Dewatering
Dewatering
(OP)
We have a 4ac construction site consisting of mass excavation, utility installation, etc where dewatering techniques are required. The plan is to discharge to an existing roadside ditch which has been designed with bio-bags for ESC.
What is normally the proper technique to accomplish this? Are sediment removal products such as dewatering bags always used? I have suggested to use dewatering bags and add bio bags at smaller intervals within the ditch. Contractor also needs to put this in their SWPPP. Any other hints of what the best techniques are to avoid erosion and contain sediment when dewatering?
What is normally the proper technique to accomplish this? Are sediment removal products such as dewatering bags always used? I have suggested to use dewatering bags and add bio bags at smaller intervals within the ditch. Contractor also needs to put this in their SWPPP. Any other hints of what the best techniques are to avoid erosion and contain sediment when dewatering?





RE: Dewatering
I have seen the results of one of the methods listed in the publication linked below using polymer enhanced BMP applications in a manmade trench where a sediment pond was pumped. It seems pretty effective but the polymers used are site specific so you would have to send a sample to the vendor to verify which polymers to use which would take additional time. Also this publication is not really a design guide in the sense that it does not tell you how long of a trench or how far to space floc logs or how many. Possibly the vendor could assist with this.
http://www.siltstop.com/altbmpguide/closedloop/WT....
RE: Dewatering
Do you have the ability to design a perforated riser or use a skimmer?
RE: Dewatering
I have used ones that are 10'x10' up to 25'x100' (we used 8 of the larger ones at a single site,let them drain out typically into a sediment trap, and then buried them in a non-structural fill area). Several environmental supply companies in the states make them and have the literature.
RE: Dewatering
The best management practice will probably be a filtration system. The bags may not be adequate.
http://www.clearcreeksystems.com/temporary/best.ht...
RE: Dewatering
usually dewatering bags, polymer treatment and floc etc is used when the discharge is potentially running back into a stream.
RE: Dewatering
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Dewatering
RE: Dewatering
What are you doing for permanent SWM? Is there any reason why you aren't doing a sed basin or trap?
RE: Dewatering
It is a BIG NO NO to pump water from dewatering into a ditch without any BMPs since a ditch is classified as a conveyance system. I have seen many sites where the contractor leaves out those controls. That is why it is typical to have several control in case one fails. Problem with direct pumping into a ditch is you can over-top your other controls if pumping more water then can be handled. Bio-Bags, are you referring to something similiar to a wattle, coir log or along those lines, used to make a check dam?
In my SWPPPs i typically call out a dewatering bag that then drains onto the controls site that goes into a vegetated swale and through the perimeter control, let is sheet flow into a ditch from the dewatering bag with wattles, check dams, ect., or if in area with curb/gutter, place wattles in curb line and then place drop inlet protector (witches hat).
Do not place a silt fence in a concentrated flow, they are not designed for that. If you have a detention pond onsite you can pump to that as well.