I need a flood control device that will cut the electrical power to a device (like a well pump) when a water leak is detected.

The FloodStop Automatic Shut-Off Valve in conjunction with the Furman Remote Power Relay will be perfect for your situation. 

Under this setup, upon leak detection, the FloodStop Valve would shut off the water, and at the same time the Furman Remote Power Relay would shut off the power, and the FloodStop can even be hooked up to your security system or Sensaphone so that you are notified of the event.