DEM-based river cross-section extraction and 1-D streamflow simulation for eco-hydrological modeling: a case study in upstream Hiikawa River, Japan

Abstract

Simulating streamflow under both high-and low-flows is required for versatile eco-hydrological modeling. Typical streamflow simulators require hydrological data such as river geometry and observed river discharge/water level as upstream/downstream boundary conditions. However, these are not always available in data-sparse regions. Furthermore, because of the potential inaccuracy of digital elevation model (DEM) data around water surfaces, this data has not generally been utilized in streamflow simulations. Therefore, this study explores the potential applicability of DEM data to extract river cross-sections, focusing on the upstream Hiikawa River, Japan. A 1-D streamflow simulation was performed using river cross-sections extracted from a 5 m LiDAR DEM and the observed dam discharge from 2018 to 2020 as the upstream boundary condition. The simulated water depths with Manning's roughness coefficients of 0.03 to 0.05 m -1/3 s reproduce the observation results with Nash-Sutcliffe coefficients of 0.91-0.97 for the whole period and 0.60-0.97 for a flood event. The accurate results for both low and high flows were considered to reflect the reasonable representations of the river cross-section. Finally, the velocity-based suitability index for Ayu (P. altivelis) was evaluated. We demonstrate applicability and several possible limitations of DEM data for eco-hydrological modeling of data-scarce rivers. KEYWORDS streamflow simulation; digital elevation models; river cross-section; Hiikawa river; eco-hydrology STUDY AREAThis study targeted the upstream reach of the Hiikawa River (Figure 1), which is a first-class river in the San-in area of Japan with a length of 153 km, a watershed area of 2070 km 2 , and riverbed gradients of greater than 0.010, 0.00125 to 0.0050, and less than 0.001 in the upstream, middle-stream, and downstream reaches, respectively. The study area is located between the upstream and middle-