Modelling of intertidal floodplains for enhanced estuarine transport and decay of faecal indicator organisms from a diffuse source

The noncompliance of microbiological quality to the standards of the EU Water Framework Directive at shellfish harvesting waters in the UK has become a serious threat to human health. The infected filter-feeding shellfish by enteric bacteria or viruses from these waters is major to the spreading of foodborne diseases as humans consumed them raw or undercooked. Although the quality of effluents from the wastewater treatment works has been improved significantly, diffuse source of pathogens from urban and agricultural settings remained as the reason to the microbiological noncompliance. The exploitation of natural wetlands along with poor management practices at catchments delivered the overloading of faecal contaminants from sources into the receiving water. In this study, a developed hydro-environmental model is novel in contributing to the understanding of the microbial behaviour on the implicit response to the complex estuarine environment from the perspective of their morphological characteristics. Besides, the extended modelling domain at intertidal floodplains is novel in contributing to the representation of the tidal creek connectivity with the sub-mesh scale design based on the hydrological characteristic of the complex floodplain topography. Furthermore, the modelled of FIO transport and decay from intertidal marshlands is novel in contributing to the inclusion of the diffuse source with the integration to the release-kinetic model and based on an active source at the wetting and drying boundary. The hydrodynamic calibration at several sites resulted in an optimum Manning’s n of 0.025. The successful integration between the bathymetric and topographic data at intertidal floodplains resulted in a significant improvement for the tidal circulation within the study area. The sensitivity analysis on the diffusive transport has suggested the decrease in the tracer diffusivity with the increase in the mesh resolution, with the concentration gradient has increased with the decrease of the former parameter. The sensitivity analysis on the bottom roughness has suggested the increase in the tracer retention at floodplains with the increase in the roughness during low tides, with the concentration in subtidal channels was less sensitive to the roughness changes during high tides. The sensitivity analysis on the microbial kinetic has suggested that MS2 coliphage experienced the biphasic decay in the estuarine environment, with the T90 value ranged at 1 hour and from 50 to 125 hours for the first and second components decay respectively. The sensitivity analysis on the FIOs transport from the diffuse ii source has suggested the increase in the spreading area and the flush-out mass with the decrease i