Presentation	Photographs	References
Internet links	Acknowledgments	About the author

In decorative architecture, waterfalls and cascades are used to please the eye and the ear. They provide a focal point as well as sounds generated by water splashing and cascading (e.g. Franklin Roosevelt memorial). Cascades can enhance the perception of a site by providing recreational facilities, an alteration of environmental factors to increase human comfort, a project image, a focal point or captivating views. In an oppressive environment (e.g. crowdy cities like Hong Kong and Tokyo), running waters can mask aggressive noise and help to provide an atmosphere of quietness and calm. They can focalise public attention on a particular setting (e.g., a theatre at Le Bosquet des Rocailles, Versailles). Water can be also a significant element in interior landscapes where water provides simultaneously tranquillity and vitality.

Stepped fountains and water staircases combine simple architectural forms with a large amount of splashing and 'white waters' (CHANSON 1997). The stepped geometry is well suited to a steep topography: i.e., La Grande Cascade de Saint-Cloud on a steep hill slope facing Paris and the Seine river, l'Escalier d'Eau du Château du Touvet on the flank of the Chârtreuse mountain range in the French Alpes. Aesthetical applications of water staircases include stepped cascades in parks and gardens (e.g. at Versailles, St-Petersburg) and stepped fountains in cities (e.g in Hong Kong, Paris, Taipei, Tokyo). Rushing waters along stepped cascades may reflect some parallel with mountain rivers or natural cataracts : e.g., the cataracts of the Nile river, the Zambesi rapids in Africa or the Rhine waterfalls. In cities stepped cascades and fountains act as 'urban oasis'. Indeed torrent streams are renown for their drinking quality (i.e. 'eau de source') and sense of freshness. Stepped cascades can be also designed as multipurpose systems : e.g., for river training, water quality systems (TOOMBES and CHANSON 2000).

History of stepped fountains, water staircases and cascades
Over the centuries fountains and cascades have been used as recreational and artistic features (CHANSON 1995,1998). Greek and Roman architects designed fountains several thousands years ago. The Muslims developed also a strong artistic sense for water gardens. The Mongols gained expertise from them after the conquest of Persia. Their descendants, the 'Mughals', imported the Moorish garden expertise in India where they built superb water gardens in Kashmir. In Europe, the tradition of stepped cascades appeared (or re-appeared) in Italy around the Renaissance period (e.g. Villa d'Este, Tivoli). The French gardeners became the Masters of stepped cascade design during the 17th century : e.g., Rueil, Marly, Sceaux, St-Cloud, Versailles. Their work influenced all the European countries for the next 200-years. Among the French designs , the gardens of Le Château de Marly were most renown. The park included several magnificent cascades (e.g. La Rivière) which were copied all over Europe including at Chatsworth (UK), Peterhof (Russia), La Granja (Spain) and Wilhemshöhe (Germany) (CHANSON 1998). At Peterhof one cascade is even called 'Marly' ! It is worth noting some design similitude between the Mughal and French gardens. PLUMPTRE (1993) noted the similarity of garden architecture between the Taj Mahal completed in 1654 and Vaux-le-Vicomte (completed in 1656). The parallel can be further extended to stepped cascade design : e.g., Nishat Bagh (around 1640) and Rueil (1638), Achabal (around 1620) and Marly (1687). The famous French and Mughal gardens were completed only few years apart albeit the absence of direct contact between the French kingdom and the Mughal empire. While the Taj Mahal and Nishat Bagh were the ultimate achievements in Mughal art, Vaux-le Vicomte and Rueil were the precursors of the 17th/18th century European water gardens and cascades.
After the 18th century, the interest for the great cascades seemed to fade away , but in the cities where stepped fountains have been built since the Roman times (e.g. Hong Kong Park). In modern times, the concept of multi-purpose cascades was re-developed. Near Chicago (USA), five re-oxygenation cascades were landscaped as leisure parks combining aesthetics and water quality enhancement. In Japan and Taiwan, stepped river training are combined with attraction parks. Another use is the fish ladders designed as both aesthetical cascades and fishways in North-America. More recently a modern "great cascade" surrounded the olympic cauldron at the Sydney 2000 Olympic Games opening ceremony. The cascade consisted of 77 flat horizontal steps and it operated in a nappe flow regime.

Discussion
Most historical stepped cascades were designed with pooled steps. The pooled step design allows a better control of the flow rate and prevent the occurrence of hydraulic jump. Urban fountains are typically designed with a small number of large steps (h = 0.2 to 1 m). The design of some cascades was quite difficult. For example, the unsteady aerated flows on the chadars at Nishat Bagh, the parallel water staircases at Château du Touvet (Figure), the water supply system at Château de Versailles. It is believed that some water garden designers had a solid hydraulic expertise.

Parallel with the historical development of stepped fountains
By their size and characteristics (e. CHANSON 1995,1998), the Great cascades of the 16th/18th century period were very similar to the stepped spillways built at the time. La Rivière de Marly was over 300-m long and it was definitively longer than any stepped weirs at the time. The cascades of La Granja, Palazzo Reale and Peterhof were also larger than most contemporary waste waterways. A comparative development of stepped fountains and spillways follows.
Greeks and Romans were renown for their urban cascades and fountains. Later the Moslems built famous water gardens in their empire. Romans and Moslems contributed to the dissemination of design expertise both in stepped fountains and in stepped spillways since Antiquity. After the Muslim era, the exchange of ideas between landscape architects and hydraulic engineers (in the field of stepped chutes) vanished. The Moor successors (e.g. the Spaniards and the Mughals) did not continue the dual expertise. The Spanish contribution to stepped spillway design was uppermost important but the design of stepped cascades was abandoned in Spain. In India, the Mughals kept only the stepped cascade tradition. Famous stepped cascades were built by the Italian, French and Mughal princes during the 16th and 17th centuries (PLUMPTRE 1993, CHANSON 1998) at a time when stepped spillways and weirs were built in Spain (e.g. Alicante dam). But no major stepped spillway was built in Italy, France nor India during the same period.
The French landscape designers who built the gardens of Versailles and Marly (and their stepped cascades) were superb surveyors and good arithmeticians. They were knowledgeable in water supply engineering (e.g. the Aqueduc de Marly supplying waters to Versailles). But they never applied their expertise to dam engineering nor river training engineering. In the reverse sense, King Philip V of Spain selected a French designer, FRÉMIN, to built the stepped cascade of La Granja despite the Spanish expertise in stepped spillways. In Russia, the tsar Peter I the Great selected another Frenchman, J.B.A. LEBLOND, to design Peterhof's Cascade while he hired a Dutchman G.W. HENNIN to design and build dams with stepped overflow. The author has found no evidence suggesting any contact or exchange between HENNIN and LEBLOND.
The lack of exchange between architects and engineers seems to have survived up to now. Today most hydraulic engineers ignore the modern expertise in stepped cascades. Reversely, most architects are unaware of the recent developments in stepped spillway hydraulics.

Detailed photographs

Photo No. 2 : La Grande Cascade de Rueil (France, 1638) : gravure of the cascade (Courtesy of the Musée de l'Histoire de Rueil-Malmaison, Mrs KALENITCHENKO and Mrs D. HELOT-LÉCROART). The château of Rueil  was built and designed by Jacques LEMERCIER in 1625. Cardinal de Richelieu bought the château in 1631. The complete garden included a Great Cascade (~ 30 steps) designed by Thomas FRANCINI and completed around 1638. The cascade was at the end of the Grande Allée. It was suggested that Rueil's cascade and gardens were inspired by Frascati (Villa Aldobrandini ?). The Cascade of Rueil inspirated the cascades of Versailles, St-Cloud and Sceaux (CHANSON 1998). The cascade was replaced by a green lawn in 1720. The 17-th century formal garden does not exist any longer. Imperatrice Joséphine stayed in Rueil and orderd a remodelling of the park.

Photo No. 3 : Bosquet des Rocailles, Château de Versailles (France, 1683) : panoramic view in June 1998.
Le Bosquet des Rocailles (or Bosquet de la Salle de Bal) was built between 1680 and 1683 by J. MANSART in the gardens of the Chateau de Versailles (France). The sculptures were by Pierre LEGROS (1629-1714) and Benoît MASSOU (1627-1684). The cascade comprises : 5 8-steps fountains, 8 7-steps fountains, and 4 4-steps fountains. The Bosquet itself was designed by LENOTRE in 1680. The scene was modified in 1690 and flowers were introduced in 1691.

Photo No. 4 : L'escalier d'eau des jardins du Château du Touvet, Le Touvet (Isère, France, 1770) : looking downstream at the water staircase with the Belledonne mountains in background (Courtesy of Mr B. de QUINSONA, copyrights Jardins du Touvet). The first "château" was built during the 13-th century. The present chateau was built in 15th century. Between 1753 and 1770, the Comte Pierre de MARCIEU re-designed the garden, including a new water staircase. The staircase is very pretty. The staircase is divided in 5 successive series of steps (pooled steps with rounded crest). From the top to the bottom :  a steep cascade (> 8 steps), a second steep cascade (9 steps), followed by a flat series of drops (6 steps, slope ~ 6 deg.), a steep cascade (10 steps, slope ~ 27 deg.), and another steep cascade (8 steps). Visit the website of the Château du Touvet : {http://www.touvet.com/}.

Photo No. 5 :  Hong Kong Park (Hong Kong) : water staircase in Sept. 1994.

Photo No. 6 : step-pooled cascade in the Floral Park at Hama-matsu, Japan on 9 March 1999. It acts as a pool-stepped spillway of an aesthetic pond. The photograph was taken in winter when the cascade was dry.
 

References

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Acknowledgments

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 http://www.uq.edu.au/~e2hchans. He also developed a gallery of photographs website {http://www.uq.edu.au/~e2hchans/photo.html} that received more than 2,000 hits per month since inception.

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