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HomeMy WebLinkAboutSPRING CREEK CENTER PUD FINAL - 17 90D - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage Report for Spring Creek Center P.U.D. Fort Collins, Colorado September 18, 1997 Prepared For: W.W. Reynolds Companies 1600 Specht Point Road Fort Collins, Colorado 80525 Prepared By: Northern Engineering Services, Inc 420 S. Howes. Suite 202 Fort Collins, Colorado 80521 Phone: (970)221-4158 Project Number: 9734.00 NORTHERN E N G I N E E R I N G September 18, 1997 City of Fort Collins Stormwater Utility 235 Mathews Fort Collins, Colorado 80522 RE: Spring Creek Center P.U.D. Fort Collins, Colorado Project Number: 9734.00 Dear Staff: Northern Engineering Services, Inc. is pleased to submit this Final Drainage Report for Spring Creek Center P.U.D. for your review. This report was prepared in compliance with technical criteria set forth in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual. If you should have any questions or comments as you review this report, please feel free to contact me at your convenience. Sincerely, NORTHERN w� _ b�J 30325 Mary B. Wohnrade, P.E. INC. 420 SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221.4158, FAX (970) 221.4159 No Text Final Drainage Report for Spring Creek Center P.U.D. Fort Collins, Colorado September 18, 1997 I. INTRODUCTION 1.1 Obiective To provide a final drainage scheme for the proposed Spring Creek Center planned unit development based on master drainageway planning and overall/ preliminary drainage concepts. Specific objectives as part of this study are: 1. To address the 75 cfs spill from Spring Creek over Timberline Road as identified in the S rin Creek Master Draina ewa Plan, (Reference 1); 2. To recognize the potential impact of the existing conditions floodplain of Spring Creek in relation to storm sewers and finished grades; 3. To consider any possible adverse effects downstream of the development due to developed stormwater. 1.2 Mapping and Surveyine Topography of the site was provided to Northern Engineering Services by Landstar Surveying with a contour interval of one (1) foot. 1.3 Site Reconnaissance A site visit was conducted on August 22, 1997 by the project engineer. Based on the topographic mapping, existing drainage basins and land use were confirmed as well as existing structures. The location and dimensions of existing culverts were verified as well as their condition and flow direction. II. SITE LOCATION AND DESCRIPTION 2.1 SiteLOcatiOn The site is located within the NW Quarter of Section 20, Township 7 North, Range 68 West of the 6th Principal Meridian in Fort Collins, Colorado. The project is bounded by Timberline Road on the west, East Prospect Road on the north and Midpoint Drive to the south. (See Vicinity Map). 2.2 Site Description ' Spring Creek Center P.U.D. is approximately 11.600 acres and has historically been open space. There are no existing structures on the site. 1 Northern Engineering Services, Inc. Final Drainage Report Spring Creek Center P.U.D. September 17, 1997 Page 2 2.3 Syrin Creek and Irrieation Laterals o Spring Creek runs through the northern portion of the site and flows from romFEMA has toward the Cache La Poudre River. The Flood Insurance Rate Map (FIRM) been used to define the regulatory floodplain (see Section I). The City of Fort Collins has also defined the 100-year floodplain for developed conditions for Spring Creek lso identifies a 75 cfs spill over Timberline Road which passes through the proposed Spring n be found in the aforementioned master drainageway report. Center site. This information can n lateral on the site which has since been abandoned. There are signs of a former irrigatio III. HISTORIC DRAINAGE BASIN 3.1 Mjor Basin Identification The site is located in the Spring Creek Drainage Basin. Reference 1 has been used as a guide in the development of the drainage and grading for the site. 3.2 Historic Drainage Patterns The site historically drains from west to east at slopes ranging from 0.57 to 2.64%. The majority of the site has historically drained to the east through developed properties and to the existing W•W• Reynolds detention pond. Historic runoff from the site, discharging to the east, has been defined at Design Point's H1 and H2 (see Section A). The 100-year discharge at Design Point's H1 and H2 are 15.4 and 4.6 cfs respectively for a total of 20.0 cfs. There is no off -site runoff entering the site. IV. DEVELOPED DRAINAGE 4.1 DeveloWd Conditions Creek Center includes: Planned development for Spring • commercial buildings and possible gas stations, • utilities including storm and sanitary sewers and water. Off -site easements for drainage and grading are not required for this development. 4.2 Design Criteria and References ort Collins rainage Design Drainage criteria outlined in both the &ji�L� ernrm Drainase Criteria Manual bythe Urm Drban Drainage and Criteria Manual �SDDCMI and Flood Control District have been referenced for this Final Drainage Study. 4.3 Hvdroloeic Criteriathe The Rational Method has been used to estimate peak stormwater runoff within nitial ear and nutes. The I developed site with a minimum time of have been used concentration io design i the proposedidrainage system major 100 year design storms which include swales, inlets and storm sewers. Rainfall intensity data for the Rational Method 1 Final Drainage Report Spring Creek Center P.U.D. September 17, 1997 Page 3 Northern Engineering Services, Inc. has been taken from IDF curves and equations generated specifically for the Spring Creek Center P.U.D. site by the computer program "Watershed Modeling" by Eagle Point (see Section B). Input of precipitation amounts for the intensity equations have been taken from the NOAA Atlas 2, Volume III - Colorado. Compared to Figure 3-1 in the SDDCM, rainfall intensities generated for the site were comparable to intensities given in Figure 3-1. 4.4 Hydraulic Criteria The City of Fort Collins Storm Drainage Design Criteria has been referenced for all hydraulic analyses. In addition, the following computer programs have been utilized: • The computer program "HY8" by the U.S. Department of Transportation, Federal Highway Administration has been used to size all culverts; • The computer program "UDINLET" has been used to analyze inlet capacities; • The computer program "Flowmaster" has been used to analyze the capacity of proposed swales. The hydraulic analysis of the 75 cfs spill across Timberline Road has been developed through the use of the HEC-2 computer model with the split flow option. 4.5 Drainase Concept Detention is not a requirement for the proposed development due to the proximity of the site to Spring Creek. Detention will be provided however, at the east end of the site, in order not to exceed historic rates. The total 100-year developed release rate from the site, which drains to the east, of 19.93 cfs (Pond 1 (7.43 cfs) and Design Point's 1 (7.0 cfs) and 13 (5.5cfs)) will not exceed the historic rate of 20.0 cfs (Design Point's H1 and 1­12). The remainder of the site will drain to Spring Creek undetained through four storm sewer systems (Storm Sewer Line's 7,8,10 and 14). Emergency overflows have been provided in the event that on -site area inlets become clogged (see Drainage Plan for location of spill points). The overflows route on -site spills to the northeast corner of the site in the vicinity of Inlet 7 where an emergency overflow weir has been provided. Ample freeboard has been provided to finished floor elevations of buildings adjacent to ponding locations. 4.6 75 cfs mill from Sprinir Creek In light of the recent flooding of Spring Creek on July 28, 1997, the spill over Timberline Road has received serious consideration. The proposed site is in the direct path of the spill which occurs, according to the field survey information, at the intersection of Timberline Road and Midpoint Drive. The computer model HEC-2 was used to model both the existing (EC-SPLT.DAT) and proposed (PC-SPLT.DAT) spill over Timberline. Based on the existing conditions model, it appears that nearly all of the 75 cfs spilled over Timberline is conveyed through the proposed Spring Creek Center site (see Section H). An unknown amount of water is conveyed back to Spring Creek via the existing swale located Northern Engineering services, Inc - Final Drainage Report Spring Creek Center P.U.D. September 17, 1997 Page 4 umes that he entire 75 on the east side of Timberline Road. The HC reek Center site.C-2 modeling Thenorth top fs is op of cub of conveyed east through the proposed SP g onto the Midpoint Drive acts as ir overflow mlTimberline Road r for water to ilt f SpechtlPoint Drive. The modeling proposed site. This we extends fately 0.75 cfs of the of existing conditions reveals the ntersehat appr coxition of Midpoint and Specht Point the rest has spilled down Midpoint Drive beyond site. and onto the proposed that approximately 60 cfs of the 75 over the top of curb Based on the proposed conditions model, it appears cfs spilled over Timberline is convened back to Road is intended to di eing, Creek via ctsthe spill towards Section H). The proposed median o Creek Center site. The at Section 1000) of the Swale 12 which is located on the east side of Timberline on the Spring modeling of proposed conditeast ions reveals e Midpoint that app ro beyond the intersection d d M o hi nt and cfs initial 75 cfs continues Specht Point. The total flow reachingthe W.W. Reynolds detention spill has been reduced from roughly V. EROSION CONTROL 5.1 Erosion Control Plan vided at the outlet of all storm sewers and will be buried Permanent riprap will be proswales with a minimum of six inches of nao minimsoze a onion 1Grass-liRa mmended time f seeding halls possible upon completion in order be based on temporary/permanent vegetation specifications given on the Grading P an. Temporary sediment control con avel filters will be isng of straw bale dikes l required atall arbe sea inlets and siltil permanent vegetation is established. Gr fencing installed in appropriate locations. See the Grading Plan for additional information VI. CONCLUSIONS 6.1 Compliance with Standards All drainage analyses have been performed ed a Urban Drainagerding to the lanccod FFood Control ins Storm Drainage Design Criteria Manual al- No ) District's Drainage Criteria Manual. No variances are requested as part of the proposed development. Final Drainage Report Spring Creek Center P.U.D. September 17, 1997 Page 5 Northern Engineering Services, Inc. REFERENCES 1). Spring Creek Master Drainaeewav Plan, City of Fort Collins, Colorado, Engineering Professionals Inc., March, 1988. 2.) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. 3.) Drainage Criteria Maunal, Urban Drainage and Flood Control District, Wright - McLaughlin Engineers, Denver, Colorado, March, 1969. Final Drainage Report Spring Creek Center P.U.D. September 18, 1997 Page 6 Northern Engineering Services, Inc. TABLE OF CONTENTS PAGE Section A: ............... Al- A3 Historic Hydrology ............................ ....... *** .... * * Section B: .............. 131- B7 Developed Hydrology ..................................................... Section C: .............. Cl- C7 Design of Inlets ............................. ...... * * ­ .... * .... *"'** Section D: Dl- D3 Design of Culverts ........................................................ Section E: El- E8 Design of Storm Sewers ............................................... Section F: ............. Fl- F7 Design of Swales ....................... Section G: Gl- Gll Detention Pond 3 Calculations ......................................... Section H: ................ Hl- H25 Timberline Road 75 cfs Spill ....................................... * ... Section 1: ............... 11-13 FIRM Information ................................... * ...... Section 1: Jl- J4 Emergency Overflow Weirs ............................ *"* ....... Section K: Kl- K4 Riprap Calculations ...................................................................... Section L: Ll- L3 Erosion Control Calculations ................................