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Home My WebLink AboutDrainage Reports - 07/25/2013I I I I I I I I I I I I I I I I I I I Preliminary Drainage & Erosion Control Study Remington Row · Fort Collins, CO Prepared far: Maxiiimo Development Group LLC 706 S. College Ave #201 Fort Collins, CO 80524 July 10, 2013 1501 Academy Ct. Ste. 203 Fort Collins, Colorado 80524 (970) 300-2508 I I I I I I I I I I I I I I I I I I I TABLE OF CONTENTS Drainage & Erosion Control Report Remington Row Fort Collins, CO PAGE I. GENERAL PROJECT LOCATION AND DESCRIPTION ........................................................... 1 A. Location ................................................................................................................ 1 8. Description of Property ........................................................................................ 1 11. DRAINAGE BASINS AND SUB-BASINS ............................................................................... 1 A. Major Basin Description ....................................................................................... 1 8. Sub-Basin Description ........................................................................................... 2 Ill. DRAINAGE DESIGN CRITERIA ............................................................................................ 2 A. Regulations ........................................................................................................... 2 8. Hydrological Criteria ............................................................................................. 2 C. Hydraulic Criteria .................................................................................................. 2 D. Variance Request .................................................................................................. 3 IV. DRAINAGE FACILITY DESIGN ............................................................................................. 4 A. General Concept ................................................................................................... 4 8. Specific Details ...................................................................................................... 6 V. CONCLUSIONS .................................................................................................................. 7 A. Compliance with Standards .................................................................................. 7 8. Drainage Concept ................................................................................................. 7 C. Water Quality ....................................................................................................... 7 VI. EROSION AND SEDIMENT CONTROL ................................................................................ 8 A. Site Description ..................................................................................................... 8 8. Stormwater Management Controls ................................................................... 10 C. Erosion Control Sequencing ............................................................................... 14 D. Final Stabilization and Long Term Stormwater Quality ..................................... 15 E. Inspection and Maintenance Procedures .......................................................... 16 F. Erosion Control Surety Calculations ................................................................... 17 VII. REFERENCES ................................................................................................................ 17 APPENDICES APPENDIX A -Runoff Calculations APPENDIX B -Detention Pond Analysis APPENDIX C -Hydraulic Analyses APPENDIX D -References APPENDIX E -Plans and Maps B11010-DralnageReport-Finall.doc I I I I I I I I I I I I I I I I I I I Drainage & Erosion Control Report Remington Row Fort Collins, CO I. General Location and Description 11. A. Location B. The Remington Row site is located in the Northwest Quarter of Section 13, Township 7 North, Range 69 West of the 6th Principal Meridian to the City of Fort Collins, Larimer County, Colorado. The site is located immediately west of Remington Street, north of Plum Street, east of the alley between College Avenue and Remington Street, and south of Laurel Street. There are no known drainages within the project site. The alley behind the site is utilized as a drainage channel for portions of the runoff from both the project site and the adjacent lots. Description of Property The Remington Row site (referred herein as "the site", "this site") is approximately 0.46 acres in size that will be developed into a multi-family housing complex. The following is a summary of the existing conditions: Ground Cover -The site currently contains three buildings and the utilities to serve the residences. The existing ground cover consists mostly of grass. Grades -In general, the majority of the site slopes southeasterly at an approximately 1% slope. Sail Type -According to the NRCS Web Soil Survey, the majority of the site consists of Fort Collins loam, 1 to 3 percent slope (Soil Type B). Utilities -Other than the service lines to each of the existing houses there are no known utilities on the site Detention Ponds and Storm Sewer-There are no detention ponds currently on the site. Drainage Basins and Sub-Basins A. Major Basin Description The site is in the Old Town Basin where any increase over the existing imperviousness is required to be detained and released at the 2-year historic rate and to provide water quality for the entire site. I B11010-DrainageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I 111. Drainage & Erosion Control Report Remington Row Fort Collins, CO B. Sub-Basin Description Historically, the runoff from this site flows off the site un-detained into the curb and gutter along Remington Street or the alley between Remington Street and College Avenue. The proposed site will continue to direct the majority of flows towards Remington Street and a small portion of the site will continue to drain towards the alley. This final drainage study includes the calculations from off-site basins OSlA and OS2A, which do not flow into the site. These flows were calculated to assist in determining the alley capacity. Drainage Design Criteria A. Regulations B. C. The design criteria for this study are directly from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards Manual and the Urban Storm Drainage Criteria Manuals Volumes 2, and 3 (referred to herein as USDCM). Hydrological Criteria In accordance with the Fort Collins policy, a minor and major storm for the Fort Collins area is identified as the 2-year and 100-year storms, respectively. A major storm for the Fort Collins area has a recurrence interval of 100 years has a peak intensity of 9.95 in/hr. These storms have been used as a basis for planning and system design. The peak flow rates for design points have been calculated based on the Rational Method as described in the USDCM with storm duration set equal to the time of concentration for each sub-basin. This method was used to analyze the developed runoff from the 2-year (minor) and the 100-year (major) storm events. The Rational Method is widely accepted for drainage design involving small drainage areas (less than 160 acres) and short time of concentrations. The Rational Method is ideal for storm sewer sizing and small detention pond sizing (for tributary areas no larger than 90 to 160 acres). Runoff coefficients were assumed based on impervious area and soil type and are given in Appendices. Hydraulic Criteria The developed site will convey runoff to the parking lot detention and water quality features in a safe and effective manner via, swales and concrete pans. 2 B11010-DrainageReport•Finall.doc I I I I I I I I I I I I I I I I I I I D. Detention Areas Drainage & Erosion Control Report Remington Row Fort Collins, CO The runoff produced by the site will be conveyed to the proposed detention areas within the development. The detention areas were sized utilizing the Rational Formula-Based Modified FAA Procedure (assuming the required pond volume is maximized at 120 minutes or less). There are two parking lot detention areas (Detention Al and Detention Bl) shown on the west side of the proposed buildings. Detention area Al will release through an orifice plate in the curb on the southeast corner or the storage area. Detention area Bl will release through an orifice plate in the curb on the northeast corner of the storage area. These small ponds will spill at an elevation that is 0.8' lower than the adjacent building's finished floor elevation. Refer to Appendix B for detention pond calculations. Water Quality Water quality is provided by four separate porous landscape detention areas and disconnected impervious areas on the site. The porous landscape detention ponds are designed based on a 12 hour drain time and UDFCD standards for Bioretention Facilities and will rely on infiltration without an underdrain system. Design infiltration rates are assumed to be 1.2 to 1.5 in/hr based on infiltration tests completed by CTL Thompson. The letter entitled lnfiltrometer Tests, Remington Annex -Coflegio Two, 705 and 715 South Remington Street, Fort Collins, CO completed by CTL Thompson, Inc. dated April 4, 2013 is included in Appendix D. Alley Capacity The alley will be an inverted crown alley that will convey the runoff northerly and southerly. For a 0.5% longitudinal slope and a 2.5% cross slope this cross section has a capacity of approximately 5.5 cfs. Open Channels Sidewalk chases and curb cuts are typically designed for the minor storm with overtopping of the curbs/sidewalks in larger storm events. In all cases on this project, the minimum 12" wide curb channel and sidewalk chase is capable of conveying the 100 year storm event. Variance Request The site is not able to provide the required water quality capture volume (359 cf) assuming porous landscape detention and a 12 hr drain time. The site is limited to the depth of the adjacent curb and gutter on Remington Street because there is no storm sewer in the immediate vicinity. The site provides 3 B11010-DralnageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I Drainage & Erosion Control Report Remington Row Fort Collins, CO 317 cf of porous landscape detention storage and additional uncalculated water quality through disconnected impervious areas. IV. Drainage Facility Design A. General Concept The site will ultimately consist of ground covered by pavement, rooftop, and landscape. All referenced tables, charts, formulas, etc. are included in the Appendix. The area, time of concentration, and runoff of each proposed sub-basin is summarized in Appendix A. The project site was divided into several different developed sub-basins as explained further below: Basin A Basin A consists of rooftop, sidewalk, parking lot, and landscaped area on the southern portion of the site. Runoff from Basin Al is directed to the parking lot detention and porous landscape detention Al, where it will release through an orifice plate southeast of the parking lot. These flows will run along the south side of the property line where they will combine with Basin A2 and be detained in porous landscape detention pond A2. The flows will then be conveyed to Remington Street through a sidewalk chase and concrete curb channel. Basin B Basin B consists of rooftop, sidewalk, parking lot, and landscaped area on the northern portion of the site. Runoff from Basin Bl is directed to the parking lot detention and porous landscape detention Bl, where it will release through an orifice plate northeast of the parking lot. These flows will run along the north side of the property line where they will combine with Basin 82 and be detained in porous landscape detention pond 82. The flows will then be conveyed to Remington Street through a sidewalk chase and concrete curb channel. Basin C Basin C consists of rooftop, sidewalk, and landscaped area on the eastern portion of the site. Runoff is directed to the east, which is then conveyed to the curb and gutter in Remington Street via sheet flow over the sidewalk. Basin OSl Basin OSl consists of pavement and landscaped area on the southwestern portion of the site. Runoff is directed un-detained to the public alley to the west of the site and then flows south towards Plum Street. 4 811010-0ralnageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I Basin OS2 Drainage & Erosion Control Report Remington Row Fort Collins, CO Basin OS2 consists of pavement and landscaped area on the northwestern portion of the site. Runoff is directed un-detained to the public alley to the west of the site and then flows north towards Laurel Street. Basin OSlA Basin OSlA consists of mostly rooftop from the building directly to the west of this proposed building. Runoff is directed to the public alley and then flows south towards Plum Street. This offsite basin was included in order to calculate the depth of flow in the alley adjacent to the proposed underground parking garage. These flows combine with Basin OSl and the sum of the two flows is shown at Design Point OSl. Basin OS2A Basin OS2A consists of mostly rooftop from several buildings directly to the northwest of this proposed building. Runoff is directed to the public alley and then flows north towards Laurel Street. This offsite basin was included in order to calculate the runoff from the 2-year storm event that will pass over the sidewalk along Laurel Street. These flows combine with Basin OS2 and the sum of the two flows is shown at Design Point OS2. Existing Basins The existing onsite basins were also calculated to quantify the existing flows that are coming from the site. They were simply broken into flows exiting the site to the northwest (Basin NW), to the southwest (Basin SW), and to the east (E). 5 B11010-DrainageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I V. Drainage & Erosion Control Report Remington Row Fort Collins, CO The spillway for Ponds Al & Bl will be over curb to the east. The spillway for Pond Al will be 0.95' below the finished floor elevation of the adjacent building. The depth of flow at Spillway A will be 0.14', which leaves it 0.81' below the adjacent finished floor elevation. The spillway for Pond B will be 0.90' below the finished floor elevation of the adjacent building. The depth of flow at Spillway B will be 0.10', which leaves it 0.80' below the adjacent finished floor elevation. Water quality is provided for Basins Al, A2, Bl & B2 by four separate porous landscape detention areas. The porous landscape detention ponds are allowed to pond up to a depth of 0.4' and will rely on infiltration without an underdrain system and evaporation. Basin C encompasses the existing house at 711 Remington Street and the runoff patterns will remain largely unchanged. This basin will get some water quality benefit from the large disconnected landscape impervious area to the east of the house. Conclusions A. B. C. Compliance with Standards Storm drainage calculations have typically followed the guidelines provided by the City of Fort Collins Storm Drainage Design Criteria and Construction Standards Manual and/or the Urban Storm Drainage Criteria Manuals Volumes 2, ond 3. There is a variance that has been requested for Water Quality. Drainage Concept The drainage system has been designed to convey the runoff to the designated design points and the detention ponds in an effective manner as safe as possible. As proposed, the site has detention pond volumes (1,292 cf) in excess of that required (1042 cf). The post detention 100-year storm runoff is calculated at 1.710 cfs, which is slightly less than the calculated rate of 1.712 cfs for the existing site. Water Quality Water quality has been provided by porous landscape detention and disconnected impervious areas. There is 317 cf of porous landscape detention volume provided for Basins Al, A2, Bl, & B2. This is less than the 359 cf of porous landscape detention that is required for the entire site as discussed in the variance request. 7 811010-0ralnageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I VI. Erosion and Sediment Control A. Site Description 1. Construction Activity Description Drainage & Erosion Control Report Remington Row Fort Collins, CO The proposed project includes the construction of two new multifamily buildings and associated site improvements. Two existing on site buildings will be completely demolished and one building will be partially demolished. The majority of the existing site features including landscaping, parking area, and sidewalk will be removed and replaced with new landscaping, parking area, and sidewalk. In addition, the adjacent paved alley to the west will be removed and replaced with a newly paved alley. New utility services will be brought to.the site from the existing mains in Remington Street and the public alley. Permanent stormwater features for water quality and quantity will be incorporated into the site including parking lot detention and porous landscape detention. The site improvements will require changes minor changes in grade on the order plus or minus two feet. 2. Proposed Sequence for Major Activities The project is expected to be constructed in one phase. The anticipated sequence for major construction activities is follows: • Installation of erosion control • Removal and demolition of buildings, pavement, utilities, landscaping, etc. • Installation of utilities • Excavation for basement foundation • Installation of building foundation • Site grading and paving • Construction of buildings • Final landscaping. Construction is estimated to begin in the summer of 2013 and be fully completed by the fall of 2014. 3. Area Estimates The site area as defined by the property boundaries is 19,897 square-feet which is also the area that will undergo clearing and grading activities. The total project area including the utilities and alley paving is approximately 27,000 square-feet. 8 B11010-0ralnageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I Drainage & Erosion Control Report Remington Row Fort Collins, CO The site areas do not include any additional offsite areas (for staging, material storage, overburden stockpiles of dirt, borrow areas, etc) other than that mentioned above. 4. Soil Description CTL Thompson completed the soils investigations for the project site and presented the results in the Geotechnical Investigation Collegio Two South Remington and East Laurel Streets, Fort Collins, Colorado. According to this report, the surficial soils are man placed sandy clay fill material. Below this fill material, there generally exists 7 feet to 13 feet of medium dense clayey sands. 5. Existing Vegetation The existing site is developed with paving, buildings and vegetative cover that is 90% established. The vegetative cover consists of well established lawn, trees and bushes and covers approximately 54% of the site. 6. Location and Description of Other Potential Pollution Sources Potential pollutant sources include sediment, uncovered soil, construction machinery, building materials, paints, and fertilizers. It is anticipated that any storage of materials or machinery will be on site and surrounded by silt fence or straw wattles. 7. Non-Stormwater Components of Discharge According to the Geotechnical Investigation Collegio Two South Remington and East Laurel Streets, Fort Collins, Colorado by CTL Thompson: Ground water was measured at 23' deep in all five borings when drilled ..... The groundwater level will vary during wetter seasons and wetter years. We suggest assuming a groundwater level rise of 5 feet above the highest elevation at which the groundwater level was measured in our borings far design and construction planning. At these depths, it is expected that groundwater will not likely be encountered during the construction of utilities. If groundwater is encountered, a temporary sediment/retention basin should be constructed to store pumped dewatering flows. The other non-storm water components of discharge include water line flushing, irrigation to establish seeding, washing out concrete trucks, and watering for dust mitigation and compaction. It is important for the contractor to manage the runoff from these items utilizing the BM P's mentioned in this report (ie silt fence and straw waddles) 9 B11010-0ralnageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I 8. Receiving Waters Drainage & Erosion Control Report Remington Row Fort Collins, CO This site is located in the Old Town Basin of Fort Collins, Colorado. Runoff from the majority of the site will drain directly to the curb and gutter in Remington Street. A small amount of runoff will drain-.to the alley which will drain to Laurel Street or Plum Street and then eventually to the east towards Remington Street. In both cases, the stormwater eventually makes it to the storm drain inlet at the northwest corner of the Remington Street and Plum Street where it enters the storm sewer system and drains to the south in Remington Street. The storm sewer system drains to a major storm sewer in Locust Street, which drains to the east and north and eventually outlets to the Cache La Poudre River south of Mulberry Street and east of Riverside Avenue. B. Stormwater Management Controls 1. SWMP Administrator The SWMP Administrator is currently: Mr. Christian Bachelet Maxiiimo Development Group LLC 706 S. College Ave #201 Fort Collins, CO 80524 Phone: 970-566-2948 2. Identification of Potential Pollutant Sources This section focuses on the identification of the potential pollutant sources and briefly discusses the Best Management Practices (BMPs) that will be used. More information on the BM P's utilized on this site is included in the next section "3. Best Management Practices". A. All disturbed and stored soils; It is expected that there will be stockpiles of dirt on the site from the utility installations and the foundation excavation. Silt Fence or Straw wattles should be placed around the outer boundary of the site to contain the runoff from the stockpiles. B. Vehicle tracking of sediments It is anticipated that the contractor will access the property from the public alley to the west. A vehicle tracking control pad may be required to reduce tracking sediment onto the alley and the adjacent streets. At the end of each workday, the Contractor shall sweep or scrape Remington Street and the public alley that may have accumulated during the workday. 10 B11010-DralnageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I C. Management of contaminated soils Drainage & Erosion Control Report Remington Row Fort Collins, CO There are not any known contaminated soils on the site. However, if the contractor encounters contaminated soils during the construction process they should stop construction immediately and notify the appropriate government authorities in accordance with good construction safety and practice. D. Loading and Unloading operations Loading and unloading will take place on the site. BMP's should be in place to keep sediment from entering the alley. E. Outdoor storage activities (building materials, fertilizers, chemicals, etc.) Storage of onsite materials including building materials, fertilizers, waterline, and sanitary sewer will be covered and placed on pallets to prevent direct contact with the ground and potential surface runoff. F. Vehicle and equipment maintenance Vehicle and equipment maintenance should be performed offsite or onsite within the perimeter silt fence or straw wattles. Vehicle and equipment maintenance shall not happen along the adjacent public streets. At a minimum all vehicle and equipment maintenance shall be performed on the hard surface or gravel areas at least 50' from any stormwater feature (ie inlet, storm sewer, concentrated runoff, swale, etc.) G. Significant dust or particulate generating processes The Contractor shall comply with applicable air pollution control requirements of the City. The Contractor shall take appropriate actions to minimize atmospheric pollution and take reasonable precautions which shall include, but not be limited to: 1. The use of water for control of dusts for construction processes such as demolition, grading, or the clearing of land. 2. Covering, at all times when in motion, open-bodied trucks transporting materials likely to give rise to airborne dusts. H. Routine maintenance activities involving fertilizers, pesticides, detergents, fuels, solvents, oils, etc; Chemicals, fuels, lubricants, and paints typical with building construction stored on-site will be in water tight containers and covered as necessary and stored in a bermed area, a storage building, or within a vehicle to act as secondary containment. I. On-site waste management practices (waste plies, liquid wastes, dumpsters, etc.); 1. Waste piles should be covered or surrounded by silt fence or straw wattles. Liquid wastes should be collected and stored in covered containers and disposed of properly. 2. Solid waste materials, including disposable materials incidental to the major construction activities, will be collected in on site dumpsters. The containers will be emptied periodically and trucked away from the site. Dumpsters should have covers. 11 B11010-DralnageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I Drainage & Erosion Control Report Remington Row Fort Collins, CO J. Contrete trutk / equipment washing, intluding the tontrete trutk thute and assotiated fixtures and equipment; A dedicated concrete washout area is necessary for this project. The contractor shall clean out equipment so that runoff is not allowed to leave site and enter the public streets or neighboring properties. K. Deditated asphalt and tontrete batth plants; There will not be dedicated asphalt or concrete batch plants on this site. L. Non-industrial waste sources such as worker trash and portable toilets Worker's trash shall be disposed of in an onsite dumpster. The site should be free of trash at the end of each working day. Portable toilets shall be utilized by construction personnel and serviced regularly by a commercial operator. They shall be located a minimum of 5 feet from the curb or 50 feet from inlets and must be anchored. If sanitary facilities are located on a paved surface, a secondary containment BMP will need to be constructed. M. Other areas or protedures where potential spills tan occur. BMP's such as tarps and drip pans should be used for painting, stucco, dry-wall etc. operations 3. Best Management Practices (BMP's) Once construction activity begins, Best Management Practices (BMP's) intended to contain sediment onsite must be constructed, inspected and repaired as necessary. Such controls must be functional before upslope land disturbance takes place. The BM P's will be installed as shown on the Grading and Erosion Control plan shown in Appendix D. They must be supplemented as on-site experience proves necessary in order to control sediment, pollutant discharge, and insure public safety. The following temporary and permanent BM P's will be installed and maintained to control on-site erosion and prevent sediment from traveling off-site during construction. The descriptions below provide some information about each BMP, but further information can be found in Urban Storm Drainage Criteria Manual, Volume 3 -Best Management Practices by Urban Drainage and Flood Control District. Temporary BMP's • Construction Fence is a temporary BMP. The contractor is to place construction fencing around development as needed to limit access by construction equipment and personal vehicles to designated areas of ingress and egress. Since the majority of site will soon be surrounded by a permanent fence, there will be limited construction fence needed on this project. 12 B11010-0rainageReport.finall.doc I I I I I I I I I I I I I I I I I I I Drainage & Erosion Control Report Remington Row Fort Collins, CO • Regular Meetings is a temporary and non-structural BMP. Regular meetings with on-site workers including builders, suppliers, landscape personnel, etc. should be conducted so that they are kept up to date with site standard operating procedures. • Silt Fence is a woven synthetic permeable fabric that filters runoff. Silt fence is a temporary barrier that is installed prior to earthmoving activities and is placed downstream of areas where runoff from construction activities is expected to occur, especially along the site perimeter to allow sediment to settle from runoff before water leaves the construction site. Silt fences will be installed per manufacturer's recommendations. Silt fence encourages sheet flow and is not intended to be used in areas of concentrated flow. If concentrated flow is encountered during the placement of the fence, an alternative BMP shall be used and the SWMP should be updated to reflect this change. • Straw Wattles are a temporary BMP that are used for a variety of purposes. They are used for inlet protection, curbside check dams, swale protection, at the bottom of slopes, or the limits of property boundaries. The straw wattles, which are meshed netting "tubes" filled with straw, excelsior, or coconut fiber. Wattles for swale protection should be installed following rough grading of channel areas. Wattles require proper installation and maintenance to ensure their performance. • Street Sweeping and Vacuuming removes sediment that has been tracked onto roadways to reduce sediment transport into storm drain systems or a surface waterway. This practice should be used on the adjacent paved road to the construction site. Paved roads should be inspected on a daily basis and more frequently as needed. • Saw Cutting Pollution Prevention prevents dust and slurry from asphalt and concrete saw cutting activities from migrating into the existing storm drain system. Slurry and cuttings shall be vacuumed during cutting and surface operations and shall not be allowed to remain on pavement surface overnight. Collected slurry and cuttings shall be disposed of in a manner that does not violate groundwater or surface water standards. • Temporary Seeding is the establishment of a temporary vegetative cover on a graded area that will be exposed for longer 30 days. Temporary seeding can be used on areas requiring temporary protection that will eventually need permanent vegetation at the completion of the construction or it can be used for areas that will be re-disturbed after a period of inactivity. The seed mix 100% smooth brome at a minimum application rate of 30 lbs/acre. Fertilizer and Mulch shall be included as specified on the plans. • Vehicle Tracking Control is a stabilized stone pad located at points of ingress and egress on a construction site and acts as a temporary BMP. The stone pad is designed to reduce the amount of mud transported onto public roads by construction traffic by removing mud and sediment from the vehicle's wheels when it drives over the gravel pad. These areas are limited to the minimum number 13 B11010-DralnageReport-Flnalt.doc I I I I I I I I I I I I I I I I I I I C. Drainage & Erosion Control Report Remington Row Fort Collins, CO necessary to provide functional construction access and installed prior to overlot grading activities. Whenever the construction entrance exists onto a public road, the road shall be cleaned at the end of each day. Vehicle Tracking Control will also be use on this site at the stockpile area exit(s). • Wind Borne Sediment and Dust Control measures will be provided during the construction process to control wind borne sediment. During grading activities, water will be applied to the disturbed soils for the purpose of maintaining cohesion with clay type soils and also to meet moisture requirements for compaction of disturbed soils. Other measures of mitigation for wind erosion may include the timely installation of seed and mulch following the establishment of final grade, and the timely installation of pavement following completion of utility trenching operations and curb construction. Open areas should be kept in a roughened condition. Permanent BMP's • Permanent Seeding and Planting is the establishment of a permanent perennial vegetation such as trees, shrubs, vines, grasses/sod, or legumes on exposed areas for final permanent stabilization in order to provide stabilization of the soil by holding soil particles in place. These items should be installed as per the approved Landscape Plan. Soil Amendments shall be incorporated in all landscape areas to a depth of 6" at a rate of 3 cubic yards per 1000 square feet of area unless 4" of loose topsoil have been imported onto the site over 4" of loosened subgrade soils. Permanent Landscaping reduces storm water runoff velocity, maintains sheet flow, protects the soil surface from erosion, promotes infiltration of runoff, and improves wildlife habitat. • Preservation of Existing Vegetation should occur where no construction activity is expected to occur. Preservation of natural vegetation is generally a permanent BMP and is applicable to construction sites with pre-existing vegetation. Only land needed for building activities and vehicle traffic needs to be cleared. Erosion Control Sequencing The erosion control sequencing for construction is as follows: Prior to Construction Preserve Existing Vegetation -Before construction commencement, areas that are not disturbed by construction activity should be preserved as needed with construction fencing, silt fencing, or other means to keep vehicular traffic out of the area to be left undisturbed. 14 811010.DralnageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I Drainage & Erosion Control Report Remington Row Fort Collins, CO Silt Fence or Strow Wattles -Before construction commencement, silt fence will be placed around the boundary of the site. These erosion control devices shall be in place, functional, and maintained during and following the construction operations. During Construction Street Sweeping and Cleaning -The adjacent streets and parking lots shall be swept and cleaned on a daily basis to ensure sediment is not being tracked away from the construction site. Concrete Washout area -An area to washout concrete trucks shall be established and maintained through the completion of the concrete work. Wind Borne Sediment and Dust Control-Wind borne sediment and dust control measures should be implemented during grading activities. Permanent Seeding-Permanent seeding or landscaping shall be placed immediately in areas that are final graded and where little future disturbance is expected. In particular, permanent seeding should be included on the side slopes of the detention pond. Temporary Seeding -The majority of the landscaped areas will be permanently seeded/planted. However, if any of the areas are left disturbed without permanent stabilization 30 days after grading, temporary seeding will be required. Post Construction BM P's shall be maintained until final site stabilization. D. Final Stabilization and Long-term Stormwater Quality Final stabilization is reached when all soil disturbing activities at the site have been completed and vegetative cover has been established with a density of at least 70 percent of pre-disturbance levels or when equivalent permanent erosion reduction methods have been utilized. Upon final stabilization, temporary BMP's may be removed. 15 B11010-DralnageReport-Flnall.doc I I I I I I I I I I I I I I I I I I I E. Drainage & Erosion Control Report Remington Row Fort Collins, CO Water quality will be provided through established landscaping and pervious areas on the site. Inspection and Maintenance Procedures Appropriate measures shall be taken to inspect and maintain existing erosion control features, as described herein or per manufacturers specifications (whichever is more stringent) and install new erosion control elements as needed. The temporary BM P's will be inspected and documented at a minimum of once every 14 days and after each precipitation or snowmelt event. Records should include complete inspection reports for each inspection, maintenance and/or repair. A record-keeping system is recommended in managing inspection and maintenance reports and should include all maintenance records, spill response, weather conditions, training, correspondence, etc. Preventative maintenance also involves the regular inspection and testing of equipment, timely maintenance of the equipment, and complete records of the maintenance and inspections of the equipment. The maintenance and inspection records should be kept on site and made available upon request. Inspections must include the observation of the construction site perimeter, runoff discharge points, disturbed areas, staging areas (including concrete washout areas and fueling areas), erosion and sediment control measures identified, and any other structural BM P's that may require maintenance. The inspection must determine if there is evidence of or potential for pollutants to enter the drainage system and if they should be modified, replaced, or added to. The following list includes some recommended maintenance procedures: • Erosion and sediment control measures determined, upon inspection, to be in need of repair shall be maintained before the next anticipated storm event or as necessary to maintain continued effectiveness of erosion and sediment control measures. If it is impractical to maintain erosion and sediment control measures before the next storm event, maintenance should be accomplished as soon as practical. • Locations where vehicles enter or exit the site shall be inspected for evidence of sediment being tracked off-site by construction traffic. Such sediment shall be removed before it can be conveyed to the receiving storm drains or creeks. • Seeded areas will be checked to see that grass coverage is maintained. Areas will be watered, fertilized and reseeded as needed. 16 B11010.0ralnageReport•Flnall.doc I I I I I I I I I I I I I I I I I I I VII. F. Drainage & Erosion Control Report Remington Row Fort Collins, CO • It is the responsibility of the Operator to maintain effective pollutant discharge controls. Actual physical site conditions or contractor practices could make it necessary to install more control than are shown on the Erosion Control Plan. For example, localized concentrations of surface runoff or unusually steep areas could require additional erosion control devices. Assessing the need for, and implementing additional controls will be a continuing aspect of the SWMP until final stabilization. This plan intends to control water-borne and liquid pollutant discharges by some combination of interception, filtration, and containment. Parties implementing this plan must remain alert to the need to periodically refine and update the plan in order to accomplish the intended goals. • Sediment that has escaped the construction site must be removed at a frequency sufficient to minimize off-site impacts. Erosion Control Surety Calculations An Engineer's opinion of probable cost for the erosion/sediment control measures has not been included because the minimum $1500 will cover this small site. References 1. Geotechnical Investigation Collegio Two South Remington and East Laurel Streets, CTL Thompson, Inc., September 23, 2010. 2. lnfiltrometer Tests Remington Annex -Collegio Two 705 and 715 Remington Street, CTL Thompson, Inc., April 4, 2013. 3. Natural Resources Conservation Service Web Soil Survey at websoilsurvey.nrcs.usda.gov/app 4. Urban Storm Drainage Criteria Manual Volume 1 and 2, Urban Drainage and Flood Control District, Denver, Colorado, June 2001, Revised April 2008 5. Urban Storm Drainage Criteria Manual Volume 3 -Best Magament Practices, Urban Drainage and Flood Control District, Denver, Colorado, November 2010 17 B11010-DrainageReport-Finall.doc I I I I I I I I I I APPENDIX A I Runoff Calculations I I I I I . I I I I I I I I I I I I I: I I I I I I I I I City of Fort Collins Rainfall Intensity-Duration-Frequency Table for using the Rational Method (5 minutes -30 minutes) Figure 3-1a Duration 2-year 10-year 100-year (minutes) Intensity Intensity Intensity (in/hr) /in/hr) (in/hr) 5.00 2.85 4.87 9.95 6.00 2.67 4.56 9.31 7.00 2.52 4.31 8.80 8.00 2.40 4.10 8.38 9.00 2.30 3.93 8.03 10.00 2.21 3.78 7.72 11.00 2.13 3.63 7.42 12.00 2.05 3.50 7.16 13.00 1.98 3.39 6.92 14.00 1.92 3.29 6.71 15.00 1.87 3.19 6.52 16.00 1.81 3.08 6.30 17.00 1.75 2.99 6.10 18.00 1.70 2.90 5.92 19.00 1.65 2.82 5.75 20.00 1.61 2.74 5.60 21.00 1.56 2.67 5.46 22.00 1.53 2.61 5.32 23.00 1.49 2.55 5.20 24.00 1.46 2.49 5.09 25.00 1.43 2.44 4.98 26.00 1.40 2.39 4.87 27.00 1.37 2.34 4.78 28.00 1.34 2.29 4.69 29.00 1.32 2.25 4.60 30.00 1.30 2.21 4.52 I I I I I I I I I ··•- I I I I I I I I I City of Fort Collins Rainfall Intensity-Duration-Frequency Table for using the Rational Method {31 minutes -60 minutes) Figure 3-1b Duration 2-year 10-year 100-year {minutes) Intensity Intensity Intensity /in/hr) (in/hr\ /in/hr\ 31.00 1.27 2.16 4.42 32.00 1.24 2.12 4.33 33.00 1.22 2.08 4.24 34.00 1.19 2.04 4.16 35.00 1.17 2.00 4.08 36.00 1.15 1.96 4.01 37.00 1.13 1.93 3.93 38.00 1.11 1.89 3.87 39.00 1.09 1.86 3.80 40.00 1.07 1.83 3.74 41.00 1.05 1.80 3.68 42.00 1.04 1.77 3.62 43.00 1.02 1.74 3.56 44.00 1.01 1.72 3.51 45.00 0.99 1.69 3.46 46.00 0.98 1.67 3.41 47.00 0.96 1.64 3.36 48.00 0.95 1.62 3.31 49.00 0.94 1.60 3.27 50.00 0.92 1.58 3.23 51.00 0.91 1.56 3.18 52.00 0.90 1.54 3.14 53.00 0.89 1.52 3.10 54.00 0.88 1.50 3.07 55.00 0.87 1.48 3.03 56.00 0.86 1.47 2.99 57.00 0.85 1.45 2.96 58.00 0.84 1.43 2.92 59.00 0.83 1.42 2.89 60.00 0.82 1.40 2.86 I I I I I I I I I I I I I I I I I I I DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF 2.0 RATIONAL METHOD For urban catchments that are not complex and are generally 160 acres or less in size, it is acceptable that the design storm runoff be analyzed by the Rational Method. This method was introduced in 1889 and is still being used in most engineering offices in the United States. Even though this method has frequently come under academic criticism for its simplicity, no other practical drainage design method has evolved to such a level of general acceptance by the practicing engineer. The Rational Method properly understood and applied can produce satisfactory results for urban storm sewer and small on-site detention design. 2.1 Rational Formula The Rational Method is based on the Rational Formula: Q=CIA (R0-1) in which: 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) Actually, Q has units of inches per hour per acre (in/hr/ac); however, since this rate of in/hr/ac differs from cubic feet per second (cfs) by less than one percent, the more common units of cfs are used. The time of concentration is typically defined as the time required for water to flow from the most remote point of the area to the point being investigated. The time of concentration should be based upon a flow length and path that results in a time of concentration for only a portion of the area if that portion of the catchment produces a higher rate of runoff. The general procedure for Rational Method calculations for a single catchment is as follows: 1. Delineate the catchment boundary. Measure its area. 2. Define the flow path from the upper-most portion of the catchment to the design point. This flow path should be divided into reaches of similar flow type (e.g., overland flow, shallow swale flow, gutter flow, etc.). The length and slope of each reach should be measured. 3. Determine the time of concentration, t" for the catchment. 2007-01 R0-3 Urban Drainage and Flood Control District I I I I I I I I I I I I I I I I I I I RUNOFF DRAINAGE CRITERIA MANUAL (V. 1) 4. Find the rainfall intensity, I, for the design storm using the calculated t, and the rainfall intensity- duration-frequency curve. (See Section 4.0 of the RAINFALL chapter.) 5. Determine the runoff coefficient, c. 6. Calculate the peak flow rate from the watershed using Equation RO-1. 2.2 Assumptions The basic assumptions that are often made when the Rational Method is applied are: 1. The computed maximum rate of runoff to the design point is a function of the average rainfall rate during the time of concentration to that point. 2. The depth of rainfall used is one that occurs from the start of the storm to the time of concentration, and the design rainfall depth during that time period is converted to the average rainfall intensity for that period. 3. The maximum runoff rate occurs when the entire area is contributing flow. However, this assumption has to be modified when a more intensely developed portion of the catchment with a shorter time of concentration produces a higher rate of maximum runoff than the entire catchment with a longer time of concentration. 2.3 Limitations The Rational Method is an adequate method for approximating the peak rate and total volume of runoff from a design rainstorm in a given catchment. The greatest drawback to the Rational Method is that it normally provides only one point on the runoff hydrograph. When the areas become complex and where sub-catchments come together, the Rational Method will tend to overestimate the actual flow, which results in oversizing of drainage facilities. The Rational Method provides no direct information needed to route hydrographs through the drainage facilities. One reason the Rational Method is limited to small areas is that good design practice requires the routing of hydrographs for larger catchments to achieve an economic design. Another disadvantage of the Rational Method is that with typical design procedures one normally assumes that all of the design flow is collected at the design point and that there is no water running overland to the next design point. However, this is not the fault of the Rational Method but of the design procedure. The Rational Method must be modified, or another type of analysis must be used, when analyzing an existing system that is under-designed or when analyzing the effects of a major storm on a system designed for the minor storm. RO--4 2007-01 Urban Drainage and Flood Control District I I I I I I I I I I I I I I I I I I I DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF 2.4 Time of Concentration One of the basic assumptions underlying the Rational Method is that runoff is a function of the average rainfall rate during the time required for water to flow from the most remote part of the drainage area under consideration to the design point. However, in practice, the time of concentration can be an empirical value that results in reasonable and acceptable peak flow calculations. The time of concentration relationships recommended in this Manual are based in part on the rainfall-runoff data collected in the Denver metropolitan area and are designed to work with the runoff coefficients also recommended in this Manual. As a result, these recommendations need to be used with a great deal of caution whenever working in areas that may differ significantly from the climate or topography found in the Denver region. For urban areas, the time of concentration, 1" consists of an initial time or overland flow time, 11, plus the travel time, 1,. in the storm sewer, paved gutter, roadside drainage ditch, or drainage channel. For non- urban areas, the time of concentration consists of an overland flow time, 11, plus the time of travel in a defined form, such as a swale, channel, or drainageway. The travel portion, 1,. of the time of concentration can be estimated from the hydraulic properties of the storm sewer, gutter, swale, ditch, or drainageway. Initial time, on the other hand, will vary with surface slope, depression storage, surface cover, antecedent rainfall, and infiltration capacity of the soil, as well as distance of surface flow. The time of concentration is represented by Equation RO-2 for both urban and non-urban areas: in which: le= time of concentration (minutes) t, = initial or overland flow time (minutes) 11 = travel time in the ditch, channel, gutter, storm sewer, etc. (minutes) 2.4.1 Initial Flow Time The initial or overland flow time, 11, may be calculated using equation RO-3: 0.395(1.1-c, )✓L 1, = 8 0_33 in which: 11 = initial or overland flow time (minutes) C5 = runoff coefficient for 5-year frequency (from Table R0-5) 2007-01 Urban Drainage and Flood Control District (RO-2) (RO-3) RO-5 I I I I I I I I I I I I I I I I I I I RUNOFF DRAINAGE CRITERIA MANUAL 0{. 1) L = length of overland flow (500 fl maximum for non-urban land uses, 300 fl maximum for urban land uses) S = average basin slope (ft/ft) Equation RO-3 is adequate for distances up to 500 feet. Note that, in some urban watersheds, the over1and flow time may be very small because flows quickly channelize. 2.4.2 Overland Travel Time For catchments with overland and channelized flow, the time of concentration needs to be considered in combination with the overland travel time, 1,. which is calculated using the hydraulic properties of the swale, ditch, or channel. For preliminary work, the overland travel time, 1,. can be estimated with the help of Figure R0-1 or the following equation (Guo 1999): V=C S 05 V W in which: V = velocity (fl/sec) c. = conveyance coefficient (from Table RO-2) s., = watercourse slope (ft/ft) (RO-4) Table R0-2-Conveyance Coefficient, C, Type of Land Surface Conveyance Coefficient, c. Heavy meadow 2.5 Tillage/field 5 Short pasture and lawns 7 Near1y bare ground 10 Grassed waterway 15 Paved areas and shallow paved swales 20 The time of concentration, 1" is then the sum of the initial flow time, 11, and the travel time, 11, as per Equation RO-2. 2.4.3 First Design Point Time of Concentration in Urban Catchments Using this procedure, the time of concentration at the first design point (i.e., initial flow time, 11) in an urbanized catchment should not exceed the time of concentration calculated using Equation RO-5. L tc=-+10 180 in which: (RO-5) le= maximum time of concentration at the first design point in an urban watershed (minutes) RO-6 2007-01 Urban Drainage and Flood Control District I I I I I I I I I I I I I I I I I I I DRAINAGE CRITERIA MANUAL r,t. 1) RUNOFF L = waterway length (ft) Equation R0-5 was developed using the rainfall-runoff data collected in the Denver region and, in essence, represents regional "calibration" of the Rational Method. The first design point is the point where runoff first enters the storm sewer system. An example of definition of first design point is provided in Figure R0-2. Normally, Equation R0-5 will result in a lesser time of concentration at the first design point and will govern in an urbanized watershed. For subsequent design points, the time of concentration is calculated by accumulating the travel times in downstream drainageway reaches. 2.4.4 Minimum Time of Concentration Should the calculations result in a t, of less than 10 minutes, it is recommended that a minimum value of 10 minutes be used for non-urban watersheds. The minimum t, recommended for urbanized areas should not be less than 5 minutes and if calculations indicate a lesser value, use 5 minutes instead. 2.4.5 Common Errors in Calculating Time of Concentration A common mistake in urbanized areas is to assume travel velocities that are too slow. Another common error is to not check the runoff peak resulting from only part of the catchment. Sometimes a lower portion of the catchment or a highly impervious area produces a larger peak than that computed for the whole catchment. This error is most often encountered when the catchment is long or the upper portion contains grassy parkland and the lower portion is developed urban land. 2.5 Intensity The rainfall intensity, /, is the average rainfall rate in inches per hour for the period of maximum rainfall of a given recurrence frequency having a duration equal to the time of concentration. After the design storm's recurrence frequency has been selected, a graph should be made showing rainfall intensity versus time. The procedure for obtaining the local data and drawing such a graph is explained and illustrated in Section 4 of the RAINFALL chapter of this Manual. The intensity for a design point is taken from the graph or through the use of Equation RA-3 using the calculated t,. 2.6 Watershed Imperviousness All parts of a watershed can be considered either pervious or impervious. The pervious part is that area where water can readily infiltrate into the ground. The impervious part is the area that does not readily allow water to infiltrate into the ground, such as areas that are paved or covered with buildings and sidewalks or compacted unvegetated soils. In urban hydrology, the percentage of pervious and impervious land is important. The percentage of impervious area increases when urbanization occurs 2007-01 R0-7 Urban Drainage and Flood Control District I I I I I I I I I I I I I I I I I I I DRAINAGE CRITERIA MANUAL 0/. 1) 2007-01 Table R0-3--Recommended Percentage Imperviousness Values Land Use or Percentage Surface Characteristics Imperviousness Business: Commercial areas 95 Neighborhood areas 85 Residential: Single-family • Multi-unit (detached) 60 Multi-unit (attached) 75 Half-acre lot or larger • Apartments 80 Industrial: Light areas 80 Heavy areas 90 Parks, cemeteries 5 Playgrounds 10 Schools 50 Railroad yard areas 15 Undeveloped Areas: Historic flow analysis 2 Greenbelts, agricultural 2 Off-site flow analysis 45 (when land use not defined) Streets: Paved 100 Gravel (packed) 40 Drive and walks 90 Roofs 90 Lawns, sandy soil 0 Lawns, clayey soil 0 * See Figures RO-3 through RO-5 for percentage imperviousness. C, = K, + (i.3 li 3 -l.44i 2 + l.135i - 0.12) for CA~ 0, otherwise CA= 0 CcD = KcD + (o.858i' -0.786i 2 + 0.774i + 0.04) Urban Drainage and Flood Control District RUNOFF (RO-6) (RO-7) RO-9 I I I I I I I I I I I I I I I I I I I RUNOFF DRAINAGE CRITERIA MANUAL r,t. 1) in which: i = % imperviousness/100 expressed as a decimal (see Table RO-3) c, = Runoff coefficient for Natural Resources Conservation Service (NRCS) Type A soils C8 = Runoff coefficient for NRCS Type B soils Ceo= Runoff coefficient for NRCS Type C and D soils K, = Correction factor for Type A soils defined in Table RO-4 Keo = Correction factor for Type C and D soils defined in Table RO-4 Table R0-4-Correctlon Factors K, and Keo for Use with Equations R0-6 and R0-7 Storm Return Period NRCS Soil Type 2-Year 5-Year 10-Year 25-Year 50-Year 100-Year CandD 0 -0.10i + 0.11 -0.18i + 0.21 -0.28i + 0.33 -0.33i + 0.40 -0.39; + 0.46 A 0 -0.08i + 0.09 -0.14i + 0.17 -0.19i + 0.24 -0.22i + 0.28 -0.25i + 0.32 The values for various catchment imperviousnesses and storm return periods are presented graphically in Figures RO-6 through RO-8, and are tabulated in Table RO-5. These coefficients were developed for the Denver region to work in conjunction with the time of concentration recommendations in Section 2.4. Use of these coefficients and this procedure outside of the semi-arid climate found in the Denver region may not be valid. The UD-Ralional spreadsheet performs all the needed calculations to find the runoff coefficient given the soil type and imperviousness and the reader may want to take advantage of this macro-enabled Excel workbook that is available for download from the District's web site www.udfcd.org under "Download" -"Technical Downloads." See Examples 7.1 and 7.2 that illustrate the Rational method. The use of the Rational method in storm sewer design is illustrated in Example 6.13 of the STREETS/INLETS/STORM SEWERS chapter. RO-10 2007-01 Urban Drainage and Flood Control District I I I I I I I I I I I I I I I I I I I DRAINAGE CRITERIA MANUAL 0/. 1) Table R0-5-Runoff Coefficients, C Percentage Imperviousness Type C and D NRCS Hydrologic Soil Groups 2-vr 5-vr 10-vr 25-vr 50-vr 0% 0.04 0.15 0.25 0.37 0.44 5% 0.08 0.18 0.28 0.39 0.46 10% 0.11 0.21 0.30 0.41 0.47 15% 0.14 0.24 0.32 0.43 0.49 20% 0.17 0.26 0.34 0.44 0.50 25% 0.20 0.28 0.36 0.46 0.51 30% 0.22 0.30 0.38 0.47 0.52 35% 0.25 0.33 0.40 0.48 0.53 40% 0.28 0.35 0.42 0.50 0.54 45% 0.31 0.37 0.44 0.51 0.55 50% 0.34 0.40 0.46 0.53 0.57 55% 0.37 0.43 0.48 0.55 0.58 60% 0.41 0.46 0.51 0.57 0.60 65% 0.45 0.49 0.54 0.59 0.62 70% 0.49 0.53 0.57 0.62 0.65 75% 0.54 0.58 0.62 0.66 0.68 80% 0.60 0.63 0.66 0.70 0.72 85% 0.66 0.68 0.71 0.75 0.77 90% 0.73 0.75 0.77 0.80 0.82 95% 0.80 0.82 0.84 0.87 0.88 100% 0.89 0.90 0.92 0.94 0.95 TYPE B NRCS HYDROLOGIC SOILS GROUP 0% 0.02 0.08 0.15 0.25 0.30 5% 0.04 0.10 0.19 0.28 0.33 10% 0.06 0.14 0.22 0.31 0.36 15% 0.08 0.17 0.25 0.33 0.38 20% 0.12 0.20 0.27 0.35 0.40 25% 0.15 0.22 0.30 0.37 0.41 30% 0.18 0.25 0.32 0.39 0.43 35% 0.20 0.27 0.34 0.41 0.44 40% 0.23 0.30 0.36 0.42 0.46 45% 0.26 0.32 0.38 0.44 0.48 50% 0.29 0.35 0.40 0.46 0.49 55% 0.33 0.38 0.43 0.48 0.51 60% 0.37 0.41 0.46 0.51 0.54 65% 0.41 0.45 0.49 0.54 0.57 70% 0.45 0.49 0.53 0.58 0.60 75% 0.51 0.54 0.58 0.62 0.64 80% 0.57 0.59 0.63 0.66 0.68 85% 0.63 0.66 0.69 0.72 0.73 90% 0.71 0.73 0.75 0.78 0.80 95% 0.79 0.81 0.83 0.85 0.87 100% 0.89 0.90 0.92 0.94 0.95 2007-01 Urban Drainage and Flood Control District RUNOFF 100-vr 0.50 0.52 0.53 0.54 0.55 0.56 0.57 0.57 0.58 0.59 0.60 0.62 0.63 0.65 0.68 0.71 0.74 0.79 0.83 0.89 0.96 0.35 0.38 0.40 0.42 0.44 0.46 0.47 0.48 0.50 0.51 0.52 0.54 0.56 0.59 0.62 0.66 0.70 0.75 0.81 0.88 0.96 RO-11 I I I I I I I I I I I I I I I I I I I RUNOFF Percentage lmoerviousness 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100% RO-12 DRAINAGE CRITERIA MANUAL f>/. 1) TABLE R0-5 (Continued)-Runoff Coefficients, C 2-vr 0.00 0.00 0.00 0.02 0.06 0.09 0.13 0.16 0.19 0.22 0.25 0.29 0.33 0.37 0.42 0.47 0.54 0.61 0.69 0.78 0.89 Type A NRCS Hydrologic Soils Group 5-vr 10-vr 25-vr 0.00 0.05 0.12 0.02 0.10 0.16 0.06 0.14 0.20 0.10 0.17 0.23 0.13 0.20 0.26 0.16 0.23 0.29 0.19 0.25 0.31 0.22 0.28 0.33 0.25 0.30 0.35 0.27 0.33 0.37 0.30 0.35 0.40 0.33 0.38 0.42 0.37 0.41 0.45 0.41 0.45 0.49 0.45 0.49 0.53 0.50 0.54 0.57 0.56 0.60 0.63 0.63 0.66 0.69 0.71 0.73 0.76 0.80 0.82 0.84 0.90 0.92 0.94 50-yr 100-vr 0.16 0.20 0.20 0.24 0.24 0.28 0.27 0.30 0.30 0.33 0.32 0.35 0.34 0.37 0.36 0.39 0.38 0.41 0.40 0.43 0.42 0.45 0.45 0.47 0.47 0.50 0.51 0.53 0.54 0.56 0.59 0.61 0.64 0.66 0.70 0.72 0.77 0.79 0.85 0.86 0.95 0.96 2007-01 Urban Drainage and Flood Control District I I I I I I I I I I I I I I I I I I I DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF I I I I I I I I .s "---'-1----'-~~u..&....i""--'--'--...i.-.... i-l,-'-...,""--~ .1 .2 .3 .5 1 2 3 s 10 20 VELOCITY IN FEET PER SECOND Figure R0-1-Estimate of Average Overland Flow Velocity for Use With the Rational Formula 2007-01 RO-13 Urban Drainage and Flood Control District I I I I I I I I I I I I I I I I I I I Bio retention T-3 containing shredded paper is not an uncommon request, although not typically provided in the proportions recommended in this BMP Fact Sheet. Compost suppliers have access to shredded paper through document destruction companies and can provide a mixture of Class I compost and shredded paper. The supplier should provide the rain garden compost mixture premixed with coarse sand. On- site mixing is not recommended. Rain Garden Compost Mixture /by volume) • 50% Class 1 ST A registered compost (approximate bulk density 1000 lbs/CY) • 50% loosely packed shredded paper (approximate bulk density 50 to 100 lbs/CY) When using diamond cut shredded paper or tightly packed paper, use the bulk densities provided to mix by weight. Rain Garden Growing Medium The supplier should premix the rain garden compost mixture (above) with coarse sand, in the following proportions, prior to delivery to the site: • 15% rain garden compost mixture described above (by volume) • 85% coarse sand (either Class C Filter Material per Table B-2 or sand meeting ASTM C-33) (by volume) Table B-1 provides detailed information on Class 1 compost. Be aware, regular testing is not required to allow a compost supplier to refer to a product as a specific ST A class. However, regular testing is required and performed through the United States Compost Council (USCC) Seal of Testing Assurance (STA) Program to be a STA registered compost. To ensure Class I characteristics, look for a Class I STA registered compost. Other Rain Garden Growing Medium Amendments The growing medium described above is designed for filtration ability, clogging characteristics, and vegetative health. It is important to preserve the function provided by the rain garden growing medium when considering additional materials for incorporation into the growing medium or into the standard section shown in Figure B-1. When desired, amendments may be included to improve water quality or to benefit vegetative health as long as they do not add nutrients, pollutants, or modify the infiltration rate. For example, a number of products, including steel wool, capture and retain dissolved phosphorus (Erickson 2009). When phosphorus is a target pollutant, proprietary materials with similar characteristics may be considered. Do not include amendments such as top soil, sandy loam, and additional compost. Full Infiltration Sections A full infiltration section retains the WQCV onsite. For this section, it is not necessary to use the prescribed rain garden growing medium. Amend the soils to provide adequate nutrients to establish vegetation. Typically, 3 to 5 cubic yards of soil amendment (compost) per 1,000 square feet, tilled 6 inches into the soil, is required for vegetation to thrive. Additionally, inexpensive soil tests can be conducted to determine required soil amendments. (Some local governments may also require proof of soil amendment in landscaped areas for water conservation reasons.) November 2010 Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual Volume 3 B-5 I I I I I I I I I I I I I I I I I I I T-3 Bio retention B-6 Table B-1. Class 1 Compost Characteristic Criteria Minimum Stability Indicator (Respirometry) Stable to Very Stable Maturity Indicator Expressed as <4 Ammonia N / Nitrate N Ratio Maturity Indicator Expressed as < 12 Carbon to Nitrogen Ratio Maturity Indicator Expressed as 8o+ I 8o+ Percentage of Germination/Vigor pH -Acceptable Range 6.0-8.4 Soluble Salts -Acceptable Range 0 - 5 mmhos/cm (! :5 by weight) Seal of Testing Assurance (STA)/Test Testing and Test Report Submittal Requirement Methods for the Examination of Composting and Compost (TMECC) Equal or better than US EPA Class A Chemical Contaminants Standard, 40 CFR 503.13, Tables I & 3 levels Pathogens Meet or exceed US EPA Class A standard, 40 CFR 503.32(a) levels Urban Drainage and Flood Control District· Urban Storm Drainage Criteria Manual Volume 3 November 2010 I I I I I I I I I I I I I I I I I I I T-3 Bio retention ensure that the pipe was not crushed or disconnected during construction. Calculate the diameter of the orifice for a 12-hour drain time using Equation B-3 (Use a minimum orifice size of3/8 inch to avoid clogging.): V D12 hour drain time = 1414 y 0·41 Equation B-3 Where: D y V = orifice diameter (in) = distance from the lowest elevation of the storage volume (i.e., surface of the filter) to the center of the orifice (ft) = volume (YYQCV or the portion of the WQCV in the rain garden) to drain in 12 hours ( fl') In previous versions of this manual, UDFCD recommended that the underdrain be placed in an aggregate layer and that a geotextile (separator fabric) be placed between this aggregate and the growing medium. This version of the manual replaces that section with materials that, when used together, eliminate the need for a separator fabric. The underdrain system should be placed within an 6-inch-thick section of COOT Class C filter material meeting the gradation in Table B-2. Use slotted pipe that meets the slot dimensions provided in Table B-3. B-8 Table B-2. Gradation Specifications for CDOT Class C Filter Material (Source: COOT Table 703-7) Sieve Size Mass Percent Passing S uare Mesh Sieves JOO 60-100 10-30 0-10 0-3 Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual Volume 3 November 2010 I I I I I I I I I I I I I I I I I I I Bio retention Table B-3. Dimensions for Slotted Pipe Pipe Diameter Slot Maximum Slot Slot Open Area' Length' Width Centers' (per foot) 4" 1-1/16" 0.032" 0.413" 1.90 in2 6" 1-3/8" 0.032" 0.516" 1.98 in2 1 Some variation in these values is acceptable and is expected from various pipe manufacturers. Be aware that both increased slot length and decreased slot centers will be beneficial to hydraulics but detrimental to the structure of the pipe. T-3 5. Impermeable Geomembrane Liner and Geotextile Separator Fabric: For no-infiltration sections, install a 30 mil (minimum) PVC geomembrane liner, per Table B-5, on the bottom and sides of the basin, extending up at least to the top of the underdrain layer. Provide at least 9 inches (12 inches if possible) of cover over the membrane where it is attached to the wall to protect the membrane from UV deterioration. The geomembrane should be field-seamed using a dual track welder, which allows for non-destructive testing of almost all field seams. A small amount of single track and/or adhesive seaming should be allowed in limited areas to seam around pipe perforations, to patch seams removed for destructive seam testing, and for limited repairs. The liner should be installed with slack to prevent tearing due to backfill, compaction, and settling. Place COOT Class B geotextile separator fabric above the geomembrane to protect it from being punctured during the placement of the filter material above the liner. If the subgrade contains angular rocks or other material that could puncture the geomembrane, smooth-roll the surface to create a suitable surface. If smooth-rolling the surface does not provide a suitable surface, also place the separator fabric between the geomembrane and the underlying subgrade. This should only be done when necessary because fabric placed under the geomembrane can increase seepage losses through pinholes or other geomembrane defects. Connect the geomembrane to perimeter concrete walls around the basin perimeter, creating a watertight seal between the geomembrane and the walls using a continuous batten bar and anchor connection (see Figure B-3). Where the need for the impermeable membrane is not as critical, the membrane can be attached with a nitrile-based vinyl adhesive. Use watertight PVC boots for underdrain pipe penetrations through the liner (see Figure B-2). November 2010 Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual Volume 3 B-9 I I I I I I I I I I I I I I I I I I I T-3 Bio retention Table B-4. Physical Requirements for Separator Fabric1 Class B Property Elongation <50%2 Elongation >50%2 Grab Strength, N (lbs) 800 (180) 510 (115) Puncture Resistance, N (lbs) 310(70) 180 (40) Trapezoidal Tear Strength, N (lbs) 3 IO (70) 180 (40) Apparent Opening Size, mm AOS < 0.3mm (US Sieve Size No. 50) n rs Sieve Size) Permittivity, sec·1 0.02 default value, must also be !!feater than that of soil Permeability, cm/sec k fabric > k soil for all classes Ultraviolet Degradation at 500 50% strength retained for all classes hours ' Strength values are m the weaker pnnc1ple direct10n 2 As measured in accordance with ASTM D 4632 Table B-5. Physical Requirements for Geomembrane Thickness Test Method ASTMD4632 ASTMD4833 ASTMD4533 ASTMD4751 ASTMD4491 ASTM D4491 ASTMD4355 Property 0.76mm Test Method (30 mil) Thickness, % Tolerance ±5 ASTMD 1593 Tensile Strength, kN/m (lbs/in) width 12.25 (70) ASTM D 882, Method B Modulus at I 00% Elongation, kN/m (lbs/in) 5.25 (30) ASTM D 882, Method B Ultimate Elongation, % 350 ASTM D 882, Method A Tear Resistance, N (lbs) 38 (8.5) ASTMD 1004 Low Temperature hnpact, °C (°F) -29 (-20) ASTMD 1790 Volatile loss, % max. 0.7 ASTM D 1203, Method A Pinholes, No. Per 8 m2 (No. per IO sq. yds.) max. I NIA Bonded Seam Strength, % of tensile strength 80 NIA B-10 Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual Volume 3 November 2010 I I I I I I I I I I I I I I I I I I I T-3 Bio retention When using an impermeable liner, select plants with diffuse (or fibrous) root systems, not taproots. Taproots can damage the liner and/or underdrain pipe. Avoid trees and large shrubs that may interfere with restorative maintenance. Trees and shrubs can be planted outside of the area of growing medium. Use a cutoff wall to ensure that roots do not grow into the underdrain or place trees and shrubs a conservative distance from the underdrain. 9. Irrigation: Provide spray irrigation at or above the WQCV elevation or place temporary irrigation on top of the rain garden surface. Do not place sprinkler heads on the flat surface. Remove temporary irrigation when vegetation is established. If left in place this will become buried over time and will be damaged during maintenance operations. Irrigation schedules should be adjusted during the growing season to provide the minimum water necessary to maintain plant health and to maintain the available pore space for infiltration. B-12 Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual Volume 3 November 2010 I I I I I I I I I I I I I I I I I I I Bioretention Table B-6. Native Seed Mix for Rain Gardens 2 Common Name Scientific Name Sand bluestem Andropogon hallii Sideoats grama Bouteloua curtipendula Prairie sandreed Calamovilfa longifolia Indian ricegrass Oryzopsis hymenoides Switchgrass Panicum virgatum Western wheatgrass Pascopyrum smithii Little bluestem Schizachyrium scoparium Alkali sacaton Sporobolus airoides Sand dropseed Sporobolus cryptandrus Pasture sage' Artemisia frigida Blue aster' Aster laevis Blanket flower' Gaillardia aristata Prairie coneflowe1 Ratibida columnifera Purple prairieclover' Dalea (Petalostemum) purpurea Sub-Totals: Total lbs per acre: I WIidflower seed (opttonal) for a more diverse and natural look. 2 PLS = Pure Live Seed. Variety Garden Butte Goshen Paloma Blackwell Ariba Patura November 2010 Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual Volume 3 T-3 PLS' Ounces lbs per per Acre Acre 3.5 3 3 3 4 3 3 3 3 2 4 8 4 4 27.5 22 28.9 B-13 I I I I I I I I I I I I I I I I I I I T-3 Bio retention Aesthetic Design In addition to providing effective stonnwater quality treatment, rain gardens can be attractively incorporated into a site within one or several landscape areas. Aesthetically designed rain gardens will typically either reflect the character of their surroundings or become distinct features within their surroundings. Guidelines for each approach are provided below. Reflecting the Surrounding • Determine design characteristics of the surrounding. This becomes the context for the drainage improvement. Use these characteristics in the structure. • Create a shape or shapes that "fix" the forms surrounding the improvement. Make the improvement part of the existing surrounding. • The use of material is essential in making any new improvement an integral part of the whole. Select materials that are as similar as possible to the surrounding architectural/engineering materials. Select materials from the same source if possible. Apply materials in the same quantity, manner, and method as original material. • Size is an important feature in seamlessly blending the addition into its context. If possible, the overall size of the improvement should look very similar to the overall sizes of other similar objects in the improvement area. Reflective Design A reflective design borrows the characteristics, shapes, colors, materials, sizes and textures of the built surroundings. The result is a design that fits seamlessly and unobtrusively in its environment. • The use of the word texture in terms of the structure applies predominantly to the selection of plant material. The materials used should as closely as possible, blend with the size and texture of other plant material used in the surrounding. The plants may or may not be the same, but should create a similar feel, either individually or as a mass. Creating a Distinct Feature Designing the rain garden as a distinct feature is limited only by budget, functionality, and client preference. There is far more latitude in designing a rain garden that serves as a distinct feature. If this is the intent, the main consideration beyond functionality is that the improvement create an attractive addition to its surroundings. The use of form, materials, color, and so forth focuses on the improvement itself and does not necessarily reflect the surroundings, depending on the choice of the client or designer. B-14 Urban Drainage and Flood Control District Urban Storm Drainage Criteria Manual Volnme 3 November 2010 I I I I I I I I I I I I I I I I I I I Map Unit Description: Fort Collins loam, 1 to 3 percent slopes-Larimer County Area, Colorado Larimer County Area, Colorado 35-Fort Collins loam, 1 to 3 percent slopes Map Unit Setting Elevation: 4,800 to 5,500 feet Mean annual precipitation: 13 to 15 inches Mean annual air temperature: 48 to 50 degrees F Frost-free period: 135 to 150 days Map Unit Composition Natural Resources Conservation Service Fort co/fins and similar soils: 85 percent Minor components: 15 percent Description of Fort Collins Setting Landfonn: Fans, terraces Landfonn position (three-dimensional): Base slope, tread Down-slope shape: Linear Across-slope shape: Linear Parent material: Alluvium Properties and qualities Slope: 1 to 3 percent Depth to restrictive feature: More than 80 inches Drainage class: Well drained Capacity of the most limiting layer to transmit water (Ksat): Moderately high to high (0.60 to 2.00 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum content: 15 percent Maximum salinity: Nonsaline (0.0 to 2.0 mmhos/cm) Available water capacity: Very high (about 25.5 inches) Interpretive groups Land capability classification (irrigated): 2e Land capability (nonirrigated): 3c Ecological site: Loamy Plains (R067XY002CO) Typical profile O to 7 inches: Loam 7 to 22 inches: Loam, clay loam 22 to 60 inches: Loam, silt loam, fine sandy loam Minor Components Larim Percent of map unit: 8 percent Web Soil Survey National Cooperative Soil Survey 11/23/2011 Page 1 of 2 I Map Unit Description: Fort Collins loam, 1 to 3 percent slopes-Larimer County I Area, Colorado I Ascalon Percent of map unit: 7 percent I Data Source Information Soil Survey Area: Larimer County Area, Colorado I Survey Area Data: Version 7, May 1, 2009 I I I I I I I I I I I I I usg Natural Resources Web Soil Survey 11/23/2011 Conservation Service National Cooperative Soil Survey Page 2 of2 I I I I I I I I I I I I I I I I I I I I APPENDIX E Plans and Maps