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Designing Hugel-Swales for cool/cold humid slopes
Posted by mary combs over 10 years ago
Recently there has been some controversy over the use of structures that some people, myself included, are calling Hugel-Swales. This article defines what I mean by that term and how the design is meant to work in my climate and soil type.
A cross-section of a Hugel-Swale, as I use the term, is shown in the first attachment.
Where I have built my first Hugel-Swale is on a 12% slope, crossing a power line easement in loam with a high clay content. We have relatively high rainfall (or snowfall) during 9 months of the year and get parched going into August and September. Given the soil type, the land tends to develop a perched water table and high runoff during the wet season, and bakes hard and cracks in late summer. The challenge is to build soil out of the clay and to stop, sink and hold water to minimise the summer drought conditions.
Under the power line, vegetation is not allowed to exceed 15 feet in height, nor can we space swales too close together or make them too wide and thereby impede access to the power line. Digging the swales too deep would risk creating drought conditions on top of the berm. By creating a sunken hugelbed downslope from the Swale, we hope to capture a significant volume of water in the rotting wood core that will bridge the summer dry season for our emerging food forest planted on the berm.
Recognising that over the space of 5 years or so, the wood core will rot and the ground above will sink, trees cannot be planted on top of the Hugelbed itself. However, trees planted on the berm can extend roots into the trench to benefit from the nutrients and moisture.
In 5 years or so, we will dig out the soil generated within the hugelbed and replenish the wood core. The hugel trenches will act as soil generating 'factories'.The soil from the trenches will be used to supplement the thin soils overlying basalt patches on parts of the property.
One advantage of creating trenches filled with wood cores is that it reduces the fire risk for the predominately pine forests. Meanwhile the hugelbeds will not only nourish the young food forest plantings but will also be planted to annual crops such as root vegetables, pulses, melons, squash, pumpkins etc, that will provide food for both the family and for farm animals.
On the berms we will be planting mixed fruit and nut trees of varieties that grow low and bushy, interspersed with support species for chop and drop and as animal forage. Soft fruit will also form part of the mix. At harvest time, imperfect or pest damaged fruit will be picked and dropped into the swales to be eaten by pastured pigs and goats. Permanent deer fence will be installed to protect the emerging food forest from wild browsers (deer, elk, moose), and to protect the young food forest from our own domestic grazers.
Small paddocks of 1/4 to 1/2 acre in size will be defined between the swales by movable solar powered, electric netting. The intention is to rotate the livestock through the paddocks on a mob grazing concept - cattle, followed by pigs, followed by poultry, followed by sheep. This pattern is expected to break the parasite cycles, make optimal use of the available fodder and enrich the quality of the soil. Improving the soil quality and the pasture is also expected to help crowd out any noxious or undesirable weeds.
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