewer system will collect the 100 year runoff generated within basin 18. Ill The storm sewer system will discharge into the proposed regional channel. The 100 year runoff from the site is proposed to be carried to the existing off-site regional detention pond by the series of, existing off-site III culverts, open channels and streets per the Preliminary/Master Drainage Study for the subject property. III III III III ,...0 , ...0 III The City of Fort Collins is currently studying the possible reconfiguration of the existing 42 inch culverts III at Webber Junior High School adjacent to Seneca Street. Depending on the outcome of this analysis, the existing 42 inch culverts may or may not be reconfigured. For this development, we have designed temporary swales and U extended the regional channel in order to deliver developed runoff from The Gates at Woodridge Second Filing and The Overlook at Woodridge Second Filing to the IIIexisting 42 inch culverts along the east property line. In addition to the 42 inch culvert study, the City of III Fort Collins is also evaluating the capacity of downstream existing improvements in regards to the new SWMM runoff flows which exceed the previously used downstream criteria. For The Gates at Woodridge and The III Overlook at Woodridge Second Filings, adequate downstream capacity in the culverts, open channels, and street systems exists to safely convey developed runoff to the loi existing Regional Detention Pond east of Regency Drive. Developed runoff from a portion of The Overlook at Woodridge Second Filing is planned to be transported in III the existing roadside ditch, along the north side of Harmony Road, east towards the City of Fort Collins existing Regional Detention Pond along Regency Drive. A III 42 inch culvert carries the flows under Regency Drive, into the existing channel and northerly to the existing regional detention pond. III At the time of construction, if for some unforeseen reason ground water is encountered during construction, a Colorado Department of Health Construction Dewatering IIIPermit would be required. C. Erosion Control Concepts IIIThe proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from The Gates at Woodridge Second Filing and The Overlook at III Woodridge Second Filing. Through the construction of the proposed erosion control concepts, the City of Fort Collins performance standards will be met. The proposed III erosion control concepts presented in this report and shown on the erosion control plan are in compliance with the City of Fort collins erosion control criteria. III I REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by 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 . Preliminary/Master Drainage Study for Woodridge by RBD, Inc. , 1111 Nil Engineering Consultants, December 27, 1991. 4 . The McClellands and Mail Creek Major Drainageway Plan by Cornell Consulting company, December 1980. 5. The Final Drainage Report for Regency Park P.U.D. by Parsons and Associates Consulting Engineers, March 30, 1987. 6. Preliminary Drainage Report for the 1990 Junior High School by RBD, Inc. , February 5, 1988 . 7 . Final Drainage Report for Poudre School District R-1 Elementary School by' Engineering Professionals, Inc. , April 1987 . !mg 011 1 III ill N