When it comes to dealing with storm-water and heavy rain run-off, you’ve got a few options. For smaller quantities which are creating puddles, a French drain or rain-garden might be the solution. For bigger problems, a dry well could well be the solution. But what is a dry well exactly and how do they work?
What Is a Dry Well?
Put simply, a dry well is a perforated container set into the ground. They’re designed to collect and disperse surface water underground where it can flow away more easily. They generally consist of:
- The dry well itself, a perforated chamber
- A gravel bed around the dry well
The area around the dry well is generally filled with gravel or rocks as a basic filter, helping stop debris from clogging up the pores. This also helps keep the out-flow regulated, avoiding causing issues from over-saturated soils around the dry well. Installations in sensitive areas and commercial premises might include filters and treatments to help avoid oils and chemicals finding their way into the water table too.
While they’re not totally dissimilar to other drainage systems like French drains in design, a dry well catch basin serves a different purpose. Where French drain allows you to move water around your property, a dry well helps counteract poor reabsorption or avoid waterlogging when conditions are extremely wet. This allows for effective recharging of the local groundwater levels, circumventing any low permeability clay layers in the local soil, boosting plant life and soil health.
How A Dry Well Works
Having answered the question “what is a dry well?” it makes sense to look at how they work. On the most basic level, they collect the water then disperse it through the soil where it can be absorbed. The process goes something like this:
Collection
Run-off is funneled into dry well from roofs, gutters, downspouts and sump pumps or anywhere else that funnels water. It’s held here until the weight of water starts to push it out into the surrounding soil.
Dispersion
Once collected in the dry well itself, the weight of the water creates a certain level of pressure. This forces the collected liquid out through the small perforations in the wall of the well and into the gravel bed. The stones that surround the dry well then further disperse this water into the surrounding soil.
This allows an even distribution and absorption, avoiding soil-erosion and surface-pooling as the ground becomes waterlogged.
Benefits of Installing a Dry Well
While digging a pit in your property then lining it with a casing and gravel may seem like an extreme course of action, dry wells come with a lot to recommend them.
Flood Prevention
A well designed and installed dry well is a fantastic defense against storm related flooding. They can hold upwards of 50 gallons at a time (and this can be increased during installation if necessary). This water is then slowly released below ground where the soil can absorb it, replenishing groundwater in a controlled manner.
Groundwater Replenishment
As the climate changes, we’re experiencing wetter winters and dryer summers than we once did. Dry wells have a vital role to play in mitigating both these phenomena. By collecting storm water during the wet seasons, then slowly releasing it below any impermeable layers of clay or loam, they can naturally replenish groundwater levels during the dry season. This is good news for gardeners and the planet alike.
Environmental Benefits
It’s no great secret that our cities and towns are dirty places. There’s no getting around the fact that when large numbers of people congregate in a small area, they cause pollution. Fumes, sewage and particulate matter all find their way into our water ways via rain water run-off. Dry wells can play an important role in minimizing this.
By filtering water before releasing it, a good proportion of the contamination can be removed before it gets into the natural environment. Likewise, because a well installed dry well releases water slowly, it can stop sewage systems being overloaded, causing overflows of all the things we’ve flushed away.
Cost Effectiveness
Depending on the quality of the soil on your property, a drywell can offer a great, cost-effective way to manage excess water. They’re remarkably simple devices, requiring only a small area of excavation work and very little maintenance. This means that while the initial installation will have a cost, it’s not exorbitant and there are little ongoing costs (occasional cleaning and a quick inspection is generally enough) for a remarkable level of efficiency.
Types of Dry Well
What is a dry well? Well, there are various variations on the theme. Each is effectively the same basic concept, a reservoir set into the ground, but there are certain differences which mark them out:
- Traditional Gravel Dry Wells: They’re simple and effective- dispersing water evenly through the soil and can be customized to fit your particular needs during design.
- Prefabricated Drywells: Modern manufacturing techniques allow a range of pre-made kits, usually made of fiberglass or plastic, to be quickly installed. They’ll also last and last, thanks to how durable modern materials are.
- Deep Pit Dry Wells: In areas with poor surface drainage or which deal with huge amounts of run-off, going deeper may be the answer. They require more effort to install- going anything up to 70ft down- but can handle the worst drainage issues.
- Modular Dry Wells: Much like the prefab versions but with much greater customizability. They allow a bespoke solution to be crafted to meet the needs of location, size, shape and other considerations.
When Should You Consider a Dry Well?
Dry wells offer a fantastic solution to problems with water not draining away naturally, but they’re not right for every situation. Here’s when you should seriously consider installing one:
Persistent Water Pooling
If your home is in a low-lying area and prone to problems with surface water pooling, especially after rain or from snow-melt, a dry well could be the answer.
Redirecting Downspouts Away from Your Foundations
While keeping your gutters and downspouts clear and flowing is vital to dealing with rain, where they lead to is every bit as important. A dry well offers a safe, environmentally friendly option.
Dealing with Run-off from Hardscaping
Just like your roof, any solid elements of your property will have to deal with run-off when it rains. Things like driveways, patios and other paved elements can create channels for water to flow where you don’t want it to. A dry well deals with this issue.
Preventing Soil Erosion
If your property sits on a slope, soil erosion around your foundations can be a serious issue. Placing a dry well at the bottom of the slope can help capture and ensure the even distribution of water, cutting down the risk to your home and garden.
Compact Spaces
Sometimes there simply isn’t room for another solution, so downwards is the only way to go. Smaller properties or urban gardens can often make great use of a dry well to deal with their run-off problems without encroaching across the boundary.
The Installation Process
Installing a dry well is generally a pretty straightforward process that runs a little like this:
- Site Inspection: Professionals will assess the site to find the perfect spot. Ideally this will be downhill and a good distance from your home.
- Excavation: This is the disruptive bit. The dry well itself will need to be dug out. How deep you go depends on how much water you expect to have to deal with. If you’re wondering how deep a dry well should be, the answer will depend on how much water you’re likely to be dealing with. Most residential dry well catch basins are about 4-8 feet deep.
- Lining and Filling: This is creating the mechanism of your dry well. The newly excavated well will be lined with fabric then filled with gravel. Alternatively, if you’re going for a prefabricated model, this will be embedded in gravel.
- Connecting it: Any existing drainage should be routed to the dry well. This could include things like sump pumps, French drains, downspouts.
- Backfilling and covering: Now we cover it over.
Usually this work can be carried out by a standard professional but if you’re dealing with a large amount of water, consulting a civil engineer might be worthwhile.
Maintenance and Lifespan
With a good maintenance routine, a modern dry well can last a lifetime. Regular inspections should warn you of developing problems and this, combined with clearing and cleaning out the debris, should ensure that you avoid clogging or overflowing issues.
So, to answer your initial question: what is a dry well? A good investment in keeping your property free of waterlogged soil and your yard looking lush.