NOVELTY - The system has two rotor assemblies (110) disposed in a conduit (6) through which water flows. Each rotor assembly has vertical blades (124) radially extending from a vertical outer hub (120) rotational about a vertical axis. Seal assemblies (112), disposed in opposing surfaces of the conduit, are contacted by the radially outer edge sections of the blades, to limit water from passing through the rotor assemblies. Rotation speed of the rotor assemblies may be controlled using e.g. a braking system.    USE - System for controlling water level in e.g. river, estuary, as well as maintaining head of water such that water level upstream is higher than that downstream. Can be used in a barrage (claimed) or a dam, as well as in power generation using flow of water, including tidal flow.    ADVANTAGE - The system controls water level in a river and or estuary, avoiding flooding arising from adverse weather conditions, while allowing the system to be installed in wide range of situations and or locations in which an existing system for generating energy from a river or from tidal flows would not be appropriate. The system is constructed in a modular manner, allowing the system to be incorporated easily to a new or existing structure. The rotor assemblies may be freed to rotate at optimum speed for energy generation, by limiting the speed of rotation of each rotor assembly to allow sufficient head of water to build up on upstream of the system. Water may be exchanged between rotor assemblies, ensuring that water flowing into a blade cavity loses only minimal momentum before impacting on the surface of the blades and imparting energy. Pivotally mounting the blades to the hub increases torque generated on the rotor assembly, increasing energy generating efficiency of the system. The rotor assemblies may be in form of modules which can be removed for servicing, repair or replacement.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a method for controlling the water level of a flowing body of water; and    (2) a system for the generation of energy from the flow of water in a body of water; and    (3) a barrage.    DESCRIPTION OF DRAWING(S) - The drawing shows the top view of a single generator assembly in a barrage.    Conduit (6)    Rotor assemblies (110)    Seal assemblies (112)    Outer hub (120)    Blades (124)