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Home My WebLink AboutSOLARIUM - PDP190016 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPermits & Engineering Company – rick@permitsandengco.com – 970-978-1627 Memo To: City of Fort Collins From: Rick Behning, P.E. cc: Solarium LLC Date: October 10, 2019 Re: Lot 1, Springwood Institute PUD (Solarium) Drainage Comparison Technical Memo This memo is intended to provide a stormwater runoff (C-Value) and over all re-developed drainage comparison for the above referenced lot located at 706 East Stuart Street. Lot 1 is 60,419 Square Feet (1.39 Acres) in size and has existing improvements that include two buildings, a parking lot and associated drive isles, walks, and landscape improvements. The proposed condition will rehabilitate the existing asphalt paved parking area and drives and expand the parking from 10 spaces to a total of 11 spaces. Additional improvements are required in the Stuart Street ROW to provide compliant sidewalks, pedestrian paths, and driveways that meet current City standards. The property is bounded on the south by East Stuart Street, on the west by residential property and the Mallards Nest Natural Area, on the north by East Alpert Court and the Spring Creek Trail, and on the East by residential properties. The site generally drains from the front ROW/Property line to the back of the lot, towards Spring Creek, which runs through the northern portion of the lot in an existing “Permanent Drainage, Utility, and Trail Easement” (Recordation Number: 92019989). As such, the FEMA mapped Spring Creek Floodplain (Zone AE) and Floodway encumber the north third of the property. A Zone AO floodplain (2’ depth of flow) runs from East Stuart Street along the east side of the subject property, northerly towards the main channel. No improvements are proposed within the actual floodplain limits, as defined by the FEMA Map Base Flood Elevations (at defined cross sections) and the existing topographic conditions. However, a future replacement of the pedestrian bridge across Spring Creek is proposed if a Floodplain Use Permit can be obtained for the future improvements. Please refer to the attached Overall Drainage, Grading, and Erosion Control Plan as excerpted from the Preliminary Utility Plan set for reference. In-between the parking lot, buildings, and landscaped areas and the Spring Creek channel is a broad vegetated buffer of blue grass that contributes to the treatment of stormwater runoff as it approaches Spring Creek. While the runoff from the parking areas is channelized before it reaches the grass buffer, it appears high frequency runoff discharges likely spread out and function more like sheet flow within this broad and flat buffer, which enhances the filtration 2 effects of the feature. On the east side of the property flows are conveyed to a flat area with slopes under 2% for a distance of approximately 87 feet x 64 feet wide (Approx. 5,600 SF). Directly between the existing buildings and Spring Creek is another vegetated buffer, which is more or less the overbank floodplain limits. This area averages about 40 feet in length by 120 feet in width (4,800 SF) with cross slopes between 2.5% and 5%. The apparent vegetative buffer extends west into the Mallards Nest Natural Area. Proposed site changes that impact drainage runoff amounts and quality are summarized as follows:  Improve East Stuart Street pedestrian facilities to be compliant with current City code requirements, including: addressing non-compliant driveway ramps, upgrading sidewalk to achieve 4’ minimum width and ADA compliant cross slopes, incorporating a clear pedestrian path from Stuart to the front door, and providing a mid-block access ramp at the existing striped cross walk.  Repair/repave deteriorated asphalt paving in existing driveway.  Expand parking lot paving to create a one-way drive with both head in and angled parking to accommodate one additional space and a Van Accessible Handicap parking space.  Enhance the parking lot with a new landscaped island and pedestrian path in the middle.  Modify the trash management system to properly size and enclose the trash and recycling area.  Incorporate a concrete drainage pan into the asphalt parking surface to mitigate a ponding condition at the SW corner of the smaller building. The site soil characteristics are that of Type B soils (Altvan-Satanta loams) outside of the Spring Creek channel (Type C (Nunn clay loam) north of and including the Spring Creek channel). See attached Web Soil Survey map for reference. Using the City of Fort Collins Tables 3.2-2 “Surface Type – Runoff Coefficients” and Table 3.2-3 “Frequency Adjustment Factors”, the existing and proposed C-Value calculations are provided (See attachment) to compare the existing conditions to the proposed conditions. The overall change in the imperviousness of the site increases from 17.0% Impervious to 17.59% Impervious. This increase appears to be negligible because the calculated runoff coefficients for the existing and proposed conditions are the same. The existing and proposed C-Values are: C2 = 0.28, C5 = 0.28, and C100 = 0.32. Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/20/2019 Page 1 of 4 4490300 4490310 4490320 4490330 4490340 4490350 4490360 4490370 4490380 4490390 4490400 4490300 4490310 4490320 4490330 4490340 4490350 4490360 4490370 4490380 4490390 4490400 494340 494350 494360 494370 494380 494390 494400 494410 494340 494350 494360 494370 494380 494390 494400 494410 40° 33' 51'' N 105° 4' 1'' W 40° 33' 51'' N 105° 3' 57'' W 40° 33' 48'' N 105° 4' 1'' W 40° 33' 48'' N 105° 3' 57'' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 25 50 100 150 Feet 0 5 10 20 30 Meters Map Scale: 1:538 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 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: 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 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 4 Altvan-Satanta loams, 3 to 9 percent slopes B 0.9 73.0% 76 Nunn clay loam, wet, 1 to 3 percent slopes C 0.3 27.0% Totals for Area of Interest 1.3 100.0% 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 9/20/2019 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 9/20/2019 Page 4 of 4 Acres Site Percentage % Impervious Weighted Landscape 1.63 83.0% 2.0% 3.3% Roofs 0.15 7.4% 90.0% 13.1% Gravel 0.03 1.4% 40.0% 1.1% Drives and Walks 0.16 8.1% 100.0% 15.9% Total 1.96 100.0% 17.0% Acres C-Value Composite C2 1.96 Landscape 1.63 0.15 0.24 Roofs 0.15 0.95 0.14 Gravel 0.03 0.50 0.01 Drives and Walks 0.16 0.95 0.15 0.28 C2 Acres C-Value Composite C5 1.96 Landscape 1.63 0.15 0.24 Roofs 0.15 0.95 0.14 Gravel 0.03 0.50 0.01 Drives and Walks 0.16 0.95 0.15 0.28 C5 Acres C-Value Composite C100 1.96 Landscape 1.63 0.19 0.31 Roofs 0.15 1.00 0.15 Gravel 0.03 0.63 0.02 Drives and Walks 0.16 1.00 0.16 0.32 C100 Solarium Runoff Coefficient Calculations Existing Acres Site Percentage % Impervious Weighted Landscape 1.63 83.4% 2.0% 3.27% Roofs 0.14 7.2% 90.0% 12.67% Gravel 0.00 0.0% 40.0% 0.00% Drives and Walks 0.19 9.5% 100.0% 18.53% Total 1.96 100.0% 17.59% Acres C-Value Composite C2 1.96 Landscape 1.63 0.15 0.25 Roofs 0.14 0.95 0.13 Gravel 0.00 0.50 0.00 Drives and Walks 0.19 0.95 0.18 0.28 C2 Acres C-Value Composite C5 1.96 Landscape 1.63 0.15 0.25 Roofs 0.14 0.95 0.13 Gravel 0.00 0.50 0.00 Drives and Walks 0.19 0.95 0.18 0.28 C5 Acres C-Value Composite C100 1.96 Landscape 1.63 0.19 0.31 Roofs 0.14 1.00 0.14 Gravel 0.00 0.63 0.00 Drives and Walks 0.19 1.00 0.19 0.32 C100 Solarium Runoff Coefficient Calculations Proposed CC CC CC CC CC CC CC CC CC CC CC X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X CC CC C S C S CC CC CC CC CC CC M CABLE TC T T G E T H Y D 150 CP - WALK N:122394.64 E:197740.35 ELE=4973.60 DESC: SET INK "X" ON CONCRETE SIDEWALK 151 CP - TEEPEE N:122641.35 E:197747.95 ELE=4962.25 DESC: SET 18" OF #4 REBAR WITH ORANGE PLASTIC CAP 152 CP - SOLARIUM N:122624.90 E:197604.95 ELE=4963.01 DESC: SET 18" OF #4 REBAR WITH ORANGE PLASTIC CAP 153 CP - WILLOW N:122446.68 E:197549.54 ELE=4971.73 DESC: SET INK "X" ON CONCRETE SIDEWALK 2-STORY STUCCO BUILDING TEEPEE 2-STORY STUCCO BUILDING CC CC D S CC CC X X X X X ELEC BRKR WITH ORANGE PLASTIC CAP FF=4972.63 FF=4973.78 FF=4971.40 FF=4980.56 FF=4971.60 STORM MANHOLE 1170 RIM=4962.91 *INVERTS NOT OBTAINED* SHED SHED SPLIT-RAIL FENCE SPLIT-RAIL FENCE SPLIT-RAIL FENCE SPLIT-RAIL FENCE SPLIT-RAIL FENCE SPLIT-RAIL FENCE WOOD PRIVACY FENCE GATE GATE GATE E. ALPERT CT E. STUART ST STOVER ST S ZONE AO FLOODPLAIN FLOODWAY FLOODWAY (ROW VARIES) 1 2 3 4 5 6 7 7 6.0' EASEMENT 6.0' EASEMENT REC. NO. 90027039 BK 1981 PG 776 6.0' EASEMENT BK 1981 PG 776 40.0' CHANNEL AND DRAINAGE EASEMENT 20.0' EASEMENT 6.0' EASEMENT BK 1981 PG 776 5.0' UTILITY EASEMENT 10.0' UTILITY EASEMENT 10.0' UTILITY EASEMENT 12.0' EASEMENT 12.0' EASEMENT 10.0' UTILITY EASEMENT 25.0' EASEMENT BK 2300 PG 940 12.5' EASEMENT BK 2300 PG 940 PERMANENT DRAINAGE, UTILITY AND TRAIL EASEMENT RECEPTION NO. 92019989 PERMANENT DRAINAGE, UTILITY AND TRAIL EASEMENT RECEPTION NO. 92019989 15.0' ACCESS EASEMENT FOR THE BENEFIT OF LOT 1, SPRINGWOOD INSTITUTE PUD PER ORDER OF CASE NO. 97 CV 235 REC. NO. 20030116451 (9-10-2003) ZONE AE FLOODPLAIN LINE 15' EXCEPTION PARCEL REC. NO. 20160043331 8 DRAFT of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 13, Sep 10, 2018 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. Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/20/2019 Page 2 of 4