water Article Parametric Terracing as Optimization of Controlled Slope Intervention Tomaž Berˇciˇc and Lucija Ažman-Momirski * Faculty of Architecture, University of Ljubljana, Zoisova 12, 1000 Ljubljana, Slovenia; [email protected] * Correspondence: [email protected] Received: 31 December 2019; Accepted: 21 February 2020; Published: 26 February 2020 Abstract: With the introduction of mechanization in agriculture, the area of terraced slopes has increased. However, in most cases, the planning of terracing in practice remains experience-based, which is no longer effective from an agricultural, geological, and hydrological point of view. The usual method of building terraces, especially terraces with earth risers, is therefore outdated, and a new method must be found for planning and building terraced areas. In addition to geographical information system (GIS) tools, parametric design tools for planning terraced landscapes are now available. Based on the design approaches for a selected plot in the Gorizia Hills in Slovenia, where we used a trial-and-error method, we improved previous results by defining a model using a computer algorithm that generates a terraced landscape on a selected slope depending on various input parameters such as the height of the terrace slope, the inclination of the terrace slope, the width of the terrace platform, and the number of terraces. For the definition of the algorithm we used the visual program tool Grasshopper. By changing the values of the input data parameters, the algorithm was able to present combinatorial simulations through a variety of different solutions with all the corresponding statistics. With such results it is much easier to make a conscious decision on which combination of parameters is optimal to prevent landslides, plan adequate drainage, and control soil movements when building terraces. The controlled slope intervention is further optimized by the introduction of a usage index (Tx), defined as the quotient of the sum of all flat areas (terrace platforms) and the total area of the plot. Keywords: terraced landscapes; agricultural terraces; parametric design; GIS terrain modelling; combinatorial simulation 1. Introduction Terraces are a global phenomenon, and their emergence is the result of various terrain, climate, and social factors. They can be found almost everywhere in the world, but they are very different in use, size, shape, and construction. In the vast majority of cases, their main function is to increase the area of arable land in places where tillage is either impossible or very difficult owing to poor soil or steep slopes. Terraces have a positive influence on higher crop yields by improving soil quality (but not in all cases [1]) and on better quality of harvests due to the better sun exposure of the plants. They can be part of a water management system, maintain the stability of the terrain, prevent erosion, and, last but not least, have a positive influence on the visual appearance of the landscape. The formation of terraces is a consequence of many factors. For example, terraces are one of the most obvious human interventions in the landscape and cover large areas of the Earth [2], they reduce slope gradient and length, they facilitate cultivation on steep slopes, and they have a generally positive effect on the integration of agricultural activities [3]: only well-lit grape leaves can be as photosynthetically active as possible [4]. Water 2020, 12, 634; doi:10.3390/w12030634 www.mdpi.com/journal/water Water 2020, 12, 634 2 of 19 Water 2020, 12, x FOR PEER REVIEW 2 of 17 In addition to the fact that terraces preserve more agricultural land, they were also built to decrease hydrologicalIn addition hazards to the and fact erosion that [terraces5]. Terraced preserve landscapes more oagriculturalffer aesthetic, land, social, they and were ecological also built values to decreasedue to their hydrological biodiversity hazard and biotopess and erosion [6]. [5]. Terraced landscapes offer aesthetic, social, and ecologicalIn the values past, slopes due to were their manually biodiversity terraced and biotopes and terraces [6]. were planned based on local needs and knowledgeIn the past, was slopes passed were down manually from generation terraced and to generation. terraces were In theplanned United based States on aslocal early needs as 1931, and knowledgean examination was ofpassed terraces down on farmsfrom generation revealed that to thegeneration. causes of In terrace the United failures States were as due early to theas 1931 terraces, an beingexamination poorly of planned, terraces improperly on farms revealed laid out, that inadequately the causes of built, terrace or carelessly failures were maintained due to the [7]. terraces One of thebeing outstanding poorly planned, causes improperly of terrace failures laid out, is theinadequately failure to preventbuilt, or watercarelessly from mai drainingntained away [7]. One from of a terracedthe outstanding field. Most causes historical of terrace terraces failures are ofis thethe benchfailure type to prevent with dry water stone from walls draining [2]. Until away the Secondfrom a Worldterraced War, field. the Most slopes historical were cultivated terraces are and of terraced the bench by type hand with (Figure dry1 stone)[8]. walls [2]. Until the Second World War, the slopes were cultivated and terraced by hand (Figure 1) [8]. Figure 1. TerracedTerraced landscapes built and maintained by hand. ( (aa)) Building Building a a dry dry stone stone wall wall in in Vrtovin, Vrtovin, Slovenia, in 2019 (photo(photo by LucijaLucija AžmanAžman Momirski).Momirski). ( (bb)) Terraced vineyards and old traditional terraces inin Vrtovin,Vrtovin, Slovenia, Slovenia, in in 2019 2019 (photo (photo by by Lucija Lucija Ažman Ažman Momirski). Momirski). (c )(c Old) Old agricultural agricultural terraces terraces in inthe the Koper Koper Hills, Hills Slovenia, Slovenia (photo (photo by Lucijaby Lucija Ažman Ažman Momirski). Momirski). (d) Old(d) Old garden garden terraces terraces in the in Karst the Karst area, area,Slovenia Sloveni (photoa (ph byoto Lucija by AžmanLucija Ažman Momirski). Momirski). (e) Old agricultural(e) Old agricultural terraces interraces Brkini, in Slovenia Brkini, (photoSloven byia f (photoMatevž by Lenarˇciˇc). Matevž Lenarčič). ( ) Old agricultural (f) Old agricultural terraces terraces in Krkavˇce,Koper in Krkavče, Hills, Koper Slovenia Hills, Slovenia (photo (photo by Lucija by Ažman Momirski). Lucija Ažman Momirski). Agricultural mechanization has changed farming [9] (Figure 2). In some places it became much easier to maintain, renew, and build new terraces. Mechanized work replaced arduous manual labor Water 2020, 12, 634 3 of 19 Agricultural mechanization has changed farming [9] (Figure2). In some places it became much easierWater 20 to20, 1 maintain,2, x FOR PEER renew, REVIEW and build new terraces. Mechanized work replaced arduous manual3 of 17 labor [10], and knowledge about handmade terraces was partly lost or was adapted to new construction methods,[10], and knowledge but remained about at an handmade experience terraces level. was partly lost or was adapted to new construction methods, but remained at an experience level. Figure 2. Terraced landscapes built and maintainedmaintained by agriculturalagricultural machinery. ( a)) Building new terraces in 2006 inin Medana,Medana, Gorizia Hills,Hills, SloveniaSlovenia (photo(photo byby LucijaLucija AžmanAžman Momirski).Momirski). ( b) Newly planted vineyard in in 2006 2006 in in Medana, Medana, Gorizia Gorizia Hills Hills,, Slovenia Slovenia (ph (photooto by byLucija Lucija Ažman Ažman Momirski). Momirski). (c) (Traditionalc) Traditional terraced terraced landscapes landscapes in inthe the Gorizia Gorizia Hills Hills,, renewed renewed every every thirty thirty years years (photo (photo by by Lucija Ažman Momirski). ( (dd)) Bizeljsko Bizeljsko area, area, Slovenia, Slovenia, terraced terraced in in the the 1960s and 1970s (photo by Matevž Lenarˇciˇc).(Lenarčič). (e) JeruzalemJeruzalem area,area, Slovenia,Slovenia, terraced terraced in in the the 1960s 1960s and and 1970s 1970s (photo (photo by by Matevž Matevž Lenarˇciˇc).( Lenarčič).f) Jeruzalem area, Slovenia, terraced in the 1960s and 1970s (photo by Lucija Ažman Momirski). (f) Jeruzalem area, Slovenia, terraced in the 1960s and 1970s (photo by Lucija Ažman Momirski). The extensive terracing in eastern Europe in the 1960s and 1970s was a consequence of agricultural The extensive terracing in eastern Europe in the 1960s and 1970s was a consequence of organization in the communist social system, in which farmers had to join agricultural collectives. agricultural organization in the communist social system, in which farmers had to join agricultural Working with machines in large vineyards was of course easier than the heavy manual labor in collectives. Working with machines in large vineyards was of course easier than the heavy manual traditional vineyards [11]. The areas intended for terracing and the slopes where terracing was carried labor in traditional vineyards [11]. The areas intended for terracing and the slopes where terracing out were enlarged [12] and the distance to settlements was increased. was carried out were enlarged [12] and the distance to settlements was increased. However, the experience-based planning of terraces is no longer effective, and therefore the intervention of experts with plans and a developed planning method are needed. Mechanization enabled farmers to first