The engineering structures of the traditional rural roads are one of the elements with greater visual impact can get to cause over the landscape. As a possible way of minimizing this impact, it`s advised to adequate the design of the new constructions to the traditional types of each region. However, the small bridges built by the “popular engineering” have been disappearing of our landscape gradually. This fact, together with the lack of specific studies on the subject, can provoke that in future we shall not be able to know the traditional constructive types characteristics of each area. The aim of this study is to determine the basic type of little bridges wich are traditional in the area of “Terra cha” (Lugo, Spain). For that, some of these engineering structures have been analysed, planned and photographed. After the analysis, it has been able to determine that the small bridges characteristics of the area are trabeated, and stony deck of one or several span.

1. AGENG EurAgEng
WARWICK 2000
Paper Number:
Title:
Authors:
Summary:
00-FB-047
LITTLE BRIDGES OF THE TRADITIONAL RURAL
ROADS OF “TERRA CHA” (LUGO, SPAIN):
TYPOLOGICAL ANALYSIS
Ortiz Sanz, J.(*); Cañas, I..;Rego, T.
Escuela Politécnica Superior. Universidad de Santiago de Compostela. Campus
Universitario. 27002 Lugo. Spain.
Tel:+34 (9)8 2252231 Fax:+34(9)8 2241835 email jortiz@correo.lugo.usc.es
The engineering structures of the traditional rural roads are one of the elements
with greater visual impact can get to cause over the landscape. As a possible way of
minimizing this impact, it`s advised to adequate the design of the new constructions to
the traditional types of each region. However, the small bridges built by the “popular
engineering” have been disappearing of our landscape gradually. This fact, together
with the lack of specific studies on the subject, can provoke that in future we shall not
be able to know the traditional constructive types characteristics of each area. The aim
of this study is to determine the basic type of little bridges wich are traditional in the
area of “Terra cha” (Lugo, Spain). For that, some of these engineering structures have
been analysed, planned and photographed. After the analysis, it has been able to
determine that the small bridges characteristics of the area are trabeated, and stony deck
of one or several span.

2. Introduction
Traditional rural roads and all the works associated have local peculiarities which
contribute to characterize the landscape of each area, forming a vast heritage built in the
rural areas as well. The gradual size increase of the agricultural vehicles (too big for the
traditional small bridges), the new constructive strategies (different from the traditional
building in common) and the new materials and available means (mass-prefabricated,
massive introduction of concrete, so on...) are provoking the progressive substitution of
the old vernacular bridges by other modern models, designed national wide. This new
engineering structures, apart from not providing “regional landscape personality”,
usually reduce the visual resources of the area; not in vain, together with the
characteristics of the horizontal alignment, this structures are appointed as the causing
of the most important visual impact of rural roads over the landscape (MOPU,1989).
Nowadays, the suitability of design to the modern buildings to the traditional typology
of each area is advised, as a possible way of minimizing the visual impact of the new
constructions (MOPU,1989). In order to reduce the visual impact of the modern
structures, it’s necessary to know traditional engineering structures. It has been
choosing the “Terra Cha” as field of activity, typical landscape of Galicia (Spain).
The present study is dealt then as a first approach to the analysis of the traditional
engineering structures. It has been choosing in concrete the “Terra Cha” as field of
activity, typical area of the northwest of Spain, with dense hydric and road networks.
These densities are because the abundant rainfall is regular all over the year, the
farmstead are found grouped numerous small disperse settlements, where a mixed
agriculture-cattle raising-forest economy is practised markedly small farm holding, with
pasture-farming as one of the most characteristic activities.
Aims
The fundamental objectives to get with this study are the following ones:
- To stablish the characteristics which propitiate differences and similarities among each
traditional engineering structures, so as to define the basic types of little bridges in
“Terra Cha”
- To determine its maintenance state and use to try analyze the present situation of this
popular rural heritage of the “Terra Cha”.
- To continue (Ortiz et al, 1998) the elaboration of a small plan catalogue of this
bridges, which permit to place its constructive characteristic on record.
Method
An analysis filing card was used, structured in four parts: “Localization”,
“Surroundings”, “Typology and Construction” and “Maintenance and Use”. Also,
sketches made in the field for the following elaboration of plains in detail. The stage of

3. looking for details of each bridges in country was concluded with the photos taken and
the occasional interview with any neighbour.
In the part of “Surrounding”, the characteristics of the bed, parallel ford, the site-
vegetation and the presence other elements (dams, fences, and so...) were studied.
In the part of “Typology and Construction”, the type of traditional engineering structure
was reflected, its basic geometry (the number of bays, the deck gradient, the approach
gradient, the horizontal angle between deck and water flow longitudinal axis and the
ground shape of abutment walls) and its building characteristic features (structural
system and materials of each element).
Regarding “Maintenance and use”, the general conservation state was observed, and the
use made of the building and the causes of disuse was determined, when it was
possible.
Results and conclusions
Surrounding
Characteristics of the water flow. Considering the horizontal alignment of bed, its
transversal section and the characteristics of the stream, it has been able to find
engineering structures in the following kinds of bed:
- “Hollowed”: so-designed to the typical natural flow across the valley, flanked
by strong slopes and horizontal alignment straight or slightly curved.
- “Meander”: referred to curved stretches, where one of the banks present a
strong slope and the other has got a slight gradient.
- “Slightly hollowed”: so-designed to the slightly hollowed beds with small
dimensions. There are usually very little important beds, whose flow scarcely
exceed 2 m width.
- “Artificial: artificial canals made in the land with vertical walls, which
generally goes across mid-hillside. Its depth is usually about 0,5 m and its width
does not generally exceed 3 m
Parallel ford. Another difference observed among the different examples is the
presence of parallel ford.
Type of surrounding vegetation. Most of the example have got abundant tree vegetation
in the surroundings. However, it´s possible to find bridges between totally herbaceous
shores, what makes them very visible.
Adjacent elements. Occasionally there are other adjacent formations -fences, dams, so
on...- which form picturesque whole image.

4. Typology and construction
Type of traditional engineering structure Of all the examples studied, there are
“pontigos” (for the transit carts) and there are “pontillóns” (for pedestrian and cattle
use).
Basic geometry
- Number of bays. Examples with intermediate piers have been found.
- Longitudinal gradient of deck: the deck are horizontal
- Gradient of the approach. The cases have been found was both accesses in
ascending gradient.
- Angle formed by the axis: The horizontal angle which form the axis of the deck
and the water flow can be about 90º or clearly different from 90º.
- Shape in ground of the abutments: the most habitual kinds of abutment
considering the shape in ground plan of the wall are followings.
- “Linear”: wall with straight ground plan, sensibly parallel to the shore
of the bed. It`s the typical case of small bridges over canals.
- “Rectangular”: with shape of a square truncated prism.
Dimensions.
- Height clearance: the hight from an inferior plan of the deck to the bottom of
the bed is very varied, but it does not usually exceed 1,5 m.
- Total span: the biggest bridge analysed was of 18,2 m.
- Usable width. The length of the cross beams varies on the use the bridge was
built for. The parameters is then one of the most characteristic of each type of
engineering structures.
Constructive characteristics.
- Materials ans Structural system. All the examples studied are trabeated with
one or several bays. The abutments are formed by bearing walls. The deck is
usually of stone.

5. Conservation and use
General conservation state. It has been considered “good” when all the elements of the
engineering structure show good aspect. It has been considered “deficient” when they
seem unsafe or have flaws (cross beams misplaced, holes in the deck, ruined balustrade,
so on...). It has been considered “ruined” if the way on the deck is not possible, the
bridge present evidence symptoms of rot or the structure has decayed. Lastly, partially
“modified” examples ave been founded.
Present use. Three categories of use have been established: “active” (when the
engineering structure is still habitually used by the inhabitants of the area), “occasional”
(when its use has diminished a lot) and in “disuse” (when it is only used in exceptional
cases or is not used).
Causes of disuse. As it was expected, the most common cause of disuse is alternative
roads. However, these small bridges go on being essential for the access of the
pedestrian and cattle to the fields.
After the analysis, it has been able to determine that the small bridges characteristics of
the “Terra Cha”. Main conclusions are:
1.- The main differences which the small bridges of “Terra Cha” presents are due to:
adjacent ford, surrounding vegetation, approach gradient and span number.
2.- The basic type of “small bridge” of the area of “Terra Cha” are trabeated, with
abutments of dry masonry and stony deck of one or several span.
BIBLIOGRAPHY
MOPU, 1989. “Guias metodológicas para la elaboración de estudios de impacto
ambiental. Nª 1: Carreteras y Ferrocarriles”. Monografías de la Dirección General de
Medio Ambiente. Madrid. P. 124-131.
Ortiz, J. Cañas, I. and Rego, T. 1998. “Engineering Structures in the Vernacular
Architecture of the Traditional Rural Roads of “Ancares” (Spain)”. 13º International
Congress on Agricultural Engineering. Rabat (Morocco)