How should the underdrain be sloped in the construction of permeable pavement?

The appropriate method of sloping the underdrain in permeable pavement construction is to direct it downward towards the outlet at a grade of 0.5% or steeper. This sloping ensures that water collected by the permeable surface drains efficiently through the underdrain system. By maintaining a downward pitch, gravity aids in the rapid removal of stormwater, thereby preventing water from pooling and potentially compromising the integrity and effectiveness of the permeable pavement. A slope of at least 0.5% is optimal as it provides sufficient grade for drainage without causing erosion or excessive velocity of water flow. This design ultimately enhances the performance of the permeable pavement system in managing stormwater runoff effectively.