After the fire in the chemical plant at Sandoz near Basel in 1986 during which great amounts of fire fighting water contaminated with chemicals flowed into the Rhine, the 7th Conference of Rhine Ministers charged the ICPR to elaborate a Rhine Alarm Model in collaboration with the Commission for the Hydrology of the Rhine watershed (CHR) for the Rhine and its main tributaries. After sudden discharges of pollutants, this model is able to calculate the development of the wave of pollutants and, since the Sandoz accident and during numerous further sudden pollutions, it has proven to be an indispensable instrument within the international Warn- and Alarm Plan (WAP) Rhine.
Within the WAP, reliable predictions of sudden pollutant waves are extremely important for a timely implementation of required measures at the right time. Among such measures are stopping the intake of raw water by drinking water works or having the fire brigade or civil protection put up oil barriers in the Rhine or its tributaries. The flow time model for the Rhine is used by the international main warning centres, the national warning centres, the warning centres of the German Länder and the institutions consulting these centres (e.g. operators of monitoring stations) and the drinking water works to predict the substance distribution of a sudden water pollution event.
The flow time model for the Rhine is a model of the Rhine from Lake Constance to the North Sea. Apart from the main stream, the tributaries Aare (draining the major part of Switzerland), Neckar, Main and Moselle are mathematically modelled. Model calibration was carried through with particular pigments (tracer) not harming aquatic organisms which were discharged into the Rhine and are measurable in very low concentrations. When required, place, time and amount of pollution, substance breakdown, floatability of substances (e.g. oils, gasoil, petrol), discharge and/or water levels serve as model input.
The model will then calculate the concentration of a substance for the observed river location depending on time, the time of the peak of the pollutant wave at the location observed and the development of the pollutant wave from the discharge location to the North Sea. This model can predict not only the development of a pollutant wave downstream but the spreading of a pollutant cloud over the width of the river. For selected periods of time (in general one day), this model is able to calculate where the wave will be in the watershed. If required, an animation may demonstrate the development of the pollutant wave from the discharge location until the North Sea. The development of the pollutant wave can be predicted with about 98 % reliability.
The flow time model for the Rhine served as a basis when developing similar models for the Danube and the Meuse.
Preparations are currently underway for a new or updated Rhine flow time model, which should be available by 2027.