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Ask the Experts : Frequently Asked Questions


Need help with an erosion control installation? Aren't sure what erosion control solution is best for you? Check out our Frequently Asked Questions sections below. If you can't find what you're looking for, Ask the Experts.

What is Erosion control?
What is the best installation for me?
How to select the right product?
How to know when to use sandbags or gravel bags?
How long do erosion control blankets last?
What does BFM stand for?
What is the difference between hydroseeding and BFM?
To hydroseed or erosion blanket is the question?
How to calculate how many bags needed?
What does BMP stand for?
What is a SWPPP?
What is NPDES?
How long do gravelbags need to stay in place?
How long do sand and gravel bags last?
Do I want burlap or poly type bags?
Why aren't straw bales recommended?
Is dirt/silt really considered a pollutant?
What is the difference between a fiber roll and a wattle?
What is the difference between sediment control and erosion control?
How often do I have to do storm inspections or test my storm water run off?




What is Erosion control?

Erosion control is any control practice that protects and prevents soil particles and surface from being detached by wind, water and rain. Also called "soil stabilization", erosion control consists of preparing the soil surface and protecting it through a number of methods. [back]


What is the best installation for me?

The best installation for your site will depend on the length of time you will need the protection for. Is the protection to be temporary or permanent? There are a variety of concepts that can provide you with the proper protection. Often time, a combination of several concepts works best. [back]


How to select the right product?

Determining whether it is a sediment control practice or an erosion control practice is important. Sediment control is applied knowing that erosion is going to occur and containment will be needed. Erosion control is a source control, or in other words, a practice to maintain the soil in its original location and state. Cost and duration are also important factors. Applications and needs vary so dramatically, that each individual case needs to be reviewed and selection determined based on the particular need. Our Ask the Experts link can provide insight and help. [back]


How to know when to use sandbags or gravel bags?

Sandbags are often used as mass elements and used on soil surfaces. Gravel bags are used in areas for desilting, such as street chevrons, and for protecting catch basin inlets and drains. If roads are graded but not paved, sand bags can be used. However, if roads are graded and paved, gravel bags should be used. [back]


How long do erosion control blankets last?

It depends on the erosion control blanket. The duration of the natural fiber blankets can last for 6-36 months in optimal conditions, depending upon the type of blanket selected. [back]


What does BFM stand for?

Bonded Fiber Matrix. A combination of crushed wood fibers, natural, and man made binders to create a product applied through a hydraulic spray machine to cover exposed or disturbed soil areas. It is a cost effective means to cover large areas with a concept comparable to erosion blankets. [back]


What is the difference between hydroseeding and BFM?

Hydroseeding includes a seed mix with wood fiber mulch, an organic binder, and fertilizer. Both are hydraulically applied. Hydroseeding can use BFM instead of the wood fiber mulch and organic binder for soil stabilization and protection from the impact of rain. BFM is often used on its own. BFM has a binding agent that binds the wood fibers together as well as a tackifying agent that adheres the material to the soil particles. [back]


To hydroseed or erosion blanket is the question?

The question that needs to be asked to answer this question is how long the temporary erosion control is needed. Hydroseed/hydromulch does not usually last as long as erosion control blankets. Prior to every rain season, the hydromulch may need to be reapplied. Established hydroseed into adequate plant cover gives a more permanent protection. With most erosion blankets, protection may be provided for several rain seasons. [back]


How to calculate how many bags needed?

Typically, one filled gravel/sand bag is used for every linear foot of protection needed based on one bag wide by one bag high configuration. Alternative configurations will require additional calculation and bags. I.e. A pyramid of bags two bags high and two bags wide at the base will require three bags for each linear foot of protection needed. [back]


What does BMP stand for?

Best Management Practice, it is a term associated with those practices selected to manage and maintain soil erosion and storm water run off quality. It was created in association with the Clean Water Act of 1972 and the resulting National Pollution Discharge Elimination System developed as application of the law. [back]


What is a SWPPP?

SWPPP stands for Storm Water Pollution Prevention Plan. It is often presented in the form of a project specific manual. For every construction site that is 1 acre or greater, industrial facilities, mines, landfills, or water treatment programs there must be a SWPPP manual prepared which is required to be on site at all times. The SWPPP includes the owner(s) and operator(s) of the site, functions of the project, schedule for the project, estimated amount of disturbed area, site location, flow of water on the site, identification of pollutants, types and locations of structural and non-structural BMP's (including an erosion control plan and storm response program), site inspection and schedule, post-construction management measures, etc. The SWPPP is not just the erosion control plan, it includes all the other aspects listed above. The SWPPP must also be reviewed and certified each year and any changes made to the site or SWPPP must be done to maintain the site in compliance with the Clean Water Act and the NPDES. Changes are done via the form of an amendment. [back]


What is NPDES?

National Pollution Discharge Elimination System. It is a result of the Clean Water Act of 1972 (CWA). It is the program developed for application of the laws defined in the CWA. [back]


How long do gravelbags need to stay in place?

Gravel bags, or other BMP's, that are used to protect catch basin inlets or drains need to be in place until the site construction activity is complete, has achieved 70% of vegetated coverage, and has been released from participation in the water quality requirements of the governing agency for the project or the water quality permit provider. [back]


How long do sand and gravel bags last?

It depends on where they are placed and the type of bag. Poly bags often last longer than burlap bags. Bags that are installed in a street area usually do not last as long as bags placed outside of traffic since they are subject to damage by vehicles driving over them. Burlap bags on asphalt do not last as long as those installed on soil. The oils from the pavement cause them to breakdown more quickly. Projected duration of poly bags are 6-9 months in optimal conditions and for burlap bags, up to 6 months in optimal conditions. The bags are engineered to breakdown under UV exposure to eliminate any long term impacts. [back]


Do I want burlap or poly type bags?

First, you want to check the specification of the city in which you will be placing the bags. Some cities allow only certain types of bags. The difference between the two types of bags is the material from which they are made. Poly bags will last longer under UV and rain degradation. Poly bags often come in bright colors, such as orange or yellow, which provide visual recognition when placed in a street area. Burlap bags perform best when used in disturbed soil area where they will remain in place for an extended amount of time. Poly bags are usually preferable. [back]


Why aren't straw bales recommended?

Straw bales have limits for application. Too often they are selected for use in situations where they are not best suited. Straw bales are not recommended for protection of catch basin and drain inlets or in concentrated flow areas such as swales, ditches, or streams. In these conditions, they are too easily undermined. Proper installation requires a sufficiently deep setting trench, installation on their side with the strings (baling twine) not in contact with the soil, and a minimum of at least 2 wood stakes driven through each bale and at least 18” into the ground. Bales must be installed very tightly together, end to end, with no gaps at all. The setting trench must be backfilled and compacted on the up-stream side. There are better performing and cost effective products for the typical applications of straw bales. Straw bales are best used, by spreading as a covering or mulch layer, over disturbed soil areas, or recently seeded areas. [back]


Is dirt/silt really considered a pollutant?

Absolutely! Silt discharging off a site is considered a pollutant. The accelerated loss and amounts of silt loss from disturbed soils in construction or farming create a huge impact of downstream or storm drain systems. The silt loading can often contribute to stream morphology and the associated changes. [back]


What is the difference between a fiber roll and a wattle?

There is usually no difference. These are typically made from straw (rice or wheat) filler. However, other materials such as flax, wood fibers, coconut fibers and other similar materials are used in the manufacture of the encapsulating mesh tubular rolls. [back]


What is the difference between sediment control and erosion control?

Sediment control usually occurs after erosion has occurred and where inadequate or no erosion control was installed or properly designed and installed. Sediment control are those practices and devices used to manage the discharge waters and soils that have been displaced by erosion that has occurred on site. Erosion control prevents erosion from occurring in the first place. Erosion control is a source control, or in other words, concepts and practices to maintain the soil in its original location and state. [back]


How often do I have to do storm inspections or test my storm water run off?

Per the EPA, a site inspection must be conducted every 7 days OR at least once every 14 calendar days and within 24 hours of the end of a storm event of 0.5 inches or greater.

Per the California regulations, a storm inspection needs to be completed 24 hours prior to a 40% chance of 0.25 in. of rain or more. A post storm inspection needs to be completed 24 hours after the end of a 0.25 in. rain event or greater. If rain persists for longer than 24 hours, an interim storm inspection needs to be completed every 24 hours.

Currently, the only time you need to test your storm water runoff is when there is evidence of a breech of any BMP's on site or visible inspection of pollutants in the water (i.e. milky or unclear wwater due to a broken bag of concrete or paint spill, oily water, excessive silt, etc.) or if your site empties directly into a listed 303d body of water. [back]