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HomeMy WebLinkAboutCITY UTILITIES SERVICE CENTER PUD PRELIMINARY - 16 90 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT40 • • T:01NC Engineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 303/226-4955 April 2, 1990 Ms. Susan Hayes Stormwater Utility Dept. City of Fort Collins P.O. Box 580 Fort Collins, CO 80522 RE: CITY SERVICE CENTER PRELIMINARY DRAINAGE REPORT Dear Susan: RBD Inc. is pleased to submit this letter as the Preliminary Drainage Report for the City of Fort Collins Service Center. PROPOSED IMPROVEMENTS This City of Fort Collins project consists of a Building Addition to the current onsite facilities and the addition of more parking facilities. The Addition will be located between the two main buildings currently occupying the site, namely the Streets Department facility (Bldg. B) and the Water & Sewer Department and Light & Power Department facility (Bldg. A). Other proposed site improvements include additional parking facilities south of the present site, realignment of the main entrance to the facility and realignment and repavement of approximately 280 feet of Wood Street along the site's frontage. Wood Street improve- ments will also include the installation of curb and gutter along the west side to the improved street section. Although the en- tire 18.8 acre site is being platted for the P.U.D. process site improvements will be limited to the western third of the site. EXISTING DRAINAGE CONDITIONS This site is located along east side of north Wood Street at its intersection with West Vine St. The site is bounded by the Colorado & Southern Railroad right of way on the south, Wood Street on the west, the Nauta property on the north and an unused Other Offices: Vail, Colorado 303/476-6340 9 Colorado Springs, Colorado (719) 598-4107 ■■r INC Engineering Consultants �Z��� 0 CLIENT .[ '� JOB NO. 344'doI PROJECT 6_-V tG,� f* 6— �-(� CALCULATIONS FOR MADE BY DATE'1�/t ��CHECKED BY —DATE SHEET 4- OF / imG 07" Cvn Gfq TiP �IC�Yt .. A G��kr 120 Y'- /a 7 O f /S2 o f- G Se -- 02 0 c� — 38ao' ,7 ,/3 0 c i io ioo y� S' S0a41 y98� = o, Fy d8a.o 01 X0,&�,s 0.93 '7Ave Qvt Cl\ec�k a'I17- a �-fsec_ 3770 = 3/ mr/tufes 9v4-4r ax(,o V 50' over/d,n.d = 8 m l'n✓�es 39 rn,'fj s 0 ON mmu � in a n a ■m�u� n �Y11 NO w 3v MAY 1984 5-3 DESIGN CRITERIA s 0 street right of way and City owned property on the east. The City owned property on the east extends to the Poudre River. The vast majority of the site is paved parking and storage areas. Most of the site sheet flows to the east and north with a small area (Basin H5) draining to the northwest. Area inlets gather limited flows on site in various locations (See Overall Drainage and Utility Plan). These inlets are tied to various storm drain pipe systems which cross the site along six different alignments. Three of these systems outfall along the north property line into the Nauta property while the remaining systems outfall to the property to the east. Offsite flows drain toward the site from the west and south. Flows from the west are intercepted by Wood Street. These flows drain to the north and south from the high point of Wood Street which corresponds to its intersection with West Vine Street. Flows from the south are limited by the railroad embankment and a 30 inch X 12 inch wooden culvert. PROPOSED DRAINAGE APPROACH No previous drainage analysis has been done in this area. On site drainage facilities appear to have been designed as interim solu- tions for drainage problems that may have been occurring at the time of their construction. Offsite issues particularly relating to the discharge of storm water flows onto adjacent properties have never been adequately addressed. Offsite areas draining toward the site are existing neighborhoods, therefore, regardless of the City's normal drainage requirements the options for han- dling undetained flows in the area are extremely limited. Based on these observations the design approach taken for this site is based on the following assumptions: 1. The existing conditions on site and in the area surrounding the site are treated as the historic conditions. 2. Because on the site's proximity to the Poudre River no on - site detention will be required. 3. Analysis is limited determining the effect of proposed im- provements to existing drainage flows and the facilities downstream. 4. Offsite drainage problems such as the impact of undetained flows ponding against the existing railroad embankment will not be addressed in this approach. 5. During final design the effect of the offsite drainage dis- charges and the acceptance by adjacent properties will be formally resolved. These assumptions clarify the overall drainage approach. A detailed explanation of the actual drainage design follows. As stated earlier, the proposed improvements will only affect the western third of the site. The only exception to this statement is a increase in the flows which are directed toward the outlet of the railroad culvert at Design Point A. Within the western third of the site flow patterns will change slightly due to the additional parking which is proposed along the south edge of the site. This additional parking is developed through the acquisition of a portion of the railroad right of way and a small triangular property south of the existing railroad. These areas which historically drained offsite (Basins Hla and Hlb) will now be directed eastward as part of a larger basin (Basin D1). Drainage from this proposed basin will drain to a low point in the new parking area and then will flow in a drainage swale to Design Point A. The Building Addition will block off drainage patterns which cur- rently flow between Buildings A and B (Basin H3). A pipe system is proposed to carry flows from the south side of the Addition through the Addition's foundation to an existing pipe system north of the new Addition. Since extending a storm drain through a building foundation is rarely done several safeguards are proposed: 1. The area draining into this pipe system has been minimized to reduce the extent of any possible drainage problem. 2. The inlets in this area and pipe extended through the build ing will be oversized to handle over 100 year undetained flows. 3. In the event of the pipe system failure this area is designed to overflow into the adjacent basin at Design Point B. The pavement elevation at Design Point B is 0.3 feet lower than the finish floor elevation of the Addition and Building A. These safeguards should address the concerns raised by routing the storm drain through the addition. Throughout the remainder of the site historical drainage patterns are closely approximated. Offsite discharge rates do increase slightly by the proposed changes. As stated earlier, the effect of these offsite discharges and their acceptance by adjacent properties will be formally resolved during final design. 0 By proceeding with this approach the drainage will flow through this site in a controlled manner. When the final design is implemented, this approach will satisfy the hydrologic and hydraulic concerns and current City of Fort Collins standards for storm water management. Sincerely, '_�'0- 114- Stan A. Myers, P. . CC: Jack Gianola, City of Fort Collins ��;�sttrtiur,rrrr 4 George Brelig, RB&B 344-001 .ON, �° �� ctysrvpl . dge �� tiV �' 16060 A. 0 • CALCULATIONS 11 �NC Engineering Consultants CLIENT R 8� • JOB NO.344-bC5 J PROJECT C IT y SMV. C "T� CALCULATIONS FOR k'UNO F F-oNS/TE MADE BY 5MX DATE 3 - Z4 CHECKED BY DATE SHEET OF t1 Q 0 N rt r O h O � 01 00 in Q 9v O -z -z Q _ p _ _ A � a a o 0 0 o I o a— N a N ry n N a N n G I amm o a a a o _o of u a 4 O Q O f1 00 in QD I I n O M 1 I N I I I in in 1 43 O O o � � N N 61 n 67 Q O 0 o �n 0 C o N �2 IN n d i 4 O - n - O M Q z z Z Q Q Q Q 4 Cl YI■1■NflAIYIY��■IN �rl NIA■IIIYII IN I WE ME I v � a a 0 z 0 co W 0 } a ? rn U) rn J W ¢ m d m wm �W U� w a> 0 � a Z c a � ¢ L o� o� U� ¢LL O LL ¢ LL J a U C } H MAY 1984 5-3 DESIGN CRITERIA WIN IN laill IIIM oil �I 1 Q 0 z 0 U) w 0 Q Q z Q, m J r W d � Wm u)w � L W Ql 0 D Q m Z c) Q � LL L om OE H o O 2 cc 0 J Q _U } MAY 1984 5-3 DESIGN CRITERIA 0 n ■r INC Engineering Consultants CLIENT V +� 11 � (� j(`'��JOBNO._! 41y (—`QO1 A PROJECT Set V ICe. 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