Stormwater Sump Pumps
Stormwater Sump Pumps
(OP)
I was asked to give some feedback for a single family residence stormwater sump pump located in Los Angeles County. This pump is used to pump the stormwater up to the street where the drainage structures are located.
Parameters:
Area - 0.5 acres
Isohyet - 7.2 inches of rainfall (50-year)
50-year flow (Using LA County ModRat Method) ~ 900gpm
If I size the pump using the 50 year storm, this makes a HUGE pump for a residential applications, which is larger than any of the off the shelf pumps I have found (seems wrong). The pump manufacturer said to use 2" over the entire area to be serviced, but he didn't know why 2".
Questions:
1. What parameters have you guys used to size sump pumps for small residential applications? (2-year storm event? 2" over the entire area, etc?)
2. Does anyone know of any package stormwater pump system that they like using for small stormwater applications?
3. HOw is drainage in light wells accounted for? Do people typically install sump pumps for lightwells if no gravity outlet on a property can be obtained or maybe fill it with gravel to have a drywell beneath it?
Parameters:
Area - 0.5 acres
Isohyet - 7.2 inches of rainfall (50-year)
50-year flow (Using LA County ModRat Method) ~ 900gpm
If I size the pump using the 50 year storm, this makes a HUGE pump for a residential applications, which is larger than any of the off the shelf pumps I have found (seems wrong). The pump manufacturer said to use 2" over the entire area to be serviced, but he didn't know why 2".
Questions:
1. What parameters have you guys used to size sump pumps for small residential applications? (2-year storm event? 2" over the entire area, etc?)
2. Does anyone know of any package stormwater pump system that they like using for small stormwater applications?
3. HOw is drainage in light wells accounted for? Do people typically install sump pumps for lightwells if no gravity outlet on a property can be obtained or maybe fill it with gravel to have a drywell beneath it?
Talk To Other Members
RE: Stormwater Sump Pumps
I am thinking of using a PACO QDSC, submersible non-clog, dual system.
Regarding light wells for the basement, if the ground does not perc well, put a slab in the bottom and tightline it to the pump sump manhole.
Mike McCann
McCann Engineering
RE: Stormwater Sump Pumps
First find out if the whole half acre is covered or paved with impervious surface such as asphalt or concrete. If not determine the areas of concrete, asphalt, lawn, etc. Use runoff coefficients of 0.95 for the conc/asphalt and 0.15 for lawn. In the eastern part we a 2” rain represents a 5 year storm and that’s what the building dept’s require.
Calculate the volume of the flow by multiplying individual areas by their corresponding runoff coef. And the 2” and then add them all up. You get a total volume in cubic feet. An 8’ leaching ring provides 42.24 ft3 of storage for every one foot of depth. Calculate the required storage depth.
If you wish to use a sump pump, find out the discharge volume per hour and reduce the storage volume by that amount. Don’t forget to check with the Town for their specific requirements, if any. Hope this helps.
RE: Stormwater Sump Pumps
RE: Stormwater Sump Pumps
RE: Stormwater Sump Pumps
You can calculate an outflow hydrograph (straight line at the pump rate) and perform a storage volume calculation. The 100-year flood elevation would probably have to be recorded on a plat (though in this case, zero outflow would probably have to be assumed) and the home should have the finished floor elevation at least 1' above the 100-year flood elevation.