Dams from the Roman Era in Spain. Analysis of Design Forms

Proceedings of the First International Congress on Construction History, Madrid, 20th-24th January 2003, ed. S. Huerta, Madrid: I. Juan de Herrera, SEdHC, ETSAM, A. E. Benvenuto, COAM, F. Dragados, 2003. Dams from the Roman era in Spain. Analysis of design forms Miguel Arenillas Juan C. Castillo A recent academic study undertaken by the authors' LOCATION AND EMPLACEMENT OF ROMAN DAMS IN (Castillo 2002; Castillo y Arenillas 2000) has SPAIN enabled the identification of remains of and references to seventy-two dams from the Roman era, Most of the dams built in Spain by the Romans -and constructed in Spain between the first and fourth particularly the largest ones- can be gathered eenturies.2 Fifty of them have been loeated and together in three main areas: the basin of the river detailed. The twenty-two outstanding, aJthough Ebro, espeeially the right bank, whose foeus may be identified on the ground, have not been able to be loeated in Zaragoza (Caesaraugusta); the area of aeeeptably eharaeterized, due in some cases to their Mérida (Augusta Emerita) along the basin of the river being ruins in a highly degraded state, others due to Guadiana, and the left bank of the river Tajo in some their being masked by repairs and reeonstruetions points near Toledo (Toletum). The natural regulation subsequent to the Roman era. A list of the properly of the rivers flowing in these sections of the Spanish eharaeterized dams is encIosed in the Appendix at mainland is low or very low, basieally as a the end of this paper, where reservoir dams are consequenee of the unequal distribution of annual ilIustrated on the one hand (21) and diversion weirs precipitation (Arenillas 2000); these cIimatie on the other (29). The main dams (nearly all of them conditions foreed the eonstruetion of reservoir dams. are large dams by present standard s) are included in In faet, tour of these dams were eonstrueted so as to Table I. ensure the water supply to the Roman towns Tabla l. Principal dams of the Roman era in Spain NAME HEIGHT RIVER BASIN Almonacid de ]a Cuba 34,0 Aguasvivas Ebro Proserpina 2],6 Las Pardillas Guadiana Cornalvo 20,8 Albarregas Guadiana Ermita Virgen del Pilar 16,7 Santa María (Aguasvivas) Ebro Alcantarilla 15 to 20 Guajaraz Tajo Muel ]3,0 Huerva Ebro Pared de los M oros 8,4 Farlán (Aguasvivas) Ebro 244 M. Arenillas. J. C. Castillo mentioned above: Muel to Caesaraugusta, Proserpina and Comalvo to Augusta Emerita, and Alcantarilla to c- ",~~.Iti1 To/etum. rf,,-/I "'" ~./-t However, this system was not the standard pattern applied by the Romans to resolve supply problems. In reality they only used it when, with good reason, climatic conditions forced them to do S03 In most cases (and frequently in Spain) they opted for riverhead collections by means of diversion weirs or Cobisa o. intakes direct from sources.4 Nambr'OCI& Nevertheless, when the Romans built regulation ~~~~= D dams in Spain they frequently differed from this pattem. Of the three areas aforementioned this can be found in the basin of the Ebro (area of Caesaraugusta) where large dams were located, as a rule, in the middle stretch of rivers of so me importance. On the other hand, in the mid-west of the CtlU6C2Q Peninsula (Emerita and To/etum) these works were AJofrtn always situated on riverheads or streams with small Q catchment basins. Pulgur M82arambroz These differences of criteria regarding the V emplacements can also be found in the structural Osonseca solutions adopted: in the Ebro the highest dams are masonry dams, whilst in the Tajo and Guadiana the dams are earth dams with retaining walls upstream. However, the smallest dams -where other forms SAN MARTiN may be found- form a more homogeneous group in DE LA MONTlNA DAM general. o 1 2 3 4km ~ t j Figure 2 Supply system to Toletum (Alcantarilla dam) r d"'~ '.S\. (A '-'---" " ir;~~="~~"¿'~ ~~ ( -~,~~ r'~ ./ ~r!' r' ~~:::---J-'~, ,. í"'~: ) r-/. .. ~\~ I ,,\ /'">-->"'.., // ~- '", I-"' ,/ STRUCTURAL FORMS r \¡.L.-v./~J~"', 1 ~-. '. ,t. fBan:elou t~l{ ~ 'L,' -o 1 ([/ /:>/;' .". ~ In the majority of the dams built in Spain by the f JI(~~{.;/) Romans there is a basic characteristic construction ; '; , ,/J:", (/rj'C:f.l,' /~" element, almost systematically repeated: the retaining !(y \,~') /~-1mI,,' ''¿ . "..~~ d l '.,/'-)'--1./'-' ) wall, used to achieve watertightness of the structure. rL.).-r', '. v -- /~I ..~~--\~/- .,,)~'" i ' ~ '""", ,J Other elements, though not a]ways, were added to ,/~I_~" 'J~-\-'\_-'-~ - ensure or complete the stability of the system. The }' ,-",o." Irrrr. Dam Roman retaining wall is a very simple concept: a lime \,. (" ,~~~ . Diversion Dam ~'OO concrete core (opus caementicium), framed by two I wall sections made of masonry (opus incaertum) or Figure 1 ashlar (opus quadratum). When the masonry was of Location of the dams in the Roman .era poor quality other wall sections were attached to the Dams trom the Roman era in Spain. Analysis of design forms 245 first ones being of increasingly better quality towards The basic fault of this structure is its extreme the exterior. The most important element of this thinness7. With such a risky geometry the presence of system was the core of opus caementicium, whose an earth embankment downstream should be purpose was to comply with the objective of retaining expected, but the materials existing there have not the water. permitted the detection of the remains 01' such a complementary structure. As a result, the Pared de los Moros undoubtedly broke, and probably quite early The large dams on the Ebro basin as the sediments 01' the reservoir have not developed much, although they also could have been swept The dam which probably conforms best to the strict away by the waters after the dam breached. They can pattern ofretaining wall is the one known as La Pared be observed, in particular, on the right bank where de los Moros (The Moors' Wall).5 It is located near they show up without excessive re-workings -natural Muniesa (Terue!) in a secondary waterway, the or artificial- since their deposition. Arroyo Farlán, the rightward tributary of the river The calcareous concretions observed in the Aguasvivas,6 which at the same time is a branch of downstream face 01'the dam are not abundant, which the Ebro, also on the right bank (Arenillas, Díaz- could indicate that the retaining wall worked properly Guerra y Cortés 1996). The dam initially formed a from the point 01'view 01'impermeability. In fact, the reservoir of approximately 150,000 cubic metres opus caementicium forming its core is 01' good capacity; nowadays it has a breach in its middle quality. section. The characteristics of the masonry -not The best pattern 01' a dam formed by a reinforced properly laid down in general, and the layout- retaining wall (that is, an improved version 01' the somewhat winding (as with the layout of the previous pattern in terms 01' resistance) is the dam of limestone outcrops in the area) enable us to think of it Almonacid de la Cubag. This is the highest dam from as a later Roman work of rural style, perhaps the Roman era preserved in the world (thirty-four dedicated, at least in part, to irrigation. The structure metres). It is located on the river Aguasvivas and has is nearly 8,5 metres in height and has a crest length of a catchment basin 01' about 1.000 square kilometres. around seventy metres. Its form is as previously Built in the era 01' Augustus and rebuilt and repaired indicated: a single wall of nearly three metres several times, this dam has a peculiar feature which thickness, formed by two masonry wall sections laid makes it even more interesting: the preserved with lime mortar (opus incaertum) and a core of opus structure is an important reconstruction 01' a previous caementicium. The coverings are of 1,I O metres structure 01'completely different formo thickness each and are built with local limestone, The first dam raised on the closure site of lightly worked. The core reaches up to seventy Almonacid must have been formed by three arches, centimetres thickness. Figure 3 Figure 4 La Pared de los Moros Dam of Almonacid de la Cuba 246 M. Arenillas, J. C. Castillo M.o. 10 15 20 m ~ - SECOND DAM - FIRST DAM Figure 5 Layout (assumingly) of the early dam of Almonacid one central and two side ones leaning against two of a rectangular central body and two stepped faces; large buttresses (Arenillas, Díaz-Guerra y Cortés downstream the stepping is double. In the central 1996). This first dam must have been breached quite body a retaining wal1 stands out which, according to early, even perhaps in the later phases of construction the data obtained from the drillings, reaches between and it also must have been rebuilt at once, its original 10 and 12 metres thickness, of which the 2,70 central structure being substantially modified, becoming the metres belong to a lime concrete core (opus typical straight gravity dam. The breach of the dam caementicium). This core is framed between two was certainly partial and probably was located on an double masonry wall sections (opus incaertum) with isolated point, the central arch for example, as in the an average thickness of about 3,70 metres upstream latter reconstruction many of the original elements and 4,60 metres downstream. In both cases the were entirely or partly preserved: the arch of the left masonry located beside the core is of worse quality edge, with elements from the buttress it was leaning than the exterior ones. against, or the intake tower, among others (Arenillas, The retaining wall belongs to the first dam and Díaz-Guerra y Cortés 1996; Hereza et al 1996).

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