Digging A Drainage Trench – Your Step By Step Guide

If your garden doesn’t have sufficient drainage then there is a serious risk of flooding. While you might think that a minor floor will simply dry up and it’s no harm done, the opposite is true. 

Improper drainage and flooding can lead to damage to the home, damage to your plants and causes rot. It’s just not worth it but you can tackle the problem by simply installing drain pipes. For this, you’ll need to dig a trench and it doesn’t need to be difficult!

How Deep Do I Need To Dig My Trench?

Before you start to plan for your drainage trench, you’ll need to make sure that you’re familiar with the correct dimensions. Generally speaking, you’re going to want your trench to be no less than 18 inches. This is the perfect depth as it gives you plenty of room to install a gravel base as well as space for the pipe. 

If you were to dig the trench any lower, you’d find that there wasn’t sufficient space for you to cover the trench once it was done and then it would be nothing but an eyesore. 

As well as considering the depth, it’s also really important to note that your drainage trench width also matters. The wider the trench, the better and you’ll want it to be somewhere between nine and twelve inches across. If it’s any less than this then it’ll affect the drainage capacity and the system won’t perform as well. 

Choosing The Right Size Pipe

Another very important consideration when digging a drainage trench is that you’re using the right size pipe. If you choose something too narrow then you’ll find that it will get easily blocked with things like rocks, dirt and other things. 

While your drain grate should help to prevent these items from getting in, it isn’t going to stop everything so a larger pipe is best to allow for clearance of organic materials. Around 4 inches should be more than enough but also consider the type of pipe you’re using. 

If you’re just creating a standard drainage trench then you’ll be fine to use a solid pipe. However, if you’ve opted for a French drain then I’d suggest going for a perforated pipe. 

What Tools Do I Need To Dig A Drainage Trench?

Because a drainage trench is not the biggest or most complex task in the world, you won’t need any specialist equipment to get the job done. For the most part, this can be done by hand, as long as you’re willing to put in a little hard graft and you’ll need a good shovel for this. 

I’d also recommend having a pickaxe on hand for any rocky or tough ground. But these are really the only tools you’ll need for a standard sized trench. 

On the other hand, if you plan to dig something longer, you might need to rent a trencher which will make life easier. These are also good if the ground is particularly rocky and can make the process far quicker. 

Step by Step Guide For Digging A Drainage Trench

Now you know exactly what you need to dig a drainage trench, I’ve created this easy to follow step by step guide. Take your time with the work; there’s no need to rush and it’s better to get it right the first time than to rush through only to realise you forgot something!

Step 1  – Planning The Dig

I would not recommend going into this job blindly. There are a few things you will need to think about before that shovel goes anywhere near the ground. Careful planning could be the making or breaking of the job so take this step seriously.

You’ll want to think about where the problem areas are in your garden and where the water is coming from. Once you have figured this out, you’ll then need to think about where you can redirect the water safely. This needs to be somewhere that’s well out of the way of your property but that also won’t interfere with your neighbours.

It’s best to direct the water downhill and as far from the problem areas as possible. A lot of people choose to use a solid pipe but perforated pipes in French drains are my preferred option as they’ll evenly distribute the water and will reduce the chances of erosion. 

Step 2 – Creating The Right Slope

The next thing you’ll need to do before you start digging is to plan your slope. As I mentioned, you must redirect the water downhill and the best measurement for this is to slope down by an inch for every ten feet of pipe.

It’s not difficult to determine the slope. You simply need to place wooden stakes along the ground at inch intervals. Place one stake at the point where your drain will begin and another where the drain will end. Now take some string and tie this between your stakes ensuring that it’s completely level.

You can now measure the difference in height between the two stakes using the string and this will tell you the slope. 

In some cases, the garden will be totally flat and this means that you’ll have your work cut out for you a little more because you’ll need to create a slope. To do this, you should dig the trench an additional inch deeper every ten feet. It’s really important to get this right because, without the right slope, the water will not drain away and all your hard work will be in vain. 

Step 3 – Start Digging

You can now use your chosen tool to start digging your trench. As we discussed earlier on, the importance of digging an adequately sized trench cannot be understated. You’ll need to make sure that it’s large enough to contain the gravel base which we’ll install later on, the pipe and enough room to cover it when you’re done. 

Dig down to at least 18 inches while ensuring that the trench remains between 9 and 12 inches wide. Of course, it’s also really important to make sure that your trench follows the slope you determined earlier, otherwise the water will not drain. 

Step 4 – Using Landscaping Fabric

Once the trench is finished, you will need to choose a water  permeable fabric with which to line it. The reason for this is that it will stop plants, weeds and grass from growing into the trench. If this happens then there’s a very good chance that the roots will block the pipes and cause damage so this is an incredibly important step. 

You’ll likely find that the landscaping fabric comes over the edges of the trench and that’s OK. We will handle this later on, for now, leave it as it is. 

Step 5 – Creating A Base For The Trench

The next step is to create a gravel base for your drainage trench. You’re going to need at least three inches of gravel at the bottom and this can be poured directly on top of your landscaping fabric. 

If you’re making a French drain then this step is even more important as the gravel will evenly filter the water into the soil. In any case, gravel is going to improve drainage, even if it was used entirely on its own!

Step 6 – The Drain Gate

Once you’re done with the gravel, you will need to think about a drain gate. You can do this either near a downspout or in an area where floods are problematic within the garden. The drain gate will take in the water that would otherwise flood and direct it along your trench.

This is why it’s important to start digging your trench at the problem area so you can easily install the drain gate at the top. 

Step 7 – The Drain Pipe

Now you’re going to need to install your drain pipe which you will attach to the outlet you have just installed. The pipe needs to sit along the base of your trench, on top of the gravel. 

There are two different types of pipe depending on what type of drain you’re building. Perforated pipes are commonly used for French drains and allow the water to be distributed below the ground all along the trench. These are great if you don’t want a splashing spout at the end. 

On the other hand, you might choose a solid drain pipe which will direct water away from the flooded area and out into a suitable area such as a rain garden, pond or gravelled area. 

Regardless of the type of pipe you choose, it’s really important to ensure that it is connected securely all the way along. Also ensure that the trench base provides solid support so there’s no risk of anything collapsing. 

Step 8 – Adding More Gravel

Now that everything is in place, you will need to cover your drain pipes in the trench over. The best thing to use for this is more gravel as it’ll further improve drainage in the area and offer a good degree of protection to the pipe.

Step 9 – Finishing Off The Fabric

Earlier, I talked about having some excess fabric and now is the time to deal with this. You can simply fold this over your gravel which will offer further protection from pesky plant roots.

Step 10 – Covering The Drainage Trench

The final step is to cover the drainage trench so that you’re not left with a mess. One of the most common options is to add more gravel. You can choose something that matches other gravelled areas in your garden so the trench will completely blend in. 

However, some people prefer to cover it over with soil and lay a lawn over the top; nobody would ever know the trench was there!

If you want to make a bit of a statement, you could line the trench with stones and create a brick border. The only limit is your imagination.

However, one thing you do need to keep in mind is that you may need to perform maintenance on the trench. To make life easier, gravel is usually the best way to cover the trench as it’s simple to remove and won’t require any additional digging. But that said, as long as you’ve followed these steps properly and paid close attention to how you’ve installed the drain, you should find that it’ll last for many years without fault.


Proper drainage is so important around your property. Without it, flooding can cause expensive damage so it’s worth taking a weekend to install a drainage trench. 

The good news is that you’ll only need some simple tools and to follow some easy steps. The depth of the trench and size of the pipe should be carefully considered but once the drain is installed, it’ll serve you for years.

Driveway Expert