Estimation and calibration of Manning’s roughness coefficients for ungauged watersheds on coastal floodplains

ABSTRACT

Knowledge of hydrodynamic behaviour is imperative for the water resource management and the sustainable development of basins. Hydraulic and hydrologic modelling are essential tools for the simulation of this behaviour. However, lack of basin assessment makes modelling input data scarce. This is the case for the Juqueriquere River basin, which comprises the major floodplains of the northern coastline of Sao Paulo State, Brazil. This region is susceptible to floods and is under pressure from real estate speculation, gas exploitation, and infrastructure development for port facilities. The purpose of this study was to estimate and calibrate Manning’s roughness coefficients of the Juqueriquere River basin, as they are mandatory data for hydraulic modelling. The estimation of Manning's n values was based on field observations. These data were inserted into the Hydrologic Engineering Center's River Analysis System (HEC-RAS) model for the calibration of the roughness coefficients in a trial and error process. The findings of this study proved that the estimation and calibration methods were efficient, with mean absolute deviations lower than 10% in the studied sections.

KEYWORDS:

• Coastal floodplains
• basin assessment
• roughness coefficient
• Manning’s equation
• HEC-RAS model

Acknowledgements

We gratefully acknowledge UNICAMP for the study support, the Australian Government for the Research Training Program (RTP) Fees Offset Scholarship at Swinburne University of Technology, the Brazilian National Council for the Improvement of Higher Education (CAPES) and REDELITORAL, for the promotion of the field campaigns and implementation of gauging stations, and EMPLASA for granting the high-resolution DSM.

Disclosure statement

No potential conflict of interest was reported by the authors.