THE BLUE WAVE,
A NEW CONCEPT OF WATERWAYS
ENABLING TO INCREASE VELOCITY
OR TO REDUCE IMPACT ON ENVIRONMENT
by Jean Marc Deplaix, Professeur à l'Ecole Supérieure des Transports
206 Bd Péreire, 75017 Paris firstname.lastname@example.org
1° The Blue Wave concept
1.1 Avoiding locks: to optimise the average speed over a waterway
1.1.1 Past history: locks, flash locks, long locks, etc
1.1.2 The concept: reach level varies while the craft advances
1.1.3 How does it work: the principle of "communicating vessels"
1.1.4 Electronic regulation of craft movement: applying techniques fully proven on roads
1.1.5 Splitting the head to diminish water consumption: a "Water Escalator" instead of a water elevator (the lock)
1.1.6 Inconveniences of locks: water usage, heavy earthworks and fixed width
1.1.7 Open to the future: gauge is not frozen by structures dimensions
1.2 Increasing velocity and reducing ecological impact: deep canals make fast waterways
1.2.1 Deep canals, as confirmed by theory: efficiency known since half a century
1.2.2 Inflated standards: with adequate regulation, transbasin traffic could use an alternate-one-way infrastructure
1.2.3 A new, narrow cross-section: narrower and deeper than existing profiles
1.2.4 An all-purpose waterway, modern and efficient: for a given speed, half the width
2° Economic aspects
2.1 A cost-effective proposal: always cheaper than a classical shape
2.2 Savings on authorisation costs: wide gauge canals possible where they were not acceptable
2.3 Avoiding rebuilding shallow locks: some 10 million € savings
3° Technical details of AFTM profile
3.1 AFTM profile and the Freycinet Network: in a given space, multiply the gauge by 10!
3.2 Deep rectangular profile: 12% better speed
3.3 Size of craft vs. design speed: at slower speed, gauge of craft can increase
3.4 Waiting at a Blue Wave: as low as 5 minutes
4° Further technical aspects of the Blue Wave
4.1 Water aspects
4.1.1 Hourly average requirements: 2.9m3/s (Class-Vb) or 1.3m3/s (Class-Va)
4.1.2 Water velocity: circa 0.2m/s in the reach
4.1.3 Water velocity at gates: nil
4.1.4 Seiche and waves: similar to that of a lock
4.2 Design velocity and size of reaches in a Blue Wave
4.2.1 Minimal size: at 8kph, 450m (Class-Vb) or 300m (Class-Va)
5° The Half-Blue Wave: Rejuvenated lock for deep-draught craft
5.1 Deepening small gauge network: Freycinet canals acting as an improved feeder network
5.2 Deepening wide gauge structures: Reuse structures instead of rebuilding them
5.3 Water requirement for Half Blue Wave: depending on the head, nil or up to 17m3/s during 3 minutes
5.4 Size of the lower pond in Half Blue Wave: from 135 to 360m
5.5 Delay in Half Blue Wave: nil, or less than 10 min at the worst
Designing a modern navigable canal usually entails recourse to high locks, in order to reduce the number of such time-consuming structures. This option is sometimes not well perceived by riparians, or difficult to inscribe in the landscape.
The Blue Wave concept avoids the high lock option, where it does not blend nicely with topography or scenery, while retaining the same average speed.
It also enables to insert "Wide Gauge" waterways in the space presently occupied by smaller ones, hardly impacting the neighbourhood.
Besides, where earlier navigation structures are re-used, locks are often of an adequate length and width but too shallow. An "Half Blue Wave" can obviate the need to reconstruct them totally.
I. THE BLUE WAVE CONCEPT
I.1. Avoiding locks
In order to optimise average speed over a waterway
Using a lock represents a loss of time compared to sailing on a waterway. It is thus tempting to avoid it. This is, however, only possible where the waterway is adequately provided with water, its natural medium.
I.1.1 Past History
Locks, flash-locks, long locks, etc
Where there is not enough water, locks appeared until now indispensable, for they require the smaller amount of water for a given head. But it stops craft for some time.
In order not to stop craft, there have been some systems for abundant rivers, such as fixed open channel and flash-locks.
The first divide canal in the world, Lin Canal in China two centuries BC, already made use of a system similar to flash-locks, the "dohmen". This system was also used on the "Grand Canal" of China for many centuries.
Later came "Long locks", some 1km long, which can be negotiated practically without complete stop (Ecluses Sans Temps Mort, see PIANC Centenary book, p.219/222). They were first built in the 20th century, on canalised rivers.
Progress in regulating techniques enables now, in waterways with quite limited available discharge (less than 6m3/s), navigation at full speed from reach to reach. This "Blue Wave" concept utilises a canal in its full width, thus enabling traffic in both directions without slowing down while passing the gates, coupled to computerised regulation.
I.1.2 The concept
Reach level varies while craft advance
The BLUE WAVE (figure 1) enables craft to negotiate, without stopping, the head drop between level A and level B. To that aim, the craft crosses a succession of horizontal reaches separated by gates (31, 32, 33, etc.) being opened in sequence, at least one (33) remaining open between two closed gates (32 & 34). Thus, levels in two contiguous reaches (42 & 43) equalise, the first lowering while the other rises, enabling traffic in both directions if required.
Passing across the open intermediate gate takes place after levels have become equal, without any discharge or eddies.
I.1.3 How doest it work ?
The principle of "communicating vessels"
In the initial stage, gate 32 is closed while gate 31 is open, so that the level of water in reach 41 corresponds to level A, and craft 2 can enter reach 41.
When downbound craft 2 is in reach 41, gate 31 is closed. Gate 32, between reaches 41 and 42, is then actuated, as shown in dotted line on figure 1. Gates 31 and 33 being closed, water levels equalise between reaches 41 and 42, as shown by dotted line 4 in figure 1. Passage of craft 2 across gate 32, open, takes place after levels have become equal. Gate 32 is then closed again, as shown in continuous line on figure 1.
Craft 3, as far as she is concerned, proceeds in opposite direction. This craft has left level B, and has reached pond 43.
As soon as gates 32 and 34 are closed, gate 33 is actuated to enable equalisation of levels, then open.
Thus, downbound craft 2 and upbound craft 3 can meet each other: The Blue Wave enables navigation in both directions.
In this view, width of gates is preferably selected in order to enable two craft to meet each other even while passing the gates of the Blue Wave. The structure constitutes thus a canal, navigable continuously in both directions from reach to reach.
I.1.4 Electronic Regulation of craft movement
Applying techniques fully proven on roads
There is an analogy, shown by names similarity, between the Blue Wave and the Green Wave, piloting traffic lights in a city: No need to go faster than design speed, on the contrary, small cars pip sports cars by arriving " just-in-time " at intersections. Further, fuel consumption in a Green Wave is far smaller, compared to nervous driving.
Green Waves are very efficient, because their synchronisation helps to save some 30 seconds (average traffic light duration) at each intersection. One can thus cross a town at 45kph in a few minutes, instead of meeting random lights imposing cumulative stops of many minutes.
Similarly, by not stopping at locks, craft moving on a Blue Wave can have a higher average speed than craft moving on a classical, wider gauge route, with its locks. The limit-velocity of craft being function of canal gauge, the same average speed can be reached on a Blue Wave with a smaller canal (the small car) than on a wider gauge canal with locks (the sports car). For instance, overall speed over the 100km Seine-Nord new project in France is just above 8kph, while it is easy to design a Blue Wave for 9kph, with a noticeably smaller canal.
Length of reaches should preferably be uniform, function of the contemplated traffic, itself linked to Wave design speed, size of craft, and her displacement (in m3): Of course, in case of emergency, craft must be able to stop before hitting the next gate.
I.1.5 Splitting the head to diminish water consumption
A "Water escalator" instead of a water elevator (the lock)
To that end, the Blue Wave has a "step", or head, of 50cm, corresponding to a cycle water usage of 1m (1/10th of the head of the lock). For an usage of water identical to a 10m-high lock, each one of its reaches can be for example 3.3 times longer than a lock, and 3 times wider. I.e., in an EuroClass-Vb waterway (total area of locks 200x12m), involve a reach 36m wide and 660m long, more than necessary for a Blue Wave. If its reaches were to have a smaller area, the water required would be reduced accordingly.
Since there should be 20 "steps" to match the head of a 10m lock, that is 21 or 22 gates depending on the site, the equation is thus simple: each individual gate should cost 1/20th of a complete lock, or less, for the system to be economical. It is too early to venture a price, but present-day locks are so costly that there is some hope.
The required discharge, for a 20Mt capacity Blue Wave per direction (one cycle par hour, 20 hours a day), is on average 4.5m3/s: This system usually requires less water than a lock.
The ship escalator, described elsewhere in this Bulletin, follows the same logic, with a double one-way passage.
I.1.6 Inconveniences of locks
Water usage, heavy earthworks and fixed width
The logic of locks leads to build them in the smaller number possible. This brings on average to reaches more or less horizontal some 10 kilometres long, for a head at the locks of 10m, height which is often considered as the most economical.
This choice has two practical consequences:
- obtaining reaches more or less horizontal over a substantial length requires high earthfills, deep cuttings or large flooding. These works are costly and/or leave visible marks in nature, which are often criticised.
- such structures make use of large quantities of water. As an example, an European Class-Vb lock, with a head of 10 metres, uses some 24 000m3 of water. On the basis of one cycle per hour, this corresponds to a discharge of more than 6.5m3/s, higher than the Blue Wave.
It should also be noted that locks restrict, for a century or more, the width of the vessels to the width selected for the design craft of the time.
I.1.7 The Blue Wave is open to further changes, as far as water consumption, size and speed of craft is concerned
Actual water availability, dimensions and speed of craft are fed to the regulating software, and not frozen by structures dimensions
By contrast, a Blue Wave requires less water than a wide gauge lock, and is far wider and deeper than the corresponding lock, thus leaving all possibilities open for larger design craft in the future.
Design speed in a Blue Wave could be 8 to 10kph, close to what is presently achieved in the reaches of good French Canals. The duration of passing the locks would then be saved, some 20 minutes each.
When water is abundant, there would be no waiting, except that of random arrival (5 to 10 min, depending on Wave characteristics), every direction would be free to move with its regulation (up to 10 "waves" per hour).
During the dry season, the number of cycles would be limited to what is available in the canal or river.
The only difficulty is to find a gating system sufficiently cheap to achieve a global price close to that of a lock.
The idea of prefabricated systems seems sensible. It is clear that the price of each gate shall condition the competitiveness of the system
Finally, the width that conditions the water requirement of the Blue Wave is that at water level, while that which governs the gauge of craft in transit is that at the bottom, or rather that corresponding to the design draught. It is thus tempting to reduce the width at water level, using vertical sides, and to deepen the waterway, enabling easily, with gates as wide as the canal, wide gauge craft to transit.
One of the preferred ways to use this invention may thus be "Ecological Wide Gauge Canals", far easier to insert in the landscape, due to their reduced cross-section and to the fact that they follow the terrain practically imperceptibly.
I.2. Increasing velocity and reducing ecological impact
Deep canals make fast waterways
It is thus possible to insert a wide gauge waterway in the space presently ascribed to a small gauge canal. In the width provided for French small gauge canals, it is in fact possible to locate a "deep-profile" canal possessing the same efficiency than a 50m-wide trapezoidal canal, 4m-deep. This type of profile can thus find many local applications. In particular, re-using the course of an existing canal can be quite useful when some landowners or some municipalities oppose to a fresh route for a classical wide gauge canal.
I.2.1 Deep canals, as confirmed by theory
Efficiency known since half a century
This optimal utilisation of space, little publicised, is backed by highly authorised supports.
For instance, fundamentals of the modern theory of ship resistance and the ensuing existence of a limit-velocity for each "canal-ship couple" were expounded in Ir. Schijf's report to PIANC in 1949, amplified in 1953.
In his 1953 report is included a graph (fig. 4) which gives "the effect of widening and deepening of a canal" on limit-velocity and some other parameters.
There he states in particular: "enlarging the cross-section by increasing the depth is more effective with regard to speeding-up navigation than enlarging by increasing the width" (PIANC 1953, Section 1, Subject 1, p. 181).
Other PIANC reports reasserted later this statement.
The report further states: "with an equal increase of F (cross sectional area), thus at equal quantities of earth removal, deepening (a canal) has a greater effect in increasing the limit-velocity than widening".
The same limit-velocity (3.12m/s) is reached in a trapezoidal canal with B=60m and a 170m2 section (n=8.5), as well as in a canal with B=50m having a 152,5m2 section (n=7.6) and in a canal with B=40m and a 132m2 section (n=6.66). The equation 132=152,5=170 (in m2) may appear absurd, it is nonetheless exact according to Schijf, provided the 132m2 canal be 6m deep, while that of 170m2 be only 3.42m deep.
In the same stroke comes the equality 8.5=7.6=6.66: A 6.66 value of the " F:f " or "n" coefficient (ratio between the cross-section of the canal and the beam area of the ship) in a 6m deep canal enables to reach the same limit-velocity as a 8.5 coefficient in a 3.42m deep canal. The difference in earth removal of the wetted section is more than 25%, not taking into account savings in the dry, often more than proportional (cuttings).
Reading the graph in a different way, for the same area (vertical lines), limit-velocity in a 6m deep canal is far superior (+17%) to that reached for d=3.5m. For instance, the area giving 3.5m/s limit-velocity with d=3.5m enables to reach 4.1m/s in a 6m deep canal.
For ease of reference, the extrapolated limit-velocity for d=6m has been added as a continuous line.
For a same 3.5m/s limit-velocity (horizontal line), the interval between the two continuous lines is more than 60m2, which means more than 60 000m3, and half a million €, difference per kilometre simply on earthmovings of the wetted cross-section.
Canals are traditionally built with sloped banks, self-stable and cheaper. But this consumes space, at least 10m in width, and does not lead to the best hydrodynamic canal shape. Vertical banks are far superior as regards space and hydrodynamics, since they provide 6% better hydrodynamic resistance with similar depth and wetted area.. Narrow canals can thus be efficient.
I.2.2 Inflated standards
With adequate regulation, transbasin traffic could use an alternate-one-way infrastructure
It has earlier been said (PIANC Congress of Seville, 1994, section I-3, French report p.19) that traffic anticipated over transbasin links was far smaller than the capacity of Class-Vb waterways, the standard deemed necessary.
For instance, with only one cycle per hour, a Class-Vb waterway has already an effective capacity of 1 million tonnes per hour of daily traffic, per direction. With 20 hours opening of the locks, it would mean 20 million tonnes per year per direction (4 400t pushed convoys).
Since the velocity in the reach is around 10kph, and since reaches are around 10km in such canals, the average traffic would take place without interruption nor delay.
An observer by the side of the canal would see only one craft or group of craft per hour, in every direction. Nevertheless, it would suppress traffic on the parallel road at the tune of one heavy truck every 18 seconds in each direction.
Bargemen would meet only one craft or group of craft during that same hour. With a perfect regulation, the passing section would hardly exceed 1km. Here can be found again an observation made at the Seville Congress, on excessive security of usual norms, because they assume passing is possible everywhere.
On the major part of wide gauge routes, waterways could be narrow, since through regulation big craft can be paced so as not to meet each other. Narrower craft could nevertheless travel without restrictions.
I.2.3 A new, narrow cross-section
Narrower and deeper than existing profiles
In order to reach a reasonable commercial speed with a wide gauge craft and yet remain in the width ascribed to a Freycinet small gauge canal, a rectangular, or trapezo-rectangular, profile must be used, with deep depth, 6m at least. If alternate one-way traffic is accepted, Europe-type craft (carrying 1 350 t and over) can navigate in such ecological waterways.
A trapezo-rectangular profile was already described in German and French reports at the 1953 Congress, and showed 5% better efficiency, with similar depth and wetted area, than a trapezoidal shape. The corresponding curve has been drawn on fig. 5, extrapolated from Schijf data. Onfig3.1, the deep version of this profile (AFTM) is displayed.
As can be seen onfig. 5, for the same speed of 3m/s, n scatters between 5.75 and 7.6. And for 3.5m/s, n spreads between 7.5 and 11.1, AFTM shape being substantially space-saver for a similar efficiency.
I.2.4 An all-purpose waterway, modern and efficient
For a given speed, half the width
With deep AFTM profile, the efficiency of a 33m-wide trapezoidal canal, 5m deep (90m2), is reached with only a width of 16.25m and a depth of 6m (75m2). A commercial speed of 7kph (limit-velocity being some 2.2m/s) will be reached in any of these canals by craft 8m-wide drawing 2.5m. Yet the smallest Freycinet canals are at least 18m wide and, rebuilt with Blue Wave AFTM profile, the whole network would accept these Class III craft, 4 times more efficient.
To accept Europe type craft, the area should be larger, and this is still feasible without touching the landscape.
In most of the cases, it shall be possible to inscribe a 23.75m wide canal, with AFTM profile, in the space constituted by the small canal and its tow path, without touching the bicentennial trees which constitute the core of the picturesque of the French small gauge canals and of the landscape that they became. Such a canal enables commercial speed of 8.5kph for Europe-type craft drawing 3m (limit-velocity being 2.63m/s). It is equivalent to a trapezoidal canal 41.6m wide at surface level and 5m deep, as far as resistance and limit-velocity is concerned, and it enables, if craft breakdowns, to overtake or meet it, for towing it away and avoiding blocking the canal.
If such a canal is further equipped with a Blue Wave system, craft, not needing to stop at all, would have an average speed of 8.5kph (Wave design velocity), usually superior to that attained, from end to end, by craft in a wide gauge canal interrupted by locks.
It would thus appear that such Ecological wide gauge canals could be adopted for modernising some ecologically sensitive waterways. The Blue Wave is in fact very ecological, because it follows closely the natural terrain, and enables to avoid excessive earthfills and cuttings, which follow and precede locks. It thus merges remarkably in the landscape.
Alternate projects, based on the Blue Wave system and deep canals, would much more respect the landscape and present uses of properties crossed by waterways. They might possibly obtain the necessary consensus to be implemented.
2. ECONOMIC ASPECTS
2.1 A cost-effective proposal
always cheaper than a classical shape
A certain number of parameters are to be taken into consideration: Width of canal, size of design craft, desired design speed and average ground slope. By hypothesis, average ground slope was taken as 1m per km.
To make it short, the cost of the concept itself (earthworks, sheetpiles, crown and gates of Blue Wave) for a CEMT Class IV or Va waterway would cost 5 million € per km with AFTM profile and 8 million € with rectangular profile. To this must be added the cost of a safety gate every 10km, which translates into 0.3 million € per km.
These prices do not include cost of bridges and relaying of existing facilities, nor landscaping, quite high in such a picturesque environment. With both profiles, they may be estimated to total some 3 million €.
All in all, one kilometre of such a Class-Va Blue Wave Ecological canal would total some 10M€ for 8kph design speed, and some 13M€ with 9kph design speed (better speed with vertical walls).
2.2 Savings on authorisation costs
Wide gauge canals possible where they were not acceptable
The interest to re-use an existing small gauge canal is really to use a space already ascribed to water transport, instead of areas currently used by other activities. The impact in the landscape of a new canal would thus be hardly noticeable. By design, its insertion in the environment represents improvements compared to the existing situation. It may then be hoped that waterways in line with the Agreement on Great European Waterways (CEMT Class IV canals and above) may be built with this technique.
Savings on authorisation costs are not really quantifiable, but the cost of not-doing a canal is obviously very high.
2.3 Avoiding rebuilding shallow locks
Some 10 million € savings!
As will be discussed below, a Half-Blue Wave can increase the permissible draught at a lock by 1m.
The cost is dramatically cheaper than a new lock, even with a 300m long lagoon.
3. TECHNICAL DETAILS OF ECOLOGICAL WIDE GAUGE CANALS
3.1 AFTM Profile and the Freycinet Network
In a given space, multiply gauge by 10 !
Let's consider a canal 23.75m wide, re-using the space ascribed to a Freycinet canal. The old canal is usually 2.2m deep, 18.80m wide at water level, 27m between trees and more than 30m of global State property. Slope of sides under water is 1/2, in the dry 2/3. Taking into account slight siltation, Freycinet canal cross-section is assumed to be 30m2. Its gauge is 250t.
The proposed AFTM profile (fig 3.1) has a 1 to 2m high bank, sloping 2/1 , with an underwater concrete toe 40 to 60cm thick, its upper part being at elevation of minimal level in the reach during Blue Wave operations.
Between this crown and the bank, reeds shall be implanted, in order to dampen waves created by the Blue Wave and passing boats.
Below the crown, can be found a row of sheetpiles, or similar, with modulus depending on ground characteristics, and usually less than 6m high. The aim of this sheetpile is ground retention, so as to offer a wetted cross-section sufficient to enable craft drawing up to 3,5m to move easily. By design, these sheetpiles never emerge, and thus do not corrode. Down to this point, AFTM profile is very similar to German KRT profile.
At the toe of this sheetpile, can be found a berm at elevation -3.5m compared to the top of the crown, some 2m wide, then a 1/2 slope, down to elevation -6m.
Depending on ground characteristics, this slope may be watertight or not. Canal bottom would be some 9.75m wide, enough since such canal is designed to work in alternate one-way traffic. But navigable guaranteed gauge would be 23.75m wide.
The aim of this berm and of this slope is to shoulder the toe of the sheetpile to reduce its cost, and to provide a better habitat to aquatic fauna and flora.
The AFTM section would be 120m2. To find excavation volume, one should add the surface part, where will take place Blue Wave level fluctuation, which corresponds to some 25m2 extra.
Each linear metre of canal would thus entail 115m3 of fresh excavation.
From hydraulic point of view, coefficient "n" must be appraised when Blue Wave is at half level, that is with a 132.5m2cross-section. "n" is thus practically equal to 4, for a large Rhine craft drawing 3m (2 500 t).
The corresponding economical speed with AFTM profile shall be 8kph.
With 3.5m draught, "n" comes to 3.37, and economical speed to 7kph.
This shows the interest of a deep canal, because with a so limited "n" coefficient, it is usually considered non-viable to move.
3.2 Deep rectangular profile
12% better speed
The advantage of depth is felt also when passing from an AFTM profile, more efficient in large canals, to a rectangular profile totalling 142.5m2.
In case of re-using a Freycinet canal, overcost of longer sheetpiles is counterbalanced by the better hydraulic efficiency, translating into 12% more speed.
"n" becomes 4.5, and economical speed rises to 9kph, greater than the proposed average speed in the French Seine-Nord Link. For 3.5m draught, "n" comes to 3.87 and v=7.8kph. With a Blue Wave, this would be the average speed over part of a canal, or even on the whole route of an interbasin canal
3.3 Size of craft vs. design speed
At slower speed, gauge of craft can increase
On a Blue Wave, maximal size of boats is dependent on their speed, which conditions the spacing of gates. Thus, at very slow speed, an " oversized object " could use a Blue Wave, provided locks upstream or downstream from the Blue Wave do not limit it.
Let us assume for instance that a Freycinet canal would be transformed into an Ecological Wide Gauge Canal, over its last 10 or 30km, to act as feeder waterway.
With gates 175m apart, and in a canal 6m deep, it would accept pleasure crafts with design speed of 15kph, Freycinet barges at 11kph, Canal du Nord barges at 8kph, one Freycinet pushing another at 6.5kph, RHK barges at 4.7kph and even 2500t Rhine barges at 2.5kph. The software would rhythm adequately craft entering the system, possibly through GSM-like interactive terminals.
3.4 Waiting at a Blue Wave
As low as 5 minutes, and never longer than the corresponding lock
Due to the fact that a Blue Wave ensures traffic in both directions simultaneously, duration of a "cycle" is shorter, at least half, than duration of total transit through the Wave structure.
This cycle duration is function mainly of the number of passing places in the structure, in case the canal is not wide enough for passing everywhere. It can be as low as twice the time taken by craft to transit one reach, and rises up to that of the equivalent lock. For a Class-Va Blue Wave, this means 7 minutes and upwards. For the short Freycinet Blue Wave just mentioned, it would mean 3 minutes and upwards, provided gates are fast enough.
Waiting time with random arrival is half cycle duration, 5 minutes for Class-Vb, and can sometimes be hardly noticeable.
A second waiting time is function of water availability. If there is enough water, craft will enter the structure as soon as cycle is complete. In dry season, it will have to wait until water resources have replenished.
Finally, in case of peaks of traffic, a delay is to be added, but it is extremely unlikely that it will ever take place in wet season.
4° FURTHER TECHNICAL ASPECTS OF THE BLUE WAVE
4.1 Water Aspects
4.1.1 Hourly average requirements:
2.9m3/s for typical Class-Vb Blue Wave, and 1.3m3/s for Class-Va Blue Wave
In order to obtain the same boat capacity than a lock, basis of calculation shall be one Blue Wave cycle per hour, because it is the classical capacity used to evaluate water requirements of canals (1 lock cycle per hour).
The higher the lock, the easier it is for a Blue Wave to require less water on average than a lock.
Assuming a 10m-head "Class-Vb lock" without saving basins, and an optimal set of Blue Wave gates, each reach of Blue Wave could be 36m wide at surface and 650m long, without using more water than the lock. Such characteristics would enable a design velocity through the Blue Wave of 12.3kph (3.4m/s). The concept of Blue Wave thus introduces no restriction on boat navigation, compared to a modern canal.
The corresponding average discharge is 6.5m3/s (36x650x1/3600). It is equal by hypothesis to that necessary to a modern "Class-Vb lock" and corresponds to a 12x195m long chamber (between gates) with 10m-head (23 400m3), emptied once per hour.
But, in a water-conscious world, referring to an hourly average discharge unnecessarily burdens the image of IWT, inferring that this discharge is permanently necessary, which is far to be the case. An adverse effect has been in particular felt against Rhône-Rhine link.
In fact, such a permanent discharge would correspond to an annual traffic of 24 cycles per day, 365 days per year, that is a theoretical capacity of 17 520 lockages per year, half upstream, half downstream. No interbasin canal, the only type of waterway where locks with 10m head are contemplated, has such an expected activity, corresponding to a traffic between 15Mt at the least and 68Mt at the most
Provided some storage is possible, it would thus be far preferable to average the use over a day. This can be done in modern waterways where one of the reach can store some 175 000m3, a volume corresponding to some 8 hours without traffic each day.
Following this approach, used hereafter, an average traffic corresponding to 16 one-hour cycles per day brings an average hourly requirement (on daily basis) of some 4m3/s. This method applies to lock as well as to Blue Wave, since it depends on traffic and not on technique. However, in case of a Blue Wave, as shown above, it enables a design velocity of some 12.3kph, far above that attainable on average over a waterway with locks.
It appears thus preferable, in order to make a fair economic comparison of the two concepts, to limit design velocity of a Blue Wave to that experienced in average over a modern canal with locks, which varies between 6 and 8kph over the whole route, depending on terrain.
For 8kph, a Class-Vb canal (36m wide at water level) and 50cm steps, water required is half that of a 10m-head modern lock. It is equivalent either to a 5m-head lock, or a 10m-head lock with 2 saving basins. In daily average, such a Blue Wave requires only 2.9m3/s, and provides for a traffic of 11 520 " lockages ", or rather Waves, per year.
This quite reasonable requirement enables to think of modern waterways in dry regions. During the worst season, the authorities could limit the speed in transit, or space out the rhythm of the waves, thus lowering water requirements, if need be, below 1m3/s.
In case of Ecological Deep Canals equipped with a Blue Wave, re-using space ascribed to an existing Freycinet canal, water requirements are even lower, since they belong to Class-Va, for 110m long boats at the most. With 300m reaches corresponding to a Blue Wave design velocity of 8kph, it comes down to an hourly 1.9m3/s, that is around 1.3m3/s in daily average.
4.1.2 Discharge & velocity in reach
Water velocity close to 0.2m/s
The average discharge during emptying of one reach into the other, in a Blue Wave, is function of the law governing the opening of gates separating each reach.
If discharge were uniform, it would be equal to the volume of the Blue Wave (Surface of the reach multiplied by thickness of the wave, i.e. half the volume used during a cycle) divided by duration of emptying, or rather duration for crossing the corresponding reach. It is thus clear that it is a direct function of design velocity.
For the design velocity retained in the comparison, i.e. 8kph, average water velocity is 0.215m/s, and average discharge 45m3/s. These values are frequently encountered on large canals during emptying of locks.
The only difficult thing consists on ensuring a practically constant discharge in the reach, in order to avoid velocity peaks which could be dangerous for boats.
A similar velocity, 0.24m/s, is found in a Blue Wave Ecological Deep Canal, in which average discharge is some 34m3/s.
4.1.3 Discharge & water velocity at gates:
The discharge is similar at the gates to what it is in reach. But, by definition, boats do cross the gates only when levels are equal on both sides and thus, no discharge nor localised slope exists between the two reaches. This is in fact one of the key-points in the patentability of the concept, compared to earlier patents. Boats have a tranquil passage through the gates.
4.1.4 Seiche and waves:
Equal to that of a lock, except for lock heads lower than 5m
The release of high discharges in canals of limited dimensions can generate surface phenomena, well known by mariners, for instance on the French Canal du Nord.
However, observing known cases leads to think that seiches will not be a problem for canals with AFTM profile.
In fact, seiches are dangerous mainly when there is little space below keel. This is not the case here, these deep canals providing more than 2.5m below keel.
Further, although this is not strictly necessary, gates are advantageously inclined in terrain direction, creating a wedge which will rapidly dampen surface waves, which on the opposite are seen reflected from lock wall to lock wall on Canal du Nord.
Besides, the slanting bank, planted with reeds, effective against boat wash, could also participate to dampen surface waves.
Finally, the law for opening of the gates can certainly be adapted to minimise this phenomenon.
4.2 design velocity and size of reaches in a blue wave
4.2.1 Minimal size of the reach of a Blue Wave
Function of design velocity:
At 8kph,length circa 450m (Class-Vb) or 300m (Class-Va)
In fact, the minimal size of reach is also the optimal size as regards water consumption. But safety considerations make it unsafe to have too short reaches.
The minimal safety distance between two gates limiting a reach, for a given design velocity, can be calculated with the help of the following formula, taking into consideration the fact that intermediate gate may not open, and that gates take some time to move:
- minimal length of each reach in metres:
L[1 + (V2 / 9)] + (0,11*D*V1/3)+(T*V), with
L: length of design craft, in m
V: design velocity of boats, in m/s
D: displacement of design craft, in m3
T: sum of time taken to manoeuvre U/S & D/S gates, in seconds
Minimal means the smallest length enabling craft, navigating at a given design velocity from reach to reach, never to slow down.
With this formula a reasonable safety is achieved, since already, at 8kph, craft finds in front of her a space equal to 1.5 time its own length, which is the stopping distance imposed on the Rhine, downbound, at double the speed.
In canal, at 8kph, stopping distance is far shorter. This enables to counterbalance the slack period due to gates manoeuvre, which shall necessarily be very brief, otherwise the concept would not be worthwhile. Each could be some 15 seconds, value already reached at some locks (Montech by example).
5. THE HALF-BLUE WAVE
Rejuvenated lock for deep-draught craft
The Half-Blue Wave (figure 2) consists in creating a lower approach pond with variable level, controlled by a wide "Blue Wave type" gate. The water contained in the lock drains into this pond or lagoon, and raises its level at the same time. It enables boats with deeper draught to use existing shallow locks. This can be useful both at selected structures on a wide gauge network, and on Freycinet, small gauge canals.
5.1 Deepening small gauge network without changing width and length of locks
Freycinet canals acting as an improved feeder network
Deepening Freycinet canals was done in past decades (by 40cm), and could be reinitiated (up to 1m), thanks to the Half Blue Wave (fig.2), to create modernised, deep feeder waterways.
Depth would be 3,20m+, enabling 2,80m draught. Another option would be 2.90m depth, for 2.5m draught.
A 50m+ downstream lagoon, with variable level, would be closed by a gate at least twice wider than those of Freycinet locks. Once an upbound craft is in lagoon, the new gate would close and lock would empty into it, raising the level by 1m at the same time. A downbound craft with 1m more draught would leave the lock and wait in the lagoon until the upbound craft enters the lock with the same improved draught. When the gates of the lock close for its upbound cycle, the new gate would open and lagoon level return to downstream elevation, together with downbound craft.
Deadweight would increase by 75% on the whole route, not only on the Freycinet segment. With the 2.5m draught option, improvement would be only 51%, but would be felt on the whole of European network.
No need to widen the canal, because the concept regulates traffic and craft may meet only at locks. Reaches would be one-way for all deep-draught craft, two-way for empty or partly loaded craft.
To deepen the route, where possible, present underwater slope would be continued down to el. -4.5. Besides, raising water level by 30cm would be ideal, and is displayed in fig.2. Modification of upstream sill will be often necessary , except in a river. With depth reaching 4.8m at centre, navigation will be markedly improved [n=5,2 (2,5m) ou 4,6 (2,8m)].
Another option (fig. 2) would be to dig only to el. -2.90 (or -2.60), with a "n" coefficient close to that existing presently (6kph).
5.2 Deepening wide gauge structures presenting an adequate width and length
Reuse structures instead of rebuilding them
On the wide gauge network, there are many structures built long ago, and too shallow. In France for instance, present gauge has recently increased by one metre in depth, while length and width have remained the same than 40 years ago. Besides, many locks built a century ago were long and broad, to harbour towed convoys, but inadequate in depth, because rivers were not developed that way.
Applying new standards would mean destroy or abandon these locks, still fully serviceable, and build new ones, at a cost, at least 20 millions € apiece. Some of these locks are hardly 20 years old, so what a waste!
On rivers, it will be easy to create a downstream pond or lagoon, closed by a Blue Wave-type gate. Dimensions and operation of such lagoon is discussed below. It would provide 1m more on the sill of existing locks, and render them up-to-date for another century or so.
On canals, modifications may be a little more elaborate, but certainly cheaper than building new locks.
5.3 Water requirements for a "Half-Blue Wave"
Equal to that of a lock, except when lock head is below 5m
Discharge required for 3m-head: 17m3/s during 3 min.
A Half Blue Wave does not present specific water requirements as long as the lock compensate for a head of some 5m or more: What was in the lock will spread over the lower approach pond, and raise it by one metre or so.
For smaller heads, a complement will be required to fill the lagoon.
Besides, duration of the lock cycle itself is not lengthened, even if extra water is used in the lower approach pond.
On the contrary, time saved due to smaller head and faster exit of downbound craft sometimes more than compensate any possible delay.
5.4 Minimal size of lower approach pond in a Half Blue Wave
From 135 to 360m, depending on width of the lower approach pond and Class of waterway
In a Half-Blue Wave, average speed of a downbound craft exiting a lock can be estimated to 1,375m/s. A 105m convoy will thus spend 2 minutes before freeing the channel. The upbound craft will then be able to resume its movement in full safety, and enter the lock. As for the downbound craft, it is then obliged to stop after 75 more metres, in order to allow upbound craft to finish entering lock.
If lower approach pond were 36m wide, its length (185 or even 135m) could be smaller than the sum of two design craft; the concept would then practically be that of an extra downstream lock, but for its capacity to enable meeting of craft.
As soon as upbound craft has entered lock, which can take 4 minutes, the downstream gate of the lock can be closed (1 minute), and the " Blue Gate ", at the downstream end of the lower approach pond, will be opened.
During lower pond emptying, downbound craft shall be moored at both ends, preferably on floating bollards, in order not to be sent adrift by the current. Emptying duration varies according to the laws of hydraulics, but it appears 4 minutes is quite feasible. Downbound craft could then resume its movement, and will achieve its lockage with 11 minutes delay at the most. In order to avoid any delay, the Half-Blue Wave will be used only where draught of one of the two craft imposes it.
On the contrary, in case of one-way lockage, downbound or upbound craft shall practically experience no delay, or even register a gain, the slow speed registered below a lock in a shallow reach being somewhat commensurate with the need to move slowly during filling/emptying of the Half-Blue Wave. The head in the lock is also 1m smaller, which accelerates the cycle.
The length of lower approach pond can thus vary, in function of its width, between 185m and 360m (Class-Vb). In case a 180m convoy would show up, one-way lockage would enable a very quick passage. On a Class-Va waterway, minimum length can be 135m, 360m enabling practically a continuous movement (at 1m/s in average).
5.5 Delay in a " Half-Blue Wave "
Nil, or less than 10 minutes at the worst, in
case two loaded convoys meet in the structure
Calculations are found above, the two values (length of lower pond and delay) being closely linked ; the following table recalls the results.
Type of waterway:
Lower approach pond Length (m) and width
Time added (min.)
With or Without
Total added or saved
With or Without
Meeting in the lower approach pond of two convoys loaded deeper than 2,80m will happen only in very high traffic, or at saturation of the lock. In other traffic hypothesis, with due advance notice, one-way lockage for each convoy could be provided.
Finally, due to smaller head at the lock, time spent in one-way lockage may be identical or smaller than the time experienced today.
These new concepts can prove quite cost-effective on all waterways where locks are too shallow for modern traffic, or in cases where siting a classical large gauge waterway encounters resistance on various grounds, be it scenery or ecology.
They enable also to design waterways with a reasonable price, and which re-use space already ascribed to some waterways, often termed obsolete for modern goods transport. At the same time, they do not create too large a change in the landscape, nor on the general line of the waterway, and are thus environment-friendly.
It is hoped that waterway engineers discover potential places for use of these concepts the world over.