How To Design a Drainage System

Step 2

Please first read Step 1 of our Drainage Guide

In Step 2 you will find information on:

  • How to design and build an affordable drainage system
  • French drain and drywell tips for your lawn
  • Downspout and foundation drainage fixes


NOTE: There are a lot of links in the article below. IT IS IMPORTANT TO USE THEM.
Most go to other pages in our Drainage Guide. They allow this complex subject to be presented in a compact form.

This section will describe both how to design your water drainage system, and maybe how to avoid having to install one at all. Gather your sketches and notes and we will get started.

Look at your notes from Step One - "How To Analyze Your Yard Drainage Problems" - to see how long it took the different areas of standing water to disappear and to decide which situation below fits your lawn or garden drainage issue. The links below will take you to specific design and installation information.

If the standing water disappeared in an hour or two...
then your lawn, yard, and garden has decent drainage and all you probably need to do is to fix any downspout problems.

If you have water collecting next to your foundation...
then you will need to check and correct the slope of the ground next to your foundation FIRST.

If there were no Rainy Rivers, or they disappeared quickly, or flowed into a safe area...
then you can focus on eliminating any Soggy Lawn Swamps by installing a French drain or building drywells to drain them quickly. Along with fixing any downspout problems.

If your drainage problems are more severe, or fit into multiple categories...
then you will have to design and install a connected drainage system utilizing the information below.


Below are important drainage system design guidelines, rules, and information

Be sure to follow the link for each topic to read more about it.

Foundation drainage and downspout issues are critical
A soggy lawn is annoying, but a flooded basement or crawlspace is expensive and potentially destructive. Always fix foundation and gutter drainage issues first.

Keep your water on your own property if at all possible
Draining your excess water away to the street or a ditch seems like a simple solution, but it just transfers your problem to others. Also your lawn, trees, and plants will be healthier if you have created a store of rain water in the subsoil for your plants to access in dry times. Only after all other options to improve your drainage and keep the water in your own soil should you send the excess off-site.

Water will flow along the path of least resistance
Water flows downhill, not uphill. Water will flow through loose gravel easier than through tight soil. Water will flow through a pipe easier that through gravel or soil. Drainage is improved when water can easily flow from soggy areas to drier areas.

A French drain is simply a trench full of gravel that moves water horizontally
A french drain collects water from a soggy area and distributes that water to drier areas. French drain systems often contain one or more pipes buried in the gravel trench to speed up the water flow.

Water can flow into, out of, or through drainage pipe
Remember that there are two types of drain pipe: perforated and solid. Perforated pipe has many holes punched or drilled into it to allow water to both enter and exit the pipe. In any drainage system design, there is often water flowing IN through the perforations in a soggy area at the same time there is water flowing OUT of the perforations in a drier area. The perforations always go on the bottom. Solid pipe is used in a drainage system to carry water PAST areas where you do not want to add more water. Most drainage systems need to use both types of pipe, in different areas.

A drywell quickly moves water deeper into the subsoil.
The purpose of a drywell is to allow water to enter the deeper subsoil faster and easier. It is simply a hole dug downward into the subsoil and filled with gravel or a sleeve. A small drywell can be dug with a posthole digger. A large drywell may use a drum or a precast concrete cylinder as a sleeve.

Designing a drainage system is a bit complex, but fortunately most of the knowledge and techniques are fairly simple.

Please read ALL of the above linked sections before going on to Step Three - "How To Diagram and Layout a Yard Drainage System"