Stage 21: Montgeron to Paris

As usual, the 2017 edition of the Tour de France ends with the circuits up and down the Champs-Élysées in the French capital. The gutter that Zdeněk Štybar tried to ride away from the bunch in conveys water from the road into the famous network of sewers responsible for carrying wastewater out of the city.


The first sewers were constructed in the 13th century under the reign of Philippe Auguste, but, like most of the city, were largely rebuilt during Haussmann’s urban renewal project on the order of Napoleon III. The new sewer system was designed by Eugène Belgrand.


A photograph of a Parisian

The sewers quickly became an iconic if subterranean part of the Parisian landscape. There is a sewer museum, and, of course, Victor Hugo, writing during the Haussmannization of Paris, was inspired to set a climactic scene of Les Misérables in the pre-Haussmann sewers of 1832.


And with the sprint win by Dylan Groenewegen, the 2017 Tour is over. Come back in about 11 months for more Les Eaux du Tour.



Stage 20: Marseille

The penultimate stage is an individual time trial in this year’s Tour de France, and it takes us through the streets of Marseille along the Mediterranean Sea, so it’s our last chance this year to take a look at Mare Nostrum.


The Port of Marseille and the Mediterranean Sea.

The Mediterranean Sea has a fascinating geological history. Formed by the tectonic motion of the African and Eurasian plates, the connection between the basin and the Atlantic Ocean closed off some 6 million years ago. In the warm climate and without continual flushing from the Atlantic Ocean, the sea dried up, and what little water was left was very saline. The Messinian Salinity Crisis ended when the Strait of Gibraltar was breached and water poured in from the Atlantic Ocean.


An interpretation of the Zanclean Flood that opened the Strait of Gibraltar and flooded the Mediterranean.

Though the sea receives freshwater inputs from rivers like our old friend the Rhône, the warm and dry “Mediterranean” climate causes significant evaporation within the basin so that the Mediterranean water is significantly saltier than the Atlantic Ocean water. Atlantic water is lighter than Mediterranean water, so it sits on top of the Mediterranean water as it flows eastward. As it evaporates, it becomes heavier, sinks in the eastern part of the sea and starts to flow west where it escapes into the Atlantic through the Strait of Gibraltar. Because it’s now a lot heavier than the Atlantic water, it sinks to the bottom of the sea and travels far offshore as a fairly coherent mass.

Time trials can be very dramatic, but Geraint Thomas in Düsseldorf, the winner, Maciej Bodnar, kind of slipped under our radar until he showed up in the stadium with an impressive time and exacted his revenge for being caught on the way into Pau. The standings for all the jerseys are basically cemented now, so we can move on to the celebrations on the Champs-Élysées tomorrow night.


Stage 19: Embrun to Salon-de-Provence

Today’s stage takes us out of the Alps along the valley of the Durance to Salon-de-Provence. The Durance, which rises in the Alps near Briançon, naturally flows into the Rhône near Avignon, but in 1966, the Canal de l’EDF was constructed to divert the waters of the Durance south, past Salon-de-Provence and through a hydroelectric station into the Étang de Berre, a coastal lagoon near Marseille.


A SPOT image of the Étang de Berre. The Canal de l’EDF empties into the kind of flat part at the top of the lagoon, to the right of the pointy bit. The sediment that you see in the left side of the lake comes out of the canal.

Diverting so much freshwater from the Durance into the lagoon caused dramatic changes in its ecosystem (Bernard et al. 2005). The salinity of the lagoon declined, and the water stratified with the less dense freshwater sitting on top. Nutrient inputs from the canal led to eutrophication as microbes excited by the higher nutrient levels eat up all the oxygen in the pond. The sediment inputs from the canal that you can see in the SPOT image above reduced the amount of light that makes it to the bottom. All of these changes stressed the seagrass communities of the lagoon. Reductions in the freshwater discharge through the power station have improved the water quality in the lagoon, but the seagrass has yet to return fully (Bernard et al. 2007).

What a win by Edvald Boasson Hagen, finally getting that elusive victory for Dimension Data! That move on the roundabout was incredible to watch.

Stage 18: Briançon to Izoard

The Alpine stages are all squeezed in right next to each other, so we start today in Briançon, just downstream from Serre-Chevalier, then head down the valley of the Durance before turning around and heading back up to the col d’Izoard, over which you would head down to get back to Briançon. And tomorrow we’ll start from Embrun, which we encountered along the Durance today. We’ll talk more about the river tomorrow as we follow it into Salon-de-Provence, but today is all about the Lac de Serre-Ponçon.


The Durance, like many of the rivers we’ve encountered this year, has a tendency to flood violently. Significant floods in the mid-19th century drove the investigation of damming the river, but it was not until the 1950s that technology progressed to the point that a dam on the Durance was possible.

The Barrage de Serre-Ponçon was completed in 1959 and holds back the second largest artificial lake (after the lac du Der-Chantecoq). Two villages were flooded by the construction of the dam: Savines was moved to the banks of the new lake while Ubaye was evacuated. The construction of the Barrage is the background for the film L’Eau Vive by François Villiers which features a soundtrack written by Guy Béart, including the title track:

If you had told me two years ago that Warren Barguil would win two stages, the polka dot jersey and come in 9th place in the Tour, I might have believed you. Last year, not so much. But wow, what a ride! Three days of racing left: the long road down the Durance to Salon-de-Provence, a time trial in Marseille and the sprint on the Champs-Élysées.

Stage 17: La Mure to Serre-Chevalier

Today’s stage takes us from La Mure on the Drac River, past Bourg d’Oisans, the site of the lake that burst to flood Grenoble in 1219, up the Arc River, over the Col du Télégraphe and then up the valley of La Valloirette to the col du Galibier before descending down the valley of the Guisane to finish in Serre-Chevalier. If we had gone north instead of east out of La Mure we would have run into the Laffrey lakes, a quartet of glacial lakes.

Grand lac de Laffrey

The grand lac de Laffrey

The four lakes, from the south end of the valley near La Mure to the head at the north, are Pierre-Châtel, Pétichet, the grand lac de Laffrey, and Mort. Each one is dammed by a moraine left by the local glacier as it receded up the valley some 11,000 years ago.

Situated as they are in a tectonically active area, it is possible to reconstruct the history of earthquakes in the region using the sediments on the bottoms of the lakes (Nomade et al. 2005). Mixing of the sediment in Pétichet and Pierre-Châtel by animals makes them less useful for paleoseismology than the grand lac de Laffrey, though.

A great stage win for Primož Roglič on the Galibier. It will probably be overshadowed, perhaps, by the drama of the general classification and the green jersey this year, but like the similarly dramatic stage to Mont Ventoux last year, it will go down in my books as a stage which Serge Pauwels almost won.

Stage 16: Le Puy-en-Velay to Romans-sur-Isère

The sixteenth stage takes us out of the Loire valley and into that of the Rhone. We end up in Romans-sur-Isère on one of the tributaries of the Rhone, the Isère River.


The Isère joins the Drac at Grenoble a little ways above Romans-sur-Isère, and the pair of them are known as the “serpent” and the “dragon,” respectively. The serpentine Isère meanders through the Grésivaudan as it makes its way to Grenoble. The Drac takes its name from the Occitan “drac,” which is a water demon that tempts children to drown.


A fountain in Grenoble with a lion grabbing the serpent

The two rivers are known for their propensity to flood, creating a massive flood in 1219. A landslide dam stopped the Romanche, a tributary of the Drac which runs past the classic Tour climb of Alpe d’Huez. This dam burst over the night of September 14 and 15, 1219, and the flood wave runs down the Romanche into the Drac. The city of Grenoble was much smaller then, centered around a meander on the Isère, so this initial flooding did not reach the city. But the flood caused the Isère to back up and flow into a lake around Meylan. When this lake emptied, its waters flooded Grenoble, causing damage and casualties largely because of a market that was being held there.


Grenoble flooded in 1733

Levees to prevent such disasters are now maintained on the Isère, the Drac and the Romanche by the Association départementale Isère Drac Romanche.

A thrilling finish for the puncheurs in the winds on the Valentinois (the valley in which Romans-sur-Isère sits). We’ll head further up the Drac tomorrow when we start from La Mure and head into the Alps.

Stage 15: Laissac-Sévérac l’Église to Le Puy-en-Velay

Today’s medium mountain stage takes us across l’Aubrac, a large volcanic plateau in the Massif Central. Glaciers carved a quartet of lakes, including the Lac de Saint-Andéol.


The lake was the site of a Celtic cult which persisted until the late 6th century. Crowds would gather on the boggy shores of the lake and toss clothes and food into the water. The practice was stopped by Saint Hilaire of Mende.

Perhaps Bauke Mollema and Chris Froome made offerings to the gods of l’Aubrac this morning. The former pulled off an impressive escape from a motivated but unfocused breakaway group, and the latter managed to hang on by his fingernails despite a series of mistakes on the penultimate climb of the day.

Stage 14: Blagnac to Rodez

A punchy stage to Rodez takes us through the valley of the Tarn River, site of a catastrophic flood in 1930.

Heavy rains at the end of February 1930, coupled with a rather wet winter which saturated the watershed, overloaded the Tarn watershed and sent 8000 cubic meters per second of water down the river (Boudou et al. 2016). For comparison, the mean annual discharge of the Tarn is about 230 cubic meters per second, and a flood of the magnitude of the 1930 flood has an average recurrence time of around 300 years.

Over 200 people lost their lives in the flood, 10,000 people were rendered homeless and damages amounted to some 500 million euros in 2015 terms. The town of Moissac was particularly hard hit as some dykes broke and inundated the town.

Revisiting the classic finish in Rodez from 2015. Michael Matthews got the win over 2015’s winner Greg van Avermaet.


Stage 13: Saint-Girons to Foix

The thirteenth stage of the 2017 Tour takes us from Saint-Girons over three hard climbs and into the town of Foix in the Ariège department where the locals like to fish for trout au toc.


Pêche au toc adapted to the small, heavily forested streams of the area, in which fly fishing is not possible. It is a kind of bait fishing in which a long rod is used to hold the hook over holes where the trout like to hang out. The off hand holds the rest of the line and senses by touch (au toc in Occitan) whether a fish has bitten.

There are a bunch of tutorials on Youtube. These guys look like they’re having fun:

A great day for the French as Warren Barguil outsprints the leading group on Bastille Day.

Stage 12: Pau to Peyragudes

The first mountain stage in the Pyrenees takes us from Pau to the ski resort of Peyragudes, just up the road from Bagnères-de-Luchon, where the equivalent stage finished last year. Along the way, we re-entered the valley of the Garonne, sister river to the Dordogne, which it joins at the Gironde estuary.


The Garonne at Saint-Béat

I think the river is more interesting near the Gironde, where a tidal bore that you can surf on propagates up through, and in the Spanish Val d’Aran where its headwaters lie. So today, I want to draw your attention to a tiny, inconsequential vernal pool not far from Saint-Béat, the Étang de Sasplays,


Nestled in a little depression on the Pic de Sacaube above the town of Fos, the Étang de Sasplays, like all vernal pools, dries up in the summer. The spring rains fill up the two components of the pond, and with them come lots of frogs which breed in the fish-free pond.


The Grand Sasplay

If the hike up the Sacaube was too much for you, there is a little cabin nearby (the Cabane d’Herechet, which has a sign in the photo).

The big men of the mountains reined in Steve Cummings before a final push by Romain Bardet wins the stage, and puts Fabio Aru in yellow.