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Home My WebLink AboutMIRAMONT SELF STORAGE PUD - FINAL - 54-87AO - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE REPORT FOR A�irarnont SeOf Siorage � �ORT COLLII�IS COLORADO � PREPARED FOa2: � � � SecurCaee Seif Storage, inc. 6551 South Revere Parkway, Suite 225 Englewood, Colorado 80'111 (303) 792-9952 PREPARED BY: JOaIAI H. {�C►NG lll DEVELOPM/EA/T CONSULTA/VT 6551 South Revere Parkway, Suite 225 Englewood, Colorado 80111. (303) 792-9952 Phone FAX (303) 792-2166 April 22,1997 � �° !. ';� �:: ; � GEPlERAL LOCATION AND DESCRIPTION This report accompanies an application for a Final P.U.D. and Finai Plat for the subject property. The P:U.D. is a two lot subdivision containing a self storage facility wrapped around an office building:: The property is tocated just south of Harmony Road at the intersection of Boardwalk Drive and Oakridge Drive in Fort Collins. It is situated in the northeast quarter of Section 1, Township 6 North, Range 69 West of the 6th Principal Meridian. � This property is a 5.3 acre parcel of unplatted land. It is bound on the north by unplatted land and Front Range Baptist Church Subdivision, on the east by Boardwalk brive and Oakhills Apartments P.U.D., on the south by Upper Meadow at Miramont P.U.D. Second �- Filing and on the west by Faitway Estates Third Filing. This property is being platted into two lots. The office parcel (Lot 2) is located on roughly 0.6 acre of land in the northeast comer of the property. The remaining "L" shaped 4.7 acre parcel (Lot 1) contains the � self storage facility. This property is located within the Oak / Cottonwood Farm O. D, P. and the Oak / Cottonwood Farm - McClellands Basin Overall Drainage Study. ,,, � ;r:; �' f ,; � � � � � � I{. IiISTORIC DI2AINAGE This property is currently vacant land with vegetation consisting mostly of native grasses and weeds. There is an existing landscaped berm along the south property line. The property generally dra,ins in a north - south direction at an average slope of around 3 percent. The property lies outside the 100-year flood plain. A small amount of off site runoff from an undeveloped area to the north affects the site. Currently, adjacent downstream drainage facilities consist only of existing 6" curb and gutter in Boardwalk Drive. The existing topography dietates three distinct historic drainage basins (H1, H2, and H3). Basin H1 is the bulk of the property and contains 4.68 acres. Drainage is from north to south and is then the diverted onto Lot 2 by the existing berm along the south property line. Eventually, runoff from H1 drains into Boardwalk. The 100-year peak runoff rate from this basin is 6.08 �fs. Basin H2 (0,21 acres) drains in a southwesteriy direction onto the existing rear yards of the single family homes in Fairway Estates, 3rd Filing, The peak 100-year runoff. from basin H2 is 0.38 cfs. Basin H3 is a 0.38 acre basin which is the berm along the southerly lot line. It drains to the south onto Upper Meadows at Miramont PUD with a 100-year peak runoff rate of 0.68 cfs. i � , ��. � A. a DR�41NA►GE DESIGN CRITERIA REGULATIONS Criteria used in preparation of this report are from the City of Fort Collins Storm Drainage Criteria and Construction Standards, dated May, 1984 (hereinafter called "Criteria"). There are no previous drainage reports other than the Overal.: Drainage Study for Oak / Cottonwood Farm - NlcClellands Basin (hereinafter, Master Study).. HYDROLOGICAL CRITERIA The initial design storm is the 10-year event and the major storm is the 100-year event as required by the Criteria. The Rational Method as outlined in the Criteria was used #or runoff calculafions. On-site detention is required by both the Criteria and the Master Study. The Master Study and an agreement befinreen the owner of this property and the surrounding properties have set the allowable runoff from this property at 0.5 cfs per acre during the 100-year storm. The FAA method with the alfowable release rate of 0,5 cfs per acre was used to calculate the required volume for each detention pond, IV. DRAINAGE FACILITY DESIGN The proposed grading divides the development into one major basin and two minor basins. They have been designated basins A through �C. Basins A is the bulk of the property and will drain into the detention pond. Basins B and C are small perimeter landscape strips which are fill sfopes required to create the on-site detention pond, Basin A(4:68 acres) is the bulk of the PUD: It contains both Iots within the PUD. It contains self storage buildings, an office building, driveways and landscaping: It will drain into the detention pond by way of curb cuts and storm sewer sized for the 100-year St0(`IYt: Basin B is a small (0.42 acre) landscaped strip along the southerly line of Lot 1. It is also a fill slope required to create the detention pond. It will drain into the rear yards of the adja.cent single famity lots in Upper Meadows at Miramont PUD 1st Filing with the exception of a small area which will drain into Boardwalk: Basin C is a small (0.17 acre) landscaped strip along the westerly {ine of the subdivision. It is a fill slope that is required to create the detention pond. It will drain into an existing swale along the property line and eventualiy into Fairway Estates, 3rd Filing. The peak 100-year runoff of 0.31 cfs from basin C is less than the 0.38 cfs currently draining onto Fairway Estates from the 0.21 acre basin H2. The historic nature of the runoff will not change since the existing swale will be maintained. � � � � OId-�ITE DETEPITIOId Since the runoff from the proposed perimeter landscaped areas is equivalent to that from the existing condiotions, the aliowable release of 0.5 cfis per acre wiil apply only to the area draining into the detention pond excluding the off-site areas to the north (basins OS2 and OS3). Basins OS2 and OS3 will drain through the property until they are developed. When they are developed, they will have their own detention ponds which will discharge into the joint driveway along the north property line and eventually directly into Broadway. The detention pond will have a 100-year volume of 37,000 cubic feet at an elevation of � 4991.00. Approximately one foot of freeboard has been provided as a safety factor. ,.... Based upon a drainage area contributing to the detention pond of 4.68 acres, The 100-year release rate from the pond will be 2.34 cfs. The pond outlet is a 12" PVC pipe � that is restricted by a 6.75'' diameter opening at the inlet. The 12" pipe will drain into the existing curb and gutter in Boardwalk through a sidewalk culvert, � � � '�._� � � An emergency overflow spillway is provided, which is directed toward Boardwalk. EROSION CONTROL Erosion control design measures have been provided in this report for this project in accordance with the Criteria. This design primarily consists of a silt fence to be placed along the westerly and southerly lot lines, for rainfall and wind erosion control, and an over-excavated detention pond. This will allow for silt created by runoff from a storm during construction to be trapped instead of adversely affe�ting downstream properties. 1'he over-excavation required for the detention pond is 500 cubic yards. The detention pond outiet will be protected by straw bafes. Construction of the site will begin immediately after approval. The entire site will be developed at one time. The project will take approximately 4 to 6 months to complete.. Seeding and paving will be completed as s.00n as possible. In any event, the site will not be uncovered for an extended length of time. These erosion control measures are shown on the attached Drainage and Erosion Control Map. V. COIVCLUSIONS This Final Drainage Report and the drainage system presented for this development has been prepared in compliance with the Criteria and Master Study. This project will aetually reduce the peak 100-year runoff from the property that contributes to Boardwalk and is therefore a benefit to #he neighborhood and the downstream drainage system. Final construction plans for the P.U.D. are also part of this submittal. The acc:ompanying Drainage and Erosion Control Map shows grading, drainage basins, appropriate cross sections and erosion control measures for the seff storage lot. Suppoiting calculations are presented in the Appendix. Prepared by; John H. King III, P.E. State of Colorado No. 20325 �. tV. REFERENCES 1. Oak / Cottonwcood Farm_ O.D.P. and_the_ Oak i_Cottonwood _�acm._- McClellands Basin, prepared by RBD, Inc., dated 11Aarch, 1995. 2:. Citv of Fort C.ollins Storm Drainaae_ Crite�ia_and_Constcuction StandaPds, dated May, 1984. �' � � � �. :a��, � . !-R,�j','. �r^ h�': �.'. �: ; , �" . k.:^, . � � , � � : � � � �? '' • ;i.i : ,n,rYi:' . i � VICINITY MAP � SCALE 1"=2000' .,,,o,,,