Which of the following conditions improves sedimentation efficiency?

Uniform, horizontal, low velocity flow across the basin is crucial for improving sedimentation efficiency because it allows sediment particles to settle out of the water more effectively. When the flow is uniform and at a low velocity, sediment particles, which can be small and easily suspended, have a better chance to gravitate towards the bottom and settle without being disturbed by turbulent forces. This kind of flow condition minimizes the resuspension of settled particles and provides a stable environment ideal for sedimentation.

In contrast, high velocity flow or enhanced turbulence can keep sediment particles suspended in the water column, preventing them from settling. A minimal surface area for sediment settlement would also hinder the process, as there would not be enough space for particles to accumulate. Therefore, maintaining a smooth and predictable low flow across the basin is essential for maximizing sedimentation efficiency.