b. Type B shall be utilized after the casting and grate are in place.
c. Type D shall be utilized in areas where other types of inlet protection are identified as incompatible with roadway and traffic conditions, causing possible safety hazards when ponding occurs at the inlet. Type D shall only be used after castings are in place on top of the inlet boxes.
Type D inlet protection shall conform to the standard drawing as shown in the plans. There shall be a three-inch space between the bag and the sides of the inlet to prevent the inlet sides from blocking the overflow; and shall only be used in inlets deeper than 30 inches from the top of grate to bottom of the inlet. If such clearance is not available, cinch or tie the sides of the bag (with rope or ties) to provide clearance.
C. Criteria Applicable to the Post-Paving / Curbing Phase of Construction
1. Inlet protection Types B, C, and D are applicable to post paving construction. See Figure 1 Inlet Protection.
• Type B shall be utilized on inlets without curb box.
• Type C shall be utilized on street inlets with curb heads. A 1½, x 3
½, (37mm by 87 mm) minimum, piece of wood shall be wrapped and secured in the fabric and placed in front of the curb head as shown in the plans. The wood shall not block the entire opening of the curb box and be secured to the grate with wire or plastic ties.
• Type D
VI. Considerations
A. When site conditions allow, inlets should be temporarily closed or sealed to prevent entrance of runoff and sediment.
B. The best way to prevent sediment from entering the storm sewer system is to stabilize the disturbed area of the site as quickly as possible, preventing erosion and stopping sediment transport at its source.
C. Storm drain inlet protection consists of several types of inlet filters and traps and should be considered as only one element in an overall erosion control plan. Each type differs in application with selection dependent upon site conditions and inlet type. Not all designs are appropriate in all cases. The user must carefully select a design suitable for the needs and site conditions.
D. Inlet protection is only as effective as the filter or barrier used around the inlet. Effectiveness decreases rapidly if the inlet protection is not properly maintained. In general, inlet protection provides relatively good removal of coarse and medium-sized soil particles from runoff however, most fine silt and clay particles will pass through the filtering mechanisms.
E. Properly maintaining inlet protection can be difficult and often inlets can become clogged. Field experience has shown that inlet protection that causes excessive ponding in an area of high construction activity may become so inconvenient that it is simply removed or bypassed, thus transmitting sediment-laden flows unchecked. In such situations, a structure with an adequate overflow mechanism should be utilized instead of simply removing the inlet protection device.
F. Inlet protection devices can be enhanced by additional excavation to increase the storage capacity around the inlet.
G. Good construction site housekeeping measures, such as keeping the gutters clean, and street sweeping are important.
VII. Plans and Specifications
Plans and specifications for installing inlet protection shall be in keeping with this standard and shall describe the requirements for applying the practice to achieve its intended purpose:
A. Location of inlet protection and type employed
B. Material spec conforming to standard
C. All plans, standard detail drawings, or specifications shall include schedule for installation, inspection, and maintenance. The responsible party shall be identified.
VIII. Operation and Maintenance
A. Remove inlet protection devices once the contributing drainage area is stabilized with appropriate vegetation or impervious area.
B. Inlet protection shall be at a minimum inspected weekly and within 24 hours after every precipitation event that produces 0.5 inches of rain or more during a 24-hour period.
C. Sediment deposits shall be removed and the inlet protection device restored to its original dimensions when the sediment has accumulated between 1/3 to 1/2 the design depth of the device, or when the device is no longer functioning as designed. Removed sediment shall be deposited in a suitable area and stabilized.
D. Due care shall be taken to ensure sediment does not fall into the inlet and impede the intended function of the device. Any material falling into the inlet shall be removed.
IX. References
Turbidity Barrier
1069 (09/05)
Wisconsin Department of Natural Resources
Conservation Practice Standard
Note: Words in the standard that are shown in italics are described in X. Definitions. The words are italicized the first time they are used.
I. Definition
A temporary fabric barrier with very low permeability, installed in or near the bed of a waterway or waterbody to minimize sediment transport and is installed parallel to flow. Turbidity barrier cannot be installed perpendicular to a moving channel.
II. Purposes
The purpose of this practice is to provide sediment containment while construction activities are occurring in or directly adjacent to a waterway or waterbody.
III. Conditions Where Practice Applies
This practice applies where construction activities intrude or are directly adjacent to a waterway or waterbody. This includes but is not limited to bridge construction, rip rap placement, utility work, streambank restoration, boat launches and dredging.
Use turbidity barriers in conditions with fine soils and flow velocities not exceeding 5 feet per second, unless additional reinforcement is installed.
IV. Federal, State, and Local Laws
Users of this standard shall be aware of applicable federal, state, and local laws, rules, regulations, or permit requirements governing the use and placement of turbidity barriers. This standard does not contain the text of federal, state, or local laws.
V. Criteria
This section establishes the minimum standards for design, installation and performance requirements.
A. Installation – Details of construction not listed in the text shall conform to the pertinent requirements of Figures 1 and 2.
1. The barrier shall be installed before construction activities are initiated in, or adjacent to the waterway or waterbody. Install the turbidity barrier as close to the construction as practical. The barrier shall remain in place and be maintained until the construction activity is completed and the disturbed area stabilized 1.
2. The ends of the barrier shall be securely anchored and keyed into the shoreline to fully enclose the area where sediment may enter the water.
3. Driven steel posts shall be used to hold the barrier in position. The maximum spacing between posts shall be 10 feet. When barrier height exceeds 8 feet, post spacing may need to be decreased.
When bedrock prevents the installation of posts, float devices may be used. Flotation devices shall be flexible, buoyant units contained in an individual flotation sleeve or collar attached to the turbidity barrier. Use solid expanded polystyrene logs or equivalent having a 49 square inch minimum end area. Do not use polystyrene beads or chips. Buoyancy provided by the flotation devices shall be sufficient to support the weight of the turbidity barrier and maintain a freeboard of at least three inches above the water surface. Refer to Figure 1.
4. The barrier and steel posts shall extend from the bottom of the waterway or waterbody to an elevation 2 feet above the anticipated high water level during the time of year and duration the barrier will be in place. The elevation shall not exceed the top of bank.
5. Ballast shall be used to hold the barrier in a vertical position. Bottom load lines shall consist of a chain incorporated into the bottom hem of the screen, of sufficient weight to serve as ballast to hold the screen in a vertical position. Additional anchorage shall be provided if necessary.
6. Danger buoys shall be used as directed by the Coast Guard or DNR permit when working in navigable waters.
7. Turbidity barriers shall be installed parallel to the direction of flow and shall not be installed across channels.
B. Material
1. Reusable components of the turbidity barrier system shall be clean and free of potential exotic species. Fabric cannot be reused.
2. Top load lines shall consist of 5/16 inch steel cable.
3. Fabric shall be selected according to the specifications in Table 1.
Source: WisDOT Spec 628.2.10.
VI. Considerations
A. The 5 feet per second flow velocity specified in Section III can be the base flow of the stream or the base flow plus the addition of storm event runoff. Base flow can be used alone for short term projects (typically one day duration, i.e. culvert installation) when the chance of precipitation is low. Longer term projects (i.e. bridge work) should consider storm flow in addition to base flow (typically the two year event).
B. If the current exceeds 5 feet per second, other methods to divert flow away from the turbidity barrier such as temporary concrete traffic barriers, coffer dams, pumping, or sheet piling should be considered.
C. Sediment that has been settled out by the turbidity barrier should only be removed if so directed by the regulatory authority because re-suspension of sediment will likely occur during the removal process. Use of polymers may help prevent resuspension of sediment. See WDNR Technical Standard 1051 Sediment Control Water Application of Polymers for further guidance.
D. Turbidity barriers are meant to manage sediment in the waterbody. The best way to prevent sediment from entering the waterbody is through the implementation of effective upland erosion control, stopping sediment transport at its source.
E. Turbidity barriers should not be used to reduce the conveyance capacity of the channel. An example is use on bridge projects where the turbidity barrier is installed adjacent to each abutment simultaneously.
F. Turbidity barriers may be installed on the banks of a waterway or waterbody if higher water levels are anticipated during construction.
VII. Plans and Specifications
Plans and specifications for installing a turbidity barrier shall be in keeping with this standard and attached detail drawing and shall describe the requirements for applying the practice to achieve its intended purpose:
A. Location of turbidity barrier.
B. Material specification conforming to standard.
C. All plans, standard detail drawings, or specifications shall include schedule sequence or notes for installation, inspection, and maintenance. The responsible party shall be identified.
VIII. Operation and Maintenance
A. Turbidity barriers shall be inspected daily and repaired if necessary.
B. Turbidity barriers shall not be removed until the water behind the barrier has equal or greater clarity than the waterway or waterbody.
C. Care shall be taken when removing the barrier to minimize the release or re-suspension of accumulated sediment.
D. To prevent the spread of exotic species turbidity barriers shall not be reused on other sites. Buoys and chains can be reused but shall be either disinfected with vinegar or cleaned with hot water greater than 104 deg. F then allowed to completely dry for a minimum period of five days. If there are any questions about the occurrence of zebra mussels, Eurasian water-milfoil, or other aquatic invasive species in a waterbody that you are working in, or intend to work in, contact your local DNR staff.
IX. References
WisDOT Facilities Development Manual: Chapter
10, Section 10, Subject 45, Turbidity Barrier
X. Definitions
Stabilized (V.A.1): Means that all land disturbing construction activities at the construction site have been completed, and that a uniform perennial vegetative cover has been established with a density of at least 70% of the cover for the unpaved areas and areas not covered by permanent structures, or that employ equivalent stabilization measures.
(Figures are available on DNR website.)
Vegetative Buffer
For Construction Sites
1054 (05/03)
Wisconsin Department of Natural Resources
