In the first few years after a streambed has been disturbed during an active restoration project, the bed is unstable, and grade-conrol structures are needed to keep it from downcutting. But it is difficult for the stream to move large rocks like those shown in the photo below, and so over the long term these kinds of structures are not desirable because they tend to restrict the natural movement of the stream. As a result, restoration professionals prefer to minimize their use and instead try to use "softer" and less intrusive approaches wherever possible. Specifically, they tend to minimize the use of J-hooks, Straight Vanes, and Cross Vanes and steer more towards armored tailouts, submerged boulders, and debris jams. As a general rule, J-hooks, vanes, and other "hard" grade-control structures should amount to 20% or less of the restoration design. Even then they should be viewed as temporary, meaning after the stream has stabilized, they will be removed. The other (and first) 80% of a good restorarion design involves selecting the appropriate design dimensions (hydraulic and meander geometry) and fitting the design to the site. If that part is done correctly, structures are still necessary but will not control the design, and the stream will be able to behave like a natural, living stream, which after all, is the goal of good restoration.