Sediment Controls

Sediment ControlsHow they work

Tom Schneider, CPESCPresident SCIECAEPA Region 6 MS4 ConferenceJuly 7, 2011San Antonio, Texas

Removal of the sediment from the storm water runoff prior to it reaching surface waters.

Defining the problem

Prevent sediment from exiting the site. Sediment control are utilized from the time

the soil is disturbed until the construction activity has ceased. At which time either temporarily or permanently erosion control can occur.

Erosion control cannot be utilized to control sediment for active areas of disturbance on construction sites.

Purpose of the Sediment Control on a construction site

Topography◦ Length of slope◦ Percent of slope

Soil type◦ Sand ◦ Silt ◦ Clay

Things that affect Sediment Controls

Storm type◦ Volume of runoff◦ Rate of runoff

First we need to understand how the sediment control will remove the sediment.◦ Sedimentation ◦ Filtration

Predicting the Performance

Sediment Controls Sedimentation Filtration

What is the one thing that we can look too that will give us a conclusive prediction of the effectiveness of a sedimentation control?

Sedimentation

Time

When runoff is detained a sufficient amount of time the sediment will settle out of the storm water runoff and will not exist the site.

If the runoff exits the control prior to the required settling time, sediment will exit the control with the runoff.

Effects of Time

I think they need a little more time.

What determines the amount of time that the runoff will need to be detained?

Soil Type

How Much Time

Soil

38 seconds = 1 foot

Sand

230 days = 1 foot

Clay

33 minutes = 1 foot

Silt

Stoke’s Law

Sediment Controls Sedimentation

◦ Time required Soil type

% sand % silt % clay

◦

Filtration

Determine the flow rate to the control◦ Every control location will have a unique flow rate.

Geographic location Topography Soil type LOCATION OF THE CONTROL ON THE SITE

Determines the drainage area of the control

TR55◦ Is an accepted flow rate model used by engineers

for the design of storm drainage systems.

Designing the Control for Time

Relate the Time required to the Flow rate into the control.◦ Based on the sites conditions I have flow rate of 2 cfs

(cubic feet per second).◦ Based on the sand silt soil type I need to retain the

runoff 33 minutes (1980 seconds)◦ 1980 seconds x 2 cfs= 3960 cf Capacity◦ 3960cf / 2cfs = 1980 seconds◦ Capacity = Time◦ Based on the location of the control and the soil type

of the site if the control detains 3960 cf of storm water runoff it will provide the amount of time required to remove the sediment.

Designing the Control

Detain not Retain

2cfs2cfs

1,980 seconds




◦ Capacity requirement Flow rate Time required

Filtration

Determining the capacity of the control Configuration

Height Length Aspect to the topography

Capacity (volume) equals Time◦ The larger the volume the more time provided

Designing the Control

Geometry

sfA

A

HBA

40

'2'20

Rectangle a of Area

sfA

A

A

HBA

20

'2'10

'2'205.

5.

Triangle a of Area

cf

sf

V

V

LAV

2000

'10020

Volume

Designing or Evaluating the Control

20 ft

10 ft

685

686

687

688

689

Scale: 1/4" = 1'

Height of Control: 2 feet

Base:

Height:

Length:

A = .5 x___x___ A = _______

Cp = A x L Cp =____x____ Cp =______

Calculate Volume

A = .5 x B x H

Profile View

Side Area

sfA

A

A

HBA

9

'2'5.4

'2'95.

5.

Length

20 ft

10 ft

685

686

687

688

689

Scale: 1/4" = 1'


Base:

Height:

Length:

A = .5 x___x___ A = _______

Cp = A x L Cp =____x____ Cp =______

Calculate Volume

A = .5 x B x H

20 20

22

99 9

9 180

Side Area

sfA

A

A

HBA

9

'2'5.4

'2'95.

5.

20 ft

10 ft

685

686

687

688

689

Scale: 1/4" = 1'


Base:

Height:

Length:

A = .5 x___x___ A = _______

Cp = A x L Cp =____x____ Cp =______

Calculate Volume

A = .5 x B x H

Profile View

20 ft

10 ft

685

686

687

688

689

Scale: 1/4" = 1'


Base:

Height:

Length:

A = .5 x___x___ A = _______

Cp = A x L Cp =____x____ Cp =______

Calculate Volume

A = .5 x B x H32

20

3 2 3

3 20 60

Rotate the Control

680681

682

683

684

3 ft

5 ft

20 ft

10 ft

Predictable performance.

The solution is not more rows of the control the solution is to provide more time

Does it matter what the control is made of?

Why Blame the Control

Not really

Hay bales, Rock berm, Concrete, Straw waddles, Marshmallows.

The result will be the same .

Location, Location, Location

The bottom of the slope is not always the best location





◦ Capacity provided Height of control Topography

Filtration

Based on the soil I know how long I need to retain the runoff.

Based on the location of the control I know the flow rate of the runoff to the control.

Based on the soil type and flow rate I know the volume of water the control needs to detain to be successful. (volume=time)

Based on the location of the control I know the volume of water that my control will detain. (Time = Effectiveness)

Will the Control Work

The term "efficient" is very much confused and misused with the term "effective". In general, efficiency is a measurable concept. In several of these cases, efficiency can be expressed as a result as percentage of what ideally could be expected, hence with 100% as ideal case.

Compare “effectiveness” , which is a vague, non-quantitative concept, mainly concerned with achieving objectives.

Efficiency and Effectiveness

For sedimentation controls efficiency and effectiveness are close to the same thing and are determined by amount of time the runoff is detained and the soil type contained within the drainage area of the control.

Filtration controls efficiency and effectiveness are not as closely connected. The efficiency can be high and the effectiveness be low.

Efficiency and Effectiveness

Soil Percent Seconds Minutes

Hours Days

Sand 97% 38 0.6333 0.010556 0.000439815

Silt 3% 1980 33 0.5 0.022916667

Clay 0% 19,872,000 331,200 5,220 230

Lopeno

Flow rate of 2cfs

1,980 seconds x 2 cfs = 3,960 cf3,960cf/2cfs=1,980 seconds

Control volume 3,960 cf

What percent of the sediment load did the control stop?


Hours Days

Sand 66% 38 0.6333 0.010556 0.000439815

Silt 24% 1980 33 0.5 0.022916667

Clay 10% 19,872,000 331,200 5,220 230

Saucel

Flow rate of 2cfs

19,872,000 seconds x 2 cfs = 39,744,000 cf39,744,000cf/2cfs=19,872,000 seconds

Control volume 3,960 cf or


1980 seconds


Hours Days

Sand 10% 38 0.6333 0.010556 0.000439815

Silt 22% 1980 33 0.5 0.022916667

Clay 68% 19,872,000 331,200 5,220 230

Kaufman Clay

Flow rate of 2cfs

19,872,000 seconds x 2 cfs = 39,744,000 cf39,744,000cf/2cfs=19,872,000 seconds

Control volume 3,960 cf or


1980 seconds






◦ Effectiveness Capacity provided Soil type

Filtration

Permit Requirements

Performance driven requirement based on NTUs (Nephelometric Turbidity Units)

Controls will need to be designed to provide for the removal of the sediment not designed to meet the permit requirements

NTUs correlate more to the color of the soil than sediment load in the soil.

Effluent Limitation Guidelines






◦ Effectiveness Capacity provided Soil type Soil color

Filtration

What is the one thing that we can look too that will give us a conclusive prediction of the effectiveness of a filtration control?

There is not one. We need to look at

◦ Storm water runoff flow rate◦ Soil type◦ Filter media opening size◦ Filter media flow rate◦ Size of the filter area

Filtration

Determine the flow rate to the control◦ Every control location will have a unique flow rate.

Geographic location Topography Soil type LOCATION OF THE CONTROL ON THE SITE

Determines the drainage area of the control

TR55◦ Is an accepted flow rate model used by engineers

for the design of storm drainage systems.

Storm Water Flow Rate

Soil type will determine what filter media would be appropriate.

Soil Type

Sand Silt Clay

Criteria for selecting the correct filter media◦ What size soil particles will pass through the filter.◦ Flow rate of the filter media (how much water will

pass through it in a given time per square foot).◦ How many square feet will be able to filter runoff.

Filter Media

Soil Percent Media 1 Media 2

Media 3 Media 4

Sand 10% Yes Yes Yes Yes

Silt 22% Yes Yes Yes No

Clay 68% Yes No Yes No

Kaufman Clay


No one knows all we know is the efficiency of the filter media.

100% 32% 100% 10%







Filtration◦ Efficiency

Soil size and distribution Filter media opening size

Flow Rate of MediaSoil Percent Media 1 Media

2Media 3 Media 4




Efficiency 100% 32% 100% 10%

10 GPM/ 0.02cfs

35 GPM/ 0.077cfs

2GPM/ 0.0044cfs

150GPM/ 0.33 cfs









◦ Capacity Flow rate of media

20 ft

10 ft

685

686

687

688

689

Scale: 1/4" = 1'


A1 = .5 x__x__ A1 =___

A3 = B x H A 3=__x__

Ta = A1 + A2 + A3

A1 = .5 x B x H

A2 = .5 x__x__ A2 =___A2 = .5 x B x H

A3 =___Flow rate (Fr): 35 gpm/per min

Fa = Ta x Fr

Fa=___x___

Fa=_______

A1A2

A3

Calculate Filtration Rate

Calculate Filtration Capacity

9 ft

20 ft

20 ft

10 ft

Side Area

sfA

A

A

HBA

9

'2'5.4

'2'95.

5.

Front Filtration Area

sfA

A

HBA

H

B

40

'2'20

'2

'20

20 ft

10 ft

685

686

687

688

689

Calculate Filtration Rate

Scale: 1/4" = 1'


A1 = .5 x___x___ A1 = _______

A3 = B x H A 3=____x____

Ta = A1 + A2 + A3

A1 = .5 x B x H

A2 = .5 x___x___ A2 = _______A2 = .5 x B x H

A3 = _______Flow rate (Fr): 35 gpm/sf

Fa = Ta x Fr

Fa = x

Fa = 20 402

2 99

99 582 35

2030









◦ Capacity Flow rate of media Filter area

Filter CapacitySoil Percent Media 1 Media 2 Media 3 Media 4




Efficiency 100% 32% 100% 10%

Flow Rate 10 GPM/ 0.02cfs

35 GPM/ 0.077cfs

2GPM/ 0.0044cfs

150GPM/ 0.33 cfs

Area 58 Sf 58 Sf 58 Sf 58 Sf

Capacity 580gpm/1.288cfs

2030gpm/ 4.51cfs

116gpm/0.257cfs

8700gpm/ 19.33cfs









◦ Capacity Flow rate of media Filter area Filter Capacity

Importance of volume capacity

Once the volume capacity of the filtration control is exceeded the sediment laden storm water runoff will bypass the control and carry the sediment with it.

Percent of Runoff TreatedSoil Percent Media 1 Media 2 Media 3 Media 4




Efficiency 100% 32% 100% 10%


35 GPM/ 0.077cfs

2GPM/ 0.0044cfs

150GPM/ 0.33 cfs



2030gpm/ 4.51cfs

116gpm/0.257cfs

8700gpm/ 19.33cfs

Flow rate to the control

2cfs 2cfs 2cfs 2cfs

Percent treated 64% 100% 12% 100%










◦ Percent treated Filter capacity Flow rate of runoff

Effectiveness of the controlSoil Percent Media 1 Media 2 Media 3 Media 4




Efficiency 100% 32% 100% 10%


35 GPM/ 0.077cfs

2GPM/ 0.0044cfs

150GPM/ 0.33 cfs



2030gpm/ 4.51cfs

116gpm/0.257cfs

8700gpm/ 19.33cfs


2cfs 2cfs 2cfs 2cfs

% of runoff treated 64% 100% 12% 100%

% sediment retained 64% 32% 12% 10%

Effectiveness of the controlSoil Percent Media 1 Media 2 Media 3 Media 4




Efficiency 100% 97% 100% 75%


35 GPM/ 0.077cfs

2GPM/ 0.0044cfs

150GPM/ 0.33 cfs



2030gpm/ 4.51cfs

116gpm/0.257cfs

8700gpm/ 19.33cfs


2cfs 2cfs 2cfs 2cfs

% of runoff treated 64% 100% 12% 100%

% sediment retained 64% 97% 12% 75%










◦ Percent treated Filter capacity Flow rate of runoff

◦ Sediment retained Efficiency Percent treated

The control (sedimentation and filtration) must provide not only adequate storage volume for the storm water runoff but also for the sediment that it will retain.

If the control is designed to only provide for the storm water runoff volume then once the sediment starts to be retained the effectiveness of the control will be reduced.

MUSLE is the correct model to predict sediment load on construction sites.

Sediment Load

Sediment Load Models

◦ USLE The equation that predicts longtime average soil losses and

runoff from specific areas in specific cropping and management systems. The erosion values reflected by these factors can vary considerably due to varying weather conditions. Therefore, the values obtained from the USLE more accurately represent long-term averages.

◦ RUSLE RUSLE has the same formula as USLE, but has several

improvements in determining factors. ◦ RUSLE2

model that predicts long-term, average-annual erosion by water and can be used for a broad range of farming, conservation, mining, construction, and forestry sites.

◦ MUSLE Predicts the amount of sediment delivered to a specified point

during a specific storm event

Sediment Controls Sedimentation Efficiency

◦ Is dependent on the time that the runoff is detained and soil type.

Capacity◦ Determined by volume

of water detained by the control.

Effectiveness is tied to Efficiency

Filtration Efficiency

◦ Determined by soil type and filter opening size

Percent treated◦ Determined by wetted

area and flow rate of filter.

Effectiveness is equal to Efficiency x Percent treated

Sediment Controls

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