Introduction of vegetation in large scale hydrodynamic models

Vegetation is known to have different effects in shallow water environments, including changes in hydrodynamics. This often creates the need to include vegetation in large scale hydrodynamic models, which nowadays can already be achieved using some software packages available in the market. This work, however, had the purpose to test simple methods to simulate vegetation in hydrodynamic models without having the need to use vegetation specific software. Method: The tests were done using the MIKE 21 hydrodynamic module, developed by DHI Software, and two simple models were tested under different wind conditions. One of them simulated submerged vegetation by reducing the bottom depth as well as increasing the flow resistance values, while the other one, used to simulate emerged vegetation, consisted only of a significant increase in the flow resistance. In order to validate the models and the results obtained some field measurements were made in a local shallow lake, Krankesjön, and it was possible to see that the emerged vegetation used was plausible and also a good approximation, which didn?t clearly happen with the emerged model. The current speed values obtained by the modeling were consistent with the values measured in the lake, always in the order of greatness of a few centimeters per second. Results: The results obtained by the numeric modeling showed evident decreasing in the current speed values after introducing the vegetation models, along in some cases with changes in the preferential flow paths. Conclusion: As an overall conclusion of the project, the submerged vegetation model showed to potentially be a good approximation to study hydrodynamics in shallow lake environments, even if used only as a preliminary study, while the emerged model didn?t prove to be so reliable. Some improvements and further tests are suggested to both models, in particular to the one for emerged vegetation, such as altering the wind friction values in the water surface over the areas with emerged vegetation to better approximate the real phenomenon. (examensarbetet är utfört vid avd. Teknisk vattenresurslära, TVRL)