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Home My WebLink AboutMARS LANDING - PDP190013 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORTPREPARED FOR: Goodwin Knight PREPARED BY: Galloway & Company, Inc. 5265 Ronald Regan Blvd., Suite 210 Johnstown, Colorado 80534 ORIGINAL PREPARATION: September 11, 2019 REVISED: September 9, 2020 MARS LANDING FORT COLLINS, COLORADO PRELIMINARY DRAINAGE REPORT PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 2 of 15 I. CERTIFICATIONS ..................................................................................................................................... 3 CERTIFICATION OF ENGINEER .................................................................................................... 3 CERTIFICATION OF OWNER ......................................................................................................... 3 II. GENERAL LOCATION AND DESCRIPTION ........................................................................................... 4 SITE LOCATION .............................................................................................................................. 4 DESCRIPTION OF PROPERTY ...................................................................................................... 4 III. DRAINAGE BASINS AND SUB-BASINS ................................................................................................. 5 MAJOR BASIN DESCRIPTION ....................................................................................................... 5 SUB-BASIN DESCRIPTION ............................................................................................................ 5 IV. DRAINAGE DESIGN CRITERIA ............................................................................................................. 6 REGULATIONS ............................................................................................................................... 6 DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS ................................................. 6 HYDROLOGICAL CRITERIA ........................................................................................................... 7 HYDRAULIC CRITERIA................................................................................................................... 7 V. DRAINAGE FACILITY DESIGN ............................................................................................................... 9 GENERAL CONCEPT ..................................................................................................................... 9 VI. EROSION AND SEDIMENT CONTROL MEASURES .......................................................................... 12 VII. FLOODPLAIN ....................................................................................................................................... 13 VIII. CONCLUSIONS .................................................................................................................................. 14 COMPLIANCE WITH STANDARDS .............................................................................................. 14 VARIANCES .................................................................................................................................. 14 IX. REFERENCES ...................................................................................................................................... 15 Appendices: A. Appendix A – Reference Material B. Appendix B – Hydrologic Calculations C. Appendix C – Hydraulic Calculations D. Appendix D – Existing Drainage Study Excerpts E. Appendix E – Proposed Condition Drainage Map TABLE OF CONTENTS PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 3 of 15 I. CERTIFICATIONS CERTIFICATION OF ENGINEER “I hereby certify that this report for the preliminary drainage design of Mars Landing was prepared by me (or under my direct supervision) in accordance with the provisions of the Fort Collins Stormwater Criteria Manual (December 2018) for the owners thereof.” To be signed and sealed at time of Final Drainage Report ______________________________________ Donald B. Cecil, PE Registered Professional Engineer State of Colorado No. 52303 For and on behalf of Galloway & Company, Inc. CERTIFICATION OF OWNER “Goodwin Knight hereby certifies that the drainage facilities for Mars Landing shall be constructed according to the design presented in this report. We understand that the City of Fort Collins does not and will not assume liability for drainage facilities designed and/or certified by our engineer. We also understand that the City of Fort Collins relies on the representation of others to establish that drainage facilities are designed and constructed in compliance with City of Fort Collins guidelines, standards or specifications. Review by the City of Fort Collins can therefore in no way limit or diminish any liability, which we or any other party may have with respect to the design or construction of such facilities.” ____________________________________ Goodwin Knight Attest: ___________________________________ Name of Responsible Party __________________________________ Notary Public __________________________________ Authorized Signature PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 4 of 15 II. GENERAL LOCATION AND DESCRIPTION SITE LOCATION Mars Landing (hereafter referred to as “the site” or “project site”) is a 3.79 acre project site located in the City of Fort Collins, Larimer County, Colorado. The project site is bound to the north by Skyway Drive, to the east by Mars Drive, to the south by undeveloped land, and to the west by undeveloped land. The project site is located on Outlot A, South College Storage Subdivision in the southeast quarter of Section 11, T. 6N., R. 69 W. of the 6th P.M, City of Fort Collins, County of Larimer, State of Colorado. Refer to Appendix A for a Vicinity Map showing the project site. DESCRIPTION OF PROPERTY The 3.79 acre project site is currently undeveloped and consists of open fallow land. Vegetation on the project site consists of mostly invasive weeds and grasses. A section of the North Loudon Ditch bisects the project site. The ditch has been abandoned and ditch flows are now conveyed via a system of underground storm sewer. This underground storm sewer does not encroach onto the project site. The Mars Drive right-of-way and the South College Storage Units site plan immediately to the east of the project site were approved and constructed between 2017 and 2019. The project site currently drains from west to east at slopes ranging from 2% to 25%. The steeper slopes up to 25% occur adjacent to the east property boundary at Mars Drive where large earthwork cuts occurred for the construction of Mars Drive. A culvert was extended under Mars Drive to the project site near the intersection with Skyway Drive as part of the South College Storage Units project. The culvert was designed to bypass runoff from the Mars Landing site under Mars Drive. A drainage analysis of the Mars Landing site and adjacent lands was performed for sizing of the culvert under Mars Drive. An offsite drainage area immediately to the west of the project site, between the west property boundary and Gateway Center Drive, was delineated as part of the South College Storage Units Final Drainage Report. This offsite area drains onto the Mars Landing site and eventually is captured by the culvert in Mars Drive. A copy of the the drainage map from the South College Storage Units Final Drainage Report are included in Appendix E. The project site covers the entire ±3.79 acre Outlot A. The proposed improvements include two multi- family residential buildings with 90 dwelling units, a clubhouse building, detached garage buildings, internal roadways, wet/dry utilities and landscaping in common and amenity areas. A small portion of Mars Drive will be added to the current road alignment and will extend from its existing terminus approximately 150’ to the south where it will terminate perpendicular to the Mars Landing project site. According to the Natural Resources Conservation Service (NRCS) Web Soil Survey, the project site consists of a mix of soil types and Hydrologic Soil Groups (HSGs)including: - Fort Collins Loam, HSG ‘C’, 16.7% of total project area - Kim Loam, HSGs ‘B’, 45.6% - Kim-Thedalund Loam, HSG ‘B’, 37.7% The predominant on-site HSG is ‘B’. Group B soils have a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep to 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. Refer to Appendix A, for the Web Soil Survey and soils information. PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 5 of 15 A geotechnical report was prepared by Earth Engineering Consultants (EEC) in July 2019 for the project site. The EEC report included site-specific borings for the project site. Nine exploratory borings were performed across the project site and discovered that subsurface conditions generally consisted of clayey sand/sandy lean clay and/or lean clay with sand subsoils, extending to underlying bedrock depths of approximately 2’ to 6’ below the ground surface. Groundwater was observed at depths of approximately 14’ to 17’ below the ground surface. III. DRAINAGE BASINS AND SUB-BASINS MAJOR BASIN DESCRIPTION The basin which includes the Mars Landing project site was included within the Final Drainage Report for the South College Storage Units by Northern Engineering, dated September 2017. Refer to Appendix D, for the South College Storage Units Drainage Exhibit. The project site is a part of Basin W1, which discharges into the culvert under Mars Drive. For purposes of this study for the Mars Landing project, Basin W1 is generally divided into two major drainage basins, Basin A and Basin B. Runoff from Basin A, will be conveyed via a system of swales, curb and gutter, underground storm sewer, and detention facilities to the culvert under Mars Drive. Runoff from Basin B consists generally of runoff that cannot be captured via the proposed conveyance system to be constructed with the Mars Landing project site. These flows will run off the property overland via overland flow into Mars Drive. A portion of the proposed improvements including the Mars Drive road extension were included in the original calculations for the South College Storage Units and are not included with this Study. The project site is enveloped entirely within the Fossil Creek drainage basin, as delineated by the City of Fort Collins Drainage Basin Master Plan. The Drainage Basin Master Plan was approved by City Council in June of 2004 and describes the flooding history of the specified basins and offers guidance for new development within the basins. The project site is shown on FEMA Map Numbers 08069C1000F and 08069C1200F. The floodplain map indicates the project exists within Zone X - Area of Minimal Flood Hazard and is, therefore, not impacted by an existing floodplain/floodway. Refer to Appendix A for a Firmette of the Flood Plain Hazard Map. SUB-BASIN DESCRIPTION The sub-basin development included herein is intended as a step toward informing future detailed preliminary and final storm drain infrastructure design. The developed drainage basins shown on sheet C8.0 will be further subdivided as the grading design evolves. A Basins: These basins are compositionally similar and comprised of the proposed building roof areas, asphalt, curb and gutter, sidewalks, landscaping, and outdoor amenity areas. These basins are intended to be captured via the on-site drainage system and routed through the proposed detention pond to the culvert under Mars Drive. B Basins: These basins are compositionally similar and are comprised of both paved drive entrances to the site, landscaped areas and sidewalk/other hardscape. Due to the location of these sub-basins directly adjacent to Mars Drive, they cannot be captured via the on-site drainage system and will runoff directly into Mars Drive. PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 6 of 15 OS1 Basin: This basin is the only offsite basin entering our site. This basin was delineated with the South College Storage Units Final Drainage Report. This land consists of open field to the west of the project site along the entire west property line. Flows from this basin will flow overland to the west property line will they enter the site evenly distributed along the property line. The Mars Landing project proposes to make landscaping improvements to this area to count toward required mitigation of habitat removal associated with the proposed development. No additional impervious cover or earthwork improvements are proposed in this offsite basin. IV. DRAINAGE DESIGN CRITERIA REGULATIONS This preliminary drainage design presented herein is prepared in accordance with the Fort Collins Stormwater Criteria Manual (December (2018). DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS The project site is enveloped entirely within the Fossil Creek drainage basin, as delineated by the City of Fort Collins Drainage Basin Master Plan. The Drainage Basin Master Plan was approved by City Council in June of 2004 and describes the flooding history of the specified basins and offers guidance for new development within the basins. Several site specific constrains helped develop the Low Impact Design Water Quality BMPs and detention pond design presented here. • The outfall for the project site is a stub out provided via the culvert under Mars Drive at the northwest corner of the site, constructed with the South College Storage Units Final Utility Plan. The invert elevation of this culvert is 5032.46. • The site configuration is disproportionate, with the north-south property boundary lines being much greater than that of the east-west boundary lines. The site is generally flat along the north- south property boundary lines, but is relatively steep along those boundary lines running east and west. • The property line is directly adjacent to Mars Drive to the east and Skyway Drive to the north. • The existing soils are unsuitable for infiltrating stormwater runoff and generally consist of clayey sand/sandy lean clay and/or lean clay with sand subsoils Due to the project site being encumbered by these constraints, we developed a strategy for implementing “The Four-Step Process” for stormwater quality management to the Maximum Extent Practicable (MEP). Each step is listed below along with a brief narrative describing the implementation strategy. Step 1 – Employ Runoff Reduction Practices All developed runoff from Drainage Basin A will be routed through the on-site detention pond. The detention pond will restrict the flowrate of stormwater leaving the site and reduce the impact on downstream drainage areas. Further, all runoff from the clubhouse and half of the developed runoff from the garage roofs will be routed across earthen swales before they are captured in the site’s storm sewer system or detention pond. Further, 90% of the project’s added impervious area will be routed through the underwater stormwater quality chambers. Step 2 – Implement BMPs that provide a Water Quality Capture Volume Approximately 90% of the project’s added impervious area will be routed through the underwater stormwater quality chambers to meet the LID requirements set forth. Sub-basins within Basin A not PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 7 of 15 routed through the underwater stormwater quality chambers will be treated using other water quality treatment methods described in other sections of this report. Generated runoff from the majority of Basin B, which will not be routed through the underwater chambers or detention pond, will pass across grass landscaped areas before they flow into Mars Drive and, eventually, public storm sewer within Mars Drive. Step 3 – Stabilize Drainageways There are no defined drainageways on the site. Earthen swales will be planted to stabilize the shallow embankments and prevent erosion. Step 4 – Implement site specific and other source control BMPs An erosion control plan and Stormwater Management Plan will be implemented to prevent erosion and control sediment on the project site and downstream drainageways during and after construction. HYDROLOGICAL CRITERIA For urban catchments that are not complex and generally 160 acres or less in size, it is acceptable to estimate the design storm runoff with the rational method. The rational method is often used when only the peak flow rate or total volume of runoff is needed (e.g., inlet sizing, storm sewer sizing or simple detention basin sizing). The Rational Method is based on the Rational Formula: Q = CiA where: Q = the maximum rate of runoff, cfs C = a runoff coefficient that is the ratio between the runoff volume from an area and the average rate of rainfall depth over a given duration for that area i = average intensity of rainfall in inches per hour for a duration equal to the time of concentration A = area, acres The runoff coefficient, C, for each basin is a weighted average of the runoff coefficient associated with each land-use type (e.g., asphalt = 0.95). Refer to Appendix A and Tables 3.2-2 and 3.2-3 which list runoff coefficient associated with each land use type and the Frequency Adjustment Factors (Cf) that were used to adjust the runoff coefficients for lower probability storm events. The one-hour rainfall Intensity-Duration-Frequency tables for use with the Rational Method of runoff analysis are provided in Table 3.4.1 (refer to Appendix B). The 2-year and 100-year storm events serve as the basis for the drainage system design. The 2-year storm is considered the minor storm event. It has a fifty percent probability of exceedance during any given year. The 100-year storm is considered the major storm event. It has a one percent probability of exceedance in any given year. The 2-year drainage system, at a minimum, must be designed to transport runoff from the 2-year recurrence interval storm event with minimal disruption to the environment. The 100-year drainage system, as a minimum, must be designed to convey runoff from the 100-year recurrence interval flood to minimize life hazards and health, damage to structures, and interruption to traffic and services. HYDRAULIC CRITERIA The storm drain system is limited to culverts and swales on the project site that will convey runoff underneath drives and parking areas to the underground water quality and above ground detention pond. PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 8 of 15 The storm drain system hydraulic analysis will be completed in a future submittal using Bentley StormCAD V8i. This software routes flows based on the longest upstream Time of Concentration (tc) at each junction. Given the controlling tc, StormCAD V8i calculates the flow at the junction with the corresponding intensity (e.g., i2 and i100) and aggregate CA. PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 9 of 15 V. DRAINAGE FACILITY DESIGN GENERAL CONCEPT The preliminary design presents the design of a system for collecting and conveying developed runoff from the proposed development at the Mars Landing project site into the on-site underground water quality basins and the above ground detention pond. Developed runoff will generally consist generally of flows generated from roof areas, paved drives and parking areas, landscaped areas, and hardscape. The developed runoff for each basin begins as overland flow at numerous locations throughout the project site. The runoff then flows via a stormwater conveyance system consisting of swales, curb and gutter, and underground storm sewer into the underground water quality system and the above ground detention pond. Significant work is required beyond that which is included herein to design the on-site stormwater conveyance and water quality and detention system. This work includes: • fine grading design; • further sub-basin delineation; • area inlet design; • swale design; • storm drain system design (i.e., hydraulic grade line analysis). SPECIFIC DETAILS A Basins These basins comprise approximately 3.45 acres. The developed runoff from these basins is captured via a system of overland flow, swales, curb and gutter, and an underground storm sewer system. Runoff from the majority of the A Basins, except for Basins A-1 & A-3, is diverted trough the below ground water quality treatment basins. Runoff from Basin A-1 will be captured via a system of curb and gutter and routed to an inlet where runoff will be treated for water quality with a Snout hood water quality BMP. Runoff from Basin-A-3 will flow overland from impervious areas included roof and hardscape across vegetated areas and grass lined swales before entering the detention pond. All A Basins are conveyed to the on-site detention pond. B Basins These basins comprise approximately 0.33 acres. The developed runoff from these basins flow overland from the two driveways along Mars Drive and across landscape areas and hardscape into Mars Drive. Due to the location of these basins immediately adjacent to Mars Drive, they cannot be captured and conveyed to the on-site water quality and detention facilities. Since the majority of these flows are routed across landscaped areas, and since this basin is spread across the entire Mars Drive right-of-way boundary adjacent to the project site, it is expected that the landscaped areas will serve as water quality buffers for runoff generated in these basins. Further, the point flows generated in these basins are considered negligible and should not have an adverse impact on the downstream stormwater infrastructure. PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 10 of 15 Underground Water Quality The underground water quality treatment system will be comprised on the Stormtech Subsurface Stormwater Management System (Stormtech) manufactured by Advanced Drainage Systems, Inc., which is an allowed method by the City of Fort Collins for the Low Impact Development (LID) stormwater management technique requirements. Stormtech utilizes underground stormwater collection chambers to achieve the necessary volume required to be treated for Water Quality. The captured volume then infiltrates through a filtering fabric at the floor of the chamber, removing contaminants. An underdrain system then captures the filtered runoff and conveys the runoff to the on-site detention pond. The total contributing area to the Stormtech system is 2.84 acres. Preliminary calculations for this study have determined that 90% of the added impervious area from the project site will be routed through the Stormtech system. The required water quality capture volume routed through the chambers was determined using the City of Fort Collins Modified FAA Method for the 2-year Return Period. Calculations for the sizing of the Underground Water Quality System are included in Appendix C. On-Site Detention Pond The on-site detention pond was sized using City of Fort Collins Modified FAA Method for the 2-year Return Period. The proposed release rate for the detention pond was determined using the allowable 0.2 cfs per acre of project area for projects within the Fossil Creek Drainage Basin. The allowable release rate was calculated to be 0.69 cfs. The pond has a volume of 36,161 cubic feet and provides the required detention control for the 100-year return period. Calculations for the sizing of the Detention Pond are included in Appendix C. The detention pond will discharge via an outlet structure that is connected directly to the culvert under Mars Drive that was constructed with the South College Storage Units. The release rate from the detention pond does not exceed the capacity of the culvert under Mars Drive. Basin OS-1 Basin OS-1 is the only offsite basin entering our site. This basin is 1.55 acres and was delineated with the South College Storage Units Final Drainage Report. This land consists of open field to the west of the project site along the entire west property line. Flows from this basin for the 100-year return period were calculated to be approximately 2.20 cfs. Runoff generated from this basin will flow overland to the west property line will they enter the site evenly distributed along the property line. The Mars Landing project proposes to make landscaping improvements to this area to count toward required mitigation of habitat removal associated with the proposed development. Given that no additional impervious cover or earthwork improvements are proposed in this offsite basin and there will be no point discharge generated from this small basin, runoff generated from this basin should be considered negligible and should have no impact on the downstream drainage system. Mars Drive Improvements A small portion of Mars Drive will be added to the current road alignment and will extend from its existing terminus approximately 150’ to the south where it will terminate perpendicular to the Mars Landing project site. A 5’ wide sidewalk along the west side of the Mars Drive right-of-way will also be constructed with this project. Conveyance of runoff generated within the Mars Drive right-of-way south of Skyway Drive was studied in the Final Drainage Report for the South College Storage Units project and is not included in this study. Runoff generated with the south portion of the sidewalk installation and the extension of Mars Drive for the Mars Landing project is included within Basins M7 and M6 of the South College Storage Units drainage study. Runoff from these basins is captured in two curb inlets, one on either side of Mars Drive. Stormwater is then conveyed from these inlets via underground storm sewer to the South PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 11 of 15 College Storage Units rain garden and detention pond. Runoff generated with the north portion of the sidewalk installation will flow overland into Mars Drive will it be captured in the existing vertical curb and gutter system that drains downhill toward Skyway Drive to the north. PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 12 of 15 VI. EROSION AND SEDIMENT CONTROL MEASURES A General Permit for Stormwater Discharge Associated with Construction Activities issued by the Colorado Department of Public Health and Environment (CDPHE), Water Quality Control Division (WQCD), will be acquired for the project site. Prior to any earth disturbing activity a Stormwater Management Plan (SWMP) will be prepared to identity the Control Measures which, when implemented, will meet the requirements of said General Permit. PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 13 of 15 VII. FLOODPLAIN According to FEMA FIRM Map Numbers 08069C1405F - effective date: 12/19/2006, the project site resides in Zone X – Area of Minimal Flood Hazard. Refer to Appendix A, pages A-X and A-X for the FIRM Map and Firmette. PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 14 of 15 VIII. CONCLUSIONS COMPLIANCE WITH STANDARDS The design presented in this preliminary drainage report for Mars Landing has been prepared in accordance with the design standards and guidelines presented in the Fort Collins Stormwater Criteria Manual. VARIANCES No variance(s) requested at this time. PRELIMINARY DRAINAGE REPORT – Mars Landing September 11, 2019 Modified September 9, 2020 Galloway & Company, Inc. Page 15 of 15 IX. REFERENCES 1. Fort Collins Stormwater Criteria Manual (December (2018) 2. Urban Drainage and Flood Control District, Drainage Criteria Manual Volumes 1 and 2, prepared by Wright-McLaughlin Engineers, originally published March 1969 and updated August 2018, and the Volume 3, prepared by Wright-McLaughlin Engineers, originally published September 1992 and updated April 2018. ` APPENDIX A REFERENCE MATERIAL ` VICINITY MAP SCALE: NTS S. COLLEGE AVE W. TRILBY RD MARS DR VICINITY MAP SITE SKYWAY DR ` NRCS SOILS MAP Hydrologic Soil Group—Larimer County Area, Colorado (Skyway Townhomes) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/27/2019 Page 1 of 4 4483270 4483290 4483310 4483330 4483350 4483370 4483390 4483410 4483430 4483450 4483470 4483490 4483270 4483290 4483310 4483330 4483350 4483370 4483390 4483410 4483430 4483450 4483470 4483490 493110 493130 493150 493170 493190 493210 493230 493250 493270 493110 493130 493150 493170 493190 493210 493230 493250 493270 40° 30' 7'' N 105° 4' 52'' W 40° 30' 7'' N 105° 4' 45'' W 40° 30' 0'' N 105° 4' 52'' W 40° 30' 0'' N 105° 4' 45'' 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: 1:1,130 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 35 Fort Collins loam, 0 to 3 percent slopes C 0.6 16.7% 54 Kim loam, 3 to 5 percent slopes B 1.6 45.6% 56 Kim-Thedalund loams, 3 to 15 percent slopes B 1.3 37.7% Totals for Area of Interest 3.5 100.0% 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. Hydrologic Soil Group—Larimer County Area, Colorado Skyway Townhomes Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/27/2019 Page 3 of 4 Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Larimer County Area, Colorado Skyway Townhomes Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/27/2019 Page 4 of 4 ` FEMA FIRMETTE USGS The National Map: Orthoimagery. Data refreshed April, 2019. National Flood Hazard Layer FIRMette 0 250 500 1,000 1,500 2,000 Feet Ü 105°5'7.24"W 40°30'16.76"N 105°4'29.78"W 40°29'49.41"N SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT HAZARD SPECIAL FLOOD AREAS Without Zone A, V, Base A99 Flood Elevation (BFE) With BFE or Depth Zone AE, AO, AH, VE, AR Regulatory Floodway 0.of 2% 1% Annual annual Chance chance Flood flood with Hazard, average Areas depth areasdrainage of less less than than one one foot square or with mile Zone X Future ChanceAnnual Conditions Flood Hazard 1% Zone X Area Levee.to with See Reduced Notes. Flood Risk due Zone X Area with Flood Risk due to LeveeZone D NO SCREEN Area of Minimal Flood Hazard Zone X Area of Undetermined Flood Hazard Zone D Channel, Culvert, or Storm Sewer Levee, Dike, or Floodwall Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of Study Jurisdiction Boundary Digital Data Available No Digital Data Available Unmapped This digital map flood complies maps if with it is FEMA's not void standards as described for the below. use of The accuracy basemap standards shown complies with FEMA's basemap The authoritative flood hazard NFHL information web services is derived provided directly by FEMA. from This the map was reflectnot exported changes on or 6/amendments 27/2019 at 5:subsequent 17:47 PM and to this does date and time. becomeor The superseded NFHL and effective by new data information over time. may change This elementsmap map image do not is appear: void if basemap the one or imagery, more of flood the following zone labels, legend, FIRM panel scale number, bar, map and creation FIRM effective date, community date. Map identifiers,images for unmapped regulatoryfor purposes. and unmodernized areas cannot be used Legend OTHER FLOOD AREAS HAZARD OF OTHER AREAS STRGUECNTUERREASL FEATURES OTHER MAP PANELS 8 1:6,000 B 20.2 The point pin selected displayed by the on the user map and is does an approximate not represent an authoritative property location. ` APPENDIX B HYDROLOGY CALCULATIONS ` PROPOSED RUNOFF CALCULATIONS Subdivision: South College Storage Subdivision Project Name: Mars Landing Location: CO, Fort Collins Project No.: Calculated By: DBC Checked By: HF INPUT User Input Date: 9/9/20 OUTPUT Calculated Value Single-Family Alley-Loaded SF Duplex/AttachedMulti-Family 95% 5% 100% A1 0.09 95 0.07 79 20 0.01 3 95 0.00 0 0.83 A2 0.39 95 0.23 57 20 0.12 6 95 0.03 8 0.71 A3 0.52 95 0.01 2 20 0.45 17 95 0.05 10 0.29 A4 0.24 95 0.17 70 20 0.04 4 95 0.02 8 0.81 A5 0.48 95 0.41 80 20 0.06 2 95 0.02 4 0.86 A6 0.86 95 0.48 53 20 0.36 8 95 0.02 2 0.64 A7 0.18 95 0.16 80 20 0.03 3 95 0.00 0 0.83 A8 0.34 95 0.00 0 20 0.00 0 95 0.34 95 0.95 A9 0.34 95 0.00 0 20 0.00 0 95 0.34 95 0.95 B1 0.14 95 0.03 21 20 0.11 16 95 0.00 0 0.37 B2 0.20 95 0.02 11 20 0.17 17 95 0.00 2 0.30 B3 0.01 95 0.01 53 20 0.00 9 95 0.00 0 0.62 A BASINS (Detention Tributary) 3.44 95 1.54 42 20 1.08 6 95 0.83 23 0.71 LID Tributary (A2 & A4-A9) 2.84 95 1.45 49 20 0.61 4 95 0.77 26 0.79 Σ Basins - B BASINS 0.35 95 0.06 17 20 0.28 16 95 0.00 1 0.34 Σ Basins - TOTAL 3.79 95 1.60 40 20 1.37 7 95 0.83 21 0.68 Area (ac) Roofs Runoff Coefficient COMPOSITE RUNOFF COEFFICIENTS Area (ac) Area Weighted Asphalt + Concrete Walks Lawns, Clayey Soil Area Weighted Runoff Coefficient Area (ac) GNK008.20 Area Weighted C2 Basin ID Total Area (ac) Runoff Coefficient Page 1 of 1 9/1/2020 Subdivision: South College Storage Subdivision Project Name: Mars Landing Location: CO, Fort Collins Project No.: Calculated By: DBC Checked By: HF Date: 9/9/20 1 2 3 4 5 6 7 8 9 10 13 14 15 16 17 18 19 20 21 22 23 24 BASIN D.A. Hydrologic C2 C5 C100 L S Ti | 2-Year Ti | 100-Year L Calculated S Cv VEL. Tt COMP. Tc | 2-Year COMP. Tc | 100-Year TOTAL Urbanized Tc Tc | 2-Year Tc | 100-Year ID (AC) Soils Group Cf=1.00 Cf=1.00 Cf=1.25 (FT) (%) (MIN) (MIN) (FT) Slope, % (%) (FPS) (MIN) (MIN) (MIN) LENGTH(FT) (MIN) (MIN) (MIN) A1 0.09 C 0.83 0.83 1.00 18 6.39 1.2 0.4 98 3.60 3.60 20 3.8 0.4 1.6 0.9 116 10.6 5.0 5.0 A2 0.39 C 0.71 0.71 0.89 21 19.00 1.3 0.7 252 1.98 1.98 20 2.8 1.5 2.7 2.2 273 11.5 5.0 5.0 A3 0.52 C 0.29 0.29 0.37 0 2.00 0.0 0.0 398 2.52 2.52 15 2.4 2.8 2.8 2.8 398 12.2 5.0 5.0 A4 0.24 C 0.81 0.81 1.00 0 2.00 0.0 0.0 125 2.78 2.78 20 3.3 0.6 0.6 0.6 125 10.7 5.0 5.0 A5 0.48 C 0.86 0.86 1.00 22 9.27 1.0 0.4 125 6.09 6.09 20 4.9 0.4 1.4 0.8 147 10.8 5.0 5.0 A6 0.86 C 0.64 0.64 0.80 16 15.13 1.4 0.9 157 4.54 4.54 20 4.3 0.6 2.0 1.5 173 11.0 5.0 5.0 A7 0.18 C 0.83 0.83 1.00 0 2.00 0.0 0.0 135 3.93 3.93 20 4.0 0.6 0.6 0.6 135 10.8 5.0 5.0 A8 0.34 C 0.95 0.95 1.00 0 2.00 0.0 0.0 64 1.56 1.56 20 2.5 0.4 0.4 0.4 64 10.4 5.0 5.0 A9 0.34 C 0.95 0.95 1.00 0 2.00 0.0 0.0 64 1.56 1.56 20 2.5 0.4 0.4 0.4 64 10.4 5.0 5.0 B1 0.14 C 0.37 0.37 0.46 0 2.00 0.0 0.0 64 7.75 7.75 20 5.6 0.2 0.2 0.2 64 10.4 5.0 5.0 B2 0.20 C 0.30 0.30 0.38 0 2.00 0.0 0.0 94 2.76 2.76 20 3.3 0.5 0.5 0.5 94 10.5 5.0 5.0 B3 0.01 C 0.62 0.62 0.78 0 2.00 0.0 0.0 26 5.65 5.65 20 4.8 0.1 0.1 0.1 26 10.1 5.0 5.0 NOTES: Ti = (1.87*(1.1 - CCf)*(L)^0.5)/((S)^0.33), S in % Cv Tt=L/60V 2.5 Velocity V=Cv*S^0.5, S in ft/ft 5 Tc Check = 10+L/180 7 For urbanized basins a minimum Tc of 5.0 minutes is required. 10 For non-urbanized basins a minimum Tc of 10.0 minutes is required 15 20 STANDARD FORM SF-2 TIME OF CONCENTRATION SUB-BASIN Tc CHECK GNK008.20 FINAL INITIAL/OVERLAND (Ti) TRAVEL TIME (Tt) (URBANIZED BASINS) Paved Areas and Shallow Paved Swales DATA Type of Land Surface Heavy Meadow Tillage/Field Short Pasture and Lawns Nearly Bare Ground Grassed Waterway Page 1 of 1 9/1/2020 Project Name: Mars Landing Subdivision: South College Storage Subdivision Project No.: GNK008.20 Location: CO, Fort Collins Calculated By: DBC Design Storm: Checked By: HF Date: TRAVEL TIME STREET Design Point Basin ID Area (Ac) Runoff Coeff. | C 2 Tc | 2-Year (min) C*A (Ac) I (in/hr) Q (cfs) Tc (min) C*A (Ac) I (in/hr) Q (cfs) Slope (%) Street Flow (cfs) Design Flow (cfs) Slope (%) Pipe Size (inches) Length (ft) Velocity (fps) Tt (min) REMARKS A1 A1 0.09 0.83 5.0 0.07 2.85 0.2 A2 A2 0.39 0.71 5.0 0.28 2.85 0.8 A3 A3 0.52 0.29 5.0 0.15 2.85 0.4 A4 A4 0.24 0.81 5.0 0.19 2.85 0.5 A5 A5 0.48 0.86 5.0 0.42 2.85 1.2 A6 A6 0.86 0.64 5.0 0.55 2.85 1.6 A7 A7 0.18 0.83 5.0 0.15 2.85 0.4 A8 A8 0.34 0.95 5.0 0.32 2.85 0.9 A9 A9 0.34 0.95 5.0 0.33 2.85 0.9 B1 B1 0.14 0.37 5.0 0.05 2.85 0.2 B2 B2 0.20 0.30 5.0 0.06 2.85 0.2 B3 B3 0.01 0.62 5.0 0.01 2.85 0.02 DIRECT RUNOFF TOTAL RUNOFF STREET PIPE STANDARD FORM SF-3 STORM DRAINAGE SYSTEM DESIGN (RATIONAL METHOD PROCEDURE) 2-Year 9/9/20 Page 1 of 1 9/1/2020 STANDARD FORM SF-3 STORM DRAINAGE SYSTEM DESIGN (RATIONAL METHOD PROCEDURE) Project Name: Mars Landing Subdivision: South College Storage Subdivision Project No.: GNK008.20 Location: CO, Fort Collins Calculated By: DBC Design Storm: Checked By: HF Date: TRAVEL TIME STREET Design Point Basin ID Area (Ac) Runoff Coeff. | C 100 Tc | 100-Year (min) C*A (Ac) I (in/hr) Q (cfs) Tc (min) C*A (Ac) I (in/hr) Q (cfs) Slope (%) Street Flow (cfs) Design Flow (cfs) Slope (%) Pipe Size (inches) Length (ft) Velocity (fps) Tt (min) REMARKS A1 A1 0.09 1.00 5.0 0.09 9.95 0.9 A2 A2 0.39 0.89 5.0 0.35 9.95 3.4 A3 A3 0.52 0.37 5.0 0.19 9.95 1.9 A4 A4 0.24 1.00 5.0 0.24 9.95 2.3 A5 A5 0.48 1.00 5.0 0.48 9.95 4.8 A6 A6 0.86 0.80 5.0 0.68 9.95 6.8 A7 A7 0.18 1.00 5.0 0.18 9.95 1.8 A8 A8 0.34 1.00 5.0 0.34 9.95 3.4 A9 A9 0.34 1.00 5.0 0.34 9.95 3.4 B1 B1 0.14 0.46 5.0 0.07 9.95 0.7 B2 B2 0.20 0.38 5.0 0.07 9.95 0.7 B3 B3 0.01 0.78 5.0 0.01 9.95 0.1 100-Year DIRECT RUNOFF TOTAL RUNOFF STREET 9/9/20 PIPE Page 1 of 1 9/1/2020 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 Tributary Area tc | 2-Year tc | 100-Year Q2 Q100 Sub-basin (acres) (min) (min) (cfs) (cfs) A1 0.09 0.83 1.00 5.0 5.0 0.2 0.9 A2 0.39 0.71 0.89 5.0 5.0 0.8 3.4 A3 0.52 0.29 0.37 5.0 5.0 0.4 1.9 A4 0.24 0.81 1.00 5.0 5.0 0.5 2.3 A5 0.48 0.86 1.00 5.0 5.0 1.2 4.8 A6 0.86 0.64 0.80 5.0 5.0 1.6 6.8 A7 0.18 0.83 1.00 5.0 5.0 0.4 1.8 A8 0.34 0.95 1.00 5.0 5.0 0.9 3.4 A9 0.34 0.95 1.00 5.0 5.0 0.9 3.4 B1 0.14 0.37 0.46 5.0 5.0 0.2 0.7 B2 0.20 0.30 0.38 5.0 5.0 0.2 0.7 B3 0.01 0.62 0.78 5.0 5.0 0.0 0.1 A BASINS (TO DETENTION) 3.44 0.71 0.89 - - 7.0 28.8 TO LID 2.84 0.79 0.98 - - 3.7 25.4 B BASINS 0.35 0.34 0.43 - - 0.00 1.48 TOTAL 3.79 0.68 0.85 - - 0.00 30.31 BASIN SUMMARY TABLE C2 C100 H:\Hartford Homes\HFHLV0001.01 Timberline Vine Dr\3. Permit Const Docs\3.04 Grading-Drainage Studies\3.04.2 Proposed Drainage Reports- Info\Hydrology\Rational\HFHLV0001.01_Drainage_Calcs_Template_v2.0-CoFC.xls ` APPENDIX C HYDRAULIC CALCULATIONS Project Number: GNK08.20 Date: 9/9/2020 Project Location: Fort Collins, Colorado Calculations By: DBC Pond Description: Detention Pond User Input Cell: Blue Text 100-year 35606 0.89 0.82 3.44 0.69 minutes seconds in/hr cubic feet cubic feet cubic feet acre-feet 5 300 9.95 9139 206.4 8932 0.21 10 600 7.72 14181 412.8 13769 0.32 15 900 6.52 17965 619.2 17346 0.40 20 1200 5.60 20574 825.6 19748 0.45 25 1500 4.98 22870 1032 21838 0.50 30 1800 4.52 24909 1238.4 23671 0.54 35 2100 4.08 26232 1444.8 24787 0.57 40 2400 3.74 27481 1651.2 25830 0.59 45 2700 3.46 28601 1857.6 26744 0.61 50 3000 3.23 29667 2064 27603 0.63 55 3300 3.03 30613 2270.4 28343 0.65 60 3600 2.86 31522 2476.8 29045 0.67 65 3900 2.71 32358 2683.2 29675 0.68 70 4200 2.59 33304 2889.6 30414 0.70 75 4500 2.48 34167 3096 31071 0.71 80 4800 2.38 34976 3302.4 31673 0.73 85 5100 2.29 35756 3508.8 32248 0.74 90 5400 2.21 36537 3715.2 32822 0.75 95 5700 2.13 37171 3921.6 33249 0.76 100 6000 2.06 37841 4128 33713 0.77 105 6300 2.00 38576 4334.4 34242 0.79 110 6600 1.94 39201 4540.8 34660 0.80 115 6900 1.88 39715 4747.2 34968 0.80 120 7200 1.84 40560 4953.6 35606 0.82 Storage Volume Modified FAA Method- Storage Colume Calculations Inputs | Tributary Area Output | Detention Volume Storm Duration Time Rainfall Intensity Inflow Volume Catchment 'C': Catchment Drainage Area, ac: Return Period for Detention Control: Required Storage, cubic feet: Required Storage, ac-ft: Release Rate, cfs: Average Outflow Storage Volume Project Number: GNK008.20 Project Location: Fort Collins, CO Date: 9/9/2020 Calculations By: DBC Pond Description: Mars Landing Detention Pond User Input Cell: Blue Text Design Point: DP A Design Storm: 100-year Required Volume: 35606 ft3 5037.20 ft Design Storm: N/A Required Volume: ft3 N/A ft Design Storm: N/A Required Volume: ft3 N/A ft Contour Elevation Contour Area Depth Incremental Volume Cummulative Volume Incremental Volume Cummulative Volume Cummulative Volume ft ft2 ft ft3 ft3 ft3 ft3 ac-ft 5032.50 0 0 0 0 0 0 0.00 5033.00 1387 0.50 347 347 231 231 0.01 5034.00 8257 1.00 4822 5169 4343 4574 0.11 5035.00 9396 1.00 8827 13995 8820 13394 0.31 5036.00 10061 1.00 9729 23724 9727 23121 0.53 5037.00 10665 1.00 10363 34087 10362 33482 0.77 5037.25 10808 1.25 13043 36767 13040 36161 0.83 Detention Pond Stage-Storage Calculations Required Volume Water Surface Elevation Average End Area Method: Conic Volume Method: 5032.0 5033.0 5034.0 5035.0 5036.0 5037.0 5038.0 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 Contour Elevation, ft Cummulative Volume, ft 3 On-Site Detention Pond Project Number: GNK08.20 Date: 9/9/2020 Project Location: Fort Collins, Colorado Calculations By: DBC Pond Description: Stormtech System - LID Requirement User Input Cell: Blue Text 2-year 4610 0.79 0.11 2.84 0.568 minutes seconds in/hr cubic feet cubic feet cubic feet acre-feet 5 300 2.85 1918 170.4 1748 0.04 10 600 2.21 2975 340.8 2634 0.06 15 900 1.87 3776 511.2 3265 0.07 20 1200 1.61 4335 681.6 3653 0.08 25 1500 1.43 4813 852 3961 0.09 30 1800 1.30 5250 1022.4 4228 0.10 35 2100 1.17 5513 1192.8 4320 0.10 40 2400 1.07 5762 1363.2 4398 0.10 45 2700 0.99 5997 1533.6 4464 0.10 50 3000 0.92 6192 1704 4488 0.10 55 3300 0.87 6441 1874.4 4567 0.10 60 3600 0.82 6623 2044.8 4578 0.11 65 3900 0.78 6825 2215.2 4610 0.11 70 4200 0.73 6879 2385.6 4493 0.10 75 4500 0.70 7067 2556 4511 0.10 80 4800 0.66 7108 2726.4 4381 0.10 85 5100 0.64 7323 2896.8 4426 0.10 90 5400 0.61 7390 3067.2 4323 0.10 95 5700 0.58 7417 3237.6 4180 0.10 100 6000 0.56 7538 3408 4130 0.09 105 6300 0.54 7633 3578.4 4054 0.09 110 6600 0.52 7700 3748.8 3951 0.09 115 6900 0.51 7895 3919.2 3976 0.09 120 7200 0.49 7915 4089.6 3826 0.09 Average Outflow Storage Volume Storage Volume Catchment Drainage Area, ac: Release Rate, cfs: Storm Duration Time Rainfall Intensity Inflow Volume Catchment 'C': Required Storage, ac-ft: Modified FAA Method- Storage Colume Calculations Inputs | Tributary Area Output | Detention Volume Return Period for Detention Control: Required Storage, cubic feet: Project: Basin ID: Depth Increment = ft Required Volume Calculation Top of Micropool Selected BMP Type = EDB Watershed Area = 2.84 acres Watershed Length = ft Watershed Slope = ft/ft Watershed Imperviousness = 77.00% percent Percentage Hydrologic Soil Group A = 0.0% percent Percentage Hydrologic Soil Group B = 0.0% percent Percentage Hydrologic Soil Groups C/D = 100.0% percent Desired WQCV Drain Time = 40.0 hours Location for 1-hr Rainfall Depths = User Input Water Quality Capture Volume (WQCV) = 0.073 acre-feet Excess Urban Runoff Volume (EURV) = 0.214 acre-feet 2-yr Runoff Volume (P1 = 0 in.) = 0.000 acre-feet inches 5-yr Runoff Volume (P1 = 0 in.) = 0.000 acre-feet inches 10-yr Runoff Volume (P1 = 0 in.) = 0.000 acre-feet inches 25-yr Runoff Volume (P1 = 0 in.) = 0.000 acre-feet inches 50-yr Runoff Volume (P1 = 0 in.) = 0.000 acre-feet inches 100-yr Runoff Volume (P1 = 0 in.) = 0.000 acre-feet inches 500-yr Runoff Volume (P1 = 0 in.) = 0.000 acre-feet inches Approximate 2-yr Detention Volume = 0.000 acre-feet Approximate 5-yr Detention Volume = 0.000 acre-feet Approximate 10-yr Detention Volume = 0.000 acre-feet Approximate 25-yr Detention Volume = 0.000 acre-feet Approximate 50-yr Detention Volume = 0.000 acre-feet Approximate 100-yr Detention Volume = 0.000 acre-feet Stage-Storage Calculation Select Zone 1 Storage Volume (Required) = acre-feet Select Zone 2 Storage Volume (Optional) = acre-feet Select Zone 3 Storage Volume (Optional) = acre-feet Total Detention Basin Volume = acre-feet Initial Surcharge Volume (ISV) = 10 ft^3 Initial Surcharge Depth (ISD) = ft Total Available Detention Depth (Htotal ) = ft Depth of Trickle Channel (HTC ) = ft Slope of Trickle Channel (STC ) = ft/ft Slopes of Main Basin Sides (Smain ) = H:V Basin Length-to-Width Ratio (RL/W ) = Initial Surcharge Area (AISV) = ft^2 Surcharge Volume Length (LISV) = ft Surcharge Volume Width (WISV) = ft Depth of Basin Floor (HFLOOR) = ft Length of Basin Floor (LFLOOR) = ft Width of Basin Floor (WFLOOR) = ft Area of Basin Floor (AFLOOR) = ft^2 Volume of Basin Floor (VFLOOR) = ft^3 Depth of Main Basin (HMAIN) = ft Length of Main Basin (LMAIN) = ft Width of Main Basin (WMAIN) = ft Area of Main Basin (AMAIN) = ft^2 Volume of Main Basin (VMAIN) = ft^3 Calculated Total Basin Volume (Vtotal) = acre-feet UDSCM WQCV (CF) WQ FLOW (CFS) CHAMBER TYPE (A) RELEASE RATE/ CHAMBER (CFS) VOLUME/ CHAMBER (CF) VOLUME/ CHAMBER + AGGREGATE (CF) NUMBER OF CHAMBERS COMBINED RELEASE RATE WQCV METHOD (CFS) FAA REQUIRED STORAGE VOLUME (CF) NUMBER OF CHAMBERS (FAA) TOTAL VOLUME (CHAMBERS ONLY) (CF) TOTAL VOLUME (CHAMBERS + AGGREGATE) (CF) COMBINED RELEASE RATE FAA METHOD (CFS) TOTAL NUMBER OF CHAMBERS REQUIRED 3179.88 1.85 SC-740 0.024 45.9 74.9 43 1.01 4610 62 2845.8 4643.8 1.46 62 85.4 51.0 4355.4 30.25 0.35 10.59 0.024 (A - COLUMN 4) CHAMBER FOOTPRINT (SF) FLOW RATE (GPM/SF) FLOW RATE PER CHAMBER (GPM) FLOW RATE PER CHAMBER (CFS)) ` APPENDIX D DRAINAGE MAPS + VARIANCE APPLICATION EXISTING DRAINAGE STUDY EXCERPTS This unofficial copy was downloaded on Jun-25-2019 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA ` APPENDIX D DRAINAGE MAPS + VARIANCE DRAINAGE APPLICATION MAPS E T T STM A1 A2 A3 A4 A5 A6 A7 A8 A9 B1 B2 B3 acres A1 0.83 1.00 0.09 acres A2 0.71 0.89 0.39 acres A3 0.29 0.37 0.52 acres A4 0.81 1.00 0.24 acres A5 0.86 1.00 0.48 acres A6 0.64 0.80 0.86 acres A7 0.83 1.00 0.18 acres A8 0.95 1.00 0.34 acres A9 0.95 1.00 0.34 acres B1 0.37 0.46 0.14 acres B3 0.62 0.78 0.01 acres B2 0.30 0.38 0.20 acres OS1 0.25 0.31 1.55 - - - - - - - - - - - - - - STAMP Date: Drawn By: Project No: Checked By: H:\Goodwin Knight\CO, Fort Collins - GNK000008.10 - Mars Landing ISP\CADD\3 CD\GNK08_C9.0_Drainage Plan.dwg - Donald Cecil - 9/1/2020 # Date Issue / Description Init. MARS LANDING PROJECT DEVELOPMENT PLAN FORT COLLINS, CO THESE PLANS ARE AN INSTRUMENT OF SERVICE AND ARE THE PROPERTY OF GALLOWAY, AND MAY NOT BE DUPLICATED, DISCLOSED, OR REPRODUCED WITHOUT THE WRITTEN CONSENT OF GALLOWAY. COPYRIGHTS AND INFRINGEMENTS WILL BE ENFORCED AND PROSECUTED. COPYRIGHT GallowayUS.com 5265 Ronald Reagan Blvd., Suite 210 Johnstown, CO 80534 970.800.3300 PRELIMINARY NOT FOR BIDDING NOT FOR CONSTRUCTION 09.09.2020 GNK000008 JEP DBC CAUTION - NOTICE TO CONTRACTOR 1. ALL UTILITY LOCATIONS SHOWN ARE BASED ON MAPS PROVIDED BY THE APPROPRIATE UTILITY COMPANY AND FIELD SURFACE EVIDENCE AT THE TIME OF SURVEY AND IS TO BE CONSIDERED AN APPROXIMATE LOCATION ONLY. IT IS THE CONTRACTOR'S RESPONSIBILITY TO FIELD VERIFY THE FIELD LOCATION OF ALL UTILITIES, PUBLIC OR PRIVATE, WHETHER SHOWN ON THE PLANS OR NOT, PRIOR TO CONSTRUCTION. REPORT ANY DISCREPANCIES TO THE ENGINEERED PRIOR TO CONSTRUCTION. 2. WHERE A PROPOSED UTILITY CROSSES AN EXISTING UTILITY, IT IS THE CONTRACTOR'S RESPONSIBILITY TO FIELD VERIFY THE HORIZONTAL AND VERTICAL LOCATION OF SUCH EXISTING UTILITY, EITHER THROUGH POTHOLING OR ALTERNATIVE METHOD. REPORT INFORMATION TO THE ENGINEER PRIOR TO CONSTRUCTION. 3. CONTRACTOR RESPONSIBLE FOR AS-BUILT DRAWINGS, TESTS, REPORTS AND/OR ANY OTHER CERTIFICATES OR INFORMATION AS REQUIRED FOR ACCEPTANCE OF WORK FROM CITY, UTILITY DISTRICTS OR ANY OTHER GOVERNING AGENCY. 4. CONTRACTOR SHALL PROTECT ALL EXISTING SURVEY MONUMENTATION. CONTRACTOR SHALL HAVE LICENSED SURVEYOR REPLACE ANY DAMAGED OR DISTURBED MONUMENTATION AT THEIR COST. Know what's before you dig. DRAINAGE PLAN C8.0 SCALE: 1"=30' 0 15 30 LEGEND: PROPOSED STORM SEWER EXISTING STORM SEWER PROPOSED STORM INLET PROPOSED LOTLINE EASEMENT LINE EXISTING MINOR CONTOUR EXISTING MAJOR CONTOUR PROPOSED MINOR CONTOUR PROPOSED MAJOR CONTOUR PROPERTY BOUNDARY EXISTING MANHOLE DRAINAGE SYMBOLS: DESIGN POINT MAJOR BASIN BOUNDARY (i.e., C-STORE) SUB-BASIN BOUNDARY (i.e., RATIONAL METHOD) OVERLAND FLOW DIRECTION (I.E., LANDSCAPING) DIRECT FLOW DIRECTION (I.E., PAVEMENT, CURB AND GUTTER) BASIN ID MINOR (2YEAR) RUNOFF COEFFICIENT MAJOR (100YEAR) RUNOFF COEFFICIENT BASIN AREA (ACRES) acres A1 0.23 0.45 1.00 A1 STORMTECH CHAMBER VOLUME AND RELEASE RATE CALCULATIONS SC-740 CHAMBER SPECIFICATIONS CHAMBER LENGTH (IN) CHAMBER WIDTH (IN) CHAMBER FOOTPRINT (SQ IN) DETENTION BASIN STAGE-STORAGE TABLE BUILDER Optional Override Area (ft^2) Length (ft) Optional Override Stage (ft) Stage (ft) Stage - Storage Description Area (ft^2) Width (ft) Mars Landing - LID Required WQCV for LID Using UDSCM LID Basins UD-Detention, Version 3.07 (February 2017) Volume (ft^3) Volume (ac-ft) Area (acre) Optional User Override 1-hr Precipitation Example Zone Configuration (Retention Pond) UD-Detention_v3.07, Basin 9/1/2020, 3:16 PM 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 of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 13, Sep 10, 2018 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Aug 11, 2018—Aug 12, 2018 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Hydrologic Soil Group—Larimer County Area, Colorado (Skyway Townhomes) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/27/2019 Page 2 of 4