Proper drainage is essential for a gravel driveway. Without it, water accumulates in ruts, creating a muddy, slippery surface that takes away from the overall beauty of a yard. Drainage options for a gravel driveway range from laying underground pipes through waterlogged areas to shaping the surface so water will naturally flow to the street. Combining multiple solutions is the best way to ensure that your driveway will last for years with minimal maintenance.
A French drain is a system of underground drain pipes that run beneath saturated areas. The pipes have holes that catch water and carry it away to dry parts of the yard or a safe outlet like the street. The pipes should run down the length of the driveway in the center or across a low-lying or flat section. Install them over synthetic filtration fabric 12 inches below the driveway surface and cover them with gravel. French drains enable water to quickly seep through the permeable surface into the pipes without harming the foundation.
During installation, layering the gravel helps establish a strong, sturdy surface with enough gaps in the bottom for underground moisture to escape. For the bottom layer, use a 4-inch-thick layer of large gravel measuring over 1 1/4 inches in diameter. The second layer should be about 6 inches thick and laid with medium, 3/4-inch gravel. Use a mix of equal parts stone dust and small gravel for the 2-inch-thick top layer. Compact each layer of rocks, and always use angular, crushed rocks, as they stabilize when compacted.
A simple way to improve the drainage of new and existing gravel driveways is to form the surface into a crown so the middle is about 2 inches higher than the sides. Use a rake to shape the gravel and compact it. Daily wear-and-tear makes tracks in the surface over time, creating spots where water can accumulate. Plan to replenish the surface with a new layer of small gravel and to reshape the crown every year or two. Avoid making the crown too steep, or vehicles will have a difficult time driving over the surface.
Lining both sides of a gravel driveway with drainage ditches provides a route for water runoff to travel through, once it runs down the sides of the driveway. Make the ditch about 10 inches wide and 18 inches deep, and shape it like a U. The bottoms of the ditches should have a slight slope toward the street of 1/8-inch deeper with every foot of distance. Fill the bottom 12 inches and the sloped walls with medium gravel, and plant flood-resistant ground cover along the top edges to absorb water while beautifying the ditches.
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