Water is not incompressible. Sound or shock wave is a compression traveling in media. (Incompressible water would transmit information with infinite speed). So, water pipe acts like a long spring, one end of which (A) is still moving with the speed sqrt(2gh) = 14 m/s (if to neglect friction in the pipe) and the other end GRADUALLY slows down (as pressure wave from higher end propagates back to the tank).Some portion of water will indeed overflow from 11 m elevated end, but far not all the water from the pipe, and the energy gain will be exactly the same as the loss of potential energy of water in the tank due to drop of water level (actually less because some energy will be stored in compressed water in the pipe). After a while water will flow back into tank and system will start oscillate (indefinitely if there is no friction).

I do not think it is worth to bother scientists on the planet Earth - any good college student will calculate for you exactly how much water will overflow, how much energy will go into compressed in the pipe water and how much kinetic energy will remain in oscillating back and forth water.