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HomeMy WebLinkAboutMIRAMONT VALLEY PUD - FINAL - 54-87AK - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND ERO�SION CONTROL STUDY FOR MIRAMONT VALLEY P.U.D. FORT COLLfNS, C�LORADO FINAL DRAINAGE AND ER6SION CONTROL STUDY FOR MIRAMONT VALLEY P.U.D. FORT COLLfNS, COLORADO March 18, 1996 Prepared for: Gary Nordic Miramont Associates 309 W. Harmony Road Fort Coilins, Colorado 80526 Prepared by: RBD, Inc. Engineering Consultants 209 South Meldrum Fort Colfins, Colorado 80521 (303) 482-5922 RBD Job No. 504-016 �� -� � � � � � � � � ��INC. Engineering Consultants 'q9 S. Meldrum Fr,i1 Collins, Colorado 80521 �70/4$2-5922 FAX: �7b/4��-6368 March 18, 1996 Mr. Basil Hamdan City of Fort Collins Utifity Services Stormwater 235 Mathews Fort Collins, Colorado 80522 RE: Final Drainage and Erosion Control Study � for Miramont Valley P.U.D. Dear Basil: � � � �� We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Study for Miramont Valley P.U.D. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. All comments made by the Stormwater Utility, to date, have been addressed. We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Respectfully, � RBD Inc. EnginE epared B . � rry . Ca ot � Pr "ect ngineer � � ng Consultants cc: Gary Nordic Dennis Donovan Reviewed by: (UNAVAILABLE) Kevin W. Gingery, P.E. Water Resources Project Manager H:IUSER\civlprojectslmiramont.val\drainage\mmvalley.rpt � Denver 303/458-5526 TABLE OF CONTENTS DESCRIPTION I. GENERAL LOCATION AND DESCRIPTION A. LOCATION B. DESCRIPTION OF PROPERTY II. DRAINAGE BASINS A. MAJOR BASIN DESCRIPTION III. DRAINAGE DESIGN CRITERfA A. REGULATIONS B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS C. HYDROLOGICAL CRITERIA D. HYDRAULIC CRITERIA E. VARIANCES FROM CRITERIA IV. DRAINAGE FACILITY DESIGN A. GENERAL CONCEPT B. SPECIFIC DETAILS V. STORM WATER QUALITY A. GENERAL CONCEPT °'i ;. EROSION CONTROL A. GENERAL CONCEPT B. SPECIFIC DETAIL �.��L CONCLUSIONS A. COMPLIANCE WITH STANDARDS B. DRAINAGE CONCEPT C. STORM WATER QUALITY D. EROSION CONTROL STANDARDS REFERENCES APPENDIX VICINIIY MAP SITE HYDROLOGY DESIGN OF INLETS AND SWALES PIPING DESIGN WATER QUALITY POND CACULATIONS EROSION CONTROL CALCULATIONS DRAINAGE AND EROSION CONTROL PLAN PAGE 1 1 1 1 1 2 2 2 2 2 2 3 3 3 4 4 4 4 5 5 5 5 5 6 � 1 3 13 31 44 58 BACK POCKET � � � � � � � I. � � � � � � � � II. � � � � FINAL DRAINAGE AND EROSION CONTROL STUDY FOR MIRAMONT VALLEY P.U.D. FORT COLLINS, COLORADO GENERAL LOCATION AND DESCRIPTION � � Location Miramont Valley P.U.D. (approximately 28 acres) is located in the southeast part of Fort Collins, bounded on the north by Miramont P.U.D. (previously known as Miramont P.U.D., Third Filing), the proposed Ramparts at Miramont P.U.D. and the proposed Miramont Village P.U.D. The entire P.U.D. is a part of the Oak/Cottonwood Farms Master Plan. The Upper Meadows at Miramont First and Second Filings, and Castleridge are northwest of this area. Miramont Valley can also be further described as being a part of Section 1, Township 6 North, Range 69 West of the 6th Principal Meridian, Larimer County, Colorado. Descr�tion of Propertv The area described as Miramont Valley P.U.D. is presently undeveloped and is being proposed as a 73 lot single family residential development. The property south of Mail Creek Irrigation Ditch is partially developed and partially native grassland. Topography south of the Mail Creek Irrigation Ditch is generally sloping from north to south at approximately 5%. DRAINAGE BASINS A. Ma�or Basin Description The area south of the Mail Creek Irrigation Ditch is part of the Mail Creek Major Drainage Basin and the Fossil Creek Major Drainage Basin, as shown on the Final Drainage and Erosion Control Plan in the back of this report. 1 . � Itl. ■ � ■ . � ■ � � � � ■ � � � � � � DRAINAGE DESIGN CRITERIA A. Regulations � C. � E. The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. Development Criteria Reference and Constraints The Overall Drainage Study for the Oak/Cottonwood Farms, prepared by RBD, Inc. May, 1992 criteria and constraints will be used in this Final Drainage Study. This Overall Drainage Study has been updated to reflect all changes made to the areas considered within the scope of that report, and was completed in conjunction with the final design of Miramont P.U.D. Miramont Valley P.U.D., located within the Fossil Creek Basin historically drains south to Mail Creek and Fossil Creek. To get to the Fossil Creek Basin, most the Valley area will drain to a water quality pond in the southeast portion of the property, which will then release into Mail Creek. A small portion of the property (Far West Roma Valley Drive) drains undetained in Mail Creek. Hvdrological Criteria The rational method was used to determine peak developed runoff from this site. The 2 year, and 100 year rainfall criteria, which was obtained from the City of Fort Collins, is the criteria used for this study. The rainfall criteria is included in the appendix. Hvdraulic Criteria All calculations within this report have been prepared in accordance with the City of Fort Collins Storm Drainage Criteria. Variances from Criteria No variances are anticipated at this time. 2 � � IV. � DRAINAGE FACILITY DESIGN A. General Conce�t Development within Miramont Valley P.U.D. will comply with the concepts � presented in the Miramont Phase 3 Preliminary Drainage Study, and with the concepts presented in the Overall Drainage Study for the Oak/Cottonwood Drainage Plan. The Mail Creek Basin and the Fossil Creek Basins allow for � undetained storm water runoff directly to Mail Creek and to Fossil Creek, although there will, in effect, be some detention in the water quality pond. A bank stabilization study was prepared for the City of Fort Collins for Mail � , Creek, and the recommendations put forth in that study have been complied with when allowing discharge into Mail Creek and Fossil Creek. � � L�.l �� � � �J � � � � , � � Taking into account the upstream flows from Miramont P.U.D. the Ramparts at Miramont P.U.D. and Miramont Village P.U.D., the peak undetained flows are 144.7 cfs and 68.4 cfs (for the 1Q0-yr storm) entering the water quality pond . There is also 20.9 cfs (for the 100-yr storm) discharging into Mail Creek in the far west portion of the property. These discharges, combined with 178 cfs from Mail Creek will give a total well below Mail Creek's maximum capacity of 1055 cfs. Specific Details Developed runoff from the areas south of the Mail Creek Irrigation Ditch, and those areas located in the Mail Creek Basin and the Fossil Creek Basin will be conveyed by curb and gutter, open channels, and storm sewer as required to reach Mail Creek. The preliminary plan for Miramont Phase 3 showed five separate points of discharge into Mail Creek/Fossil Creek, but we have narrowed this to two, with one being from the water quality pond. The western portion of Lemay Avenue, when developed, adjacent to this area will not be routed on site. Developed flows from Miramont P.U.D., the Ramparts at Miramont P.U.D., and Miramont Village P.U.D. enter the site from points along the north property line of Miramont Valley P.U.D. The first point, Highcastle Drive, allows upstream developed flows to pass directly into Miramont Valley, and then be captured in a curb inlet, which releases to the water quality pond. The second point, Belvedere Place will connect to the new Southridge Greens Boulevard and be captured in another curb inlet which also released to the water quality pond. Finally, the remainder of Miramont P.U.D., the Ramparts at Miramont P.U.D. and Miramont Village P.U.D. will also be routed into the water quality pond through storm sewers. For a more 3 � � � � � V. � � � � � � � "JI. � detailed diagram, please see the Drainage and Erosion Control Study in the back of this report. Within the Valley project, all basins with the exception of 410, 411, and 419 will be conveyed via curb and gutter street capacity to appropriate curb inlets, discharging into storm sewers, and eventually into the water quality pond. Basins 410, 411, and 419 drain undetained into Mail Creek. STORM WATER QUALITY A. General Concept Beginning in October of 1992, water quality of storm water runoff was required to be addressed on all final design. Miramont Valley P.U.D. development is anticipating construction beginning in the fall of 1996. Therefore for this study, we have sought to find various Best Management Practices for the treatment of storm water runoff which could be implemented in the final design process. When Miramont P.U.D. was approved, along with it were approved several erosion control practices dealing with offsite drainage. These erosion control practices, such as the silt berm along Mail Creek, will be applicable to the Valley development as well. A small water quality pond has been designed at the southeast end of Miramont Valley P.U.D. We have made our best attempts to route as much developed runoff as feasible through this pond. With the Miramont P.U.D. project, a protective siltation berm was installed along the northerly bank of Mail Creek to provide some water quality measure for silt and debris to settle out prior to flows entering Mail Creek. EROSION CONTROL A. General Concept � Miramont Valley P.U.D. development lies within the Moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility zone per the City of Fort Collins Zone maps. Per the City of Fort Collins Erosion Control Reference � Manual for Construction Sites, the erosion control performance standard was calculated to be 81.3%. The erosion control measures as specified on the Final Drainage and Erosion Control plan will allow for a performance � standard in excess of 94.64%. The performance standard after construction has been calculated to be 97.31 %. � � All construction activities must also comply with the State of Colorado � � � � � � � � � � � � v�i. � � � � � � �. � � i� permitting process for Stormwater Discharges associated with construction activities. A Colorado Department of Health NPDES permit will be required before any construction grading can begin. �pecific Detail This area is mostly undisturbed, but some of the northern portion was seeded during Miramont P.U.D. construction. However, when additional overlot grading needs to be done, all newly disturbed areas, shall have a hay or straw mulch shall be applied over the seed at a rate of 2 tons/acre, and the mulch shall be adequately anchored, tacked or crimped into the soil. It is not necessary that the lots be seeded if they are to be built on within 4 weeks of overlot grading. A silt fence shall be placed at the downhill side of the site, as shown on the Drainage and Erosion Control Plan. After the utilities have been installed, the roadway surfaces should receive the pavement structure. After installation of the curb inlets sidewalk culverts, they should be filtered with a combination of concrete blocks, '/2 inch wire screen, and 3/4 inch course gravel. All pipe entrances and swale outlets shall be protected by straw bale barriers as well. A copy of the Erosion control Security Deposit Obligation letter is included in the appendix of this report. CONCLUSIONS � � Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. Draina9e Concept The proposed drainage concepts presented in this study and shown on the final utility plans adequately provide for the conveyance of developed runoff from Miramont Valley P.U.D. The concepts shown here will also allow for the development to occur and be in compliance with the Fossil Creek Basin Master Plan, and the Mail Creek Basin Master Plan. This site will also be in compliance with the Overall Drainage plan for the Oak/Cottonwood Farm. 5 ■ � C. Storm Water Qualitx .Because Storm Water Quality has become a requirement, this site has _ catered to the need to address the storm water quality aspect. The open landscaped channels within this project and the existence of a siltation berm ■along the north side of Mail Creek Ditch will help control the water quality of - the developed runoff. The primary measure, however, is the installation of a water quality pond at the southeast property corner. � � D. Erosion Control Concept Per the City of Fort Collins Erosion Control Reference Manual for Construction sites, this project has met the recommended performance standard calculated. All measures taken to control erosion should be maintained as designed until final landscaping has taken hold. REFERENCES � 2 �3 Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1991, revised March 1994. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. McClellands Basin Master Drainage Plan, by Greenhorn and 0'Mara, Inc. 1986. 4. Overall Drainage Study for the Oak/Cottonwood Farm and Preliminary Drainage Study for the Upper Meadow at Miramont First Filing, Fort Collins, Colorado, by RBD, Inc., May 4, 1992. 5. Preliminary Drainage and Erosion Control Study for Miramont 3rd Phase P.U.D., by RBD, Inc. dated February 4, 1994. 0 5 . � ■ J ■ ■ � � � � � .. M �•.74H � 1- � VICINTITY MAP � � � � �� � � � V� �