Contributing Area for Water Quality Volume
Contributing Area for Water Quality Volume
(OP)
This is in NYS. I have a linear highway project that involves reconstructing a portion of the pavement and addition of new pavement over what is now pervious area. The work area drains to a road side swale in which we plan to construct a wet swale to address the Water quality requirements of Phase II. I also have 25 acres of hillside that drain into this swale (not across the project, just into the swale from the other side). I understand that I would need to size any feature to accommodate the contributing area or use flow diverters to intercept the hill side and direct it around the swale, but what I am wondering about is the “A” in the water quality volume required to be treated calculation. {WQv = (P)(R)(A)/12}. Since the offsite area is not going through my site is the "A" the area of my work (disturbed area so to speak) or is it the entire drainage basin going to the practice, according to the manual. You see how a simple 100’ lane widening can result is huge water quality volumes to be treated if the offsite area going to the practice is significant.
Thanks for any help....
Thanks for any help....
RE: Contributing Area for Water Quality Volume
Will your regulator give you a little wiggle room? Infill and road widening sometimes get treated less strictly especially if you might have to condemn land for a treatment option.
RE: Contributing Area for Water Quality Volume
Thanks
RE: Contributing Area for Water Quality Volume
RE: Contributing Area for Water Quality Volume
RE: Contributing Area for Water Quality Volume
RE: Contributing Area for Water Quality Volume
The only problem with that is that the treatment method selected is highly dependent on inflow rate and quantity. I do not work with the NY reg.s but am familiar with them and much of the East Coast and West Coast reg.s. All of the research that I have been able to find that they base their water quality calculations on are based on the treatment method sized for the total inflow shed.
RE: Contributing Area for Water Quality Volume
RE: Contributing Area for Water Quality Volume
I was a little confused. I read about the diversion but then dmx stated:
"... Since the offsite area is not going through my site is the "A" the area of my work (disturbed area so to speak) or is it the entire drainage basin going to the
practice, according to the manual. ..."
It seemed to contradict the diversion statement. This is the typical question since sometimes there is a thought that since only some of the water needs treatment,however since residence time is a principal design consideration in wet swales I jumped to the conclusion that all water would enter the "practice" which I defined in my head as the swale. A lot of stormwater manuals call treatment options practices so I have some excuse.
I like your comment especially because I simply cannot imagine that an agency could make you treat offsite drainage that you divert around your project and your treatment device. Never even considered that a question before. I need a bigger box.
RE: Contributing Area for Water Quality Volume
1. Calculate the WQ volume based on all the flow coming to the BMP
- or -
2. Divert the flow that you don't want/need to treat around the BMP
I don't think you can just disregard the flow from an offsite area because the volume affects the treatment. Depending on the topography, it could even cause resuspension of the solids that you are trying to settle out.