Zafar et al. (2026) Temporal transferability of spatially derived Manning’s roughness across flood regimes in the Mississippi River

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-02-26
• Authors: Mohsin Zafar, Mantha S. Phanikumar
• DOI: 10.1016/j.jhydrol.2026.135186

Research Groups

• Department of Civil & Environmental Engineering, Michigan State University
• MSUAgBioResearch

Short Summary

This study evaluated the temporal transferability of spatially derived Manning's roughness values across different flood regimes in the Middle Mississippi River using a 2D hydrodynamic model. It demonstrated that a single set of spatially variable, temporally invariant roughness values provided excellent model performance over a decade, suggesting that hydrological forcing, rather than temporal changes in roughness, is the primary cause of model discrepancies.

Objective

• To evaluate the temporal transferability of spatially derived Manning's roughness values across various flood regimes in the Middle Mississippi River.

Study Configuration

• Spatial Scale: Middle Mississippi River
• Temporal Scale: Flood events in 2011, 2019, and 2022, covering a decade of flood regimes.

Methodology and Data

• Models used: High-resolution 2D unstructured grid hydrodynamic model
• Data sources: USGS gauge data for water surface elevations and discharge, high-resolution flood inundation extents from Planet Labs Dove satellites (for 2019 and 2022).

Main Results

• The hydrodynamic model exhibited excellent performance across all simulated years (2011, 2019, 2022).
• Nash–Sutcliffe Efficiency (NSE) values ranged from 0.98 to 0.99 for water surface elevations and 0.92 to 0.99 for discharge.
• Strong agreement was observed with flood inundation extents derived from satellite data.
• Discrepancies in model performance, particularly in 2011 flood peak magnitude and timing, were attributed to unaccounted inflows (e.g., from tributaries) not represented in the boundary conditions, rather than changes in roughness.
• The study concluded that consistent model performance using spatially derived, temporally invariant roughness over a decade indicates that reductions in performance are more likely due to hydrologic forcing (missing flow inputs) than temporal variations in roughness.

Contributions

• This study provides strong evidence for the temporal transferability of spatially derived Manning's roughness values across different flood regimes over a decade, challenging the common assumption that roughness must be adjusted for each event.
• It highlights that hydrological forcing (e.g., unrepresented tributary inflows) can be a more significant factor in model discrepancies than temporal changes in roughness.
• The research advocates for a careful assessment of evidence before employing time-dependent roughness values and discourages treating Manning's n as a free, catch-all calibration parameter.

Funding

• Not specified

Citation

@article{Zafar2026Temporal,
  author = {Zafar, Mohsin and Phanikumar, Mantha S.},
  title = {Temporal transferability of spatially derived Manning’s roughness across flood regimes in the Mississippi River},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.135186},
  url = {https://doi.org/10.1016/j.jhydrol.2026.135186}
}