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Hydrology and European Watersheds

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Home >> Hydrology and European Watersheds

There are a lot of concerns about the river levels since last years drought. I can see this due to the web site statistics. And it is an important questions for a lot of people in river cruise forums. People interested in cruising Europe want to know the the water level for a particular month, and are sometimes really disappointed when they learn that it is too hard to say. WHY is it so hard to predict the river levels? Therefore I try to provide some background information on watersheds, river courses and the main areas where the cruiseable rivers in Europe draw their water from. If you don't mind, try to answer this counter question: Can you tell me the weather situation for your home town in 4 month from now? You might have a good guess, based on experience, but to be on the safe side (or not to disappoint me) you would give me a temperature range. Now we are dealing not only with one city but a whole area, and try to figure out how the weather will be in about 12 - 15 month. Furthermore, rivers run through very different geological areas, sometimes from 2400m / 8000ft down to sea level. That means we have to keep a lot of short and long time effects in mind. First, let me give you an idea about the geological formations that form the european water sheds (which do not care about country borders), then we deal with meteorology, hydrology and the seasonal difficulties.

Watersheds in Europe

Before we talk about the effects (and the most important rivers for cruises en detail), I created a watershed overlay for you. Blue lines are the rivers, while the colored areas mark the watershed, the area where a particular river draws its water from.

I did try to mark the area as accurate as possible by using height lines, overlays and the GPS coordinates down to 2nd degree tributary sources of a river system. However, there might be some minor mistakes, still, I guess it gives you a rough idea about the complexity of the problem. The areas without colors do have rivers, but they are just to insignificant for this overview. The Meuse / Scheldt and Rhine delta forms a wide estuary, so I could have overlapped the areas, but decided to pretend that there is a precise border between both rivers. But that will be an article of its own.

Watershed discharges into Ocean Color Main River(s) of this shed
Adriatic Sea Blue Po
Atlantic Ocean Blue Douro
Atlantic Ocean Cyan Tejo
Atlantic Ocean Green Guadalquivir
Atlantic Ocean Yellow Guadiana
Baltic Sea Blue Weichsel
Baltic Sea Magenta Oder
Bay of Biscaya Cyan Loire
Bay of Biscaya Red Garonne
Black Sea Red Danube
Mediterrean Sea Orange Ebro
Mediterrean Sea Yellow Rhone, Saone
North Sea Cyan Elbe, Vlatva
North Sea Green Meuse, Scheldt
North Sea Orange Rhine, Main, Moselle, Saar
North Sea Red Thames
North Sea Yellow Weser
The Channel Blue Somme
The Channel Magenta Seine


You will easily see, that most sources of rivers are located in 3 different areas. As we have mainly west wind in Europe, lets start in this order:

* The Pyrenees and the mountain ranges on the Iberian Plateau. The Pyrenees seperate the Iberian Peninsula (Spain and Portugal) from France. It's snow and reservoirs water mainly via the Garonne river in France into the Bay of Biscaya. All mountain ranges (like the Sistema Central mountains) in Spains heartland run from east to west, and so do the valley. As you can see, the Douro, Tejo, Guadalquivir and Guadiana more or less run parallel from east to west and dewater rather long but narrow areas into the Atlantic Ocean. Only the Ebro river runs the other way from west to east along the Pyrenees to the Mediterrean.
* Most rivers in western Europe start in the same area. They draw their water from the Alps, while most of their tributaries have their sources in the Black Forest or its twin, the Vogese midlands. The alps supply the major rivers: Rhine, Rhone and the Danube (and on the italian side of the alps, the Po river as well). Actually the Danube has its source in the Black Forest at the confluence of Breg and Briegach, but a significant number of its tributaries start in the alps. The Seine, Saone, Moselle, Saar and Meuse sources are really close together at the european water divide in the Vogese.
* Eastern Plateau: Tatra and Caparthian Mountains. The main area where eastern European rivers draw their water from. The Elbe and Vlatva run from the czech plateau down to the North Sea, while the Oder and Weichsel rivers dewater into the Baltic Sea. A lot of minor rivers discharge via the lower Danube into the Black Sea.


is the 'study of the movement, distribution, and quality of water on Earth'. Well, we don't need to care about the quality, lets mainly focus on movement and distribution, as this is the concern 'do we have enough water under the keel?' So how does the water cycle look like? The United States Geological Survey explains it as following.

water cycle

Water evaporates from the oceans, condensates as clouds, precipitates and runs down the rivers to the oceans, where it evaporates again. It is more complicated, as water can evaporate from a river as well (resulting in a drop of river levels of up to 10 centimeters per hour / acutally this is not just the evaporating but supported by a groundwater low). There are different parameters that influence the water level of rivers. Whereas we can divide them in two groups: The groundwater discharge and the surface run off. An extraordinary dry autumn caused the low river levels on the Rhine and the Danube in November and December 2011. While a surface run off due to heavy rain usually causes high water level peaks (but don't last very long).

The most important parameters for the water cylce

* Underground: How good can it bind water? Does it allow water to seep into the ground water, or is it impermeable like clay?
* Vegetation: Forests or dense vegetation slows water down on the surface, allows more water to seep into the underground. It buffers short time peaks after heavy rainfalls.
* Elevation: The higher the altitude, the later snow melts. Rivers that begin in the midlands will run out of snow (bound water) in their reservoirs around march to april (causing high water). By contrast, the skiing season in the alps just ends around the end of april, so there is plenty of snow left to melt. Rivers that dewater the high mountains usually reach their highest water level later than midland rivers.
* Natural or artificial reservoirs: Does the course of a river include lakes? The Rhine and the Rhone flow down from the alps via Lake Constance, respective Lake Geneva. These huge reservoirs can buffer high water peaks in springtime. And they can still provide water during low water periods. By contrast, the Danube lacks such a reservoir. Damns and barrages work similar as man made objects along the rivers. * Other man made interferences: Did river regulations take place? A canalised river bed provides a more stable waterlevel than a free flowing river that meanders through the landscape. It is more secure to navigate, this reduces the risk of collision or ships running aground (do not underestimate this problem, even if you ship is fine, it may be blocked by another stranded vessel). But it allows water to flow at a higher speed, causing underground erosion and tends to short peak floodings.

Some of these parameters do not change at all. Some change very slowly, like the vegetation. While the construction of artificial objects (like to canalize a river bed, or to construct a damn) takes time, but once they exist, they have a dramatic affect on the speed of the water cylce.

Surface runoff / Seasonal influences

It is even more complicated, so lets try to combine the water cycle with the seasons of the year. Let me just outline the most important questions for every season. Winter of Season before / Early Spring: How much did it snow in the high mountains? The snow in the alps usually melts away slowly, so the Danube has its highest water levels in May (as its major tributaries like the Inn, Iller and Isar and Drave dewater the alps as well). But if there was still a lot of snow in spring time in the midlands (where most tributaries have their origin) like the Rhine, this melts away usually in March, and can cause a significant rise of the river levels which can last for 7-10 days (depends on the temperature.). And if you combine a warm spring (early snow melt down) with rain you get a nice flooding. Spring: Usually the April / May can bring high water due to melting snow in its source areas. Furthermore you have to expect short term highs due to surface run offs caused by heavy rain. Actually this can happen all year long, but in the spring time most river levels are higher than in summer or autumn. If you want to be on the safe side, you should consider a cruise from June - August, but then prices increase while river levels drop.

Summer: Usually the winter / spring effects are gone around May or June. This is the most stable seasonal condition.

Summer / Autumn: Problems can arise in both ways: If the summer was extraordinary dry and long, your ship can get low water problems. While heavy rainfalls in autumn can cause high water problems as well.

Winter: Until last years drought, I thought of winter rather as a very stable situation. The river levels are usually not very high but cruiseable. Should the temperature drop down to the frost point, you get snow. Keep in mind that snow does not affect the water levels immediately - so the altitude of the snow line is imporant. Another force majeure can arise from extraordinary cold weather. In December 2010 the Main Danube Canal froze over while there were still cruises going on.

Wind Directions

So we dealt with snow melt as a major source of rivers. Now how about rain? For rain you need clouds, which are moved by the wind. All rivers exept the spanish rivers draw their water from and discharge between 42°N - 53°N latitude . While the spanish rivers are in the range of 37°N - 42°N. So Europe's rivers are quite in the middle of the westerlies. In other words, there is usually west wind. Does this affect cruises? If you cruise from west to east, you will most likely have the same weather formation 'following' you, while traveling the other direction may result in more weather changes. Unfortunately, this is true for sunshine and rain. If you want to make a geological variable decisive, I rather advice to check the height profile (if you want to cruise up / or downstream) instead of the wind direction. The wind and the geological formations explains the concentration of river sources in the Vogese, Black Forest and the western Alps. The moist west wind from the Atlantic ocean hits the first mountain range that blocks its way east. And that are the Alps, the Vogese (and if we prolongue it to the north, the Ardennes).

However there are a few winds that may influence and disturb the 'usual' wind flow:

* The Mistral winds that flow from north to south through central France. From its center down the Rhone valley to the Camargue. This is the only wind which directly affects cruises, as it helps to clear the sky in the narrow Rhone valley very quickly.
* The Levante: A (South) East to West from Africa to Spain (more or less upstream the Ebro valley). Available as 'dry' and 'moist' levante.
* Eastern Europe Bora and Etesian winds. Continental winds that bring dry air from eastern (continental) Europe down to the Adriatic Sea and can blow with a speed of up to 100km/h, 60 mph.
* Foehn and Sirocco. Both transport air from the mediterrean northbound.

Notes on important rivers

In the process of writing this article it turned out that would bloat the article here, so I created a new category for each river. This text is already long enough and shall rather provide background information on river levels. So I will put the info on each river where it fits best, on the info page of each river. Please have a look at the rivers overview. Let me just mention one major are that companies cruise: The waterways of Belgium and the Netherlands include dozens of rivers and canals. A significant part of them is accessible for ocean going vessels, so there are designed for ships that are much bigger than the usual river cruise ship, which usually draws a maximum of 2 m / 6 ft and has a height of 6 m / 18 feet. Therefore the first sensor for the Rhine's gauge is at Emmerich, upstream of Arnhem.


As you see, it is impossible to know the situation one year ahead. That's why weather and river levels usually fall under the Force majeure clause of your contract. There are so many parameters, which can cause the river levels to rise or drop up to one meter / three feet per day. Most of the time everything is fine, but low water, high water or frozen canals can occur every time of the year (except for the frozen canals of course). Still, if you are preparing your cruise, the watershed map at the begin of this article gives you an idea for the area where you should keep track of the weather situation. You might want to check the list of rivers article for the water level data on a particular river at the moment.