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HomeMy WebLinkAboutSUMMERHILL PUD PRELIMINARY - 41 93 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTshall be adequately anchored, tacked or crimped into the soil per the methods shown on the Drainage and Erosion Control plan. After the utilities have been installed, the roadway surfaces should receive the pavement structure. The straw bale barriers should be installed in conjunction with the overlot grading process. VI. 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. B. Drainage Concept The proposed drainage concepts adequately provide for the transmission of developed on -site runoff to the detention pond south of the New Mercer Canal and then onto natural drainage patterns into the Larimer #2 Canal. The remainder of the site is adequately routed onto Prospect Drive per the concept of the Canal Importation Storm Drainage Basin Master Plan. C. Erosion Control Concept rThe proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from the Summerhill P.U.D.. Through the construction of the proposed .erosion control concepts, the City of Fort Collins performance standards will be met. The proposed erosion control concepts presented in this report and shown on the erosion control plan G are in compliance with the City of Fort Collins erosion control criteria. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984, Revised January 1992. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. 5 0 Basin 6 consists of the offsite drainage area which flows onto Underhill Drive from the west and is routed across the bridge over the New Mercer Canal and into the retention pond. Basin 7 consists of the area on the south side of the canal tributary to, and including, the retention pond. The runoff flows from basins 4 through 7 are currently retained in the existing pond south of the canal. This pond is temporary until improvements are built to accept the runoff. In keeping consistent with the City's policy of not allowing for retention, an area outlet is to be installed in the pond to allow for controlled release. The pond is to be able to store the difference of runoffs between the 100 year developed flow and the 2 year historic flow. Due to the runoff being so low for the 2 year historic storm, an orifice plate was designed to fit below the grate of the area inlet. This plate will control the release rate from the pond keeping it to the historic 2 year flow rate. The flow is released into the natural drainage patterns which flow to the south into the Larimer #2 Canal. EROSION CONTROL A. General Concept The Summerhill P.U.D. is in the High Rainfall and Moderate Wind Erodibility Zones per the City of Fort Collins zone maps. The potential exists for erosion problems during construction, and after construction until the disturbed ground is again vegetated. It is anticipated that construction will begin in the Fall of 1993, and be completed in the Spring of 1994. Per the City of Fort Collins Erosion Control Reference Manual for Construction Sites and related calculations in the appendix, the erosion. control performance standard for this site is 78.6%. From the calculations in the appendix, the effectiveness of the proposed erosion control plan is 80.3% during the construction portion of this development. Therefore the erosion control plan as specifically detailed below, will meet the City of Fort Collins requirements. B. Specific Details After the overlot grading has been completed, all disturbed areas, not in a roadway, shall have a temporary vegetation seed applied per the City of Fort Collins specification. After seeding, a hay or straw mulch shall be applied over the seed at a rate of 2 tons/acre, minimum, and the mulch 4 N 10 IV DRAINAGE FACILITY DESIGN A. General ConWt The Summerhill P.U.D. is planned as a multi -family residential housing development. The site will consist of 62 units. Storm water flows for the northeasterly portion of the site will be routed to Westbridge Drive and then onto Prospect Road. Flows from the southwesterly portion of the site will be routed onto Underhill Drive, and then across the New Mercer Canal into an existing retention pond on the south side of the canal. An area outlet will be installed in the pond to allow for outflow. Included in the back pocket of this report is the drainage plan for the Summerhill P.U.D.. B. Specific Details Basins 1 and 2 consist of the front half of the northeast lots and the adjacent private roadway. Flow is directed along the private road in a concrete trickle pan. Calculations for the capacity of the pan and roadway are included in the appendix. The basins join together at the low point in the northeast corner of the private road. Flow is to be directed across the street by a cross pan, and then into a grass lined swale. The cross slope of the street is to be transitioned in the area of the cross pan to allow for drainage. The grass lined swale is to outlet into a metal sidewalk culvert and onto Westbridge Drive. The culvert will not handle flows from a large storm, but is to be installed to keep low flows from flowing over the sidewalk and depositing sediment along the walk. Basin 3 consists of the rear portion of the lots of Basins 1 and 2, and all of Westbridge Drive. Flow from the rear of the lots is to sheetflow over the sidewalk onto Westbridge Drive. The flow is then directed along the gutter onto Prospect Road, along with the runoff from Basins 1 and 2. This concept is consistent with what was planned for in the Canal Importation Storm Drainage Basin Master Plan. Basins 4 and 5 consist of the southwest portion of the site. Flows are directed along the gutters or along the rear of the lots onto Underhill Drive. Flow is then to be directed along Underhill across the existing bridge over the New Mercer Canal and into the existing retention pond south of the canal. 3 B. Sub -Basin Description Historic drainage patterns of the subject site are two thirds of the site draining northeasterly across the site onto Prospect Road. The remaining third of the site currently drains southwesterly into the New Mercer Canal. 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 Canal Importation Storm Drainage Basin Master Plan criteria and constraints are being utilized in this Final Drainage Study. Drainage criteria not specified in the Canal Importation Drainage Basin Master Plan will be in accordance with the City of Fort Collins Storm Drainage Design Criteria and Construction Manual. C. Hydrological Criteria The Rational method is being used to determine runoff peak flows from the site and surrounding off -site tributary areas. The 2 and 100 year rainfall criteria, which was obtained from the City of Fort Collins, is the criteria which was utilized. The criteria is included in the appendix. D. Hydraulic Criteria All calculations within this study have been prepared in accordance with the City of Fort Collins Drainage Criteria. E. Variances from Criteria No variances are being sought for this project. 1 2 A °9 40 FINAL DRAINAGE AND EROSION CONTROL STUDY FOR SUMMERHILL P.U.D. FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location The Summerhill P.U.D. development is located in the southwest part of Fort Collins, on the south side of Prospect Road, between Taft Hill Road and Shields Street. A vicinity map of the proposed site is included in the appendix. More particularly, the site is situated in the east half of the northwest quarter of Section 22, Township 7 North, Range 69 West of the 6th P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Propert The Summerhill P.U.D. contains 5.28 acres more or less. The area is currently undeveloped and is being proposed for multi -family residential construction with 62 units. The site currently consists of pasture. The New Mercer Canal flows in the west to east direction immediately south of the site. Topography for the site has two thirds sloping from the southwest to the northeast at approximately 1.7%, while the remainder of the site slopes from the northeast to the southwest at approximately 4.0%. II. DRAINAGE BASINS A. Major Basin Description The Summerhill P.U.D. lies within the Canal Importation Storm Drainage Basin. No major drainageway exists within the site. I I TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION 1 A. LOCATION 1 B. DESCRIPTION OF PROPERTY 1 II. DRAINAGE 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 2 D. HYDRAULIC CRITERIA 2 E. VARIANCES FROM CRITERIA 2 IV. DRAINAGE FACILITY DESIGN 3 A. GENERAL CONCEPT 3 B. SPECIFIC DETAILS 3 V. EROSION CONTROL 4 A. GENERAL CONCEPT 4 B. SPECIFIC DETAILS 4 VI. CONCLUSIONS 5 A. COMPLIANCE WITH STANDARDS 5 B. DRAINAGE CONCEPT 5 C. EROSION CONTROL CONCEPT 5 REFERENCES 5 APPENDIX VICINITY MAP 1 HYDROLOGY 2 DETENTION 7 DESIGN OF SWALES AND SIDEWALK CULVERTS 11 EROSION CONTROL 14 CHARTS, FIGURES AND TABLES 20 INC. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 303/482-5922 FAX:303/482-6368 July 6, 1993 Ms. Kate Malers City of Fort Collins Utility Services Stormwater 235 Mathews !!� Fort Collins, Colorado 80522 1 RE: Final Drainage and Erosion Control Study for Summerhill P.U.D. Dear Kate: We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Study for Summerhill P.U.D.. 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 1 Zi Bailey Design Engineer Other Offices: Denver 303/458-5526 • Vail 303/476-6340 3 a FINAL DRAINAGE AND EROSION CONTROL STUDY FOR SL7vB ERHILLP.U.D. FORT COLLINS, COLORADO July 6, 1993 Prepared for: Mel Price 2400 Vajobi Court Fort Collins, Colorado 80526 Prepared by: RBD, Inc. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 (303) 482-5922 RBD Job No. 506-001 I I A I I I I I I I I I I I I r I i i FINAL DRAINAGE AND :OSION CONTROL STUDY FOR SUM IERHILLP.U.D. FORT COLLINS, COLORADO