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Hydropower projects are under increasing pressure to demonstrate that fish passage solutions perform effectively, not just hydraulically, but biologically. Licensing reviews, modernization efforts, and stakeholder expectations all require defensible, science-based evidence that passage systems support successful migration under real-world conditions.

Traditional evaluations rely heavily on hydraulic metrics such as velocity, depth, turbulence, and attraction flow patterns. These measures are essential. They define the physical environment fish must navigate. But they often assume that fish respond uniformly to those conditions, as if they are passive particles carried by the flow.

In reality, fish are active decision-makers. They conserve energy. They avoid obstacles. They respond to velocity gradients. They follow one another. They adjust movement based on crowding, fatigue, and environmental cues. Ignoring these behaviors can oversimplify how passage systems truly perform. Emergent™, developed by Kleinschmidt Associates, introduces a behavior-informed modeling framework designed to close that gap.

MODELING FISH AS AUTONOMOUS AGENTS

Built on agent-based modeling principles, Emergent treats each fish as an autonomous agent rather than a passive object within a flow field. Each simulated fish carries its own energy budget, fatigue state, swimming capability, and behavioral tendencies.

As fish move through a modeled river reach or fishway, they respond dynamically to hydraulic conditions and physical features. Velocity gradients, shallow-water areas, structures, and attraction flows influence individual decision-making. The model captures how fish adjust their paths, when they hesitate, when they expend energy, and when they succeed or fail to pass.

This distinction matters.

Instead of simply determining whether hydraulic criteria are met, Emergent evaluates how energetically demanding passage may be. Fatigue accumulation and energy expenditure directly influence migration success, post-passage survival, and broader ecological outcomes. By tracking these factors, the model provides a more complete picture of biological performance.

CAPTURING SCHOOLING AND REAL-WORLD MOVEMENT

Fish migration is rarely an isolated event. Many species move in groups, respond to neighbors, and alter behavior based on crowding or social cues. These collective dynamics can significantly influence route selection, congestion points, and passage success rates. Conventional hydraulic models cannot represent these interactions because they treat fish as independent units.

Emergent incorporates schooling and social behavior into the simulation. Agents can cluster, follow one another, and adjust their decisions based on nearby fish. This allows the model to reveal high-use corridors, behavioral bottlenecks, and variability in outcomes across a migrating population.

For project teams, these insights are particularly valuable. A fishway that appears hydraulically adequate may still produce unintended congestion or energy strain when real behavioral patterns are considered. By identifying these dynamics early, teams can refine designs before construction or retrofit.

INTEGRATING HYDRAULIC RIGOR WITH BIOLOGICAL REALISM

Emergent builds directly on established hydraulic modeling tools such as HEC-RAS. Site-specific hydraulic outputs form the foundation of the simulated river environment, ensuring that biological modeling remains grounded in physical reality.

Within that environment, fish agents navigate spatially explicit conditions derived from the hydraulic model. As they move, Emergent records trajectories, time to passage, energy use, fatigue accumulation, and success rates.

The framework produces clear, actionable outputs, including spatial heat maps of movement pathways, probability-of-success analyses, and visual simulations that make behavioral patterns visible. These tools support transparent communication among engineers, biologists, regulators, operators, and other stakeholders.

For hydropower owners, that transparency is critical. Modeling results must withstand technical review and contribute meaningfully to collaborative decision-making.

PRACTICAL VALUE FOR HYDROPOWER PROJECTS

Emergent is designed as a decision-support tool for real-world applications. It can be used to:

• Compare alternative fishway configurations
• Evaluate attraction flow strategies
• Assess technical versus nature-like designs
• Examine operational scenarios under varying flow conditions
• Support adaptive management planning

By simulating how fish are likely to respond under multiple design or operational alternatives, project teams can identify potential performance issues before they become costly field challenges.

This proactive evaluation reduces uncertainty, strengthens regulatory defensibility, and supports more confident investment decisions. It also helps move discussions beyond threshold-based criteria toward a more nuanced understanding of biological effectiveness.

ALIGNING ENGINEERING DECISIONS WITH ECOLOGICAL OUTCOMES

As fish passage requirements continue to shape hydropower licensing, modernization, and restoration initiatives, integrating ecological realism into engineering practice is increasingly important. Regulators and stakeholders are asking more detailed questions about performance, variability, and long-term outcomes.

Emergent™ represents an advancement in modeling capability that bridges hydraulic rigor and biological understanding. By treating fish as living organisms navigating dynamic systems — rather than passive particles in a flow field; the framework offers a clearer view of how passage solutions perform under real conditions.

For the hydropower industry, that clarity supports resilient project design, improved ecological outcomes, and science-based collaboration.

Behavior-informed modeling does not replace hydraulic analysis. It builds upon it, adding the behavioral dimension necessary to design passage systems that truly function as intended.

And in an environment where performance, transparency, and defensibility matter more than ever, that distinction makes a difference.

To learn more, email us at [email protected] or visit us at kleinschmidtgroup.com.