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HomeMy WebLinkAboutMCCLELLAND OFFICE PARK II - PDP - 54-98 - REPORTS - DRAINAGE REPORTMCCLELLAND OFFICE PARK VICINITY.MAP FD,R"ONO RD.L OR ART';i v0I. GILGALAD WT I RUTS Q AV. 9 DUKE d2. MIRRORMERE CIR> ). BUDDING LEAFOR a 3a. CHETWOOD DR. y .� pRHELL AV.v,o-4 YAI E C4MBRIDGEa' L LT CT u ENS �+u{RINCE8:PRINCE �N AY OR 'wu a = RD. w E. a DRAKE r gWAGONWHE L DR Ot: � W =` ...., e..� IWINCHE T� R R. mu R. 0 H(ATHER ' - wr m o e N itTHUNDERBIRO W, 1 CT. r DR %C s a ¢ � a a w PKWY. 'Site -1 4 -ip tt,,�� �TjrIPP^`i AN •w ORIFT io 1 Z zl�AfiBOR \AV. 0W> iWY. o �.. E S4 O. 'uwi SAI I! ne �I C�B NI AV. REGER. A, I�e.9 00 % RGJNO i 'PON4 Q.%V' I J Z \ OR Sd NOSP r DEN-yI 2. vJ a �{ BOWII Z PLE: AV. N -�3n p W M y ALBION Y. c RD 0 04RDWA K VUO0`: ��! WARREN umi r S R. R tp 1' 2000' pollutants to filter out of the stormwater runoff before the runoff is conveyed off - site. The inlet with the permanent water quality feature will be regularly cleaned and maintained by the property owners. The cleaning schedule will be determined by the final submittal. D. Erosion Control Concept The proposed erosion control concepts adequately provide for the control of wind and rainfall erosion from the McClelland Office Park II. 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. VIII. REFERENCES 1. Storm Drainage Design Criteria and Construction Standards by the City of Fort Collins, Colorado, May 1984, interim revision January 1997. 2. Erosion Control Reference Manual for Construction Sites by the City of Fort Collins, Colorado, January 1991. 3. Final Drainage and Erosion Control Study for the McClelland Office Park PUD, RBD INC., May 4, 1984. VII. Those roads that are to be paved as part of the McClelland Office Park II project must have a 1-inch layer of gravel mulch (1/4-11/2" gravel) applied at a rate of at least 135 tons/acre immediately after overlot grading is completed. The pavement structure shall be applied as soon as possible after the utilities have been installed. If the disturbed areas will not be built on within one growing season, a permanent seed shall be applied. After seeding, a hay or straw mulch shall be applied over the seed at a minimum rate of 2 tons/acre, and the mulch shall be adequately anchored, tacked or crimped into the soil. In the event a portion of the roadway pavement surface and utilities will not be constructed for an extended period of time after overlot grading, a temporary vegetation seed and mulch shall also be applied to the roadway areas as discussed above. All construction activities must also comply with the State of Colorado permitting process for Stormwater Discharges Associated with Construction Activity. 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. 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 existing drainage facilities on the subject site. The existing drainage system only has the capacity to convey the 2-year developed flows off of the site; however, in a 100-year event, the parking area has the capacity to contain the 100-year developed flows from Basin 1 while maintaining the 2-year historic release rate. If, at the time of construction for some unforeseen reason, groundwater is encountered, a Colorado Department of Health Construction Dewatering Permit would be required. C. Stormwater Quality Concept The proposed design has addressed the water quality aspect of stormwater runoff. A temporary inlet filter and silt fencing will be installed during construction, and a permanent water quality feature will be installed at the existing area inlet at the final stages of construction. This will provide an opportunity for stormwater �o , V. STORMWATER QUALITY A. General Concept The water quality of stormwater runoff must be addressed on all final design utility plans. McClelland Office Park II has sought to find various Best Management Practices for the treatment of stormwater runoff. McClelland Office Park II will be providing an inlet filter around the existing area inlet, and silt fencing along the north and east property lines during construction in order to provide a mechanism for pollutants to settle out of the stormwater runoff before flows are directed off - site. Also, a permanent water quality feature will be installed at the existing area inlet located in Basin 1. VI. EROSION CONTROL A. General Concept This development lies within the moderate Rainfall Erodibility Zone and the Moderate Wind Erodibility Zone per the City of Fort Collins zone maps. After completion of the McClelland Office Park II, the potential exists for both wind and rainfall erosion because of the time required for the new vegetation to take hold. The Erosion Control Performance Standard (PS) during construction for this project was computed to be 8 1. 1 per the criteria in the City of Fort Collins Erosion Control Reference Manual for Construction Sites. The Effectiveness (EFF) of the proposed erosion control plan was calculated to be 85.40. Along with the silt fencing and gravel inlet filter, the proposed erosion control methods should meet the City of Fort Collins' requirements. A copy of the calculations has been included in the Appendix. An erosion control cost estimate is also included in the Erosion Control section of the Appendix. B. Specific Details Before construction is to begin, a gravel inlet filter shall be applied at the existing area inlet located in Basin 1. It shall be filtered with a combination of concrete blocks, 'h-inch wire screen, and'/4-inch coarse gravel. Also before construction, a temporary silt fence shall be installed around the north and east boundries of the site. After overlot grading has been completed, all disturbed areas not in a roadway or greenbelt area shall have temporary vegetation seed applied. After seeding, a hay or straw mulch shall be applied over the seed at a rate of 2 tons/acre minimum, and the mulch shall be adequately anchored, tacked, or crimped'into the soil. Basin 4 is located north of Lot 2 and consists of landscaped area. A small Swale will convey the developed flows east towards the proposed parking lot. The flow ' will enter the parking lot through a 2-foot curb cut. Runoff from Basin 1 will be conveyed by a combination of gutter, trickle pan, and overland flows across the parking lot towards the existing area inlet located south of Lot 3. Several curb chases are utilized to convey the flow towards the existing inlet. In order to minimize off -site flows and remain consistent with the original report, the runoff from the.buildings shall drain towards the front and sides of the building to enable the flows to be conveyed into the parking lots. Similar to the original McClelland Office Park PUD design, it is proposed that the parking areas of Basin 1 will provide stormwater detention for the proposed sight as well as a portion of the original McClelland Office Park PUD development. The detention pond will have capacity to contain the 100-year storm event while maintaining the requested 1.5 feet of depth over the existing inlet. An orifice plate ' will be used to restrict the outflow from the parking lot to the 2-year historic release rate, which is 0.88 cfs and was calculated with the original McClelland Office Park PUD design. In the event that the outlet becomes clogged, the runoff will leave the site through the main entrance and will flow east through the adjacent parking lot and into Harvard Street. All the detention pond calculations for McClelland Office Park PUD and McClelland Office Park II are located in the appendix of this report. An area inlet will be installed in Basin 2 and it will tie into the existing stormdrain system. The runoff from Basin 2 will flow east and enter the existing system through the proposed area inlet located southeast of the Lot 3 building. S Stormwater from Basin 3 flows east to an off -site commercial development adjacent to the site, as it has historically. It will remain a landscaped area and will drain east to the off -site, commercially developed sites. It is not anticipated that the flows generated from the above area will exceed the historical amounts previously draining off -site. 4 C. Hydrologic Criteria The Rational Method for determining surface runoff was used for the project site. The 2-year and 100-year storm event intensities, provided by the City of Fort Collins, were used in calculating runoff values. 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 We are requesting to have 1.5 feet of ponding near the existing area inlet in the parking lot. There are 70 proposed parking spaces for the site, of which 11 will have a ponding depth greater than 1 foot. Ten of the existing spaces will also have a ponding depth greater then 1 foot. IV. DRAINAGE FACILITY DESIGN A. General Concept The majority of on -site runoff produced by the McClelland Office Park II development, Basins 1 and 4, will flow towards the center of the site and into an existing area inlet, which was designed and built with original McClelland Office Park PUD. The runoff is then routed off -site towards the northeast via the existing stormdrain system. The existing stormdrain system accepts the developed flow from Basin 2 through the proposed area inlet located southeast of the Lot 3 building. A small portion of the on -site runoff, Basins 3, will drain off -site towards the north and east, as it has historically. Please refer to the drainage and erosion control plan in the back pocket of this report. B. Specific Details McClelland Office Park II has been broken down into four (4) sub -basins. The sub -basin designations correspond to the Basin 2 designation of the 1984 McClelland Office Park PUD Drainage Report. 3 buildings. The proposed site can be seen on the Drainage and Erosion Control Plan in the back of this report. II. DRAINAGE BASINS A. Major Basin Description As shown on the Fort Collins Stormwater Basin Map, McClelland Office Park II lies within the Foothills Basin. Runoff from the site is routed to the northeast boundary of the site through a series of stormdrain pipes. B. Sub -basin Description McClelland Office Park II has been divided into 4 sub -basins. Basin 1 contains the area that drains to the existing area inlet, which includes a majority of the proposed on -site development as well as a portion of the existing building and parking lot. Basin 2 consists of a small portion of the proposed southeast parking. The developed flow from this basin is conveyed east and is intercepted by a proposed area inlet, which will allow the runoff to enter the existing storm drainage system. Basin 3 is primarily a landscaped area behind the Lot 3 building and the runoff simply flows east to the adjacent parking lot. The 100-year developed flows from this basin are minimal and should not impact the adjacent lot. The developed flow from Basin 4, also a landscaped area, will enter the proposed parking lot through a 2 foot curb cut. There are not any off site basins that are contributing flow to the project site. All of the above sub -basins are shown on the Drainage and Erosion Control Plan in the back pocket of this report. III. DRAINAGE DESIGN CRITERIA A. Regulations The City of Fort Collins Storm Drainage Design Criteria is being used for the subject site. B. Development Criteria Reference and Constraints The 1984 McClelland Office Park PUD Drainage Report states that the ponding in the parking area is limited to a maximum depth of 1.5 feet, and the outfall pipe from the parking area has been designed and constructed to release at the 2 year historic rate. McClelland Office Park II has been designed to be in conformance with the 1984 McClelland Office Park PUD Drainage Report, which is located in the appendix of this report. 2 FINAL DRAINAGE AND EROSION CONTROL STUDY FOR MCCLELLAND OFFICE PARK II FORT COLLINS, COLORADO I. GENERAL LOCATION AND DESCRIPTION A. Location McClelland Office Park II is a portion of the original McClelland Office Park PUD. The site is located east of McClelland Drive, north of West Swallow Street, and approximately 500 feet south of West Harvard Street in Fort Collins, Colorado. It is bordered by commercial properties on the north, south, and west. McClelland Office Park II location can also be described as situated in the Northeast 1/4 of Section 26, Township 7 North, Range 69 West of the 6th P.M., City of Fort Collins, Larimer County, Colorado. The site location can be seen on the second page of the Appendix. B. Description of Property Existing Conditions McClelland Office Park II contains approximately 2.4 acres, more or less, and is located north of the original McClelland Office Park PUD. The property is being R proposed for commercial development within the City of Fort Collins Zoning !J District and will be developed consistent with the existing Mcclelland Office Park PUD. Existing asphalt covers the central portion of the site, and the topography generally slopes toward an existing area inlet at approximately 2.5 percent. Native grasses presently cover the north and east portions of the site which, slopes from west to east at approximately 1.5 percent. Proposed Conditions The proposed development consists of two, compartmentalized, commercial buildings and associated parking. The buildings have approximately 7500 square feet each and the rest of the site consists mainly of parking lots and sidewalks with landscape area in the islands of the parking lot and around the perimeter of the TABLE OF CONTENTS DESCRIPTION PAGE I. GENERAL LOCATION AND DESCRIPTION 1 A. Location 1 B. Description of Property 1 II. DRAINAGE BASINS 2 A. Major Basin Description 2 B. Sub -basin Description 2 III. DRAINAGE DESIGN CRITERIA 2 A. Regulations 2 B. Development Criteria Reference and Constraints 2 C. Hydrologic Criteria 3 D. Hydraulic Criteria 3 E. Variances from Criteria 3 IV. DRAINAGE FACILITY DESIGN 3 A. General Concept 3 B. Specific Details 3 V. STORMWATER QUALITY r 5 A. General Concept 5 VI. EROSION CONTROL 5 A. General Concept 5 B. Specific Details 5 VII. CONCLUSIONS 6 A. Compliance with Standards 6 B. Drainage Concept 6 C. Stormwater Quality Concept 6 D. Erosion Control Concept 7 VIII. REFERENCES 7 APPENDIX VICINITY MAP 2 HYDROLOGY --- 4 AREA INLET AND 2 FT CURB CUT 10 DETENTION POND ANALYSIS 13 EROSION CONTROL 18 ORIGINAL OFFICE PARK PUD DRAINAGE REPORT 24 CHARTS, TABLES, AND FIGURES 33 iii THE SEAR -BROWN GROUP FULL -SERVICE DESIGN PROFESSIONALS FORMERLY RBD, INC. 209 SOUTH MELDRUM FORT COLLINS, COLORADO 80521-2603 970-482-5922 FAX:970-482-6368 February 3, 1999 Mr. Basil Hamdan City of Fort Collins Water Utilities--Stormwater 700 Wood Street Fort Collins, Colorado 80522 RE: Final Drainage and Erosion Control Study for McClelland Office Park II Dear Basil: We are pleased to resubmit to you, for your review and approval, this Final Drainage and Erosion Control Study for McClelland Office Park II. 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, The Sear -Brown Group Prepared by: q�,t c 1�C97,rr>^�J Traci Downs, E.LT. Design Engineer cc: File 812-004A Dr. Overton Reviewed by: Jim Allen -Morley, P.E. Senior Engineer NEW YORK • PENNSYLVANIA COLORADO•UTAH STANDARDS IN EXCELLENCE EQUAL OPPORTUNITY EMPLOYER Final Drainage and Erosion Control Study McClelland Office Park II, Fort Collins, Colorado February, 1999 THE SEAR -BROWN GROUP Standards in Excellence