Flooded parking lots are a common problem that apartment complexes face. Not only do they make tenants unhappy, but they can reduce the overall amount of parking your apartment has available — tenants won't park in spaces that they know flood badly even during minor storms. Thankfully, there are a number of drainage solutions to fix this problem. Here's what you can do to keep your apartment complex's parking lot from flooding during storms.
Divert Rainwater Away From Your Parking Lot and Onto Permeable Land
The first step is to divert as much rainwater as possible away from your parking lot. Parking lots are impermeable surfaces (except for porous concrete parking lots, which is quite expensive to install), so it's important to keep as much water off of them as possible. An inundated parking lot can easily overflow your catch basin, since there's no soil for the water to saturate.
The best way to accomplish this is to dig a swale somewhere on your property and ensure that a portion of your rain gutters are directed towards the swale. A swale is a U-shaped grade of land that surrounding groundwater will naturally flow towards, allowing the soil in the swale to become fully saturated with water. Water will eventually evaporate from the swale once the rains have stopped.
A landscaping company can dig a swale anywhere on your property where there's soil available. You can landscape a swale to beautify your apartments, but you need to select plants that are very water-tolerant — swales often become marshy since they collect so much groundwater. Diverting rainwater away from your parking lot and into your swales makes the most use out of the permeable surfaces on your property, allowing the earth to bear some of the burden of heavy rain instead of your catch basin.
Improve Drainage Around the Parking Lot With French Drains
Next, you'll need to make sure that your parking lot is well-drained. Installing French drains around your parking lot is the best way to accomplish this. French drains consist of a level of gravel with a layer of filter fabric on top. You can also install a porous pipe within the gravel layer to increase their ability to move water quickly.
French drains work as a drainage solution because water always takes the path of least resistance. Water flows downhill, so it will always naturally gravitate towards a deep trench dug in the soil. Water also moves laterally within the soil once it encounters resistance such as shallow bedrock or compacted soil, which means it will eventually end up being carried away by the French drain — gravel provides little resistance to water and the porous pipe provides absolutely none. The French drains should be directed towards your catch basin.
Install a Sump or Sump Pump to Fight Severe Storms
The final problem that apartments encounter with their parking lots is flooding during severe storms. This usually occurs when your catch basin itself is flooded — whether you're using city storm drains or a drain field as a catch basin, heavy flooding can eventually cause it to back up into your parking lot.
Tenants typically expect heavy flooding in the parking lot during severe storms, but there is a way to prevent it from happening. You can either dig a sump somewhere on your property or install a sump pump near the catch basin. A sump is a deep hole that's filled with gravel and it functions as an alternate catch basin. Excess rainwater will be held there until the surrounding soil begins to dry out.
A sump pump is useful as a drainage solution when you have permeable land on your property that's uphill. You can use the sump pump to pump water uphill onto this permeable land, dig a swale there and then allow the soil to saturate.
While parking lots provide many drainage challenges for property managers, there are always ways to solve them. It's best to work with a professional landscaping company that installs commercial drainage solutions, as they can measure the grade of your property and determine where the worst drainage issues are occurring. By installing proper drainage and diverting as much rainwater away from your parking lot and onto permeable soil as possible, you'll be able to stop your parking lot from flooding and keep your tenants happy.