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
Conservation Practice Standard
Note: Words in the standard that are shown in italics are described in IX. Definitions. The words are italicized the first time they are used.
I. Definition
An area of dense vegetation1 intended to slow runoff and trap sediment. Vegetative Buffers are commonly referred to as filter or buffer strips.
II. Purpose
The purpose of this practice is to remove sediment in sheet flow by velocity reduction.
III. Conditions Where Practice Applies
This practice applies to areas where sediment delivery is in the form of sheet and rill erosion from disturbed areas.
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 a vegetative buffer. 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.
Vegetative Buffer
Disturbed Area ↓Direction of Flow↓
Width
↓
←———Length ——————→
A. The vegetative buffer shall be located along the entire length of the down slope edge of the entire disturbed area for which the practice is being applied.
B. The vegetative buffer shall be located on the contour.
C. The width of the vegetative buffer shall have slopes less than 5%.
D. The disturbed area draining to the vegetative buffer shall have slopes of 6% or less.
E. The vegetative buffer shall have a minimum width of 25 feet. 25 feet is adequate for disturbed areas up to 125 feet upslope from the vegetative buffer. An additional one foot of width shall be added to the buffer for every 5 feet exceeding 125 feet upslope of the disturbed area draining to the vegetative buffer.
F. To minimize compaction and destruction of the vegetative cover, designate the vegetative buffer as an area of no disturbance. Construction equipment shall be excluded from the designated area. Vegetative buffers shall be clearly shown on plans and marked in the field.
G. Vegetative buffers shall be densely vegetated prior to upslope soil disturbance.
VI. Considerations
A. Maintaining sheet flow is critical to the function of a vegetative buffer. In some conditions, a level spreader may need to be constructed at the upslope side of the vegetative buffer to minimize concentrated flow.
B. Vegetative buffers may require large land areas compared to other erosion control practices.
C. Trees should not be cut down to establish a vegetative buffer. Other erosion control measures are preferred.
VII. Plans and Specifications
A. Plans and specifications for vegetative buffers shall be in keeping with this standard and shall describe the requirements for applying the practice to achieve its intended purpose. The plans and specifications shall address the following:
1. Location of vegetative buffer.
2. Limits and slopes of disturbed area and any additional contributory drainage area.
3. Dimensions and slope of vegetative buffer.
B. 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. Vegetative buffers shall be inspected for proper distribution of flows, sediment accumulation and signs of rill formation. Vegetative buffers shall at a minimum be inspected weekly and within 24 hours after every precipitation event that produces 0.5 inches of rain or more during a 24-hour period.
B. If the vegetative buffer becomes silt covered, contains rills, or is otherwise rendered ineffective, other perimeter sediment control measures shall be installed. Eroded areas shall be repaired and stabilized. Repair shall be completed as soon as possible with consideration to site conditions.
C. A stand of dense vegetation shall be maintained to a height of 3–12 inches.
D. Prior to land disturbance the perimeter of vegetative buffers shall be flagged or fenced to prevent equipment from creating ruts, compacting the soil and to prevent damage to vegetation.
IX. Definitions
Dense vegetation (I): is defined as an existing stand of 3–12 inch high grassy vegetation that uniformly covers at least 90 % of a representative 1 square yard plot. Woody vegetation shall not be counted for the 90% coverage. No more than 10% of the overall buffer can be comprised of woody vegetation.
Level Spreader (VI.A): Level spreaders disperse flows over a wide area, dissipating the energy of the runoff and creating sheet flow. Common types of level spreaders are weirs and stone trenches.
Sheetflow (II): Sheet flow is over plane surfaces, where runoff water flows in a thin uniform sheet across the land before it collects in a concentrated flow.
Sheet and Rill Erosion (III): Sheet and rill erosion is the removal of soil by the action of rainfall and shallow overland runoff. It is the first stage in water erosion. As flow becomes more concentrated rills occur. As soil detachment continues or flow increases, rills will become wider and deeper.
Width (V.E): Is measured in the direction of flow.
Frost-Protected Shallow Footings
In lieu of frost walls, the code recognizes frost-protected shallow foundations designed per ASCE 32, "Design and Construction of Frost-Protected Shallow Foundations". The department also recognizes the similar design standards of U.S.HUD "Design Guide for Frost-Protected Shallow Foundations", available for free download from
www.huduser.org/publications/destech/desguide.html and summarized below. Consult it or the ASCE standard for full design and installation information, including a more flexible, detailed design method that should be used for heated buldings with attached, unheated garages.
Note that both standards offer design methods for both heated and unheated buildings. For heated buildings, the designs rely upon containing the building's heat under the footings to avoid frost heaving. In the case of unheated buildings, the designs rely upon containing the earth's natural warmth under the footings and slab by the use of more extensive insulation. (For both design approaches, compliance with their frost-protection requirements is not necessarily the same as compliance with the ch.
SPS 322 Energy Conservation standards for slab-on-grade designs.)
Because the simplified heated building design methods rely upon buildings, including attached garages, with at least a 63 degree internal temperature, it is important the building designer consult with the owner regarding their intended use. Even if the initial owner plans to keep the building heated throughout the winter, future owners may use it otherwise. Therefore, the designer should be sure to communicate the operational needs of the building through means such as building placarding, notating the Rescheck Energy Report, and/or recording relevant information on the property deed. Failure to do so may cause severe structural damage to the building if future owners do not keep the building heated.
Unheated Building Design
1 Also see s.
SPS 322.33 for additional slab-edge insulation requirements.
2 Units are degrees Fahrenheit. See estimate provided on Mean Annual Temperature Contour Map.
3 Air freezing index shall be based on maximum year expected for a 100-year return period. See estimate provided on AFI Contour Map.
4 Ground insulation to the building interior can be extended beneath the entire slab where it is desired to protect the entire slab from frost heave action.
5 Ground insulation to the building interior can be in one horizontal plane (as shown in the detail) and covered with non frost-susceptible fill or the insulation maybe placed directly beneath the slab.
6 Insulation thickness recommendations are for extruded polystyrene (XPS) insulation.
