A joint research team, with members from the Korea Institute of Civil Engineering and Building Technology (KICT) and Deltares of the Netherlands, predicted future changes in a river’s vegetation landscapes by using an eco-morphodynamic model, according to South Korea’s National Research Council of Science and Technology.
KICT and Deltares applied the model to the Naeseongcheon Stream in Korea, which belongs to a temperate monsoon climate region with large seasonal hydrological fluctuations. Most of the Naeseongcheon Stream has characteristics as a natural river. Its riverbed is mainly composed of sand, with movement due to hydrological fluctuations. Consequently, the vegetation dynamics are active.
The study result predicted that, by 2031, vegetation cover would increase in the stream and the area covered by willow trees would occupy up to 20 percent of the river area.
If widely adopted, this type of modeling could help river management efficiency by allowing managers to plan their practices in advance.
The Model
The model combines a vegetation model with Delft3D software, which is widely used for river hydraulics. Delft3D computes flow velocity, water depth and elevation of a riverbed. Then, the vegetation model simulates the germination, settlement, growth, and mortality of vegetation based on the Delft3D computation. Simultaneously, vegetation properties are converted to flow resistance and fed back into Delft3D.
Modeling the Stream
KICT has been conducting long-term monitoring on Naeseongcheon Stream since 2012, including LiDAR and hydrological surveys and vegetation map production, before significant vegetation establishment in the stream had begun. This monitoring data was used to build and verify the eco-morphodynamic modeling.
The modeling area is approximately 5 kilometers long curved reach, located in the middle-lower section of the Naeseongcheon Stream. The width is approximately 300 meters, and the grid of the model was constructed considering the actual vegetation distribution which had occurred narrowly along the shoreline.
After conducting modeling for a 2012-2019 period, the results were compared with the observed data. Compared with the ratio of coverage of tree species in the land cover map made with aerial photos, the area fraction of willow trees in the model result had similar coverage ratio. In 2014, actual willow tree coverage was 2.02 percent; in the model, it predicted a coverage of 2.21 percent. In 2016, the model adequately reproduced the actual situation by simulating the survival and growth of vegetation in the spring and the mortality of vegetation after a flood.