One of the most important elements of designing a proper drainage system is determining how much rainwater is falling on your property and what to do with this volume of water.
Here is a list of a few things that you will need:
- Paper
- A pen or pencil
- A tape measure
- A calculator.
Now that we have calculated the rain water run-off we need to convert the run-off into volume. We multiply the run-off by the length of time in minutes that we are collecting the runoff. Check the rainwater requires in your municipality. They will let you know how much water you must store on your property and how much water you are allowed to release to the public rain system. Many municipalities follow the first flush rule. This rule states that the first 15 minutes worth of run-off must be stored on your property. The first flush picks up:
- oil,
- pesticide,
- fertilizers
- Other pollutants that are located on the ground.
By capturing and storing this water on site, these chemicals are not washed into the public rain system. Recalling from our previous example, 24 gallons per minute times 15 minutes equals some 360 gallons of water to be stored.
To figure out how to store the water: The flo-well and easy drain are two products often recommended for storing water run-off. A flow well is a sub-surface manufactured dry well used to temporarily store run-off water as it percolates into the ground. The flo-well is a gravel free alternative to a traditional dry well. There are two ways to install a flo-well. Either directly in the soil or with gravel backfill.
A flo-well installed without any backfill can hold 50 gallons of water. If you choose to install to a flo-well this way you will need seven flo-wells to store 360 gallons of water. If you backfill around the flo-well with 1 foot of gravel this system will store 145 gallons of water in this configuration you would need 3 flo-wells to store 360 gallons of water.
Easy drain is a gravel free alternative to a traditional gravel French-Drain.
Easy drain can be used to drain, pipe away or even store excess rain run-off. Easy drain is available in two sizes; 7 inch or 8 inch total diameter. The 7 inch diameter is primarily available in California and 8 inch everywhere else. The 7 inch size can hold 11 gallons of water per 10 foot section. If you wanted to store all 360 gallons of water using just 7 inch easy drain you would need 32 sections of 10 foot. The 8 inch diameter easy drain can hold 16 gallons of water per 10 foot section. It would take 23 sections of 10 foot to store 360 gallons of water.
Easy drain and flo-wells have been designed to work together to create a complete drainage system. Here are two different ways to store 359 gallons of water using flo-wells and easy drain together.
Five flo-wells installed without backfill can store 250 gallons, 9 sections of 7 inch easy drain can store 103 gallons of water. Together they hold 353 gallons of water.
OR
If we use flo-wells installed with one foot of gravel backfill an 8 inch easy drain, 2 flo-wells can store 290 gallons and 4 sections of easy drain can store 63 gallons. Together this system can also store 353 gallons of water.