View source for Effect of vegetation on hydromorphodynamics

[[Category:Tools]][[Category:Vegetation Models]]

Vegetation can influence river hydrodynamics by changing the turbulent flow field and the averaged velocity profiles in comparison with those that can be commonly found in
non-vegetated flows. In this way, vegetation potentially has a relevant effect on flow resistance, sediment transport and bank dynamics (see Table 1).

[[File:VegHymoInteractions_Hydromorphodynamics.png|center|thumb|600px| Table 1. Models for the effects of vegetation on hydromorphodynamics.]]

===Vegetation and flow resistance===

[[File:VegHymoInteractions_FlowRes.png|center|thumb|500px| Table 2. Summary of model characteristics on vegetation and flow resistance.]]

Future research is needed on the following topics:

- effect of different types and growth stages of vegetation (rigid or flexible) and different vegetation densities on flow turbulence structure and secondary currents of a stream;

- effect of plant reconfiguration with increasing flow velocity on drag;

- effect of the spatial distribution of vegetation at a reach scale on flow resistance;

- uprooting, breakage of plants during high-flow conditions may give rise to significant changes in flow resistance between the rising and falling limbs of the hydrograph;

- develop suitable parameterization to characterize different species.


===Vegetation and bank dynamics===
Tables 3 and 4 summarise the suitability of models with bank stability and accretion, respectively, for the analysis of hydromorphological pressures or the design of restoration measures.

[[File:VegHymoInteractions_BankStab.png|center|thumb|500px| Table 3. Summary of model characteristics on vegetation and bank stability.]]

[[File:VegHymoInteractions_BankAcc.png|center|thumb|500px| Table 4. Summary of model characteristics on vegetation and bank accretion.]]

Future research and modelling challenges:

- More work is needed to better understand the hydrological effects of riparian vegetation and to incorporate them into models of bank erosion and failures.

- Another area of knowledge gaps concerns modelling interactions of the various erosion processes and mass failures, and the relative role of vegetation on near-bank hydrodynamic flow conditions, erodibility parameters, and shear strength. In order to extend results from a bank profile to a reach and account for variability of hydrodynamic, geotechnical, and vegetational conditions, vegetation should be included into 3-D morphodynamic models.

- Concerning bank accretion modelling is still in its infancy. Recommendations relate to three main aspects: the inclusion of vegetation dynamics, the influence of the high variability of flows, and the up-scaling of the effects acting at different scales.