Draining Away The Rain

Rain, Rain Go Away

Recent heavy rains flooded our garage, creating a wonderful excuse to play in the mud. I awoke to find sheets of water pouring down our sloping driveway, overwhelming the curtain drain that is supposed to keep the garage dry.

As I investigated, I realized that our network of gravel-lined drains had silted over and were no longer functioning. Hmm. Armed with my garden pick and a slim-bladed poacher’s spade, I started trenching past the edge of the concrete garage apron. Slowly, slowly, water began to move downhill into the woods instead of into the garage.

After an hour or so of lone trenching, I roped my son and daughter-in-law into the act. Since the day was relatively warm for December, building dams and shoveling water and gravel felt rather fun. Eventually, we were able to uncover and reactive our drains, leading the water into a wooded bank and down a grassy slope. Best of all, our garage was clean and for the first time in years could actually house a car!

Dealing With Drainage

In our rainy Northwest, where clay soils and hardpan are prevalent, drainage is one of the most critical issues to be addressed in garden design. Whether you are building or moving into a new home or rediscovering drainage issues, the best time to assess your drainage needs is during our rainy season, typically from October through May.

During and after a hard rain, notice and document (pictures are great) where water moves through or collects on your property. If lawn becomes swampy, might excess water be redirected to an area that will be less impacted, such as woodland or a densely planted shrubbery? Could it flow into a local storm drainage system?

Building A Bio-Sponge

One excellent way to take up excess water is with a bio-sponge bed full of plants that enjoy standing water. In order not to create a thirsty monster, choose natives that are accustomed to wet winters and dry summers. For instance, twiggy dogwoods, compact willows, reed grasses and many carexes (or would that be carices?) will readily absorb excess water in winter, yet not need watering in summer (once their roots are well established).

Blueberries on Hummocks

Blueberries also thrive in sunny, moist areas, especially when planted in raised beds or on hummocks of mounded soil. With their brilliant fall coloring and vivid summer fruit, they look spectacular planted along a low berm tucked around a rain garden or that soggy place in the lawn.

Capture and Divert

Ideally we capture and divert excess water where it enters the property. Never pass on the problem by dumping water on the neighbors’ property. Instead, create a bio-sponge planting of twiggy dogwoods and willows to capture excess water. Smaller finger drains will also feed lesser amounts of water into wooded or shrubby areas of the garden.

Once you know where the water comes from and where you prefer to send it, all that’s left to do is to choose a drainage method and start digging your trench.

Dry Streambeds

A dry streambed is a shallow ditch or swale that meanders and curves around or through a garden to divert seasonal water. These are most attractive and visually intriguing when lined with rock of varying sizes. The most commonly used type is called bull rock, generally in the 2-6 inch range. Keep rocks in scale with the overall project: Larger rocks create a more serene look, while a jumble of small rocks look cluttered and haphazard.

Straight runs look artificial, so vary the width of the streambed here and there for a natural appearance. Make curves wider and shallower than the straighter sections. Blend an occasional larger boulder into a mix of bull rock, drain rock, river rock and gravel.

Dig In To French Drains

French drains are gravel filled trenches that redirect water away from lawn, garden, driveway or whatever. Less decorative than dry streambeds, they can be incorporated into pathways or run alongside a driveway.

Make your French drain trench at least 12-18 inches deep and 18-24 inches wide. To pull water away, make the pitch at least a quarter-inch drop for every foot of run. To test it, pour in water and see if it runs quickly downhill. If water pools or drains sluggishly, you need more pitch. If it flows rapidly, back-fill the drainage ditch with clean 5/8” drain rock. River run works fine, but crushed rock will compact better, allowing foot traffic and carts easier access.

Drain Boxes and Pipe

Where a lot of water is involved on a frequent basis, a combination of drain boxes and drain pipe is most effective. Keep the garden lovely by installing the catch basins or collection boxes in functional yet discreet locations.

Catch basins are connected to drain pipes that carry water away. Often the first sections of drain pipe will be solid, leading to perforated pipe that lets water percolate out slowly. Typical drain pipe is 4” in diameter, and comes in 10 foot and 100 foot pieces (cut it with a saw or “cuts everything” scissors).

Cover the bottom of the trench with a wide sheet of pipe sleeve or filer cloth topped with an inch or two of clean, crushed gravel. Now place the pipe perforated side down on top of the gravel. Backfill with more clean gravel then wrap the gravel-surrounded pipe with the filter cloth or sleeve to prevent silting. Top the ditch off with more clean gravel and let it rain!

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3 Responses to Draining Away The Rain

  1. Ben Atkinson says:

    I recently purchases your organic gardening book, and have a question related to drainage for my lawn. I’m really having trouble finding the 1/4 – 1/2″ crushed clean rock you recommend for improving drainage. I live in Kent, WA, any ideas on where I can get this? I can find several places that have 5/8″ crushed clean rock, is that too big?

    • Ann Lovejoy says:

      Hi Ben,

      You can use the larger stuff as long as it is crushed, clean gravel (smalls washed out). You will probably need to use a bit more compost to cover it completely, but the new grass will be just as happy no matter what size gravel you find. Hope that helps!

      Ann

  2. Failure to deal with future tree or shrub root growth is common with many home owner installs, and quite a few landscaper installs of French drains.

    The 12″ depth mentioned earlier, is often preferable if no real need to go deeper exists: plus, our soils often have little sideways movement of water. One advantage of going shallow, is an easier renovation in the future if sediments start accumulating in the French drain. Then it’s easier to dig up and clean or replace the pipe.

    MDV
    Oregon

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