Land Management and Landsildes in North of Portugal,

7/31/2019 Land Management and Landsildes in North of Portugal,

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Land management and landslides in

the North of Portugal

International Symposium on Geography, 2-5 June, Antalya Turkey

A. [email protected]

J. [email protected]

M. [email protected]

Peso da Rgua -RDD

Peso da Rgua -RDD


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Research Goals

The landslides in the north of Portugal, resulting of theconstruction of road and railway infrastructures,displayed the importance of knowing thegeomorphologic dynamic of slopes. On the other hand,the increasing number of slope movement events showsthat the slope dynamics is being disregarded in the land

management strategies.

Several examples that we will present makes self-evident that many of the landslides in the north ofPortugal are closely related to mans action in the

slopes.

In this way, this research work intends to contribute toin-deep knowledge of the root causes and unchaining

factors of slope movements aiming to prevent that mansactions collide with the natural balance.


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The anthropic action and theslope movements

The anthropic action can increase the susceptibility of

slopes to the occurrence of slope movements, interactingand reinforcing the natural conditioning factors oremerging as direct cause of slope instability.

The urbanization, the construction of communicationroutes and other infra-structures, as well as, thepreparation of the land to farming practices oblige,especially in hilly areas, to profound morphologicalalterations. These deep changes in the terrainmorphology, in the land cover and in the land use arealmost always associated to a complete alteration ofnatural hydrological processes, conditioning the infiltrationand the surface runoff.


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Under natural conditions, the slope movements in the

mountain areas of north Portugal are more probable to occurwith great slopes (25 to 35) and in alteration mantles of roughtexture.

With human intervention, that changes natural conditions, thesame processes of hillsides evolution may affect smallerslopes. The opening of trenches at the hillside base is perhapsone of the practices that most frequently affect its dynamic.

Even in places where there is a high susceptibility to theoccurrence of hazardous processes related with slope

dynamics, it is often the human intervention that will unchainthe process and transform it into a disaster.

The human presence represents

frequently a factor of instability.


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The current Portuguese agrarian landscape is undoubtedlymarked by several viticultural regions characterised by poor,

steep lands. The Douro Demarcated Region is precisely one ofthose regions, where throughout the years, strong people

helped create what Orlando Ribeiro considered as the vastestand most magnificent human undertaking of the Portuguese

territory (RIBEIRO, O., 2nd Ed, p.78), classified on 14December 2001 as World Heritage Site.

Lithologic

characteristicsof RDD


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Rainfall (mm)

In general terms, the precipitation decreases as temperature rises: from south to east.The entire region has low levels of precipitation (often below 1000mm): the sub-region

of Douro Superior has the lowest levels of precipitation (400-500mm/year) in contrastwith Baixo-Corgo with approximately 700-1000mm/year.

Average yearly precipitation in RDD(1931-1960)

The climate of Douro Demarcated

Region is characterised by its

Mediterranean character, this

means a short winter and early,

intense, dry and long summers.

Another characteristic of the

Mediterranean climate is the

distribution of rainfall throughout

the year, concentrated in the endof autumn and beginning of

winter with a secondary

maximum in April or May, and a

period of summer drought clearly

marked.


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Morph o logy o f t he v in eya rd t e r r aces i n RDD

The evolution of viticulture following the phylloxeraplague was marked by the preferential occupationof gentler slopes and the increase in the distancebetween supporting walls.

The system of traditional vineyard, used until theend of the 20th century is characterised bystructuring the slopes in terraces of variabledimension that are supported by walls.

The system of traditional vineyard comprises themethods of terraces and vinha a eito, in whichthe terraces are wider, the distance between the

walls is bigger and the platform is stepper.


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Traditional vineyards

Example of traditional vineyard, formed by terraces supported by walls. In this kindof plantation system, the drainage network was carefully conceived and a continuous

maintenance of the drainage channels was ensured to prevent the collapse of thewalls, as well as, to reduce the soil erosion.


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Viniculture slopes in RDD:

Evolution of morphologic patterns

Among the new systems of plantation are included:vineyard planted according to level curves;

vineyard planted in non-supported terraces and

vinha ao alto planting of the rows up the face of the

slopes.

The modern plantation systems,which evolved from the end of the1970s, are characterisedessentially by the suppression of

the supporting walls of theterraces.


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New system s of plantat ion

vineyard planted in non supported terraces

The new plantation systems of vineyards

are aggressive farming techniques, whichchanges the morphology of the slopeleading to the development of artificialsurface formations, such as schistdeposits made of debris resulting from therock destruction by heavy machinery.

On the other hand, these plantation techniques

completely disrespects the water courses,occupying the stream bed, making deviations tothe natural flow way and canalizing the waterlines.The change of the slope shape, the alteration ofthe surface materials and the disruption of thenatural hydrological processes induces the

occurrence of landslides, debris flows, as well asother types of processes such as gullies.


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Landsildes 2001

More than 150roads and trackswere affected

Some are representedby dots, but others

given the frequencyand proximity arerepresented by lines,extending for severalkms and affecting the

roads continuously.

Number of landslides occurred in 2000/01which affected road structures

During this hydrologic year, there are records

of about 270 landslides affecting road systems.


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Landslides 2001

Road network

Municipality boundarie

In the most affected area it is possible to observe the great number of landslides, that

were recorded almost continuously in many places. The cases where the entire roadwas blocked are frequent.

The recuperation of some communication routes demanded an intervention in almostthe entire road.

Road affected by landslides in January 2001


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The drainage system and its impacts

over the road network

Landslides 2001

Road network

Hidrographic network

There is a matchbetween the area thatwas affected bylandslides and thepoints where theroads overpass thewaterlines.


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The drainage system and its impactsover the road network

Due to the predominance of schist subtract, the water drainage system

is extremely complex. It is easy to find a road that crosses severalwaterlines (either sporadic, temporary or permanent).

However, the main sources of slope instability, related to the roadnetwork, are the characteristics of the infrastructure, the related

engineering design process and the abandonment of the associateddrainage systems.

The construction of the road may influence de natural drainage inseveral ways: Ignoring the waterlines by landfilling the streams bed; Channelizing the streams with under-dimensioned pipes; Not providing the necessary maintenance to the drainage systems,

particularly in what concerns to its cleaning and unblocking.


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The inadequacy of drainage infra-structures

to the streams flow during flood events

The construction of the roads often leads

to the obstruction of the waterlines, to theunder-dimensioning of the drainage pipesregarding the extreme events and, insome cases, to its total inexistence.

These drainage problems are worsened bythe change of the waterlines course,especially in the case of torrential streams.


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The steepness of road barriers

Some slope movements are strictly related with the abruptness of the slopes

jointly with the existence of road barriers that cutting the slope almost verticallyorigins dangerous cliffs highly susceptible to rock fall and debris flows.


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Rainfall analysisComparative analysis between the yearly average rainfall and

the extreme values recorded in the hydrologic year 2000/01

0

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400

600

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1400

1600

Rainfall(mm)

Peso da Rgua St Marta Penajia Meso Frio

Yearly average rainfall Hydrologic year rainfall

The records of all rainfall stations under analysis have always presented much higher values thanthe 30-year climatic average, with especial focus in Peso da Rgua Station, over passing almosttwice the yearly average precipitation.


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Rainfall analysisComparative analysis between the monthly average rainfall

and the extreme values recorded in the hydrologic year 2000/01

0

50

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Rainfa

ll(mm)

Outubro Novembro Dezembro Janeiro Fevereiro Maro Abril Maio Junho Julho Agosto Setembro

Date

Month average rainfall Hydrologic year rainfall 2000/01

The rainfall station of Peso da Rgua shows that the yearly rainfall in 2000-2001 concentratedmostly between November and March.


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1stStudy-case

National Route - EN 313 - Nogueira

Near the village of Nogueira therehas been an huge number of slope

movements. Two of the mostdestructive debris flows affected theNational Route (EN 313), that isparticularly important for roadcommunications within this region.

Indeed, this road is the mainconnection between the nearest bigtowns: Vila Real and Peso da Rgua.


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Study-case of NogueiraLocation of the most destructive landslides that

affected the National Route - EN 313

Landslides 2001

In the place where the two main debris flows occurred the amount of landon the road was so great that it was obstructed for more than a year.


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Landslide that affected the National Route -

EN 313

Detail of the debris flow that affected EN 313, nearDetail of the debris flow that affected EN 313, near NogueiraNogueira..

In the photo we may see the starting point of the debris flowIn the photo we may see the starting point of the debris flowand the dimension of its scar that affected the road.and the dimension of its scar that affected the road.


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Study-case of Nogueira - EN - 313

Alternative way


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Study-case of Nogueira - EN - 313Alternative way

The road that has been closed to traffic during a year was a crucial

communication structure at a regional level, affecting not only the

accessibility to the small local villages, but also the connection

between the two greatest cities of the Demarcated Region of Douro,

Vila Real (50,000 inhab.) and Peso da Rgua (20,000 inhab.).

There was only one viable alternative connection: the National

Route n. 2, which have also been affected by the slope movements,

but not so severely. Despite the fact that the damages were not solarge, this road is not suited for heavy vehicle traffic (trucks,

coaches). Actually, this road is very narrow, has a bed pavement, a

sinuous design, a great number of curves and, in some stretches, it

has a strong steepness.


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Landslides2001

2ndStudy-case

Destruction of the only access to 3 rural villages

In the following

example it is possibleto see that the accessto 3 villages became

very difficult, sincecar traffic was

completely blocked

for three days andvery conditioned for a

month during therepair works. All

roads in the area wereaffected as a

consequence of thelarge number of slope

movements thatblocked all roads.

It was not only the large urban centres that were isolated, since it was impossible to travel on EN313, but it was also impossible to travel to Nogueira, which is a parish centre.


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Detail of the road affected nearDetail of the road affected near

the village namedthe village named TanhaTanha

Construction of a bridge, near the village ofVilarinho de Tanha, during the recovery stage ofthe Municipal Route that was washed way by a

torrential stream.

Slope movements that affected theSlope movements that affected the

road near the village ofroad near the village of AlfolesAlfoles..


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3rd Study-case

National Route n. 222

Finally, the

example of theNational Route

222, whichconnects the cityof Peso da Rgua

and the touristcity of Pinho.

This vitalconnection was

affected by a very

serious slopemovement in the

night of 28thDecember 2002.

This kind of hazardous processes affects this road very frequently


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Debris flow that affected the



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Debris flow that affected the


Debris flow that affected the National Route 222 in an area of steep

slopes (over 40) occupied with vineyards planted in non-supported terraces.

As one may observe in the photo in the precedent slide, the naturaldrainage network was completely transformed. The natural course of

an intermittent stream (represented by the blue line) was deviatethrough an artificial pipe (represented by the red line) that wasbroken by a small slope movement, inducing the drainage of thewater directly to the slope (detail photo on the left). Thus, this firstsmall slope movement created the favourable conditions to the

development of the second movement, much more bigger anddestructive.

This slope movement resulted undoubtedly of the uncompleteddrainage system of the pluvial waters, being the surface runoff

drained by a temporary solution, as we may confirm in the detailphoto on the right.


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Rainfall analysisDaily rainfall - total and acumulated values - recorded in "Peso da Rgua" in December 2002

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Dailyrainfall(mm)

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Accumulatedrainfall(mm)

Daily Rainfall Accumulated rainfall

As one may observe in the Rainfall Chart the daily precipitation was around 30 mm and the monthly accumulatedprecipitation was around 250mm. This continuous period of heavy rainfall lead to the soil saturation, increasing therunoff rate, the sub-surface flow, favouring, therefore, the slope instability.


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AlternativeWay

Alternative way to the


The road wasblocked for a year.The less expensive

alternative, butonly suitable forpassenger cars,

was to travel

through the roadrepresented by theblue line, much

narrower. Theincrease of the

distance resulting

from the trafficdivert was of 23KM. The heavyvehicle traffic

would now have totravel more 60 KM.


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Number of

events costs ()

Government

help()

Government

help (%)

Alij 18 638.524,20 349.158,50 54,7

Meso Frio 21 2.026.625,10 1.246.994,70 61,5

Mura 9 1.152.223,10 249.398,90 21,6

Peso da Rgua 12 5.379.582,90 1.496.393,70 27,8

Sabrosa 10 329.510,90 299.278,70 90,8

Santa Marta Penaguio 11 2.154.806,90 1.745.792,60 81

Vila Real 74 4.490.604,30 748.196,80 16,7

TOTAL 155 16.171.877,50 6.135.214,10 37,9

Economic impacts of the slope movement

risk in the most affected Municipalities

Besides other economic impacts (like losses of agricultural productions and property damages,for instance), the money spent to repair the roads affected by slope movements in January2001 amounted to approximately 17 million euros in the 7 municipalities. The Portuguese Statecontributed, in average, with 40%. However, the States contribution to some municipalities,

such as Santa Marta de Penaguio and Sabrosa, was of more than 80%, since their annualbudgets could not support the involved costs.


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The main permanent factors that influence the occurrence of an elevatednumber of slope movements (particularly landslides and debris flows) in

Demarcated Region of Douro are:

- The lithological features of this region, marked by the schist soilscontaining high quantities of clay.- The naturally accentuated slope of the hillsides, often superior to 30;

- The steepness of the road barriers (>85) and of the slope embankment (>40),- The inexistence or the inadequacy of drainage systems, which often arenot designed to extreme rainfall events;- The insufficient maintenance of drainage systems, particularly in whatconcerns to the cleaning of the pipes and open channels;- The change of the natural course of the streams and of the surface runoff.

In these favorable conditions, the slope movements are quickly triggered by

the high levels of rainfall, which are recorded by long periods of time,between the months of December and March in RDD.

Conclusions

Documents

Land Management and Landsildes in North of Portugal,