Category: Drainage

Posted on

Three of Virginia’s Most Pervasive Drainage Myths

I talk to a lot of people. It’s part of my job. And a topic that comes up all the time is drainage. I’ve seen bad advice given at parties, online, and even by well-intentioned but uninformed contractors. So that being said, here’s my list of three drainage myths that need to stop.

1. FRENCH DRAINS SOLVE EVERYTHING.

First, a definition: a French drain generally means a trench, lined with a filter fabric to prevent silt from entering, filled with a perforated pipe surrounded by clean gravel. This pipe runs through the yard and terminates somewhere that the water can flow out and away. It’s that last part that seems to escape people, the fact that the water has to have somewhere to go. I’ve talked with folks who have nightmare scenarios with a low spot and nowhere to move that water, and inevitably at least one person has told them “you need a french drain.” No, no they don’t. With nowhere for the water to go, a French drain just moves the water a foot underground, and any additional water goes right back on top of the french drain.

2. WHEN ALL ELSE FAILS, DIG A DRYWELL.

Granted, this is location dependent. Where I grew up in Rhode Island we had sandy soil that wouldn’t hold water long at all, so drywells were great. In fact, that’s where the effluent from my mom’s washing machine goes, to keep it out of the septic tank.

Virginia clay is a different story. To explain why it’s a problem, let’s look at what a drywell is trying to achieve.

We have a large volume of water where we don’t want it, and there’s no way to get it off the property on the surface. The goal with a drywell is to move it all to one spot underground so it can percolate back into the water table. The challenge is sizing a drywell appropriately. The less free-draining your soil is, the bigger the pit needs to be. Otherwise, one rain squall fills the drywell, and if the next storm comes before the water oozes its way down, your original water problem pops right back. Like this guy:

punchyclown

Now sometimes there is no other option that to put that water underground, but in that case we may need a sump pump that discharges the water somewhere else. It’s my last resort, because I’d always rather keep stormwater out of the storm sewer, but there are times when it can’t be helped. If you’re going to pursue a solution like this, just make sure that wherever you’re discharging the water 1) doesn’t break any laws, and 2) doesn’t adversely affect your neighbor(s) because they can sue you and they’ll likely win.

3. “THIRSTY” PLANTS WILL MITIGATE MY WATER PROBLEM.

How much water can you drink in a day? Now, point to where the bladder is on this birch tree:

Gill03

 

See the problem? A tree will take up as much water as it needs and, using the roots and vascular system, distribute that water where it’s needed. Anything more? Best case scenario, the plant sits in muck for a while. Worst case scenario, the plant’s roots rot and it dies.

We plant water-loving plants in mucky areas because they are what grows there, not because they’ll turn Shrek’s swamp into a verdant meadow.

SHREK

Are you still confused about how to handle your water issues? We’re experts, you should call us! 703-679-8550. I’d love to learn more about your project and discuss next steps.

Posted on

How Do I Address Hillside Erosion?

Water can cause a lot of damage. Any time you have a slope you have the potential for water and erosion issues, and it’s my job as a landscape designer to address identify and address these issues. There is no one size fits all solution to erosion issues, but we can start by understanding the causes of erosion.

Two factors that I look at when resolving an erosion issue are volume of water and velocity of water. Sometimes the problem is volume: there is so much water being dumped in one spot that it’s going to have destructive force. I’ve seen this with water rushing off the end of a driveway, or if there are several downspouts dumping in the same area.

Velocity is an issue with a steep slope. It can also be an issue with a long slope where the volume and momentum of the water build up. We actually encountered this at one of the estate properties I designed. The slope looked pretty gentle but it was so long, and the underlying soil was such hard clay, that the water washed out all the beds every time it rained.

How do we deal with these issues? If at all possible, the first place to look is where the water is entering the slope. Can we redirect it, or can we at least disperse it so that the force is spread more evenly over a larger area? From there we can also look at solutions that will slow the water flow.

A lot of people say “I need a retaining wall to slow the water flowing down this hill.” Ok, that might work; more often, I see walls that don’t do a darn thing to slow the water. Surface water just rockets over the top of the wall, which can make a pretty waterfall – but it accomplishes nothing. This is why the right design begins with a detailed analysis, including documenting grades and elevations. In many cases a wall (which is an expensive solution) isn’t actually required.

To finish the project we still need to make sure that the slope is stabilized. Plant material is what we’re talking about. If the slope is gentle enough and it can be maintained, turfgrass is an inexpensive and effective choice. Various groundcovers can be used for lower maintenance, and I’ve even designed hillside gardens with a mix of trees, shrubs, and perennials.

If you have an erosion or drainage issue that needs addressed, you need the services of an experienced design professional. Contact me to start the process.

Posted on

Drainage and Infrastructure Are Not Like Milk Duds

I’m still recovering from Halloween – 538 trick-or-treaters is a LOT Of kids – and it’s still framing how I look at things. Of the nearly $200 we spent on candy we have a bowlful left, and as I was pawing through the bowl for a mid-morning snack I kept encountering Milk Duds. Boxes and boxes of Milk Duds. They’re ok, I suppose, but I’ve never met anyone who got excited about them. It takes some amazing skill to be able to combine chocolate and caramel, two awesome flavors, in a way no one loves.

A lot of people look at the essential foundations of the landscape as if they were Milk Duds, something that you can’t avoid but don’t love. It doesn’t have to be that way! I’ve already gone on and on about dry streambeds as an attractive way to move water through the landscape. It’s also possible to move stormwater in a more formal way, using it as a water feature. When I took care of the grounds at the Salk Institute in La Jolla, California, I got to see a really neat way of handling rainwater. Here’s the wide-angle view of the buildings:

Every floor has a balcony overlooking the central courtyard, but what architect Louis I. Kahn did was he stepped each balcony back as they got higher, so that the rainwater flowed off the flat roof onto the edge of the balcony, through the scuppers, and onto the balcony below that, and on and on for the six floors of the building.

Source: tourguidetim.com

The idea was to create a series of cascading waterfalls, and it was a really cool idea. Now, ideas do come down to execution. If you worked at the Salk and wonder why you never really saw this, sadly, the reality check is that clearly the concrete company who poured the floors didn’t get the memo. In a heavy rain, water pooled on the balconies and flowed the wrong way, right into the labs. Rainy days meant all of us – landscapers, carpenters, plumbers – grabbed long-handled squeegees and saved Science from Nature. Hm. Is there an allegory in there?

Regardless, Louis I. Kahn’s design intent shows that drainage and infrastructure can be handled artfully. Where a lesser architect may have channeled the water into drains and hidden plumbing runs that daylighted in the scrub above the cliffs, he made them a feature. That’s a testament to what design can do. Thus inspired, I’m off to see if maybe microwaving Milk Duds makes them better.

Posted on

Dry Streambeds for Drainage in the Landscape

Often when I’m meeting with a landscape design client in the DC metro area, drainage comes up as a concern. Sometimes the client knows he or she has an existing problem while other times I can look at what they want to do and see that we’ll then have to move the water somewhere. Around here it’s tough, because our clay soils are quickly saturated. If we’re running water across a lawn area and there’s sufficient slope that water doesn’t pool, it’s easy to move that water. When moving a good volume of water through a planting bed – especially on a significant slope – we need to control and direct that flow. That’s where a dry streambed can be a useful feature that also looks good.

In the case above, we pulled back the sod and we could see a defined channel (swale) where the water was already flowing. It was a couple of feet closer to the wall than I had it on plan, but one thing I’ve learned is that if you’re fighting water, come heavily armed or be prepared to lose. Rather than fight nature, we shifted the streambed to follow the existing flow.

As with any part of the landscape, proper construction is key to a good result. We clear and shape the area under the dry streambed, lay down a heavyweight fabric barrier that prevents silts from migrating up from the soils, and install the river stone. I use a mix of sizes, from boulders all the way down to 1-3″ river stone, to give it a natural look. Designed and installed properly, a dry streambed can help alleviate water issues – and look great doing it.

Posted on

What is a Concrete Turndown Edge on a Patio, Anyhow?

Sounds so fancypants, doesn’t it? I have a few projects underway that need one, and it’s a simple concept that sounds more involved than it is.

When installing a patio, you want it to have a slight pitch so water doesn’t pool on the surface. If we’re lucky, the grade slopes away from the house at a similar pitch as the patio, so we can prep the base and pour the slab on grade. If there’s a massive difference in grade, we may need a retaining wall at or just beyond the edge of the patio. What about the middle ground between the two?

A turndown edge lets us build up the edge of a patio without the expense of having to build a retaining wall under it. We simply form up the edge, shape the gravel under the slab to create a shape similar to the image, and pour the concrete. Now you know what a concrete turndown edge is, should it come up as part of your northern Virginia landscape design.

Posted on

Using Dry Stream Beds for Drainage

Here in Virginia we have clay soils that don’t drain particularly well. We also get a fair bit of rainfall. When new subdivisions are built, especially in northern Virginia, the county-mandated drainage plan often moves water through everyone’s backyards towards a county storm drain. If you have a newer home, you may even have a legally designated stormwater easement on your survey plat.

What this means is that for many homeowners, you’re likely to have a fair bit of water moving through your yard during a storm event. When you moved in, the builder had probably sodded your backyard, and well-established grass stands up reasonably well to a decent volume of water moving across it.

Sometimes grass isn’t an option, though. Maybe trees have grown up and grass will no longer grow, and you’re experiencing erosion. Maybe your new patio or plant beds mean that water needs to be diverted. Or, as was the case for these folks, the slope was so steep that keeping the grass cut was a miserable experience.

So, the decision was made to turn the area in front of the downhill fence into a planting bed. Having all your mulch washed into a pile against the fence is never fun, so I looked at where the swale was most pronounced – this is where the water was flowing – and built a dry creek bed to carry the water.

We also used a number of plants to help hold the slope, including winter jasmine, cotoneaster, and pachysandra. As the birch trees grow up and fill out, this will be a nice little oasis in suburbia.

Fighting nature is hard. Working with it – whenever you can – is the better choice.

 

Posted on

Simple Factoids About Landscape Drainage

Last night I signed contracts with some great folks, and they asked me to add some drainage work while the crews are out there. We walked out to look at what was going on, and as usual I was appalled. When their patio was installed, the contractor connected the downspouts on the rear of the house to 4″ corrugated drain pipe. These come together in a “Y”, and then a short piece goes out to a low spot in the yard. Here, the pipe turns straight up and is covered with a grate flush with the lawn.

Hmm. So when it rains, water burbles up out of this contraption and pools at the corner of the screen porch for a couple of days. Plus, all the rainwater at the back of the house is being brought together into a single 4″ pipe. Idiots. So in the interest of breathing some common sense into landscape and drainage design, here are some points to ponder:

  1. Water flows downhill. Elementary, my dear Watson, but often overlooked. Don’t terminate a drainpipe in a flat area if five more feet lets you terminate on a slope. And remember to keep a constant pitch downhill!
  2. Corrugated pipe is fine, but smooth-bore is better. We’re usually gently pitched when running drain lines away from the house, which means the water isn’t moving super fast. That means sediment and funk from the roof can get stuck in the ribs of corrugated pipe and eventually clog. An even bigger issue is that smooth PVC drainpipe is rigid, so it’s easier to keep it pointed downhill. Corrugated pipe will conform to the ground around it, so after settling and a few years of frost there are uphill sections. See point # 1.
  3. 4 + 4 + 4 +4 does not equal 4. All too often I see companies hook 4 or 5 downspouts together into one 4″ pipe. Guess what? That’s a lot of water, and may well be too much for the pipe. If you add water to a funnel faster than it can drain out, what happens? If you want to get an idea of how much water comes off your roof in one storm, there’s a cool rainfall harvest calculator on this page.
  4. Pop-ups are ok, but daylight is better. Pop-up emitters serve a purpose. If you have to end a drain line in the grass, a pop-up emitter keeps you from destroying the line with your mower. It’s also a mechanical system that can fail. If the site allows it, you’re better off ending with the open end of the pipe pointed downhill – what we call “daylighting”.
  5. Be a good neighbor. This one’s pretty huge. Think about where your water is going if you move it to a discharge point out in the yard. If you’re in a subdivision where water moves through the backyards, what does it do to your neighbors if you build raised beds and block that flow? Not only is it rude and crappy, it’s often illegal to alter the drainage in a way that adversely affects your neighbor. Just food for thought.

Drainage doesn’t have to be overly complicated, but it’s definitely worth planning properly. Most residential systems won’t fail this spectacularly, but why risk it?

River birch is a great choice for wet areas!

Posted on

Why Is This Retaining Wall Failing?

I walk by this wall whenever I walk to the post office in downtown Culpeper. Walls like this are pretty common in older neighborhoods like mine. Leaning and generally unhappy walls are, sadly, pretty common as well. So what gives? Why do these walls look like they’re ready to flop over on the sidewalk?

There are several possible explanations. The first is insufficient footer, or failure to tie the wall in with the footer. When building a masonry retaining wall in Virginia you generally want to dig down 24″ below grade, so you’re below the frost line. You then pour a beefy footer (thickness varies depending on application), often with rebar coming up from the footer to tie the wall to the footer. Our home was built in 1906 and renovated in the 1950s, and I can tell you with certainty that there was not a lot of digging to frost depth being done way back then.

Another possibility is insufficient drainage behind the wall. Water is a wall’s worst enemy. Hydrostatic pressure is a major cause of wall failure. The way we avoid a buildup of pressure is by using a “drainage chimney” of clean gravel behind the wall, along with periodic weep holes.

What makes this wall great for illustrative purposes is the fact that the wall likely started to fail because of hydrostatic pressure (water buildup behind the wall). This pushed the top of the wall forward, creating a gap between the wall and the slab. What’s right above the slab? Downspouts! So not only do we have a gap, we’re pouring gallons upon gallons of water behind the wall with every storm. Awesome.

So how would I fix this wall? I think we’re beyond the point of fixing something like this, and it needs to come out. Improper construction is hard to correct, and when it gets this bad – there’s no Band-Aid big enough.

Posted on

What Landscape Work Can Be Done in Fall and Winter?

I get this question a lot this time of year. I get my fall rush once the kids are back in school, it takes a few weeks to get through the design process, and suddenly we’re just past Halloween. Is it too late? It depends on what you’re doing.

Plants

Woody trees and shrubs can be planted almost year-round in Virginia. With the exception of last winter, I’ve had plants go in – and do well – all winter long. As long as the ground isn’t too hard for us to get a pick and shovel in, we can plant woody trees and shrubs. Perennials are another matter. They are generally too delicate to plant after about November 1st, because we’re pretty certain to get a hard frost after that point. I did a post a while back that talks about safe frost dates for northern Virginia.

Asphalt

Most asphalt companies in Virginia shut down sometime in December, and open up again in April. If we’re redesigning a driveway, we need to keep this in mind.

Concrete & Mortar

Concrete is going to be the happiest when the nighttime temperatures stay above freezing. That’s not to say that concrete work shuts down for the winter. On cold days, my masons have set up tents with propane heaters and laid stone all day long in t-shirts. At night, thermal blankets can be placed on flatwork to keep the temperatures high enough. Pointing up and cleaning can get slowed down a bit because the concrete stays “green” longer, but that’s not a problem as long as the mason knows what s/he is doing.

Pavers

Pavers (and segmental retaining walls) can be tricky in the winter. The problem happens when you have a significant amount of rain, sleet, or snow on the base or sub-base. If this moisture is allowed to freeze, you can have long-term settling problems. The solution is to keep the area as dry as possible, and use thermal blankets or other means to keep the base material from freezing. Again, the work can be accomplished in the winter, it just requires a knowledgeable contractor.

Ponds and Waterfalls

These can certainly be installed in the winter, but temperatures below freezing can make working with water less fun than on a sunny, 70 degree afternoon.

Decks, Porches, Pergolas

As long as snow’s not a problem, these can be built all year long

And what if you’re just starting to think about the design process? Winter is a great time to start the design process. I’m currently booking December and January projects. If you have a project you’d like to start planning, send me an email and let’s get started!

Posted on

How Do Permeable Pavers Work?

Permeable pavers are becoming a popular choice, especially in Northern Virginia. As local governments have become more concerned about stormwater management, they’ve clamped down on the amount of runoff that leaves your property. If your total square footage of impervious surfaces exceeds the percentage allowed (they typically include homes, garages, sheds, pools, patios, and driveways), you either have to scale back your project, install a rain garden, or utilize permeable pavers.

Calling them permeable pavers, however, isn’t 100% accurate, as the water does not penetrate the paver itself. Rather, the pavers are designed to have gaps between them that allow water to pass through into the soil. An effective installation is all about the base.

Installation methods vary by manufacturer, and you should always follow their directions or those of a local soil engineer. This is what Techo-Bloc recommends in their installation instructions for the Permea paver:

  • Excavate to the required depth (base + bedding layer + paver thickness)
  • Place a layer of geotextile fabric on the soil to prevent soil particles from migrating into the base stone
  • Install a minimum 6″ deep layer of 3/4″ clean aggregate (in VA, it’s sold as 57 stone) and compact
  • Place another layer of geotextile fabric atop this aggregate base
  • Install a 2″ layer of 1/4″ clean stone (sold here as #8 stone) and compact
  • Lay the pavers per the manufacturers instructions, setting them hand tight (lugs will act as spacers)
  • Install border pavers
  • Install curbing or edging blocks
  • Install 3/8″ stone between the joints
  • Compact the entire patio

So what’s the big deal if you go off script and lay permeable pavers like you would standard pavers? Well, for starters, you’re likely to get some uneven settling from improper compaction (remember my post about problems with paver patios?). You’ll also get a patio that won’t allow water to flow through it. A standard patio base is 21A or crusher run- an aggregate mix with a variety of particle sizes all the way down to “fines.” When compacted, all these particles lock together, and good luck getting water to drain.

The good news is that the paver manufacturers see the direction the market is headed, and have provided thorough documentation for how to use their pavers. If you’re installing the pavers yourself, just do what they say. If you’re hiring someone, ask them what materials they’re using. If they mention 21A or sand, it’s time to find a different installer.