Is there a need for hydrological modelling in decision support systems for nuclear emergencies

Full text: Potential releases from nuclear installations may contaminate both the terrestrial and the aquatic environment. Significant dose contributions via the aquatic pathways were shown for releases from Oak Ridge Laboratory (on the Clinch River-Tennessee River basin), for releases from the 'Mayak' plant (on the Techa River - Ob River system) and finally for releases from Chernobyl (on the Dnieper River basin and on the Scandinavian lake system via atmospheric fallout). Of highest concern was the contamination of drinking water, as the public is very sensitive to the quality of this essential nutrient. Consumption of aquatic food products and contamination of terrestrial crops via irrigation are potential exposure pathways which have to be considered in addition in case of a contamination of the aquatic environment. National hydrological services were, among others, responsible for the surveillance of the national water ways. This includes also monitoring of radioactive substances on a routine basis. Besides taking measurements at various locations, models might be available to predict the water discharge and to some extend also the concentration of pollutants in some of the most important river systems. Therefore, one can argue that these services, as they are part of the emergency management team in case of a nuclear emergency, should be able to support decision making to the extend necessary. However, the advice from the hydrological services might be limited to the analysis of the present situation including only limited prediction capabilities mainly focusing on the behaviour of radionuclides in the main river systems in relation to the preduction of drinking water. Contrary to this, a complete hydrological model chain has been established in the RODOS system, covering all relevant processes from the runoff from contaminated areas, transport in river systems and reservoirs, behaviour of radionuclides in lakes and finally the modelling of coastal areas. To this purpose simulation programs of different complexity, ranging from compartmental approaches up to 3-D computer models, have been developed and integrated into the RODOS system. They consider the water transport and also the transport and dispersion of radionuclides in the three phases, dissolved, bound on suspended particles and bound on bottom depositions. Results of this model chain are further processed in the aquatic food chain and dose module and can build the basis for some simple countermeasure strategy modelling. Countermeasures at present considered are mainly liming of lakes and restriction of food consumption. More complex measures such as dam building were up to now not introduced in the hydrological model chain. This paper discusses the advantages and disadvantages of the two approaches and highlights also the limits of the support which can be provided by a national hydrological Service. National arrangements in the Netherlands, Ukraine, and Germany will be considered as examples. Some ideas will be presented which may lead to a closer co-operation between national hydrological services and hydrological models implemented in decision support systems. (author)