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9 Cards in this Set

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When can a silt fence be used or not used?

To treat sheet flow only. not concentrated flows. Where the size of the drainage area is no more than one-quarteracre per 100 feet of silt fence length; the maximum gradientabove the barrier should be less than 2:1. Use around the disturbed area.

Where is a silt fence placed?

An effort should be made to locatesilt fence at least 5 feet to 10 feet beyond the toe of slope. perpedicular to slope.

Four factors affecting soil erosion potential

- soil type - particle size/gradation/structure/permeability


- vegetative cover


topography - slope length/gradient/orientation


climate (precip - frequency/intensity/duration)

What are the basic strategic goals of the development of an erosion and sediment control plan?

1) Erosion Control - keep the soil in place - minimize erosion in disturbed areas


2) Sediment Control. Minimize off-site transport of sediment - capture sediment from disturbed areas





What are the basic runoff considerations when developing an erosion and sediment control plan?

1) review existing runoff patterns


2) review post-development runoff patters


3) determine how to manage runoff as project is developed. Sequencing.




Runoff from undisturbed areas should be diverted from newly graded areas until they are stabilized! Runoff from disturbed areas should be captured!

What are three main factors that should be considered when designing a Retention pond?

1) Maximize flow length between inlet and outlet. This extends the flow path before the water exists and increases the time for sedimentation and pollutant settlement. 3:1 length to width ratio.


2) Pond should be expanded gradually (in width) in the direction of flow. water entering the pond spreads out uniformly and displaces existing water, eliminating dead zones.


3) Pool depth between 4-8'.

What are the three main factors to be considered when designing a DETENTION basin?

1) Length-to-width ratio not as critical as in a retention pond, but an elongated form is still preferred. Flow length from inlet and outlet should be maximized.


2) Side slopes should not be steeper than 3:1. Less steep preferred. Floor should have 2% min slope toward the outlet. Provide access 10' wide.


3) a low-flow channel should be provided to reduce drying time and improve usability.

Should infiltration devices remove sediment and particulates?

Not really... the will clog. Sediment should be removed by the use of filter strips or sediment traps before entering infiltration device.

What might be the main differences between and infiltration (pond) basin, detention basin, and retention basin?

They are practically the same. However a detention basin is sloped to drain and the soil may not have good permeability. It may have a low flow channel as well.




The bottom of an infiltration basin would be flatter, not include a "low flow" channel, and may include a settling basin and level spreader on the inlet.




A retention basin may have an impermeable liner and would create a permanent pool, which would only be released if water level reaches above drain outlet (or over spillway).