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Home My WebLink About7-ELEVEN @ COLLEGE & MAGNOLIA - PDP/APU - PDP120026 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTDRAINAGE REPORT FOR 7-ELEVEN – COLLEGE AND MAGNOLIA Fort Collins, Colorado November 30, 2012 OWNER/DEVELOPER: Verdad Real Estate 1121 Grant St. Denver, CO 80203 ENGINEER 7853 E. Arapahoe Ct., Suite 2500 Centennial, CO 80112 303-841-9365 f: 303-548-6212 Prepared by: Kevin S. Roth, P.E. REG PROJECT NO. 120805 TABLE OF CONTENTS I. GENERAL LOCATION AND DESCRIPTION ...................................................................... 2 A. Location ........................................................................................................................... 2 B. Description of Property..................................................................................................... 2 C. Floodplain Submittal Requirements.................................................................................. 3 II. DRAINAGE BASINS AND SUB-BASINS ............................................................................ 3 A. Major Basin Desciption .................................................................................................... 3 B. Sub-Basin Description ..................................................................................................... 3 III. DRAINAGE DESIGN CRITERIA ......................................................................................... 4 A. Regulations ...................................................................................................................... 4 B. Development Criteria Reference and Constraints ............................................................ 4 C. Hydrological Criteria ......................................................................................................... 4 D. Hydraulic Criteria ............................................................................................................. 5 E. Floodplain Regulation Compliance ................................................................................... 5 F. Modifications of Criteria.................................................................................................... 5 IV. DRAINAGE FACILITY DESIGN .......................................................................................... 5 A. General Concept .............................................................................................................. 5 B. Specific Details ................................................................................................................ 6 V. CONCLUSIONS .................................................................................................................. 8 A. Compliance with Standards ............................................................................................. 8 B. Drainage Concept ............................................................................................................ 8 VI. REFERENCES .................................................................................................................... 9 APPENDIX A –FIRM, floodplain, and Soils Maps.................................................... A APPENDIX B – Hydrologic Calculations .................................................................. B APPENDIX C – Detention Calculations ................................................................... C APPENDIX D ........................................................................................................... D MAP POCKETS....................................................................................................... D 1) DRAINAGE PLAN AND DETAILS ................................................................... D W. MULBERRY ST. S. COLLEGE AVE. W. MAGNOLIA ST. S. MASON ST. W. OLIVE ST. SITE CANYON AVE. W. MOUNTAIN AVE. N NOT TO SCALE December 3, 2012 7-Eleven – College and Magnolia Drainage Report Page 2 I. GENERAL LOCATION AND DESCRIPTION A. Location The proposed site is located in the northwest quadrant of the intersection of South College Avenue and West Magnolia Street. Refer to the previous page for the location shown on the Vicinity Map. More specifically this project is comprised of Lots 1 and 2 of Block 113 in Fort Collins, located in the southeast 1/4 of Section 11, Township 7 North, Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. The site is bounded by South College Avenue (140’ right-of way) to the east, West Magnolia Street (100’ right-of-way) to the south, a public alley (20’ right-of-way) to the west, and the existing Clocktower Square Condos building to the north. This area is part of the high density Downtown District for zoning and planning purposes. The site is located within a City of Fort Collins regulatory 100-year floodway and flood fringe area in the Old Town Basin. The area is not considered a floodway according to FEMA. The flood maps are included in Appendix A. B. Description of Property The 7-Eleven College and Magnolia (Project) consists of an area of 0.436 acres. The site is currently covered with a packed gravel parking lot with several trees on the site. The site is located within a City of Fort Collins regulatory flood fringe area in the Old Town Basin. The surrounding right-of-ways for College and Magnolia are considered to be within the 100-year floodway. The area is not considered a floodplainaccording to the FEMA Flood Insurance Rate Map for the area. The flood maps are included in Appendix A. The proposed development will consist of a convenience store and associated access roads and parking. Accessible sidewalks will be connected to the existing sidewalks in the surrounding right-of-way. Revisions to the public right-of-way will include expanding the existing southern and eastern drive entrances and removing the second drive entrance along West Magnolia Street. No existing major irrigation facilities are located within the site nor impact the site directly. The proposed land use will be a convenience store with associated parking lot. December 3, 2012 7-Eleven – College and Magnolia Drainage Report Page 3 C. Floodplain Submittal Requirements Revisions to the Floodplain will be addressed via separate document according to the requirements of the “City of Fort Collins Floodplain Review Checklist”. The design will comply with the City of Fort Collins floodplain regulations as outlined in Chapter 10 of the City of Fort Collins Municipal Code. The intent of the proposed design will raise the building roughly 24” above the Base Flood Elevation (BFE) for the area, exceeding the minimum amount for new construction to be raised above the flood elevation. In order to raise the building above the floodway elevation as required by Chapter 10, the site will be raised to provide access. As a result, a LOMR/CLOMR will be prepared by a separate floodplain modification process prior to approval and construction. II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Desciption The Old Town Drainage Basin is a high-density, urban drainage basin located in north- central Fort Collins. The majority of the runoff from the Basin drains east to the Poudre River. The basin is entirely urbanized. Future planning for the basin will utilize improvements to the storm infrastructure to reduce the regular flooding that occurs in the area. No known irrigation facilities are located within 150’ of the property boundary. B. Sub-Basin Description Historically, the site flows from the northeast corner to the College and Magnolia intersection, across the gravel parking lot. A small portion of the site along the west property line drains to the alley right-of-way. Slopes on the site range from 0.6% to 3%. The College Avenue right- of-way adjacent to the site drains to the north. The Magnolia Street right-of-way adjacent to the site drains to the west. The alley drains to the south. The proposed development will match the existing drainage patterns as closely as possible. The overall site will drain to the south and east, with one small portion draining to the alley along the west property line. December 3, 2012 7-Eleven – College and Magnolia Drainage Report Page 4 The site is not impacted by any offsite flows during minor storm events. During small events, the runoff will be contained within the surrounding curb and gutter in Magnolia and College. The building to the north drains to College and to the alley without impacting the 7-Eleven site. During major storm events, the site is included in the flood fringe for the Old Town drainage basin and may experience flooding on the site from the off-site basin to the west. The building finished floor will be set at an elevation of 4994.00, roughly 2’ above the anticipated Base Flood Elevation, to prevent flooding of the building. III. DRAINAGE DESIGN CRITERIA A. Regulations Deviations from the criteria are not requested for development of the proposed site. B. Development Criteria Reference and Constraints The site is included in the Old Town Master Drainage Plan and has been designed to conform to the master plan. Since the area experiences regular flooding, the building elevation will be raised 2’ above the Base Flood Elevation (BFE) for the property to a finished floor elevation of 4994.0. Adjacent drainage studies do not impact this site. The site is constrained on three sides by City right-of-way. The drainage patterns within the right-of way have not been impacted by the proposed development. The proposed on-site sidewalks will tie into the existing sidewalks within the right-of-way. The proposed vehicular access from College and Magnolia will tie back into the existing roadway without affecting the existing slopes in the curb and gutter. C. Hydrological Criteria Hydrologic calculations have been prepared for the 100-year storm events. All calculations have been prepared using the Rational Method Formula. Proposed Time of Concentration and Rational Method calculations and references have been included in Appendix B. December 3, 2012 7-Eleven – College and Magnolia Drainage Report Page 5 Stormwater detention has been included on site. Water quality treatment for the site and surrounding area is provided offsite by the Udall Natural Area water treatment facility. The hydrology of the site has been designed according to the City of Fort Collins criteria. D. Hydraulic Criteria The capacity of the proposed on-site curb and gutter and concrete pan will be designed to convey the major storm. Although Fort Collins design criteria requires designing curb and gutter for the minor storm, the final design intends to demonstrate that the major storm can be conveyed through the site via curb and gutter. Revisions to the Floodplain will be addressed via separate document according to the requirements of Chapter 10 of the City of Fort Collins Municipal Code. The design will comply with the City of Fort Collins floodplain regulations. E. Floodplain Regulation Compliance Revisions to the Floodplain will be addressed via separate document according to the requirements of the “City of Fort Collins Floodplain Review Checklist”. The design will comply with the City of Fort Collins floodplain regulations. A CLOMR/LOMR will be prepared by a separate floodplain modification process prior to construction. F. Modifications of Criteria Modifications to criteria are not requested for this project. IV. DRAINAGE FACILITY DESIGN A. General Concept The proposed site will generally follow the existing patterns. Runoff will drain via overland flow and roof drains to the proposed parking lot and drive isle. The access then drains from a high point in the northwest corner, south to Magnolia Street, and east to College Avenue. A small portion of the site will continue to drain to the alley on the west. The drainage patterns for the surrounding right-of-way will not be modified with the development of the site. The site is not impacted by any offsite flows during minor storm events. During small events, the off-site runoff will be contained within the surrounding curb and gutter in Magnolia and College. During major storm events, the site is included in the flood fringe for the Old Town December 3, 2012 7-Eleven – College and Magnolia Drainage Report Page 6 drainage basin. The building finished floor has been set above the anticipated base flood elevation for the area to prevent flooding of the building. All proposed design calculations for the proposed site improvements have been included in Appendix B. B. Specific Details All runoff coefficients are based on the City Runoff Coefficients for Zoning Classifications. The site is a commercial business, so the Coefficient is 0.95 for all three basins, per Table RO-10. Basin A - Design Point 1 Basin A consists 0.240 acres located on the west side and center of the proposed site. All of the building roof drains will be directed to the west side of the building to the parking area and drive isle. Runoff to the drive isle is conveyed via curb and gutter to the parking lot detention pond. The parking lot drains via a concrete channel to an outlet structure in the landscaped area to the south of the pond. The pond outfalls to Design Point 1, located at the southern property line. This basin drains through a curb cut to the West Magnolia Street right-of-way and is conveyed off-site via the existing Magnolia curb and gutter. Q100 = 2.27 cfs Basin B - Design Point 2 Basin B consists of 0.019 acres along the west property line. The entire basin drains west into the alley right-of-way and south to Design Point 2 at the southern property line. The alley drains south to West Magnolia Street. Q100 = 0.18 cfs Basin C - Design Point 3 Basin C consists of 0.131 acres of landscaped area, parking, and drive isles located in the northeastern half of the site. The drive isle then drains east via curb and gutter to a sidewalk chase which outfalls to Design Point 3 at the property boundary. This December 3, 2012 7-Eleven – College and Magnolia Drainage Report Page 7 portion of the site runs offsite, undetained. Runoff is conveyed off-site via the existing South College Avenue curb and gutter. Q100 = 1.24 cfs Basin D - Design Point 4 Basin D consists of 0.019 acres of landscaped area, sidewalks, and the bike rack located east of the building along South College Avenue. Runoff from this basin is not concentrated, but runs overland to the College Avenue curb and gutter. Q100 = 0.18 cfs Basin E - Design Point 5 Basin E consists of 0.026 acres of landscaped area and sidewalks located south of the building along West Magnolia Street. Runoff from this basin is not concentrated, but runs overland to the Magnolia Street curb and gutter. Q100 = 0.25 cfs Detention is proposed for the site in the form of a parking lot detention pond. This detention pond will provide storage for the east side of the site. The building roof drains will be directed to the west side so that the roof runoff also reaches the detention pond. Due to the elevation restrictions on the site, portions of the site will continue to flow to College Avenue undetained. The concentrated flows from Basin C, totaling 1.24cfs during the major storm event, cannot be directed to the parking lot detention pond due to the constraints of the surrounding property to the north and the existing roadway elevations on the east and south. Basins B, D, and E also flow offsite undetained, but none of these basins are concentrated prior to reaching the surrounding right-of-way. For the area of Basin B, the required detention volume is 1,086 cfs. This volume has been determined using the modified FAA method. The allowable unit release for the pond has been determined using the 2-year runoff for the existing site. The parking lot has been designed to maximize the detention volume in the area while also protecting the existing tree in the corner, as required by the City forestry department. The southwest corner of the parking lot detention area drains into a landscaped area and then to the Magnolia Street December 3, 2012 7-Eleven – College and Magnolia Drainage Report Page 8 right-of-way through a 4” PVC pipe and concrete channel. The maximum volume available in the area with the restrictions of the site is 803 cubic feet. A water quality component has not been included in the detention pond design. Water quality for the area is provided by the Udall Natural Area water treatment facility. Maintenance access will be via the drive isle through the site. The slopes for the site are flat and will not prevent access for maintenance vehicles. The site does not have any easements or tracts proposed for drainage purposes. No additional off-site facilities are needed to convey the minor or major flows from the site. V. CONCLUSIONS A. Compliance with Standards The design has been prepared to meet the City of Fort Collins Stormwater Criteria Manual. The site has been designed to meet the City of Fort Collins Master Drainage Plan. The site has been designed in compliance with the City of Fort Collins Floodplain regulations. Revisions to the Floodplain will be addressed via separate document according to the requirements of the Chapter 10 of the City of Fort Collins Municipal Code. The design will comply with the City of Fort Collins floodplain regulations. The site has been designed in compliance with State of Colorado and Federal regulations. B. Drainage Concept The proposed site will not create a negative impact on the storm runoff in the area. The proposed convenience store is being developed on a site that is zoned for commercial development. Therefore the project meets the requirements for the master plan for the downtown area. December 3, 2012 7-Eleven – College and Magnolia Drainage Report Page 9 VI. REFERENCES 1. City of Fort Collins, Storm Drainage Design Criteria and Construction Standards. Utilities Department, Stormwater Division. 2. Urban Drainage and Flood Control District, Urban Storm Drainage Criteria Manual. Regional County of Governments, Denver, CO, June 2001 (with current revisions) 3. FIRM Flood Insurance Rate Map, Larimer County, Colorado and Incorporated Areas. Panel 979 of 1420. Map Number 09069C0979H. Revised May 2, 2012. APPENDIX A –FIRM, floodplain, and Soils Maps A-1 # 4 990 4989 4988 4995 4994 4996 4987 4997 4992 4991 4993 4998 4999 5000 4990 4990 4993 4994 4999 4994 Mason St Olive St College Ave Magnolia St College Ave ¤£287 35 493320 493320 493350 493350 493380 493380 493410 493410 493440 493440 493470 493470 493500 493500 4492380 4492380 4492410 4492410 4492440 4492440 4492470 4492470 4492500 4492500 4492530 4492530 4492560 4492560 4492590 4492590 4492620 4492620 4492650 4492650 0 50 100 200 300 Feet 0 10 20 40 60 ± Meters 40° 35' 5'' 105° 4' 35'' 40° 34' 55'' 105° 4' 35'' 40° 34' 55'' 40° 35' 5'' 105° 4' 45'' 105° 4' 45'' Map Scale: 1:1,460 if printed on A size (8.5" x 11") sheet. Soil Map—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/8/2012 A-3 Page 1 of 3 MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Units Soil Ratings A A/D B B/D C C/D D Not rated or not available Political Features Cities Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Map Scale: 1:721 if printed on A size (8.5" × 11") sheet. 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 accurate map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: UTM Zone 13N NAD83 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 7, May 1, 2009 Date(s) aerial images were photographed: 8/6/2005 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 10/30/2012 Page 2 of 3 A-4 Hydrologic Soil Group Hydrologic Soil Group— Summary by Map Unit — Larimer County Area, Colorado (CO644) Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 35 Fort Collins loam, 1 to 3 percent slopes B 2.2 100.0% Totals for Area of Interest 2.2 100.0% 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 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 10/30/2012 Page 3 of 3 A-5 Engineering Properties This table gives the engineering classifications and the range of engineering properties for the layers of each soil in the survey area. Depth to the upper and lower boundaries of each layer is indicated. Texture is given in the standard terms used by the U.S. Department of Agriculture. These terms are defined according to percentages of sand, silt, and clay in the fraction of the soil that is less than 2 millimeters in diameter. "Loam," for example, is soil that is 7 to 27 percent clay, 28 to 50 percent silt, and less than 52 percent sand. If the content of particles coarser than sand is 15 percent or more, an appropriate modifier is added, for example, "gravelly." Classification of the soils is determined according to the Unified soil classification system (ASTM, 2005) and the system adopted by the American Association of State Highway and Transportation Officials (AASHTO, 2004). The Unified system classifies soils according to properties that affect their use as construction material. Soils are classified according to particle-size distribution of the fraction less than 3 inches in diameter and according to plasticity index, liquid limit, and organic matter content. Sandy and gravelly soils are identified as GW, GP, GM, GC, SW, SP, SM, and SC; silty and clayey soils as ML, CL, OL, MH, CH, and OH; and highly organic soils as PT. Soils exhibiting engineering properties of two groups can have a dual classification, for example, CL-ML. The AASHTO system classifies soils according to those properties that affect roadway construction and maintenance. In this system, the fraction of a mineral soil that is less than 3 inches in diameter is classified in one of seven groups from A-1 through A-7 on the basis of particle-size distribution, liquid limit, and plasticity index. Soils in group A-1 are coarse grained and low in content of fines (silt and clay). At the other extreme, soils in group A-7 are fine grained. Highly organic soils are classified in group A-8 on the basis of visual inspection. If laboratory data are available, the A-1, A-2, and A-7 groups are further classified as A-1-a, A-1-b, A-2-4, A-2-5, A-2-6, A-2-7, A-7-5, or A-7-6. As an additional refinement, the suitability of a soil as subgrade material can be indicated by a group index number. Group index numbers range from 0 for the best subgrade material to 20 or higher for the poorest. Rock fragments larger than 10 inches in diameter and 3 to 10 inches in diameter are indicated as a percentage of the total soil on a dry-weight basis. The percentages are estimates determined mainly by converting volume percentage in the field to weight percentage. Percentage (of soil particles) passing designated sieves is the percentage of the soil fraction less than 3 inches in diameter based on an ovendry weight. The sieves, numbers 4, 10, 40, and 200 (USA Standard Series), have openings of 4.76, 2.00, 0.420, and 0.074 millimeters, respectively. Estimates are based on laboratory tests of soils sampled in the survey area and in nearby areas and on estimates made in the field. Liquid limit and plasticity index (Atterberg limits) indicate the plasticity characteristics of a soil. The estimates are based on test data from the survey area or from nearby areas and on field examination. Engineering Properties–Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/8/2012 Page 1 of 3 A-6 References: American Association of State Highway and Transportation Officials (AASHTO). 2004. Standard specifications for transportation materials and methods of sampling and testing. 24th edition. American Society for Testing and Materials (ASTM). 2005. Standard classification of soils for engineering purposes. ASTM Standard D2487-00. Engineering Properties–Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/8/2012 Page 2 of 3 A-7 Report—Engineering Properties Absence of an entry indicates that the data were not estimated. The asterisk '*' denotes the representative texture; other possible textures follow the dash. Engineering Properties– Larimer County Area, Colorado Map unit symbol and soil name Depth USDA texture Classification Fragments Percentage passing sieve number— Liquid limit Plasticity index Unified AASHTO >10 inches 3-10 inches 4 10 40 200 In Pct Pct Pct 35—Fort Collins loam, 1 to 3 percent slopes Fort collins 0-7 *Loam CL-ML, CL A-4 0 0 100 100 85-95 60-75 25-30 5-10 7-22 *Loam *Clay loam CL A-6 0 0 95-100 90-100 85-95 60-75 25-40 10-20 22-60 *Loam *Silt loam *Fine sandy loam CL, CL- ML, ML A-4 0 0 95-100 90-100 80-95 50-75 20-30 NP-10 Data Source Information Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 7, May 1, 2009 Engineering Properties–Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/8/2012 Page 3 of 3 A-8 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. 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. Physical Soil Properties–Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/8/2012 Page 1 of 4 A-9 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. 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." Physical Soil Properties–Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/8/2012 Page 2 of 4 A-10 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 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/8/2012 Page 3 of 4 A-11 Report—Physical Soil Properties 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, 1 to 3 percent slopes Fort collins 0-7 -44- -41- 10-15- 20 1.25-1.40 4.23-42.34 0.14-0.18 0.0-2.9 1.0-2.0 .28 .28 5 5 56 7-22 -38- -36- 18-27- 35 1.45-1.55 4.23-14.11 0.16-0.18 3.0-5.9 0.0-0.5 .24 .24 22-60 -42- -38- 12-20- 27 1.45-1.55 4.23-14.11 0.16-0.18 0.0-2.9 0.0-0.5 .24 .24 Data Source Information Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 7, May 1, 2009 Physical Soil Properties–Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 10/8/2012 Page 4 of 4 A-12 APPENDIX B – Hydrologic Calculations SOUTH COLLEGE AVENUE (140' ROW) WEST MAGNOLIA STREET (100' ROW) ALLEY (20' ROW) B-1 COMPOSITE RUNOFF COEFICIENT & PERCENT IMPERVIOUS CALC'D BY: KSR PROJECT: DATE: 12/03/12 PROJ. NO: SCS Soil Type: B REVISED : Per City of Ft. Collins Table 3-3 Land coverage C %I* Roof 0.95 90 Gravel Packed 0.50 40 Drives and Walks 0.95 100 Soil 0.25 0 * Values taken from the Urban Drainage and Flood Control District's Strom Drainage Criteria Manual, Vol. 1 Basin Basin Area (ac) Roof (ac) Gravel Packed (ac) Drives / Walks (ac) Pervious Ground (ac) C100 %I ONSITE BASINS A 0.436 0.001 0.436 0.50 50.05 C100 Intensity q Area Q (cfs/ac) (ac) (cfs) Minor Storm 0.5 2.85 1.425 0.436 0.62 Major Storm 0.5 9.95 4.975 0.436 2.17 q (Minor Storm) = Allowable Unit Release Rate for Pond Sizing Basin Basin Area (ac) Roof (ac) Gravel Packed (ac) Drives / Walks (ac) Pervious Ground (ac) C100 %I ONSITE BASINS A 0.436 0.096 0.256 0.085 0.81 81.37 C100 Intensity q Area Q (cfs/ac) (ac) (cfs) Minor Storm 0.81 2.85 2.3085 0.436 1.01 Major Storm 0.81 9.95 8.0595 0.436 3.52 Proposed Site Runoff Calculation Q = CIA Proposed Land Use Existing Land Use 7-Eleven College and Magnolia 120805 Existing Site Runoff Calculation Q = CIA B-2 CALCULATED BY: KSR JOB NO: 120805 DATE: 10/2/2012 PROJECT: 7- Eleven College and Magnolia CHECKED BY: REVISED: FINAL REMARKS Tc AREA C100 LENGTH SLOPE Ti LENGTH SLOPE VELOCITY Tt COMPOS. TOTAL Tc = (L/180)+10 BASIN (AC) (FT) % (MIN) (FT) % Cv (FPS) (MIN) Tc (MIN) LENGTH (MIN) (MIN) A 0.240 0.95 20 2.00 -2.7 185 1.00 20.00 2.0 1.5 5.0 205 11.1 5.0 B 0.019 0.95 16 2.00 -2.4 5.0 16 10.1 5.0 C 0.131 0.95 50 2.00 -4.3 80 1.00 20.00 2.0 0.7 5.0 130 10.7 5.0 D 0.019 0.95 14 2.00 -2.3 5.0 14 10.1 5.0 E 0.026 0.95 8 2.00 -1.7 5.0 8 10.0 5.0 Cv = Conveyance Coefficient TOV =(1.87(1.1-CCf )D^1/2)/s^1/3 Land Surface Cv Heavy Meadow 2.5 Cf= 1.25 for 100 year storm Tillage/field 5 PAGE: 1/1 Short pasture and lawns 7 Nearly bare ground 10 Grassed waterway 15 Paved areas and shallow paved swales 20 DATA TIME (Ti) (Tt) (URBANIZED BASINS) STANDARD FORM SF-2 TIME OF CONCENTRATION SUB-BASIN INITIAL/OVERLAND TRAVEL TIME Tc CHECK DEVELOPED BASINS B-3 CALCULATED BY: KSR STANDARD FORM SF-3 JOB NO: DATE: PROJECT: 7-Eleven College and Magnolia CHECKED BY: STORM DRAINAGE SYSTEM DESIGN DESIGN STORM: 100 YR (RATIONAL METHOD PROCEDURE) TRAVEL TIME BASIN (s) DESIGN POINT AREA (AC) RUNOFF COEFF Tc (min) C x A (AC) I (IN/HR) Q (CFS) Tc (MIN) S(C x A) (AC) I (IN/HR) Q (CFS) SLOPE (%) STREET FLOW (CFS) DESIGN FLOW (CFS) SLOPE (%) PIPE SIZE (IN) LENGTH (FT) VELOCITY (FPS) Tt (min) REMARKS A 1 0.24 0.95 5 0.23 9.95 2.27 B 2 0.019 0.95 5 0.02 9.95 0.18 C 3 0.131 0.95 5 0.12 9.95 1.24 D 3 0.019 0.95 5 0.02 9.95 0.18 E 3 0.026 0.95 5 0.02 9.95 0.25 Page: DIRECT RUNOFF TOTAL RUNOFF STREET PIPE 120805 10/2/2012 B-4 APPENDIX C – Detention Calculations Project: Basin ID: Design Information (Input): Design Information (Input): Catchment Drainage Imperviousness Ia = 81.37 percent Catchment Drainage Imperviousness Ia = 81.37 percent Catchment Drainage Area A = 0.240 acres Catchment Drainage Area A = 0.240 acres Predevelopment NRCS Soil Group Type = B A, B, C, or D Predevelopment NRCS Soil Group Type = B A, B, C, or D Return Period for Detention Control T = 2 years (2, 5, 10, 25, 50, or 100) Return Period for Detention Control T = 100 years (2, 5, 10, 25, 50, or 100) Time of Concentration of Watershed Tc = 5 minutes Time of Concentration of Watershed Tc = 5 minutes Allowable Unit Release Rate q = 1.43 cfs/acre Allowable Unit Release Rate q = 1.43 cfs/acre One-hour Precipitation P1 = 0.82 inches One-hour Precipitation P1 = 2.86 inches Design Rainfall IDF Formula i = C1* P1/(C2+Tc)^C3 Design Rainfall IDF Formula i = C1* P1/(C2+Tc)^C3 Coefficient One C1 = 28.50 Coefficient One C1 = 28.50 Coefficient Two C2 = 10 Coefficient Two C2 = 10 Coefficient Three C3 = 0.789 Coefficient Three C3 = 0.789 Determination of Average Outflow from the Basin (Calculated): Determination of Average Outflow from the Basin (Calculated): Runoff Coefficient C = 0.58 Runoff Coefficient C = 0.71 Inflow Peak Runoff Qp-in = 0.38 cfs Inflow Peak Runoff Qp-in = 1.64 cfs Allowable Peak Outflow Rate Qp-out = 0.34 cfs Allowable Peak Outflow Rate Qp-out = 0.34 cfs Mod. FAA Minor Storage Volume = 30 cubic feet Mod. FAA Major Storage Volume = 1,086 cubic feet Mod. FAA Minor Storage Volume = 0.001 acre-ft Mod. FAA Major Storage Volume = 0.025 acre-ft 5 <- Enter Rainfall Duration Incremental Increase Value Here (e.g. 5 for 5-Minutes) Rainfall Rainfall Inflow Adjustment Average Outflow Storage Rainfall Rainfall Inflow Adjustment Average Outflow Storage Duration Intensity Volume Factor Outflow Volume Volume Duration Intensity Volume Factor Outflow Volume Volume minutes inches / hr acre-feet "m" cfs acre-feet acre-feet minutes inches / hr acre-feet "m" cfs acre-feet acre-feet (input) (output) (output) (output) (output) (output) (output) (input) (output) (output) (output) (output) (output) (output) 5 2.76 0.003 1.00 0.34 0.002 0.000 5 9.62 0.011 1.00 0.34 0.002 0.009 10 2.20 0.004 0.75 0.26 0.004 0.001 10 7.67 0.018 0.75 0.26 0.004 0.014 15 1.84 0.005 0.67 0.23 0.005 0.001 15 6.43 0.023 0.67 0.23 0.005 0.018 20 1.60 0.006 0.63 0.21 0.006 0.000 20 5.57 0.026 0.63 0.21 0.006 0.020 25 1.41 0.007 0.60 0.21 0.007 0.000 25 4.93 0.029 0.60 0.21 0.007 0.022 30 1.27 0.007 0.58 0.20 0.008 -0.001 30 4.44 0.031 0.58 0.20 0.008 0.023 35 1.16 0.008 0.57 0.20 0.009 -0.002 35 4.04 0.033 0.57 0.20 0.009 0.024 40 1.07 0.008 0.56 0.19 0.011 -0.002 40 3.72 0.035 0.56 0.19 0.011 0.024 45 0.99 0.009 0.56 0.19 0.012 -0.003 45 3.45 0.036 0.56 0.19 0.012 0.025 50 0.92 0.009 0.55 0.19 0.013 -0.004 50 3.22 0.038 0.55 0.19 0.013 0.025 55 0.87 0.009 0.55 0.19 0.014 -0.005 55 3.03 0.039 0.55 0.19 0.014 0.025 60 0.82 0.009 0.54 0.19 0.015 -0.006 60 2.85 0.040 0.54 0.19 0.015 0.025 65 0.77 0.010 0.54 0.18 0.016 -0.007 65 2.70 0.041 0.54 0.18 0.016 0.025 70 0.74 0.010 0.54 0.18 0.018 -0.008 70 2.57 0.042 0.54 0.18 0.018 0.025 75 0.70 0.010 0.53 0.18 0.019 -0.009 75 2.45 0.043 0.53 0.18 0.019 0.024 80 0.67 0.010 0.53 0.18 0.020 -0.010 80 2.34 0.044 0.53 0.18 0.020 0.024 85 0.64 0.010 0.53 0.18 0.021 -0.011 85 2.24 0.045 0.53 0.18 0.021 0.024 90 0.62 0.011 0.53 0.18 0.022 -0.012 90 2.15 0.045 0.53 0.18 0.022 0.023 95 0.59 0.011 0.53 0.18 0.024 -0.013 95 2.07 0.046 0.53 0.18 0.024 0.023 100 0.57 0.011 0.53 0.18 0.025 -0.014 100 2.00 0.047 0.53 0.18 0.025 0.022 105 0.55 0.011 0.52 0.18 0.026 -0.015 105 1.93 0.048 0.52 0.18 0.026 0.022 110 0.53 0.011 0.52 0.18 0.027 -0.016 110 1.87 0.048 0.52 0.18 0.027 0.021 115 0.52 0.011 0.52 0.18 0.028 -0.017 115 1.81 0.049 0.52 0.18 0.028 0.020 120 0.50 0.012 0.52 0.18 0.029 -0.018 120 1.75 0.049 0.52 0.18 0.029 0.020 125 0.49 0.012 0.52 0.18 0.031 -0.019 125 1.70 0.050 0.52 0.18 0.031 0.019 130 0.47 0.012 0.52 0.18 0.032 -0.020 130 1.65 0.050 0.52 0.18 0.032 0.019 135 0.46 0.012 0.52 0.18 0.033 -0.021 135 1.61 0.051 0.52 0.18 0.033 0.018 140 0.45 0.012 0.52 0.18 0.034 -0.022 140 1.56 0.051 0.52 0.18 0.034 0.017 145 0.44 0.012 0.52 0.18 0.035 -0.023 145 1.52 0.052 0.52 0.18 0.035 0.017 150 0.43 0.012 0.52 0.18 0.037 -0.024 150 1.49 0.052 0.52 0.18 0.037 0.016 155 0.42 0.012 0.52 0.18 0.038 -0.025 155 1.45 0.053 0.52 0.18 0.038 0.015 160 0.41 0.012 0.52 0.18 0.039 -0.026 160 1.42 0.053 0.52 0.18 0.039 0.014 165 0.40 0.013 0.52 0.18 0.040 -0.027 165 1.39 0.054 0.52 0.18 0.040 0.014 170 0.39 0.013 0.51 0.18 0.041 -0.029 170 1.35 0.054 0.51 0.18 0.041 0.013 175 0.38 0.013 0.51 0.18 0.042 -0.030 175 1.33 0.054 0.51 0.18 0.042 0.012 Project: Basin ID: DETENTION VOLUME BY THE MODIFIED FAA METHOD 7-Eleven College and Magnolia UDFCD DETENTION BASIN VOLUME ESTIMATING WORKBOOK Version 2.31, Released August 2012 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0 50 100 150 200 250 300 350 Volume (acre-feet) Duration (Minutes) Inflow and Outflow Volumes vs. Rainfall Duration Minor Storm Inflow Volume Minor Storm Outflow Volume Minor Storm Storage Volume Major Storm Inflow Volume Major Storm Outflow Volume Major Storm Storage Volume 1-UD-Detention_v2.31.xls, Modified FAA C-2 12/3/2012, 10:49 AM CALCULATED BY: KJS JOB NO: 120805 DATE: PROJECT: 7-Eleven College and Magnolia CHECKED BY: REVISED: DESIGN AREA RELEASE RATES RELEASE RATES YEAR (AC) (CFS/AC) (CFS) 100 0.240 1.43 0.34 0.436 Ac. 81.37 i 81% Total Area: Composite I% Release Rates determined by the existing 2- year runoff for the entire site (q). Refer to Composite Runoff Coefficient and Percent Impervious Calculations. DETENTION POND VOLUME AND RELEASE RATE POND RELEASE RATES Imperviousness SOIL GROUP B Parking Lot Detention Pond 11/29/2012 Total Area C-3 CALCULATED BY: JOB NO: 120805 DATE: PROJECT: CHECKED BY: REVISED: Elevation Stage Area Volume Cumulative Volume (FT^3) Cumulative Volume (AC-FT) 4991.4 0 0 0 0 0 4991.5 0.1 0.6 0.02 0.02 0.000 4991.6 0.2 57 2.11 2.11 0.000 4991.7 0.3 145 9.76 11.88 0.000 4991.8 0.4 352 24.10 35.98 0.001 4991.9 0.5 725 52.74 88.71 0.002 4992 0.6 1224 96.37 185.08 0.004 4992.1 0.7 1674 144.31 329.39 0.008 4992.2 0.8 2025 184.67 514.06 0.012 4992.33 0.93 2424 288.79 802.86 0.018 Equation used: VOL= 1/3 (STAGEX+1 -STAGEX )(AREA X+1 +AREAX +(AREAX +1XAREAX )) 1/2 Required 100-Year Volume + 1/2 EURV (cf) From UDFCD Spreadsheet: KJS 11/29/2012 7-Eleven College and Magnolia DETENTION POND SIZING MAJOR STORM Parking Lot Detention Pond C-4 CALCULATED BY: JOB NO: 120805 DATE: PROJECT: 7-Eleven College and Magnolia CHECKED BY: REVISED: OUTLET CONTROLS POND INFORMATION 100-Yr WS= 4992.33 Major Storm Orifice Sizing Proposed 4" Pipe Outlet (invert) 4991.37 Pipe Outlet Proposed OUTLET PIPE center= 4991.53667 Orifice Equation Q=Cv*A*√2gh WEIR ELEVATION = 4992.5 g (ft/s2) 32.2 Cv* 0.6 *(sharp edged orifice) ORIFICE SIZING -Major Storm h100 100-YearWSE (ft) 0.96 Release (cfs) Allowed 0.34 A100 (ft2) 0.072 A10 (in2) 10.378 Orifice Plate to be placed over the top 1" of the outlet pipe, providing 0.0702 ft2 outlet area. Proposed Pond 3 KJS DETENTION POND SIZING 12/3/2012 FILING No. 8 C-5 APPENDIX D MAP POCKETS 1) DRAINAGE PLAN AND DETAILS TSB 4992 4993 4993 4993 4993 4992 4992 4993 4993 4993 4992 4992 4992 4993 1 Know what's R CALL 2-BUSINESS DAYS IN ADVANCE BEFORE YOU DIG, GRADE OR EXCAVATE FOR THE MARKING OF UNDERGROUND MEMBER UTILITIES. 1 FLOODPLAIN NOTES: 1. PORTIONS OF THIS PROJECT ARE LOCATED WITHIN A CITY REGULATED FLOODPLAIN AND FLOODWAY FOR THE OLD TOWN BASIN AND MUST COMPLY WITH CHAPTER 10 OF CITY CODE. 2. ALL WORK PROPOSED WITHIN THE CITY REGULATORY FLODPLAIN AND FLOODWAY MUST BE PRECEDED BY AN APPROVED FLOODPLAIN USE PERMIT. 3. NO-RISE CONSTRUCTION IS REQUIRED FOR ALL SITE WORK WITHIN THE FLOODWAY. PRE-CERTIFICATION OF NO-RISE IS REQUIRED FOR AS-BUILT CONDITIONS. 4. STORAGE OF MATERIALS OR EQUIPMENT, EITHER TEMPORARY OR PERMANENT, IS NOT ALLOWED WITHIN THE FLOODWAY. FLOODPLAIN TO BE MODIFIED BY SEPARATE FLOODPLAIN MODIFICATION PROCESS. 180 0.37 0.013 0.51 0.18 0.044 -0.031 180 1.30 0.055 0.51 0.18 0.044 0.011 185 0.36 0.013 0.51 0.18 0.045 -0.032 185 1.27 0.055 0.51 0.18 0.045 0.010 190 0.36 0.013 0.51 0.18 0.046 -0.033 190 1.25 0.056 0.51 0.18 0.046 0.010 195 0.35 0.013 0.51 0.18 0.047 -0.034 195 1.22 0.056 0.51 0.18 0.047 0.009 200 0.34 0.013 0.51 0.18 0.048 -0.035 200 1.20 0.056 0.51 0.18 0.048 0.008 205 0.34 0.013 0.51 0.18 0.049 -0.036 205 1.18 0.057 0.51 0.18 0.049 0.007 210 0.33 0.013 0.51 0.18 0.051 -0.037 210 1.16 0.057 0.51 0.18 0.051 0.006 215 0.33 0.013 0.51 0.17 0.052 -0.038 215 1.14 0.057 0.51 0.17 0.052 0.006 220 0.32 0.014 0.51 0.17 0.053 -0.039 220 1.12 0.058 0.51 0.17 0.053 0.005 225 0.31 0.014 0.51 0.17 0.054 -0.041 225 1.10 0.058 0.51 0.17 0.054 0.004 230 0.31 0.014 0.51 0.17 0.055 -0.042 230 1.08 0.058 0.51 0.17 0.055 0.003 235 0.30 0.014 0.51 0.17 0.057 -0.043 235 1.06 0.059 0.51 0.17 0.057 0.002 240 0.30 0.014 0.51 0.17 0.058 -0.044 240 1.05 0.059 0.51 0.17 0.058 0.001 245 0.30 0.014 0.51 0.17 0.059 -0.045 245 1.03 0.059 0.51 0.17 0.059 0.000 250 0.29 0.014 0.51 0.17 0.060 -0.046 250 1.01 0.059 0.51 0.17 0.060 -0.001 255 0.29 0.014 0.51 0.17 0.061 -0.047 255 1.00 0.060 0.51 0.17 0.061 -0.001 260 0.28 0.014 0.51 0.17 0.062 -0.048 260 0.98 0.060 0.51 0.17 0.062 -0.002 265 0.28 0.014 0.51 0.17 0.064 -0.049 265 0.97 0.060 0.51 0.17 0.064 -0.003 270 0.27 0.014 0.51 0.17 0.065 -0.051 270 0.96 0.061 0.51 0.17 0.065 -0.004 275 0.27 0.014 0.51 0.17 0.066 -0.052 275 0.94 0.061 0.51 0.17 0.066 -0.005 280 0.27 0.014 0.51 0.17 0.067 -0.053 280 0.93 0.061 0.51 0.17 0.067 -0.006 285 0.26 0.014 0.51 0.17 0.068 -0.054 285 0.92 0.061 0.51 0.17 0.068 -0.007 290 0.26 0.014 0.51 0.17 0.069 -0.055 290 0.91 0.062 0.51 0.17 0.069 -0.008 295 0.26 0.014 0.51 0.17 0.071 -0.056 295 0.89 0.062 0.51 0.17 0.071 -0.009 300 0.25 0.015 0.51 0.17 0.072 -0.057 300 0.88 0.062 0.51 0.17 0.072 -0.010 305 0.25 0.015 0.51 0.17 0.073 -0.058 305 0.87 0.062 0.51 0.17 0.073 -0.011 Mod. FAA Minor Storage Volume (cubic ft.) = 30 Mod. FAA Major Storage Volume (cubic ft.) = 1,086 Mod. FAA Minor Storage Volume (acre-ft.) = 0.0007 Mod. FAA Major Storage Volume (acre-ft.) = 0.0249 DETENTION VOLUME BY THE MODIFIED FAA METHOD 7-Eleven College and Magnolia Determination of MAJOR Detention Volume Using Modified FAA Method (For catchments less than 160 acres only. For larger catchments, use hydrograph routing method) (NOTE: for catchments larger than 90 acres, CUHP hydrograph and routing are recommended) UDFCD DETENTION BASIN VOLUME ESTIMATING WORKBOOK Version 2.31, Released August 2012 Determination of MINOR Detention Volume Using Modified FAA Method 1-UD-Detention_v2.31.xls, Modified FAA C-1 12/3/2012, 10:49 AM 4992 4997 4994 4990 4995 4998 4994 4995 4992 4996 4996 4991 4995 4993 4998 S MASON ST S HOWES ST MATHEWS ST S MELDRUM ST REMINGTON ST W OAK ST S COLLEGE AVE W OLIVE ST W MYRTLE ST W MAGNOLIA ST W MULBERRY ST CANYON AVE E OAK ST E OLIVE ST S SHERWOOD ST E MYRTLE ST E MULBERRY ST MONTEZUMA FULLER ALLEY S SHERWOOD ST # 49 90 4989 4988 4995 4994 4996 4987 4997 4992 4991 4993 4998 4999 5000 4990 4990 4993 4994 4999 4994 4992 4997 4994 4990 4995 4998 4994 4995 4992 4996 4996 4991 4995 4993 4998 S MASON ST S HOWES ST MATHEWS ST S MELDRUM ST REMINGTON ST W OAK ST S COLLEGE AVE W OLIVE ST W MYRTLE ST W MAGNOLIA ST W MULBERRY ST CANYON AVE E OAK ST E OLIVE ST S SHERWOOD ST E MYRTLE ST E MULBERRY ST MONTEZUMA FULLER ALLEY S SHERWOOD ST Areas outside of FEMA and City mapped 100-year and 500-year floodplains. Local drainage problems may still exist. Low Risk . 0 200 400 800 Feet All floodplain boundaries are approximate. This information is based on the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) and the City of Fort Collins Master Drainageway Plans. This letter does not imply that the referenced property will or will not be free from flooding or damage. A property not in the Special Flood Hazard Area or in a City Designated Floodplain may be damaged by a flood greater than that predicted on the map or from a local drainage problem not shown on the map. This map does not create liability on the part of the City, or any officer or employee thereof, for any damage that results from reliance on this information. High Risk City Floodway - Area of 100-year floodplain with greatest depths and fastest velocities. City Flood Fringe - May Include: - Areas of FEMA 100-year floodplain (FEMA Zones A, AE, AO, and AH) - Areas of City 100-year floodplain including ponding areas and sheet flow areas with average depths of 1-3 feet. There is a 1% annual chance that these areas will be flooded. Moderate Risk May include: - Areas of FEMA 500-year floodplain (FEMA Zone X-shaded). - Areas of FEMA or City 100-year floodplain (sheet flow) with average depths of less than 1 foot. - Areas protected by levees from the 100-year flood. City Flood Risk Map Printed: 6/21/2010 A-2