Chapter 2

2. Vineyard terrancing

Terracing consists of the transformation of natural sloping land into a new profile formed by flat strips of a certain width (terrace), connected by new slopes of a higher gradient than the original natural slope of the land. This has two main functions: 

• To preserve the sol and retain the water. In general, agricultural planting requires the previous clearing of the land to remove any existing plant life, including roots. The soil is therefore unprotected against erosion, which may act aggressively due to the natural slope of the land. The basic mission of terracing is the controlled runoff of rainwater so that soil erosion is avoided as much as possible. Furthermore, controlled runoff increases the possibilities of water infiltration to the root area of the plant.

The loss of soil fertility may be compatible with certain viticulture practices that base grape quality on a reduction in the production capacity of the stock. However, in the cultivation systems discussed in this Manual, maintaining the soil and its fertility is important for the plant to express all its vigour (see Chapter 3).

• To make working the vineyard easier, particularly through mechanisation with no labour-related risks of machinery overturning. Terraces act as flat service passageways from where all operations involved in vineyard cultivation can be carried out (pruning, disease control, collection, etc.). Slope maintenance work can also be carried out from the terraces. Vineyard mechanisation to increase productivity requires a terrace width that is the minimum necessary for the corresponding agricultural machinery to pass along.

 

Predominance of terraced vineyards in the Priorat region

The municipality of Porrera covers an area of 2.896 ha, which is equivalent to 16.5% the Priorat designation of origin area. The average gradient of the municipality is 46% and its altitude is mostly between 200 m and 600 m above sea level. 60% of traditional vineyards in Porrera were abandoned between 1986 and 2003, from the 256 ha of 1986 to the 107 ha of 2003. During that same period, terraced vineyards increased from 20 ha to 291 ha, a 1,450% growth. In the more recent period between 1998 and 2003, traditional vineyards grew barely 12% (from 95 ha to 107), whereas terraced vineyards increased by 260%, from 111 ha in 1998 to 291 ha in 2003. This strong increase in terraced vineyards has continued over the past four years. As a whole, vineyards in Porrera increased by 44% between 1986 and 2003 and 93% between 1998 and 2003. These figures are considered representative of the overall evolution of Priorat. Source: R. Cots-Folch et al./Agriculture, Ecosystems and Environment 115 (2006) 88-96.

2.1. Conventional terraces

Terracing involves action on the mountain that modifies the natural conditions to a greater or less extent.

Work undertaken by the University of Lleida in the Priorat region characterises the main design parameters of conventional terraces built over the past decade (Figure 2.1). The following is of note: 

• The width of terraces varies between 2.37 and 5.91 m, although most widths are between 2.4 and 3 m, with an average of 2.95 m, in order to be able to plant two rows of stock on each terrace with enough space between them for machinery to pass.
• The gradient of the terrace slopes varies between 24º and 56º, with an average of 39.4º, in areas with natural slopes of between 18º and 36º (32 and 73%), with an average of 29º (55%).

Quarry effect
Quarry effect

In general and synthetically, conventional terraces are built in line with a predominant criterion: the cost of construction. More complex financial calculations are not made, which bear in mind other costs with repercussions that may be greater in the long term (loss of useable land, terrace maintenance, low productivity, etc.). In addition to this is insufficient environmental and landscape sensitivity, especially by viticulture companies whose management is unfamiliar with the cultural tradition and identity of the mountain region in question.

This group of causes endures because there are no clear, objective and well-documented technical recommendations to guide vine growers and construction machinery operators.

The conventional design of terraces may lead to environmental and operational problems in vineyard operations.

2.1.1 Environmental problems

• Impact on the landscape
  The steel natural gradient of the land, together with gentle artificial slopes and notable terrace widths lead to very high, long slopes that tend to disrupt the harmony of the landscape. A “quarry” effect is caused, especially when flat-land cultivation is sought to be reproduced in the mountains.

Forcing the construction of sections of straight terraces for easier vineyard control creates extremely artificial polygonal profiles that do not blend into the surroundings. Furthermore, this type of profile requires the transverse transportation of soil, making the work more difficult and expensive.

Polygonal terraces generate an artificial landscape

• Soil erosion
  Erosion may be intense due to the excessive length of slopes, thus increasing runoff, and especially due to a lack of a well-designed terrace drainage system:

- Continuous and constant slopes are not implemented along the entire terrace for controlled runoff. Furthermore, drainage crossways to the terraces are often not planned.

- Some terraces act as drainage for others, which generate an accumulation of sediments on recipient terraces.  

Badly drained terraces. Lengthways slopes lead to lower points from where the water will run off downhill. If the rain is heavy, sideways runoff may cause significant damage to the vineyard.

Severe erosion on a slope, putting some stock at risk Repairs on eroded slopes	Repairs on eroded slopes

Soil erosion by rainwater Water erosion of soil is a complex phenomenon of degradation in which the force of the water breaks up, pulls away and moves the horizontal surfaces of the terrain. This is a natural process made worse by human intervention, particularly through certain agricultural practices. Water erosion acts through two basic mechanisms:  Impact of raindrops. The tapping of drops of rainwater against the soil pulls off and moves its particles. In the case of very heavy rain, the force of the drops destroys the structural components of the soil. This process is accompanied by a decrease in porosity, given that most of the volume of pores in soil corresponds to the space between its aggregates. The erosive power of water is emphasised by the alternating of long periods of drought that leave the land dry, cracked and with no significant plant life to relieve the impact of downpours. Runoff. This is the water erosion mechanism par excellence. Rainwater that does not penetrate the soil runs along its surface and drags soil particles along with it. Runoff erosion depends on several factors: the rainfall, the density of plant cover, the topography of the land and the hydrological resistance and properties (penetration speed, water storage capacity and hydraulic conductivity) of the soil affected. The following must be noted among the many negative impacts of erosion: Reduced thickness of the soil layer on the plots affected. In areas with scarcely developed soil, this may lead to a complete loss of the soil layer. • Decreased soil fertility, associated to the leaching of minerals and the loss of organic matter and nutrients. Destabilisation of slopes and increased risk of landslides. Aggradation of adjacent areas (agricultural land, irrigation installations, roads, etc.) due to the effect of sediment dragging. Chemical substances from fertilisers and pesticides that are dragged along by sediments may eutrophicate or pollute watercourses.

• Low soil use
  To obtain a certain grape production, an under-optimised design of the terraces (width, slope gradient, etc.) means that the soil surface used is far greater than that strictly required. For example, a terrace width of almost three metres is insufficient for three rows of stock but too much for machinery to run along with two rows of stock. The flat-land planting criteria cannot be reproduced in the mountains, where the land must be made the most of to minimise the traumatic effects that terracing always involves to some extent.

The landscape and hydrological conditioning factors mean that mountain soil is a scarce resource that must be used productively. As can be seen later on in the Manual (Section 4.1), the techniques developed in Life Priorat provide the same grape production as with conventional techniques, but using a much smaller area of land.  

2.1.2 Vineyard operation problems

	Occupational risk In some plantations, the roads to the terraces are too steep because they are laid out perpendicular to the level lines. This involves a labour-related risk with regards to machinery traffic. The risk is maximised on the bends accessing the terraces, particularly when driving a tractor and a trailer. Reduced labour productivity The natural slope of the land is often variable along the level lines. A solution sometimes applied to prevent terraces with steep slopes from being built, which would make work difficult and worsen erosion problems, involves increasing the width of the terrace. A variable width must be used by planting a higher number of rows of stock, which leads to unproductive routes and complicated manoeuvres to access all the vines. Another solution applied to avoid this problem is to build intermediate terraces that end up draining off into other terraces, generating the erosion problems already indicated. Moreover, work cannot be comfortable carried out behind the inner row of stock (e.g. for slope maintenance work) that also tend to aggradate to some extent due to slope erosion. Heterogeneous soil fertility When the land is built using the conventional technique of cutting the top of the mountain and filling the bottom part, the inner row of stock is planted directly on a compact substrate without the top layer of soil, whereas the outer row (valley side) is planted on turned over soil. This means that fertility cannot be homogeneous.
Riesgo laboral: accesos perpendiculares a las líneas de nivel, con una pendiente excesiva
Dificultad para optimmizar las labores de cultivo, debido a la anchura variable de las terrazas

2.2. Sustainable terracings techniques

The experiment carried out by Mas Martinet shows that the environmental and operative problems of conventional terraces can be overcome through the application of appropriate design criteria. This section describes the main criteria developed that have given good results in the Priorat region.

Figure 2.2 shows the different variables involved in the design of terraces: 

• For a given normal slope (α), the terrace is defined by establishing any two of the remaining parameters. For example, if the width of the terrace (a) is established, on decreasing the slope (β) gradient, the height between terraces (h) increases. However, if the width of the terrace (a) is reduced, the slope (β) gradient can be decreased without increasing its height (h). 
• The slope gradient (β) is always greater than the natural gradient of the hillside (α). 

2.2.1 Blending of terraces into the countryside

	The basic design criterion is for the terrace-vineyard as a whole to adapt as much as possible to the natural morphology of the land, minimising land movements and introducing no artificial forms that could grossly stand out from their surroundings. In general, the height of the slopes (h) is limited to 1.5 m. This criterion is basic so that aggradation does not disturb the harmony of the landscape. For greater slope heights, terracing becomes extremely visible and stands out from its surroundings, giving the vineyard the aspect of a quarry and the greater the high of the slope, the more noticeable it becomes. In any terracing, the stock can be plated on the terrace or on the slope. When the vine is planted on the slope, the limitation of its height may be somewhat more flexible, as the plant life will help the slope blend into the surroundings. However, it is wise not to exceed slope heights of 2 m in any case. The width of the terraces (a) must be limited according to the natural gradient of the land, so that the above criterion is respected at all times, i.e. the slope height does not exceed 1.5 m. Where small modern machinery is used, the terrace width may be as little as only 1.3 m. This is the terrace width preferred by Mas Martinet and the only one used currently in its plantations (the may reach 1.5 m in width in some cases). It only allows for one row of stock to be planted per terrace and requires the building of a greater number of terraces than those used were the width to accept two or more rows of stock, making the work more expensive. To compensate for this, the height of the slope is lower and the area can be adapted much more easily to the mountain morphology. A single row of stock on the outer part of the terrace also has advantages regarding the landscape, given that the eye of a distant observer follows the ends of the stock in a straight line, without it being broken by other rows of stock located on the inner part of the terrace. This also makes access to the slope easier for maintenance purposes. Both this and the previous criterion are completely incompatible with the construction of large levelled areas for the reproduction of flat-land vines, particularly on steep natural slopes.
Centre left is a plantation on a terrace, with slopes measuring over 1.5 m in height. The appearance of the lower three terraces improves as the slope height decreases. On the right of the photo is a plantation on a slope that blend in very well with the landscape, as terracing is almost imperceptible
Natural land with a gradient of over 60%. The slopes do not exceed 2 m in height; slope plantation

The ground layout of the terraces follows the level lines that are generally curved. Polygonal layouts are avoided, as they give the vineyard an artificial look that stands out from its surroundings. This criterion makes the use of conventional, straight vine training difficult or means that shorter sections have to be used. However, this is not a problem if the vigour control techniques indicated in Chapter 3 are applied.
The plant life on the peak is respected.	Terraces measuring a constant 1.3 m in width; note the constant lengthways gradient.	The terraces follow the level curves with no polygonal shapes
The line of mountain peaks (where the gradient changes), especially if steep, and its plant life are respected and terraces are started several metres downhill. The rocky outcrops and older trees, uniqueness, landscape value or representativeness of the agricultural past of the estate are preserved in the terraced area to break up the continuity of the vineyard (green islands) and to provide a shaded area where workers can rest. In larger vineyards, autochthonous trees may have to be specifically planted. If a large tree is incompatible with the implementation of the vineyard, it may be worth replanting it elsewhere. The huts and other buildings with a cultural or tourist value are also respected.

The plant life of any banks of the gulleys or streams running alongside the vineyard and the plant life on the border of the vineyard are also respected, not only for their contribution to the landscape but because they retain the soil, act as a visual reference and maintain agroforestry biodiversity.

On all accounts, the conservation of these areas is planned in advanced before the earthworks are started.

• The area around the access paths to the estates and the path itself are also worth attention. As well as connecting the vineyards or the crop-growing land, providing access to the estates and enabling agricultural machinery to get around, paths are a privileged platform for observing the countryside, from where the uniqueness and details of the region that are imperceptible from more distance observatories can be appreciated. Wherever compatible with agricultural use, paths are open and accessible for public use in order to find a meeting point between the wine culture and its landscapes and society and to help form part of the network of infrastructures supporting wine tourism.

New access paths to estates have been opened within the framework of the Life-Priorat project.
Certain design criteria are considered particularly important:

• Widths over 5 m are avoided. Where necessary, small, wider sections are built for heavy vehicles to be able to pass each other.
• Slopes and borders are finished and protected from erosion using appropriate plant life.
• Lengthways and sideways slopes are ensured good runoff.
• Where necessary, soft paving is used that blends in with the countryside.
• The use of urban-type signposting is avoided.

2.2.2 Prevention of erosion and controlled run-off of rainwater

The terraces are built on a constant 3% lengthways slope and a 4-5% sideways slope towards the  mountain. As a result, the vertical distance between terraces remains constant throughout. To strictly respect this criterion, excavation machinery equipped with a laser level is be used, as  shown later on in this section. This involves precise building work that requires a person with specific training in driving the machine (the machines must be adapted to the mountain and not viceversa).   All of the terraces drain off to side drainage channels. The terraces change the hydrological system of the mountain. Water no longer runs over the different natural slopes of the land until it reaches the water courses but is channelled along well-built terraces to concentrate at its end points, increasing its erosive force. As a result, it is extremely important to plan the safe channelling of this water to natural watercourses where it can cause no damage. Hence, all terraces must drain into drainage channels built for this purpose with the greatest guarantees of resistance and stability. The optimum solution will depend on the morphology and resistance of the mountain formation on which the vineyard is located.
Terraces with a constant lengthways gradient and width	Slope finishing with a constant height by laser levelling

This limitation to the length of the slope has very few repercussions in practice if a slope height of below 1.5 m is respected.

• Maintaining the good condition of terraces at all times is a basic condition for ensuring controlled water drainage and, ultimately, the stability of all the terracing:
  • Any accumulation of sediments or other obstacles on the terraces that hinder or prevent water from passing must be removed. Water must drain along the length of the terrace without accumulating and jumping sideways towards the valley, which would dangerously increase its erosive force.
  • Maintenance must be increased on the narrow terraces built by Mas Martinet (1.3-1.5 m), given that the section available for water to pass is quickly used up in the event of an obstacle.
  • Maintenance is also particularly important on the access paths to the terraces where the gradient and the length of the slopes and, therefore, the risk of erosion and sediment accumulation are greater. Furthermore, significant flows from the entire lengthways drainage of different terraces can accumulate at these points.

In Mediterranean areas where the episodes of heavy rain are relatively frequent, the controlled runoff of water is critical point in the construction of terraces. Where the necessary preventative measures are not strictly observed, extremely serious damage may be caused to the vineyard and adjoining areas, to the point of risking the survival of operations. The drainage network must be planned before starting terracing work.

It can therefore be concluded that the risk of erosion does not depend on the natural gradient of the land but on the design of the terraces: a badly designed vineyard on a 25% gradient will experience more erosion than well designed terraces on a 50% gradient.

2.2.3 Construction technique used for terraces and slope stability

When the construction technique of cutting the top part of the mountain and filling the bottom part is used, a fragile surface between solid ground and the soil on top is created that often leads to landslides, even during unexceptional episodes of rain (see Section 2.1). Where terraces run perpendicular to the N-S direction of the general slate units strata of the Priorat unit, the risk of landslides is greater.

In view of this situation, the constructive solution applied to Mas Martinet terraces has proven to be effective, even in torrential rain. It consists of ploughing and turning over the soil mass to a depth that is sufficient to ensure all the terrace rests on a base of solid ground that slopes slightly inwards. The greater the natural gradient of the land the deeper the ploughed soil must be to ensure that any contact with the solid mountain is almost horizontal. In practice, a minimum depth of 1 m is plough, which is the average depth reached by the roots of the vine (agronomic criterion).

Even when applying this construction technique, there may be minor problems of landslides, particularly during episodes of fine rain that penetrates the outside of the soil. If these landslides are appropriately fixed during the first two years of the terraces, the problem is solved and will not occur in subsequent years, given that the terracing settles. 

Once the width has been established, the slope height will depend on its gradient (β) and on the natural gradient of the land (α). The stable gradient of the slopes is a function of the internal angle of friction and cohesion of each type of soil ploughed. A direct cutting laboratory test assesses these basic parameters. In line with the construction technique used on terraces developed by Mas Martinet, the experiment on the Priorat “Licorella”1 slate soil shows that slopes with a gradient of up to 65º - 70º are stable.

All experiments carried out by Mas Martinet regarding the construction of sustainable terraces have been undertaken in collaboration with the company Coll de la Teixeta (www.teixeta.cat) located in Falset (Priorat, Tarragona).(), ubicada en Falset (Priorato, Tarragona).

2.3.4 Effective and safe vineyard operations

	As already indicated, the terracing land is ploughed to a minimum depth of 1 m so that the roots of the vine have fewer problems in spreading at any point of the plantation. Furthermore, the earth retains water more easily, as it increases its fine material content. Where the earth is not turned over, water in slaty earth such as that of the Priorat region tends to escape through cracks or a layer of sludge is formed that allows for run-off without infiltration. The width of the terrace remains constant throughout as, therefore, does the number of rows of stock in order to avoid non-productive movement or complicated manoeuvres with machinery.  Access to the terraces is zigzagged so that the gradient does not exceed 10-15%. This leads to the loss of a certain amount of space and the formation of small slope sections with a height or length above the maximums indicated, although occupational safety when moving with machinery is gained. With steep gradients, the risk of overturning the tractor is considered inadmissible, particularly at points where terraces are entered on a bend and where towing a trailer or other machinery.
Terraces with a constant width following level curves
Zigzagged accesses to terraces to improve ocupational safety

 

Landscapes with sustainable terracing.

¹María Concepción Ramos et al., Sustainability of modern land terracing for vineyard plantation in a Mediterranean mountain environment - The case of the Priorat ..., Geomorphology (2006).