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Install Pump to prevent flooding

Install Pump to prevent flooding

(OP)
I am currently working with a property owner who owns a building in an industrial park. When he bought the building he did not realize that during heavy rains his building will flood. This is because his neighbors filled in the drainage ditches to expand their parking lots, not knowing they were causing his future building to flood. The neighbors are not excepting responsibility and refuse to re establish the ditches.

Now he owns this said building and would like to keep the water from flooding him out. To help come up with a solution I have created a drainage model of the contributing area. The area consists of 5.60 acres of paved surfaces. The calculated runoff to his building (low point) is approximately 20.9 cfs with a rain intensity of 3.89 in/hr and a time of concentration at 20 min.

I would like to install a pump that will collect the water and pump the water to a ditch line that is up hill of his property. The distance to the ditch from the pump is approximately 350 feet with an elevation difference of approximately 5 feet. I would like some assistance in sizing the right pump discharge that will keep up with a storm event and collect the water before it makes it to the building. Can someone give me some advice on the best way engineer this?

Thank you!

RE: Install Pump to prevent flooding

21 cfs is about 9,000 gallons per minute. that would be a very large pump. suggest that you need a detention basin to capture the water and reduce the pumping rate. or sue the adjacent property owners for causing flooding, might be a better option

RE: Install Pump to prevent flooding

(OP)
I agree. I have room to construct a detention pond with a volume of approximately 12,000 cu. ft.. With a runoff rate of approximately 9000 gallons per minute, the pond will be filled in about 10 minutes. This is where I get a little confused. I feel that by constructing the detention pond I should be able to reduce my pump size but by how much is the question.

RE: Install Pump to prevent flooding

(OP)
I have a storm event that will produce:

Runoff volume = 104,999 Gallons
Runoff Rate = 7,000 gpm

My detention Pond can hold 94,097 gallons
Pond will fill = 13.44 minutes

I believe that all I need to to is pump the difference between the runoff volume and pond volume in 13.44 minutes or less. Right?

If this is true Then all I need to do is Pump 10,902 Gal. in 13.44 minutes or less. This calcs out to 811.16 GPM. Right?

RE: Install Pump to prevent flooding

To verify the pump sizing you can do a pond routing calculation, with the pump as the primary outlet mechanism. This will let you evaluate the system operation with different storage and pump configurations. The routing calculation will give you a pump outflow hydrogrpah, plus the pond WSE vs time, so you can verify that the pond doesn't overtop. However, you still need to handle an overtoppng event in an acceptable manner. Whatever storm you design for there is still a chance it will be exceeded, especially with out increasingly unpredictable weather. Hopefully you have a way to convey the overflow off-site without adversely impacting your client or the neighbors.

To do the analysis you will need a modeling tool such as HydroCAD that can specifically handle pump outlets, including the switching behavior. For details see www.hydrocad.net/pumps.htm

Peter Smart
HydroCAD Software
www.hydrocad.net

RE: Install Pump to prevent flooding

(OP)
psmart - This is great information since HydroCAD is my new favorite engineering software. I am in a time crunch and some answers are needed immediately. Can you say if I'm headed in the right direction from the calcs provided above?

RE: Install Pump to prevent flooding

Your calculations should give you a starting point to select a possible pump, but you need to setup the model to see how it will actually behave. The model will allow for frictional losses and the (higher) discharge elevation, which can significantly reduce the nominal pump capacity. To run the model you will need a complete head-discharge rating curve for the candidate pump. For a start you may want to look at the sample pump project that is preinstalled with HydroCAD, as well as the training video referenced at www.hydrocad.net/pumps.htm

Peter Smart
HydroCAD Software
www.hydrocad.net

RE: Install Pump to prevent flooding

i would be doing a hard look at whether or not there was a local or state permit that was skipped by the neighbors and appeal to the authority holding jurisdiction

RE: Install Pump to prevent flooding

It's been illegal to flood your neighbors out by monkeying with drainage patterns as far back as the Magna Carta and the Code of Justinian. Arguably the Egyptian Book of the Dead had rules against this. I would be very surprised to discover the local or state government doesn't have a prohibition against this.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Install Pump to prevent flooding

Just pump half the water back onto your neighbor's property and pump the rest into the storm system.

That will make points, right?

If you do go to a pumped system, make it a dual system, all backed up with an emergency generator.

Mike McCann, PE, SE (WA)


RE: Install Pump to prevent flooding

If you have fisheries related problems, although it may be your only feasible solution, the outfall from the pump would most likely not match any applicable 10, 25, 100 year, or whatever year flow rate restrictions. You would have to check that out with the local jurisdiction.

Mike McCann, PE, SE (WA)


RE: Install Pump to prevent flooding

(OP)
Thank you to everyone who responded to my thread. Like most projects it comes down to money and how much risk the owner is willing to take on.

RE: Install Pump to prevent flooding

Do you have any idea if the soil below the property is water-logged or not? Way back in grade school, I've seen workers drilling some holes (coring machines with drill holes, 2" dia.) on the concrete pavements and filling them back with gravel. The idea was tro minimize runoff; water was allowed to seep underground through those bored holes!

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