Which slope percentage is recommended for swale designs to ensure effective water flow?

For effective water flow in swale designs, a slope percentage of less than 1% is recommended. This gentle slope encourages the smooth movement of water through the swale, reducing the likelihood of erosion and allowing for better infiltration into the surrounding soil. When the slope is too steep, as can be the case with higher percentages, water can flow too quickly, leading to issues such as erosion and the potential for sediment being washed away.

A slope of less than 1% facilitates manageable water velocity, ensuring that stormwater is effectively conveyed while providing adequate time for infiltration and pollutant filtration. As water passes slowly through a swale designed with this gentle slope, it also allows for the natural treatment processes to occur, which are essential for improving water quality before it enters larger bodies of water or drainage systems. Therefore, the recommendation for a slope of less than 1% aligns with best management practices in stormwater management, promoting both effective conveyance and environmental stewardship.