Wouldn’t you just assume a fixed stage/discharge relationship. It seems to me that the variations in pump output would be minor compared to the variations of the inflow hydrograph. If pump output varies significantly with storage depth a stage/storage/discharge relationship should be fairly easy to set up. Any stormwater detention program should be able to handle it. There are many shareware or inexpensive programs on the net or a spreadsheet could be set up to do it. Of course, you could spend lots of money and use a Haested (sp?) program. Am I oversimplifying the problem?

I agree. However, when multiple pumps are used to adress multiple deisgn storms it gets tricky. For example, three pumps can be used so that only one pump satifies a 1 yr storm and a second pump kicks in to support the first pump (lead pump) for a 5yr storm, and the third kicks in so that all pump handle the 25 yr storm. However, even for the 25 yr storm, the lead pump is activated during the first hours(before peak)and the second kicks on when the first pump can't keep up and the inflow reaches the spring line of the inflow pipe. The 3rd pump would kick on when the water in the wet well reaches the crown, where the capacity of all pumps matches the 25 yr peak flow. It could be done with a spread sheet, but I am hoping that a simple program exist that allows me to input pump curves and inflow curves for different storm events and magically sizes the wet well for max effeciency.

Thanks for the reply.

Have you tried SWMM? It is not the easiest to set up but once you have enter your pump curves and established their parameters, you don't have make any other adjustments. What programs are you using now?

Thanks dycster,

Can I get SWMM from EPA of their web site?

Currently, I use a spread sheet to estimate the inflow using a method similar to SCS's
hydrograph. I plot the inflow hydrograph and treat it like a reservoir problem to estimate flow
rates. I then use haestad's watercad program to evaluate different pumps (I use a reservoir
to simulate the pump station). Watercad allows me to simulate pump on/off scenarios and
different pump curves. I don't know if any one has tried this before but would like some feed
back.

Thanks again for your response.

You can obtain SWMM through the EPA website. Yes I have used a similar method that you are using and found it to be very tedious and it is very easy to forget something when you are dealing with multiple pumps. The last time I talked with haestad, they indicated that they were integrating their pump routines into HydroCad. I don't know if they have complete this yet. Another method that I have used is to use a waste water wet well program, I can't remember the name, which has options for multiple pumps and multiple stage configurations. Although it would be more convienent to use a single program, the wet well program will give you multiple rating curves that you could set up in a hydrologic model that kicks in a set stages.

Keep in mind a storage amount you need, in other words how much can a sump fill befors you need to pump it.  The pumps should keep up with the demand and you might want to use 50% of the peake storm as a rule of thumb for the outflow.  Take 10 minutes of the peake time on the curve and see how much water you have. you do not want your pumps running with out a break to cool down.