Some Hydraulics of Roman Aqueducts. Myths, Fables, Realities. A Hydraulician's perspective
by Hubert CHANSON (
M.E., ENSHM Grenoble, INSTN, PhD (Cant.), DEng (Qld), Eur.Ing., MIEAust., MIAHR
Div. of Civil Engrg., Univ. of Queensland, Brisbane QLD 4072, Australia
Detailed photographs
Related links
Chaponost, Gier -  Mornant, Gier Arches de Sainte Croix, Fréjus Fréjus
Pont-du-Gard, Nîmes Pont de Bordnègre, Nîmes Biternay, Brévenne Full-size dropshaft Full-size dropshaft, R3


Roman aqueducts supplied waters to cities for public baths (thermes) and toilets (latrines) (HODGE 1992, FABRE et al. 2000), in addition of public fountains. They were long subterranean conduits, following contours lines, with flat longitudinal slopes : i.e., 1 to 3 m per km, even less at Nîmes (0.24 m/km). Numerous aqueducts were used for centuries and some are still in use (e.g. Carthage, Mons). Their construction was a huge task, often performed by the army under the guidance of military hydraulic engineers. Their cost was extra-ordinary considering the real flow rate (i.e. less than 400 L/s) : about 1 to 3 millions sesterces per kilometre in average (FEVRIER 1979, LEVEAU 1991) (1).
Despite superb ruins, little is known of the hydraulics of the Roman aqueducts. What was the flow rate ? How did they operate ? How were they designed ? Who were the hydraulic engineers ? How did they learn their expertise ?

Hydrology and operation of some Roman aqueducts

The hydrology of some catchment areas supplying Roman aqueducts were recently studied. For example, the "source de l'Eure" at Uzés supplying the Nîmes aqueduct, the "source de Gorze" feeding the Gorze aqueduct (Metz), the "source du Thou" and "ruisseau d'Arches" supplying the Mont d'Or aqueduct (Lyon) and the "sources de la Siagnole" feeding the Mons aqueduct (Fréjus), which are all in use today (2).
Overall, recent hydrological data show large variations in streamflows. During dry periods, the daily flow was typically less than 10% of the maximum discharge. While the flow rates during Roman times are unknown, it is plausible that hydrological variations were similar to present trends. This suggests that the aqueducts conveyed relatively low flows during dry periods.

Regulation Basins

Several aqueducts were equipped with regulation basins installed along the canal. For example, at Ars-sur-Moselle (Metz); at the Vallée de l'Eure, upstream of Pont-du-Gard, at Lafoux along the Nîmes aqueduct; at Segovia upstream of the aqueduct bridge. Most regulation basins were equipped with a series of gates and an overflow system. Basic hydraulic considerastions imply that undershoot gates were used to regulate the aqueduct flow while overshoot gates were used for the overflow discharge (CHANSON 2000b).
Hydraulic calculations were conducted for two large regulation basins on the Gorze and Nîmes aqueducts. The results demonstrated that the undershoot gate openings had to be small : i.e., between 2 and 10 cm at Gorze, and between 3 and 12 cm at Nîmes (CHANSON 2000b,c). This type of operation implied fine gate opening adjustment systems to enable precise flow regulation.

Discussion : what type of flow regulation ?

Water supply operation can be based upon two different techniques : on/off (i.e. 100% or 0%), or a dynamic flow regulation. In the former case, the gates were open constantly, and the waters flowed to the cities, without further regulation than the force balance between gravity and flow resistance (e.g. CHANSON 1999a). The gates and valves were used to stop the flow for repairs, maintenance and cleaning. Dynamic flow regulation is commonly used in modern times and it involves a series of operation to respond constantly to the users' demand. In Roman times, this type of operation would have required an engineer in charge of the regulation, gangs of workmen operating the gates and a good communication system along the aqueduct canal.

Dropshaft cascades

Although most aqueducts had a mild slope, some steep sections were documented along few aqueducts (CHANSON 2000a, 2002a,c). Three designs of steep sections were commonly used: i.e, smooth steep chute, stepped chute and cascade of dropshafts. The latter is most unusual, even in modern times.
A dropshaft (3) is a vertical shaft connecting two canals at different vertical elevations. Such a structure is commonly used in sewer systems today (e.g. MERLEIN et al. 2002). A dropshaft is an energy dissipator. Roman dropshafts were characterised by a deep pool and a relatively wide shaft, compared to modern designs. A recent study showed that the Roman dropshaft design was most efficient (CHANSON 2002a,2004).
The Roman engineers devised also cascades de dropshafts : i.e, a succession of dropshafts installed in-line. Well-documented dropshaft cascades include Recret (Yzeron, Lyon) and Madinat-al-Zhara (Valdepuentes, Cordoba). Other dropshaft cascades existed at Montjeu (Autun) and Cuicul (Alg). The construction of a dropshaft cascade was a very difficult task, with numerous subterranean conduits, connected by vertical shafts, in a steep topography (e.g. Valdepuentes). Even in modern times, the task would be a major engineering challenge ! The successful operation of dropshaft cascades for centuries (4) demonstrates a sound design, and a solid hydraulic experience, if not expertise.
Recently, some hydraulic studies of Roman dropshaft models were conducted in 1/3 scale models and at full-scale (e.g. CHANSON 1999b, 2002a,d, 2004,2004b,2007). The results highlight a satisfactory dropshaft operation for a wide range of flow conditions and dropshaft geometries, but for a narrow range of discharges. The latter range may be predicted analytically (CHANSON 1998, pp. A1-A7).


Two shapes of dropshafts were typically used : rectangular and circular. For example, circular at Valdepuentes and Cherchell; rectangular at Recret, Vaugneray. At Valdepuentes, one dropshaft cascade, Fuentes de la Teja-Madinat al Zahra, included three shafts with an outlet canal at 90-degree with the inlet canal direction (VILLANUEVA 1993 1996). Such a geometry was rare, although there were possibly 5 shafts with such a disposition at Montjeu (Autun). It was a very efficient hydraulic design in terms of energy dissipation (CHANSON 2002a,d).
The literature on Roman dropshafts contains a number of discrepancies and errors. For example, most writings on the Brisecou (Montjeu) dropshaft cascade derived from a drawing of ROIDOT-DELEAGE (1879?), which is physically impossible (5). In contrast, the Valdepuentes aqueduct at Cordoba is well-documented (LOPEZ-CUERVO 1985, VILLANUEVA 1993,1996).


A culvert is a short conduit to allow stream flows beneath an embankment. The Romans built a number of culverts beneath major roads (BALLANCE 1951). Some culverts were also built beneath aqueducts. An impressive culvert was the multi-cell box culvert underneath the Nîmes aqueduct at vallon No. 6, downstream of Pont du Gard (CHANSON 2002b,c). Unique features of the culvert were a multi-cell design, a large size and a modern hydraulic design.
The culvert could pass up to 4.2 m3/s, almost 12 times the maximum discharge capacity of the Nîmes aqueduct. In the barrel, the flow velocities were about 2.5 m/s for a 3 m3/s flow rate. This structure shows that Roman engineers understood hydrology and runoff, and that they had a solid hydraulic design experience.


In conclusion, the writer is very impressed by the hydraulic knowledge, experience and expertise of the Roman engineers who designed the regulation basins, dropshaft cascades and culverts. They knew much more that most modern hydraulic engineers ! Yet we know so little of their background.


(1) Today this would represent about 20 to 60 millions US$ per km. For comparison, the construction of the Tarong water pipeline (Australia, 70 km long, Q = 0.9 m3/s) costed about 100,000 US$ per km in 1994 !
(2) At Uzés, the catchment area was about 45 km2. Flow rate measurements, conducted between 1967 and 1978, gave an average daily discharge of about 29,600 m3/day, with maximum daily flow of 143,400 m3/day and minimum daily output of 10,800 m3/day (FABRE et al. 1991). At Gorze, the catchment area was 58 km2. Measurements between 1997 and 1998 showed an average daily source flow rate of 8,050 m3/day, with maximum flow rate of about 11,000 m3/day and minimum daily flow rate of less than 1,100 m3/day. At Mons, measurements of the sources de la Siagnole were conducted between 1981 and 1993 (VALENTI 1995a,b). The average daily flow was 97,200 m3/day, with a maximum daily output of 1,550,000 m3/day and a minimum daily flow of zero (dry). For the Mont-d'Or aqueduct, modern data suggest an average daily flow of 1,400 m3/day, with daily minimum and maximum of 250 and 4,500 m3/day respectively. (BURDY 2002).
(3) Dropshaft = puit de rupture (in French) = Tosbecken or Fallschaft (in German) = pozo resalto (in Spanish).
(4) for example, the dropshaft cascades of the Valdepuentes aqueduct (Cordoba) were re-used by the Muslims (VILLANUEVA 1993).
(5) Hubert CHANSON inspected the Brisecou cascade in September 2000, and he studied the original manuscript of Jean ROIDOT-DELEAGE (1794-1878).

Detailed photographs

1- Gier aqueduct (Lyon, France) - Le Mornantay (Mornant) in June 1998 ;  Chaponost in June 1998 : looking at the arcades from the head tank of the Beaunant siphon (i.e. looking toward the upstream)
2- Les Peirou dam (France 1891) in June 1998 - The present dam was built on the foundation of the Roman arch dam at Glanum [Ref.: CHANSON and JAMES 1998, Research Rep. CE157]. More about Arch dams ...
3 - Brévenne aqueduct (Lyon France) -  Biternay in Sept. 2000, inside view looking upstream
4- Nîmes aqueduct, France.
    Pont du Gard, Nîmes aqueduct, France in June 1998 - View from the right bank
    Pont de Bordnègre in Sept. 2000 : inlet view, showing the bridge pier shaped to cut the waters. Culvert beneath the aqueduct between Combe de Sartanette and Combe Saint Joseph, downstream of Pont du Gard. Main culvert cell (0.8-m wide).
5- Fréjus aqueduct (France). Photo No. 1 : arches de Sainte Croix; Photo No. 2 : looking upstream; Photo No. 3 : looking dowsntream (14 Sept. 2000).

Roman dropshaft ('puit de rupture')
6- Roman dropshaft in operation : Recret model (Aug. 1998) [Ref.: CHANSON 2000, Am Jl Archaeology, CHANSON 2002, Jl of Hyd. Res.] Regime R1 : the usual operation mode in Roman aqueduct (photo dc/h = 0.06) ; Regime R2 : high risks of erosion and damage at the intake of downstream conduit (photo dc/h = 0.12) ; Regime R3 : at large flow rates, usual operation in modern sewer dropshaft (photo dc/h = 0.22)
7- Roman dropshaft in operation : Valdepuentes model (90-degree angled outlet) (Aug. 1999) [Ref.:  CHANSON 2000, Am Jl Archaeology, CHANSON 2002, Jl of Hyd. Res.]
8- Full scale hydraulic model of Roman dropshaft. Drop in invert elevation: 1.7 m, pool depth: 1 m, shaft dimensions: 0.75 m by 0.76 m, flow rates: 5 to 70 L/s (CHANSON 2004, Jl Irrig. & Drainage Engrg). Regime R1 : photograph for Q = 7.6 L/s (July 2002) ; Regime R3 : photograph for Q = 67 L/s (Aug. 2002)

Related links

{} Gallery of photographs
{} History of arch dams
{} Lacus Curtius
{} Gorze aqueduct
{} Mons aqueduct
{} Traianus
Constantinople water supply system

References and Bibliography

BALLANCE, M.H. (1951). "The Roman Bridges of the Via Flaminia." Papers of the British School at Rome, Vol. 19, pp. 78-117 & plates xiv to xix.
BURDY, J. (2002). "Les Aqueducs Romains de Lyon." Presses Universitaires de Lyon, Lyon, France, 204 pages.
CHANSON, H. (1998). "The Hydraulics of Roman Aqueducts : Steep Chutes, Cascades and Dropshafts." Research Report No. CE156, Dept. of Civil Engineering, University of Queensland, Australia, 97 pages. (PDF version at EprintsUQ)
CHANSON, H. (1999a). "The Hydraulics of Open Channel Flows : An Introduction." Butterworth-Heinemann, Oxford, UK, 512 pages.
CHANSON, H. (1999). "Dropshaft Cascades in Roman Aqueducts." Proc. 28th IAHR Congress, Graz, Austria, Session B12, 6 pages. (download PDF file)
CHANSON, H. (2000a). "Hydraulics of Roman Aqueducts : Steep Chutes, Cascades and Dropshafts." American Jl of Archaeology, Vol. 104, No. 1, Jan., pp. 47-72. {PDF file : [6 Mb]}
CHANSON, H. (2000b). "A Hydraulic Study of Roman Aqueduct and Water Supply." Aust. Jl of Water Resources, I.E.Aust., Vol. 4, No. 2, pp. 111-120. Discussion: Vol. 5, No. 2, pp. 217-220.   (Download PDF File)
CHANSON, H. (2002a). "An Experimental Study of Roman Dropshaft Hydraulics." Jl of Hyd. Res., IAHR, Vol. 40, No. 1, pp. 3-12. (Download PDF File)
CHANSON, H. (2002b). "Hydraulics of a Large Culvert beneath the Roman Aqueduct of Nîmes." Jl of Irrigation and Drainage Engrg., ASCE, Vol. 128, No. 5, Oct., pp. 326-330. (Download PDF File)
CHANSON, H. (2002c). "Certains Aspects de la Conception hydrauliques des Aqueducs Romains." ('Some Aspect on the Hydraulic Design of Roman Aqueducts.') Jl La Houille Blanche, No. 6/7, pp. 43-57 (ISSN 0018-6368) (in French). (Download PDF File)
CHANSON, H,. (2002d). "An Experimental Study of Roman Dropshaft Operation : Hydraulics, Two-Phase Flow, Acoustics." Report CH50/02, Dept of Civil Eng., Univ. of Queensland, Brisbane, Australia, 99 pages (ISBN 1864996544). (Download PDF files [2.5 Mb])
CHANSON, H. (2004). "Hydraulics of Rectangular Dropshafts." Jl of Irrigation and Drainage Engrg., ASCE, Vol. 130, No. 6, pp. 523-529 (ISSN 0733-9437). (Download PDF file)
CHANSON, H. (2004b). "Understanding Air-Water Mass Transfer at Rectangular Dropshafts." Jl of Environ. Eng. and Science, Vol. 3, No. 5, pp. 319-330 (ISSN 1496-256X). (Download PDF file)
CHANSON, H. (2007). "Air Entrainment Processes in Rectangular Dropshafts at Large Flows." Journal of Hydraulic Research, IAHR, Vol. 45, No. 1, pp. 42-53 (ISSN 0022-1686). (PDF file at UQeSpace)
CHANSON, H. (2008). "The Hydraulics of Roman Aqueducts: What do we know? Why should we learn ?" Proc. World Environmental and Water Resources Congress 2008 Ahupua'a, ASCE-EWRI Education, Research and History Symposium, Hawaii, USA, Invited Plenary, 13-16 May, R.W. BADCOCK Jr and R. WALTON Eds., Paper 166, 16 pages (ISBN: 978-0-7844-0976-3). (PDF file at UQeSpace)
FABRE, G., FICHES, J.L., and PAILLET, J.L. (1991). "Interdisciplinary Research on the Aqueduct of Nîmes and the Pont du Gard." Jl of Roman Archaeology, Vol. 4, pp. 63-88.
FABRE, G., FICHES, J.L., and PAILLET, J.L. (2000). "L'Aqueduc de Nîmes et le Pont du Gard. Archéologie, Géosystème, Histoire." CNRS Editions, CRA Monographies Hors Série, Paris, France, 483 pages & 16 plates.
FEVRIER, P.A. (1979). "L'Armée Romaine et la Construction des Aqueducs." Dossiers de l'Archéologie, Séries Les Aqueducs Romains, Vol. 38, Oct./Nov., pp. 88-93.
HODGE, A.T. (1992). "Roman Aqueducts & Water Supply." Duckworth, London, UK, 504 pages.
LEVEAU, P. (1991). "Research on Roman Aqueducts in the past Ten Years." Future Currents in Aqueduct Studies, Leeds, UK, T. HODGE ed., pp. 149-162.
LOPEZ-CUERVO, S. (1985). "Medina Az-Zahra Ingeniera y Formas." Publicaciones del Ministerio de Obras Publicas y Urbanismo, Madrid, Spain169 pages (in Spanish).
ROIDOT-DELEAGE, J. (1879?). "Autun Ancient et Moderne." Société Eduenne, Autun, France, 2 volumes.
VALENTI, V. (1995a). "Aqueduc Romain de Mons à Fréjus. 1. Etude Descriptive et Technique. Son Tracé, son Profil, son Assise, sa Source ..." Research Report, Fréjus, France, 97 pages.
VALENTI, V. (1995b). "Aqueduc Romain de Mons à Fréjus. 2. Etude Hydraulique. Son Débit ... de sa Mise en Service à son Déclin." Research Report, Fréjus, France, 123 pages.
VILLANUEVA, A.V. (1993). "El Abastecimiento de Agua a la Cordoba Romana. I : El Acueducto de Valdepuentes." ('The Water Supply of the Roman Cordoba. I : Aqueduct of Valdepuentes.') Monografias No. 197, Universidad de Cordoba, Servicio de Publicaciones, Cordoba, Spain, 172 pages (in Spanish).
VILLANUEVA, A.V. (1996). "El Abastecimiento de Agua a la Cordoba Romana. II : Acueductos, Ciclo de Distribución y Urbanismo." ('The Water Supply of the Roman Cordoba. II : Aqueduct, Distribution System and Urbanism.') Monografias No. 251, Universidad de Cordoba, Servicio de Publicaciones, Cordoba, Spain, 222 pages (in Spanish).


Hubert CHANSON thanks all the people who provided him with relevant information, in particular: Prof. C.J. APELT, University of Queensland; Mr G. BERGE Jussy (Fra); Dr D. BLACKMAN, Monash University; Dr J. BURDY, Lyon, France; Ms P. CHARDON-PICAULT, Autun (Fra); Ms CHOU Y.H., Brisbane; Dr J.L. FICHES, France; Dr A.T. HODGE, Carleton University (Can); Mr G. ILLIDGE, University of Queensland; Mr C. LEFEBVRE, Châtel-St-Germain (Fra); Dr P. LEVEAU, Université d'Aix-en-Provence; Mr J.C. LITAUDON, Saint-Etienne (Fra); Mr D. MURPHY, Houston (USA); Prof. N. Rajaratnam, University of Alberta (Can); Société Mosellane des Eaux, France; Mr A. STRASBERG, Musée Rolin, Autun (Fra); Mr V. VALENTI, Fréjus (Fra); Dr A.V. VILLANUEVA, University of Cordoba; Dr A.I. WILSON, Oxford.


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Hubert CHANSON is a Professor in Civil Engineering, Hydraulic Engineering and Environmental Fluid Mechanics at the University of Queensland, Australia. His research interests include design of hydraulic structures, experimental investigations of two-phase flows, applied hydrodynamics, hydraulic engineering, water quality modelling, environmental fluid mechanics, estuarine processes and natural resources. He has been an active consultant for both governmental agencies and private organisations. His publication record includes over 620 international refereed papers and his work was cited over 3,700 times (WoS) to 6,300 times (Google Scholar) since 1990. Hubert Chanson is the author of several books : "Hydraulic Design of Stepped Cascades, Channels, Weirs and Spillways" (Pergamon, 1995), "Air Bubble Entrainment in Free-Surface Turbulent Shear Flows" (Academic Press, 1997), "The Hydraulics of Open Channel Flow : An Introduction" (Butterworth-Heinemann, 1st edition 1999, 2nd editon 2004), "The Hydraulics of Stepped Chutes and Spillways" (Balkema, 2001), "Environmental Hydraulics of Open Channel Flows" (Butterworth-Heinemann, 2004), "Applied Hydrodynamics: an Introduction of Ideal and Real Fluid Flows" (CRC Press, 2009), and "Tidal Bores, Aegir, Eagre, Mascaret, Pororoca: Theory And Observations" (World Scientific, 2011). He co-authored two further books "Fluid Mechanics for Ecologists" (IPC Press, 2002) and "Fluid Mechanics for Ecologists. Student Edition" (IPC, 2006). His textbook "The Hydraulics of Open Channel Flows : An Introduction" has already been translated into Spanish (McGraw-Hill Interamericana) and Chinese (Hydrology Bureau of Yellow River Conservancy Committee), and the second edition was published in 2004. In 2003, the IAHR presented him with the 13th Arthur Ippen Award for outstanding achievements in hydraulic engineering. The American Society of Civil Engineers, Environmental and Water Resources Institute (ASCE-EWRI) presented him with the 2004 award for the Best Practice paper in the Journal of Irrigation and Drainage Engineering ("Energy Dissipation and Air Entrainment in Stepped Storm Waterway" by Chanson and Toombes 2002). Hubert Chanson edited further several books : "Fluvial, Environmental and Coastal Developments in Hydraulic Engineering" (Mossa, Yasuda & Chanson 2004, Balkema), "Hydraulics. The Next Wave" (Chanson & Macintosh 2004, Engineers Australia), "Hydraulic Structures: a Challenge to Engineers and Researchers" (Matos & Chanson 2006, The University of Queensland), "Experiences and Challenges in Sewers: Measurements and Hydrodynamics" (Larrate & Chanson 2008, The University of Queensland), "Hydraulic Structures: Useful Water Harvesting Systems or Relics?" (Janssen & Chanson 2010, The University of Queensland), "Balance and Uncertainty: Water in a Changing World" (Valentine et al. 2011, Engineers Australia). He chaired the Organisation of the 34th IAHR World Congress held in Brisbane, Australia between 26 June and 1 July 2011. He chairs the Scientific Committee of the 5th IAHR International Symposium on Hydraulic Structures to be held in Brisbane in June 2014.
 His Internet home page is He also developed a gallery of photographs website {} that received more than 2,000 hits per month since inception.

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