Stage 21: Chantilly to Paris

The final stage of the 2016 Tour de France finally takes us out of the basin of the Rhône and into the Seine watershed as we ride towards Paris, the Champ-Elysées and the conclusion of the greatest race on Earth.

The Seine rises northwest of Dijon and flows northwest through Paris to its estuary at Le Havre on the English Channel.

Earlier this summer, persistent rains enlarged the Seine, along with several other European rivers, and the Seine rose to over 6 meters above its usual height in Paris. Four people were killed in the floods, electricity was lost, the trains were shut down, and the Louvre and Musée d’Orsay were closed so curators could move the art to safety. These floods, while tragic, were not the worst Paris has seen. In 1910, waters rose over 8 meters, and the streets flooded.

The streets were dry today though, for a classic sprint on the Champs-Elysées. André Greipel pulls off the win ahead of Alexander Kristoff and Peter Sagan, but it was the guys of Team Sky who secured yet another Tour de France win for Chris Froome.

via Team Sky

Check back next year for some more great cycling and hydrology!

Stage 20: Megève to Morzine

The penultimate stage of the 2016 Tour de France takes us from the finishing town of the mountain time trial, over a few mountains and down into the valley of La Dranse de Morzine, a river system that eventually, as La Dranse, empties into Lake Geneva at the Delta de La Dranse.

The delta lies near the town of Thonon-les-Bains on the southern, French bank of the lake. It was made into a natural reserve in 1980. It was later incorporated into the Natura 2000 network of protected areas in the European Union. The natural reserve does not, however, protect the entire delta, much of which has been developed. It is a 53 hectare site on the banks of the Dranse where it meets the lake.

Jon Izaguirre pulls away from the Shark of Messina on the descent off the Joux Plane for the stage win. Froome stays in yellow despite his rough day yesterday. It’s off to Paris, the Seine and the Champs-Elysées tomorrow!

Stage 19: Albertville to Saint-Gervais Mont Blanc

An interesting day of racing, once again in the shadow of Mont Blanc. Another mountain storm, not quite so intense as the one on the way to Andorre-Arcalis, made the roads especially treacherous towards the finish. At the beginning, we passed Lac d’Annecy, another of the glacial lakes of France.

Lake Annecy is oligotrophic: it has very low biological productivity because of low nutrient content. This results in very clear water. This impressive water quality is the work of the Syndicat Mixte du Lac d’Annecy, which was founded by the surrounding communes in 1957 to clean up the lake. They started by treating sewage flowing into the lake from these communes and have expanded into an organization of 114 surrounding communes which collectively make decisions to manage the water quality of the lake.

A wet ride into Saint-Gervais for the first French stage winner in this year’s Tour, the always-entertaining Romain Bardet. Just two stages to go!

Stage 18: Sallanches to Megève

The 17 kilometer mountain time trial — the shortest stage the Tour de France has seen — did not give us many opportunities to see some impressive hydrological features. Those that we did see were the impressive glaciers atop the Mont Blanc massif in whose shadow each of the rider set off on his own today. The largest of these is called the Mer de Glace, the “sea of ice.”

The Mer de Glace runs from the northwest side of the Mont Blanc massif into the valley of the Arve river just north of the ski resort. Chamonix (see this Google Earth photo, or have more fun by visiting Mont Blanc in Google Earth yourself. The three-dimensional views they render are pretty spectacular).

merdeglace

As with most glaciers in the world, this one is retreating fairly quickly.

Vincent et al. (2014) estimated the parameters of a model for the mass balance of the Mer de Glace and projected their model into the future, predicting a retreat of 1200 m by 2040.

Chris Froome rode 1200 meters in about a minute this afternoon, crushing the already fantastically impressive time of Tom Dumoulin for the stage win, a preview of the Olympics one can only hope.

  • Vincent, C., M. Harter, A. Gilbert, E. Berthier, and D. Six. “Future fluctuations of Mer de Glace, French Alps, assessed using a parameterized model calibrated with past thickness changes.” Annals of Glaciology 55, no. 66 (2014): 15-24.

Stage 17: Berne to Finhaut-Émosson

Right after the second category three climb, the Col des Mosses, we descend back into the valley of the Rhône, this time before it empties into the southeastern side of Lake Geneva (Lac Léman) — the river that we saw in France emerges from the southwestern side of the Lake.

The area of the lake that we pass today is yet another Ramsar site: Les Grangettes, the Rhône delta in the lake. The actual inflow of the river into the lake is an impressive sediment plume.

Most of the delta of the river is composed of sediments on the bottom of the lake. Where exactly those sediment end up depends on the relative density of the lake waters and the river water (Moscariello 2012). When the river water is denser than the warm waters on the surface of the lake (the epilimnion) but lighter than the cooler deep waters (the hypolimnion) the sediment-heavy river water floats on the boundary between the two lake layers and is transported out into the lake. The Coriolis force pushes these waters to the north, and the fine silt sediment settles out in a fan to the north. When the river water is denser than the hypolimnion, the river water flows down to the lake bottom, where it carves out a network of submarine channels.

  • Moscariello, Andrea, Frédéric Arlaud, Yosef Akhtman, Flavio S. Anselmetti, and Ulrich Lemmin. “Searching the Rhone delta channel in Lake Geneva since François Alphonse Forel.” Archives des Sciences 65 (2012): 103-118.

Stage 16: Morains-en-Montagne to Bern

We make our way into our fourth country of this year’s Tour today, running through the valleys of the Jura before arriving in the Swiss capital, Bern. Along the way, we pass the largest lake entirely in Switzerland, the Lac de Neuchâtel or the Neuenbergersee.

Lake Neuchâtel is, like the others around it, a glacial lake, exposed after the end of the Würm glaciation around 12,000 years ago.

The lake was naturally oligotrophic with low biological production and good water quality. Human impacts increased the phosphorus load into the lake until the 1980s when Swiss water treatment plants began removing phosphorus and phosphorus detergents were banned (Lang 1999). Since then, the lake has recovered to an oligotrophic condition.

The reed marshes on the less-developed south bank of the lake are a Ramsar wetland, as is the shallow bay and marshes between Cudrefin and the Thielle canal which connects Lake Neuchâtel to the Lac de Bienne.

yvonand-2

The Grande Cariçaie, part of the Rive Sud wetlands

And wouldn’t you know? Peter Sagan did it again with a very close sprint win over Alexander Kristoff. A rest day for the riders and Les Eaux tomorrow before we start our course through the Alps.

  • Lang, Claude. “Contrasting responses of oligochaetes (Annelida) and chironomids (Diptera) to the abatement of eutrophication in Lake Neuchâtel.”Aquatic Sciences 61, no. 3 (1999): 206-214.

Stage 15: Bourge-en-Bresse to Culoz

The fifteenth stage of this year’s Tour takes us from the northeastern end of the Dombes over the Jura mountains and back into the valley of the Rhône. At the finish in Culoz, we got to see the first non-artificial lake we’ve discussed here at Les Eaux du Tour: the Lac du Bourget.

The Lac du Bourget was formed along with nearby lakes Annecy and Geneva after the retreat of the Rhône glacier after the Würm glaciation around 14,000 years ago (Vernet and Favarger 1982).

The lake is mesotrophic, meaning it has a moderate level of biological production and fairly good water quality. It is this water quality that has attracted many to the resort town of Aix-les-Bains on its shores. At the north end of the lake near the outlet that connects it to the Rhône is a set of marshes and bogs called the Marais de Chautagne which, together with the Lac du Bourget, form a Ramsar site. During floods on the Rhône, water actually flows into the lake and the marshes, but hydroelectric developments on the Rhône have limited this flooding to a few days per year. The Marais de Chautagne also forms a kind of wetland complex with the Marais de Lavours on the other side of the Rhône, just south of today’s finishing line in Culoz where the young Colombian Jarlinson Pantano outsprinted the new King of the Mountains Rafał Majka for the win.

Source: https://upload.wikimedia.org/wikipedia/commons/2/2f/La_Chautagne%2C_Savoie.jpg

Looking from today’s big climb of the Grand Colombier over the Marais de Chautagne (center) and the Lac du Bourget (right). The Marais de Lavour is at the bottom right.

  • Vernet, Jean-Pierre, and P-Y. Favarger. “Climatic and anthropogenic effects on the sedimentation and geochemistry of Lakes Bourget, Annecy and Léman.” Hydrobiologia 91 (1982): 643-650.

Stage 14: Montélimar to Villars-les-Dombes (Parc des Oiseaux)

The last real stage for the sprinters until Paris takes us to the Parc des Oiseaux, a bird sanctuary situated in the Dombes, a glacial plateau between the Saône and Ain rivers with hundreds of artificial fish ponds.

These ponds were first constructed in the late Middle Ages by Benedictine monks who wanted to ensure an adequate supply of carp to eat during Lent and expanded by landlords eager to cash in on the potential for carp farming. The farmers in the region drain the ponds every few years and grow cereal crops on the fertile bottom sediments (Williams 1987, Wezel et al. 2013). A dynamic set of property rights emerged to mediate between the different landowners who would end up sharing a single pond during the flooded “evolage” period (Williams 1987).

Dimension Data pulls off win number 5 with yet another powerful outing by Mark Cavendish in the Parc des Oiseaux. A hilly stage tomorrow before we get into the mountains and the final week of racing through the Alps.

  • Wezel, Alexander, Joel Robin, Mathieu Guerin, Florent Arthaud, and Dominique Vallod. “Management effects on water quality, sediments and fish production in extensive fish ponds in the Dombes region, France.”Limnologica-Ecology and Management of Inland Waters 43, no. 3 (2013): 210-218.
  • Williams, D. Dudley. “Applied Aspects of Temporary Waters.” In The Ecology of Temporary Waters, pp. 144-162. Springer Netherlands, 1987.

Stage 13: Bourg-Saint-Andéol to La Caverne du Pont d’Arc

A somber mood hung over the individual time trial today because of the terrible happenings in Nice the previous night. But we were provided with some cheering views of the Gorges de l’Ardèche today.

Around thirty kilometers of the Ardèche near its confluence with the Rhône are incised into carbonate rocks. The resulting landscape is a spectacular karst valley with the natural bridge called the Pont d’Arc one of the most famous views of the region, visible behind the last time check on the time trial course today.

The water also carves dramatic caves into the hills, most importantly the Chauvet Cave, Werner Herzog’s Cave of Forgotten Dreams, and home to the earliest known cave paintings.

Another consequence of the lithology of the Ardèche catchment, carbonate towards the mouth and bedrock igneous towards the head, means that flows in the river can be flashy, resulting in severe floods. Hydrologists have discovered that long historical records from the region can help them reconstruct and estimate this flood risk (Naulet et al. 2001).

Tom Dumoulin powered through to an impressive time trial victory today while the GC was shaken by the great times of Chris Froome and Bauke Mollema to the Caverne du Pont d’Arc, a replica of the Chauvet Cave.

  • Naulet, R., M. Lang, D. Coeur, and C. Gigon. “Collaboration between historians and hydrologists on the Ardeche river (France).” In The Use of Historical Data in Natural Hazard Assessments, pp. 113-129. Springer Netherlands, 2001.

Stage 12: Montpellier to Mont Ventoux

We entered the watershed of the Rhône today, and we’ll be in it for the rest of the race until the final day, when we meet the Seine in Paris. All the water we see until then will flow into the Mediterranean by way of the Camargue.

With the damming of the Nile, the Rhône has become the major source of freshwater and sediment to the Mediterranean Sea (Sempéré et al. 2000). By the time it gets there, it has picked up a lot of carbon and nitrogen from its watershed. Why then, does the Gulf of Lion — the part of the Mediterranean Sea off the Languedocian coast — not have a hypoxic zone?

Hypoxic zones form when microorganisms in the ocean are stimulated to produce by high nutrient inputs to the coast. Phytoplankton take up these nutrients and use them to grow, storing oxygen by photosynthesis. When they die, however, they sink and are decomposed by bacteria, consuming oxygen from the water column. With enough phytoplankton, a bloom, this process can eat up all the oxygen in a fairly enclosed basin of water. The “dead zone” at the mouth of the Mississippi River is probably the most famous of these.

So why doesn’t the Rhône have a dead zone at its mouth? The water that comes out of the Rhône doesn’t stay in the Gulf of Lion for long, just about 6 days, compared to around 95 days for the Mississippi River mouth (Rabouille et al. 2008). The strong winds in the region, which we’ve seen to the detriment of the riders (and the benefit of Sagan and Froome yesterday), also blow the water around the Gulf of Lion, churning up what would otherwise be a well-stratified water column. Oxygen-rich water can be transported down to the bottom, and a hypoxic zone does not form.

What a finish today! I never thought I would see Chris Froome, several-time champion of the Tour de France, try to run up the Mont Ventoux. Let’s just hope that the silly but frustrating finish of today’s stage doesn’t cast a shadow on the rest of our stay in the Rhône basin.

  • Sempéré, Richard, Bruno Charrière, France Van Wambeke, and Gustave Cauwet. “Carbon inputs of the Rhone River to the Mediterranean Sea: biogeochemical implications.” Global Biogeochemical Cycles 14, no. 2 (2000): 669-681.
  • Harrison, P. J., M. Dagg, and B. McKee. “Comparison of hypoxia among four river-dominated ocean margins: The Changjiang (Yangtze), Mississippi, Pearl, and Rhoˆne rivers.” Continental Shelf Research 28 (2008): 1527-1537.