Hi, and welcome back!
The equation for this is:
power (in watts) = head (in meters) * flow (in liters per second) * gravity (which is 9.81m/s^2)
Plugging in what we know:
5000 = 9.81hf
Divide by 9.81:
hf = 509.68
However, hydro generators are not perfectly efficient. On average, they are 70% efficient (with the 30% being lost to heat and other non-electrical energies).
0.70hf(reallife) = 509.68
hf(reallife) = 728.12
You need the product of the head (in meters) and flow rate (in liters per second) to be 728.12.
If you prefer flow in cubic meters per second: You need the product of the head (in meters) and flow rate (in cubic meters per second) to be 0.72812.
For example, if the head is 10 meters, you'd need a flow rate of 72.8 liters (0.0728 cubic meters) per second.
Ref: (does it with kilowatts and liters per second) http://www.reuk.co.uk/Calculation-of-Hydro-Power.htm
Ref: (does it with kilowatts and meters cubed per second) http://practicalaction.org/practicalanswers/product_info.php?products_id=41
I hope this helps. Let me know if you have any questions,