The Role of Realistic Channel Geometry Representation in Hydrological Model Predictions

Abstract

A key element in hydraulic and hydrologic modeling is the specification of representative channel geometry. For continental‐scale modeling, the large amount of high‐resolution data required, as well as the considerable computational effort needed to incorporate such data, has led to simplifying assumptions such as rectangular or trapezoidal channels for river reaches. The National Water Model (NWM) uses a trapezoidal channel representation for 2.7 million river reaches to forecast water discharge for the entire continental United States. This has created uncertainties in when to initiate hydraulic predictions. The aim of this study is to: (1) evaluate the impact of simplified (NWM trapezoidal) channel geometry representation on hydrological model predictions and (2) suggest an improved representation of channel geometry while maintaining parsimony in model input and runtime. The Hydrologic Engineering Center’s River Analysis System model was used to simulate hydraulic dynamics in three study sites under varying streamflow conditions (including flooding) with four different geometry representations at each site: NWM (trapezoidal), surveyed, and two proposed generalized geometries. Statistical analyses show that more realistic channel geometry improves simulated Muskingum‐Cunge routing parameters and stage/discharge predictions, indicating potential for geometric improvements to enhance hydrological models like the NWM.

Featured Collection Introduction: National Water Model III

“…The final paper in this collection by Wu et al (2021) is somewhat unique from papers in previous featured collections but could supplement the work of Brackins et al (2021) as relates to channel geometry data collected by volunteers. Recognizing that (1) data collected by agencies are limited (2) these data could be supplemented by data collected by volunteers (Kampf et al 2018), and (3) data collected by volunteers could have, or be perceived to have, less reliability than agency‐collected data, Wu et al explored approaches for determining the uncertainty in these types of data.…”

Comprehensive analysis of the NOAA National Water Model: A call for heterogeneous formulations and diagnostic model selection

“…Some applications have also focused on using the the historic data to study issues such as seasonal low flow in the Colorado River basin (Hansen et al, 2019), the one-way surface-groundwater flux in the Northern High Plains Aquifer during extreme flow events (Jachens et al, 2020), operational flood map generation (Johnson et al, 2019); cross section representation (Brackins et al, 2021); and reservoir inflow performance (Viterbo et al, 2020). In the latter, the authors specifically found that NWM inflows in snow-driven basins outperformed those in raindriven and that basin area, upstream management, and calibrated basin area influenced the ability to reproduce daily reservoir inflows.…”

Comprehensive Analysis of the NOAA National Water Model: A Call for Heterogeneous Formulations and Diagnostic Model Selection

“…Some applications have also focused on using the historical simulations to study issues such as seasonal low flow in the Colorado River basin (Hansen et al., 2019), the one‐way surface‐groundwater flux in the Northern High Plains Aquifer during extreme flow events (Jachens et al., 2020), operational flood map generation (Johnson et al., 2019), cross section representation (Brackins et al., 2021), and reservoir inflow performance (Viterbo et al., 2020). In the latter, the authors specifically found that NWM inflows in snow‐driven basins outperformed those in rain‐driven and that basin area, upstream management, and calibrated basin area influenced the ability to reproduce daily reservoir inflows.…”