Keywords

1 Introduction

The Blue Wave is a locking structure that allows simultaneous navigation in both directions of navigation, without stopping in most cases, and at a speed depending on the local topography.

Its principle has been described in an issue of PIANC Bulletin, N°108, september 2001.

It could be used, in lieu of a set of locks, on a Canal which is presently being improved to CEMT Class Va, far upstream from Paris, the Canal from Villiers to Beaulieu (Petite Seine, France).

This paper will show that the proposed solution is more respectful of the environment and landscapes than the lock option. Thus, since the set speed of the concept is practically the optimum speed permitted by the cross-section of the canal, it can be said that the site of the Canal from Villiers to Beaulieu is optimal for the application of the Blue Wave principle.

2 The Blue Wave Concept

In cities, traffic lights are synchronised, so as to allow vehicles, running at a set speed, to travel without finding a red light. This is called Green Wave.

Similarly, on a canal, the Blue Wave concept enables craft to never stop, while encountering differences of elevation. If the Lock is akin to an elevator, the Blue Wave is an escalator. The difference of elevation is broken in a number of steps, each usually some 1 m high, and the reach varies up or down while the craft is moving, albeit at slow speed. In contrast, the craft does not move in a lock, and needs to have, between 2 locks, a large canal to ply sufficiently fast to compensate for this stop.

figure a

As can be seen on the figure, boats can navigate up and down at the same time, provided sufficient passing space is provided. Locks cannot do that. Another advantage, on shallow terrain, is that the Blue Wave can stick to the slope of the natural terrain, while, for a lock, there must be deep trenches or high embankments which, apart from being costly, are very conspicuous in the landscape. This is less and less accepted.

In natural rivers with rapids (less than 5 m fall), a Blue Wave can enable to navigate on a parallel canal across the rapids. This will be of use on African, South American, and Asian rivers, where there are many shallow rapids.

Similarly, where a bend is short-circuited, for hydraulics reasons the main flow has to continue to use the bend, and there is a slight difference of level between the two ends of the by-pass. With a set of Blue Wave gates at each end that alternatively open, it is possible to compensate for this slight fall, while the natural hydraulics of the river remain unchanged.

In canals, the cross section of the canal can be smaller with a Blue Wave than with a set of locks, and yet retain the same average speed on the whole voyage. A canal designed for 6.7 km/h is much cheaper to excavate than the one designed for 10 km/h.

Let us assume a 10 km canal designed for 10 km/h, with a 10 m high lock at the end. It takes roughly 1.5 h to cross both. 6.7 km/h on average, or 1.85 m/s.

A Blue Wave needs 10 km to overcome 10 m. At 1.85 m/s, this is 5400 s or 1.5 h, with a canal designed for 6.7 km/h only, thus a much smaller cross-section.

If the 12 gates needed for a Blue Wave are not more expensive than a 10 m lock, with all its concrete, then a Blue Wave is cheaper than a classical waterway.

The design speed depends on the local topography and the length of the craft.

3 Application to Bray-Nogent Project

3.1 The Bray-Nogent Project History

In the eighties, the improvement of the Bray-Nogent waterway was already planned. It was thought possible to seize an opportunity and excavate a large gauge canal parallel to the existing Villiers-Beaulieu canal, the excavated material being needed to create the platform of a Nuclear Power Plant nearby. There was actually 8 borrow pits, so that the water table would not be impaired, but the Bray-Nogent waterway was deferred, and the borrow pits were left unused.

40 years later, the project is on the verge to be implemented, and a classical canal with one lock has been designed parallel to the Villiers-Beaulieu canal. This project is using the borrow pits, but the 4.44 m fall at the lock obliges to raise the banks of the new canal over 12 km (2 × 6 km), to deepen some borrow pits (4 km) and to take the actions necessary to stabilise the water table, a very touchy problem in this area.

3.2 The Blue Wave Solution

It was thought possible to fruitfully apply the Blue Wave technique there:

By using the borrow pits, the structure very faithfully respects the current levels of these bodies of water, which avoids costly measures to restore the water table. In addition, only the banks of the 2 upstream cells need to be raised, and by 1 m only, against 16 km in the lock option, by up to 4 m!

These two points confirm that the proposed solution is more respectful of the environment and landscapes than the lock option.

Here, the set speed may be 2 m/s, i.e. 7.6 km/h, very close to the commercial speed permitted by the wet section of the canal.

It is possible to form 10 reaches of 1,000 m each, separated by collapsible doors (mitre or valve) with a feeding system from one reach to the other. The depth available in the borrow pits is sufficient for the navigation of the project boats (31.9 m2 of wetted section). For the economy of the system, it would be preferable, but not essential, for the width of the different reaches to be identical, and not to exceed 50 m at the water surface. In this case, the volume exchanged from reach to reach will be 25,000 m3, since it is on average a section of 0.5 m that thus passes from one reach to the other.

The first two reaches are used to dampen level variations of the Seine in the reach of Beaulieu, between 60.60 (Normal Pond Level-RN/NPL) and 61.57 (Reference Water Level-LER/RWL). The following figures, extrapolated from VNF documents, show the kinematics for a downhill boat.

3.2.1 Downstream Movement at Normal Pond Level

At NPL, at the green light, the boat (or the group of boats) enters reach 1 towards reach 2, both being at the upstream pond level, and while it travels in it at 2 m/s, the door pk0 closes. It then enters reach 2, since gate pk1 has remained open, and, as soon as it enters, this gate pk1 closes, while in synchronization (as soon as it is completely closed) reach 2 begins to empty into reach 3 with a flow rate between 50 and 100 m3/s.

When the equality of levels is reached (duration approximately 360 s) the gate pk2 opens, and the boat passes into reach 3 which is then at elevation 60.10.

If a rising boat were in this reach, it can enter reach 2 before gate pk2 closes. This crossing operation can be carried out simultaneously, if the doors are wide enough (30 m), or in succession, under the control of lights, if they are narrower (18 m).

For the downstream boat, the gate pk2 closes as soon as any rising boat has crossed it, reach 3 empties into reach 4 until the levels are equal (59.60), at which time the gate pk3 opens to allow the passage of the boat in reach 4.

The operations are repeated step by step, with 5 crossing possibilities over the entire route.

figure b

3.2.2 Downstream Movement in Flood Condition

If the Beaulieu reach is higher than the NPL, up to the RWL (or the Highest High Water), the first reach is used to dampen this variation:

At RWL, at the green light, the boat (or the group of boats) enters reach 1, and while it travels through it at 2 m/s, the gate pk0 closes, while in synchronization (as soon as it is completely closed) reach 1 begins to empty into reach 2 with a flow between 50 and 100 m3/s. The excess volume is rejected downstream by dumping in the reach 3 above or around the gate pk2.

figure c

When the equality of levels is reached (duration approximately 360 s) the door pk1 opens, and the boat passes in the reach 2 which is then at the elevation 60.60. We are then in the same situation as before, see above the NPL conditions.

3.2.3 Upstream Movement at Normal Pond Level

For rising boats, the principle is similar, and is explained within the figure for NPL conditions, see below:

figure d

If the Seine is at RWL or in full flood, gates pk10 and pk9 are open or anyway already at the same flood level, since the level in reach 9 is practically identical to that of the Seine RWL (56.58). In extreme flood, both reaches will be at flood level, possibly even reach 8.

At the green light, reach 10 and reach 9 are travelled at set speed by the upbound boat. As soon as gate pk9 is crossed, it closes and while the boat travels along reach 9, reach 8 empties into reach 9 until the levels are equal (57, 10, or higher), which then allows the gate pk8 to be opened in front of the rising boat, which can enter reach 8, and so step by step until pk0.

4 Conclusion

We can see that the site of the Canal de Villiers in Beaulieu is optimal for the application of the Blue Wave principle, since the set speed is practically the commercial speed allowed by the wet section of the canal.

The structure would be crossed in 5,000 s (1 h 23), while crossing the same canal with passing through a lock would last at best 5,400 s (1 h 30).

Regarding the waiting time in front of the structure, the maximum duration of a possible red light before entering the structure would only be 1,000 s (16 min 40 s), while the mathematical expectation of waiting in front of the lock would be 30 min (duration of ½ cycle), according to the Operation Programme.

By integrating the average of a possible wait, the passage with lock would last 2 h, and only 1 h 39 with the Blue Wave.

Thus, using a Blue Wave in Canal de Beaulieu would seem to be a better proposition than a Lock.