Impact of linear infrastructure on floodplains on inundation characteristics

Linear infrastructure such as roads, bridge crossings, protective dams cause significant changes of the floodplains topography and flow characteristics. To estimate the anthropogenic impact on the changing of inundation characteristics we applied two-dimensional hydrodynamic modeling approach. The study is focused on wide populated floodplains areas of the Ob River near Surgut city (Western Siberia, Russia), Lena River near Yakutsk city (Eastern Siberia), Amur/Zeya Rivers near Blagoveshchensk (Far East). STREAM_2D software (authors V. Belikov et al.), which is based on the numerical solution of two-dimensional Saint-Venant equations on a hybrid curvilinear quadrangular and rectangular mesh, and includes sediment transport and ice modules, was used for the simulations. Detailed topography and bathymetry data, obtained as results of field surveys, were used for model setup. All linear infrastructure in river channels and floodplains, including dams, cities embankments, existing and under construction bridges, road embankments were taken into account in the model grid and relief. Second version of the model relief was constructed excluding infrastructure. Calibration and verification of the model were performed for modern conditions using data of field surveys and data of gauging stations. Additional verification of simulated flooded areas and the water level in ungauged reaches was done using high resolution satellite optical images and satellite altimetry measurements. For impact analysys two modeling scenarios were considered for each key area: modern conditions of flow with all infrastructure and natural conditions without any constructions. More pronounced effect of the infrastructure on the flooding zones was identified for the floodplains of Amur/Zeya Rivers near Blagoveshchensk and Heihe cities: the area of flooding in modern conditions decreased by 10%, which led to an increase in the average depth of flooding by 10%, and the average flow velocity in the modeling area by 2-5%. Significant backwater effects due to linear infrastructure on the floodplains were identified for the Ob River, water levels upstream the existing bridge transect can rise more than 0.5m and observed at a distance of more than 30 km.

The numerical experiments were designed within the framework of the Governmental Order to Water Problems Institute, Russian Academy of Sciences, subject no FMWZ-2022-0001. The Ob River floodplain model was adopted with the financial support of RSF № 22-27-00633.