Loading...
The URL can be used to link to this page
Your browser does not support the video tag.
Home
My WebLink
About
PROSPECT AND COLLEGE HOTEL - PDP190014 - SUBMITTAL DOCUMENTS - ROUND 1 - STORMWATER MANAGEMENT PLAN
Preliminary Stormwater Management Report for Prospect and College Hotel Fort Collins, CO Prepared For Saunders Commercial Development Company 1705 17th Street, Suite 350 Denver, CO, 80202 9/16/2019 Project No. 18111 Prospect and College Hotel September 16, 2019 Page 1 Project No. 18111 September 16, 2019 Project No. 18111 PRELIMINARY (PDP) STORMWATER MANAGEMENT REPORT FOR PROSPECT AND COLLEGE HOTEL A PORTION OF LOT 2 OF FOX SHOPPING CENTER SUBDIVISION FORT COLLINS, COLORADO I. Overview Narrative The proposed project is an infill development that will include the construction of a new multi-level hotel building and supporting infrastructure improvements. The purpose of this report is to identify the required stormwater management and water quality facilities for the developed site. The design standards governing this project are the Fort Collins Stormwater Criteria Manual (FCSCM), Dec 2018 and the Mile High Flood District’s Urban Storm Drainage Criteria Manual (USDCM), Volume 1-3. II. General Project Location The subject property is located at 1623 South College Avenue, Fort Collins, Colorado, 80525 (Site) in the Northeast Quarter of Section 23, Township 7 North, in Range 69 West of the Sixth Principal Meridian, in the City of Fort Collins, Larimer County, Colorado. The Site lies within a portion of Lot 2 of the Fox Shopping Center Subdivision and is approximately situated at the southwest corner of South College Avenue and West Prospect Road. The property is bounded on the north by West Prospect Road and Schraders Gas Station, to the west and south by commercial businesses (Fox Shopping Center and Choice Center) and to the east by South College Avenue. III. Existing Site Information The proposed Prospect and College Hotel is located on a portion of existing Lot 2 of Fox Shopping Center Subdivision. The site has a net area of approximately 2.0083 acres and is located within the City limits of Fort Collins. Currently, the property accommodates an existing retail building occupied by Chuck E. Cheese and Fort Collins Furniture and Mattress consisting mostly of asphalt parking lot and rooftop. Major Basin Description The project site lies within the Spring Creek Basin which stormwater from the project site ultimately flows to. Spring Creek is a major watercourse that flows from Spring Canyon Dam at Horsetooth Reservoir to the Cache La Poudre River. This basin encompasses nearly nine square miles in central Fort Collins. The basin mostly contains residential development but also includes parks, open space and areas of commercial and industrial development. Sub-Basin Description` The property itself slopes generally to the north and east with stormwater runoff entering into an existing 20-foot Type R curb inlet along South College Avenue adjacent to the Schraders Gas Station. The City has stated that the downstream stormwater piping cannot accept 100% of the “historic” runoff and, due to that, the crown of College Avenue overtops with excess runoff that flows overland and to the east on a circuitous flow path to Spring Creek. The existing site provides no detention or water quality treatment of existing storm runoff prior to entering the College Avenue storm line system. Prospect and College Hotel September 16, 2019 Page 2 Project No. 18111 According to the NRCS website, the site consists mainly of Fort Collins and Altvan-Satanta loams with a classification of Type B & C soils. Refer to Appendix A for soil classification information. According to the Flood Insurance Rate Map (FIRM) for Larimer County, Colorado, Panel No. 979 of 1420, Map No. 08069C0979H, revised May 2, 2012, the proposed development is outside of any special flood hazard areas (see Appendix A). IV. Project Description The proposed project will consist of a new 6-story hotel building with approximately 83,356 square-feet of gross floor area and supporting utilities consisting of storm sewer, sanitary sewer and waterline improvements. Surface improvements include a new paved parking lot, landscaped areas and concrete sidewalk surrounding the buildings. Part of the City of Fort Collins required improvements will include the extension of utility services from existing sewer, water, and storm drain that are not located within the boundary of Lot 2. This project also proposes the removal all existing surface improvements within Lot 2 in order to accommodate the proposed improvements. Off-site improvements will mainly consist of a stormwater outfall pipe to convey stormwater from the site to the existing drainage channel to the west. V. Drainage Design Criteria A. Regulations/Development Criteria The design standards governing this project are the Fort Collins Stormwater Criteria Manual (FCSCM), Dec 2018 and the Mile High Flood District’s Urban Storm Drainage Criteria Manual (USDCM), Volume 1-3. B. Four-Step Process The overall stormwater management strategy employed with the proposed project utilizes the “Four Step Process” to minimize adverse impacts of urbanization on receiving waters. The following is a description of how the proposed development has incorporated each step. Step 1 – Employ Runoff Reduction Practices Several techniques have been utilized with the proposed development to facilitate the reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the current use by implementing multiple Low Impact Development (LID) strategies. Proposed techniques include providing landscaped island and buffer areas throughout the site to reduce the overall impervious area, to minimize directly connected impervious areas (MDCIA), providing a central bioretention island to slow the runoff rate, grading the site such that runoff is routed over a longer distance to reduce the time of concentration prior to the ultimate outfall point. Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with Slow Release The efforts taken in Step 1 will facilitate the reduction of runoff; however, urban development of this intensity will still generate stormwater runoff that will require additional BMPs and water quality. The majority of stormwater runoff from the site will ultimately be intercepted and treated using bioretention prior to the ultimate outfall point with the remaining to be treated via a grassed lined drainage channel that the site discharges to. Prospect and College Hotel September 16, 2019 Page 3 Project No. 18111 Step 3 – Stabilize Streams There are no major drainageways within the subject property, however, the proposed outfall discharges off-site into an existing grassed drainage channel to the west. Proposed stabilization and treatment to the stream at the outfall will include a concrete flared end section, riprap with fabric underlayment and a concrete forebay to settle out larger particles. Step 4 – Implement Site Specific and Other Source Control BMPs The proposed project will improve upon site specific source controls compared to historic conditions: The proposed development will provide LID and water quality treatment; thus, eliminating sources of potential pollution previously left exposed to weathering and runoff processes. C. Hydrological Criteria 1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in Figure 3.4-1 of the FCSCM, serve as the source for all hydrologic computations associated with the proposed development. Tabulated data contained in Table 3.4-1 has been utilized for Rational Method runoff calculations. 2. The Rational Method has been employed to compute stormwater runoff utilizing coefficients and calculation methods contained in Chapter 5, Section 3.2 of the FCSCM. 3. Three separate design storms have been utilized to address distinct drainage scenarios. A fourth design storm has also been computed for comparison purposes. The first design storm considered is the 80th percentile rain event, which has been employed to design the project’s water quality features. The second event analyzed is the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third event considered is the “Major Storm,” which has a 100-year recurrence interval. 4. The fourth storm computed, for comparison purposes only, is the 10-year event. 5. No other assumptions or calculation methods have been used with this development that are not referenced by current City of Fort Collins criteria. 6. The City has noted in the original concept meeting held in 2018 that detention will not be required, however, LID techniques to improve water quality should be implemented where possible. D. Hydraulic Criteria 1. All drainage facilities proposed with the project are designed in accordance with criteria outlined in the FCSCM and/or the USDCM. 2. As stated above, the subject property is not located in a City designated floodplain. The proposed project does not propose to modify any natural drainageways. E. Modifications of Criteria 1. The proposed development is not requesting any modifications to criteria at this time. Prospect and College Hotel September 16, 2019 Page 4 Project No. 18111 VI. Proposed Drainage Facilities A. General Concept The intent of the proposed design is to safely and adequately convey the minor and major design storm given the site’s existing constraints and off-site flooding concerns by the City that were previously mentioned. 1. As stated, one of the main objectives of the project drainage design was to capture and re-direct a portion of the site’s existing runoff to the west that would otherwise convey to the east, in an effort to assist the City in reducing the routine flooding that occurs at the southwest corner of South College Avenue and West Prospect Road. Based on initial calculations, approximately half of the existing peak flows would be redirected to the west drainage channel that would have otherwise flowed to South College Avenue drainage system. 2. Other than the portion of the site to be re-directed to the west, the remaining portion of the site is proposed to generally maintain historic drainage patterns, with all developed runoff being directed into the existing College Avenue storm line system. The proposed site will reduce overall site imperviousness, and will provide water quality treatment in an onsite bioretention system and an off- site, 1,200-foot long, grassed drainage channel that the re-directed flow ultimately discharges to. A more detailed description of the projects sub-basins and drainage patterns is provided below. B. Specific Details The proposed storm drainage system will collect runoff via sheet flow and curb and gutter and convey to proposed area and curb inlets. The storm drain piping will then convey the collected stormwater to the south and west to an existing drainage channel that ultimately flows to Spring Creek approximately 1,200 feet to the south of the discharge point. One of the inlets will collect overflows within a proposed bioretention facility central to the site. An off-site easement will be needed to encompass the proposed outfall storm piping from the Site to the west drainage channel. An MOU between the City and Developer will need to be established for hard and soft cost sharing of this outfall. Permission to discharge into the west channel will also need to be obtained from the owners of the easement the drainage channel is contained within. 1. There are seven total sub-basins for the project. A detailed description of each sub- basin and the drainage system within them is described as follows: Basin 1: This basin is approximately 1.10 acres and includes on and off-site flows from the south and west, respectively. This basin consists mainly of asphalt and concrete surfaces with minor landscaping. This basin flows to the proposed bioretention facility, via sheet flow and curb and gutter, to the northeast of the sub-basin with total composite imperviousness at 93%. Basin 2: This basin is comprised of approximately 0.30 acres and includes on-site flows generally from the west of the proposed building. This basin also flows to the proposed bioretention facility, via sheet flow and curb and gutter, and consists mainly of asphalt and concrete surfaces with minor landscaping. This sub-basin has a total composite imperviousness of 94%. Prospect and College Hotel September 16, 2019 Page 5 Project No. 18111 Basin 3: This sub-basin represents the bioretention facility itself and is considered mostly pervious with a minor element of concrete. An area inlet is proposed to capture overflows from the facility and convey to the underground storm system. The area is approximately 0.06 acres and has a composite imperviousness of 9.0%. Basin 4: This sub-basin lies to the north of the site and includes on and off-site flows. The design point is a Type 13 area inlet located to the east of the sub-basin that stormwater coveys to by sheet and curb and gutter flow. This area is comprised of mostly asphalt with some elements of landscaping and concrete. This sub-basin has a total composite imperviousness of 93%. Basin 5: This small sub-basin flows, via sheet and curb and gutter, to the design point to the east of the sub-basin comprised of a combination inlet. This basin contains asphalt and concrete and has a composite imperviousness of 99%. Basin 6: This sub-basin consists of roof-top only. Flows from the roof are anticipated to connect directly to the underground storm piping. Total composite imperviousness is 90%. Basin OS-1: Flows that cannot be collected in the proposed system comprise this sub- basin and are located along the east edge of the property. Runoff from this basin will flow historically to the College Avenue right-of-way and convey north to the existing Type R inlet located just north of the site. 2. Please see preliminary LID Treatment Exhibit and Water Quality Capture Volume (WQCV) computations provided in the Appendix D. 3. Final design details, and construction documentation shall be provided to the City of Fort Collins for review prior to Final Development Plan approval. 4. Stormwater facility Standard Operating Procedures (SOP) will be provided by the City of Fort Collins in the Development Agreement. C. Low Impact Development (LID) The LID requirement option for this project is treating at least 75% of the new and/or modified impervious areas which translates to approximately 67,954 square feet of area to be treated. Proposed LID elements intended to meet this requirement is an on-site bioretention facility and an off-site grass-lined drainage channel. 1. Proposed Bioretention A bioretention facility is proposed for the central portion of the site to provide treatment through sand media while providing some level of groundwater recharge. Approximately 40,111 square feet of contributory area (from new and/or modified impervious area) would convey to the bioretention facility and would result in approximately 0.027 acre-ft of water quality capture volume (WQCV) required to be treated. Based on the size of the proposed bioretention, approximately 0.03 acre-feet to 0.04 acre-feet of the WQCV would be treated. The remaining would overflow into the storm system and discharge into the west grassed drainage channel described below. Overall, the bioretention facility would treat approximately 45% of the new and/or Prospect and College Hotel September 16, 2019 Page 6 Project No. 18111 modified impervious area required to be treated with the remaining areas to be treated by the drainage channel. However, approximately 27,843 square feet of off-site undisturbed flow from the west adjacent properties would also be treated through the bioretention. Refer to LID Treatment Area Exhibit in Appendix D. 2. Grass Lined Drainage Channel All captured stormwater from the site will discharge into the grassed drainage channel off site and to the west, including the filtered flow from the bioretention facility. Discharged stormwater is anticipated to fully infiltrate into the grass-lined channel well in advance of entering into the downstream receiving Spring Creek approximately a quarter mile south of the proposed outfall point. Infiltration of the remaining 30% of the required runoff to be treated (from new and/or modified impervious area) is anticipated to be treated by the grassed channel. A stabilized outfall to include a flared end section and concrete forebay is also proposed. VII. Variance Requests (if necessary) The proposed development is not requesting any variances at this time. VIII. Erosion Control Erosion and sediment control will be achieved through construction control measure to include various BMPs selected from the FCSCM such as silt fencing, vehicle tracking devices, inlet/outlet protection and curb protection, concrete washout, vehicle tracking control and stabilized staging areas. Preliminary BMP locations are shown in the corresponding Preliminary Utility Plans associated with this report. A separate Erosion Control Report and Erosion Control Plans will be provided at Final Development Plan submittal. IX. Conclusion The proposed drainage system design will provide safe conveyance of the minor and major storm events while providing increased water quality treatment compared to the existing condition. A substantial improvement to the routine flooding at College and Prospect is also anticipated. A. Compliance with Standards 1. The drainage design proposed with the proposed project complies with the City of Fort Collins’ Stormwater Criteria Manual. 2. The drainage design proposed with this project complies with requirements for Spring Creek Basin. 3. The drainage plan and stormwater management measures proposed with the proposed development are compliant with all applicable State and Federal regulations governing stormwater discharge. 4. The erosion control materials that will be submitted with the final plans will comply with the requirements set forth by the City of Fort Collins’ Stormwater Criteria Manual and the Urban Storm Drainage Criteria Manual. Prospect and College Hotel September 16, 2019 Page 7 Project No. 18111 B. Drainage Concept 1. The drainage design proposed with this project will effectively limit any potential flooding and/or damage associated with runoff quantities while effectively treating runoff through water quality mitigation features. 2. The drainage concept for the proposed will assist in reducing the routine flooding that currently occurs at the southwest corner of West Prospect Road and South College Avenue. Prospect and College Hotel September 16, 2019 Page 8 Project No. 18111 REFERENCES 1. City of Fort Collins, December 2018, Fort Collins Stormwater Criteria Manual. 2. Mile High Flood District, 2001 (November 2010 with some sections updated April 2018), Urban Storm Drainage Criteria Manual, Volume 3, Stormwater Quality. 3. United States Department of Agriculture Natural Resources Conservation Service; Web Soil Survey; accessed on-line September 2019. 4. Federal Emergency Management Agency; FEMA Flood Map Service Center; accessed on-line September 2019. APPENDICES 1. Appendix A - Site Information a. Vicinity Map b. Existing Site Aerial c. ALTA/NSPS Land Title Survey d. Proposed Site Plan e. NRCS Soils Data f. FEMA Map 2. Appendix B – Existing and Proposed Imperviousness a. Existing versus Proposed Impervious Area Exhibit 3. Appendix C – Rational Method Calculations a. Storm Criteria b. Rational Method Calculations 4. Appendix D – LID Information a. LID Treatment Exhibit b. WQCV Calculations 5. Appendix E – Drainage Basin Map a. Drainage Basin Map APPENDIX A Prospect and College Hotel – Fort Collins, CO 18111 Map data ©2019 Google 1000 ft Google Maps Page 1 of 1 https://www.google.com/maps/@40.5677659,-105.0800875,15.37z 9/4/2019 Midtown Fort Collins Hotel Existing Site Aerial 600 ft N ➤➤ N © 2018 Google © 2018 Google © 2018 Google 0 30 SCALE: 1:30 30 15 60 PRELIMINARY DEVELOPMENT PLAN NORTH FILE: PROJECT NO: CAD: QUALITY ASSURANCE: DRAWING HISTORY DATE DESCRIPTION FORT COLLINS, COLORADO 80525 SITE PLAN PROSPECT AND COLLEGE HOTEL 1623 SOUTH COLLEGE AVENUE FORT COLLINS, COLORADO C3.1 JET 18111_SITE_PROD.DWG ICS/LMH 2019/09/16 FIRST PDP SUBMITTAL - - - - - - - - - - - - - - 18111 PLAN NOTES 1 NEW ASPHALT PAVING NEW CONCRETE WALK NEW ACCESSIBILITY RAMP NEW 4" PAINTED YELLOW STRIPE AT 3' O.C. (TYP.) NEW PAINTED INTERNATIONAL DISABLED SYMBOL NEW 4" PAINTED YELLOW PARKING STRIPE (TYP.) NEW CONCRETE DRIVE APPROACH PER CDOT STANDARDS NEW PRE-CAST PIN DOWN CONCRETE PARKING STOP NEW ADA SIGNAGE IN FRONT OF ALL ADA SPACES (TYP.) NEW TRASH PAD AND ENCLOSURE (SEE ARCH. FOR DETAILS) 2 3 4 5 6 7 8 9 10 CITY OF FORT COLLINS, COLORADO UTILITY PLAN APPROVAL APPROVED: CHECKED BY: CHECKED BY: Soil Map—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/21/2019 Page 1 of 3 4490490 4490520 4490550 4490580 4490610 4490640 4490670 4490700 4490730 4490490 4490520 4490550 4490580 4490610 4490640 4490670 4490700 4490730 493320 493350 493380 493410 493440 493470 493500 493320 493350 493380 493410 493440 493470 493500 40° 34' 2'' N 105° 4' 44'' W 40° 34' 2'' N 105° 4' 36'' W 40° 33' 54'' N 105° 4' 44'' W 40° 33' 54'' N 105° 4' 36'' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 50 100 200 300 Feet 0 15 30 60 90 Meters Map Scale: 1:1,310 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 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 3 Altvan-Satanta loams, 0 to 3 percent slopes 3.2 38.4% 4 Altvan-Satanta loams, 3 to 9 percent slopes 1.0 11.9% 35 Fort Collins loam, 0 to 3 percent slopes 3.8 45.1% 76 Nunn clay loam, wet, 1 to 3 percent slopes 0.4 4.6% Totals for Area of Interest 8.4 100.0% Soil Map—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/21/2019 Page 3 of 3 Larimer County Area, Colorado 35—Fort Collins loam, 0 to 3 percent slopes Map Unit Setting National map unit symbol: 2tlnc Elevation: 4,020 to 6,730 feet Mean annual precipitation: 14 to 16 inches Mean annual air temperature: 46 to 48 degrees F Frost-free period: 143 to 154 days Farmland classification: Prime farmland if irrigated Map Unit Composition Fort collins and similar soils: 85 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Fort Collins Setting Landform: Interfluves Down-slope shape: Linear Across-slope shape: Linear Parent material: Pleistocene or older alluvium derived from igneous, metamorphic and sedimentary rock and/or eolian deposits Typical profile Ap - 0 to 4 inches: loam Bt1 - 4 to 9 inches: clay loam Bt2 - 9 to 16 inches: clay loam Bk1 - 16 to 29 inches: loam Bk2 - 29 to 80 inches: loam Properties and qualities Slope: 0 to 3 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Low Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.20 to 2.00 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum in profile: 12 percent Salinity, maximum in profile: Nonsaline (0.1 to 1.0 mmhos/cm) Sodium adsorption ratio, maximum in profile: 0.5 Available water storage in profile: High (about 9.1 inches) Interpretive groups Land capability classification (irrigated): 2e Map Unit Description: Fort Collins loam, 0 to 3 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 1 of 2 Land capability classification (nonirrigated): 4c Hydrologic Soil Group: C Ecological site: Loamy Plains (R067BY002CO) Hydric soil rating: No Minor Components Nunn Percent of map unit: 10 percent Landform: Terraces Landform position (three-dimensional): Tread Down-slope shape: Linear Across-slope shape: Linear Ecological site: Loamy Plains (R067BY002CO) Hydric soil rating: No Vona Percent of map unit: 5 percent Landform: Interfluves Landform position (two-dimensional): Backslope, footslope Landform position (three-dimensional): Side slope, base slope Down-slope shape: Linear Across-slope shape: Linear Ecological site: Sandy Plains (R067BY024CO) Hydric soil rating: No Data Source Information Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 13, Sep 10, 2018 Map Unit Description: Fort Collins loam, 0 to 3 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 2 of 2 Larimer County Area, Colorado 3—Altvan-Satanta loams, 0 to 3 percent slopes Map Unit Setting National map unit symbol: jpw2 Elevation: 5,200 to 6,200 feet Mean annual precipitation: 13 to 15 inches Mean annual air temperature: 48 to 50 degrees F Frost-free period: 135 to 150 days Farmland classification: Prime farmland if irrigated Map Unit Composition Altvan and similar soils: 45 percent Satanta and similar soils: 30 percent Minor components: 25 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Altvan Setting Landform: Benches, terraces Landform position (three-dimensional): Side slope, tread Down-slope shape: Linear Across-slope shape: Linear Parent material: Mixed alluvium Typical profile H1 - 0 to 10 inches: loam H2 - 10 to 18 inches: clay loam, loam, sandy clay loam H2 - 10 to 18 inches: loam, fine sandy loam, silt loam H2 - 10 to 18 inches: gravelly sand, gravelly coarse sand, coarse sand H3 - 18 to 30 inches: H3 - 18 to 30 inches: H3 - 18 to 30 inches: H4 - 30 to 60 inches: H4 - 30 to 60 inches: H4 - 30 to 60 inches: Properties and qualities Slope: 0 to 3 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Low Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.60 to 2.00 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum in profile: 10 percent Map Unit Description: Altvan-Satanta loams, 0 to 3 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 1 of 3 Available water storage in profile: Very high (about 13.2 inches) Interpretive groups Land capability classification (irrigated): 3e Land capability classification (nonirrigated): 3e Hydrologic Soil Group: B Hydric soil rating: No Description of Satanta Setting Landform: Terraces, structural benches Landform position (three-dimensional): Side slope, tread Down-slope shape: Linear Across-slope shape: Linear Parent material: Mixed alluvium and/or eolian deposits Typical profile H1 - 0 to 9 inches: loam H2 - 9 to 18 inches: loam, clay loam, sandy clay loam H2 - 9 to 18 inches: loam, clay loam, fine sandy loam H2 - 9 to 18 inches: H3 - 18 to 60 inches: H3 - 18 to 60 inches: H3 - 18 to 60 inches: Properties and qualities Slope: 0 to 1 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Low Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.60 to 2.00 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum in profile: 10 percent Available water storage in profile: Very high (about 27.4 inches) Interpretive groups Land capability classification (irrigated): 1 Land capability classification (nonirrigated): 3c Hydrologic Soil Group: B Hydric soil rating: No Minor Components Nunn Percent of map unit: 10 percent Hydric soil rating: No Larim Percent of map unit: 10 percent Hydric soil rating: No Map Unit Description: Altvan-Satanta loams, 0 to 3 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 2 of 3 Stoneham Percent of map unit: 5 percent Hydric soil rating: No Data Source Information Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 13, Sep 10, 2018 Map Unit Description: Altvan-Satanta loams, 0 to 3 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 3 of 3 Larimer County Area, Colorado 4—Altvan-Satanta loams, 3 to 9 percent slopes Map Unit Setting National map unit symbol: jpwf Elevation: 5,200 to 6,200 feet Mean annual precipitation: 13 to 15 inches Mean annual air temperature: 48 to 50 degrees F Frost-free period: 135 to 150 days Farmland classification: Farmland of statewide importance Map Unit Composition Altvan and similar soils: 55 percent Satanta and similar soils: 35 percent Minor components: 10 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Altvan Setting Landform: Fans, benches, terraces Landform position (three-dimensional): Base slope, side slope, tread Down-slope shape: Linear Across-slope shape: Linear Parent material: Mixed alluvium Typical profile H1 - 0 to 9 inches: loam H2 - 9 to 16 inches: clay loam, loam, sandy clay loam H2 - 9 to 16 inches: loam, fine sandy loam, silt loam H2 - 9 to 16 inches: gravelly sand, gravelly coarse sand, coarse sand H3 - 16 to 31 inches: H3 - 16 to 31 inches: H3 - 16 to 31 inches: H4 - 31 to 60 inches: H4 - 31 to 60 inches: H4 - 31 to 60 inches: Properties and qualities Slope: 6 to 9 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.60 to 2.00 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Map Unit Description: Altvan-Satanta loams, 3 to 9 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 1 of 3 Calcium carbonate, maximum in profile: 10 percent Available water storage in profile: Very high (about 13.7 inches) Interpretive groups Land capability classification (irrigated): 4e Land capability classification (nonirrigated): 4e Hydrologic Soil Group: B Hydric soil rating: No Description of Satanta Setting Landform: Terraces, structural benches Landform position (three-dimensional): Side slope, tread Down-slope shape: Linear Across-slope shape: Linear Parent material: Mixed alluvium and/or eolian deposits Typical profile H1 - 0 to 9 inches: loam H2 - 9 to 14 inches: loam, clay loam, sandy clay loam H2 - 9 to 14 inches: loam, clay loam, fine sandy loam H2 - 9 to 14 inches: H3 - 14 to 60 inches: H3 - 14 to 60 inches: H3 - 14 to 60 inches: Properties and qualities Slope: 3 to 6 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Well drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.60 to 2.00 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum in profile: 10 percent Available water storage in profile: Very high (about 27.4 inches) Interpretive groups Land capability classification (irrigated): 2e Land capability classification (nonirrigated): 3e Hydrologic Soil Group: B Hydric soil rating: No Minor Components Nunn Percent of map unit: 6 percent Hydric soil rating: No Larimer Percent of map unit: 4 percent Map Unit Description: Altvan-Satanta loams, 3 to 9 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 2 of 3 Hydric soil rating: No Data Source Information Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 13, Sep 10, 2018 Map Unit Description: Altvan-Satanta loams, 3 to 9 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 3 of 3 Larimer County Area, Colorado 76—Nunn clay loam, wet, 1 to 3 percent slopes Map Unit Setting National map unit symbol: jpxq Elevation: 4,800 to 5,600 feet Mean annual precipitation: 13 to 15 inches Mean annual air temperature: 48 to 50 degrees F Frost-free period: 135 to 150 days Farmland classification: Prime farmland if irrigated Map Unit Composition Nunn, wet, and similar soils: 90 percent Minor components: 10 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Nunn, Wet Setting Landform: Alluvial fans, stream terraces Landform position (three-dimensional): Base slope, tread Down-slope shape: Linear Across-slope shape: Linear Parent material: Alluvium Typical profile H1 - 0 to 10 inches: clay loam H2 - 10 to 47 inches: clay loam, clay H2 - 10 to 47 inches: clay loam, loam, gravelly sandy loam H3 - 47 to 60 inches: H3 - 47 to 60 inches: H3 - 47 to 60 inches: Properties and qualities Slope: 1 to 3 percent Depth to restrictive feature: More than 80 inches Natural drainage class: Somewhat poorly drained Runoff class: Medium Capacity of the most limiting layer to transmit water (Ksat): Moderately low to moderately high (0.06 to 0.60 in/hr) Depth to water table: About 24 to 36 inches Frequency of flooding: Rare Frequency of ponding: None Calcium carbonate, maximum in profile: 10 percent Salinity, maximum in profile: Nonsaline to very slightly saline (0.0 to 2.0 mmhos/cm) Available water storage in profile: Very high (about 19.8 inches) Interpretive groups Land capability classification (irrigated): 2w Map Unit Description: Nunn clay loam, wet, 1 to 3 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 1 of 2 Land capability classification (nonirrigated): 3s Hydrologic Soil Group: C Hydric soil rating: No Minor Components Heldt Percent of map unit: 6 percent Hydric soil rating: No Dacono Percent of map unit: 3 percent Hydric soil rating: No Mollic halaquepts Percent of map unit: 1 percent Landform: Swales Hydric soil rating: Yes Data Source Information Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 13, Sep 10, 2018 Map Unit Description: Nunn clay loam, wet, 1 to 3 percent slopes---Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/30/2019 Page 2 of 2 Report—Physical Soil Properties Three values are provided to identify the expected Low (L), Representative Value (R), and High (H). Physical Soil Properties–Larimer County Area, Colorado Map symbol and soil name Depth Sand Silt Clay Moist bulk density Saturated hydraulic conductivity Available water capacity Linear extensibility Organic matter Erosion factors Wind erodibility group Wind erodibility index Kw Kf T In Pct Pct Pct g/cc micro m/sec In/In Pct Pct 3—Altvan- Satanta loams, 0 to 3 percent slopes Altvan 0-10 -42- -38- 16-20- 23 1.20-1.30 -1.40 4.23-9.17-14.11 0.14-0.16-0. 18 0.0- 1.5- 2.9 1.0- 1.5- 2.0 .28 .28 3 5 56 10-18 -35- -38- 20-28- 35 1.20-1.30 -1.40 4.23-9.17-14.11 0.15-0.16-0. 17 3.0- 4.5- 5.9 0.5- 0.8- 1.0 .32 .32 18-30 -45- -43- 8-12- 15 1.30-1.40 -1.50 4.23-9.17-14.11 0.12-0.14-0. 15 0.0- 1.5- 2.9 0.5- 0.8- 1.0 .43 .43 30-60 -96- - 2- 0- 3- 5 1.50-1.55 -1.60 141.14-423.07- 705.00 0.02-0.03-0. 04 Physical Soil Properties–Larimer County Area, Colorado Map symbol and soil name Depth Sand Silt Clay Moist bulk density Saturated hydraulic conductivity Available water capacity Linear extensibility Organic matter Erosion factors Wind erodibility group Wind erodibility index Kw Kf T In Pct Pct Pct g/cc micro m/sec In/In Pct Pct 4—Altvan- Satanta loams, 3 to 9 percent slopes Altvan 0-9 -42- -38- 16-20- 23 1.20-1.30 -1.40 4.23-9.17-14.11 0.14-0.16-0. 18 0.0- 1.5- 2.9 1.0- 1.5- 2.0 .28 .28 3 5 56 9-16 -35- -38- 20-28- 35 1.20-1.30 -1.40 4.23-9.17-14.11 0.15-0.16-0. 17 3.0- 4.5- 5.9 0.5- 0.8- 1.0 .32 .32 16-31 -45- -43- 8-12- 15 1.30-1.40 -1.50 4.23-9.17-14.11 0.12-0.14-0. 15 0.0- 1.5- 2.9 0.5- 0.8- 1.0 .43 .43 31-60 -96- - 2- 0- 3- 5 1.50-1.55 -1.60 141.14-423.07- 705.00 0.02-0.03-0. 04 0.0- 1.5- 2.9 0.0- 0.3- 0.5 Physical Soil Properties–Larimer County Area, Colorado Map symbol and soil name Depth Sand Silt Clay Moist bulk density Saturated hydraulic conductivity Available water capacity Linear extensibility Organic matter Erosion factors Wind erodibility group Wind erodibility index Kw Kf T In Pct Pct Pct g/cc micro m/sec In/In Pct Pct 35—Fort Collins loam, 0 to 3 percent slopes Fort collins 0-4 36-43- 50 28-38- 48 16-19- 26 1.44-1.47 -1.50 4.23-9.17-42.34 0.15-0.15-0. 17 1.7- 2.1- 3.5 1.0- 1.5- 2.0 .43 .43 5 5 56 4-9 30-42- 45 20-26- 50 20-32- 35 1.45-1.49 -1.53 1.41-2.82-14.11 0.15-0.16-0. 16 2.3- 4.6- 5.1 0.5- 0.8- 1.0 .32 .32 9-16 30-42- 45 20-26- 50 20-32- 35 1.45-1.49 -1.53 1.41-9.17-14.11 0.15-0.16-0. 16 2.1- 4.2- 4.9 0.5- 0.8- 1.0 .28 .28 16-29 35-47- 50 20-32- 38 20-21- 30 1.48-1.50 -1.51 1.41-9.17-14.11 0.15-0.15-0. 16 1.5- 1.7- 3.3 0.0- 0.3- 0.5 .43 .43 29-80 35-47- 50 20-32- 38 20-21- 30 1.48-1.50 -1.51 Physical Soil Properties This table shows estimates of some physical characteristics and features that affect soil behavior. These estimates are given for the layers of each soil in the survey area. The estimates are based on field observations and on test data for these and similar soils. Depth to the upper and lower boundaries of each layer is indicated. Particle size is the effective diameter of a soil particle as measured by sedimentation, sieving, or micrometric methods. Particle sizes are expressed as classes with specific effective diameter class limits. The broad classes are sand, silt, and clay, ranging from the larger to the smaller. Sand as a soil separate consists of mineral soil particles that are 0.05 millimeter to 2 millimeters in diameter. In this table, the estimated sand content of each soil layer is given as a percentage, by weight, of the soil material that is less than 2 millimeters in diameter. Silt as a soil separate consists of mineral soil particles that are 0.002 to 0.05 millimeter in diameter. In this table, the estimated silt content of each soil layer is given as a percentage, by weight, of the soil material that is less than 2 millimeters in diameter. Clay as a soil separate consists of mineral soil particles that are less than 0.002 millimeter in diameter. In this table, the estimated clay content of each soil layer is given as a percentage, by weight, of the soil material that is less than 2 millimeters in diameter. The content of sand, silt, and clay affects the physical behavior of a soil. Particle size is important for engineering and agronomic interpretations, for determination of soil hydrologic qualities, and for soil classification. The amount and kind of clay affect the fertility and physical condition of the soil and the ability of the soil to adsorb cations and to retain moisture. They influence shrink-swell potential, saturated hydraulic conductivity (Ksat), plasticity, the ease of soil dispersion, and other soil properties. The amount and kind of clay in a soil also affect tillage and earthmoving operations. Moist bulk density is the weight of soil (ovendry) per unit volume. Volume is measured when the soil is at field moisture capacity, that is, the moisture content at 1/3- or 1/10-bar (33kPa or 10kPa) moisture tension. Weight is determined after the soil is dried at 105 degrees C. In the table, the estimated moist bulk density of each soil horizon is expressed in grams per cubic centimeter of soil material that is less than 2 millimeters in diameter. Bulk density data are used to compute linear extensibility, shrink-swell potential, available water capacity, total pore space, and other soil properties. The moist bulk density of a soil indicates the pore space available for water and roots. Depending on soil texture, a bulk density of more than 1.4 can restrict water storage and root penetration. Moist bulk density is influenced by texture, kind of clay, content of organic matter, and soil structure. Physical Soil Properties---Larimer County Area, Colorado Midtown Hotel Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/21/2019 Page 1 of 6 Saturated hydraulic conductivity (Ksat) refers to the ease with which pores in a saturated soil transmit water. The estimates in the table are expressed in terms of micrometers per second. They are based on soil characteristics observed in the field, particularly structure, porosity, and texture. Saturated hydraulic conductivity (Ksat) is considered in the design of soil drainage systems and septic tank absorption fields. Available water capacity refers to the quantity of water that the soil is capable of storing for use by plants. The capacity for water storage is given in inches of water per inch of soil for each soil layer. The capacity varies, depending on soil properties that affect retention of water. The most important properties are the content of organic matter, soil texture, bulk density, and soil structure. Available water capacity is an important factor in the choice of plants or crops to be grown and in the design and management of irrigation systems. Available water capacity is not an estimate of the quantity of water actually available to plants at any given time. Linear extensibility refers to the change in length of an unconfined clod as moisture content is decreased from a moist to a dry state. It is an expression of the volume change between the water content of the clod at 1/3- or 1/10-bar tension (33kPa or 10kPa tension) and oven dryness. The volume change is reported in the table as percent change for the whole soil. The amount and type of clay minerals in the soil influence volume change. Linear extensibility is used to determine the shrink-swell potential of soils. The shrink-swell potential is low if the soil has a linear extensibility of less than 3 percent; moderate if 3 to 6 percent; high if 6 to 9 percent; and very high if more than 9 percent. If the linear extensibility is more than 3, shrinking and swelling can cause damage to buildings, roads, and other structures and to plant roots. Special design commonly is needed. Organic matter is the plant and animal residue in the soil at various stages of decomposition. In this table, the estimated content of organic matter is expressed as a percentage, by weight, of the soil material that is less than 2 millimeters in diameter. The content of organic matter in a soil can be maintained by returning crop residue to the soil. Organic matter has a positive effect on available water capacity, water infiltration, soil organism activity, and tilth. It is a source of nitrogen and other nutrients for crops and soil organisms. Erosion factors are shown in the table as the K factor (Kw and Kf) and the T factor. Erosion factor K indicates the susceptibility of a soil to sheet and rill erosion by water. Factor K is one of six factors used in the Universal Soil Loss Equation (USLE) and the Revised Universal Soil Loss Equation (RUSLE) to predict the average annual rate of soil loss by sheet and rill erosion in tons per acre per year. The estimates are based primarily on percentage of silt, sand, and organic matter and on soil structure and Ksat. Values of K range from 0.02 to 0.69. Other factors being equal, the higher the value, the more susceptible the soil is to sheet and rill erosion by water. Erosion factor Kw indicates the erodibility of the whole soil. The estimates are modified by the presence of rock fragments. Erosion factor Kf indicates the erodibility of the fine-earth fraction, or the material less than 2 millimeters in size. Physical Soil Properties---Larimer County Area, Colorado Midtown Hotel Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/21/2019 Page 2 of 6 Erosion factor T is an estimate of the maximum average annual rate of soil erosion by wind and/or water that can occur without affecting crop productivity over a sustained period. The rate is in tons per acre per year. Wind erodibility groups are made up of soils that have similar properties affecting their susceptibility to wind erosion in cultivated areas. The soils assigned to group 1 are the most susceptible to wind erosion, and those assigned to group 8 are the least susceptible. The groups are described in the "National Soil Survey Handbook." Wind erodibility index is a numerical value indicating the susceptibility of soil to wind erosion, or the tons per acre per year that can be expected to be lost to wind erosion. There is a close correlation between wind erosion and the texture of the surface layer, the size and durability of surface clods, rock fragments, organic matter, and a calcareous reaction. Soil moisture and frozen soil layers also influence wind erosion. Reference: United States Department of Agriculture, Natural Resources Conservation Service. National soil survey handbook, title 430-VI. (http://soils.usda.gov) Physical Soil Properties---Larimer County Area, Colorado Midtown Hotel Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/21/2019 Page 3 of 6 PROJECT LOCATION APPENDIX B Prospect and College Hotel – Fort Collins, CO 18111 EXHIBIT B NORTH 50 0 SCALE:1" = 100' 50 100 SURFACE AREA (SF) % IMPERV. IMPERV. AREA (SF) ROOFTOP 14,593 90 13,134 CONCRETE 10,620 90 9,558 ASPHALT 51,062 100 51,062 LANDSCAPE 16,639 2 333 TOTAL 92,914 74,086 EXISTING PROPOSED SURFACE AREA (SF) % IMPERV. IMPERV. AREA (SF) ROOFTOP 22,032 90 19,829 CONCRETE 7,928 90 7,135 ASPHALT 54,615 100 54,615 LANDSCAPE 8,339 2 167 TOTAL 92,914 81,746 APPENDIX C Prospect and College Hotel – Fort Collins, CO 18111 FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5) 2.0 Runoff Methodologies 3.1 Rational Formula Page 3 2.0 Runoff Methodologies There are two runoff analysis methodologies that are approved by the City: the Rational Method and the Stormwater Management Model (SWMM). In general, the chosen methodology should follow the basin size limitations listed in Table 2.0-1 below. SWMM must also be used to assess the performance of multiple detention basins in parallel or in series in a particular watershed. The City is the determining authority with respect to the appropriate methodology to use under uncertain circumstances. Please note that the Colorado Urban Hydrograph Procedure (CUHP) is not allowed to be utilized for hydrology analysis for Fort Collins area projects because this procedure is calibrated using Denver/Boulder rainfall data. Table 2.0-1: Runoff Calculation Method Project Size Runoff Calculation Method < 5 acres Rational Method Required 5-20 acres Rational Method or SWMM Accepted ≥ 20 acres SWMM Required Reference: Drainage Report submittal requirements must be prepared in accordance with the criteria set forth in Chapter 2: Development Submittal Requirements. 3.0 Rational Method 3.1 Rational Formula The methodology and theory behind the Rational Method is not covered in this Manual as this subject is well described in many hydrology reference books. However, the Rational Method procedure is generally provided in the following sections. Runoff coefficient calculations, rainfall data, and the time of concentration formula are specific to the City and are included below. The Rational Formula is represented by the following equation: 𝐐𝐐 = 𝐂𝐂𝐂𝐂𝐂𝐂 Equation 5-1 Where: Q = Peak Rate of Runoff, cfs C = Runoff Coefficient, dimensionless I = Rainfall Intensity, in/hr A = Area of the Basin or Sub-basin, acres FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5) 3.0 Rational Method 3.2 Runoff Coefficients Page 4 3.2 Runoff Coefficients Runoff coefficients used for the Rational Method are determined based on either overall land use or surface type across the drainage area. For Overall Drainage Plan (ODP) submittals, when surface types may not yet be known, land use shall be used to estimate flow rates and volumes. Table 3.2-1 lists the runoff coefficients for common types of land uses in the City. Table 3.2-1. Zoning Classification - Runoff Coefficients Land Use Runoff Coefficient (C) Residential Urban Estate 0.30 Low Density 0.55 Medium Density 0.65 High Density 0.85 Commercial Commercial 0.85 Industrial 0.95 Undeveloped Open Lands, Transition 0.20 Greenbelts, Agriculture 0.20 Reference: For further guidance regarding zoning classifications, refer to the Land Use Code, Article 4. For a Project Development Plan (PDP) or Final Plan (FP) submittals, runoff coefficients must be based on the proposed land surface types. Since the actual runoff coefficients may be different from those specified in Table 3.2-1, Table 3.2-2 lists coefficients for the specific types of land surfaces. FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5) 3.0 Rational Method 3.2 Runoff Coefficients Page 5 Table 3.2-2. Surface Type - Runoff Coefficients Surface Type Runoff Coefficients Hardscape or Hard Surface Asphalt, Concrete 0.95 Rooftop 0.95 Recycled Asphalt 0.80 Gravel 0.50 Pavers 0.50 Landscape or Pervious Surface Lawns, Sandy Soil, Flat Slope < 2% 0.10 Lawns, Sandy Soil, Avg Slope 2-7% 0.15 Lawns, Sandy Soil, Steep Slope >7% 0.20 Lawns, Clayey Soil, Flat Slope < 2% 0.20 Lawns, Clayey Soil, Avg Slope 2-7% 0.25 Lawns, Clayey Soil, Steep Slope >7% 0.35 3.2.1 Composite Runoff Coefficients Drainage sub-basins are frequently composed of land that has multiple surface types or zoning classifications. In such cases a composite runoff coefficient must be calculated for any given drainage sub-basin. The composite runoff coefficient is obtained using the following formula: ( ) t n i i i A C xA C ∑ = = 1 Equation 5-2 Where: C = Composite Runoff Coefficient Ci = Runoff Coefficient for Specific Area (Ai), dimensionless Ai = Area of Surface with Runoff Coefficient of Ci, acres or square feet n = Number of different surfaces to be considered At = Total Area over which C is applicable, acres or square feet 3.2.2 Runoff Coefficient Frequency Adjustment Factor The runoff coefficients provided in Table 3.2-1 and Table 3.2-2 are appropriate for use with the 2-year storm event. For any analysis of storms with higher intensities, an adjustment of the runoff coefficient is required due to the lessening amount of infiltration, depression retention, evapotranspiration and other losses that have a proportionally smaller effect on high-intensity storm runoff. This adjustment is FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5) 3.0 Rational Method 3.3 Time of Concentration Page 6 applied to the composite runoff coefficient. These frequency adjustment factors, Cf, are found in Table 3.2-3. Table 3.2-3. Frequency Adjustment Factors Storm Return Period (years) Frequency Adjustment Factor (Cf) 2, 5, 10 1.00 25 1.10 50 1.20 100 1.25 3.3 Time of Concentration 3.3.1 Overall Equation The next step to approximate runoff using the Rational Method is to estimate the Time of Concentration, Tc, or the time for water to flow from the most remote part of the drainage sub-basin to the design point under consideration. The Time of Concentration is represented by the following equation: 𝐓𝐓𝐜𝐜 = 𝐓𝐓 𝐢𝐢 + 𝐓𝐓𝐭𝐭 Equation 5-3 Where: Tc = Total Time of Concentration, minutes Ti = Initial or Overland Flow Time of Concentration, minutes Tt = Channelized Flow in Swale, Gutter or Pipe, minutes 3.3.2 Overland Flow Time Overland flow, Ti, can be determined by the following equation: 𝐓𝐓𝐢𝐢 = 𝟏𝟏.𝟖𝟖𝟖𝟖(𝟏𝟏.𝟏𝟏−𝐂𝐂𝐂𝐂𝐂𝐂𝐟𝐟)√𝐋𝐋 √𝐒𝐒 𝟑𝟑 Equation 3.3-2 Where: C = Runoff Coefficient, dimensionless Cf = Frequency Adjustment Factor, dimensionless L = Length of Overland Flow, feet S = Slope, percent CXCF PRODUCT OF CXCF CANNOT EXCEED THE VALUE OF 1 OVERLAND FLOW LENGTH L=200’ MAX IN DEVELOPED AREAS L=500’ MAX IN UNDEVELOPED AREAS FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5) 3.0 Rational Method 3.4 Intensity-Duration-Frequency Curves for Rational Method Page 7 3.3.3 Channelized Flow Time Travel time in a swale, gutter or storm pipe is considered “channelized” or “concentrated” flow and can be estimated using the Manning’s Equation: 𝐕𝐕 = 𝟏𝟏.𝟒𝟒𝟒𝟒 𝐧𝐧 𝐑𝐑𝟐𝟐/𝟑𝟑 𝐒𝐒𝟏𝟏/𝟐𝟐 Equation 5-4 Where: V = Velocity, feet/second n = Roughness Coefficient, dimensionless R = Hydraulic Radius, feet (Hydraulic Radius = area / wetted perimeter, feet) S = Longitudinal Slope, feet/feet And: 𝐓𝐓𝐭𝐭 = 𝐋𝐋 𝐕𝐕𝐂𝐂𝐕𝐕𝐕𝐕 Equation 5-5 3.3.4 Total Time of Concentration A minimum Tc of 5 minutes is required. The maximum Tc allowed for the most upstream design point shall be calculated using the following equation: 𝐓𝐓𝐜𝐜 = 𝐋𝐋 𝟏𝟏𝟖𝟖𝐕𝐕 + 𝟏𝟏𝐕𝐕 Equation 3.3-5 The Total Time of Concentration, Tc, is the lesser of the values of Tc calculated using Tc = Ti + Tt or the equation listed above. 3.4 Intensity-Duration-Frequency Curves for Rational Method The two-hour rainfall Intensity-Duration-Frequency curves for use with the Rational Method is provided in Table 3.4-1 and Figure 3.4-1. TC • A MINIMUM TC OF 5 MINUTES IS REQUIRED IN ALL CASES. • A MAXIMUM TC OF 5 MINUTES IS TYPICAL FOR SMALLER, URBAN PROJECTS. FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5) 3.0 Rational Method 3.4 Intensity-Duration-Frequency Curves for Rational Method Page 8 Table 3.4-1. IDF Table for Rational Method Duration (min) Intensity 2-year (in/hr) Intensity 10-year (in/hr) Intensity 100-year (in/hr) Duration (min) Intensity 2-year (in/hr) Intensity 10-year (in/hr) Intensity 100-year (in/hr) 5 2.85 4.87 9.95 39 1.09 1.86 3.8 6 2.67 4.56 9.31 40 1.07 1.83 3.74 7 2.52 4.31 8.80 41 1.05 1.80 3.68 8 2.40 4.10 8.38 42 1.04 1.77 3.62 9 2.30 3.93 8.03 43 1.02 1.74 3.56 10 2.21 3.78 7.72 44 1.01 1.72 3.51 11 2.13 3.63 7.42 45 0.99 1.69 3.46 12 2.05 3.50 7.16 46 0.98 1.67 3.41 13 1.98 3.39 6.92 47 0.96 1.64 3.36 14 1.92 3.29 6.71 48 0.95 1.62 3.31 15 1.87 3.19 6.52 49 0.94 1.6 3.27 16 1.81 3.08 6.30 50 0.92 1.58 3.23 17 1.75 2.99 6.10 51 0.91 1.56 3.18 18 1.70 2.90 5.92 52 0.9 1.54 3.14 19 1.65 2.82 5.75 53 0.89 1.52 3.10 20 1.61 2.74 5.60 54 0.88 1.50 3.07 21 1.56 2.67 5.46 FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5) 3.0 Rational Method 3.4 Intensity-Duration-Frequency Curves for Rational Method Page 9 Figure 3.4-1. Rainfall IDF Curve – Fort Collins Prospect and College Hotel Fort Collins, Colorado LAND USE AND IMPERVIOUSNESS 9/12/2019 18111 Surface Type Runoff Coefficients % Impervious Asphalt 0.95 100% 2-Year Cf 1.00 Concrete 0.95 90% 10-Year Cf 1.00 Rooftop 0.95 90% 100-Year Cf 1.25 Gravel 0.50 40% Landscape < 2% 0.10 2% Landscape 2-7% 0.15 2% BASIN IMPERVIOUS CALCS Basins Conveying to On-Site Detention Basin to North Total Area, A Total Area, A 2-Year 10-Year 100-Year % Basin Description sf Acres Asphalt Rooftop Concrete Landscape Composite Composite Composite Composite Design Point Area (sf) Area (sf) Area (sf) Area (sf) Runoff Coefficient Runoff CoefficientRunoff Coefficient Impervious, I Developed 1 Flow to bioretention 48849 1.12 42671.8 0.0 2855.1 3322.1 0.89 0.89 1.00 93% 2 Flow to bioretention 13024 0.30 10169.6 0.0 2314.1 540.4 0.91 0.91 1.00 94% 3 Bioretention 2767 0.06 0.0 0.0 216.4 2550.6 0.17 0.17 0.21 9% 4 Northern Parking Lot 33460 0.77 30863.8 0.0 269.5 2326.7 0.89 0.89 1.00 93% 5 North Eastern Parking Lot 7284 0.17 6570.0 0.0 714.0 0.0 0.95 0.95 1.00 99% 6 Building 14593 0.34 0.0 14593.0 0.0 0.0 0.95 0.95 1.00 90% OS-1 Off site basin 12925 0.30 2320.5 0.0 4120.4 6484.1 0.52 0.52 0.65 48% Fort Collins Rational Calculations_2-10-100-Yr.xlsx Prospect and College Hotel Fort Collins, Colorado 9/12/2019 181110 Note: Assumed C-value for flow over grassy surfaces is 0.25 (0.31 for 100-yr) Assumed C-value for flow over hard surfaces is 0.95 (1.00 for 100-yr) TIME OF CONCENTRATION CALCULATIONS INITIAL FLOW - Ti C*Cf C*Cf C*Cf INIT. INIT. Trvl 1 Trvl 1 Trvl 1 Tc = BASIN Is Length 2-yr Cf= 10-yr Cf= 100-yr Cf= L1 S1 Ti 2-yr Ti 10-yr Ti 100-yr L 2 V T2 Sum Ti +Tt Design Point >200' ? Flow path material 1 1 1.25 (ft) (%) (min) (min) (min) (ft) (f/s) (min) (min) 1 NO 2 0.95 0.95 1.00 28.00 0.00 9.12 9.12 6.08 407.35 2.95 2.30 8.4 2 NO 2 0.95 0.95 1.00 86.61 0.02 9.19 9.19 6.12 155.55 3.57 0.73 6.9 3 NO 1 0.25 0.25 0.31 31.00 0.03 30.16 30.16 27.95 129.00 4.62 0.47 10.9 4 NO 2 0.95 0.95 1.00 200.00 0.04 11.62 11.62 7.74 60.00 5.44 0.18 7.9 5 NO 2 0.95 0.95 1.00 60.00 0.02 8.52 8.52 5.68 101.00 2.83 0.59 6.3 6 NO 2 0.95 0.95 1.00 100.00 0.01 13.00 13.00 8.67 5.0 OS-1 NO 2 0.95 0.95 1.00 23.00 0.01 5.77 5.77 3.85 388.24 3.64 1.78 5.6 TRVL 2 Fort Collins Rational Calculations_2-10-100-Yr.xlsx Prospect and College Hotel Fort Collins, Colorado 9/12/2019 18111 PEAK FLOW CALCULATION Type AREA C2 C10 C100 Tc* I 2 I 10 I 100 Q Q Q BASIN 2-yr 10-yr 100-yr Design Point (acres) (min) (in/hr) (in/hr) (in/hr) (cfs) (cfs) (cfs) 1 Flow to bioretention 1.12 0.89 0.89 1.00 8.4 2.40 4.10 8.38 2.40 4.10 9.40 2 Flow to bioretention 0.30 0.91 0.91 1.00 6.9 2.67 4.56 9.31 0.73 1.25 2.78 3 Bioretention 0.06 0.17 0.17 0.21 10.9 2.21 3.78 7.72 0.02 0.04 0.10 4 Northern Parking Lot 0.77 0.89 0.89 1.00 7.9 2.52 4.31 8.80 1.72 2.95 6.76 5 North Eastern Parking Lot 0.17 0.95 0.95 1.00 6.3 2.67 4.56 9.31 0.42 0.72 1.56 6 Building 0.34 0.95 0.95 1.00 5.0 2.85 4.87 9.95 0.91 1.55 3.33 OS-1 Off site basin 0.30 0.52 0.52 0.65 5.6 2.85 4.87 9.95 0.44 0.76 1.93 * If time of concentration was less than 5 minutes, 5 minutes was used. Basin Characteristics Intensities Sub-basin Fort Collins Rational Calculations_2-10-100-Yr.xlsx APPENDIX D Prospect and College Hotel – Fort Collins, CO 18111 Prospect and College Hotel Water Quality Capture Volume (WQCV) Calculations On-Site Bioretention Total Area of New and/or Modified Impervious Area Contributory to Bioretention = 40,111 sq-ft a= 0.8 12-Hour Drain Time I= 95% WQCV= 0.358 Watershed-Inches A= 0.921 Acres V= 0.027 Acre-Feet Therefore; 1,196 cubic-feet of WQCV (at 12 inch depth) is required to be treated Additional off-site runoff treated 27,843 square feet of area Off-Site Grassed Drainage Channel Total Area of New and/or Modified Impervious Area Contributory to grassed drainage channel = 36,951 sq-ft a= 1 40-Hour Drain Time I= 90% WQCV= 0.401 Watershed-Inches A= 0.848 Acres V= 0.028 Acre-Feet Therefore; 1,236 cubic-feet of WQCV (at 12 inch depth) is required to be treated Additional off-site runoff treated 18,806 square feet of area Summary: 2,432 cubic-feet of total WQCV to be treated on and off-site 46,649 total area of additional off-site runoff will be treated (35% of all combined sub-basins) Approximately 45% to be treated through on-site bioretention The remianing 30% to be treated off site via grassed channel An additional acre of off-site runoff will be treated through both measures � = ���� 12 � ���� = �(0.91� � − 1.19� � + 0.78� ⬚ ) APPENDIX E Prospect and College Hotel – Fort Collins, CO 18111 55 0.87 1.48 3.03 22 1.53 2.61 5.32 56 0.86 1.47 2.99 23 1.49 2.55 5.20 57 0.85 1.45 2.96 24 1.46 2.49 5.09 58 0.84 1.43 2.92 25 1.43 2.44 4.98 59 0.83 1.42 2.89 26 1.4 2.39 4.87 60 0.82 1.4 2.86 27 1.37 2.34 4.78 65 0.78 1.32 2.71 28 1.34 2.29 4.69 70 0.73 1.25 2.59 29 1.32 2.25 4.60 75 0.70 1.19 2.48 30 1.30 2.21 4.52 80 0.66 1.14 2.38 31 1.27 2.16 4.42 85 0.64 1.09 2.29 32 1.24 2.12 4.33 90 0.61 1.05 2.21 33 1.22 2.08 4.24 95 0.58 1.01 2.13 34 1.19 2.04 4.16 100 0.56 0.97 2.06 35 1.17 2.00 4.08 105 0.54 0.94 2.00 36 1.15 1.96 4.01 110 0.52 0.91 1.94 37 1.16 1.93 3.93 115 0.51 0.88 1.88 38 1.11 1.89 3.87 120 0.49 0.86 1.84 1.41-9.17-14.11 0.15-0.15-0. 16 1.5- 1.7- 3.3 0.0- 0.3- 0.5 .43 .43 76—Nunn clay loam, wet, 1 to 3 percent slopes Nunn, wet 0-10 -35- -34- 27-31- 35 1.25-1.30 -1.35 1.41-2.82-4.23 0.15-0.18-0. 20 3.0- 4.5- 5.9 2.0- 3.0- 4.0 .24 .24 5 6 48 10-47 -28- -30- 35-43- 50 1.20-1.25 -1.30 0.42-2.32-4.23 0.15-0.17-0. 18 6.0- 7.5- 8.9 0.0- 1.0- 2.0 .24 .24 47-60 -36- -39- 15-25- 35 1.20-1.25 -1.30 1.41-2.82-4.23 0.10-0.14-0. 18 0.0- 1.5- 2.9 0.0- 0.3- 0.5 .24 .37 Data Source Information Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 13, Sep 10, 2018 Physical Soil Properties---Larimer County Area, Colorado Midtown Hotel Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/21/2019 Page 6 of 6 .05 .05 Satanta 0-9 -43- -40- 10-18- 25 1.30-1.35 -1.40 4.23-9.17-14.11 0.14-0.16-0. 18 0.0- 1.5- 2.9 1.0- 1.5- 2.0 .32 .32 5 5 56 9-14 -38- -36- 18-27- 35 1.35-1.38 -1.40 4.23-9.17-14.11 0.15-0.17-0. 19 3.0- 4.5- 5.9 0.5- 0.8- 1.0 .32 .32 14-60 -42- -38- 10-20- 30 1.35-1.43 -1.50 4.23-9.17-14.11 0.14-0.17-0. 19 0.0- 1.5- 2.9 0.5- 0.8- 1.0 .37 .37 Physical Soil Properties---Larimer County Area, Colorado Midtown Hotel Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/21/2019 Page 5 of 6 0.0- 1.5- 2.9 0.0- 0.3- 0.5 .05 .05 Satanta 0-9 -43- -40- 10-18- 25 1.30-1.35 -1.40 4.23-9.17-14.11 0.14-0.16-0. 18 0.0- 1.5- 2.9 1.0- 1.5- 2.0 .32 .32 5 5 56 9-18 -38- -36- 18-27- 35 1.35-1.38 -1.40 4.23-9.17-14.11 0.15-0.17-0. 19 3.0- 4.5- 5.9 0.5- 0.8- 1.0 .32 .32 18-60 -42- -38- 10-20- 30 1.35-1.43 -1.50 4.23-9.17-14.11 0.14-0.17-0. 19 0.0- 1.5- 2.9 0.5- 0.8- 1.0 .37 .37 Physical Soil Properties---Larimer County Area, Colorado Midtown Hotel Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/21/2019 Page 4 of 6 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 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. Soil Map—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/21/2019 Page 2 of 3 CHECKED BY: CHECKED BY: CHECKED BY: CITY ENGINEER DATE WATER & WASTEWATER UTILITY DATE STORMWATER UTILITY DATE PARKS & RECREATION DATE TRAFFIC ENGINEER DATE ENVIRONMENTAL PLANNER DATE 11 NEW BIKE RACKS 12 COURT YARD TRANSFORMER PAD GENERATOR SET AREA LUGGAGE OFF LOADING SPACE VINE FENCE 13 14 15 16 NOTE: -EXISTING UNDERGROUND INSTALLATIONS & PRIVATE UTILITIES SHOWN ARE INDICATED ACCORDING TO THE BEST INFORMATION AVAILABLE TO THE ENGINEER. THE ENGINEER DOES NOT GUARANTEE THE ACCURACY OF SUCH INFORMATION. SERVICE LINES (WATER, POWER, GAS, STORM, SEWER, TELEPHONE & TELEVISION) MAY NOT BE STRAIGHT LINES OR AS INDICATED ON THE PLANS. STATE LAW REQUIRES CONTRACTOR TO CALL ALL UTILITY COMPANIES BEFORE EXCAVATION FOR EXACT LOCATIONS. -UNLESS OTHERWISE SPECIFIED, ALL CONSTRUCTION LAYOUT AND STAKING SHALL BE PERFORMED UNDER THE RESPONSIBLE CHARGE OF A LAND SURVEYOR LICENSED IN THE STATE WHERE THE PROJECT IS LOCATED AND BY A PARTY CHIEF OR ENGINEERING TECHNICIAN EXPERIENCED IN CONSTRUCTION LAYOUT AND STAKING TECHNIQUES AS ARE REQUIRED BY THE SPECIFIC TYPE OF WORK BEING PERFORMED. 17 CONCRETE DRAIN PAN