Which material is NOT used to stabilize a B-3 swale's flow channel?

The correct answer is that concrete slabs are not typically used to stabilize a B-3 swale's flow channel. B-3 swales are designed primarily for managing stormwater and erosion control in a natural manner. Therefore, the materials utilized for their stabilization and protection often include those that promote vegetation and allow for natural processes.

Gabion baskets are often used in erosion control because they are filled with rocks and can withstand heavy flows while promoting vegetation growth around them. Seed and mulch are crucial for establishing vegetation in the swale, aiding in soil stabilization and erosion control through the growth of roots. Similarly, 4"-7" stone is used effectively in channels to facilitate flow while minimizing erosion. These materials support the ecological function and aesthetic of the swale.

In contrast, concrete slabs would be considered too rigid and unnatural for a swale. They would disrupt the natural flow of water, potentially leading to increased erosion issues downstream and detracting from the swale's intended function as a stormwater management feature. Therefore, the use of the other materials aligns with the goals of maintaining ecological balance and effectiveness in managing water flow.