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HomeMy WebLinkAbout1.00 General Application Materials_Part24SC-10 Chemical Treatment (CT) CT-2 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Maintenance and Removal Chemical feed systems for sedimentation ponds or tanks should be maintained in accordance with manufacturer's recommendations and removed when the systems are no longer being used. Accumulated sediment should be dried and disposed of either at a landfill or in accordance with applicable regulations. Barriers and devices containing chemicals should be removed and replaced when tears or other damage to the devices are observed. These barriers should be removed and properly disposed of when the site has been stabilized. Sediment Retention Device (SRD)SC-11 March 2023 SC-11 Photographs SRD-1 and SRD-2. WattleFence installed in a channelized area with the goal of removing sediment and channel dissipation 1); and, 2) the same device operating under heavy rain events. Description A sediment retention device (trademarked product WattleFence) is constructed using a fleece of coconut fiber wrapped in a biodegradable jute woven fabric. The installed device has a vertical height of 9" with a 6" splash apron and is attached to wooden stakes. Wattlefence provides the combined features of wattles and silt fence including sediment reduction and turbidity reduction. Appropriate Uses Sediment retention devices can be used in the following applications: As perimeter control for stockpiles and the site. As check dams in small drainage ditches. For channel dissipation in areas of concentrated flow On disturbed slopes to shorten flow lengths (as an erosion control). As inlet and outlet protection. As part of multi-layered perimeter controls. Sediment retention devices work well in combination with other layers of erosion and sediment controls. Design and Installation When installed on slopes, sediment retention devices should be installed along the contour (i.e., perpendicular to the flow) to avoid concentrating flows into channels. When installed for other uses, such as perimeter control, the device should be installed in a way that will not produce concentrated flows. For example, a "J-hook" installation may be appropriate to force runoff to pond and evaporate or infiltrate the fencing in multiple areas rather than concentrate in one and cause erosive conditions parallel to the control measure. An example of this kind of installation is shown in section SC-2 (Sediment Control Logs) of this manual. WattleFence is designed to be installed without trenching, an advantage over sediment control logs. The device is trenched at intervals depending on the desired application.Yes N Western Green WattleFence Product Literature SC-11 Sediment Retention Device (SRD) SC-11 March 2023 Design details and notes for sediment retention devices are presented below. The device must be properly trenched and staked into the ground to prevent undercutting, bypassing and displacement. Improper installation can lead to poor performance. Be sure that sediment retention devices are properly trenched, anchored and tightly jointed. Maintenance and Removal Sediment retention devices are designed to allow runoff to flow through the control measure, as long as they are properly maintained and kept free of sediment build up. Remove accumulated sediment before the depth is one-half the height of the device and repair damage to the device, typically by replacing the damaged section. Sediment retention devices are designed to biodegrade. Once the upstream area is stabilized, remove and properly dispose of the device. Areas disturbed beneath the logs may need to be seeded and mulched. Sediment retention devices are biodegradable and may occasionally be left in place during final stabilization. However, removal is typically recommended after final reclamation of the site is achieved. Western Green WattleFence Product Literature Sediment Retention Device (SRD)SC-11 March 2023 SC-11 Western Green WattleFence Product Literature SC-11 Sediment Retention Device (SRD) SC-11 March 2023 Western Green WattleFence Product Literature Construction Phasing/Sequencing (CP)SM-1 November 2010 Urban Drainage and Flood Control District CP-1 Urban Storm Drainage Criteria Manual Volume 3 Photograph CP-1. Construction phasing to avoid disturbing the entire area at one time. Photo courtesy of WWE. Description Effective construction site management to minimize erosion and sediment transport includes attention to construction phasing, scheduling, and sequencing of land disturbing activities. On most construction projects, erosion and sediment controls will need to be adjusted as the project progresses and should be documented in the SWMP. Construction phasing refers to disturbing only part of a site at a time to limit the potential for erosion from dormant parts of a site. Grading activities and construction are completed and soils are effectively stabilized on one part of a site before grading and construction begins on another portion of the site. Construction sequencing or scheduling refers to a specified work schedule that coordinates the timing of land disturbing activities and the installation of erosion and sediment control practices. Appropriate Uses All construction projects can benefit from upfront planning to phase and sequence construction activities to minimize the extent and duration of disturbance. Larger projects and linear construction projects may benefit most from construction sequencing or phasing, but even small projects can benefit from construction sequencing that minimizes the duration of disturbance. Typically, erosion and sediment controls needed at a site will change as a site progresses through the major phases of construction. Erosion and sediment control practices corresponding to each phase of construction must be documented in the SWMP. Design and Installation Control measures appropriate to the major phases of development should be identified on construction drawings. In some cases, it will be necessary to provide several drawings showing construction-phase control measures placed according to stages of development (e.g., clearing and grading, utility installation, active construction, final stabilization). Some municipalities in the Denver area set maximum sizes for disturbed area associated with phases of a construction project. Additionally, requirements for phased construction drawings vary among local governments within the UDFCD boundary. Some local governments require separate erosion and sediment control drawings for initial control measures, interim conditions (in active construction), and final stabilization. Erosion Control Moderate Sediment Control Moderate Site/Material Management Yes SM-1 Construction Phasing/Sequencing (CP) CP-2 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Typical construction phasing control measures include: Limit the amount of disturbed area at any given time on a site to the extent practical. For example, a 100-acre subdivision might be constructed in five phases of 20 acres each. If there is carryover of stockpiled material from one phase to the next, position carryover material in a location easily accessible for the pending phase that will not require disturbance of stabilized areas to access the stockpile. Particularly with regard to efforts to balance cut and fill at a site, careful planning for location of stockpiles is important. Typical construction sequencing control measures include: Sequence construction activities to minimize duration of soil disturbance and exposure. For example, when multiple utilities will occupy the same trench, schedule installation so that the trench does not have to be closed and opened multiple times. Schedule site stabilization activities (e.g., landscaping, seeding and mulching, installation of erosion control blankets) as soon as feasible following grading. Install initial erosion and sediment control practices before construction begins. Promptly install additional control measures for inlet protection, stabilization, etc., as construction activities are completed. Table CP-1 provides typical sequencing of construction activities and associated control measures. Maintenance and Removal When the construction schedule is altered, erosion and sediment control measures in the SWMP and construction drawings should be appropriately adjusted to reflect actual "on the ground" conditions at the construction site. Be aware that changes in construction schedules can have significant implications for site stabilization, particularly with regard to establishment of vegetative cover. Construction Phasing/Sequencing (CP)SM-1 November 2010 Urban Drainage and Flood Control District CP-3 Urban Storm Drainage Criteria Manual Volume 3 Table CP-1. Typical Phased Control Measure Installation for Construction Projects Project Phase Control Measures Pre- disturbance, Site Access Install sediment controls downgradient of access point (on paved streets this may consist of inlet protection). Establish vehicle tracking control at entrances to paved streets. Fence as needed. Use construction fencing to define the boundaries of the project and limit access to areas of the site that are not to be disturbed. Note: it may be necessary to protect inlets in the general vicinity of the site, even if not downgradient, if there is a possibility that sediment tracked from the site could contribute to the inlets. Site Clearing and Grubbing Install perimeter controls as needed on downgradient perimeter of site (silt fence, wattles, etc). Limit disturbance to those areas planned for disturbance and protect undisturbed areas within the site (construction fence, flagging, etc). Preserve vegetative buffer at site perimeter. Create stabilized staging area. Locate portable toilets on flat surfaces away from drainage paths. Stake in areas susceptible to high winds. Construct concrete washout area and provide signage. Establish waste disposal areas. Install sediment basins. Create dirt perimeter berms and/or brush barriers during grubbing and clearing. Separate and stockpile topsoil, leave roughened and/or cover. Protect stockpiles with perimeter control measures. Stockpiles should be located away from drainage paths and should be accessed from the upgradient side so that perimeter controls can remain in place on the downgradient side. Use erosion control blankets, temporary seeding, and/or mulch for stockpiles that will be inactive for an extended period. Leave disturbed area of site in a roughened condition to limit erosion. Consider temporary revegetation for areas of the site that have been disturbed but that will be inactive for an extended period. Water to minimize dust but not to the point that watering creates runoff. SM-1 Construction Phasing/Sequencing (CP) CP-4 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Project Phase Control Measures Utility And Infrastructure Installation In Addition to the Above Control Measures: Close trench as soon as possible (generally at the end of the day). Use rough-cut street control or apply road base for streets that will not be promptly paved. Provide inlet protection as streets are paved and inlets are constructed. Protect and repair control measures, as necessary. Perform street sweeping as needed. Building Construction In Addition to the Above Control Measures: Implement materials management and good housekeeping practices for home building activities. Use perimeter controls for temporary stockpiles from foundation excavations. For lots adjacent to streets, lot-line perimeter controls may be necessary at the back of curb. Final Grading In Addition to the Above Control Measures: Remove excess or waste materials. Remove stored materials. Final Stabilization In Addition to the Above Control Measures: Seed and mulch/tackify. Seed and install blankets on steep slopes. Remove all temporary control measures when site has reached final stabilization. Protection of Existing Vegetation (PV) SM-2 November 2010 Urban Drainage and Flood Control District PV-1 Urban Storm Drainage Criteria Manual Volume 3 Photograph PV-1. Protection of existing vegetation and a sensitive area. Photo courtesy of CDOT. Description Protection of existing vegetation on a construction site can be accomplished through installation of a construction fence around the area requiring protection. In cases where upgradient areas are disturbed, it may also be necessary to install perimeter controls to minimize sediment loading to sensitive areas such as wetlands. Existing vegetation may be designated for protection to maintain a stable surface cover as part of construction phasing, or vegetation may be protected in areas designated to remain in natural condition under post-development conditions (e.g., wetlands, mature trees, riparian areas, open space). Appropriate Uses Existing vegetation should be preserved for the maximum practical duration on a construction site through the use of effective construction phasing. Preserving vegetation helps to minimize erosion and can reduce revegetation costs following construction. Protection of wetland areas is required under the Clean Water Act, unless a permit has been obtained from the U.S. Army Corps of Engineers (USACE) allowing impacts in limited areas. If trees are to be protected as part of post-development landscaping, care must be taken to avoid several types of damage, some of which may not be apparent at the time of injury. Potential sources of injury include soil compaction during grading or due to construction traffic, direct equipment-related injury such as bark removal, branch breakage, surface grading and trenching, and soil cut and fill. In order to minimize injuries that may lead to immediate or later death of the tree, tree protection zones should be developed during site design, implemented at the beginning of a construction project, as well as continued during active construction. Design and Installation General Once an area has been designated as a preservation area, there should be no construction activity allowed within a set distance of the area. Clearly mark the area with construction fencing. Do not allow stockpiles, equipment, trailers or parking within the protected area. Guidelines to protect various types of existing vegetation follow. Protection of Existing Vegetation Functions Erosion Control Yes Sediment Control Moderate Site/Material Management Yes SM-2 Protection of Existing Vegetation (PV) PV-2 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Surface Cover During Phased Construction Install construction fencing or other perimeter controls around areas to be protected from clearing and grading as part of construction phasing. Maintaining surface cover on steep slopes for the maximum practical duration during construction is recommended. Open Space Preservation Where natural open space areas will be preserved as part of a development, it is important to install construction fencing around these areas to protect them from compaction. This is particularly important when areas with soils with high infiltration rates are preserved as part of LID designs. Preserved open space areas should not be used for staging and equipment storage. Wetlands and Riparian Areas Install a construction fence around the perimeter of the wetland or riparian (streamside vegetation) area to prevent access by equipment. In areas downgradient of disturbed areas, install a perimeter control such as silt fence, sediment control logs, or similar measure to minimize sediment loading to the wetland. Tree Protection 1 Before beginning construction operations, establish a tree protection zone around trees to be preserved by installing construction fences. Allow enough space from the trunk to protect the root zone from soil compaction and mechanical damage, and the branches from mechanical damage (see Table PV-1). If low branches will be kept, place the fence outside of the drip line. Where this is not possible, place fencing as far away from the trunk as possible. In order to maintain a healthy tree, be aware that about 60 percent of the tree's root zone extends beyond the drip line. Table PV-1 Guidelines for Determining the Tree Protection Zone (Source: Matheny and Clark, 1998; as cited in GreenCO and WWE 2008) Distance from Trunk (ft) per inch of DBH Species Tolerance to Damage Young Mature Over mature Good 0.5' 0.75' 1.0' Moderate 0.75' 1.0' 1.25' Poor 1.0' 1.25' 1.5' Notes: DBH = diameter at breast height (4.5 ft above grade); Young = <20% of life expectancy; Mature = 20%-80% of life expectancy; Over mature =>80% of life expectancy Most tree roots grow within the top 12 to 18 inches of soil. Grade changes within the tree protection zone should be avoided where possible because seemingly minor grade changes can either smother 1 Tree Protection guidelines adapted from GreenCO and WWE (2008). Green Industry Best Management Practices (BMPs) for the Conservation and Protection of Water Resources in Colorado: Moving Toward Sustainability, Third Release. See www.greenco.org for more detailed guidance on tree preservation. Protection of Existing Vegetation (PV) SM-2 November 2010 Urban Drainage and Flood Control District PV-3 Urban Storm Drainage Criteria Manual Volume 3 roots (in fill situations) or damage roots (in cut situations). Consider small walls where needed to avoid grade changes in the tree protection zone. Place and maintain a layer of mulch 4 to 6-inch thick from the tree trunk to the fencing, keeping a 6-inch space between the mulch and the trunk. Mulch helps to preserve moisture and decrease soil compaction if construction traffic is unavoidable. When planting operations are completed, the mulch may be reused throughout planting areas. Limit access, if needed at all, and appoint one route as the main entrance and exit to the tree protection zone. Within the tree protection zone, do not allow any equipment to be stored, chemicals to be dumped, or construction activities to take place except fine grading, irrigation system installation, and planting operations. These activities should be conducted in consultation with a landscaping professional, following Green Industry BMPs. Be aware that soil compaction can cause extreme damage to tree health that may appear gradually over a period of years. Soil compaction is easier to prevent than repair. Maintenance and Removal Repair or replace damaged or displaced fencing or other protective barriers around the vegetated area. If damage occurs to a tree, consult an arborist for guidance on how to care for the tree. If a tree in a designated preservation area is damaged beyond repair, remove and replace with a 2-inch diameter tree of the same or similar species. Construction equipment must not enter a wetland area, except as permitted by the U.S. Army Corps of Engineers (USACE). Inadvertent placement of fill in a wetland is a 404 permit violation and will require notification of the USACE. If damage to vegetation occurs in a protected area, reseed the area with the same or similar species, following the recommendations in the USDCM Revegetation chapter. Construction Fence (CF)SM-3 November 2010 Urban Drainage and Flood Control District CF-1 Urban Storm Drainage Criteria Manual Volume 3 Photograph CF-1. A construction fence helps delineate areas where existing vegetation is being protected. Photo courtesy of Douglas County. Description A construction fence restricts site access to designated entrances and exits, delineates construction site boundaries, and keeps construction out of sensitive areas such as natural areas to be preserved as open space, wetlands and riparian areas. Appropriate Uses A construction fence can be used to delineate the site perimeter and locations within the site where access is restricted to protect natural resources such as wetlands, waterbodies, trees, and other natural areas of the site that should not be disturbed. If natural resource protection is an objective, then the construction fencing should be used in combination with other perimeter control measures such as silt fence, sediment control logs or similar measures. Design and Installation Construction fencing may be chain link or plastic mesh and should be installed following manufacturer’s recommendations. See Detail CF-1 for typical installations. Do not place construction fencing in areas within work limits of machinery. Maintenance and Removal Inspect fences for damage; repair or replace as necessary. Fencing should be tight and any areas with slumping or fallen posts should be reinstalled. Fencing should be removed once construction is complete. Construction Fence Functions Erosion Control No Sediment Control No Site/Material Management Yes SM-3 Construction Fence (CF) CF-2 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Construction Fence (CF)SM-3 November 2010 Urban Drainage and Flood Control District CF-3 Urban Storm Drainage Criteria Manual Volume 3 Vehicle Tracking Control (VTC) SM-4 November 2010 Urban Drainage and Flood Control District VTC-1 Urban Storm Drainage Criteria Manual Volume 3 Photograph VTC-1. A vehicle tracking control pad constructed with properly sized rock reduces off-site sediment tracking. Description Vehicle tracking controls provide stabilized construction site access where vehicles exit the site onto paved public roads. An effective vehicle tracking control helps remove sediment (mud or dirt) from vehicles, reducing tracking onto the paved surface. Appropriate Uses Implement a stabilized construction entrance or vehicle tracking control where frequent heavy vehicle traffic exits the construction site onto a paved roadway. An effective vehicle tracking control is particularly important during the following conditions: Wet weather periods when mud is easily tracked off site. During dry weather periods where dust is a concern. When poorly drained, clayey soils are present on site. Although wheel washes are not required in designs of vehicle tracking controls, they may be needed at particularly muddy sites. Design and Installation Construct the vehicle tracking control on a level surface. Where feasible, grade the tracking control towards the construction site to reduce off-site runoff. Place signage, as needed, to direct construction vehicles to the designated exit through the vehicle tracking control. There are several different types of stabilized construction entrances including: VTC-1. Aggregate Vehicle Tracking Control. This is a coarse-aggregate surfaced pad underlain by a geotextile. This is the most common vehicle tracking control, and when properly maintained can be effective at removing sediment from vehicle tires. VTC-2. Vehicle Tracking Control with Construction Mat or Turf Reinforcement Mat. This type of control may be appropriate for site access at very small construction sites with low traffic volume over vegetated areas. Although this application does not typically remove sediment from vehicles, it helps protect existing vegetation and provides a stabilized entrance. Vehicle Tracking Control Functions Erosion Control Moderate Sediment Control Yes Site/Material Management Yes SM-4 Vehicle Tracking Control (VTC) VTC-2 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Photograph VTC-2. A vehicle tracking control pad with wheel wash facility. Photo courtesy of Tom Gore. VTC-3. Stabilized Construction Entrance/Exit with Wheel Wash. This is an aggregate pad, similar to VTC-1, but includes equipment for tire washing. The wheel wash equipment may be as simple as hand-held power washing equipment to more advance proprietary systems. When a wheel wash is provided, it is important to direct wash water to a sediment trap prior to discharge from the site. Vehicle tracking controls are sometimes installed in combination with a sediment trap to treat runoff. Maintenance and Removal Inspect the area for degradation and replace aggregate or material used for a stabilized entrance/exit as needed. If the area becomes clogged and ponds water, remove and dispose of excess sediment or replace material with a fresh layer of aggregate as necessary. With aggregate vehicle tracking controls, ensure rock and debris from this area do not enter the public right-of-way. Remove sediment that is tracked onto the public right of way daily or more frequently as needed. Excess sediment in the roadway indicates that the stabilized construction entrance needs maintenance. Ensure that drainage ditches at the entrance/exit area remain clear. A stabilized entrance should be removed only when there is no longer the potential for vehicle tracking to occur. This is typically after the site has been stabilized. When wheel wash equipment is used, be sure that the wash water is discharged to a sediment trap prior to discharge. Also inspect channels conveying the water from the wash area to the sediment trap and stabilize areas that may be eroding. When a construction entrance/exit is removed, excess sediment from the aggregate should be removed and disposed of appropriately. The entrance should be promptly stabilized with a permanent surface following removal, typically by paving. Vehicle Tracking Control (VTC) SM-4 November 2010 Urban Drainage and Flood Control District VTC-3 Urban Storm Drainage Criteria Manual Volume 3 SM-4 Vehicle Tracking Control (VTC) VTC-4 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Vehicle Tracking Control (VTC) SM-4 November 2010 Urban Drainage and Flood Control District VTC-5 Urban Storm Drainage Criteria Manual Volume 3 SM-4 Vehicle Tracking Control (VTC) VTC-6 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Stabilized Construction Roadway (SCR)SM-5 November 2010 Urban Drainage and Flood Control District SCR-1 Urban Storm Drainage Criteria Manual Volume 3 Photograph SCR-1. Stabilized construction roadway. Description A stabilized construction roadway is a temporary method to control sediment runoff, vehicle tracking, and dust from roads during construction activities. Appropriate Uses Use on high traffic construction roads to minimize dust and erosion. Stabilized construction roadways are used instead of rough-cut street controls on roadways with frequent construction traffic. Design and Installation Stabilized construction roadways typically involve two key components: 1) stabilizing the road surface with an aggregate base course of 3-inch-diameter granular material and 2) stabilizing roadside ditches, if applicable. Early application of road base is generally suitable where a layer of coarse aggregate is specified for final road construction. Maintenance and Removal Apply additional gravel as necessary to ensure roadway integrity. Inspect drainage ditches along the roadway for erosion and stabilize, as needed, through the use of check dams or rolled erosion control products. Gravel may be removed once the road is ready to be paved. Prior to paving, the road should be inspected for grade changes and damage. Regrade and repair as necessary. Stabilized Construction Roadway Functions Erosion Control Yes Sediment Control Moderate Site/Material Management Yes Stabilized Staging Area (SSA) SM-6 November 2010 Urban Drainage and Flood Control District SSA-1 Urban Storm Drainage Criteria Manual Volume 3 Photograph SSA-1. Example of a staging area with a gravel surface to prevent mud tracking and reduce runoff. Photo courtesy of Douglas County. Description A stabilized staging area is a clearly designated area where construction equipment and vehicles, stockpiles, waste bins, and other construction-related materials are stored. The contractor office trailer may also be located in this area. Depending on the size of the construction site, more than one staging area may be necessary. Appropriate Uses Most construction sites will require a staging area, which should be clearly designated in SWMP drawings. The layout of the staging area may vary depending on the type of construction activity. Staging areas located in roadways due to space constraints require special measures to avoid materials being washed into storm inlets. Design and Installation Stabilized staging areas should be completed prior to other construction activities beginning on the site. Major components of a stabilized staging area include: Appropriate space to contain storage and provide for loading/unloading operations, as well as parking if necessary. A stabilized surface, either paved or covered, with 3-inch diameter aggregate or larger. Perimeter controls such as silt fence, sediment control logs, or other measures. Construction fencing to prevent unauthorized access to construction materials. Provisions for Good Housekeeping practices related to materials storage and disposal, as described in the Good Housekeeping Control Measure Fact Sheet. A stabilized construction entrance/exit, as described in the Vehicle Tracking Control Control Measure Fact Sheet, to accommodate traffic associated with material delivery and waste disposal vehicles. Over -sizing the stabilized staging area may result in disturbance of existing vegetation in excess of that required for the project. This increases costs, as well as requirements for long-term stabilization following the construction period. When designing the stabilized staging area, minimize the area of disturbance to the extent practical. Stabilized Staging Area Functions Erosion Control Yes Sediment Control Moderate Site/Material Yes SM-6 Stabilized Staging Area (SSA) SSA-2 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 See Detail SSA-1 for a typical stabilized staging area and SSA-2 for a stabilized staging area when materials staging in roadways is required. Maintenance and Removal Maintenance of stabilized staging areas includes maintaining a stable surface cover of gravel, repairing perimeter controls, and following good housekeeping practices. When construction is complete, debris, unused stockpiles and materials should be recycled or properly disposed. In some cases, this will require disposal of contaminated soil from equipment leaks in an appropriate landfill. Staging areas should then be permanently stabilized with vegetation or other surface cover planned for the development. Minimizing Long-Term Stabilization Requirements Utilize off-site parking and restrict vehicle access to the site. Use construction mats in lieu of rock when staging is provided in an area that will not be disturbed otherwise. Consider use of a bermed contained area for materials and equipment that do not require a stabilized surface. Consider phasing of staging areas to avoid disturbance in an area that will not be otherwise disturbed. Stabilized Staging Area (SSA) SM-6 November 2010 Urban Drainage and Flood Control District SSA-3 Urban Storm Drainage Criteria Manual Volume 3 SM-6 Stabilized Staging Area (SSA) SSA-4 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Temporary Diversion Methods (TDM)SM-8 June 2012 Urban Drainage and Flood Control District TDM-1 Urban Storm Drainage Criteria Manual Volume 3 Photograph TDM-1. This coffer dam, installed to allow grading and stabilization of the stream bank, consists of concrete blocks covered by an impermeable linear held in place by sand bags. Description Temporary diversion methods are used to reroute water from a stream or restrict flows to a designated portion of the stream channel to allow for construction activities to take place in the stream, along the banks or beneath the active channel. Temporary diversion methods are often required during the construction of detention ponds, dams, in-stream grade control structures, utility installation and other activities, including maintenance, that require working in waterways. Temporary diversion methods include temporary diversion channels, pump-arounds, piped diversions, coffer dams and other similar practices. The primary purpose of all temporary diversion methods is to protect water quality by passing upstream flows around the active construction zone. Appropriate Uses Temporary diversion methods are appropriate in situations when it is necessary to divert the flow around the area where work is being conducted. Temporary diversion methods vary with the size of the waterway that is being diverted. For large streams, a temporary diversion may consist of berms or coffer dams constructed within the stream to confine flow to one side of the stream while work progresses on the “dry” side of the berm. For smaller streams and often for construction of dams and detention basins, a temporary diversion method may divert the entire waterway. For short duration projects (typically less than a month of active construction) with low baseflows, a pump and/or bypass pipe may serve as a temporary diversion. Whenever a temporary diversion is used, construction should be scheduled during drier times of the year (November through March) to the extent feasible, and construction in the waterway should progress as quickly as practical to reduce the risk of exceeding the temporary diversion capacity. Timing and duration of construction are primary considerations for determining the design flow most appropriate for a diversion. A sizing method that does not consider these variables is overly simplistic and can result in inflated project costs and land disturbances that provide little to no water quality benefit. Additionally, disturbing more area than necessary can result in increased erosion. Temporary diversion method section and approach should occur on a project- and site-specific basis. For short duration projects (typically associated with maintenance of utilities and stream crossings and minor repairs to outfalls and eroded banks) constructed during dry times of the year, diversion construction can create greater disturbance and mobilization of sediment than all of the other earth disturbing activities of the project combined, and the cost of the diversion could be a significant percentage of the overall project cost. If it can be reasonably determined, based on area and duration of disturbance, that channel work will result in less disturbance and movement of sediment than would occur through installation of a temporary diversion, it is reasonable to exempt these activities from the requirement to construct a temporary diversion. Temporary Diversion Channel Functions Erosion Control Yes Sediment Control No Site/Material Management No SM-8 Temporary Diversion Methods (TDM) TDM-2 Urban Drainage and Flood Control District June 2012 Urban Storm Drainage Criteria Manual Volume 3 On the other end of the spectrum, a basis of design for a temporary diversion in excess of the methodology presented in this Fact Sheet may be appropriate for longer duration projects and/or projects where the consequences of exceeding diversion capacity are significant in terms of public safety, damage to infrastructure and property, environmental impacts, damage or delay to the project and other factors. In short, engineers should recognize that temporary diversions must be thoughtfully analyzed on a case-by-case basis, considering site-specific circumstances. Design Considerations Selection and design of temporary diversion methods should consider many factors, including: Will construction of a temporary diversion cause greater environmental impacts than if the project is constructed without a temporary diversion? This frequently applies to short duration, small scale projects associated with maintenance activities such as bank erosion repair, drop structure and pond maintenance, outfall improvements/repair and other limited construction activities. Size of stream, tributary watershed area and anticipated flow rates during construction. Special consideration should be given to large streams with large tributary areas with higher flow rates since the sizing methodology presented in this Fact Sheet is based on data from watersheds less than 20 square miles. Any special water quality or aquatic life conditions the waterway. Nature of surrounding land use, property ownership, and easements in the project area are important considerations in determining feasibility and methods for temporary diversions. For example, in a highly urbanized setting or an area with limited right-of-way, there may not be adequate space to construct a diversion channel. Seasonal variations in stream hydrology (baseflow vs. peak flow). o Irrigation flows: If an irrigation ditch enters the stream, it is recommended that the ditch company be contacted to confirm when flows from the ditch may be expected. o Weather (storm runoff): If diversions are constructed in summer months when thunderstorms and flash flooding can occur, contractors will need to track weather forecasts closely and provide additional protection when higher flows from runoff are anticipated. The UDFCD Alert System can be used for daily forecasts and to provide warnings for severe weather. Probability of flood flows exceeding diversion capacity and/or diversion failure. Consider the consequences of exceedance or failure such as: o Public safety o Environmental o Legal o Regulatory o Economic o Project disruption/delay Realistic estimation of project duration and time of year during which construction will occur. Temporary Diversion Methods (TDM)SM-8 June 2012 Urban Drainage and Flood Control District TDM-3 Urban Storm Drainage Criteria Manual Volume 3 Comparison of the overall project costs to the temporary diversion costs (design and construction) and determining the costs and benefits of different diversion strategies relative to the protection that they provide. Permitting requirements for overall project and for diversion methods (United States Army Corps of Engineers, United States Fish and Wildlife Service, Colorado Department of Public Health and Environment, Federal Emergency Management Agency, Division of Water Resources, local governments, and others). Permit requirements and existing vegetative cover may limit the allowable area disturbance. Public safety aspects. For example, if a pipeline is being used, consideration should be given to public access and inlet protection. Legal considerations, which are a function of many different factors such as property ownership, history of localized flooding, or parties that will have interest in project. Design and Installation 1.Determine if a diversion is appropriate based on appropriate uses and design considerations stated earlier. As noted, in some cases, constructing a project under wet conditions is preferable to constructing a temporary diversion to create dry conditions, especially if construction of the temporary diversion will require a significant amount of disturbance relative to the overall project. 2.Determine project duration. “Long duration” projects are projects that last longer than three months and in many cases are Capital Improvement Projects or traditional land development projects. “Short duration” projects are projects that are completed within one month or less and generally are associated with maintenance and repair activities. “Interim duration” projects are projects that will last longer than one month but up to three months. 3.Determine the time of year in which construction will occur. 4. Gather necessary temporary diversion sizing parameters that may include tributary area, imperviousness, project duration safety factor, and seasonal sizing coefficient. 5. Apply applicable sizing methodology and perform necessary calculations (provided following this section). Use engineering judgment to determine if the temporary diversion design flow is adequate for the specific project. 6.Determine appropriate method of diversion. Follow the design steps for the selected method discussed below. Channel Diversion – For smaller streams, construction of dams and detention basins, or as the site allows, a channel diversion may divert the entire waterway as illustrated in Figure TDM-1. SM-8 Temporary Diversion Methods (TDM) TDM-4 Urban Drainage and Flood Control District June 2012 Urban Storm Drainage Criteria Manual Volume 3 Selecting a Diversion Method Selection of the appropriate diversion type is largely site specific. The best choice represents the most efficient method while keeping disturbance to a minimum. Berm or Coffer Dam – A berm or coffer dam is appropriate for streams of all sizes to confine flow to one side of the stream. Piped Diversion – A bypass pipe is generally appropriate for short duration projects with low baseflows. Pumped Diversion – A pumped diversion may be appropriate for short duration projects with low baseflows. It may also be the only option where space for the diversion is limited as shown in photograph TDM-2. 7.Consider developing an emergency action plan, as a precaution, for rapidly removing equipment and materials with potential to contribute pollutants to runoff from the waterway in advance of imminent runoff with the potential to exceed diversion capacity. The emergency action plan should designate an individual who will be on the site throughout most of the construction project with the authority to order that work be halted and equipment and materials with potential to contribute to stormwater pollution be moved to high ground outside of the active channel. The emergency action plan should identify where equipment and materials removed from the channel will be stored temporarily during a runoff event that is expected to exceed temporary diversion capacity. The UDFCD Alert System and warnings of the potential for severe weather issued by UDFCD should be consulted daily during construction. Channel Diversion 1. Use sizing methodology to determine temporary diversion design flow rate. 2.Determine channel slope based on existing and proposed site conditions. Perform initial channel sizing calculations using Manning's Equation. Determine maximum permissible velocities based on lining material. Pay particular attention to diversion channel entrance, bends, transitions and downstream return to stream where scour forces may require greater protection. Unlined channels should not be used. Table TDM-1 gives Manning's "n" values for the most commonly used lining materials. Because temporary diversion channels typically are not in service long enough to establish adequate vegetative lining, they must be designed to be stable for the design flow with the channel shear stress less than the critical tractive shear stress for the channel lining material. 3.Determine the channel geometry and check the capacity using Manning's Equation and the "n" value given in Table TDM-1. The steepest side slope allowable is two horizontal to one vertical (2:1), unless vertical walls are installed using sheet piling, concrete or stacked stone. Consideration for public access and safety should be accounted for when determining channel geometry. 4. Determine depth of flow. A maximum depth of 1-foot is allowed for flows less than 20 cfs and a maximum of 3 feet for flows less than 100 cfs. (Flows in excess of 100 cfs should be designed in accordance with the Major Drainage chapter in Volume 1). Provide a minimum of 0.5 feet of freeboard above the design water surface elevation. Temporary Diversion Methods (TDM)SM-8 June 2012 Urban Drainage and Flood Control District TDM-5 Urban Storm Drainage Criteria Manual Volume 3 Table TDM-1. Manning’s n Values for Temporary Diversion Channel Design Lining Material Manning's n Depth = 0 to 1.0 ft Manning's n Depth = 1.0 to 3.0 ft Manning's n Depth = 3.0 to 5.0 ft Plastic Membrane 0.011 0.010 0.009 Straw/Curled Wood Mats 0.035 0.025 0.020 Riprap, Type VL 0.070 0.045 0.035 Riprap, Type L 0.100 0.070 0.040 Riprap, Type M 0.125 0.075 0.045 Note: Use manufacturer's Manning's n when available. See the Major Drainage chapter of the USDCM for riprap gradation. Erosion protection should extend a minimum of 0.5 feet above the design water depth. Berm or Coffer Dam For coffer dams or berms that are intended to isolate a portion of the stream from the work area steps 1- 4 should be applied to the “wet” side of the coffer dam or berm. 1. Use sizing methodology to determine temporary diversion design flow rate. 2. Determine channel slope based on existing and proposed site conditions. 3. Perform initial channel sizing calculations using Manning's Equation. Determine maximum permissible velocities based on lining material. Because temporary diversion measures typically are not in service long enough to establish adequate vegetative lining, they must be designed to be stable for the design flow with the channel shear stress less than the critical tractive shear stress for the channel lining material. This stability criterion applies to the stream-side of berms when berms are used to isolate a work area within a stream. 4.Determine the channel geometry and check the capacity using Manning's Equation and the "n" value given in Table TDM-1. The steepest side slope allowable is two horizontal to one vertical (2:1), unless vertical walls are installed using sheet piling, concrete or stacked stone. Provide a minimum of 0.5 feet of freeboard above the design water surface elevation. Piped Diversion 1. Use sizing methodology to determine temporary diversion design flow rate. 2. Size the pipe to accommodate the design flow using no more than 80 percent of the pipe full flow capacity. Select a Manning’s n value based on the type of pipe material that will be used (concrete n = 0.013 [typ.], corrugated metal pipe n = 0.024 [typ.]). SM-8 Temporary Diversion Methods (TDM) TDM-6 Urban Drainage and Flood Control District June 2012 Urban Storm Drainage Criteria Manual Volume 3 “Long duration” projects last longer than three months. “Short duration” projects are completed within one month or less. “Interim duration” projects last longer than one month and up to three months. Photograph TDM-2. Despite a relatively significant baseflow, a pumped diversion was selected for this Lakewood Gulch project due to a lack of space crossing Federal Boulevard. Photo courtesy of City and County of Denver. Pumped Diversion 1. Use sizing methodology to determine temporary diversion design flow rate. 2. A backup pump (or pumps) with capacity equal to or greater than the diversion design flow rate should be on site and in good working order at all times. Sizing Methodology The methodology for sizing of temporary diversion methods was developed using baseflow observations and Crest Stage Indicator (CSI) peak flow data collected from 21 watersheds within the UDFCD boundary. These data were collected over extended periods of time (up to 31 years) and, as a result, provide a sound statistical basis for the sizing methodology. Determine sizing procedure to use based on the project duration. •“Long duration” projects last longer than three months and in many cases are Capital Improvement Projects or traditional land development projects. •“Short duration” projects are completed within one month or less and generally are associated with maintenance and repair activities. For these projects, it is recommended that the temporary diversion be sized based on the statistics identified for baseflows (i.e., vs. peak flows) and be of sufficient size to convey a flow that has a less than 50% chance of being exceeded between November –March, including a project duration safety factor. •“Interim duration” projects will last longer than one month but up to three months. In these projects, engineering judgment must be applied, drawing on sizing methods for “short duration” and “long duration” project criteria and the time of year of construction to develop a basis of design for the temporary diversion method that is appropriate for the project. It is highly recommended that projects involving temporary diversions be constructed between November and March. If a short duration project requiring a temporary diversion must be conducted between April and October, the extended weather forecast should be evaluated to avoid periods of anticipated precipitation and a conservative safety factor should be applied. Additional protection may need to be provided for the site if higher flows from runoff are anticipated. Temporary Diversion Methods (TDM)SM-8 June 2012 Urban Drainage and Flood Control District TDM-7 Urban Storm Drainage Criteria Manual Volume 3 Sizing Procedure for Long Duration Projects (duration greater than three months) 1.Determine the tributary drainage area, A, in square miles. 2.Determine the watershed imperviousness (adjusted as appropriate for disconnected impervious area, see Chapter 3). 3. Determine the design peak flow rate according to Figure TDM-2. Note: For long duration projects, or where the consequences of diversion failure warrant, a larger design flow may be necessary, and/or a more detailed, site-specific hydrologic analysis. Figure TDM-2 may be used to estimate the design discharge for the sizing of temporary diversion methods for projects exceeding three months in duration. The curves in this figure were originally developed using annual peak flow data collected from 17 watersheds within the UDFCD boundary and then updated in 2012 using annual peak flow data from 21 watersheds with CSI gages. These data were collected over extended periods of time (up to 31 years) and, as a result, provide a sound statistical basis for the figure. The data supporting Figure TDM-2 were taken during the high flood potential period of April through September. Figure TDM-2 provides estimated 2-year peak flow rates with the upper 5% and lower 95% confidence limits shown and is based on watershed imperviousness for small waterways (25 square miles or less).1 Because Figure TDM-2 was developed using data from small watersheds, it is not appropriate to extrapolate from this figure for larger, more complex watersheds. For larger waterways (e.g., South Platte River, Sand Creek, Bear Creek, etc.), including ones controlled by flood control reservoirs (e.g., Chatfield Dam, Cherry Creek Dam, etc.), site-specific hydrologic analysis and risk assessment will be necessary to evaluate the appropriate level of protection to be provided by the temporary diversion. For any size watershed, it is important that the designer understand watershed characteristics to determine applicability of the simplified method and how these characteristics influence the choice of diversion method. It is also important to recognize that larger floods can and do occur. It is the responsibility of the designer and the contractor to assess their risk of having the temporary diversion being exceeded and to evaluate the damages such an event may cause to the project, adjacent properties and others. 1 There are a multitude of factors affecting rainfall-runoff response of a watershed in addition to impervious area. Other factors include soil types, total area, fraction of connected/disconnected impervious area, watershed shape, topography and many other factors). Figure TDM-2 provides a simplified design tool based on watershed imperviousness but should not be blindly relied upon without due consideration of other factors including those listed above and others. SM-8 Temporary Diversion Methods (TDM) TDM-8 Urban Drainage and Flood Control District June 2012 Urban Storm Drainage Criteria Manual Volume 3 When a diversion is determined to be appropriate, safety factors and K values in Table TDM-2 are minimum recommended values. Depending on the many factors to consider in selecting and sizing a temporary diversion listed above, higher values for K and S may be appropriate. Sizing Procedure for Short Duration Projects (one month or less of active construction) 1.Determine the tributary drainage area, A, in square miles. 2.Select a safety factor, S, based on project duration from Table TDM-2. Short duration projects have been broken down further into projects less than two weeks and projects from two weeks up to one month. 3.Select the sizing coefficient, K, corresponding to the month in which the project will occur (see Table TDM-2). For projects that span two months with different K values, use the greater of the two K values. For short duration projects that will occur during the traditionally dry period of the year (November through March) a K value of 0.2 is recommended. For short duration projects that will occur April through October, and wet weather is not predicted, a K value of 0.5 is recommended. Table TDM-2.Temporary Diversion Sizing Coefficients and Safety Factors for Short Duration Projects Time of Year Project Duration Safety Factor, S Temporary Diversion Sizing Coefficient, K November - March Less than 2 weeks 1.0 0.2 November - March 2 weeks to 1 month 1.5 0.2 April - October Less than 2 weeks (during dry weather conditions) 1.0 0.5 April - October 2 weeks to 1 month 1.5 0.5 Note: K coefficients were developed from regression analysis of baseflow data from USGS Crest Stage Indicator (CSI) data to approximate flows that have a less than 50% chance of being exceeded between November - March. 4. Calculate the recommended temporary diversion design flow rate using equation TDM-1: Q = S K A (Equation TDM-1) In which, Q = temporary diversion design flow rate for short-duration projects (cfs). S = safety factor coefficient from Table TDM-2 based on duration. K = diversion sizing coefficient from Table TDM-2 based on seasonality. A = tributary area (square miles). Temporary Diversion Methods (TDM)SM-8 June 2012 Urban Drainage and Flood Control District TDM-9 Urban Storm Drainage Criteria Manual Volume 3 Example of Short-Duration Temporary Diversion Sizing Methodology Project Location: Goldsmith Gulch Downstream (north) of E. Cornell Avenue Planned project will involve approximately 0.12 acres of disturbance for bank stabilization, which will be completed within two weeks during the November to March time period. Using StreamStats, the gross contributing watershed area was determined to be approximately 6.2 mi2. Based on project duration and seasonal timing, Table TDM-2 yields S = 1.0, K = 0.2. Equation TDM-1 can be used to calculate the recommended diversion flow: Q = S K A Q = 1.0  0.2  6.2 mi2 = 1.2 cfs Had this been a larger restorative maintenance project that will last 4 weeks, but will be started and completed within the November through March period, application of Equation TDM-1 and the recommended safety factor suggest the following diversion design flow: Q = S K A Q = 1.5  0.2  6.2 mi2 = 1.9 cfs Of course, if the observed condition at the construction site suggests a higher flow, this should be estimated and used instead. Sizing Procedure for Interim Duration Projects (longer than one month and up to three months) When projects last longer than one month but up to three months, a combination of sizing methods should be applied. The recommended temporary diversion flow rate should be evaluated using both the sizing procedure for short duration projects as well as the sizing procedure for long duration projects. These calculated flow rates should be weighed in combination with site-specific factors to determine an appropriate design flow rate. Each site should be evaluated individually to determine factors that may affect the design flow choice. For example, the designer may select to use the more conservative design flow for an interim duration project occurring in July and August where a chance for wet weather is forecast and flooding or damage to the area surrounding the project is unacceptable. Maintenance and Removal Because temporary diversions are one of the most critical control measures for work in waterways, they must be inspected and maintained frequently to remain in effective operating condition. Flow barriers should be inspected at the start and end of each workday and at any time that excess water is noted in dry work areas. For diversion channels, the diversion channel itself should be inspected for signs of erosion, and the lining should be repaired or replaced if there are signs of failure. Check armoring at the diversion return point to the waterway, and add additional armoring if erosion is noted. Water should not be allowed to flow back through the natural stream until all construction is completed. After redirecting the flow through the natural channel, temporary diversion measures should be removed. For temporary diversion channels, lining materials should be removed, and the diversion channel should then be backfilled and stabilized. Points of tie-in to the natural channel should be protected with riprap sized SM-8 Temporary Diversion Methods (TDM) TDM-10 Urban Drainage and Flood Control District June 2012 Urban Storm Drainage Criteria Manual Volume 3 material in accordance with the Major Drainage chapter in Volume 1. Figure TDM-1. Typical Temporary Diversion Channel Former Location of Stream Bank Former Location of Stream Bank Temporary Diversion Methods (TDM)SM-8 June 2012 Urban Drainage and Flood Control District TDM-11 Urban Storm Drainage Criteria Manual Volume 3 Figure TDM-2. Temporary Diversion Facility Sizing Nomograph for Long Duration Projects (Duration in excess of three months) Based on 2-year Peak Flows - Denver Metropolitan and Adjacent Areas, Updated April 2012 SM-8 Temporary Diversion Methods (TDM) TDM-12 Urban Drainage and Flood Control District June 2012 Urban Storm Drainage Criteria Manual Volume 3 Temporary Diversion Methods (TDM)SM-8 June 2012 Urban Drainage and Flood Control District TDM-13 Urban Storm Drainage Criteria Manual Volume 3 Dewatering Operations (DW)SM-9 November 2010 Urban Drainage and Flood Control District DW-1 Urban Storm Drainage Criteria Manual Volume 3 Photograph DW-1. A relatively small dewatering operation using straw bales and a dewatering bag. Photograph DW-2. Dewatering bags used for a relatively large dewatering operation. Description The control measuress selected for construction dewatering vary depending on site-specific features such as soils, topography, anticipated discharge quantities, and discharge location. Dewatering typically involves pumping water from an inundated area to a control measure, and then downstream to a receiving waterway, sediment basin, or well-vegetated area. Dewatering typically involves use of several control measures in sequence. Appropriate Uses Dewatering operations are used when an area of the construction site needs to be dewatered as the result of a large storm event, groundwater, or existing ponding conditions. This can occur during deep excavation, utility trenching, and wetland or pond excavation. Design and Installation Dewatering techniques will vary depending on site conditions. However, all dewatering discharges must be treated to remove sediment before discharging from the construction site. Discharging water into a sediment trap or basin is an acceptable treatment option. Water may also be treated using a dewatering filter bag, and a series of straw bales or sediment logs. If these previous options are not feasible due to space or the ability to passively treat the discharge to remove sediment, then a settling tank or an active treatment system may need to be utilized. Settling tanks are manufactured tanks with a series of baffles to promote settling. Flocculants can also be added to the tank to induce more rapid settling. This is an approach sometimes used on highly urbanized construction sites. Contact the state agency for special requirements prior to using flocculents and land application techniques. Some commonly used methods to handle the pumped water without surface discharge include land application to vegetated areas through a perforated discharge hose (i.e., the "sprinkler method") or dispersal from a water truck for dust control. Dewatering Operations Functions Erosion Control Moderate Sediment Control Yes Site/Material Management Yes SM-9 Dewatering Operations (DW) DW-2 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Dewatering discharges to non-paved areas must minimize the potential for scour at the discharge point either using a velocity dissipation device or dewatering filter bag. Design Details are provided for these types of dewatering situations: DW-1. Dewatering for Pond Already Filled with Water DW-2 Dewatering Sump for Submersed Pump DW-3 Sump Discharge Settling Basin DW-4 Dewatering Filter Bag Maintenance and Removal When a sediment basin or trap is used to enable settling of sediment from construction dewatering discharges, inspect the basin for sediment accumulation. Remove sediment prior to the basin or trap reaching half full. Inspect treatment facilities prior to any dewatering activity. If using a sediment control practice such as a sediment trap or basin, complete all maintenance requirements as described in the fact sheets prior to dewatering. Properly dispose of used dewatering bags, as well as sediment removed from the dewatering control measures. Depending on the size of the dewatering operation, it may also be necessary to revegetate or otherwise stabilize the area where the dewatering operation was occurring. Dewatering Operations (DW)SM-9 November 2010 Urban Drainage and Flood Control District DW-3 Urban Storm Drainage Criteria Manual Volume 3 SM-9 Dewatering Operations (DW) DW-4 Urban Drainage and Flood Control District November 2010 Urban Storm Drainage Criteria Manual Volume 3 Dewatering Operations (DW)SM-9 November 2010 Urban Drainage and Flood Control District DW-5 Urban Storm Drainage Criteria Manual Volume 3 Temporary Stream Crossing (TSC)SM-10 June 2012 Urban Drainage and Flood Control District TSC-1 Urban Storm Drainage Criteria Manual Volume 3 Description Where an actively flowing watercourse must be crossed regularly by construction vehicles, a temporary crossing should be provided. Three primary methods are available: Culvert crossing Stream ford Temporary bridge Culvert crossings and fords are the most commonly used methods. Due to the expense associated with a temporary bridge, these are used primarily on long- term projects. Appropriate Uses Construction vehicles shall be kept out of waterways to the maximum extent practicable. Use a temporary stream crossing when it is absolutely necessary to cross a stream on a construction site. Construct a temporary crossing even if the stream or drainageway is typically dry. Multiple stream crossings should be avoided to minimize environmental impacts. A permit is required for placement of fill in a waterway under Section 404 of the Clean Water Act. The local office of the U.S. Army Corps of Engineers (USACE) should be contacted concerning the requirements for obtaining a 404 permit. In addition, a permit from the U.S. Fish and Wildlife Service (USFWS) may be needed if endangered species are of concern in the work area. Typically, the USFWS issues are addressed by a 404 permit, if one is required. The municipality of jurisdiction should also be consulted, and can provide assistance. Other permits to be obtained may include a floodplain development permit from the local jurisdiction. Design and Installation Design details are provided for these types of stream crossings: TSC-1. Culvert Crossing TSC-2. Ford Crossing TSC-3. Flume Crossing Temporary Stream Crossing Functions Erosion Control Yes Sediment Control Yes Site/Material Management No Photograph TSC-1. A temporary stream crossing using culverts. Photo courtesy of Tom Gore. SM-10 Temporary Stream Crossing (TSC) TSC-2 Urban Drainage and Flood Control District June 2012 Urban Storm Drainage Criteria Manual Volume 3 A culvert crossing should be sized appropriately with consideration for the duration of construction and seasonal variation of flows. The sizing methodology provided in the Temporary Diversion Methods Fact Sheet is also appropriate for determining the design flow for temporary stream crossings. Culvert sizing must account for the headwater and tailwater controls to properly size the culvert. For additional discussion on design of box culverts and pipes, see the Major Drainage chapter in Volume 1. The designer also needs to confirm that the riprap selected is appropriate for the conditions in the channel being crossed. When a ford must be used, namely when a culvert is not practical or the best solution, the ford should be lined with at least a 12-inch thick layer of Type VL (D50 = 6 inches) or Type L (D50 = 9 inches) riprap with void spaces filed with 1-1/2 inch diameter rock. Ford crossings are recommended primarily for crossings of ephemeral (i.e. intermittently, briefly flowing) streams. For a temporary bridge crossing, consult with a structural and/or geotechnical engineer for temporary bridge design or consider pre-fabricated alternatives. Maintenance and Removal Inspect stream for bank erosion and in-stream degradation. If bank erosion is occurring, stabilize banks using erosion control practices such as erosion control blankets. If in-stream degradation is occurring, armor the culvert outlet(s) with riprap to dissipate energy. If sediment is accumulating upstream of the crossing, remove excess sediment as needed to maintain the functionality of the crossing. Remove the temporary crossing when it is no longer needed for construction. Take care to minimize the amount of sediment lost into the stream upon removal. Once the crossing has been removed, stabilize the stream banks with seed and erosion control blankets.