490 / 2024-04-30 10:22:05

Hydrography Setting for Medium- to Long-term Bio-hydromorphology Dynamics Prediction Of An Actual River

hydrography setting, bio-hydromorphology, vegetation dynamics, riverbed evolution

Subtheme 3: Eco-hydraulics and Environment > Topic 4: Ecological Regulation and Hydrological Connectivity

Predicting the medium- to long-term riparian vegetation dynamics and its mutual interaction with hydro-geomorphology will be important for riverine management under anthropogenic activities and global warming. As for the medium- to long-term prediction of bio-hydromorphology dynamics of an actual river, the balance between calculation accuracy and calculation load is necessary to be discussed to achieve efficient river management. In this study, we propose one hydrography setting method, which may identify the hydrologic characteristics dominant to vegetation and river morphology dynamics. A gravel-bed river in the Chubu region of Japan was selected as the study site. In the Chubu region of Japan, the seed dispersal for vegetation recruitment and riparian vegetation growth was assumed to occur from December to April, and from May to September, respectively. Flooding, which may induce vegetation destruction, typically occurs in September or October at the study site.

The vegetation dynamics processes were set as recruitment, growth and expansion, and destruction each year accounting for both prevalent biological processes and hydrological conditions. However, not all hourly flow conditions in the medium- to long-term bio-hydromorphology dynamics simulation were considered for the real-world river. In this study, only representative flows for determining the vegetation recruitment, growth, destruction, and riverbed evolution for each year were considered. The seed dispersal flow was set as smaller of the discharge during the seed dispersal period and the critical discharge for the D₅₀ sediment movement. The flood pulse was set as the flow surpassing the threshold value for the provoking vegetation removal and riverbed evolution.

The proposed hydrography setting method was applied to our study site to predict the riparian vegetation and river morphology dynamics for about 15 years. The consistency of riparian vegetation dynamics between simulation and investigation showed that the proposed method was available for the bio-hydromorphology dynamics prediction of an actual river.