One of the most common and sometimes costly mistakes that is made when creating a new landscape is not paying attention to or having a drainage plan.
Through the desire to create an aesthetically beautiful property the homeowner may inadvertently forget that water comes from numerous sources. Rainwater not only wets the property directly, but indirectly as well.
Rain falling on the roof of a home, generally collects in rain gutters and then is directed to down pipes. The down pipes then send the water through a spout to the lawn or driveway. If the landscaping has not been designed to direct the water away from home foundations, sever basement flooding and wall damage may occur.
Many properties have lot line grading, which allows for the flow of excess rainwater to be channeled between homes to roadways that have storm sewers others may have their backyards graded to allow for water to flow to the far end of the backyard and then be directed to a storm sewer. Inadvertently changing the grading, even by a few inches can channel the water in a different direction, such as your basement or worse, your neighbors.
If you are re-grading your property as part of your landscape project I would highly recommend the use of a laser level. Place the laser level at the corners of the buildings on your property and point them towards the direction of the drainage. If you discover objects, such as mounds of earth, planters, steps or walkways that are higher than the position of the laser level on the property you can do one of two things. Lower the level of the obstruction or make sure that there is an adequate drainage path around the obstruction.
The same problem exists for raised flower and vegetable beds. Water must drain naturally from these beds in order to avoid water collecting just below the surface of the ground and rotting the roots of the plants. Gravel bases should always be placed at the bottom of any earth mound to give the water a place to drain. Water relief channels should always be provided in retaining walls to avoid water collection that can cause walls to lean and if they are made of lumber the water will cause the lumber to rot. Excess ground water can also cause walkways to lift.
As with any landscaping project, proper planning is the key to success.