Rather than focusing on one specific building for this assignment, I chose to focus on a landscaping technique that I found very interesting this summer. Terraced landscapes are often found in countries surrounding the Mediterranean (and occasionally Asian countries as well), but rarely seen elsewhere around the world, and I chose to explore their significance as a part of water and agricultural systems around the Mediterranean Basin.
While we did not spend a great amount of time in class focusing on the actual duties of the farmer, the Bay Game and its different farming techniques were intriguing to me. The choices we had were limited, and all focused on regular acres of land and how we chose to farm those as a unit. Terraced landscapes, however, introduce a whole new
way of looking at farming and agriculture. In the Mediterranean, there are various mountain chains and many hills that make farming difficult. Terraced landscapes are one way to use these sloping terrains efficiently, and it is traditionally one of the oldest ways to save both soil and water.
The purpose of this style, as defined by Dorren and Ray, is that it is “created to intercept surface runoff, encourage it to infiltrate, evaporate or be diverted towards a predetermined and protected safe outlet at a controlled velocity to avoid soil erosion.” Terraced landscapes can be a great way to reduce soil erosion and slow down water so that it can be actually used rather than just move straight down a hill. The slope, width, shape, and construction process of a terrace are what determine its use and function, as terraces are designed for multiple reasons.
“Terraced slopes have long formed an integral element of the Mediterranean landscape. To northern Europeans, such a landscape often evokes romantic and idyllic images of sun-drenched hills rich with grapevines, olives, and citrus trees. However, in reality, Mediterranean terraced landscapes are better perceived as a human response to a harsh and demanding environment. The relative scarcity of land suitable for arable agriculture gave rise to an intensive form of cultivation which demanded a high input of labour with little mechanical aid” (Rolé). Historically, this technique is a very common landscape pattern throughout the area because it provides a solution to the difficult soil conditions, and therefore it renders cultivation possible, helps to controls erosion, and provides a better conservation of moisture than the original hillside.
Terraces are often created by rearrangement of their original soil into a new, more rigid configuration, as seen in the diagram below. The soil is cut from the original slope and set onto either a higher or lower portion of the slope, forming a more angular gradient. This new, flattened area is much more conducive to growing Mediterranean crops such as fruit trees and vegetables. These flattened areas are supported by drystone wall structures. These walls are well-designed to be used as a support for this type of farming for many reasons: they are highly porous structures where rocks are fitted in such away to secure the fundamental rocks in their places while maximizing drainage, they are held together only by the angular shape of the rock structure and do not use mortar (another method to maximize drainage), and their internal structure is secured by an infill of smaller stones that help maintain both the structures’ rigidity and its porous quality.
A major reason that terracing is put into place is to help protect hillsides from erosion and landslides. Water erosion is one of the major causes of soil loss and degradation, and by implementing terraces it reduces the slope steepness and divides the slope into short, flat or gently sloping sections. During periods of heavy rainfall (which typically occur in or around the month of June for this area), a large portion of the water permeates through the soil surface while the remainder becomes runoff. The runoff concentrates in natural depressions and runs down the hill until it reaches natural deposition zones. As runoff increases, velocity, volume, and erosion force also increase. “The critical runoff velocity, at which soil particles that have been detached from soil aggregates begin to be transported over the surface, is 5 m/s in sandy soils and 8 m/s in clay soils” (Dorren and Ray). Terraces decrease this amount of runoff by providing improved infiltration strategies that increase the soil moisture content.
The type of terrace chosen for any particular area depends on four main elements: its function, its construction process, the size of the terrace base, and the terrace shape. Retention terraces (more leveled) are designed to accumulate and retain runoff and are recommended for low rainfall areas with permeable soils and for land with less than 8% slope. Graded (diversion) terraces have a slope in them and they are designed to intercept or divert runoff into protected waterways; these terraces are found in high rainfall regions and for slopes between 8% and 20%. The construction process involves excavating soil from one part of the slope and moving it to another (similar to the above diagram), although regions differ in their exact placement and formation of the landscape. The size of the terrace base and its shape affect the distance that the soil and water can move. In some regions, the vegetation cover on the terrace is more critical than the type of terrace for erosion.
Water moves through the terraces at varying rates depending on the climate. In low rainfall regions, the flow of the water is natural and it absorbs into the soil on each terrace fairly evenly. There is some intentional permeation through the drystone walls so that the terraces don’t become flooded, but overall the water is evenly distributed. Often, a grass waterway is included in the design of these terraces to be used as an emergency spillway of an exceptionally high precipitation rate. In heavy rainfall areas, however, there are manmade systems designed to capture the excess water and drain it to an intentional depository where it can be stored and used in drier seasons.
While terraces are an extremely effective way to control water and soil erosion, they can become a serious burden if left unattended. “The advantages of terraces have ensured their survival into the present millennium; however, they often demand a great deal of maintenance and their neglect, or abandonment, often creates considerable infrastructural problems” (Rolé). Farmers should consider the fact that this technique is a great long-term investment if their land has varying topography, but they also need to be aware of the maintenance and upkeep that these landscapes require.
SOURCES:
Cyffka, Bernd & Bock, Michael. “Degradation of Field Terraces in the Maltese Islands- Reasons, Processes, and Effects.” Glaciologia. 2008. Web. 28 Oct. 2011.
<http://www.glaciologia.it/wp-content/uploads/FullText/full_text_31_2/06_Cyffka_119_128.pdf>
Dorren, Luke & Rey, Freddy. “A review of the effect of terracing on erosion.” Soil Conservation and Protection for Europe. Web. 28 Oct. 2011.
<http://www.ecorisq.org/docs/Dorren_Rey.pdf>
Matthee, J. & Russell, W.B. “Bench Terracing.” Conservation of Farmland in KwaZulu-Natal. 1997. Web. November 2 2011.
“Modern Terrace Systems.” Journal of Soil and Water Conservation. 1983. Web. 1 Nov. 2011.
<http://www.jswconline.org/content/38/4/336.full.pdf>
Ogrin, Dusan. “Mediterranean Landscapes: Contribution to a Better Management.” Proirity Actions Programme. 2005. Web. 2 Nov. 2011.
<http://www.pap-thecoastcentre.org/Landscape_Report-OGRIN.pdf>
“Predicting Rainfall Erosion Losses.” United States Department of Agriculture. Dec. 1978. Web. 1 Nov. 2011.
<http://www.ars.usda.gov/SP2UserFiles/ad_hoc/36021500USLEDatabase/AH_537.pdf>
Rolé, Avertano. “The Terraced Landscapes of the Maltese Islands.” Landscape-Europe. 2007. Web. 28 Oct. 2011.
<http://www.landscape-europe.net/files/405-420%2520correctie.pdf>
annesleyb 
The picture of terraces isn’t mine, but all of the diagrams are!
Thanks Annesley!