An Ancient Form Made New:

Dry Stacked Retaining Walls

By Leslie McGuire, managing editor

Sam Rice and his crew of three men built this series of six terraced dry stacked walls with a combined length of 350 linear feet in two and a half days.

?EUR??,,????'??The resulting combination of the waterfall, lion and walls looks as if it had been designed to be one continuous project.?EUR??,,????'??

The art of terracing is a Best Management Practice that controls soil erosion and protects water quality by eliminating rainwater runoff on slope areas. It is, in fact, also a very ancient practice that?EUR??,,????'???s been used for thousands of years. Employing dry stacked retaining walls to form the terraces was used by Sam Rice of BB Mofic, LLC, a family owned Landscape Design and Contracting firm, with wonderful results.

This residence in Guthrie, Oklahoma was backed up by a golf course on which the developer had created six dams across a couple of streams in order to create six ponds. The house was on one of the sites with a pond and a dam. When the waterfall was already completed, the owners called in Sam Rice. The front of the property ran for 14 feet across the top of one of the dams, and the 40 percent grade down to the pond was steep and needed to be managed to control runoff and soil erosion. It was decided that a terraced set of dry stacked stone walls would not only control soil erosion, but would also enhance the property.

The primary challenge was building the first course, which was at water level. They built that course from above the wall?EUR??,,????'??+since they couldn?EUR??,,????'???t stand in the water?EUR??,,????'??+and had to work beneath their feet.

 

They backfilled behind the new walls with topsoil (12 yards were delivered) and had to hand carry the soil down the hill in buckets, just as they had to hand carry the concrete for the footings.

A well-built dry-stacked wall is far better than one that has been mortared because dry stacking leaves spaces for groundwater to drain through.

?EUR??,,????'??I did a very basic design plan,?EUR??,,????'?? says Rice. ?EUR??,,????'??But it varied some from the final result for two reasons. The first was that the actual grade was determined by the leveling methods described earlier, and secondly, the homeowner added some additional footage.?EUR??,,????'??

?EUR??,,????'??We utilized the waterfall to establish grade for the desired height of each course. We did this by using a combination of the laser level and string level, which helped address the primary challenge of incorporating the walls into the hillside. The resulting combination of the waterfall, lion and walls looks as if it had been designed to be one continuous project.?EUR??,,????'??

?EUR??,,????'??We dug a six foot by eight foot footing and filled with nearly three yards of 2500 pound test, ready mix concrete to assure a stable base,?EUR??,,????'?? says Rice. A cement truck delivered the concrete, but couldn?EUR??,,????'???t get close to the site. So Rice and his crew had to wheelbarrow the cement 120 yards from the street, and then hand carry it down the hillside to the pond in five gallon buckets because of the severe grade change.

This Medieval curtain wall in Rocca Di Manerba, Italy, was built following the lines of the earlier Neolithic terrace wall, partially protecting it from destruction.

Terraced farming in Malaysia, the Philippines and Oceania goes back at least 3,000 years. In Hawaii, 700-year-old terraced dry stacked walls are still being used.

The footings were dug and poured in one day. They came back the next morning and started to lay in the rocks. ?EUR??,,????'??We didn?EUR??,,????'???t count each individual stone,?EUR??,,????'?? says Rice, ?EUR??,,????'??but nearly all of the material used was Texas cut limestone with a little granite.?EUR??,,????'?? The stones were laid in a random ashlar pattern rather than running bond or soldiers and sailors. Random ashlar involves using rectangular shaped stones laid in no particular order. Smaller stones are then placed between each course. Rice estimates that they used approximately seven tons of rock using the dry stack method, which doesn?EUR??,,????'???t involve using any mortar. They battered each course as they went. Each wall was approximately 16 inches high with a total wall length of 350 linear feet.

By not using any mortar, the resulting small holes here and there will allow the wall to ?EUR??,,????'??weep?EUR??,,????'?? water. This provides yet another way of slowly allowing accumulated water to trickle into the soil below. In addition, plants will eventually start to grow through the cracks. If the owner has particular plants in mind, they can actually be jammed into the spaces being careful not to rip them up too much, but giving them a snug place to send down their roots.

As part of an irrigation system that included dams, irrigation channels and cross valley walls, the ancient peoples of Yemen were able to control seasonal monsoon rains, minimize erosion, and water their plantings.

?EUR??,,????'??We then backfilled the terraced planting beds behind each wall with 12 yards of friable topsoil. The homeowner chose to plant her own selection of plant material. ?EUR??,,????'??We backfilled behind the new walls with topsoil?EUR??,,????'???I had 12 yards delivered,?EUR??,,????'?? says Rice. ?EUR??,,????'??We had to hand carry the soil down the hill in buckets as well.

He then built some steps out of some of the larger pieces to facilitate traversing the bank/slope and left the remaining unused stones for the homeowner to use.

The owners of the property put in the plant materials which include Lantana which is actually, according to Sherry Ragon, quite drought resistant in the Oklahoma heat with minimal dead heading. In addition,there are geraniums, marigolds, and Coleus on the left which are also heat and sun tolerant.

Terraced dry stacked walls provide a number of benefits. Peak discharges of water are reduced because the runoff is temporarily stored and sediment as well as other contaminants settle out behind the terrace ridge before polluting any water in the receiving pond. They are also very effective at controlling erosion because they intercept rainfall runoff as it starts down a slope, preventing any large accumulations of flow on the surface. This reduces the potential for sheet and rill erosion. The terraces break up one long slope into a series of short ones. This also gives soil particles that do erode a chance to settle out in the basin behind the terrace ridge.Now, not only is the slope protected from erosion, but the pond at the bottom of the slope is protected from contaminants such as fertilizer and herbicides used on the slope grass.

Because of their years of experience, Sam Rice?EUR??,,????'???s firm was able to ensure a fully integrated flow between the hardscape and softscape elements on the slope. In addition, because of their experience in the design/construction of water gardens, ponds, streams and waterfalls, they were able to devise an integrated plan that protected both the slope and the pond?EUR??,,????'??+while looking beautiful.

The stones were laid in a random ashlar pattern rather than running bond or soldiers and sailors. Random ashlar involves using rectangular shaped stones laid in no particular order. Smaller stones are then placed between each course. Rice estimates that they used approximately seven tons of rock.

A Short Ancient History

Terracing is a Best Management Practice, which controls soil erosion and protects water quality by eliminating rainwater runoff on slope areas. It is, in fact a very ancient practice that?EUR??,,????'???s been used for thousands of years in ancient Egypt, North, South and Central America, China, the Philippines and Hawaii, Africa, Asia and Europe. The earliest solid evidence of terracing in most regions are much the same?EUR??,,????'??+from 3000 to 2000 BC.

A series of dams and terraced walls built in ancient Yemen in southern Arabia from the first century BC to the sixth century AD created a very effective irrigation system. In addition it allowed the locals to control the erosion effects of annual floods and high energy rain storms. When these were allowed to fall into disrepair after 1640 AD, the remarkably stable environment they had produced led to destructive patterns of erosion that ultimately made the area unusable.

Changing the way water moves means the sediment accumulations on each terrace change and enhance the character of the soil. The plants that grow then have a cascading effect on the rest of the natural world. Not only does the soil change character, but the plants growing in the enhanced soils cause a change in the kinds of animals and insects found.

Terraced walls that have been excavated at Rocca di Manerba in Italy date back to 4000 BC. Succeeding changes and rebuilding were excavated showing that the walls were in replaced several times. A 16th century Medieval wall was built that followed the same pattern as the earlier one.