Abstract: For flow running over a patch of two-dimensional submerged vegetation in a river, it adjusts itself through five stages: upstream adjustment, initial adjustment, mixing layer development, boundary layer development, and exit flow adjustment. For a patch relatively short, i.e. much shorter than the length required by becoming fully-developed, exit flow adjustment is more important to the flow dynamics in the patch. Different patch lengths and vegetation densities have been examined in this work to study their effects on flow velocity, Reynolds stress, and turbulence intensity. Exit velocity was estimated using a depth-averaged model of mean velocity development along the flow, and downstream recovery length LR analyzed by applying the theory of mixing layer development. The results show that for the patches with the same length, denser vegetation has a shorter recovery length, larger peak Reynolds stress, and more turbulence kinetic energy downstream of the patch. And their values of Lm (i.e. locations of the peak stress) and LR are nearly the same. For the patches with the same vegetation density, the longer ones need a shorter recovery length and have larger peak stress and stronger turbulences. Finally, shelterbelt design is discussed in terms of the hydrodynamics related to vegetation patch features.