Preliminary Flood Risk Assessment
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PRELIMINARY FLOOD RISK ASSESSMENT Final Report May 2013 P a g e | 1 Contents 1. Introduction .......................................................................................................................................... 4 1.1 The Role of a Preliminary Flood Risk Assessment ....................................................................... 4 1.2 Structure of this report ................................................................................................................ 6 2. The Malta Water Catchment District ................................................................................................... 7 2.1 Geology ....................................................................................................................................... 10 2.2 Geomorphology .......................................................................................................................... 13 2.3 Land-use ...................................................................................................................................... 15 2.4 Climate ........................................................................................................................................ 16 2.5 Hydrogeology ............................................................................................................................. 17 2.6 Surface waters ............................................................................................................................ 20 2.7 Existing flood defence structures .............................................................................................. 20 3. Sources of Flooding ............................................................................................................................ 21 3.1 Flooding from Rivers .................................................................................................................. 21 3.2 Rainfall Flooding ......................................................................................................................... 21 3.3 Flooding from the sea ................................................................................................................ 22 3.4 Flooding from groundwater ....................................................................................................... 23 3.5 Flooding from infrastructural failure ......................................................................................... 23 4. Flooding History ................................................................................................................................. 24 4.1 Rainfall Flooding ......................................................................................................................... 25 4.2 Flooding from the sea ................................................................................................................ 30 5. Future Flooding .................................................................................................................................. 31 5.1 Future flood risk ......................................................................................................................... 31 5.2 Future Flooding and Climate Change ......................................................................................... 36 5.3 Significant Flood Risk Areas ....................................................................................................... 36 6. Summary and Conclusions ................................................................................................................. 38 7. References .......................................................................................................................................... 40 P a g e | 2 List of Figures Figure 1: The Malta River Basin District ........................................................................................................ 8 Figure 2: The catchment areas in the Malta River Basin District .................................................................. 9 Figure 3: The Geology of the Maltese Islands ............................................................................................. 12 Figure 4: Topography of the Maltese Islands ............................................................................................. 14 Figure 5: Land use in the Maltese Islands ................................................................................................... 16 Figure 6: Distribution of precipitation based on an average annual rainfall of 550mm ............................ 18 Figure 7: The main aquifers in the Maltese Islands .................................................................................... 19 Figure 8: Catchments that have experienced previous pluvial flooding .................................................... 24 List of Tables Table 1: Typical lithology, thickness and hydrological characteristics of Maltese Formations .................. 11 Table 2: Average rainfall depth (Malta Airport MetOffice for the climate period 1961-1990) .................. 17 Table 3: Past flood events ........................................................................................................................... 28 Table 5: Estimated number of people and properties within the catchment areas covered by the NFRP 35 P a g e | 3 1. Introduction In the Floods Directive floods are defined as the temporary covering by water of land not normally covered by water. This term is a generic term to include floods from rivers, mountain torrents, Mediterranean ephemeral water courses, and floods from the sea in coastal areas, and may exclude floods from sewerage systems. Floods occur when the natural or man-made channels are unable to carry all the water, leading to rising water flows that flow over the banks and flood the surrounding dry land. Malta does not have any natural surface water bodies. The physical characteristics of the island together with the uneven distribution of rainfall do not allow for the formation of natural surface water bodies. Malta however does have a number of dry valley systems that are dry throughout most of the year. These dry valley systems act as a conveyance channel for the surface water that accumulates as a result of a rainfall event. Water flows along the valley bed for only a couple of hours as this is quickly discharged into the sea. As a result of this rapid discharge of water into the sea, there is no accumulation of water flow within the valley channel and no water flows over the valley channel and onto the surrounding dry land. Along the years, some of these dry valley systems have been built-up and the valley channel incorporated into the main roads. This results in water flowing through the main roads once the valley channel is reactivated following a rainfall event. This has led to the general public perceiving the reactivation of the valley channel as a flood event whereas in reality this is the natural mechanism by which surface water flow is conveyed along the valley bed. 1.1 The Role of a Preliminary Flood Risk Assessment Floods have been recognised as potentially undermining Europe’s drive towards sustainable development with the adverse effects they have on the economy. Directive 2007/60/EC on the assessment and management of flood risks (European Floods Directive) aims to manage the P a g e | 4 risks that floods pose to human health, the environment, cultural heritage and economic activity. This directive was transposed as the Assessment and Management of Flood Risks Regulations (L.N. 264 of 2010). Article 4 of the Floods Directive requires all Member States to undertake a Preliminary Flood Risk Assessment (PFRA) for each river basin district, unit of management of the portion of an international river basin district or unit of management lying within their territory. The objective of the PFRA is to identify areas where the risks associated with flooding might be significant. Following the completion of the PFRA, Article 5 requires member states to identify areas for which significant flood risks exist (APSFR).The identification of floodable areas is not due under Article 4, but under Article 6 of the Directive, through the production of the flood hazard and flood risk maps for all areas identified as APSFR. Areas with a significant flood risk will then be assessed further to develop measures to manage and reduce the flood risk through the creation of a flood risk management plan. The identification of areas with potential significant flood risk has to be based on available or readily derivable information adhering to the requirements specified in the directive (Article 4). The Directive gives no definition for the term ‘significant’ therefore each Member State has the flexibility to determine which areas are considered to have a significant flood risk potential within a national context. In accordance with the requirements of the directive, the assessment presented in this report has considered all types of flooding, including natural sources, such as that which can occur from rivers, the sea and estuaries, heavy rain and groundwater, and the failure of built infrastructures. It has also considered the impacts that flooding can have on people, property, business, the environment and cultural heritage. P a g e | 5 1.2 Structure of this report The report is structured as follows, to ensure that all the requirements of Article 4 are met: • An