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Understanding transport through the water system
Hydrological modelling was used to investigate how contamination can move through the surface-water network. For the Aa of Weerijs case, travel times were calculated between an upstream hypothetical contamination source and locations up to 14 km downstream. The simulations showed that travel times vary considerably throughout the year because of changing hydrological conditions. The model compared these travel times with a microbial decay timescale. During periods when contaminated water travels quickly through the system, microorganisms may reach downstream irrigation locations before substantial decay has occurred. The results therefore show that distance alone is not enough to assess microbial risk: hydrological conditions determine how rapidly contamination actually reaches downstream users.
Figuur: Hydrological model output for the Aa of Weerijs case study. The figure shows travel times from a fictive upstream contamination source to downstream locations at 7, 10, 11 and 14 km. Where the travel-time curves fall below the T99 line (6 days), E. coli-contaminated water can reach the irrigation intake before substantial decay has occurred.
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