Models to characterize pollution sources to delimit bathing areas
Pollutants have serious impacts on the quality of bathing waters. Therefore, it is necessary to identify the sources of pollution and the receiving coastal zones, taking into account that the entire drainage basin could be the possible source of pollution for the connected bathing areas.
According to the different land use included in the drainage basin, i.e. agriculture, industry, urban settlements, the pollution sources can be of different typology and intensity.
To these other sources of pollution are to add because located in the coastal areas such as discharges of wastewater disposal networks or related to infrastructures near bathing waters like power plants or port basins.
Except for the sources near the coastal zones, bathing waters quality is closely associated to the water quality of the hydrographic network.
In compliance with the Directive 76/160, local periodical surveys repeated on the condition of fresh flowing waters at their source and of the surrounding environment together with stagnant fresh waters and seawater to define the geographical, topographic profile, the volume and nature of all pollutant discharges and their effects according to their distance from the afferent bathing areas.
Water restoring plans established by the Legislative Decree 152/99 have the main goal of restoring water ecosystems through managing water resources by preventing and reducing possible impacts on the water environment. This concept of risks prevention underpins the Bathing Directive EC/2006/7.
Point sources of pollution, such as domestic or industrial discharges, are easy to identify and control, but also diffuse pollution sources can have strong contamination effects on streams. In some agricultural areas, for instance, the use of fertilizers and pesticides causes water pollution due to run-off and leaching. Therefore, it is possible to verify the diffusion of the bacterial charge form the surrounding environment to the river through phenomena of surface, sub-surface, deep flow.
Generally, it is defined point pollution source that source related to a well identifiable or definable area. Diffuse sources are linked to an indirect pollution that originates from different sources related to the diverse typologies of land use. Therefore, the correlation between pollution extent and land use is clearly acknowledged.
If, from one side, it is quite simple to discriminate point sources from diffuse sources by observing their geometrical and physical features, on the other side it is not possible to subdivide and classify them clearly, when the focus passes to the identification of the sources affecting the quality of bathing waters.
As an example, the run-off process of surfaces, both in urban and rural areas, is to be included within the diffuse sources of pollution. However, the receiving body (for instance a river) carries the pollutant contribution to its terminal section (the mouth), transforming this diffuse source into a point source, or a considerably reduced source.
If it is considered the urban area (or rural) directly connected to bathing waters, the diffuse pollution source does not change, because there is not the hydraulic downstream effect of water disposal (i.e. hydrographic network).
Considering the difficulty of classifying uniquely a source as point or diffuse, it is suggested the adoption of land use models enabling the evaluation of the pollution loads originated by multiple factors (economic social, climatic, hydrological conditions) that vary spatially and temporally starting from the input data (e.g. geological, hydrological, on water quality) collected through monitoring activities and mathematical models.
This synergy between different typologies of modelling instruments for the study of the hydrological-hydraulic component and of the marine coastal component, to validate with in-situ observations, improves the knowledge of the ecosystem and of the correlation among determining factors, pressures, and impacts on bathing waters.