When Dealing With Drainage, Do It Right

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Water Water Everywhere

Over the past few decades, we’ve seen “hundred year” weather events become every-few-year events. Even diehard deniers of global warming are grudgingly admitting that when it comes to weather, things just ain’t what they used to be. Thus, I am not alone in having an outdated, overwhelmed drainage system. The 30 year old curtain drain around the house failed for the first time last week, and a (rather expensive) visit from Roto Rooter proved that our roof drains also need repair and upgrading.

Sadly, we’ve already had drainage work done twice in the past six years. Happily, my housemate works for a realtor. She pointed out that good realtors are always being asked for service worker recommendations by both buyers and sellers. Because their name and reputation are on the line, experienced realtors can steer you to very good workers who are pleasant, courteous, very efficient and reasonably priced. What’s not to love?

Digging For Progress

When the garden looks like a little lake, it’s time to take a deep breath and make the call for help. Thus, I did. Now, a very knowledgeable young man is helping me figure out exactly what needs to be done to handle not just the water we’ve got but to accommodate the very real possibility that we’ll be experiencing very heavy rains more and more often in the near future.

Presently, our long, sloping driveway drains almost directly into the garage (it makes a little detour to flood the garden as well). The standard drain installed by the home builder some 18 years ago proved woefully inadequate for the big rains of recent years. It will be well worth the $1,000 or so this will cost to insure a dry home and garden as well as a firm driveway.

French Drains Ahoy

French drains are deservedly popular in the maritime Northwest. Thanks to combinations of soil types, sloping land, and house siting, many Northwestern properties do not drain as well as we would like them to. Many a backyard becomes a swamp in winter. Many a garden turns into a bog whenever it rains for a few hours. Worse still, many a slope starts slipping in wet weather.

Bluffs and slopes can be treacherous indeed. Overwatering in summer, excess tree cutting, and careless clearing make matters worse, but part of the problem is built in. Most Northwestern homes are built over a dense layer of hardpan (glacial till), almost impenetrable soil that often lies just a few inches below the surface.

When It Rains, It Pours

When it rains, the water percolates fairly quickly through sandy loam, gravel, or top soil. When water meets hardpan on a flat site it pools up, the starts traveling along the clay layer. Soon the yard becomes a quagmire. The soil turns sour and anaerobic and plants start to die because they can’t breathe.

On sloping sites like mine, water hits the hardpan and starts to form sheets that can run like underground rivers beneath the topsoil. Soon, the sodden soil becomes unstable. If the slope is steep enough and the soil is wet enough, you get slippage or even a landslide.

Check It Out

If you have had drainage problems in the past, take time to inspect your existing drainage systems now. Check guttersv, catch basins, drains, bioswales and any aboveground pipes to be sure nothing is clogged by leaves or fir needles. Lift the lids of any catch basins and manholes and take a peek. Most have two or three set screws to hold them in place. Excess sediment can prevent proper filtration, so scoop out any gunk you find in there.

Tile or relief drains may have accumulated grit and clay on top. This can create a kind of glazed surface that sheds rather than absorbs water. If breaking it up with a rake doesn’t work, try replacing a few inches of soil with clean 1/2 inch gravel. (Clean gravel has no smalls–the fine particles that clog drains easily.)

Build A Bioswale

Water-absorbing bioswales look something like dry stream beds. They are usually lined with a special blend of grasses that help control erosion. Often, feeder drains direct excess water into the swales, which channel the water into a storm drain or retention pond. If a swale runs well for part of its length, but seems to have less water instead of more as it moves along, you have a problem.

Often, this means that the swale crosses a patch of sandy soil and the water is leaching out too soon. Patching the side wall with clay or bentonite can help, as can adding a section of perforated drainage pipe to get water past the leak point. During the next downpour, make a tour of the yard and check to see that all the drainage pipes are flowing strongly. Any that stay dry or have only weak flow might be clogged or need repair.

Free Advice From the State

Check your state department of ecology for free advice on how to handle drainage and erosion issues. In Washington State, two very informative booklets called  ‘Slope Stabilization and Erosion Control Using Vegetation’ and ‘Surface Water and Groundwater on Coastal Bluffs’ are available for free online:



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3 Responses to When Dealing With Drainage, Do It Right

  1. Charlie says:

    I have similar drainage problems so the information was very useful and thank you for the Washington State websites. I did go to the site and found additional useful information.

  2. Awesome blog you have here but I was curious if you knew of any community forums that cover the same topics discussed here? I’d really like to be a part of group where I can get comments from other experienced individuals that share the same interest. If you have any suggestions, please let me know. Thanks a lot!

    • Ann Lovejoy says:

      If you are on Facebook, there are quite a few garden forums of the sort you describe, including at least one for Northwestern gardeners. Take a look and see if it meets your interests/needs!

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