Hydrodynamic assessment of hard-bed interventions in a major navigable river

Overview

Navigation along the Paraguay River depends on maintaining sufficient depth through a series of naturally shallow segments known as pasos. In several of these, the riverbed consists of compacted or rocky material, forming hard bottoms that may restrict vessel draft during low-water periods. Proposed interventions aim to improve navigability while ensuring that the hydraulic response of the river—and its broader environmental setting—remains within acceptable limits.

HCS contributed to this effort through a hydrodynamic modeling study designed to quantify the potential effects of deepening several hard-bottom reaches. The work supported the technical evaluation of navigation improvements within an environmentally sensitive and hydrologically complex system.

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The Challenge

The Paraguay River exhibits strong seasonal fluctuations and has recently experienced extreme low-water conditions. These variations, combined with increasing navigation demand, have intensified the need to evaluate how local interventions could influence:

• Water levels during low-flow periods
• Flow velocities in and around critical reaches
• The propagation of any hydraulic changes upstream or downstream
• Environmental conditions in the intervention zones

Some hard-bed reaches have historically raised concerns about whether they exert hydraulic control during low water, meaning that modifying them could potentially alter upstream water levels. A technically robust assessment was required to understand whether these concerns were justified.

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Our Contribution

HCS developed a one-dimensional hydrodynamic model representing several hundred kilometers of the river, covering the full set of hard-bed reaches under evaluation. The model incorporated:

• Detailed bathymetric data for each critical reach
• Long-term hydrometric information from stations along the river
• Representative boundary conditions for low-water scenarios
• A systematic calibration and validation process based on observed water levels and discharge measurements

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Figure 1: Model extent, general view

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Scenario Evaluation

The analysis involved comparing river conditions with and without the proposed interventions, focusing on:

• Typical low-water scenarios used for design
• An extreme low-water scenario to test system sensitivity
• Variations in hydraulic roughness to bracket uncertainty

For all cases, the model quantified changes in water surface elevation and velocity, allowing a clear assessment of the spatial extent and magnitude of the hydraulic response.

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Key Findings

Model results showed that:

• The effects of deepening hard-bed areas are local, confined to the immediate vicinity of each intervention.
• No cumulative lowering of water levels was detected along the large-scale profile of the river, even under extreme low-water conditions.
• Outside the modified reaches, changes in water levels are negligible, and flow velocities remain broadly similar to baseline conditions.
• Variations in hydraulic roughness do not materially alter the overall conclusion: impacts are localized and limited in magnitude.

These findings provided a clear, quantitative basis for decision-making regarding navigation improvements.

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Figure 2: Model detail on one of the sectors with planned interventions

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Outcomes and Client Value

The study delivered:

• A data-driven hydraulic assessment consistent with the requirements of local authorities
• A validated modeling framework to support the design of navigation interventions
• Evidence-based conclusions showing that proposed modifications do not produce significant large-scale hydraulic impacts
• A technical foundation for integrating engineering decisions with environmental considerations

HCS helped establish a robust understanding of how targeted interventions interact with the broader hydraulic behavior of the Paraguay River, supporting a balanced and well-informed approach to navigation enhancement.