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HomeMy WebLinkAboutPINECONE APARTMENTS AND NEIGHBORHOOD CONVENIENCE PUD FINAL - 60 91E - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE INECONE APARTMENTS P.U.D. FORT COLLINS, COLORADO 1 i VI. CONCLUSIONS A. Compliance with Standards All computations that have been completed within this report are. in compliance with the City of Fort Collins Erosion Control Reference Manual for Construction Sites and the Storm Drainage Design Criteria Manual. In addition, all computations are in compliance with the Overall Drainage Study for the Pinecone P.U.D. prepared by RBD, Inc. in June, 1992. B. Drainage Concept The proposed drainage concepts presented in this report and on the construction plans adequately provide for the transmission of developed on - site runoff to the interim regional channel section along the northerly boundary of the project site. The on -site detention pond will provide adequate storage requirements per the projections of the SWMM computer model, with an additional 1 foot of freeboard. An emergency overflow weir will also be constructed at the northeast corner of the pond. Peak release rates from the pond are below the maximums specified in the Overall Drainage Study for the Pinecone P.U.D. In addition, the peak flow rate for the 100-year design storm in the Fossil Creek Reservoir Inlet Ditch has not been projected to exceed 799 cfs. The interim channel section along the northerly boundary of the site will be improved to convey 100 cfs with additional capacity as freeboard. In addition, the Apartment finished floor elevations as established by the grading plan do allow for the future development of the Ultimate regional channel section. C. Erosion Control Concept The proposed erosion control concepts presented in this report adequately provide for the control of wind and rainfall erosion from the Pinecone Apartments site. Throughout the construction of the proposed erosion control implements, 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. A REFERENCES 1. Storm Drainage Design Criteeria and nuary 19 Construction Standards by the City of Fort Collins, Colorado, Revised 2. Erosion Control Refere 1 e Manual for Construction Sites by the City of Fort Collins, Colorado, January 199 3, Foothills Basin (Basin G) Drainage Master Plan, Fort Collins, Colorado, by Resource Consultants Inc. February 1981. 4. overall Drainage Study for the Pinecone P.U.D. Fort Collins, Colorado, by RBD, Inc., June 4, 1992. I, 7 FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE PINECONE APARTMENTS P.U.D. FORT COLLINS, COLORADO November 30, 1992 Prepared for: Client: The W.W. Reynolds Companies 4909 Pearl East Circle, Suite 300 Boulder, Colorado 80301 Prepared by: RBD, Inc. Engineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 (303) 226-4955 Engineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 303/226-4955 FAX:303/226-4971 November 30, 1992 Ms. Kathy Malers City of Fort Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 RE: Final Drainage and Erosion Control Study for the Pinecone Apartments P.U.D. Dear Kathy: We are pleased to submit to you, for your review and approval, this Final Drainage and Erosion Control Study for the Pinecone Apartments 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 Roger A. Curtiss, P.E. Project Engineer Other offices: Denver 303/453-5526 • Vail 303/476-6340 • Longinont 303/678-9584 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. SUBBASIN DESCRIPTION 2 III. DRAINAGE DESIGN CRITERIA 2 A. REGULATIONS 2 B. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS 2 C. HYDROLOGICAL CRITERIA 2 D. HYDRAULIC CRITERIA 3 E. VARIANCES FROM CRITERIA 3 IV. DRAINAGE FACILITY DESIGN 3 A. GENERAL CONCEPT 3 B. SPECIFIC DETAILS 3 V. EROSION CONTROL 5 A. GENERAL CONCEPT 5 B. SPECIFIC DETAILS 5 VI. CONCLUSIONS 6 A. COMPLIANCE WITH STANDARDS 6 B. DRAINAGE CONCEPT 6 C. EROSION CONTROL CONCEPT 6 REFERENCES 7 APPENDIX VICINITY MAP & PARTIAL SWMM SCHEMATIC 2 SITE HYDROLOGY 3 DETENTION POND 8 REVISIONS TO THE ORIGINAL SWMM MODEL 11 ORIGINAL SWMM MODEL INPUT DATA FILE 17 REVISED SWMM MODEL INPUT DATA FILE - 2 YEAR 22 REVISED SWMM MODEL INPUT DATA FILE - 100 YEAR 27 REVISED SWMM MODEL OUTPUT FILE - 32 2 YEAR (SUMMARY OUTPUT ONLY) REVISED SWMM MODEL OUTPUT FILE 40 100 YEAR (COMPLETE OUTPUT) DESIGN OF INLETS, STORM SEWER AND CHANNELS 76 RIPRAP DESIGN 89 EROSION CONTROL 92 CHARTS, TABLES AND FIGURES . 97 FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE PINECONE APARTMENTS P.U.D. FORT COLLINS, COLORADO GENERAL LOCATION AND DESCRIPTION A. Location The Pinecone Apartments are a part of the Pinecone P.U.D., located east of Timberline Road, 2000 feet north of Horsetooth Road and the proposed High School site, south of the Colorado State University Agronomy Research Center. Proposed Vermont Drive will border the project on the south, and proposed Pinecone Circle will border the site on the east. The site is shown on the excerpt of the Overall Drainage Study included in the appendix. More particularly, the project can be described as situate in the southwesterly portion of Section 29, Township 7 North, Range 68 West of the Sixth P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property The Pinecone Apartment site contains approximately 12.7 acres of land, more or less. A small portion in the southwest corner of the site will be used as Commercial site. The existing site contains a small farmstead, with several buildings surrounded by farm land to the south and east. The Foothills Regional Channel runs through the northwest corner and along the northerly boundary of the proposed site. The majority of the site slopes towards the east at approximately 1%. Several irrigation lines and a storm sewer pipe run through the north portion of the site. II. DRAINAGE BASINS A. Major Basin Description The Pinecone Apartments and the Pinecone P.U.D. lie within Reach 2 of the Foothills Basin (Basin G) Drainage Master Plan, by Resource Consultants " Inc. dated February, 1981. This project is also contained within the Overall Drainage Study for the Pinecone P.U.D., prepared by RBD, Inc. dated June 4, 1992. The Pinecone Apartment site is represented in the Foothills Basin SWMM model as Basin 61. This basin is drained by conveyance element 210, which is also the on -site detention facility. 1 B. Sub -basin Description The Pinecone site has been broken down into six sub -basins, 1, 2, 3, 4, 60,and 0-1. Subbasins 1,2,3 and 4 were originally modelled in Basin 61 of the Master plan. Subbasin 0-1 was originally a part of Basin 62 of the Master plan. The SWMM model has been corrected as a part of this report to include this area as a part of Basin 61. Subbasin 60 was also originally a part of Basin 61. The SWMM model was corrected to include this area as a part of Basin 60 of the Master plan. III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Drainage Design Criteria is being used for the subject site. B. Development Criteria Reference and Constraints The Overall Drainage Study for the Pinecone P.U.D., Fort Collins Colorado, and the Preliminary Drainage Study for the Pinecone Apartments, Fort Collins, Colorado., criteria and constraints are being utilized in this Final Drainage Study. Drainage criteria not specified in the Overall Drainage Study will be in accordance with the City of Fort Collins Storm Drainage Design Criteria and Construction Standards Manual. The Overall Drainage Study for the Pinecone P.U.D. recommends using on - site detention and using multiple release rates of not more than 14 cfs for the 2-year design storm, and 24 cfs for the 100-year design storm. It is also a requirement from the Overall Drainage Study that the ultimate peak 100- year flows in the Fossil Creek Reservoir inlet ditch not exceed 799 cfs. C. Hydrological Criteria The SWMM hydrological model was used in the Foothills Basin (Basin G) Drainage Master Plan. The SWMM model analyzed the developed flows within the basin with the ultimate developments in place. A copy of the original SWMM computer model was obtained from the City of Fort Collins Stormwater Utility, and was updated to include the final development criteria used in the Pinecone Apartments project. A copy of the original input data file as well as the revised input data files are included in the appendix of this report. E The Rational Method for determining surface runoff was used for this project site. The 2 year and 100 year storm event criteria, obtained by the City of Fort Collins, was used in calculating runoff values, and for sizing drainage structures. These calculations and criteria are included in the appendix of this report. D. Hydraulic Criteria All 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. E. Variances from Criteria No variances are being sought for the proposed project site. IV. DRAINAGE FACILITY DESIGN A. General Concept All on -site developed runoff from subbasins 1, 2, 3, 4, and 0-1 will flow to the east towards an on -site detention pond (Conveyance Element 210) located at the easterly corner of the site. Detained flows from this pond will be released to an interim regional channel section which flows from west to east along the northerly boundary of this project. Developed flows from subbasin 60 will not be detained and will sheet flow directly to the interim regional channel section. B. Specific Details Subbasin 1 is essentially the westerly half of the Apartment project. Developed flows from this subbasin will be directed towards the central parking area, and directed easterly to a series of metal sidewalk culverts. There flows will be directed easterly through subbasin 2 and on to the on - site detention pond provided. Berms will be constructed along the westerly edge of subbasin 1 to prevent flows from overtopping Timberline road and entering the Apartment site from the west. Subbasin 2 is essentially the easterly portion of the Apartment complex site. Flows from this basin will also be directed to the center parking are and transported easterly on the surface along with developed flows from subbasin 1 to the on -site detention pond. 3 Subbasin 3 contains the commercial convenience center, the northerly portion of Vermont Drive, and the northwesterly portion of Pinecone Circle up to the property limits. Developed flows from this subbasin will be by curb and gutter to a future curb inlet to be located in Pinecone Circle. With this development, Vermont Drive will only be built up past the second entry into the Apartment Development. The remainder of Vermont Drive and Pinecone Circle will be completed later. Developed flows from Timberline Road south of Vermont Drive and the south half of Vermont Drive will be routed through the proposed High School site, south of Pinecone Apartments. Subbasin 0-1 represents the flows that will be directed north and east to the Pinecone Apartments on -site detention pond. The area from this subbasin has been subtracted from Basin 62 of the SWMM model and included in the area of Basin 61. A complete calculation breakdown of the additions and modifications done to the original SWMM model can be found in the appendix. Subbasin 60 includes the easterly half of Timberline Road north of Vermont Drive and adjacent to this development, along with the area from the apartment complex to the regional channel section. This area has been added to the area of Basin 60 of the Master plan, and subtracted from the area of Basin 61. Basin 60, per the Overall Drainage Plan was free release to the Regional Channel. The Regional Channel section used for this development was sized to accommodate 100 cfs (calculations are included in the appendix). This is the capacity of the downstream interim regional channel section recently constructed. Ultimate flows in this channel when all development has occurred are projected to be approximately 450 cfs for the 100-year storm C event. The finished grading for the apartments accounts for the development of this future ultimate regional channel section. The on -site detention pond to be constructed for this site will contain approximately 1.1 acre-ft of storage (up to elevation 4926.5), with an additional 1 foot of freeboard. The required detention per the SWMM computer model is 1.0 acre-ft. Detained release from this pond will be by a multiple release structure, with a projected peak release for the 2-year design storm of 4 cfs and a projected peak release for the 100-year design storm of 21 cfs. This is below the maximum allowable release rates as specified in the Overall Drainage Study for the Pinecone P.U.D. (projections are from the SWMM computer model, included in the appendix). Additionally, the pond will also contain irrigation storage water for the proposed development, below the detention storage provided. 4 r. V EROSION CONTROL A. General Concept This development lies with the Moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. It is anticipated that the initial overlot grading of the site will occur during the c early part of 1993. The Erosion Control Performance Standard (PS) for the site was computed to be 78.1% per the City of Fort Collins Erosion Control Reference Manual for Construction Sites. The Effectiveness (EEF) of the proposed erosion control plan was calculated to be 79.3%. Therefore, the Erosion Control plan as detailed in this report meets the City of Fort Collins requirements. B. Specific Details Before overlot grading, the permanent detention pond shown in subbasin 4 shall be initially constructed such that it will function as a sediment trap for the improvements planned in subbasins 1, 2, 3, 4, and 0-1. The initial detention pond, for sediment collection, must contain at least 0.92 acre-ft of volume, an outlet pipe with a gravel filter, and an emergency spillway per the detail shown in the construction plans. Once the temporary vegetative seed and mulch, roadway asphalt and concrete have been installed, the detention pond can be converted into a final pond. After the overlot grading has been completed, all disturbed areas not in a roadway or building pad, shall have temporary vegetative seed applied per the specifications on the plans. After seeding, a hay or straw mulch shall be applied over the seed at a rate of 2 tons/acre minimum and the mulch should be adequately anchored, tacked, or crimped into the soil. After the utilities have been installed, the roadways and parking areas should receive the pavement structure. After installation of the curb inlets and metal sidewalk culverts, they shall be filtered with a combination of concrete blocks, 1/2" wire screen and course gravel, constructed according to the details in the construction plans. In the event that a portion of the road or parking lot pavements and utilities will not be constructed for an extended period of time after overlot grading, apply temporary vegetation seed and mulch to the pavement areas as discussed above. 5