There is a general rule that I learned in nuclear training relating the volumetric flow rate of a centrifugal pump to the pump head and power required to operate it. It was memorized as VHP to 123. The connection is that if you double the volumetric flow rate of the pump, you must increase its head by 4 and its power by 8 (the 123 refers to the exponent behind VHP). This means if a pump that can move 1 gallon a minute takes 100 W of power, to make the same pump move 2 gallons a minute would require 800 W, and to move 8 gallons a minute would require ~50 KW. But we also have to remember that the depth of the water is only perhaps 15 feet a maximum. This will limit the pump output as well (the pump head). Obviously the design of the pumps plays a large factor in how much power they use, but it is obvious that there is a certain size limitation for the pumps. The reason that it is going to take weeks to pump out New Orleans has to do with the fact that these pumps do have a limited capacity and making larger pumps might be unfeasible (due to power limitations).
Many times it is better to install twice as many pumps to double the flow rate while using half the power than if you doubled the flow rate of the existing pumps (either by making them physically larger, raising the voltage, or by increasing the current).
CNN gave the authorities the address. The family is in East New Orleans on the roof. Their neighbor is hanging onto a tree.
Doesn't that only apply if the bulk of the energy of the pump is being lost to fluid resistance in a fixed-sized pipe? In the case of New Orleans levy pumps, the vast majority of the energy used by the pumps would be used to increase the potential energy of the water pumped (i.e. pumping water uphill).