Permaculture and the Three Epochs Curriculum: Earthworks Cont’d

Posted on | August 29, 2010 | No Comments

EARTHWORKS AND EARTH RESOURCES Terra-forming is one of our oldest and greatest skills, neither the public at large nor those in architectural or agricultural fields have fully realized the potential of earthworking machines in the modern sense. Earthworks are necessary and ethical where they:

• Reduce our need for energy.

• Diversify our landscape for food production.

• Permanently rehabilitate damage.

• Save materials.

• Enable better land use, or help re-vegetate the earth. Earth can be moved for productive reasons, many of them classified as landscape restitution:

• To create shelter; to assist with foundations and to make areas level for floors.

• To terrace hill slopes for stable padi crop, wet terrace, or gardens.

• To raise banks or to dig ditches as defenses against flood, fire, attack or wandering vegetation eaters.

• To drain or fill areas, to direct water flow or runoff.

• To create access roads to those places we commonly visit.

• To get at earth materials, ochres, clays, minerals, and fuels.

• To make holes foe any number of reasons and of greatly varying sizes from fence posts to dams, wells to deeply drilled bores.

• To create special storages and enlarge living space.

• To stop erosive forces carrying off soils.

• To prevent noise pollution.

• To permit recharge of ground waters as swales and ripping. Earth can be moved with hand held and mechanical diggers, ditchers, augers, drills, blades, buckets, shoes, rakes, ploughs, rippers, delvers, scoops, earthplanes, loaders, rock cutters, draglines, excavators and dredgers. We also move earth with explosives, hydraulic jets, and as an unintentional result of erosive processes generally. Planning earthworks prior to the actual job is essential for placement, soil tests, surveying and pegging, topsoil storage and re-use planning, and preparing for plant up afterwards. Planting after earthworks needs serious planning not only for stability, but also to make the most of the opportunity of dominating the bare soil with appropriate plant regimes. We will be in a race with the volunteer weeds seeds to occupy as much space as possible first. As soon as the earthworks have finished we need to over seed with fast growing pioneer ground covers and shrubs and at the same time plant in, bulbs, divisions of clumpers, cuttings, tube pot pioneer trees and larger potted up main trees as the eventual climax layer. On steep and difficult slopes a net and pan pattern of mini earthworks will help establish pioneers as will logs and branches pegged across the slope to hold mulch. Dam walls should not be planted with anything that has a tap root that may penetrate the dam wall, and crack the wall if blown over or pipe the wall through when the tree dies. Bamboo and other clumpers are ideal as are willows and palms. Slope measurements can be made in many ways, the three most common are degrees 45`, percentages 50% and proportion 1:1. The average safe slopes used by engineers are:

• Gravels 1:1.5

• Clay well drained 1:2

• Clay wet 1:4 Levels and leveling is performed to ensure spillways work, drains run, gutters flow, buildings sit level and numerous other applications. Leveling equipment can be very sophisticated or extremely simple from a satellite positioning laser level, laser level, theodolite, transit level, hose levels, plane table to simple A-frames. Most of the survey work we need to do is measuring level and very slight grades all of which has been done in the past just using water to check level and the speed of water movement to assess gradient. Types of earthworks:

• Banks need to be constructed stable for control of water and soil slump. Many methods can be used to prevent slump from cuts above terraces or roads, and need careful planning, vegetation established on banks always assists stability.

• Benching a slope can be used to create roads and house sites. These are quick and easy to cut with a side casting machine, like a bulldozer or a grader on shallower slopes, the lower side becoming a good tree growing position of increased soil depth. Benches can slope slightly off the hill for drainage. In stable soils benches can slope into the hill and infiltrate water to the trees below the bench acting like a swale. Cross wall drains may need to be made every 20 to 30 meters to prevent runoff erosion. These are very useful and functional elements especially in steep country. Terracing on country that has enough mulch materials, compost supplies and water can be very stable productive systems. The exception to this is when:

• Terraces built in unstable soils and sediments.

• In areas with hydraulic pressure from water.

• Bunds not constructed stable.

• Large proportion of the landscape is terraced in annual crop with no tree mulch input to crop.

• High rainfall areas terraced and concentrating runoff. Trees on bunds and between, above and below terraces, should form 40 to 60% of the total landscape, creating a polyculture system creates the best sustainable results. Terrace construction always starts at the bottom and goes up hill, pulling topsoil down from the next terrace above, finally the surplus stockpiled topsoil of the bottom terrace is transported to the top terrace of the series. In the tropics terraces should occupy no more than 30% of the catchments landscape and no more than 5% in drylands.

References:

-Bauman, Greg, Steel in the Field, National Agricultural Library, Beltsville, Md., 1997. -Bradshaw, A.D. and Chadwick, M.J., The Restoration of Land, University of California Press, 1980.

-Hunt, Donnell, Farm Power and Machinery Management, Iowa State Uni. Press, Ames, Iowa, 1995.

-Mollison, Bill, Permaculture: A Designer’s Manual, Tagari Publications, Tyalgum Australia, 1988.

-Pripps, Robert, How to Restore Your Farm Tractor, Motorbooks International, Osceola, Wis., 1992.

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