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HomeMy WebLinkAboutMIRAMONT SELF STORAGE PUD - PRELIMINARY - 54-87AM - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL STUDY FOR vIIRA.MONT SELF STORAGE P.U.D., LOT 2 FORT COLLINS, COLORADO A dirrainu n% Tlie Sear-Brnwre Grnup FINAL DRAINAGE AND EROSION CONTROL STUDY FOR MIRAMONT SELF STORAGE P.U.D., LOT 2 FORT COLLINS, COLORADO December 23, 1996 Prepared for: Wheeler Commercial Property Services, LLC 1125 West Drake Road Fort Collins, Colorado 80526 Prepared by: RBD, Inc. Engineering Consultants A division of the Sea�• Brown Group 209 South Meldrum Fort Collins, Colorado 80521 (970) 482-6368 RBD Job No. 154-014 Revised: �! � � � �INC. Englneering Consultants 1 �lirixinn ��/'7'bc Sear-BroN��� Crorrp 209 S. Meldrum Fnrt Collins, Colorado 80521 `)7iU 1�2-5�)2� December 23, 1996 � Mr. Basil Hamdan City of Fort Collins Utility Services Stormwater � 235 Mathews Street Fort Collins, Colorado 80522 � � RE: FINAL DR.AIlVAGE AND EROSION CONTROL STUDY FOR THE MIIZAMONT SELF STORAGE P.U.D., LOT 2 Dear Basil: � We are pleased to submit to you for your review and approval, this Final Drainage and Erosion Control Study for the Miramont Self Storage P.U.D. All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. � I � I � � I � We appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Respectfully, RBD Inc. Engineering Consultants Prepared by: Pe Project anager Reviewed by: David K. Thaemert, P.E. Water Resources Project Engineer I� cc: 154-014(A) Correspondence � � � H:\USER\civil\projects\miramont. of�ldrainfin.rpt I �r,nunr ;;n;',�45; ,. �� ,^C; � � � � � TABLE OF CONTENTS DESCRIPTION PA E GENERAL LOCATION AND DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Location 1 Description of Property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 � DRAINAGE BASINS ....................................................... 1 Major Basin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Sub-Basin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 � � � DRAINAGE DESIGN CRITERIA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Regulations......................................................... 2 Development Criteria Reference and Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Hydrological Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Hydraulic Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Variances from Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 DRAINAGE FACII.ITY DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 � GeneralConcept ..................................................... 3 Specific Details ...................................................... 3 � STORM WATER QUALITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 EROSION CONTROL 4 � GeneralConcept ..................................................... 4 Specific Details ...................................................... 5 � � � � CONCLUSIONS........................................................... 5 Compliance with Standards . . . . . . . . . . . . . . . . . . ........................... 5 Drainage Concept .................................................... 5 Storm Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Erosion Control Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 REFERENCES............................................................ 7 APPENDTX VICINITY MAP � HYDROLOGIC CALCULATIONS DETENTION POND CALCULATIONS SWMModel FOR McCLELLAND'S MASTER DRAINAGE BASIN � EROSION CONTROL TABLES AND FIGURES � 2 10 13 23 � � � � � � Ie � FINAL DRAINAGE AND EROSION CONTROL STUDY FOR THE MIRAMONT SELF STORAGE P.U.D., LOT 2 FORT COLLINS, COLORADO GENERAL LOCATION AND DESCRIPTION A. Location The 1Vliramont Self Storage P.U.D. is located south of Harmony Road between � Boardwalk Drive and the Fairway Estates Third Filing. It can also be described as being immediately north of the Upper Meadow at l�tiramont First Filing P.U.D. More specifically, this site is located in the Northeast Quarter of Section 1, Township 6 � North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, Larimer County, Colorado. � � � � � � II. � � � � � B. Description of Propertv The 1VTiramont Self Storage P.U.D. is being developed by delineating two lots on the property. Lot 1 consists of 4.395 acres and will contain storage unit facilities. Lot 2 consists of 0.873 acres and will contain an office building. This report only presents the drainage and erosion control study for Lot 2. The Miramont Self Storage P.U.D. site is currently undeveloped and sparsely covered with natural ground vegetation. Small trees have been planted along a berm that closely parallels the southern border of the site. Utility boxes and electric pedestals are located in the southeast corner of the site. The site slopes from north to south at a grade of approximately 4%. The proposed purpose for the subject site is currently understood to be for privately owned and operated storage units. DRAINAGE BASINS A. Major Basin Description The project site is located within the McClellands Basin. No major drainage way exists within the Miramont Self Storage P.U.D. � � B. Sub-B1sin Descri�tion � The Miramont Self Stora�e P.U.D. lies within Basin 202, as laid out in the McClellands Basin Regional SWMModel. Basin 202 contains the Mirarnont Self Storage P.U.D., Front Range Baptist Church, Bank One at Harmony Market, and an � unplatted piece of land owned by LGT Real Estate. The completion of this project will partially develop Basin 202. � � III. � � � � � � � Detention for Basin 202 is provided by on-site ponds - one for each of the four sites. Miramont Self Storage has been divided into two lots, each providing its own detention. DRAINAGE DESIGN CRITERIA � : C. � The release rate from the pond was obtained by proportioning the acceptable release ra.te from Basin 202 on a per-acre basis, and then applying that to the acreage for Lot 2. � � _—', I �� � �� D. Hvdrlulic Criteria Regulations The City ofFort Collins Stonn Drainage Design Criteria is being used for this subject site. Development Criteria Reference and Constraints As stated earlier, flows from the site contribute to an on-site detention pond Basin 202, as shown on the Overall Drainage Plan for the McClellands Basin. Basin 202 was originally modeled with an impervious percentage of 50.00%, and was consequently modified based on the new site layout. H, d� rological Criteria The Rational Method is being used to determine run-off peak flows from the study site. Rainfall criteria for this study was obtained from the City of Fort Collins and is included in the Appendix. The 10- and 100-year rainfall criteria were utilized to determine the developed flou�s. All calculations within this study have been prepared in accordance with the City of Fort Collins Drainage Criteria. 2 � � � � � � � IV. � � � � E. Variances from Criteria We are asking for a variance on the freeboard at this location on the premise that the potential overtopping flow is rendered benign by simply entering the existing storm sewer system, thus posing no threat to property. A variance for erosion control is also sought. The effectiveness during construction is 37.7 instead of the rainfall performance standard of 83.8. We feel that the measures provided will effectively prevent sediment transport to adjacent areas and any further measures are unnecessary. ARAINAGE FACILITY DESIGN A. : �eneral Concept Storm water for Lot 2 will sheet flow southward across the parking lot and be intercepted by curb chases that direct the flow into two metal covered sidewalk culverts. The sidewalk culverts transport the flow into the detention pond. Discharge from the detention pond will be regulated through an orifice plate structure attached to a 12-inch PVC drain pipe. The drain pipe will terminate at an earthen swale that will carry the flow into a metal covered sidewalk culvert. The sidewalk culvert discharges the on-site flow into the existing storm drain system. Specific Details � The required storage for the detention pond has been calculated to be 0.157 acre-feet using the FAA method. The average release rate from the site has been calculated to � be 0.45 cfs. In order to achieve this release rate, the acceptable release from Basin 202, 11.1 cfs wa.s apportioned on a per acre basis over the entire basin, giving a 0.51 cfs per acre release. The value was then multiplied by the acreage of the site, 0.88 � acres, to give 0.45cfs. This rate will be controlled by an orifice plate structure attached to the upstream end of the 12 -inch PVC drain pipe. � � �] � � The detention pond has been designed to realize a 100-year water surface elevation of 5089.63. The proposed grading plan provides 1 foot of freeboard at an elevation of 5090.50 around such critical areas as the building foundation and the southern property boundary. There is less freeboard at overflow point in the access drive. The highpoint elevation of the flowline at the PCR of the south curb parking lot entrance is 5090.13. This gives a freeboard of 0.50 feet at this location. Overtopping flow at this location will follow the curb chase and enter the existing storm sewer. We are asking for a variance on the freeboard at this location on the premise that the potential overtopping flow is rendered benign by simply entering the existin� storm � ■ ■ � � � � V. � � � VI. � � � � � � � � � � Lot 1, to the west of Lot 2 will be discharging detained runoff in a manner similar to Lot 2. However, due to tight condition of detaining runoff on Lot 1, the engineer for that lot needed to drain directly to Boardwalk Drive, by cross-cutting the Lot 2 pond, and laying a 12" PVC drain pipe directly to the sidewalk chase at Boardwalk Drive. By doing this, he was able to maintain a very flat slope from the Lot 1 pond, and have the pond volume be greater than would have been if it had drained through the Lot 2 pond. STORM WATER QUALITY A. General Concept The water quality of storm water runoff must be addressed on all final design utility plans. Construction is anticipated to begin in Summer of 1996. We have sought to find various Best Management Practices for the treatment of storm water runoff. Though there is little that may be done as most of the drainage facility is already provided, we have sought to improve Storm water quality with the methods called out in the Erosion Control and Drainage Plan. EROSION CONTROL A. General Conce.pt The Miramont Self Storage P.U.D, lies within the Moderate Rainfall and Wind Erodibility Zone per the City of Fort Collins zone maps. The potential e�sts for silt movement during construction of the parkin.,,�/driveways and building. Thus the new improvements will be subjected to both wind and rainfall erosion. Per the Gitv of Fort Collins Erosion Control Reference Manual for Construction Sites and related calculations in the appendix, the erosion control performance standard (PS) for the subject site during construction is 79.6 and after construction is 93.7 From the calculations in the appendix, the effectiveness(EFF) of the proposed erosion control plan is 72.9, during construction and 98.07 after construction. It is anticipated that the construction duration of this project will be less than S weeks due to the limited amount of work to be completed, therefore the erosion control plan as specifically detailed below, should meet the City of Fort Collins requirements. A copy of the erosion control calculations is included in the Appendix. An erosion control �scrow cost estimate of $2427 is also included in the Erosion Control Seciion of the Appendix. :� � � � � � � � VII. � � � � � � � � � B. �pecific Details Immediately upon completion of over lot grading the silt fencing shown on the drainage and erosion control plan should be installed. In order to protect the curb chases from receiving e�cessive silt deposits, the curb chases will have gravel filters installed around them. The above items can be removed once asphalt and landscaping in their respective areas have been completed. CONCLUSIONS A. : C. � Compliance with Standards All computations within this report have been completed in compliance with the City of Fort Collins Storm Drainage Design Criteria. Drainage Concept The proposed dra.inage concepts presented in this report and shown on the Drainage and Erosion Control Plan are in compliance with the City of Fort Collins drainage criteria. This project was designed to be in conformance with the intent of the McClelland's Basin Master Drainage Plan. Storm water OualitX Because storm water quality has become a requirement, the site has addressed this storm water aspect. We have designed the erosion control to reduce the sediment which runs into the storm water system. The on-site detention pond also provides a settling period during which impurities may be filtered out of the stormwater runoii before leaving the site. �rosion Control Concept The proposed erosion control plan adequately provides for the control of wind and rainfall erosion from the study site. A variance has been requested to allow an effectiveness during construction of 37.7 instead of the calclulated performance standard of 83.8. The proposed erosion control concepts presented in tliis report and shown on the Erosion Control Plan are in compliance with the City of Fort Collins erosion control criteria. � REFERENCES 1. City of Fort Collins, Storm Draina_e Design Criteria and Construction Standards, May 1984, Revised 1992. 2. City of Fort Collins, Erosion Control Reference Manual for construction Sites, January 1992. 3. Overall Drainage Study for Oak/Cottonwood Farm, McClellands Basin, Fort Collins, Colorado, by RBD, Inc., May 4, 1992, revised October 10, 1994. 4. McClellands Basin 100-year Master Plan Update (County Road 9 to Fairway Estates) for Proposed Modifiications to the Oakridge Village Regional Detention Pond, Fort Collins, Colorado, by RBD, Inc., April 1, 1996 � � - � � � � � � � . � � � � � � i� � I� ' I .� � � � � � � � � � � '.�J VICINITY MAP �'