PREDICTIONS OF EVENT-BASED PESTICIDE FLUX AT THE CATCHMENT SCALE: A MODEL EVALUATION EXERCISE

摘要

The modelling of water flow and pesticide transfer at the catchment scale for individual rainfall events represents a valuable approach to ⅰ) bring added value to water fluxes collected within the context of monitoring activities, ⅱ) optimise monitoring strategies and, ⅲ) evaluate hydrological and pesticide fate models. Very few pesticide fate models have been developed for application at the catchment scale. In the present study we assumed a conservative behaviour of pesticides and focused on the modelling of water flow across a 40-ha French catchment using the modified GR5 model. The replicability of sensitivity and uncertainty analyses was investigated by varying, the number of model runs and the goodness-of-fit index. Results from the analyses were found to be replicable for the four parameters which have the largest influence on flow predictions. The work suggested that the goodness-of-fit index 'Nashrac' is the most appropriate indicator amongst the three which were investigated. The use of Nashrac led to uncertainty intervals which comprised the observed water flows. The overall shape of the pesticide flux curve was adequately reproduced although observations were occasionally outside the uncertainty interval. Overall, it is felt that the GR5 modified model has the potential to support the design of sampling strategies for water and pesticide fluxes at the catchment scale.