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HomeMy WebLinkAboutSUBWAY @ 651 SE FRONTAGE RD. - PDP - PDP120016 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFINAL DRAINAGE AND EROSION CONTROL REPORT LOT 17, INTERCHANGE BUSINESS PARK FORT COLLINS, COLORADO IV. DRAINAGE FACILITY DESIGN A. General Concept 1. Drainage Problems encountered include the potential for discharging developed runoff to an adjacent private property. The original Interchange drainage report does not require on site detention. To mitigate the potential impact to the neighboring property, detention is provided and release directed to the public right of way. 2. Detention storage and water quality is achieved by the use of an extended detention basin. Outlet works are designed for the water quality and 100 year release rate. Due to the small size of the site and small release rate, a separate release for the minor storm is impractical. 3. Detention specifics are summarized as follows: Water Quality Volume 435 cf Water Quality Elevation 4,929.62 ft 100 Year Detention Volume 2,141 cf 100 Year + WQ Volume 2,576 cf 100 Year + N/Q Elevation 4,930.84 ft Volume Provided 2,927 cf Overflow Elevation 4,931.00 ft Freeboard 1.00 ft Outlet Orifice Size 7/8 in 4. Pond Maintenance access can be from the site parking lot. 5. An access and maintenance easement will be provided by separate document in the form and style required by the City. 6. Required offsite facilities to convey drainage include the existing roadside ditch along State Highway 14 Frontage Road. V. CONCLUSIONS A. Compliance with Standards 1. Proposed drainage facilities are in compliance with the Fort Collins Stormwater Criteria Manual. 2. Proposed drainage facilities are in compliance with the City's Master Drainage Plan. Specifically the aforementioned Interchange Drainage Study. 3. Proposed drainage facilities are in compliance with the City's floodplain regulations. 4. Proposed drainage facilities are in compliance with known State and Federal regulations. FINAL DRAINAGE AND EROSION CONTROL REPORT LOT 17, INTERCHANGE BUSINESS PARK FORT COLLINS, COLORADO A level of IVIDCIA is achieved by routing roof runoff to surface discharge and conveyance to the detention/water quality pond via grass swale. This meets step 1 of the 4 step process. Step 2 is achieved with the use of an extended detention water quality facility. Step 3 involves drainage channel stabilization. There are no drainageways on the site. The type of commercial establishment proposed does not generate the level of point source pollutants normally seen on larger scle commercial or industrial sites. In an effort to meet step 4 of the process, trash bins should be provided with lids and kept closed when not immediately in use. C. Development Criteria Reference and Constraints 1. See previous sections for detailed discussions of the previous drainage study. Since increased runoff generated by development does not flow in the appointed path, and since increased runoff may have a tendency to enter the adjacent private property, detention is proposed for this site. Detention release will be to the roadside ditch to the north effectively mitigating increased runoff to the adjacent site. 2. Adjacent drainage studies are not negatively impacted by this development. 3. Site constraints dictate that an extended detention water quality system be used in lieu of a sand filter as there is not adequate depth to outfall for the sand filter underdrain. Existing streets and utilities are not affected by the drainage of the developed site. D. Hydrologic Criteria 1. The design rainfall event or this site is the 100 year storm. 2. Runoff is calculated using the rational method. 3. Detention storage is calculated using Urban Drainage Formula. Allowable discharge is calculated by the 2 year historic runoff. 4. The design storm recurrence interval is the 100 year storm. 5. All calculations are based upon criteria standard methods. E. Hydraulic Criteria 1. Pipe capacity is calculated by the Manning formula. 2. No alternate design criteria is used. 3. No modifications to the 100 year flood plain are proposed. 4. No modifications to a natural drainageway are proposed. F. Floodplain Regulations Compliance The site is not within a floodplain. G. Modifications of Criteria No modifications to the criteria are requested. 2. 3. 2. FINAL DRAINAGE AND EROSION CONTROL REPORT LOT 17, INTERCHANGE BUSINESS PARK FORT COLLINS, COLORADO Boxelder Creek. This weir is labeled 1B in the Interchange drainage report. Ponding at this location is calculated to an elevation of 4933.21. The ponding limit is shown shaded on the attached drainage map prepared for this report. Additional observations in the Interchange report indicate that detention is not required for the individual lots in the development. Water quality concerns were not addressed in the Interchange report. The Subway parcel is located within basin 1 as shown on the Interchange drainage map. It was the intent of the original report that runoff from the Subway parcel, Lot 17, be directed easterly along Denrose Court and discharge via open channel to Boxelder Creek. In reality, Lot 17 cannot flow as prescribed due to as -built grades on the adjacent streets. In the present/historic condition, site runoff flows to the west onto the adjacent property. As the site is currently depressed, runoff to the adjacent site likely only occurs in more extreme rainfall events. The Boxelder Creek basin in the immediate area of the Subway site is developed with commercial land uses. Remaining undeveloped lots in the area are zoned for commercial development. There are no irrigation facilities in the immediate area of the proposed Subway development. Sub -Basin Description Site topography slopes down from the adjacent street to the east to a flat site depressed approximately 1' from the adjacent property to the west in the historic condition. Excess runoff will flow offsite to the west onto private property if storm water ponds sufficiently to fill the depressed site. The proposed developed site will drain to the north to a new detention and water quality facility with discharge to the adjacent roadside ditch along State Highway 14 Frontage Road. Expanding upon the basin discussion above, the shaded area on the attached drainage plan indicates the 100 year ponding limits associated with Boxelder Creek. As indicated, this area does not infringe upon the Subway site. As added protection from the flood elevation of 4933.21 indicated in the Interchange report, a ridge line is graded to elevation 4934.5 behind the sidewalk at the northeast corner of the Subway site. This provides in excess of 1 foot of freeboard above the 100 year flood elevation. Should flooding occur in excess of the 100 year event, storm water will overflow to the west along the State Highway 14 Frontage Road. III. DRAINAGE DESIGN CRITERIA A. Regulations No deviations from the criteria are requested. B. MDCIA and the 4 Step Process FINAL DRAINAGE AND EROSION CONTROL REPORT LOT 17, INTERCHANGE BUSINESS PARK FORT COLLINS, COLORADO PART 1 - DRAINAGE I. GENERAL LOCATION AND DESCRIPTION A. Location 1. Vicinity Map — Reference Drainage Plan in the back pocket 2. The site is situated in the NW 1/4 of Section 15, Township 7 N, Range 68 W of the 6th P.M. 3. Adjacent streets are State Highway 14 Frontage Road to the north and SE Frontage Road to the east. 4. There are no major drainageways on or adjacent to the site. On site easements include utility easements on all sides of the site as well as a PSCo easement along the northern portion of the site. 5. Surrounding developments include un-platted land to the west and Interchange Business Park to the east and south. State Highway ROW lies to the north. B. Description of Property 1. Site area is 0.51 acres. 2. Ground cover consists of native grass and weeds. Site soils are classified as loam. Site topography slopes down from the adjacent street to the east to a flat site depressed approximately 1' from the adjacent property to the west. 3. There are no major drainageways on the site. 4. Proposed site development consists of the construction of a new 1,400 sf Subway restaurant with associated parking and utilities. 5. There are no irrigation facilities on the site. 6. proposed land use is commercial -retail. C. Floodplain Submittal Requirements 1. The site is not within a floodplain. II. DRAINAGE BASINS AND SUB -BASINS A. Major Basin Description The site as shown on Flood Insurance Rate Map Number 08069C1003G is - located in zone x areas to be outside the 0.2% chance of annual Floodplain. The site is tributary to the Boxelder Creek basin. A previous study was conducted by Northern Engineering and results reported in a study entitled "Final Drainage Report for Interchange Business Park" dated April 13, 2001. In this report, findings indicate that flooding from Boxelder Creek will collect at the low point in the Southeast Frontage Road south of the intersection with State Highway 14. A weir was created at this, point which directs the flood waters to the east to FINAL DRAINAGE AND EROSION CONTROL REPORT LOT 17, INTERCHANGE BUSINESS PARK FORT COLLINS, COLORADO Prepared By: Perception Design Group, Inc. 6901 South Pierce Street, Suite 350 Littleton, CO 80128 Contact: Jerry W. Davidson, P.E. (303) 232-8088 Prepared For: Excell Fund Development, LLC 3400 East Sayaud Avenue, Suite 290 Denver, CO 80209 (303) 321-5372 Contact: Virgil Shouse Job No. 2012-004 May 16, 2012 Prepared Under the Direct Supervision of Jerry W. Davidson, P.E. Colorado Registration No. 30226 For And On Behalf Of Perception Design Group, Inc.