I recently read the following: "check the quantity of freeboard below the [catch]basin hood." In this context, is "freeboard" to be understood as the available holding capacity (of a particular catch basin) before the water it collects reaches the level of the overflow line?
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Catch basin-freeboard-concept
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Thank you CVG for your response. I do agree with you, but that would be the definition of freeboard. Please note, however, that the quoted language is from an RFP. And within the context of that statement it seems to imply something else.
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Yes, it looks that way.
Or, it may well be that the definition is "expanded" to mean volume. That is, once the vertical distance--freeboard--is measured or determined (the rpf deals with existing CBs), a volume can be calculated (the holding capacity before it reaches the flowing) for each CB.The sum of those volumes of all CBs evaluated will give you a total holding capacity of water collected before the water collected is conveyed. In a sense, freeboard although a length, it implies a volume; because that lenght may associated with 2 other dimensions of a 3D-structure (CB may be squared, rectangular or circular; freeboard in a channel, the "volume" would be width X length, and so on...)
Thank you so much for your input.
Or, it may well be that the definition is "expanded" to mean volume. That is, once the vertical distance--freeboard--is measured or determined (the rpf deals with existing CBs), a volume can be calculated (the holding capacity before it reaches the flowing) for each CB.The sum of those volumes of all CBs evaluated will give you a total holding capacity of water collected before the water collected is conveyed. In a sense, freeboard although a length, it implies a volume; because that lenght may associated with 2 other dimensions of a 3D-structure (CB may be squared, rectangular or circular; freeboard in a channel, the "volume" would be width X length, and so on...)
Thank you so much for your input.
catch basins that I am familiar with do not store any water before discharging. They begin to discharge as soon as any water enters the basin. perhaps you are thinking of some other type of catch basin with a large sump below the outlet pipe.
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cvg--The CBs I am dealing with are installed in large cities. And from the bottom of these (there are various types) basins to the bottom lip of the pipe (usually 12" dia. pipe) that connects the CB to a nearby sewer, the minimum design height is 3 feet (4 feet is typical). As with time CBs will fill (debris, etc.) that height is reduced, thus reducing that available volume--holding capacity. These CBs require maintanence; they are opened and cleaned.
cntw1953--you are correct, in open channel flow that is the freeboard.
cntw1953--you are correct, in open channel flow that is the freeboard.
I too work on storm drains in "large cities", they rarely if ever contain sumps and so the term freeboard to describe the depth of the sump is completely foreign to me. Standard designs for the cities I have worked with do not allow a sump.
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I think that maybe the RFP is after all correct. The purpose of a freeboard is to manage a "surge" in whatever structure they're used. If you think about it, a "small" rainstorm may not bring about enough water that would reach the point of discharge (pipe) of the catch basins I am dealing with and therefore what the rfp calls the "quantity of freeboard" (calculated as the following volume: height from bottom of CB to bottom of pipe x area of cb) is in fact handling the surge. If it continues raining, however, there will be an overspill (as the freeboard will not be able to handle the surge) and the water will rise until discharge commences through the discharge pipe. So in that sense, the "quantity of freeboard" is that volume.
This has been a good exercise and I thank you for it,
This has been a good exercise and I thank you for it,
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msquared48
Structural
I think that this value would depend on the storm, pipe size in and out, and the outlet capacity.
If you get into a serious backwater condition where head has to be generated in the catch basin for more water to flow through the downstream pipe, the "freeboard" will not only be much less at any particular catch basin, but also lowered at any catch basin upstream due to the increased tailwater head at the downstream catch basin.
H*(). Now I'm confused!
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
If you get into a serious backwater condition where head has to be generated in the catch basin for more water to flow through the downstream pipe, the "freeboard" will not only be much less at any particular catch basin, but also lowered at any catch basin upstream due to the increased tailwater head at the downstream catch basin.
H*(). Now I'm confused!
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
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msquared48--please see that my initial questions was related to the following quote: "check the quantity of freeboard below the [catch]basin hood" (from an RFP) listed as one of the tasks of the selected consultant.
Now, please take a look at the attached sketch as it does represent well the catch basins in consideration, and then let me know what you think.
Now, please take a look at the attached sketch as it does represent well the catch basins in consideration, and then let me know what you think.
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