Trackfiend
Civil/Environmental
- Jan 10, 2008
- 128
I was asked to check on a design for a bioretention area. Another engineer calculated that a certain percentage of the flow from the design storm needed to be routed to the bioretention area and the rest could bypass to the main outlet. The method he used to calculate the flow is called the "Uniform Intensity" approach. The equation is:
Q = .21 x C x A x K
Out of roughly 6 cfs, the routed flow for bioretention purposes was calculated to be 0.8 cfs. The inflow from the storm event will be captured by a sump area and pumped to the bioretention area (not sure if should be pumped to begin with). The method I am using in analyzing this is to determine the point at which the inflow to the sump reaches 0.8 cfs and then check to see what the water level is at that point in the sump. Once I've determined the w.s. level for 0.8 cfs of inflow, then I'm setting up a pump to start pumping that first volume of stormwater that has collected in the sump. I have several questions concerning this:
1. Would determing the w.s. level from inflow (0.8 cfs) and then pumping that first volume of water be a correct way to handle the "first flush" to be treated?
2. I am setting up a SWMM model for this exercise and was wondering what type of pump would best fit this model? I am currently using a type 3 (head vs. flow). The pump is sitting in a "wet well" style sump.
3. I have been advised to use a pump with a capacity for pumping 0.8 cfs. This sounds extreme since this would be a 360 gpm pump. Wouldn't a smaller pump that pumps at a slower rate but draws down the first flush contained in the sump be sufficient? And once this first volume of water is pumped out, shouldn't the pump be turned off so that the bioretention area is not overloaded?
I apologize if the info given isn't clearly stated. Any insight would be greatly appreaciated.
Q = .21 x C x A x K
Out of roughly 6 cfs, the routed flow for bioretention purposes was calculated to be 0.8 cfs. The inflow from the storm event will be captured by a sump area and pumped to the bioretention area (not sure if should be pumped to begin with). The method I am using in analyzing this is to determine the point at which the inflow to the sump reaches 0.8 cfs and then check to see what the water level is at that point in the sump. Once I've determined the w.s. level for 0.8 cfs of inflow, then I'm setting up a pump to start pumping that first volume of stormwater that has collected in the sump. I have several questions concerning this:
1. Would determing the w.s. level from inflow (0.8 cfs) and then pumping that first volume of water be a correct way to handle the "first flush" to be treated?
2. I am setting up a SWMM model for this exercise and was wondering what type of pump would best fit this model? I am currently using a type 3 (head vs. flow). The pump is sitting in a "wet well" style sump.
3. I have been advised to use a pump with a capacity for pumping 0.8 cfs. This sounds extreme since this would be a 360 gpm pump. Wouldn't a smaller pump that pumps at a slower rate but draws down the first flush contained in the sump be sufficient? And once this first volume of water is pumped out, shouldn't the pump be turned off so that the bioretention area is not overloaded?
I apologize if the info given isn't clearly stated. Any insight would be greatly appreaciated.