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Home My WebLink AboutMIRAMONT VILLAGE PUD - FINAL - 54-87AJ - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL STUDY FOR HE MIRAMONT VILLAGE P.U.D. FORT COLLINS, COLORADO FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE MIRAMONT VILLAGE P.U.D. FORT COLLINS, COLORADO March 18, 1996 Prepared for: James Company 2919 Vaimont Road, Suite 109 Boulder, Colorado 80301 Prepared by: RBD, inc. Engineering Consultants 209 South Meldrum Fort Collins, Colorado 80521 (970) 482-5922 RBD Job No. 607-008 �� ' � � � � ��ir�c. Engineering Consultarats .'il9 S. Meldrum Fnrt Collins, Colorado 805�1 ' , %0/482-5922 °, � �70/48?-F3f, ; March 1 �, 1996 � Mr. Basil Hamdan City of Fort CQilins Utility �ervices Stormwater � 23� IVlafihews Fort G�Ilins, �Coloradr� 80522 � RE: Finaf Drain�ge an�d Er�sion Gontrol 5fiuc�y ��or Miramont Village P.U.D. � � � � � � �� Dear B�sil�. VJe are pie�se� to submit to you, far your review and approval, this Fina{ Drainage anc! Erosion Contrcl Study for Miramont Village P.U.D. All computations within this repo�t have been completed in com�liance with the City of Fort Coliins Storm Drai�age Design Criteria �/Ve aopreciate your tirr�e and consideration in reviewing this submittal. Please call if you have any questior�s. Respectfully, RBD Inc. Engineering Consultants Prepar��i By: ' �' i , � � �;��! °�,� _ • ,,i',� / l - i. ._ - Patricia Kroetc� Project Engineer Reviewed by: (UNAVAILABLE) David K. Thaemert, P.E. Water Resources Project Engineer � 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 CRITERIA 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 VI. EROSION CONTROL A. GENERAL CONCEPT B. SPECIFIC DETAILS VII. CONCLUSIONS A. COMPLIANCE WITH STANDARDS B. DRAINAGE CONCEPT C. STORM WATER QUALITY CONCEPT D. EROSION CONTROL CONCEPT REFERENCES APPENDIX VICINITY MAP SITE HYDROLOGY DESIGN OF INLETS AND OVERFLOW SWALE STORM PIPE SIZING EROSION CONTROL CALCULATIONS CHARTS, TABLES, AND FIGURES PAGE 1 1 1 1 1 2 2 2 2 2 2 3 3 3 �� 5 5 5 5 5 6 6 6 7 1 3 9 15 � � � � � I. � FINAL DRAINAGE AND EROSION CONTROL STUDY FOR MlRAMONT VILLAGE, P.U.D. FORT COLLINS, COLORADO GENERAL LOCATION AND DESCRIPTION , A. Location � Miramont Village P.U.D. (approximately 10.79 acres) is located in the southeast part of Fort Collins, bounded on the north by The Ramparts at Miramont P.U.D., by Fossil Creek on the south, and on the east by Lemay � Avenue. The entire P.U.D. is a part of the OaWCottonwood Farms Master Plan. The Upper Meadows at Miramont First and Second Filings, and Castleridge are northwest of this area and The Ramparts at Miramont is � directly north of this site. Miramont Village 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. � B. Description of PropertX � The area described as Miramont Village P.U.D. is presently undeveloped and is open ground covered with native grasses. The property is generally sloping from north to south at approximately 5%. Runoff historically sheet � flows to the south and into Fossil Creek. This site is being proposed as a 52 lot residential development. � II. � DRAINAGE BASINS A. Major Basin Description � The project site is located in the Fossil Creek Drainage Basin and is described in the report Fossil Creek Drainaqe Basin Master Drainaqewav PlannincLStudy, prepared by Simons, Li & Associates, Inc., 1982 and is � further described in the Overall Drainage Study for the Oak/Cottonwood Farms, prepared by RBD, Inc. May, 1992 and revised January, 1995. � � �' � � � III. � .� � � � �� LI � � � � � � � � � � � � DRAINAGE DESIGN CRITERIA A. Regulations � C. 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 (Revised January 1995) criteria and constraints will be used in this Final Drainage and Erosion Control 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 Village P.U.D., located within the Fossil Creek Basin historically drains south to Fossil Creek. The Miramont Village area will drain undetained into a water quality structure and then into Fossil Creek which lies south of this property. Hydrological Criteria The rational method was used to determine developed runoff from this site. The 2 year, and 100 year rainfall criteria, which was obtained from the City of Fort Collins, were used in calculating runoff values for this study. These calculations and rainfall criteria are included in the appendix. D. Hydraulic Criteria All hydraulic calculations within this report have been prepared in accordance with the City of Fort Collins Storm Drainage Criteria and are included in the Appendix. E. Variances from Criteria No variances from City of Fort Collins Storm Drainage Criteria are being sought for this project. 2 � � � � � � � � � � � � � IV. DRAINAGE FACILITY DESIGN � � Generai Concept Development within Miramont Village P.U.D. will comply with the concepts presented in the Fossil Creek Drainage Basin Master Drainageway Planning Study and 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. The proposed drainage and grading plan is included in the back pocket of this report. Specific Details This site has been broken into six on-site drainage basins and four off-site basins. The off-site basins 0-1 through O-4 are an area of the Ramparts at Miramont that will sheet flow south and onto the Miramont Village site. Runoff from basin 0-3 joins the flow from on-site basin 1 and will flow into an 8 foot curb inlet (Inlet 10). Runoff from basin 2 will flow via curb and gutter to Inlet 20 (6' type R). Runoff from basin 3 flows via curb and gutter Inlet 30 (8' type R) and drainage from basin 4 flows into a 6 foot curb inlet (Inlet 40). Runoff from basins O-2, 0-4, and 5 combine and flow via curb and gutter into inlet 50 which is a 16 foot curb inlet. The combined runoff from all of the basins flow via storm pipe to the south and into an existing curb inlet (designed with the Miramont Valley, P.U.D. project) in Southridge Greens Boulevard. See the Appendix for inlet and storm pipe sizing calculations. Inlets 10 through 50 have been sized to accept all of the runoff from the 2 � year storm and a majority of the runoff from the 100 year storm (see Appendix). Flow from the 100 year storm will pond at the inlet and at inlets � 10 through 40 the ponding depth is less than 6". At inlet 50 the ponding depth is 8.5" which exceeds the depth of the curb and gutter. The water will pond in the open space to the north of the inlet and in the street to the south � of the inlet. Inlets 10 through 40 will have an emergency overflow swale in the open space to the south of each street. Both swales have been sized to accept the 100 year flow in the unlikely event of both inlets being 100 � percent clogged (see the Appendix for swale calculations). In the event that inlet 50 becomes clogged, the flow will overtop the high point in the entrance and flow to the inlet in Southridge Greens Boulevard. � � � Runoff from basin 6 sheet flows onto Southridge Greens Boulevard and is collected in the curb and gutter and is then conveyed into the existing curb inlet in Southridge Greens Boulevard. This inlet will be the collection point 3 � � � � � �J for the on-site runoff and the flows from Southridge Greens Boulevard. From this point, a storm pipe will convey this water to the southwest into a proposed water quality pond. Pollutants will be allowed to settle out and the storm water will be released directly into Fossil Creek. Some of the runoff from the Ramparts at Miramont (2.11 cfs) will flow over the proposed retaining wall at the northerly boundary of this site. Flow depth over the wall was calculated to be 0.2" (see Appendix). This amount of flow was determined to have no erosion impact on the retaining wall footing and no erosion remediation is proposed. � , Flows from Lemay Avenue have been accounted for in the Final Drainage and Erosion Control Study for Lemay Avenue Improvements by RBD, Inc. in � May, 1995. Flows in Southridge Greens Boulevard are accounted for in the Final Drainage and Erosion Control Study for Miramont Valley, P.U.D. by RBD, Inc. currently under review at the City. � V. STORM WATER QUALITY � L.�! L� � � � �_I � � � A. General Concept The Miramont Village development is anticipating construction beginning in the fall of 1996. Best Management Practices for the treatment of storm water runoff have been incorporated into the design for this project. The BMP's included in the erosion control plan for this site are installation of silt fence and gravel inlet filters during construction. Also included is a water quality pond that is being designed and will be constructed with the Miramont Valley, P.U.D. Runoff from the Miramont Village site will be routed to this pond via the storm sewer system in Southridge Greens Boulevard. This pond will provide a mechanism for pollutants to settle out of the storm water runoff prior to being released into Fossil Creek. All construction aetivities must comply with the State of Colorado permitting process for Storm water Discharges Associated with Construction Activity. A Colorado Department of Health NPDES Permit will be required before any construction grading can begin. � � � � VI. � � � � � � � � � � � � VII. � � � � � EROSION CONTROL A. �� General Conce�t The Miramont Village Site is in the Moderate 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 revegetated or paved. It is anticipated that construction will begin in June of 1996. �ecific Details Erosion control for this site during construction includes gravel filters for all of the inlets on the site and silt fence to be installed along the downstream perimeter of the site. All areas that remain disturbed for more than four weeks will require seeding and mulching to prevent excess erosion. During the four week period, disturbed areas shall be roughened. After construction, the streets will have a paved surface and the individual units will be constructed. The open areas and the yards of the units will be seeded or sodded to reduce the erosion potential. Calculations for erosion control performance standards were completed per the City of Fort Collins Erosion Control Reference Manual for Construction Sites and are included in the appendix. The erosion control perFormance standard for this site during construction is 82.5%. The effectiveness of the proposed erosion control plan during construction is 82.7%. The erosion control performance standard after construction was calculated to be 97.1 %.The effectiveness of the proposed erosion control plan after construction is 97.5%. Therefore, the erosion control plan will meet the City of Fort Collins criteria. CONCLUSIONS A. Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Erosion Control Reference Manual for Construction Sites and the Storm Drainage Design Criteria Manual. 5 � � B. � � � � � � � � � �I � � � � �,� � � � Drainage Concept C. � 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 Village P.U.D. The combination of on-site street capacities and the on-site storm sewer system will provide for the developed flows to reach the proposed off-site water quality pond. This pond is being designed and constructed to account for flows generated by the Miramont Village site. The concepts shown here will also allow for the development to occur and be in compliance with the Fossil Creek Basin Master Plan. This site will also be in compliance with the Overall Drainage plan for the Oak/Cottonwood Farm. If groundwater is encountered at the time of construction, a Colorado Department of Health Construction Dewatering Permit will be required. Storm Water Quality Concept Because storm water quality has become a requirement, the proposed design has addressed this storm water aspect. Water from this site will be routed to a grass-lined water quality pond which will provide an opportunity for storm water pollutants to filter out of the storm water runoff before the runoff flows into Fossil Creek. Erosion Control Concept The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from Miramont Village. Through the construction of the proposed erosion control concepts, the City of Fort Collins performance standard 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. � � � � �� VICINITY MAP � rooTM ROA� W � > � a W G' W J J � U ��V� phKR1DGE DRIVE w � i < } < F,�. � \rG5' _ SpUT1-iRiDGE FpS� �E� � PORTNER RES VICINITY MAP SCALE: 1 "=2000' H:,RAAONY ROAD PROJECT SITE �