Assessment of Flooding Impact on Water Supply Systems: A Comprehensive Approach Based on DSS

Abstract

The assessment of flood impact on a Water Supply System (WSS) requires a comprehensive approach including several scales of analysis and models and should be managed in the Water Safety Plans (WSP), as recommended in the EU Water Directive 2020/2184. Flooding can affect the quality of groundwater and surface water resources and can cause supply service interruption due to damaged infrastructures. A complete approach to address flood impact on WSS is required but not yet available, while only specific aspects were investigated in details. This work introduces a comprehensive tool named WAter Safety Planning Procedures Decision Support System (WASPP–DSS) developed in the context of MUHA (Multihazard framework for Water Related risks management) project. The tool is mainly addressed to small water utilities (WU) for supporting WSP development and is based on two main premises: 1) a correct approach for WSS risk analysis requires a multi-hazard perspective encompassing all the system components and different hazards; 2) other institutions in addition to WUs have to be involved in WSS risk analyses to harmonize monitoring and response procedures. The tool is here applied on risks associated to flooding and demonstrated for three case studies. The WASPP–DSS, tested by eight WUs, was found a potentially valid support for small WUs that must start drafting the WSP in a comprehensive way and can provide a common shared scheme. Improvements are desirable, as including a specific section to consider the issue of loss of water resources from reservoirs due to overflow.

Impact of Flooding and Drought Risks on the Cost of Bond Financing for Water Utilities

“…28 For example, floods might damage or render inoperable infrastructure, necessitating expensive repairs or interrupt water sales. 48 On the other hand, droughts might require the purchase of water at higher prices, significant investment in drought-resistant technologies or protection from saltwater infiltration in source waters. In addition to the impact on asset value, these hazards also increase the uncertainty and volatility of cash flows, further influencing bond yields.…”

“…To investigate the observed premium, we employ the Merton pricing model to decompose this premium into two components: a reduction in water utility asset valuation (typically based on the net present value of discounted future cash flows), and an increase in the volatility of these cash flows (detailed in Supporting Information D). For example, floods might damage or render inoperable infrastructure, necessitating expensive repairs or interrupt water sales . On the other hand, droughts might require the purchase of water at higher prices, significant investment in drought-resistant technologies or protection from saltwater infiltration in source waters.…”

Natural hazard risk analysis in the framework of water safety plans

“…The WASPP-DSS (the reader can refer to Barbetta et al (2022) and Romano et al (2022) for a detailed description of the tool) allows for a first analysis aimed at ranking the hazards and related risks impacting a given WSS. Having a shared scheme of analysis may boost comparison among different WSPs, promoting collaboration among WUs acting in close territories or, in some cases, having interconnections.…”