Dane County Stormwater Manual

User Tools

Site Tools

Trace:
erosion_control

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
erosion_control [2022/05/19 12:12] – adminerosion_control [2022/05/19 12:14] (current) – admin
Line 7: Line 7:
 [{{:wiki:images:conceptual_erosion.png?400|Figure 1: Conceptual model of erosion}}] [{{:wiki:images:conceptual_erosion.png?400|Figure 1: Conceptual model of erosion}}]
  
-There are a variety of strategies for minimizing soil loss from construction sites.  These include preventing soil detachment, diverting runoff around disturbed areas, and trapping sediment carried by runoff before it leaves the site.  The most important strategy for controlling construction site erosion is preventing soil particle detachment through soil stabilization.  Vegetation should be re-established as soon as possible after land is disturbed.  In the meantime, other erosion control practices, such as [[polymer and other additives|polymers]], [[erosion matting]], and [[mulching]] must be in place.  A second line of defense is to prevent runoff from contacting detached soil particles by diverting runoff around disturbed areas.  Diversions minimize the opportunity for runoff to entrain detached soil particles and carry them offsite.  Finally, when soil particles are detached and carried by runoff, practices that slow and/or trap sediment must be installed to prevent suspended sediment from leaving the site and entering water bodies.+\\ 
 + 
 +There are a variety of strategies for minimizing soil loss from construction sites.  These include preventing soil detachment, diverting runoff around disturbed areas, and trapping sediment carried by runoff before it leaves the site.  The most important strategy for controlling construction site erosion is preventing soil particle detachment through soil stabilization.  Vegetation should be re-established as soon as possible after land is disturbed.  In the meantime, other erosion control practices, such as [[polymer and other additives|Polymers]], [[erosion matting]], and [[mulching]] must be in place.  A second line of defense is to prevent runoff from contacting detached soil particles by diverting runoff around disturbed areas.  Diversions minimize the opportunity for runoff to entrain detached soil particles and carry them offsite.  Finally, when soil particles are detached and carried by runoff, practices that slow and/or trap sediment must be installed to prevent suspended sediment from leaving the site and entering water bodies.
  
 =====Performance Standards===== =====Performance Standards=====
 To minimize erosion from construction sites and protect the county’s lakes and streams from sediment pollution, it's required that plans for all construction sites include practices that meet the standards in the table below. To minimize erosion from construction sites and protect the county’s lakes and streams from sediment pollution, it's required that plans for all construction sites include practices that meet the standards in the table below.
  
-^Standard Name^Performance Requirement^Purpose^Applicability^+^Standard^Performance Requirement^Purpose^Applicability^
 |Sheet and Rill Erosion|Limit cumulative sediment deposition to 5 tons/acre/year|Minimize soil loss and prevent water quality and aquatic habitat degradation|All sites requiring an erosion control plan| |Sheet and Rill Erosion|Limit cumulative sediment deposition to 5 tons/acre/year|Minimize soil loss and prevent water quality and aquatic habitat degradation|All sites requiring an erosion control plan|
 |Gully and Streambank Erosion|Prevent gully and streambank erosion|Minimize soil loss and prevent water quality and aquatic habitat degradation|All sites requiring an erosion control plan| |Gully and Streambank Erosion|Prevent gully and streambank erosion|Minimize soil loss and prevent water quality and aquatic habitat degradation|All sites requiring an erosion control plan|
Line 23: Line 25:
 ====Table 1: Non-structural practices==== ====Table 1: Non-structural practices====
  
-^Non-Structural Practices^Applicable Standard^Site Applicability^Maintenance Requirement^Environmental Concerns^Special Consideration^+^Practice^Applicable Standard^Site Applicability^Maintenance Requirement^Environmental Concerns^Special Consideration^
 |[[Construction Scheduling]]|Sheet and Rill Erosion|Widely Applicable|Low|None|Can greatly reduce erosion from a site| |[[Construction Scheduling]]|Sheet and Rill Erosion|Widely Applicable|Low|None|Can greatly reduce erosion from a site|
 |[[Deep Tilling]]|Sheet and Rill Erosion|Widely applicable on sites where heavy grading has occurred|Very Low|None|Should be timed after grading has occurred; Buried Utilities| |[[Deep Tilling]]|Sheet and Rill Erosion|Widely applicable on sites where heavy grading has occurred|Very Low|None|Should be timed after grading has occurred; Buried Utilities|
Line 33: Line 35:
  
 ====Table 2: Structural practices==== ====Table 2: Structural practices====
-^Non-Structural Practices^Applicable Standard^Site Applicability^Maintenance Requirement^Environmental Concerns^Special Consideration^+^Practice^Applicable Standard^Site Applicability^Maintenance Requirement^Environmental Concerns^Special Consideration^
 |[[Buffer Strip]]|Sheet and Rill Erosion|Applicable when already installed|Low|None|Sufficient/suitable land area; Must be used in conjunction with other practices| |[[Buffer Strip]]|Sheet and Rill Erosion|Applicable when already installed|Low|None|Sufficient/suitable land area; Must be used in conjunction with other practices|
 |[[Permanent Diversion]]|Sheet and Rill Erosion|Widely Applicable|Moderate|Possible erosion of diversion structure if diverted runoff carries a large sediment load| Must be carefully designed to prevent property damage| |[[Permanent Diversion]]|Sheet and Rill Erosion|Widely Applicable|Moderate|Possible erosion of diversion structure if diverted runoff carries a large sediment load| Must be carefully designed to prevent property damage|
Line 43: Line 45:
 |[[Silt Fence]] and [[Silt Sock]]|Sheet and Rill Erosion|Widely Applicable|High|Sediment transport; High rates of failure if not properly installed and maintained; Disposal|Longevity, proper installation| |[[Silt Fence]] and [[Silt Sock]]|Sheet and Rill Erosion|Widely Applicable|High|Sediment transport; High rates of failure if not properly installed and maintained; Disposal|Longevity, proper installation|
 |[[Slope Drain]]|Sheet and Rill Erosion; Gully Erosion|Applicable on sites that are vulnerable to convey runoff downslope|Moderate|Possible erosion around inlet & outlet|Pipe size| |[[Slope Drain]]|Sheet and Rill Erosion; Gully Erosion|Applicable on sites that are vulnerable to convey runoff downslope|Moderate|Possible erosion around inlet & outlet|Pipe size|
-|[[Stone Check Dam]]|Sheet and Rill Erosion; Gully Erosion|Applicable to vegetated ditches and swales, Drainage areas <2 acres| Low to Moderate|Does not remove smaller suspended solids||+|[[Stone Check Dam]]|Sheet and Rill Erosion; Gully Erosion|Applicable to vegetated ditches and swales, Drainage areas <2 acres| Low to Moderate|Does not remove smaller suspended particles| |
 |[[Stone Tracking Pad]]|Sheet and Rill Erosion|Widely Applicable|Low to High|None|Cost effective; Must use >3" clear stone| |[[Stone Tracking Pad]]|Sheet and Rill Erosion|Widely Applicable|Low to High|None|Cost effective; Must use >3" clear stone|
 |[[Stone Weeper]]|Sheet and Rill Erosion; Gully Erosion|Applicable to vegetated ditches and swales, Drainage areas <2 acres|Low to Moderate|Does not remove smaller suspended particles| | |[[Stone Weeper]]|Sheet and Rill Erosion; Gully Erosion|Applicable to vegetated ditches and swales, Drainage areas <2 acres|Low to Moderate|Does not remove smaller suspended particles| |
Line 53: Line 55:
  
 [{{ :wiki:images:trapping_efficiency_1_.png?600 |Figure 2: Trapping efficiency based on Plano silt loam soil distribution}}] [{{ :wiki:images:trapping_efficiency_1_.png?600 |Figure 2: Trapping efficiency based on Plano silt loam soil distribution}}]
 +
 +\\
  
 In Dane County, it is not feasible to trap particles smaller than 5 µm from a cost/benefit and engineering standpoint.  In a pond that is two feet deep, trapping the 5 µm particle requires a settling time of 6 hours, which is feasible for pond design.  However, the particle settling time increases exponentially with decreasing particle size (Figure 3).  For example, trapping the 3 µm instead of the 5 µm particle increases the required settling time from 6 to 24 hours, but only increases the expected trapping efficiency by 5%.  Designing a pond with a settling time of 24 hours would be much more costly and require a larger land area.  Thus, a soil loss standard lower than 5 tons/acre/year would provide small additional benefit at a very high cost.  Dane County’s approach is equivalent to the intent of the performance standards for construction sites in the Department of Natural Resources’ Chapter [[https://docs.legis.wisconsin.gov/code/admin_code/nr/100/151/III/11/6m/b/2|NR 151]]. In Dane County, it is not feasible to trap particles smaller than 5 µm from a cost/benefit and engineering standpoint.  In a pond that is two feet deep, trapping the 5 µm particle requires a settling time of 6 hours, which is feasible for pond design.  However, the particle settling time increases exponentially with decreasing particle size (Figure 3).  For example, trapping the 3 µm instead of the 5 µm particle increases the required settling time from 6 to 24 hours, but only increases the expected trapping efficiency by 5%.  Designing a pond with a settling time of 24 hours would be much more costly and require a larger land area.  Thus, a soil loss standard lower than 5 tons/acre/year would provide small additional benefit at a very high cost.  Dane County’s approach is equivalent to the intent of the performance standards for construction sites in the Department of Natural Resources’ Chapter [[https://docs.legis.wisconsin.gov/code/admin_code/nr/100/151/III/11/6m/b/2|NR 151]].
erosion_control.1652976736.txt.gz · Last modified: by admin
Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki