Manual of techniques for sustainable mountain viticulture Josep Lluís Pérez Verdú

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Soil erosion

Erosion may be intense due to the excessive length of slopes, thus increasing runoff, and espe-

cially 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 reci-

pient 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. 

Polygonal terraces generate an artificial landscape

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Severe erosion on a slope, putting some stock at risk 

Repairs on eroded slopes

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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 ero-

sion acts through two basic mechanisms:

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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 com-

ponents 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.

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Runoff. This is the water erosion mechanism par excellence. Rainwater that does not pene-

trate 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: 

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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. 

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Decreased soil fertility, associated to the leaching of minerals and the loss of organic matter

and nutrients.

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Destabilisation of slopes and increased risk of landslides. 

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Aggradation of adjacent areas (agricultural land, irrigation installations, roads, etc.) due to the

effect of sediment dragging.

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Chemical substances from fertilisers and pesticides that are dragged along by sediments may

eutrophicate or pollute watercourses. 

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Both problems lead to an accumulation of water in land depressions, also due to sediments that

act as a small dam. When this stagnation of water breaks, water and mud run off with notable des-

tructive force, which is multiplied as they run downhill and may form gullies and cause extreme

destruction. 

The building of terraces should not invade natural watercourses such as gulleys or streams. With

heavy rain, water will seek its natural course and will end up severely eroding the terracing. Any

repair work undertaken, as well as being extremely expensive, will be useless in light of a new epi-

sode of Mediterranean rainfall. In these cases, the sediments dragged along as a result of erosion

may be large and create serious problems downstream, such as the aggradation of neighbouring

estates or roadway infrastructures. 

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Slope instability

The studies carried out in the Priorat region by the University of Lleida

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show that landslides are

frequent, even with unexceptional episodes of rain. 74 different landslides were identified during

the work in the municipality of Porrera. An exponential relationship was observed between the

volume of the landslides and the length of the slope. The movements detected caused damage to

plants and infrastructures (vine training, irrigation, etc.). Landslides also hindered or prevented

machinery from running along the terraces. It is precisely this difficulty and the steep gradients that

greatly complicate the access of the necessary machinery to restore damaged terraces. 

When a loader is used for earthworks, the terraces are formed using the conventional technique of

cutting the top part of the mountain and filling the bottom part. Hence, the moved (cut) soil is pla-

ced on the mountain in its natural state. This creates a fragile surface between the solid ground of

the mountain and the soil on top, making landslides more likely (see Section 2.2.3).

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Low soil use

To obtain a certain grape production, an under-optimised design of the terraces (width, slope gra-

dient, 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 reprodu-

ced in the mountains, where the land must be made the most of to minimise the traumatic effects

that terracing always involves to some extent.  

At the top of the photo, terraces that are too wide,

with little soil use; slopes of varying height that

make erosion control difficult

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María Concepción Ramos et al., Sustainability of modern land terracing for vineyard plantation in a Mediterranean mountain

environment - The case of the Priorat ..., Geomorphology (2006).

Vineyard built by filling in a natural gully instead of

forming terraces on the mountain with drainage to

the gully

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