Free Flow

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ransboundary

ater

anagement

onwards, pluvial elements prevail. Now the highest

run-off occurs in February, the lowest in September.

Past achievements

The Rhine Alarm model was developed with ICPR. It

was initiated by the Rhine Ministers conference after

the Sandoz accident in 1986 and accepted during

the 8th Conference of Rhine Ministers. Participating

institutes are the Federal Office for the Environment

in Bern (Switzerland), the Service de la Navigation in

Strasbourg (France), the Federal Institute of Hydrology

(BfG)in Koblenz, the Albert-Ludwigs-University of

Freiburg in Germany and Dutch organizations such as

Rijkswaterstaat in Lelystad and the Technical University

and Deltares in Delft.

The Rhine Alarm model delivers effective forecasts

at various alarm stations in cases of strong water pollu-

tion in the catchment. Forecasts of the travel time and

distribution of harmful substances are highly impor-

tant for all water users such as water boards and water

supply companies, in order to implement the necessary

measures in time.

The model covers the Rhine River from Lake

Constance to the North Sea, including the main tribu-

taries such as the Aar, Neckar, Main and Moselle. Input

to the model calculations includes the location and

conditions of the initial pollution, decomposition and

drift capacity of the harmful substances, discharges and/

or water levels, geometry and dispersion. Calibration of

the model was done by tracer tests. The model calcu-

lates, the concentration as a function of time as well as

the point of time and scope of the maximum concen-

tration for every alarm station along the Rhine. The

forecasts of progress time and concentrations are accu-

rate to about 89 per cent and 95 per cent respectively.

The knowledge of the Rhine Alarm model was incor-

porated into the set-up of the model for the Danube

River. For the Danube model a cross-flow of the pollu-

tion module has been implemented which is also

included in the latest version of the Rhine Alarm model.

So, what has started with a catastrophe in the past has

resulted in a well-implemented alarm model which

helps ensure better, timely reaction in urgent situations.

Knowledge exchange with other river basins (South

America to the Rio Bermejo) in Argentina took place

through a twinning project, with a site-mission and a

symposium held in 2007.

CHR’s counterpart was the

Binational Commission for the Development of the

Bermejo River Basin (COBINABE) in Argentina. During

the field visit the sediment problems in the upper part and

middle reach of the Bermejo river basin were addressed.

The basin of the Rio Bermejo has various types of

climates, with precipitation ranging from 200 mm/year

to over 2,000 mm/year within a few dozen kilometres.

Population density is quite low in terms of central

European countries. Main traffic routes are constructed

along the river stretches and are prone to natural hazard

activities. Soil loss and adequate land use is a major

problem for local populations in the river basin. Traffic

well-founded prognoses can only be made if the processes in the river

system are understood. This, in turn, requires a thorough knowledge of

the historical development of hydrological parameters. Therefore, CHR

has undertaken a detailed analysis of changes in the run-off regimes of

the Rhine and its tributaries in the twentieth century and their potential

causes: natural climate fluctuations, anthropogenic climate change and

direct human interventions such as river regulations and embankments,

barrage weirs, reservoirs, water transfers and changes in land use.

Run-off regime

The flow of a watercourse, whether it is a small brook or large river,

strongly depends on the amount of precipitation in the catchment.

The water volume that is not lost to evaporation or plant transpira-

tion eventually runs off; fluctuations in run-off are controlled by the

temporal distribution of precipitation and evaporation. If precipita-

tion falls as snow, it is released with a time delay when melting or

stored as ice in glaciers for even longer periods of time. In a nutshell,

‘run-off regime’ means the intra-annual run-off of a stream that can

be regularly expected.

The major tributaries in Germany (Neckar, Main and Moselle)

consistently show a pluvial regime. Due to the distribution of rain-

fall and the seasonal differences in evaporation intensity, mean

run-off reaches its maximum in the winter months and its minimum

in August and September. As the river proceeds, the run-off regime

of the Rhine reflects the natural and man-made impacts resulting

from its gradual catchment expansion. In the process, none of the

joining tributaries succeeds in imposing its own regime character

on it – but the plethora of feeding rivers downstream increases the

complexity of the run-off regime in the Rhine.

Owing to the dominant alpine influence, the Basel Rhine gauge

shows a typical nival regime that is superimposed by tributaries with a

pluvial character further downstream. As these tributaries bear signifi-

cantly less water than the Rhine, the basic nival character of the Rhine

regime continues to exist up to the confluence with the Main river.

Not until reaching the Middle Rhine do the rivers Main and Moselle

eventually cause major changes. From the Andernach gauging station

Restoration of gravel banks of the Thur River, a tributary of the Rhine in Switzerland

Image: CHR