Which of the following is NOT a purpose of an endwall?

An endwall serves several essential functions in managing drainage systems, particularly in relation to pipes that handle water flow. One of its primary roles is to ensure stability and support; it holds the embankment away from the pipe, preventing any potential collapsing or settling that could lead to structural issues. Additionally, endwalls are designed to prevent the flotation of pipes, especially in situations where water levels may rise and exert upward pressure on the pipe. By doing this, they help maintain the integrity and functionality of the drainage system.

Another critical purpose is to protect the roadway from erosion. Endwalls effectively channel water into the drainage system, reducing the risk of water pooling or causing erosion around the roadway edges.

The option regarding enhancing water flow speed does not align with the primary purposes of an endwall. Instead, the focus of an endwall is more about sustaining structural integrity and preventing erosion rather than increasing the speed of water flow. In fact, while it facilitates water passage, it is typically designed to manage flow rather than enhance it. Therefore, this understanding of an endwall's roles clarifies why "enhance water flow speed" is the correct response to the question.