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HomeMy WebLinkAboutSUMMERHILL PUD FINAL - 41 93A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTMAP APPENDIX 1 I I I I I I I I 11 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. 3. "Supplemental Drainage Report for Underhill P.U.D., Phase I" by Engineering Professionals, Inc., March 1982. 4. "Hydrologic Analysis and Final Hydraulic Design, West Prospect Road Drainage, Fort Collins, Colorado" by Lidstone & Anderson, Inc., February 1993 tl VI. CONCLUSIONS A. B. C. Q Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. Drainage Concept The proposed drainage concepts adequately provide for the transmission of developed on -site runoff to the retention pond south of the New Mercer Canal.The remainder of the site is adequately routed onto Prospect Drive per the concept Prospect Road Improvement Storm Drainage Study. STORM WATER (QUALITY Storm water quality aspects have been considered in the design of Summerhill P.U.D.. The retention pond south of the New Mercer Canal provides for the filtering of pollutants from a large portion of the site, while a low velocity drainage swale provides for filtering for the remainder of the site. Erosion Control Concept The 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 are in compliance with the City of Fort Collins erosion control criteria. IM Flows from the southwest portion of the site and from the area west of the site are directed to the retention basin south of the canal. The retention basin will be able to filter out any pollutants as water seeps away into the soil. 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 79.1% 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 shall 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 prior to beginning the overlot grading process. 5 what was planned for in the Prospect Road Improvement Storm Drainage Study. 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 to the end of the cul-de-sac. Here it enters a drainage swale to transport it across the existing bridge over the New Mercer Canal and into the existing retention pond south of the canal. Runoff from basin 7 enters the swale along the back property before flow crosses the canal. Basin 6 consists of the offsite drainage area which flows onto Underhill Drive from the west and is routed across the bridge along with flows from basins 4,5 and 7 in a drainage swale over the New Mercer Canal and into the retention pond. Basin 8 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 8 are to be retained in the existing pond south of the canal. This pond is temporary until improvements are built to accept the runoff. The retention pond was built with the Phase I construction of Underhill P.U.D., criteria for the sizing of the pond is included in the appendix. Flows entering the pond are essentially the same as they were with the Phase I Underhill design. Previous 100 year flows crossing the canal were 27.4 cfs, compared to flows calculated to be 25.0 for the Summerhill P.U.D.. V. STORM WATER QUALITY w A. General Concept Beginning in October of 1991, the water quality of storm water runoff was required to be addressed on all final design utility plans. The Summerhill P.U.D. has an anticipated construction date beginning in Fall of 1993. Therefore, water quality issues are being addressed in this report. B. Specific Details The north portion of the site drains onto Westbridge Drive and then onto Prespect Road. The drainage swale transporting the flow from the private streets is set at a relatively flat grade, which is ideal for water quality. The low velocities allow .the storm water to filter out polltants into the grass lined swale. Because of the importance of water quality, we are not proposing to construct concrete trickle pans along the swale. 1 4 i E. Variances from Criteria A variance is being sought for this project to allow for continued storm drain retention in the pond south of the channel. This is to be a temporary pond until the City completes planned drainage improvements in this area. IV. DRAINAGE FACILITY DESIGN IA. General Concept 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. 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, concentration points 1 and 2. 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. Flows above the capacity of the culvert will overtop the walk and sheetflow onto the street. 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 or onto Prospect Road. The flow on Westbridge Drive is then directed along the gutter onto Prospect Road, along with the runoff from Basins 1 and 2. This concept is consistent with 3 I 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 report entitled Hydrologic Analysis and Final Hydraulic Design, West Prospect Road Drainage" criteria and constraints are being utilized in this Final Drainage Study. Drainage criteria not specified in the report 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. 2 I 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 Property 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 the northeast two thirds of the site sloping from the southwest to the northeast towards Prospect Road at approximately 1.7%, while the remainder of the site slopes from the northeast to the southwest towards the New Mercer Canal at approximately 4.0%. 0 II. DRAINAGE BASINS A. Maior Basin Description The Summerhill P.U.D. lies within the Canal Importation Storm Drainage Basin. No major drainageway exists within the site. El 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 3 IV. DRAINAGE FACILITY DESIGN 3 A. GENERAL CONCEPT 3 B. SPECIFIC DETAILS 3 V. STORM WATER QUALITY 4 A. GENERAL CONCEPT 4 B. SPECIFIC DETAILS 4 VI. EROSION CONTROL 5 A. GENERAL CONCEPT 5 B. SPECIFIC DETAILS 5 VII. CONCLUSIONS 6 A. COMPLIANCE WITH STANDARDS 6 B. DRAINAGE CONCEPT 6 C. STORM WATER QUALITY 6 D. EROSION CONTROL CONCEPT 6 REFERENCES 7 APPENDIX VICINITY MAP 1 HYDROLOGY 2 RETENTION 7 DESIGN OF SWALES AND SIDEWALK CULVERTS 11 EROSION CONTROL 18 EXCERPTS FROM THE WEST PROSPECT ROAD DRAINAGE REPORT 26 CHARTS, FIGURES AND TABLES 33 INC. Engineering Consultants 209 S. Meldrum Fort Collins, Colorado 80521 303/482-5922 FAX:303/482-6368 September 7, 1993 5 Ms. Kate Malers City of Fort Collins Utility Services Stormwater 235 Mathews d Fort Collins, Colorado 80522 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, r 7 . 4 RBD Inc. Engine ring Consultants ° Tim J. ey ��tttttltuiuunNi�iyi Design Engineer :��o�NRppO R: ;;SlF�i� JOEN 7 �QOV�. o CooVnp �N1 : �`` 27362 Roger A. Curtiss P.E.9°F�• s c so~ Project Engineer Other Offices: Denver 303/458-5526 • Vail 303/476-6340 ,a FINAL DRAINAGE AND EROSION CONTROL STUDY FOR SUMMERHILL P.U.D. FORT COLLINS, COLORADO September 7, 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 FINAL DRAINAGE AND EROSION CONTROL STUDY FOR SUMMERHILL P.U.D. FORT COLLINS, COLORADO I I I i I i i i i 7 LJ ■ 0