More about soil cement:
Soil cement is not just soil but
(Emphasis mine)
Introduction: Soil cement is a composite material composed of soil, cement, and water that is used to create a strong and durable construction material. The process involves mixing soil, cement, and water in proportions and compacting the mixture to form a solid mass. The result is a strong and...
www.engineeringcivil.com
So, it sounds like it was there to support the riverboat track. Structural support.
Since you can't even see the track through the water, I'm uncertain how it could be there for aesthetics.
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