Hydrodynamic and Morphodynamic Modeling for Dredging Feasibility in a River System

Overview

A river navigation corridor presented several shallow zones (“critical passes”) where sediment deposition restricted transit and required potential dredging interventions. Authorities sought a rigorous evaluation of the hydraulic feasibility, environmental impact, and expected maintenance dredging volumes associated with alternative interventions.

HCS conducted a comprehensive 2D hydrodynamic and morphodynamic modeling study, examining flow conditions under multiple hydrological scenarios, assessing the effects of proposed dredging options, and estimating medium-term sedimentation patterns to support decision-making.

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The Challenge

The study reach is characterized by:

• Strong interactions between the main river and a secondary channel
• Highly variable hydrology, including low-flow, medium-flow, and flood conditions
• Significant sediment inputs from upstream tributaries
• Morphological complexity

These processes create fluctuating navigation depths and require periodic interventions. The client needed to understand:

• How different dredging options influence water levels, velocities, and flow distribution
• Whether proposed interventions could improve navigation under low-flow conditions
• Hydraulic forces acting on newly excavated channels during floods
• Expected annual sedimentation as a basis for maintenance-dredging planning

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Our Contribution

HCS applied a robust numerical modeling framework that combined hydrodynamics, sediment-transport and morphodynamics.

1. Two-Dimensional Hydrodynamic Modeling

A 2D shallow-water model was implemented using a non-structured mesh with local refinement in critical zones. The model incorporated:

• A digital elevation model combining bathymetry, topographic profiles, and remote sensing data
• Spatially varying roughness (Manning coefficients)
• Boundary conditions defined by observed discharges and water levels
• Representation of both confined and overbank flows under flooding conditions

Model stability, domain configuration, and calibration were documented in detail.

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2. Calibration and Validation with Field Measurements

The model was calibrated and validated using:

• Water-surface elevations recorded during a dedicated survey campaign
• Velocity measurements from multiple transects across the river
• Measured tributary inflows

Two independent field campaigns were used to validate both level and velocity fields, achieving very good agreement.

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Figure 1: Comparison of water level along the modelled reach

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Figure 2: Comparison of velocity magnitudes with ADCP transect

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3. Scenario Analysis for Dredging Interventions

Multiple hydrological conditions were modeled:

• Low flow (critical for navigation)
• Medium flow (representative for impact assessment)
• High flow (design of structural protections)
• An extreme low-water event reconstructed from monitoring data

For each hydrological state, different configurations were simulated:

• Current bathymetry
• Channel excavation
• Removal of a local sediment deposit

Results were compared in terms of:

• Flow distribution between the main channel and the secondary channel
• Changes in water levels (typically only centimeters)
• Velocity fields and their spatial redistribution
• Navigation depths along the barge route

In all cases, differences in the main river were small, confirming low hydraulic impact, while excavation produced the expected improvements within the intervention zone.

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4. Flood Scenario and Hydraulic Stresses

A flood scenario was modeled to evaluate the stability of the excavated channel. Results included:

• High but manageable velocities within the excavated section
• Flow patterns confirming the adequacy of the modeled domain for flooding conditions

This analysis provided guidance on the type of protection required along exposed margins.

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5. Morphodynamic Modeling and Sedimentation Forecasting

The sediment-transport model (coupled to the hydrodynamic solution) represented:

• Bedload and suspended-load transport of coarse sand
• Two granulometric classes based on measured samples (d₅₀ of 250 and 500 µm)
• Bed composition, porosity, settling velocities, and critical shear stresses
• A morphological acceleration factor to simulate yearly evolution

The model evaluated:

• Expected annual sedimentation in the excavated channel
• Sensitivity to grain size, bed thickness, and morphological parameters
• Locations of sediment accumulation and erosion linked to hydraulic conditions

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Key Findings

The integrated hydrodynamic–morphodynamic assessment provided the client with:

• High-confidence simulations of water levels and flow velocities under multiple hydrological conditions
• Verification of minimal hydraulic impacts of proposed interventions on the main river flow
• Clear identification of velocity reductions and depth increases within the intervention area
• Quantified hydraulic stresses during flood conditions to support design of bank protections
• Annual sedimentation estimates suitable for planning maintenance dredging

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Outcomes and Client Value

HCS delivered a technically robust modeling framework that helped the client:

• Evaluate the hydraulic feasibility of dredging options
• Understand system behavior under critical low-flow conditions
• Prepare for extreme events through predictive modeling
• Estimate maintenance requirements based on morphodynamic evolution
• Make informed decisions regarding long-term navigation improvements

This project illustrates the capacity of HCS to integrate hydrodynamics, sediment transport, and scenario-based analysis for complex river engineering challenges.