Earthworks II

EEC Forest Stewardship is getting some surprise earthworks at the end of September 2022. Our luck in having a neighbor with excavator and a week of time to share in helping us get some swales dug in our fenced pastures a decade ahead of schedule. The neighbor has been very generous with his time to come over, and another neighbor was generous enough to let us drive the machine through their property into our back field. Cooperation like this between neighbors is so special, and we’ll continue the generous exchange with pet and farm sitting, labor sharing, and even free consulting in land design and animal system setups. It’s a win win for all involved on the land.

What are these earthworks for? Well, our main goal at EEC is to slow, sink, and save water. Swales are the fastest way to collect large volumes of water sheeting off the landscape, preventing the loss of freshwater from the soil by stopping it’s run down hill. Catchment systems like this store the water in the ground by slowing it’s flow, holding it, and letting the moisture sink into the soil slowly. We’ve got some pasture space where water sheets down hill during heavy rain events, leaving the land and flooding into the creek and away from our soil. When this landscape was covered in temperate rainforest, the rain was sunk and stored by large trees and their elaborate web of roots and forest duff which acted like a huge sponge, soaking up the rain and slowly drinking from it all year. Now, with so much forest removed, much of the rains sheet off the dry soil and leave the ground parched. Swales start the process of retaining water, which supports the planting of new trees on the down hill side of each new earthworks feature.

Swales do not have to be deep too work, but they should always have a berm of the dug out dirt piled down hill of the swale to support the slowing and sinking of the water. Another important design feature of swales is being on keyline in the topography. This means the bottom of the swale should have no real slope along its length. If there is slope, the water falling into the swale will be channeled, forming a current which can erode the ground even more. Swales should not create flow, but slow and stop the water along the full length of the swale. Diversion swales are dug to move water, to drain a wet area, or send water to a larger collection point, like a pond. Keyline design moves water through swales slowly to spread it across a larger landscape. We are not trying to move the water away, so we dug the swales with as little change in the base topography as possible.

Because these earthworks happened on short notice, we did not have time to use accurate measuring systems like an a-frame to accurately map our topography first. This means we’ll be doing a lot of observation this winter to see what the water does when it flows into these swales. If the dug space fills up nicely with no overflow, and the water sinks in, we have dug the swales evenly enough to retain the water, which is what we’re going for. If the swale fills, spills over, and allows the water to keep flowing down hill, we’ll make the swales a little deeper next year and address any low points or slopes sections with better leveling measurements next summer. It’s a bit of a risk, but again, we didn’t dig very big swales or very long ones, so the water should slow, sink, and save in the soil nicely.

We did put in one catchment basin in a seasonal wet space where we want to direct the water away from our road. This swale will move water into its center, which we dug just a bit deeper and wider to collect a larger volume. This winter we will observe how much water fills the basin, and if it’s more than the ground can hold, we’ll plan to put in a culvert to send the water on down to the creek when it overflows. Before putting in this basin, the water would sheet across the landscape here and soften the ground where our road crosses. Though we don’t drive on this land in the winter, we’d like to firm up the road’s base by directing the water into another space nearby. This basin may become a small, seasonal pond with wetland plantings. It’s hard to imagine wetlands here in late summer. All the soil was dry and easy to dig at this time. In future, with the help of these swales and catchment basins, the ground will retain more of that crucial winter rain to counter our growing summertime drought.

One other earthworks feature we implemented was a waterbar on the road, just above a major topographic change into steeper slope. We’re hoping that by diverting the water above the hill, we can prevent it streaming down the road, cutting into the land and eroding the ground where our vehicles drive. I installed another bar above, near the barn last fall. I dug it by hand, and it worked beautifully. We channeled that water into the pond, and prevented more erosion down hill. This waterbar will do the same, though we’re channeling into the woods, where it can sink into the trees of a more established forest with sponge capacity. We’ll still be doing a lot of observing to see how much water is moved, where it goes, and if the forest capacity is enough to slow and sink the flow. If not, we’ll build an additional catchment basin with controlled outflow to prevent future erosion. Again, all of these earthwork features are to catch and keep water on the landscape to strengthen water retention in the soil. If we move it away from one area, we have to have another place ready to receive it.

Working with the landscape like this takes a lot of planning, observing, and mapping of your topography. Moving water across contours can be a tricky thing, that’s why we focus on sinking the water in, not sending it away. There are strict laws here in King County Washington regarding moving water across your land, especially if your sending it off your property onto someone else’s. That’s against the law, and with good reason, imagine what would happen to people living far below someone directing all their water down hill? Flooding out your neighbors is a serious thing, and the laws protecting against it are very important to be aware of- especially in a region with a lot of rain. As the weather becomes more and more extreme, we’re seeing first hand the volume of water increasing across our property. Last year, our well established swales filled to the brim for the first time. Luckily, they are built to overflow into each other and down to the pond, which has never reached it’s outflow capacity. If it does, there is a catchment basin below and a slow meander down to the creek on our land. There is also a backup overflow basin off the pond, which could hold additional flooding in a major weather event. So far, we have not come close to this kind of event, but we’re prepared none the less.

Observing the flow of water into your earthworks is crucial to knowing if they are preforming correctly on your land. If the swales channel water into a torrent of moving erosion hazard, you may be in for some bad flooding. That’s part of why we did smaller swales with limited movement across the terrain. These earthwork features are there to catch and save, or direct minimal flow off roads and into intact forest land that will soak up the excess. If we do note any flow, we’ll map those spots for future swales and/or redesign existing swales to better hold and sink. One other crucial thing to think about in designing swales is access. Once you put in a big ditch on the land, you can’t drive through it any more. If you have livestock, make the swale edges gradual, so an animal can crawl in and out of them without struggle. That’s why our swales are gradual and shallow. We don’t want to trap our sheep in a hole. There’s a lot to think about when implementing earthworks on your land. Laws, terrain, machinery, and access all dictate much of what you can do. Be sure to also map soil types and existing water flow before digging.

Almost ten years of mapping, observing, and planning made it possible for EEC to say yes to earthworks on short notice. We do not recommend just bringing in an excavator and playing around- you might end up with a seasonal stream in your back yard that flows into a neighbor’s basement. Scale is also important- if you have minimal acreage, hand dig your features and create small catchments that cannot flood. Our 10 acre parcel has room to host bigger features, but we still start small and do a lot of mapping to better understand what’s already going on. The changing weather extremes also play a huge part in how our earthworks succeed. We plan all our earthworks to handle the catastrophic flooding potential that could one day become the norm in our region. The sequestering of water in the soil also helps protect against summer wildfire threat, keeping our ground damp and less prone to drought. These advantages and more make earthworks on the landscape a crucial part of our restoration goals here at EEC.

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