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HomeMy WebLinkAboutPLANETSCALE LIVING - PDP200015 - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE RELATED DOCUMENT April 27, 2021 City of Fort Collins Public Works and Development (Stormwater Department) 201 Laporte Ave, Fort Collins, CO 80521 RE: Drainage Letter – Low Impact Development Project: 2020-006 (TT) Serdar Badem, 906 E Stuart St, Fort Collins, CO 80525 To Whom it may Concern: This Drainage Letter is for analysis of on-site drainage for Low Impact Development for Project 2020-006 (TT) Serdar Badem, 906 E Stuart St, Fort Collins, CO 80525. The project is in Fort Collins, Colorado and will entail converting (remodeling) an existing childcare center into an affordable housing 4-Plex. The site (parcel #9724106924) is located 850 feet west of S. Lemay Avenue and 1,200 feet south of E. Prospect Road. Access is taken from E. Stuart Street directly to the south. The property is within the Low Density Mixed-Use Neighborhood District (L-M-N) zone district and is subject to Administrative (Type 1) Review. The existing drainage on site has no drainage structures and minimal surface flow (on-site or off-site). Most of the existing site (Figure 1) consists of Concrete access and driveway; most of the southern portion of the site, the concrete footprint of building, concrete patio and the remaining consists of grass/dirt/gravel mixture with trees. The existing site is flat with minimal to zero slopes throughout the site. To the east there is an HOA Easement that parallels the site and Spring Meadows Court. The HOA will not allow any construction and/or stormwater work within this area. Because of this limitation, the project will be implementing Low Impact Development drainage solutions using City of Fort Collins Stormwater Criteria Manual – Chapter 7, Section 6.0 and Appendix C – LID Implementation Manual. Because of the inability to go of site with any of the on-site run-offs; the project will design LID solutions that will improve the entire site. Table 1 Below shows that around forty-two percent of the existing site is impervious (Areas 2 & 4) and the remaining pervious areas (1 & 3) are limited because of no positive slope and random native material mixed with dirt, grass, gravel and rocks. The proposed solution will be to implement Pavers and Landscape Beds/Areas throughout most of the site, which will improve and be below the 1000 s.f. requirement for LID water quality requirement (Table 1). No LID water quality requirement will be needed for this site. Table 1 Figures 1 (existing) and Figure 2 (Proposed) [correspond with Table 1] Figure 1 - Existing Figure 2 – Proposed MAJOR DRAINAGE BASINS & SUB-BASINS A. The site is not within a Floodplain; the site does not lie within the Regulatory Floodway Zone. (All new construction is outside the floodway boundaries). There are no storm drainage structures located in the property. All flows inflow and outflow are surface. The main site is made up of existing building, parking and access road south front which is concrete. The northern/western portion of the existing site is native grass / dirt / gravel. The existing southern access drive and eastern concrete areas are standing water and minimal surface flows to eastern HOA easement towards Spring Meadows Court. This project will not be allowed to construct any drainage structures or grading within the HOA Easement. B. Drainage analysis – Mile High Flood District: Rational Method v.2 was used (spreadsheet-based calculations for surface, %I runoff). C. The proposed site is with an Urban Drainage Area. The site is LID and all drainage and runoff with be onsite controlled with Pavers and landscaped control areas. The proposed site will match exiting grades and historic flows. D. Basins & Sub-Basins: BASIN 1 – (0.25 Acres) Existing Site with existing structure; full area. Sub-basin 1a - (0.06 Acres, %I 0.10) This area will remain with no change to grade or surface. Existing area with no construction. Sub-basin 1b - (0.10 Acres, %I .40) New parking area with permeable pavers. No change in grade or historic. Sub-basin 1r - (0.07 Acres, %I .95) Proposed building and boundary. Foundation remains. No change in FF or grades around building. Matching grades and flows away from structure. Sub-basin 1c - (0.02 Acres, %I 0.10) Proposed area in front of building. No change in grade (match existing from building). Removed and re-aligned new sidewalk. Landscape area. Sub-basin 1d - (0.03 Acres, %I .10) New proposed detached sidewalk (adjusted from existing front area. No change in grade. Proposed access moved to eastern edge. FINISH FLOOR ELEVATIONS The Finish Floors have been established to set at 4980.75. Proposed site will match flow patterns and drain as per existing conditions. FLOOD PLAINS The site is not within a Floodplain; There is no documented history of flooding. MAINTENANCE PLAN: Owner will complete a monthly maintenance inspection once a month to clean and remove any trash, debris and vegetation that is restricting or not allowing pavers and/or landscape areas to drain. This will include any mowing or trimming of landscaped areas. Any repairs to the grading because of washout and/or sedimentation will be removed. CONCLUSIONS Proposed construction will have minimal to no impact to the existing flows onsite / offsite. The design drainage will provide measures that protect public health, safety, and the general welfare of the proposed site and surrounding areas; plus have no impacts on public rights-of-way or offsite properties. The proposed project includes 816.48 sf (<1000 s.f.) of added/modified impervious area. The project will treat 48.30% of this area (5854.14 sf) using permeable pavers and run-on to the pavers. The proposed project provides 7.86% of new impervious area as permeable pavers (1520 sf) located in parking areas within the site. The project will treat new impervious area using a combination of LID treatments (both permeable pavers and landscape beds/areas). A summary LID Compliance Table is provided below. Summary In summary, the proposed project incorporates permeable pavers as the primary component of stormwater LID treatment. The proposed solution will be to implement Pavers and Landscape Beds/Areas throughout most of the site, which will improve and be below the 1000 s.f. requirement for LID water quality requirement (Table 1). No LID water quality requirement will be needed for this site. This project and memo are in compliance with the City of Fort Collins Stormwater Criteria Manual (December 2018) and associated references to the latest version of the Urban Drainage and Flood Control District Manual. If you have any questions regarding this submittal, please do not hesitate to contact me by email at apowell@pec-inc.co or by phone at (720) 409-2454. Thank you. Adam A. Powell, PE PEC Inc (From Fort Collins Stormwater Criteria Manual - 6.0 Low Impact Development) This Section of this Chapter presents information that is specific to the City of Fort Collins and may be a significant deviation from the information presented in the UDFCD Manuals. Utilizing UDFCD methodologies for Low Impact Development (LID) designs may not be accepted by FCU. In February 2013, Fort Collins City Council adopted Ordinance No. 152, 2012, to incorporate provisions implementing LID principles; with the goal to declare that the purpose of the City Stormwater Utility is to provide an integrated, sustainable stormwater management program that reflects the community’s values of protecting and restoring the City’s watersheds. This was subsequently modified and updated in January 2016 with Ordinance No. 007, 2016 to allow for some added flexibility in the implementation of the LID policy. Reference: Both the initial LID ordinance, Ordinance No. 152, 2012, and the subsequent ordinance, Ordinance No. 007, 2016, can be found on the City of Fort Collins website. LID is simply defined as an integrated, sustainable stormwater management program that requires a distributed, closer to the source stormwater runoff control that simulates natural processes and relies mainly on filtration and infiltration to locally treat and manage stormwater runoff. Integration of LID systems into the drainage design is required for all development projects in order to comply with the City’s policies on LID, the requirements of this Manual, the City Code and the Land Use Code. LID systems provide a higher degree of stormwater quality treatment than that provided with standard water quality design. The implementation of LID systems requires one of the following two options: 1) 50% of the newly added or modified impervious area must be treated by LID techniques and 25% of new paved (vehicle use) areas must be pervious. 2) 75% of all newly added or modified impervious area must be treated by LID techniques. Impervious surfaces are defined as hardscape surfaces that do not allow stormwater to infiltrate into the ground. Impervious surfaces include asphalt and concrete surfaces, concrete curbs, gutters, sidewalks, patios and rooftops. (Impervious surface areas must be assumed for single family residential lots when overall impervious areas are being determined for residential developments. The assumed areas must then be included in LID calculations.) “Added” impervious area stated in the two options above is further defined as existing vegetation (or pervious) areas becoming hardscape (or impervious) areas. “Modified” impervious area stated in the two options above is further defined as existing impervious areas on an existing site being removed and replaced with other impervious surfaces through a redevelopment process (i.e. existing asphalt surface becoming a rooftop surface). Mill and overlay of asphalt areas is not considered a “modified” impervious area. “Paved” areas, as stated in option 1 above are generally considered to be private vehicle use areas only. Reference: Refer to the City of Fort Collins LID Implementation Manual in Appendix C for detailed information and requirements on LID systems. (From Fort Collins Stormwater Criteria Manual - 6.2 Permeable Pavement) The term “permeable pavement” is a general term to describe any one of several pavement systems that allow infiltration of water into the layers below the pavement through openings within the pavement surface. Use of permeable pavements is an accepted Low Impact Development (LID) practice in Fort Collins and is often used in combination with other BMPs to provide full treatment and slow release of the WQCV. In addition, there are some installations in Fort Collins that have also been designed with an outlet control and increased depth of aggregate material in order to provide quantity detention in excess of the water quality (80th percentile) storm event. Design considerations for permeable pavement systems are presented in the LID Implementation Manual, included in Appendix C. Included here are some general design requirements applicable for all types of LID system designs in Fort Collins. • Overall added or modified impervious areas that amount to less than 1000 square feet (< 1000 sf) on a site will not require LID system treatment for water quality. • For development sites that are adding or modifying 1000 square feet of imperviousness or more (≥ 1000 sf) are required to implement LID system treatment at the site. The LID system is allowed to treat existing imperviousness in exchange for the newly added imperviousness if the surface character is similar (e.g. existing pavement may be treated in lieu of newly added rooftop) • For single-family residential developments, LID must be placed in tracts or common areas for ownership and maintenance by the HOA. LID systems installed as part of the development requirement shall not be placed on single-family lots. • LID is not required for private, single-family residential improvement projects that are not a part of a larger subdivision project. (i.e. an existing lot in an older part of Fort Collins that is being re-built) APPENDIX A (VICINITY MAP) APPENDIX B (N.O.A.A. ATLAS 14) Soil Map—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/1/2020 Page 1 of 3449024044902604490280449030044903204490340449036044903804490400449024044902604490280449030044903204490340449036044903804490400494760494780494800494820494840494860494880 494760 494780 494800 494820 494840 494860 494880 40° 33' 52'' N 105° 3' 43'' W40° 33' 52'' N105° 3' 37'' W40° 33' 46'' N 105° 3' 43'' W40° 33' 46'' N 105° 3' 37'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 40 80 160 240 Feet 0 10 20 40 60 Meters Map Scale: 1:887 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features 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: 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 Survey Area Data: Version 15, Jun 9, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Aug 11, 2018—Aug 12, 2018 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. Soil Map—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/1/2020 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 95 Satanta loam, 1 to 3 percent slopes 2.4 72.8% 101 Stoneham loam, 1 to 3 percent slopes 0.9 27.2% Totals for Area of Interest 3.3 100.0% Soil Map—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/1/2020 Page 3 of 3 APPENDIX C Designer: Company: 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr Date: 1-hour rainfall depth, P1 (in) =0.83 1.09 1.40 1.78 2.14 2.86 3.63 Project: a b c Location: Rainfall Intensity Equation Coefficients =28.50 10.00 0.786 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr Overland Flow Length Li (ft) U/S Elevation (ft) (Optional) D/S Elevation (ft) (Optional) Overland Flow Slope Si (ft/ft) Overland Flow Time ti (min) Channelized Flow Length Lt (ft) U/S Elevation (ft) (Optional) D/S Elevation (ft) (Optional) Channelized Flow Slope St (ft/ft) NRCS Conveyance Factor K Channelized Flow Velocity Vt (ft/sec) Channelized Flow Time tt (min) Computed tc (min) Regional tc (min) Selected tc (min)2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr 0.06 0.07 0.14 0.31 0.38 0.47 0.57 68.53 68.53 24.30 1.47 1.93 2.48 3.15 3.79 5.06 6.43 0.00 0.01 0.02 0.06 0.09 0.14 0.22 0.29 0.32 0.38 0.50 0.55 0.61 0.68 27.89 27.89 19.20 1.67 2.19 2.81 3.58 4.30 5.75 7.29 0.05 0.07 0.11 0.18 0.24 0.35 0.50 0.79 0.81 0.82 0.85 0.86 0.87 0.88 3.44 3.44 5.00 2.82 3.70 4.75 6.04 7.26 9.70 12.31 0.15 0.21 0.27 0.36 0.44 0.59 0.76 0.06 0.07 0.14 0.31 0.38 0.47 0.57 60.11 60.11 24.30 1.47 1.93 2.48 3.15 3.79 5.06 6.43 0.00 0.00 0.01 0.02 0.03 0.05 0.07 0.06 0.07 0.14 0.31 0.38 0.47 0.57 14.15 14.41 14.41 1.92 2.52 3.24 4.12 4.95 6.62 8.40 0.00 0.01 0.01 0.04 0.06 0.09 0.14 0.000 0.00 0.000 85.00 0.001 0.00AREA 1b 0.10 24.55 24.30 AREA 1d 0.03 B 10.0 20.00 0.002 5.00 0.001 10 0.32 0.26 9.85 AREA 1c 0.02 B 10.0 50.00 Cells of this color are for calculated results based on overrides AAP PEC 1/14/2021 4-Plex Affordable Houseing - PRO Fort Collins, CO Version 2.00 released May 2017 7 0.07 0.00 19.20 AREA 1r 0.07 B 95.0 15.00 0.002 0.00 0.020 20 2.83 0.00 0.000 20 0.20 0.00B 40.0 0.00065.00 Rainfall Intensity, I (in/hr) 0.32 0.00 24.30100.0010.00 Peak Flow, Q (cfs) Calculation of Peak Runoff using Rational Method Overland (Initial) Flow Time Channelized (Travel) Flow Time Time of ConcentrationRunoff Coefficient, C Subcatchment Name Area (ac) NRCS Hydrologic Soil Group Percent Imperviousness AREA 1a 0.06 B 10.0 Select UDFCD location for NOAA Atlas 14 Rainfall Depths from the pulldown list OR enter your own depths obtained from the NOAA website (click this link) Cells of this color are for required user-input Cells of this color are for optional override values I 𝑖𝑛/ℎ𝑟=a ∗Pଵ b + t ୡ ୡ t୧ =0.395 1.1− Cହ L୧ S୧ ଴.ଷଷ t୲ =L୲ 60K S୲ = L୲ 60V୲ Computed tୡ = t ୧ + t ୲ Regional tୡ =26 − 17i + L୲ 60 14i + 9 S୲ Selected tୡ = max t୫୧୬୧୫୳୫ ,min Computed tୡ ,Regional tୡ t୫୧୬୧୫୳୫=5 (urban) t୫୧୬୧୫୳୫=10 (non-urban) Q 𝑐𝑓𝑠= CIA APPENDIX D GRADING AND DRAINAGE PLAN AQUA ROC™ OFFERS CLASSIC APPEAL WITH A GREEN SOLUTION BY REDUCING WATER RUN-OFF. OTHER FEATURES INCLUDE LOW MAINTENANCE AND LONG-LASTING DURABILITY Amaretto Harvest Blend SHAPES & SIZES For more info, visit Belgard.com LAYING PATTERNS AVAILABLE COLORS ESTIMATING CHART SQFT/ PALLET SQFT/ LAYER LAYER/ PALLET UNITS/ PALLET UNITS/ SQFT WEIGHT/ PALLET 2-PIECEMODULAR41/2 x 9 x 31/8 (large unit) 41/2 x 41/2 x 31/8 (half unit)90 10.125 (large unit) 1.125 (half unit) 8 352 (288 large & 64 half units) 3.56 3095 lbs © 2019 Oldcastle® APG, Inc. All Rights Reserved. BEL19-102 Amcor 333 S. Redwood Rd. North Salt Lake, UT 84054  (800) 800-4004 TOSCANA VICTORIAN 41/2 x 9 x 31/8 41/2 x 41/2 x 31/8 AQUA ROC™ OFFERS CLASSIC APPEAL WITH A GREEN SOLUTION BY REDUCING WATER RUN-OFF. OTHER FEATURES INCLUDE LOW MAINTENANCE AND LONG-LASTING DURABILITY • Features a clean modular shape • Permeable paver that reduces water run-off • ADA compliant • A very strong and durable paver that will last for years to come • Supports heavy vehicular loads • Great for residential or commercial applications • Sold in Herringbone machine lay pattern only FEATURES & BENEFITS 1-PIECE HERRINGBONE (MACHINE LAY) BELGARD.COM | 877-235-4273 136 NOTES:AutoCAD® hatch pattern les can be downloaded frombelgard.com for use in architectural drawingsSome patterns may not necessarily reect thepercentages of stone sizes within a particular pallet.In some cases you may have extras in one or more ofthe sizes. This must be accounted for in your planningand design. Scale:1/2" = 1'-0" Percentages are based on area by paver. For more pattern options visit Belgard.com/products/pavers .Aqua RocHerringbone100%Paver A (4-1/2 x 9) Swatches represent product color only, not surface texture, dimensions or shape. Machine lay, product will contain 1/2 units equating to 9 sqft per pallet. Mechanical Installation Only