Cross river detector apparatus

Cross-river detector apparatus is described in which one or more elements 100, each incorporating detector means, is/are disposed, in use, across a water course. Means 2 is provided for supporting the elements 100, and the elements 100 are pivotable with respect to the support means 2. In one embodiment, the elements comprise a plurality of vertical fins disposed parallel to one another at spaced intervals across the water course. The fins are pivotable in a vertical plane. Means may be provided to restrict pivoting. In another embodiment, the elements comprise a plurality of flaps 100 that are in closely spaced side by side relation and disposed to lie adjacent the surface of the water course. Preferably the flaps are individually freely pivotable. The pivot axis is preferably disposed clear of the water. Height adjustment means may be provided for high water or flood conditions. The fin or flap elements 100 may be subject to buoyancy adjustments and their pivot position controlled via pneumatic pistons.