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HomeMy WebLinkAboutPINECONE APARTMENTS AND NEIGHBORHOOD CONVENIENCE PUD PRELIMINARY - 60 91C - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT1P PRELIMINARY DRAINAGE STUDY FOR THE PINECONE APARTMENTS FORT COLLINS, COLORADO FIGURE I. GENERAL. LOCATION MAP •\•. � �"^�� Fb�s � °:hid OF THE �� �F r FOOTHILLS BASIN NORTH Vine Dr �` x SCALEI°=6000 v1 PRELIMINARY DRAINAGE STUDY FOR THE PINECONE APARTMENTS FORT COLLINS, COLORADO March 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 RBD Job No. 088-004 I NC. Engineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 303/226-4955 FAX:303/226-4971 March 30, 1992 Ms. Susan Hayes City of Fort. Collins Utility Services Stormwater 235 Mathews Fort Collins, Colorado 80522 RE: Preliminary Drainage Study for the Pinecone Apartments Dear Susan: We are pleased to submit to you, for your review and approval, this Preliminary Drainage Study ,for the Pinecone Apartments. 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 J lle K. Ohms, P.E. P 'ect Engineer Kevin W. Gingery, P.E. Project Manager Other offices: Denver 303/778-7338 • Vail 303/476-6340 • Longmont 303/678-9584 TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION A. LOCATION 1 B. DESCRIPTION OF PROPERTY I II. DRAINAGE BASINS A. MAJOR BASIN DESCRIPTION 1 B. SUB -BASIN DESCRIPTION 2 III. DRAINAGE DESIGN CRITERIA 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 A. GENERAL CONCEPT 3 B. SPECIFIC DETAILS 3 V. EROSION CONTROL A. GENERAL CONCEPT 4 VI. CONCLUSIONS A. COMPLIANCE WITH STANDARDS 5 B. DRAINAGE CONCEPT 5 ' REFERENCES 5 APPENDIX VICINITY MAP 1 HYDROLOGY 2 DETENTION 8 INLET & STREET CAPACITY 12 REGIONAL CHANNEL 15 PRELIMINARY DRAINAGE STUDY FOR THE PINECONE APARTMENTS FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location The, Pinecone Apartments are a part of the Pinecone P.U.D., located east of Timberline Road and north of Horsetooth Road, in the southeast part of Fort Collins, Colorado. The site is bounded on the north by the Colorado State University Agronomy Research Center, on the west by Timberline Road, and on the south by a proposed street named Vermont. The site is shown on the Vicinity Map in the Appendix. More particularly, the site is situated 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 PrORert The Pinecone Apartments site contains 12.7 acres of land, more or less. The existing site contains a small j 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 edge of the subject site. The majority of the site slopes toward the east. Several irrigation lines run through the north portion of the site. II. DRAINAGE BASINS A. Maior Basin Description The Pinecone Apartments and the Pinecone P.U.D. lie within Reach 2 of the Foothills Basin, per the Foothills Basin (Basin G) Drainage Master Plan, by Resource Consultants Inc. dated February, 1981. The Foothills Channel, for the Foothills Basin, traverses through the northern portion of the Pinecone P.U.D. The Foothills Basin Drainage Master Plan indicates that the ultimate Foothills Regional Channel may possibly include an improved open channel along with a 24" storm sewer system, as shown in the Appendix, on page 16. Other possible channel configurations are under consideration. Since the channel will have constant flows, the final design will incorporate conveyance of low flows. Additional information concerning the Foothills Regional Channel is contained within the Master Drainage Study for the Pinecone P.U.D., prepared by R.B.D., Inc., dated March 2, 1992. B. Sub -Basin Descrivtion As described above, the historic drainage pattern for the subject site is generally toward the east. Upstream offsite flows from west of Timberline Road enter the site through three 54" CMP's crossing under Timberline Road. These three pipes outlet directly into the Foothills Channel, with the discharge capacity of the pipes presently limited to 100 cfs. There is no offsite runoff contribution from the north or the south of the Pinecone P.U.D. III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being followed for the subject site. As was mentioned in the Master Drainage Study for the Pinecone P.U.D., the drainage design for the Pinecone Apartments proposes to incorporate a deviation, explained below, from the Foothills Basin Drainage Master Plan. B. Development Criteria Reference and Constraints The Pinecone P.U.D. Master Drainage Study follows the Foothills Basin Drainage Master Plan criteria and constraints for Reach 2. The drainage design for the Pinecone Apartments will remain consistent with the direction set by the Pinecone P.U.D. Master Drainage Study. The previously mentioned deviation from the Foothills Basin Master Plan involves the relative sizes of the four detention ponds within the Pinecone P.U.D. Pond 210 of the Pinecone P.U.D. Master Plan is within the subject site. The Foothills Basin Master Plan provided for detention in Pond 210 for runoff from areas to the north and south of the proposed Vermont Street. The Pinecone Apartments front on the north side of Vermont Street. As e proposed in the Master Drainage Study for Pinecone P.U.D., Pond 210 will detain flows only from the aY> apartment area, and no additional flows from the area south of the proposed Vermont Street. The preliminary 2 drainage design uses the release rates for Pond 210 as outlined in the Pinecone P.U.D. Master Drainage Study. C. Hydrological Criteria The initial and major storm return periods are 2-year and 100-year, respectively. Although the site will include some business land use in the form of a neighborhood convenience shop, the majority of the site will be used for residential purposes. The Rational Method is used to compute the runoff for the various design points within the subject site. The analysis methods used are consistent with the City of Fort Collins Storm Drainage Criteria. The hydrological calculations are located in the appendix. D. Hydraulic Criteria All calculations within this study have been prepared in accordance with the City of.Fort Collins Storm Drainage Criteria. Calculations for detention sizing are located in the appendix. E. Variances from Criteria No variances are being sought for the Pinecone Apartments site. IV. DRAINAGE FACILITY DESIGN A. General Concept All flows from the Pinecone Apartments will drain toward the east, into the onsite detention pond. The north half of the bordering street, Vermont, plus both sides of the bordering street on the east side will also drain into this detention pond. The detention pond will release into the Foothills Regional Channel. The preliminary design excludes any flows from Timberline from entering the sub -basin via the intersection of Vermont Street with Timberline. A crosspan at the intersection is shown on the Preliminary Drainage Plan. B. specific Details The apartments and bordering streets on the south and east are divided into four sub -basins. These sub -basins are shown on the Preliminary Drainage Plan, included in the back pocket. The very northwest corner of the site is not included in the drainage analysis for the apartment area. This corner will probably drain directly into the Foothills Channel, and does not affect the rest of the site. The existing Foothills Channel to the east of Timberline Road, is a temporary channel, as stated in the Pinecone P.U.D. Master Drainage Study. This channel was developed to carry 100 cfs of stormwater runoff. The proposed construction of the apartments will necessitate relocating the channel. All reaches of this temporary channel will eventually be upgraded to its ultimate capacity of 430 cfs, and will be called the Foothills Regional Channel. A portion of the regional channel will lie wholly within the subject site, in the northwest corner. To the east, along the northern boundary of the site, only the south 1/2 of the regional channel right-of-way is within the site. Although the regional channel right-of-way is only partially contained within the subject site, the full channel section will be constructed along the north side of the site, in conjunction with the construction of the Pinecone Apartments. The channel construction would start at the west property line, continue along the north side of the subject site, and end at the eastern side of the subject site. The full design, to carry the ultimate capacity of the regional channel, will be done during final design. Since the existing channel carries 100 cfs, the developer is responsible for constructing a relocated channel with an equal capacity. The City's requirement to construct a channel with a capacity of 430 cfs is considered an oversizing. Therefore, the channel construction will be eligible for reimbursement by the City of Fort Collins, due to over -sizing. The reimbursement would be limited to the extent that the regional channel, with 430 cfs capacity, exceeds the capacity of the historic channel, i.e., 100 cfs. The proposed streets bordering the apartments on the south and east have adequate capacity for the 100-year runoff. Several existing irrigation lines cross through the subject site, and will need to be relocated around the site. The actual relocations will be determined during final design. 4 V. EROSION CONTROL A. General Concept The Pinecone Apartments site lies within the Moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. At the time of final design, the erosion control performance standard will be calculated, and appropriate measures will be taken to control erosion form the site. This is in accordance with the City of Fort Collins Erosion Control Reference Manual for Construction Sites. 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 onsite runoff into a detention facility, then release into what will become the Foothills Regional Channel. The proposed curb inlets and storm sewer system will convey the 2-year runoff into the proposed detention facility. At the design points, the 100-year stormwater runoff will be conveyed via swales, where the 100-year flows will exceed the capacity of the proposed inlets. The proposed streets adjacent to the subject site will have adequate capacity to carry the 100-year runoff. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. 2. Foothills Basin (Basin G) Drainage Master Plan, Fort Collins, Colorado, by Resource Consultants Inc., February 1981. 3. Master Drainage Study for the Pinecone P.U.D., Fort Collins, Colorado, by RBD, Inc., March 2, 1992. 5