Abstract
Many source water protection regulations simply define protection zones according to fixed geographical distances. A more precise approach would be to estimate water travel times from any point in the watershed to the drinking water intake, using a hydrological model in which watershed characteristics and hydrological regimes (dry, rainy) are taken into account. Is a data-intensive and, therefore, more precise approach really better than a simple geographical-based approach for source water protection? The aim of this paper is to present a methodology to compare a geographical-based approach for delimiting water source protection areas with a Soil and Water Assessment Tool (SWAT) hydrological model-based approach in terms of water travel times within a watershed. The watershed of the water treatment plant (WTP) in Quebec City (Canada) was used as a case study. Results reveal that implementing a geographical-based approach might be adequate to protect water intakes against non-point sources of contamination. However, in the event of point source contamination, the simpler approach is less appropriate, especially in a drought situation. SWAT results for four subwatersheds studied indicated that WTP operators would have less than 30 h to react to a point-source contamination event during a median rainy week and from 10 h to about 4 days during a dry week. The geographical-based approach, however, was unable to determine the effects of weather events on water travel times. The use of a hydrological-based model is, thus, more useful for the implementation of an emergency plan, based on weather events. • Characteristics of a watershed (area, land use, slopes and river length) and hydrological scenarios influence water travel times. • Delimiting a protection zone, a set distance from a water intake, can protect it against non-point sources of contamination. • Using a modelling approach allows the study of a wide range of technical and management scenarios that can be used to develop warning systems.
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