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HomeMy WebLinkAboutTHE HUB ON CAMPUS - PDP - PDP160038 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENTkimley-horn.com 1001 Warrenville Road, Suite 350, Lisle, IL 60532 630 487 5550 PRELIMINARY DRAINAGE MEMORANDUM To: City of Fort Collins From: Lesley Netzer Kimley-Horn and Associates, Inc Date: November 29, 2016 Re: The Hub 1415 West Elizabeth Street Fort Collins, CO Introduction Kimley-Horn and Associates, Inc., serves as the engineering consultant for CORE Fort Collins 1415 Elizabeth LLC. They are proposing to construct a multi-family residential and retail building with an associated parking garage at 1415 West Elizabeth Street in Fort Collins, Colorado (Larimer County). The site is approximately 1.93 acres and spans three existing parcels. The site work includes demolition, grading, stormwater management, water, sanitary sewer, paving installation, and landscape improvements. The “Urban Drainage and Flood Control District Manual” Volumes 1, 2, and 3 (UDFCD Manual) and the Fort Collins Amendments to the UDFCD, with latest revisions, were used to prepare the stormwater approach and calculations. Existing Conditions The approximate 1.93-acre project consists of three separate parcels, currently developed as a restaurant, brewery, and associated parking lot. The site is bound to the east and south by multi- family residential buildings and to the west by a recently developed commercial/retail center. The site has frontage along W. Elizabeth Street, where the existing stormwater drainage for the site outfalls. The site is part of the Old Town Drainage Basin, stormwater runoff flows to Spring Creek, ultimately tributary to the Poudre River. Based on the NRCS soils map provided in Appendix A, the expected soils on site are mainly Altvan- Satanta Loams having a hydrologic soil group rating B. Currently developed, the site is approximately 88.1% impervious. The site is located within City of Fort Collins Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map Number 08069C0978G, revised May 2, 2012 and is designated as an area outside the 500-year floodplain. The FEMA Firmette is included in Appendix B. Proposed Conditions The proposed development includes a mixed-use building, consisting of both multi-family residential as well as retail space along W. Elizabeth Street. In addition, a parking garage is proposed southwest Page 2 kimley-horn.com 1001 Warrenville Road, Suite 350, Lisle, IL 60532 630 487 5550 of the main structure. The proposed impervious percentage is 71.5%, a net decrease in impervious area of approximately +/-13,800 square feet. Reference the existing and proposed area exhibit in Appendix C. Runoff for the site will primarily be directed to the proposed pervious paver system located on the south, west, and east sides of the building. Roof drains for the proposed mixed use building will discharge on the surface, directing flow to the pervious pavers. Runoff from the parking garage will be directly routed to the proposed storm sewer system. The storm sewers will be properly sized for a minor storm event (2-10 year storm) per Volume 1, Chapter 4 of the Fort Collins Amendments to the UDFCD. Adequate provisions will also be made to pass a major storm event (100-year storm) through the development. Since there is a net decrease in percent impervious from existing conditions to proposed, detention will not be required for the development with respect to stormwater release. Water Quality and BMP Selection The proposed development will be required to meet all applicable water quality design criteria referenced in Volume 3, Chapter 3.0 of the UDFCD Manual. The manual recommends a four-step process for treating the required water quality volume as shown below. 1. Employ runoff reduction practices - The redevelopment on an urban site provides limited opportunities to employ runoff reduction practices. The site has been developed to install landscaping wherever pavement (or building) is not required for the functionality of the site. 2. Implement BMPs that provide a water quality capture volume with a slow release – The majority of site will be treated by “Permeable Interlocking Concrete Pavement” (Pervious Pavers) per Volume 3, Chapter 4, Section T-10.1 of the UDFCD Manual. 3. Stabilize Drainage Ways – Not applicable. This development is not adjacent to a stream, nor does it directly impact the downstream water body (Spring Creek). 4. Implement site specific and other source control BMPs –Trash and recycling containers will be provided on site. Vehicular parking will be located inside the parking structure to reduce potential for contamination discharges. The water quality volume required in permanent best management practices is calculated below: 𝑊𝑄𝐶𝑉 (𝑊𝑎𝑡𝑒𝑟𝑠ℎ𝑒𝑑 𝐼𝑛𝑐ℎ𝑒𝑠) = 𝑎(0.91𝐼 3 − 1.19𝐼 2 + 0.78𝐼) I = Composite Tributary Imperviousness [%/100] = 0.72 a = Coefficient of drain time (a = 0.8 for 12-hour drain time) 𝑊𝑄𝐶𝑉 (𝑊𝑎𝑡𝑒𝑟𝑠ℎ𝑒𝑑 𝐼𝑛𝑐ℎ𝑒𝑠) = 0.8[0.91(. 72) 3 − 1.19(. 72) 2 + 0.78(. 72)] = 0.227 𝑖𝑛𝑐ℎ𝑒𝑠 𝑉𝑜𝑙𝑢𝑚𝑒 = (𝑊𝑄𝐶𝑉) 12 𝐴 WQCV = Watershed Inches (calculated above) A = Tributary Area (acres) 𝑉𝑜𝑙𝑢𝑚𝑒 = (𝑊𝑄𝐶𝑉) 12 𝐴 = 0.227 12 1.9 = 0.036 𝑎𝑐 − 𝑓𝑡 = 1,570 𝐶𝐹 Page 3 kimley-horn.com 1001 Warrenville Road, Suite 350, Lisle, IL 60532 630 487 5550 In total, there will be approximately 9,500 SF of pervious pavers with a 6” stone base and 4” perforated underdrain. Assuming 40% porosity, this equates to 1900 CF of water quality storage in the stone voids, thus meeting the 1,570 CF requirement. Per Volume 3, Chapter 3 of Fort Collins Amendments to the UDFCD;  50% of the newly added or modified impervious area must be treated by LID techniques and  25% of the new paved areas must be pervious. The pervious pavers will consist of 61% of the proposed pavement areas, thus meeting the second requirement. Approximately 1.20 acres of the site (62% of site runoff) will be tributary to the pavers, thus more than 50% of the site will be treated by the water quality BMP. Attachments  NRCS Soils Map  FEMA Floodplain Map  Existing and Proposed Area Exhibit Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/14/2016 Page 1 of 4 4491420 4491440 4491460 4491480 4491500 4491520 4491540 4491420 4491440 4491460 4491480 4491500 4491520 4491540 491200 491220 491240 491260 491280 491300 491320 491340 491360 491380 491200 491220 491240 491260 491280 491300 491320 491340 491360 491380 40° 34' 28'' N 105° 6' 14'' W 40° 34' 28'' N 105° 6' 6'' W 40° 34' 24'' N 105° 6' 14'' W 40° 34' 24'' N 105° 6' 6'' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 45 90 180 270 Feet 0 10 20 40 60 Meters Map Scale: 1:927 if printed on A landscape (11" x 8.5") sheet. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Hydrologic Soil Group Hydrologic Soil Group— Summary by Map Unit — Larimer County Area, Colorado (CO644) Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 3 Altvan-Satanta loams, 0 to 3 percent slopes B 2.0 95.7% 76 Nunn clay loam, wet, 1 to 3 percent slopes C 0.1 4.3% Totals for Area of Interest 2.1 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/14/2016 Page 3 of 4 Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/14/2016 Page 4 of 4 FOUND #4 REBAR FOU L.S. FOUND 1 1/4" YELLOW PLASTIC CAP L.S. NO. 27927 ELIZABETH STREET FOUND #4 REBAR FOUND 1 1/4" YELLOW SALES RETAIL SPACE RESIDENTIAL RESIDENTIAL PARKING GARAGE REDEVELOPMENT (REFERENCE ONLY) ELIZABETH STREET © THE HUB COLORADO STATE 1415 W. ELIZABETH STREET FORT COLLINS, CO 80521 EX1.0 EXISTING AND PROPOSED AREAS AREA SUMMARY AREA LEGEND PROPOSED CONDITIONS 1" = 30' EXISTING CONDITIONS 1" = 30' NORTH Survey Area Data: Version 10, Sep 22, 2015 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Apr 22, 2011—Apr 28, 2011 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/14/2016 Page 2 of 4