Maybe you have heard - that Water Wins, Every Time - This is true for many construction and maintenance items - Pavement in particular is very susceptible to water damage.
Pavement failure is most often caused by water beneath the surface. According to studies, pavement subgrades that are saturated just 10% of the time have a 50% reduction in actual useful life. So keeping the pavement dry is important!
Have any Doubt? Check out Photo 1 – these concrete carport footings are 12 years old and have been heaved over 30" inches out of the ground! REALLY! And a real nightmare for the property manager and owners who have to solve it. How does this happen? If you guessed water you are right! These footings did NOT extend below the frost line ( typically 48" is standard for these and other type of posts)
How does this affect your pavement? A second photo below shows "dimples" from the static load of vehicle front tires. Front tires have heavier loads than the rear tires due to the engine being in the front of most cars. In these photos, the depressions are 3-5 inches deep. The pavement isn't compacting more, in fact there is only 3" of pavement present. The wet subgrade underneath the paving cross section is mixing with the subgrade (clay) and in doing so - losing the ability to withstand loads- particularly these heavy static loads that sit for long periods of time. The aggregate (stone) gets forced down, and the clay moves upward- the paving loses its support and the depression occurs.
Surface water - leads to subgrade water. Not only will standing water cause damage to new pavements, but cracks will let in a large amount of surface water - getting in to the subgrade and multiplying the rate of subgrade failures.
Stopping water is a challenge and since "water wins" controlling it and channeling it away from your pavement is critical to building a pavement that will be long lasting.