Grading and Drainage Plan: To Swell or Not to Swale?
In this article we will be covering the primary reasons homeowners should evaluate and implement a proper grading and drainage plan, as well as methods that can be incorporated to help maximize the infiltration of water into our soil whilst simultaneously maximizing natural drainage away from the home’s foundation.
Expansive Soils and Their Effect On Your Foundation
The Proper implementation of a grading and drainage plan is vital for those of us living in and around the Gulf Coast region, particularly home’s built in areas known to have expansive soils. The primary reason to control the moisture levels around your home is for the stability of your foundation. The oft used analogy in regards to expansive soils is that of a sponge. When we add water to a sponge, the sponge expands, however; if we compress the sponge or allow it to dry out, it would shrink. This same principle applies to the soils beneath your home. That is why, during periods of low rainfall it is critical to ensure that the perimeter of your home’s foundation receives a controlled amount of moisture.
Characteristics of a Functional Swale
A common way to passively control the moisture that collects on your property is to implement a swale. A swale is a natural or man-made sloping of the uppermost soil horizons which gently routes water to a designated location off of your property, while maximizing soil infiltration and limiting the harmful effects of property line erosion.
- Most effective way to passively control the amounts of rainfall that your property receives
- The uppermost soil surface slopes at a minimum 6″ within the first 10′
- Provides a positive slope away from home’s foundation, yet gentle enough to maximize infiltration
- Discharges to a suitable collection point
The image above depicts the ideal method of passively controlling the water that introduces itself onto our soil throughout the years. It is important to note that the goal of a properly defined swale is not just to collect and reroute water. An effective swale should also control the rate at which surface drainage flows. Remember, a gentle but controlled flow of surface water discharge will provide your home’s soil with a sustained moisture level without creating erosion problems.
The effectiveness of your swale will depend largely on the method utilized to build your homes pad and foundation. Avoid using ground cover material with high porosity, such as pea gravel, bull rock or other coarse grain surfaces. Porous materials allow increased rates of water infiltration to rapidly pass through your soil and into the layers below, ignoring all your hard work at controlling your homes moisture levels. A more efficient method utilized is to provide an impervious upper surface like healthy layered sod, mulch, and other fine grained soils.
Gutters and Underground Drains
However, with the close proximity of neighboring homes within the more urban areas, implementing a functional swale may not always be possible. The addition of gutters, underground drains, and catch basins are all options available to home’s within a close proximity. The overall function of the guttering and underground drainage system is the same. Keep water from over-saturating your bearing soils. Remember, the number one reason that home’s experience differential movement that requires correction is caused by poor soil conditions. A proper guttering system will collect and route water approximately five feet away from your foundation, to a location that can safely manage the volume.