**1. Introduction**

In recent decades, the increase of human settlements and activities in coastal areas is causing a significant impact on the resilience of the world's coastal and marine natural capital. The coastal environment is a dynamic ecosystem where natural and anthropogenic processes add up and interact, modifying their geomorphological, physical, and biological characteristics. Coastal areas are also defined as ecotones, which are very important from an ecological point of view as they are a natural transition zone between two different and adjacent ecological systems.

The human pressures are different and include climate change, overfishing, offshore commerce, and land-based activities. The several pressures on the coastal ecosystem and the possible overlapping pressures can cause cumulative adverse effects [1–3]. Land-based stressors link coastal marine systems to terrestrial human activities and represent dominant stressors in coastal ecosystems [1, 4–6]. Nutrient and chemical pollution run-off create coastal eutrophication, harmful algae blooms, or hypoxic or anoxic dead zones [4, 6–8], and these impacts are able, not only to harm coastal species and ecosystems [9–11] but also affect human health [12, 13] and economic activities.

A few research is available, where the impacts of human wastewater on coastal ecosystems and community health [14–17] are assessed. The combined effects from multiple pressures are not still considered in management or planning processes and this reduces the overall resilience of marine ecosystems.

According to the Water Framework Directive [18], 93% of the European marine area is under different pressures from human activities and about 28% of its coastline is affected by pressures causing changes in hydrographic conditions, for example, in seawater movement, temperature, and salinity. According to the hydromorphological pressure assessments made in coastal waters, the main sources are atmospheric deposition and discharges from urban wastewater treatment plants on the coast, or further in the catchment area [14, 19–21].

Coastal developments modify natural hydrological conditions and impact habitats where the pressure at the catchment scale is the highest on the coastline of the Mediterranean Sea. Intense human activities in regions surrounding enclosed and semi-enclosed seas, such as the Mediterranean, always produce, a strong environmental impact causing increasing coastal and marine degradation, in the long term. The sustainable development in the Mediterranean area is influenced by diverse factors, such as i) the rapid growth of the urbanisation rate; ii) the increase in tourism; iii) the rapid development that determines the degradation of coastal areas; iv) water scarcity; and v) commercial activities. This condition highlights the need to define mitigation strategies, using timely and action-oriented information.

Due to its morphology, the Italian Peninsula can be divided into two main basins that can be considered semi-enclosed. The first includes the western Mediterranean, limited eastward by the Sicilian channel, and characterised by wide abyssal plains. The second, the eastern Mediterranean, dominated by the Mediterranean ridge system, is characterised by more complex morphology. In Italy, populated areas are mainly concentrated along with coastal areas than the rest of the territory; according to the Corine Land cover data [22], the Italian coast has a length of about 8300 km: more than the 9% of the littoral is now artificially bordered by works grazing the shore (3.7%), ports (3%) and partially superimposed structures on the coast (2.4%). The artificialisation of housing and transport structures in coastal areas is gradually increasing. It has been estimated that a relative increase of the 5% in the area 10 km away from the shore was generally recorded in European countries between 2000 and 2006 [23].

#### *Coastal Water Quality: Hydrometeorological Impact of River Overflow and High-resolution… DOI: http://dx.doi.org/10.5772/intechopen.104524*

The assessment of the sea and coastal systems and their interaction, based on scientific knowledge, are the indispensable basis for the management of human activities, in view of promoting the sustainable use of the seas and coasts and conserving marine ecosystems and their sustainable development.

In 1975, 16 Mediterranean states and the European Community under the auspices of the United Nations Environment Programme (UNEP) defined the Action Plan for the Mediterranean (MAP) [24, 25], aimed at protecting the environment and promoting sustainable development in the Mediterranean basin. The 19th Meeting of the Contracting Parties in 2016 agreed on the Integrated Monitoring and Evaluation Programme of the Mediterranean Sea and Coast and related evaluation criteria (IMAP) [26] which establishes the principles of integrated monitoring: for the first time, biodiversity and non-native species, pollution and marine, coastal, and hydrographic litter will be considered in an integrated way. The IMAP implementation defines 27 common indicators, foreseen in the Integrated Monitoring and Evaluation Programme, in line with the UNEP/MAP Barcelona Convention. The prediction and monitoring of water quality are among the main activities to be carried out for the protection of coastal ecosystems.

As for the prediction, water quality is strongly influenced by atmospheric events that could affect the pollution management systems, such as rainfall-dependent sewage drains and tributary river flow. For this reason, river mouths act as critical links between the hinterland and the sea. The prediction of river discharges and overflows using hydrometeorological models can be fundamental for indirect estimation of water quality, given that the drainage network runoff is closely related to the supply of marine nutrients, favouring algal proliferation and eutrophication phenomena. It also contributes to the increase in the concentration of faecal bacteria, such as *Escherichia coli* recognised as a faecal indicator organism in the European legislation, which contaminates marine bioindicators, such as bivalve molluscs. This condition has a relevant socio-economic impact; for example, it limits the consumption of bivalve molluscs collected from contaminated waters. The reductions in water quality after high precipitation events and the subsequent increase in river discharges lead local authorities to close shellfish harvesting areas after large events. But the inability of local authorities to accurately predict these events or to immediately assess the water quality exacerbates the losses of fishing economies.

From the above premises, it is clear that knowing the ecological status of water bodies is of critical importance to monitor how human activities are impacting or, the other way around, impacting by the coastal ecosystem. Monitoring coastal waters, indeed, is fundamental for both the evaluation of ecosystem health and as a support to local fishing economies, in terms of sustainability and site selection. Member States of the European Union are required, by the EU Marine Strategy Framework Directive [6] and the Water Framework Directive [18], to preserve territorial waters within the first nautical mile and achieve good ecological status. According to the European Environment Agency water assessment [20], only 46% of water bodies are actively monitored, 23% of monitoring did not include *in situ* water sampling and 4% still had unknown ecological status [27]. The proportion of water bodies without observation data is much larger than the ones for which monitoring is granted and for those monitored, in most cases, the status of surface waters was not classified as "good" [28]. Satellite observations offer a solution to the current limits shown by conventional water sampling methods—they allow to achieve much wider spatial and temporal coverage and larger water bodies. Remote mapping, therefore, is complementary to *in situ* sampling, both essential for supporting decisions on coastal aquaculture operations. It can also provide support in quantifying elements of environmental status that are currently not reported, such as phytoplankton blooms. In this context, the European Union together with the European Space Agency has boosted the development of the most advanced satellite-based instruments to observe optical water quality. Through the Copernicus framework, the spatial sector has had significant investment in recent years, and this enhances the cost-benefit of using satellite-based technologies for monitoring surface waters, also being satellite data freely available.

As for the environmental surveillance, coastal water status can be monitored by satellite high-resolution optical spectroradiometers, capable to retrieve suspended sediments or algae presence, at spatial resolutions of up to 10 meters [23, 29].
