While retaining walls are designed and built to hold back earth and fill they will also hold back and channel water. The water that builds up behind a retaining wall is referred to as “hydrostatic pressure” and the external force of the material/fill held behind your wall coupled with the weight of the water is often enough to seriously compromise the integrity of your wall and even cause failure and collapse.
A good drainage system should be an integral part of any retaining wall design. Depending on the type of material being used to build the wall there are a variety of ways to integrate sufficient drainage such as weep holes, lateral drains, blanket drains and also the use of very granular soil or fill.
Don’t underestimate the external forces that are being applied to your retaining wall as there are many retaining walls throughout our area that have failed due to poorly thought out or non-existent drainage. Don’t let your contractor make this mistake!