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HomeMy WebLinkAboutPINECONE PUD THE TOWER SHOPPES PRELIMINARY - 60 91L - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT'RELEM NARY DRAINAGE EROSION CONTROL STUDY TOWER SHOPPES P.U.D. CITY OF FORT COLLINS T,,,, 1 1 ooa P REFERENCES 1. Storm Drainage Design Criteria and Construction Standards, by the City of Fort Collins, Colorado, May 1984. 2. Erosion Control Reference Manual for Construction Sites, by the City of Fort Collins, Colorado, January 1991. 3. Urban Stormwater Quality Management Guidelines, prepared for the American Society of Civil Engineers, prepared by Wright Water Engineers, Inc., Denver, Colorado and Camp Dresser McKee, Orlando, Florida, 1991. 4. Overall Drainage Study for the Pinecone P.U.D., prepared by RBD, Inc.Engineering Consultants, June, 1992. 5. Final Drainage Report for the New Fort Collins High School, prepared by Meline & Irelan, Inc., November 1993. d VICINITY MAP 7 ` I DRAKE RD. } PROJECT SITE w J Iwu�I � 1' HORSETOOTH RD. J ci U w a I HARMONY RD. VICINITY MAP PRELEMI NARY DRAINAGE AND EROSION CONTROL STUDY TOWER SHOPPES P.U.D. CITY OF FORT COLLINS June 2, 1994 Prepared for: ' W. W. Reynolds Companies 1600 Specht Point Drive, Suite El Fort Collins, Colorado 80525 Prepared by: u RBD, Inc. Engineering Consultants 209 South Meldrum Street Fort Collins, Colorado 80521 (303) 482-5922 RBD Job No. 088-011 June 2, 1994 I Mr. Glen Schlueter City of Fort Collins Utility Services Stormwater I235 Mathews Street Fort Collins, Colorado 80522 I RE: Preliminary Drainage and Erosion Control Study for Tower Shoppes P.U.D. Dear Glen: We are pleased to resubmit to you, for your review and approval, this Preliminary Drainage and Erosion Control Study for Tower Shoppes 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 Prepared by: Reviewed by: i 4« �� - -- David K. Delaney, P. Kgvin W. Gingery, P.E. Design Engineer Water Resources Project Manager I I 1 1 1 TABLE OF CONTENTS DESCRIPTION I. GENERAL LOCATION AND DESCRIPTION I A. LOCATION B. DESCRIPTION OF.PROPERTY II. DRAINAGE BASINS AND SUB -BASINS A. MAJOR BASIN DESCRIPTION B. SUB -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 VII. CONCLUSIONS A. COMPLIANCE WITH STANDARDS I_DRAINAGE CONCEPT C. STORM WATER QUALIFY D. EROSION CONTROL CONCEPT REFERENCES APPENDIX VICINITY MAP HYDROLOGY EXCERPTS FROM FINAL DRAINAGE REPORT for NEW FORT COLLINS HIGH SCHOOL OVERFLOW CHANNEL AND INLET DESIGN CHARTS, TABLES, & FIGURES PAGE 1 1 1 N 2 2 3 3 3 3 4 4 5 5 5 5 lei 7 9 10 15 18 PRELIMINARY DRAINAGE AND EROSION CONTROL STUDY TOWER SHOPPES P.U.D. CITY OF FORT COLLINS I. GENERAL LOCATION AND DESCRIPTION A. Location The, Tower Shoppes project is located in the southeast part of Fort Collins. The project is bounded on the south by Horsetooth Road, on the west by Timberline Road, and on the north and east by the new Fort Collins High School currently under construction. The tract on which the project is located contains approximately 11.74 acres and will be developed into a commercial development. The project site is shown on the Vicinity Map in the Appendix. More particularly, the site is situated in the southwest quarter of Section 29, Township 7 North, Range 68 West of the 6th P.M., City of Fort Collins, Larimer County, Colorado. B. Description of Property The site of the Tower Shoppes P.U.D. is currently vacant land. Previous use for the site was agricultural. The existing site is presently open ground covered with native grasses with several abandoned irrigation trenches running in the east -west direction. Currently, the site topography is uniformly sloping toward the northeast corner at approximately 1.4%. An abandoned concrete irrigation diversion box is located in the southwest corner of the site. II. DRAINAGE BASINS AND SU -BASINS IA. Major Basin Description i The project site is located in the Foothills Drainage Basin and is included in the Overall Drainage Study for the Pinecone P.U.D. B. Sub -Basin Description Flows from the site, in a developed condition, were included as part of the drainage study for the adjacent New Fort Collins High School, as prepared by Meline & Irelan, Inc. A portion of that report and overall drainage map for the area is included in the Appendix. W Under the study by Meline & Irelan, Tower Shoppes development was split into two sub -basins. The western basin (approximately 6 acres) was assumed to flow in a northeasterly direction with 10 yr. flows intercepted by a curb inlet and carried by the school storm sewer system to detention areas located along the east edge of the school property. The 100 yr flows for this basin were to.be conveyed by an overflow channel between the school . and commercial buildings then overland sheet flow to the ponds: Flows from the eastern basin (approximately 7 acres) also flow in a northeast direction with 10 yr. flows intercepted and carried by the schools' system to detention ponds, and 100 yr. flows overflowing and conveyed by sheet flow to swales leading to the detention ponds. III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. The criteria established by the Final Drainage Report for the New Fort Collins High School, by Meline & Irelan, dated November, 1993, which includes requirements of the Pinecone Drainage Study will also be followed for this project. B. Development Criteria Reference and Constraints The criteria established by the Final Drainage Reportfor the New Fort Collins High School, prepared by Meline & Irelan, dated November, 1993, will be used for this site. As detailed in the drainage report for the school, the Tower Shoppes site was divided into basins #2 and #3 (west and east respectively, see portion of overall drainage map in appendix). Maximum anticipated developed 10 yr. runoff, as --detailed in the report to be intercepted and conveyed by the school system, for these basins respectively are 20.6 cfs and 23.9 cfs. - The report by Meline & Irelan addressed 100 yr. flows from the subject site as being conveyed by a combination of storm sewer, overflow channel, and overland sheet flow. Maximum anticipated developed 100 yr. flows from the entire site was 81 cfs. C. Hydrological Criteria The rational method was used to determine runoff peak flows from the site. The 10 and 100 year rainfall criteria, obtained from the City of Fort Collins, will be utilized. This criteria is included in the Appendix. OQ D. Hydraulic Criteria All calculations within this report have been prepared in accordance with the City of Fort Collins Storm Drainage Criteria. ,E. Variances from Criteria No variances from City of Fort Collins Storm Drainage Criteria are being sought at this time. M DRAINAGE FACILITY DESIGN A. General Concept All on -site developed flows for the Tower Shoppes site will be conveyed by parking lot sheet flow and gutter flow to two interception points along the northern side of the property. All 10 yr. flows from the site will be intercepted and carried by storm sewer to detention and 100 yr. flows will overflow the storm sewer system and overland flow to detention. No on -site detention is intended for the site. The developed runoff will be detained in a series of detention ponds located along the east boundary of the High School Property. Included in the back pocket of this report is the Tower Shoppes P.U.D Preliminary Grading & Drainage Plan. B. Specific Details Sub -basin Design Consistent with the F.C.H.S. drainage plan, the subject site is separated -into two drainage sub -basins. It is proposed that all on -site developed 10 yr. flows from these basins be collected by a series of area inlets which will tie into the school stormwater system at the designed locations. At a maximum ponding depth of 0.33 ft. all on -site developed flows in excess of the 10 yr. event will either enter ' a drainage channel or sheet flow to detention ponds on the school site. No off -site flows will enter the Tower Shoppes site. However, drainage basin #3 I of the F.C.H.S. drainage plan has been split into two sub -basins, basin #2 and basin #3, for this report (see included Preliminary Grading & Drainage Plan). Basin #3 includes offsite flows from the north half of Horsetooth Road, a portion ' of the high school South parking lot, and the school courtyard adjacent on the north. Although basin #3 flow is not from the subject site, it is combined with ' on -site flows to ensure conformance with the overall plan for the F.C.H.S. site. Roof Drain System and On -site Storm Drain System The Anchor Tenant building will have a roof drain system. The downspouts will be located along the back (east) side of the building and drain onto the parking lot pavement and in turn sheet flow to the area inlets of sub -basin #2. The remaining structures will have gutter systems which will drain onto the ground and overland flow to basin outlets. The proposed area inlets and storm drain piping will collect all surface runoff flows less than or equal to the 10 yr. storm. Flows in excess of the 10 yr. event will be conveyed overland to detention. There is no on -site detention intended at the inlets. The inlets and piping will be sized at final design. Existing Inlets There is an existing 12' curb inlet at the outlet of the overflow channel. This inlet is intended for collecting all 10 yr. flows and smaller for sub -basin #3 of this report. The inlet was not intended to take any flow from the subject tract. Existing Detention Pond The existing detention ponds along the east edge of the school site was sized in the Final Drainage Report for the New F.C.H.S. The developed flows calculated for the Tower Shoppes project are similar to the flows accounted for in the final design of these ponds. The pond size will be checked during final design. V. STORMWATER QUALITY A. General Concept It is anticipated that the. water quality of stormwater runoff will eventually be required to be addressed on all final design utility plans. For this preliminary study, we have considered the downstream impacts of the stormwater runoff. Stormwater which is released from the site will enter a permanent stormwater- - - detention pond. The detention pond will serve as a means of settling out suspended particles. VI. EROSION CONTROL A. General Concept The Tower Shoppes Commercial Development site lies. within the Moderate Rainfall Erodibility Zone, and within the Moderate Wind Erodibility Zone, per the City of Fort Collins zone maps. Because the existing site slopes generally at 1.4%, the potential exists for minor erosion problems during the construction phases of the project. S In accordance with the City of Fort Collins Erosion Control Reference Manual for Construction Sites, the erosion control performance standard will be calculated at the time of final design, and appropriate measures will be taken to control erosion from the site. VII. 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 conveyance and release of developed on -site flows into the existing storm drain system of -the adjacent F.C.H.S. Flows up to the 10 yr. event are collected and carried by an existing storm sewer system, and larger flows are conveyed overland to existing detention facilities on the adjacent school property. C. Storm Water Quality The developed flows will be directed toward the detention pond east of the F.C.H.S. Stormwater quality will be controlled by allowing pollutants to settle out in the detention pond. D. Erosion Control Concept At the time of final design, the erosion control performance standard will be calculated, and appropriate measures will be determined to control erosion from the site. The erosion control measures will be consistent with the City of Fort Collins Erosion Control`Reference Manual for Construction Sites. d