This will give you the total head you have available. When I know the total head, how can I translate this into pressure. If there's lots of water power available, or no way to store water uphill, varying the load on the alternator to keep the frequency constant seems to fit better than solenoid operated diverters. Water cooled resistors can be simpler and smaller. And reduce air pollution.
Water heating seems a good load as well.
It takes 2.3 kWh to boil away a gallon of water. Some water wheels are more controllable than others.