Useful? - Forced Main for Storm Drain System 3

[sdynamic]

Are there any problems to design "force main" for a main storm drain system for several commercial sites? Several commercial sites have their own storm drain basins with pump stations.

(Existing Situations)
1. There are several local basins with pump stations
2. Each pump discharges stormwater to the main gravity system
3. There will be a big pump station to discharge the entire flow in to a river nearby (because it's a gravity system)
4. The size of the main gravity pipe will be min. 72 inch

We want to replace the above gravity & main storm drain system with a force main.

The reasons to think of this force main system are

1. Reduce the storm drain pipe size (e.g., a force main!)
2. Avoid the huge pump station, e.g., each local pump station will help remove this big pump station at the end

The overall flows from the entire sites will be more than 120 cfs.
Are there any problems in this concept in terms of costs, maintenance, operation, efficiency, etc?

I have desinged local force main but not for the main storm drain system like above.

Any comments or advice would be highly appreciated.

 

[RWF7437]

"Are there any problems to design "force main" for a main storm drain system for several commercial sites" ?

Yes, many many problems.

For example;

Such a pump station would require several large pumps with a combine horsepower approaching 1,000 hp.

A single force main to carry 120 cfs @ 5 ft/sec would need to be about 66" in diameter. Large, pressure pipe of this size is very expensive and might need to be custom made.

To be considered reliable several backup pumps would also need to be installed.

To be considered reliable the pump station would need backup power ( 1000 hp ?).

To be considered reliable the station itself would need to be protected from flooding .

Operating costs for the anticipated useful life of the station would need to be budgeted for by someone.

How sure are you of the 120 cfs design flow and what level of protection would that afford, to what properties, and what is the value of those properties ?

What are the consequences if the station fails ?

Be careful and good luck.

 

[rconner]

Perhaps a good sort of case study may be New Orleans?

 

[bimr]

There would be a potential problem in management of the combined system. How would you apportion the costs for operating and maintenance? You would also have to develop a "utility" that would be responsible for operating the system. Most comme4rcial projects would not be interested in such an arrangement.

While a combined system may be practicable and buildable, the long term operating and maintenance considerations may not work.

To determine whether or not a combined system is economical, you would have to prepare a systems analysis and compare total costs of ownership including capital and maintenance costs, etc.

 

[sammyk]

Holy Smokes...120 cfs for "several commercial sites"? Even with detention basins? My last sanitary lift station was for less than 2 cfs peak and it cost $1.0 million with the forcemain.

Reread all the above posts (especially RWF's), calculate your peak gpm and if it even comes close to 120 cfs, depending on specs, you're easily looking at the tens of millions of dollars.

Though, this would be a pretty cool project on your resume.