Incorporating Network Scale River Bathymetry to Improve Characterization
of Fluvial Processes in Flood Modeling
Abstract
Several studies have focused on the importance of river bathymetry
(channel geometry) in hydrodynamic routing along individual reaches.
However, its effect on other watershed processes such as infiltration
and surface water (SW) – groundwater (GW) interactions has not been
explored across large river networks. Surface and subsurface processes
are interdependent, therefore, errors due to inaccurate representation
of one watershed process can cascade across other hydraulic or
hydrologic processes. This study hypothesizes that accurate bathymetric
representation is not only essential for simulating channel
hydrodynamics but also affects subsurface processes by impacting SW-GW
interactions. Moreover, quantifying the effect of bathymetry on surface
and subsurface hydrological processes across a river network can
facilitate an improved understanding of how bathymetric characteristics
affect these processes across large spatial domains. The study tests
this hypothesis by developing physically-based distributed models
capable of bidirectional coupling (SW-GW) with four configurations with
progressively reduced levels of bathymetric representation. A comparison
of hydrologic and hydrodynamic outputs shows that changes in channel
geometry across the four configurations has a considerable effect on
infiltration, lateral seepage, and location of water table across the
entire river network. For example, when using bathymetry with inaccurate
channel conveyance capacity but accurate channel depth, peak lateral
seepage rate exhibited 58% error. The results from this study provide
insights into the level of bathymetric detail required for accurately
simulating flooding-related physical processes while also highlighting
potential issues with ignoring bathymetry across lower order streams
such as spurious backwater flow, inaccurate water table elevations, and
incorrect inundation extents.