Especially here in Arizona where we have torrential monsoon rains, any pavement construction work should seriously consider the proper installation of the accompanying drainage systems. Failure to properly drain a pavement, aside from inconveniencing others, can damage the paving itself. Standing water compromises the integrity of the materials, and over time, will result in cracks and holes that would require repairs, if not outright replacement of the entire pavement.
Before a pavement is placed, the ground surface must not only be adequately compacted and leveled. It must also be shaped and graded so that it drains well and it drains towards the right direction. Water that does not properly drain can wash out the underlying substrate of dirt, gravel or other aggregates used between the raw earth and the paved surface. Once the base layer is washed away, the asphalt or concrete paving becomes more susceptible to cracking, breaking, and the formation of potholes.
Even on relatively flat areas, most professional paving contractors say that the paved surface should be given at least a two-percent slope and a crown of at least a quarter-inch per foot for proper drainage. Other considerations include evaluating the potential runoff from any surrounding structure’s downspouts, walkways and patios. Ideally, a pavement should be built so that it slopes towards some free-draining open ground or a natural watercourse like a ditch, stream or river. If this is not possible, then the pavement may be sloped in the direction of the installed filter drains, soakaway systems, swales and other subsurface drainage structures that can hold water where it will percolate and evaporate back to the environment over an extended length of time. If this alternative is also not available, the next preferable option would be to simply direct the flow of water from the pavement to the existing surface water gullies that carries the run-off into the storm-water sewers.
Ideally too, a pavement should slope away from any building to prevent surface water from “hanging” or “clinging” against the masonry where it could lead to problems with damp. Finally, it may be important to know that there are also some jurisdictions where allowing water to drain away from private paths, parking lots, driveways and pavements towards a public highway, street or footpath is already illegal and punishable. If you’re in one of these areas, make sure that you do something about your pavement drainage system right away if you want to avoid the hassle of being issued a citation and having to pay fines.
