A model experiment about the hydraulic roughness of natural turf used in riverbank was carried out in flume. To examine the rationality of experimental design, the hydraulic roughness coefficient of plexiglass-flume was tested firstly. The result was 0.0085, which is quite normal. Then the tested hydraulic roughness caused by vegetation ranges from 0.020 to 0.090 for the chosen plants, which is also acceptable. Furthermore, the tested incipient velocities of krasnozem, and paddysoil had the range of 0.55~0.65m·s-1 and 1.0~1.1m·s-1, respectively. All these experimental results are in normal range, which means that the design of this experimental is rational. Experimental research illustrate that, the roughness coefficient of plant reduces with the increasing of flow velocity. When the mean flow velocity is over 3m·s-1, Mannings n values vary between 0.025 and 0.035. This phenomenon is accord with the theoretic analysis. During the scouring process, not only the flow velocity, but also the flow duration has an obvious effect on the coarseness of vegetative bed.

Flexible vegetations supply great effect on river bank protection. It is important to study the critical flow conditions, including bed shear stress, scour duration and frictional velocity etc, causing damage of grass-covered revetment. Laboratory experiments prove that, destruction of turf can be estimated by observing the variation of water head. The experimental shear stress above vegetation zone has nonlinear relation with velocity square, which agrees with theoretic derivation. Before the turf destruction occurring, shear stress above vegetation zone increases with the scour duration and then goes to stabilization. This mentioned Shear stress will change suddenly when local scour damage happens, or keep stabilization while affine damage is on-going. Under the same flow conditions, the critical bed shear stress of reinforced turf is larger than that of natural turf. As far as the same-form revetments are concerned, the bed shear stress at breaking point increases with the flow velocity.

Hydrodynamic characteristic is an important reference to select vegetation material of ecological revetment engineering. In this paper, embankment will be divided into bottom-protection zone, key-protection zone, hydrophilic zone, landscape zone according to hydrodynamic characteristics of different water levels. Vegetations adapting to different protection area analyzed and discussed. With the example of ecological revetment in Naji reservoir in Guangxi, China, vegetation selection on different protection zone is demonstrated.