On Dead Hedges, Drainage, and Erosion Control

On Dead Hedges, Drainage, and Erosion Control

Sunday, April 21, 2024

One of the biggest long-term challenges we face as we turn our five-acre forest into a five-acre forest-garden is controlling water flow. Our north side is down-slope from several acres of cleared land, buildings, and parking lots. Our south side has an ephemeral creek that drains into a small wetland at the back of the property. Arkansas has lots of intense rain events. An inch or more in a day is normal, and it’s not unusual to get two or three. And with the instability caused by climate change those events are getting more extreme and frequent.

There are several gulleys already running across the property. Some are being actively cut every time we have a flash flood. The largest, Broken Chair Hollow, will eventually be converted into a surface reservoir for irrigation. Until we do that though, we need to keep it from getting deeper.

As we remove invasive plants and disturb soil by building beds, we could easily make the erosion problems worse. So every step we take has to account for the impacts on water flow.

Our water control plan has multiple goals:
-- Slow the flow rate across the top of the soil; allowing it to soak in, not run off
-- Prevent active erosion of surface soil in our beds
-- Prevent movement of soil amendments into the creek and wetland
-- Retain rain in the garden plots to reduce the need for watering
-- Drain well enough that plants aren’t waterlogged
-- Stop, and eventually reverse, the formation of gulleys
We have settled on several simple methods to do this.

One is orienting our beds across the slope of the earth, creating a terrace. Our standard arrangement is a three-foot-wide raised bed, with three-foot aisles between them, with a minimum lift of six inches. This means that each 100-foot length of aisle can temporarily store over a thousand gallons of water.  Fortunately our soil is very permeable and can absorb several inches of standing water per day.  Even after a severe flood, our aisles don’t stay muddy very long.

Getting all the beds oriented exactly across the slope is impractical. Most of the slope in the area we call the playground is from north to south, so we oriented the beds east to west. But there is still more than a foot of drop from one end of those beds to the other. To keep all the aisles from becoming creeks, we will have to build up obstructions and end caps to stop the downhill flow. Figuring out exactly where and what to do is a project for this spring. It will involve us standing in the middle of the field in a downpour, watching what happens.

To slow the rate of flow in the aisles – and in the areas we have cleared, but are not yet cultivating – we will plant cover. This will include clover, native wildflower and grass mixes, and crops such as legumes and brassicas which have the added advantage of providing nutrients and green mulch organics to enrich the soil.

Another technique we’ve been using with great results is the creation of dead hedges. Dead hedges aren’t as common in the USA, as they are the UK and Europe. I was reminded that they’re a thing by Jake Rayson (@natureworks@mas.to). He creates beautiful works of art, ours are much more crude, being more about function than aesthetic. He might even chastise me for calling our constructions dead hedges when they’re really little more than organized brush piles.

Two dead hedges at the edge of the woods.  The first is just a low stack of long thin logs. The second is a brushpile, waist high, braced between living trees.

I’m a little perplexed by the scarcity of dead hedges here; but I think it all comes down to culture. There are some possible downsides to building long stacks of loose brush and I think Americans focus on those and don’t consider the benefits. I’ve already had a number of people questioning the wisdom of this technique.

The first thing I hear is that it’s a fire risk. This is true: a dead hedge can be a fire hazard. I don’t think I’d want one running near my house if I was in a grassfire zone. We’re in a mature forest with ample rain and humidity. They are not, and will not be next to areas of tall dry grass. Also, as we fill them in with compost their flammability will be greatly reduced.

The next thing I hear is “It’ll attract varmints.” Yes, it will. That’s a benefit, not a downside. Our dead hedges already provide habitat to multiple bird species, non-venomous snakes, and untold numbers of insects, slugs, worms and other essential bits of a healthy ecosystem. I’m willing to risk having to evict an occasional skunk or woodrat in exchange for having wildlife in the garden. Thus far we haven’t had any problems, as our local raptor population views rats and skunks as tasty snacks.

I think part of it too is an ingrained consumerism and an aesthetic sense that opposes anything wild looking in favor of the polished look of manufactured products. I’ve seen people clear large swaths of land, burn the brush piles, then build a very expensive fence around the result. They could have instead simply piled the cut limbs into a dead hedge and saved the money.

While ours aren’t as neat as some of the pieces of art woven from willow branches that I’ve seen in England, we have settled on the right way to build one for our purposes. The first tier is a single or double line of logs near the upslope border. Ideally this first tier is already beginning to decay. This slows the surface flow of water. On this we build a pile of smaller branches and brush at least three feet high and three feet wide. These smaller bits will catch leaves and general detritus as the rain and wind wash them down. On top of this goes another round of logs to compress everything and hold it in place. As we go along, we will pile more small bits, shredded leaves, woodchips, clippings, and other compost ingredients on top. Over time the dead hedges will collapse into beautiful beds of organic matter.

In the currently evolving gulleys, we will build what are effectively dead hedges across the flow of water. These will be supported in the back with reasonably tight log piles and the front filled with finer organic materials such as leaves. This will create semi-permeable dams that will catch the eroded material and allow it to sediment out, slowly filling it in.

Working with, rather than against, the natural desire of water to flow downhill we should be able to meet all our water management goals.

Saturday, April 27, 2024
I love what you&#039;re doing! The dead hedges make all the sense in the world for your application. The neighbor left a large pile of cedar limbs and foliage on our property line, leftover from harvesting as timber. I worried about the fire danger for about 5 years. It&#039;s been 20 years or more since, and a fire never started and the pile disintegrated, to the point it isn&#039;t recognizable as a brush pile anymore. <br />I am glad it is you with the chainsaw and not me. <br />~From one of TPS biggest fans.~