**Assessing and Mitigating Ice-Jam Flood Hazards and Risks: A European Perspective**

**Karl-Erich Lindenschmidt 1,\* , Knut Alfredsen <sup>2</sup> , Dirk Carstensen <sup>3</sup> , Adam Chory ´nski <sup>4</sup> , David Gustafsson <sup>5</sup> , Michał Halicki <sup>6</sup> , Bernd Hentschel <sup>7</sup> , Niina Karjalainen <sup>8</sup> , Michael Kögel <sup>3</sup> , Tomasz Kolerski <sup>9</sup> , Marika Korna´s-Dynia <sup>10</sup>, Michał Kubicki <sup>11</sup>, Zbigniew W. Kundzewicz <sup>4</sup> , Cornelia Lauschke <sup>12</sup>, Albert Malinger <sup>13</sup> , Włodzimierz Marszelewski <sup>14</sup>, Fabian Möldner <sup>3</sup> , Barbro Näslund-Landenmark <sup>15</sup>, Tomasz Niedzielski <sup>6</sup> , Antti Parjanne <sup>16</sup>, Bogusław Pawłowski <sup>14</sup>, Iwona Pi ´nskwar <sup>4</sup> , Joanna Remisz <sup>6</sup> , Maik Renner <sup>17</sup> , Michael Roers <sup>17</sup>, Maksymilian Rybacki <sup>13</sup>, Ewelina Szałkiewicz <sup>13</sup> , Michał Szydłowski <sup>9</sup> , Grzegorz Walusiak <sup>6</sup> , Matylda Witek <sup>6</sup> , Mateusz Zagata <sup>18</sup> and Maciej Zdralewicz <sup>13</sup>**


**Abstract:** The assessment and mapping of riverine flood hazards and risks is recognized by many countries as an important tool for characterizing floods and developing flood management plans. Often, however, these management plans give attention primarily to open-water floods, with ice-jam floods being mostly an afterthought once these plans have been drafted. In some Nordic regions, ice-jam floods can be more severe than open-water floods, with floodwater levels of ice-jam floods often exceeding levels of open-water floods for the same return periods. Hence, it is imperative that flooding due to river ice processes be considered in flood management plans. This also pertains to European member states who are required to submit renewed flood management plans every six years to the European governance authorities. On 19 and 20 October 2022, a workshop entitled "Assessing and mitigating ice-jam flood hazard and risk" was hosted in Pozna´n, Poland to explore the necessity of incorporating ice-jam flood hazard and risk assessments in the European Union's Flood Directive. The presentations given at the workshop provided a good overview of flood risk assessments in Europe and how they may change due to the climate in the future. Perspectives from Norway, Sweden, Finland, Germany, and Poland were presented. Mitigation measures, particularly the artificial breakage of river ice covers and ice-jam flood forecasting, were shared. Advances in ice

**Citation:** Lindenschmidt, K.-E.; Alfredsen, K.; Carstensen, D.; Chory ´nski, A.; Gustafsson, D.; Halicki, M.; Hentschel, B.; Karjalainen, N.; Kögel, M.; Kolerski, T.; et al. Assessing and Mitigating Ice-Jam Flood Hazards and Risks: A European Perspective. *Water* **2023**, *15*, 76. https://doi.org/10.3390/ w15010076

Academic Editor: Olga Petrucci

Received: 30 November 2022 Revised: 14 December 2022 Accepted: 16 December 2022 Published: 26 December 2022

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

processes were also presented at the workshop, including state-of-the-art developments in tracking ice-floe velocities using particle tracking velocimetry, characterizing hanging dam ice, designing new ice-control structures, detecting, and monitoring river ice covers using composite imagery from both radar and optical satellite sensors, and calculating ice-jam flood hazards using a stochastic modelling approach.

**Keywords:** European Union's Floods Directive; hydro-electric power; ice-jam flood hazard; ice-jam flood risk; space-borne remote sensing

#### **1. Introduction**

On 19 and 20 October 2022, a workshop entitled "Assessing and mitigating ice-jam flood hazard and risk" was held in Pozna´n, Poland, hosted by the first author with sponsorship from the Global Water Futures research program (https://gwf.usask.ca/ accessed on 14 December 2022). The workshop brought together an international team of engineers, scientists, and officials from universities, research facilities, and government agencies from Europe to review the state-of-the-art developments of and explore advances in ice-jam flood hazard and risk assessments. Government agencies from central, eastern, and northern European countries (e.g., Norway, Sweden, Finland, Germany, and Poland) are in need of new tools to assess ice-jam hazards and risks in order to propose new means of mitigating consequences of ice jamming and ice-jam flooding to communities, infrastructure, and ship navigation. These are issues that will also help research and ice-flood management of rivers in other cold-region countries (e.g., U.S.A., Canada, and Russia) affected by river ice processes and ice flooding.

The Pozna´n workshop was opened by a welcome from Professor Klaudia Borowiak, the Dean of the Faculty of Environmental and Mechanical Engineering at the Pozna ´n University of Life Sciences. It ran over the course of two half days with numerous presentations, as listed in Table 1. Most of the participants are shown in the group photo in Figure 1. This workshop was a follow-up to the workshop entitled "Developing an ice-jam flood forecasting system for the Oder River" held in Wroclaw, Poland on 26 and 27 November 2018 [1]. The Pozna ´n workshop summarized in this commentary extends the capabilities of the ice-jam flood forecasting discussed in the Wroclaw workshop by to exploring methods and requirements for the assessment and mapping of ice-jam flood hazards and risks from a European perspective. An important question posed at the workshop was: should ice-jam flood hazard and risk assessment and mapping be explicitly mentioned in the EU Floods Directive, at least for members of Nordic countries and countries with continental climates? Comments from Norway, Sweden, Finland, Germany, and Poland are provided in the section "Potential of including ice-jam flood hazard and risk in the EU Floods Directive" below. The section is preceded by "Flood risk and the European Union's Floods Directive" and "Changes to flood risk and ice-jam flood risk due to future climate" to provide background information on the EU Floods Directive and to provide some context on how ice-jam flood risk may change with the climate in the future. Presentations that introduced measures to mitigate ice-jam flood risk and technical advances in ice research to help improve ice-jam flood risk characterization are also summarized in subsequent sections below. Remarks on the workshop outcomes and an outlook for future research themes related to ice-jam floods conclude the commentary.

The paper is structured to capture the topics presented at the workshop. Section 2 provides introductory material in the topic of flood risk and how it is administered in the EU Floods Directive. Section 3 provides a perspective of future flood risk in a changing climate. Perspectives from Norway, Sweden, Finland, Germany, and Poland of including ice-jam flood risk in the EU Floods Directive are provided in Section 4. Section 5 explores different techniques used to mitigate ice-jam risks, such as artificial breakage, flood warning systems, and ice-jam flood forecasting. Current technical advances in river ice research are showcased in Section 6, with topics on particle tracking velocimetry to monitor icejam covers, hanging dam characterization, design of ice-control structures, processing composite radar and optical space-borne remote sensing imagery for ice characterization, implementing air-borne remote sensing tools (drones) for ice-cover monitoring, and new modelling approaches in quantifying ice-jam flood hazards. Conclusions and an outlook are found at the end of the paper. and to provide some context on how ice-jam flood risk may change with the climate in the future. Presentations that introduced measures to mitigate ice-jam flood risk and technical advances in ice research to help improve ice-jam flood risk characterization are also summarized in subsequent sections below. Remarks on the workshop outcomes and an outlook for future research themes related to ice-jam floods conclude the commentary.

**Table 1.** Oral talks presented at the workshop. **Table 1.** Oral talks presented at the workshop.


*Water* **2022**, *14*, x FOR PEER REVIEW 3 of 23

**Figure 1.** Most of the participants of the workshop: 1. Cornelia Lauschke, 2. Maciej Zdralewicz, 3. Tomasz Kolerski, 4. Grzegorz Walusiak, 5. Maik Renner, 6. Joanna Remisz, 7. Michal Halicki, 8. Matylda Witek, 9. Dirk Carstensen, 10 Michal Kubicki, 11. Bogusław Pawłowski, 12. Michael Roers, 13. Karl-Erich Lindenschmidt, 14. Tomasz Niedzielski, 15. Michal Szydlowski, 16. Ewelina Szalkiewicz, 17. Wlodzimierz Marszelewski, 18. Iwona Pinskwar, 19. Maksymilian Rybacki, 20. Michael Kögel, 21. Zbigniew W. Kundzewicz, 22. Marika Kornas-Dynia, 23. Mateusz Zagata, and 24. Adam Chorynski (photo taken by Bogusław Pawłowski). **Figure 1.** Most of the participants of the workshop: 1. Cornelia Lauschke, 2. Maciej Zdralewicz, 3. Tomasz Kolerski, 4. Grzegorz Walusiak, 5. Maik Renner, 6. Joanna Remisz, 7. Michal Halicki, 8. Matylda Witek, 9. Dirk Carstensen, 10 Michal Kubicki, 11. Bogusław Pawłowski, 12. Michael Roers, 13. Karl-Erich Lindenschmidt, 14. Tomasz Niedzielski, 15. Michal Szydlowski, 16. Ewelina Szalkiewicz, 17. Wlodzimierz Marszelewski, 18. Iwona Pinskwar, 19. Maksymilian Rybacki, 20. Michael Kögel, 21. Zbigniew W. Kundzewicz, 22. Marika Kornas-Dynia, 23. Mateusz Zagata, and 24. Adam Chorynski (photo taken by Bogusław Pawłowski).

#### **2. Flood Risk and the European Union's Floods Directive 2. Flood Risk and the European Union's Floods Directive**

are found at the end of the paper.

*Water* **2022**, *14*, x FOR PEER REVIEW 4 of 23

According to the Intergovernmental Panel on Climate Change (IPCC), risk is defined as the potential for consequences where an object of value is at stake and where the outcome is uncertain. The components of such risks are hazards, exposure, and vulnerability. Referring to Figure 2, a hazard is the potential occurrence of a physical event that may cause adverse impacts. The "presence of people, livelihoods, species or ecosystems, environmental functions, services, and resources, infrastructure, or economic, social, or cultural assets in places and settings that could be adversely affected" [2] is referred to as exposure. Vulnerability can be understood as the "propensity or predisposition to be adversely affected" [2]. According to the Intergovernmental Panel on Climate Change (IPCC), risk is defined as the potential for consequences where an object of value is at stake and where the outcome is uncertain. The components of such risks are hazards, exposure, and vulnerability. Referring to Figure 2, a hazard is the potential occurrence of a physical event that may cause adverse impacts. The "presence of people, livelihoods, species or ecosystems, environmental functions, services, and resources, infrastructure, or economic, social, or cultural assets in places and settings that could be adversely affected" [2] is referred to as exposure. Vulnerability can be understood as the "propensity or predisposition to be adversely affected" [2].

The paper is structured to capture the topics presented at the workshop. Section 2 provides introductory material in the topic of flood risk and how it is administered in the EU Floods Directive. Section 3 provides a perspective of future flood risk in a changing climate. Perspectives from Norway, Sweden, Finland, Germany, and Poland of including ice-jam flood risk in the EU Floods Directive are provided in Section 4. Section 5 explores different techniques used to mitigate ice-jam risks, such as artificial breakage, flood warning systems, and ice-jam flood forecasting. Current technical advances in river ice research are showcased in Section 6, with topics on particle tracking velocimetry to monitor icejam covers, hanging dam characterization, design of ice-control structures, processing composite radar and optical space-borne remote sensing imagery for ice characterization, implementing air-borne remote sensing tools (drones) for ice-cover monitoring, and new modelling approaches in quantifying ice-jam flood hazards. Conclusions and an outlook

**Figure 2.** Components of flood risk [3]. **Figure 2.** Components of flood risk [3].

"*The purpose of [the European Union's Floods] Directive is to establish a framework for the assessment and management of flood risks, aiming at the reduction of the adverse consequences for human health, the environment, cultural heritage and economic activity associated with floods in the [European] Community.*" [4; Chapter 1, Article 1]. *"The purpose of [the European Union's Floods] Directive is to establish a framework for the assessment and management of flood risks, aiming at the reduction of the adverse consequences for human health, the environment, cultural heritage and economic activity associated with floods in the [European] Community."* [4]; Chapter 1, Article 1.

Implementation of the Floods Directive is on a six-year cycle with the European Union's member states required to follow three consecutive steps: (i) preliminary flood risk assessments, (ii) hazard maps and flood risk maps, and (iii) flood risk management plans (FRMP). The ultimate goal is to devise a FRMP for each member state to: Implementation of the Floods Directive is on a six-year cycle with the European Union's member states required to follow three consecutive steps: (i) preliminary flood risk assessments, (ii) hazard maps and flood risk maps, and (iii) flood risk management plans (FRMP). The ultimate goal is to devise a FRMP for each member state to:


#### **3. Changes to Flood Risk and Ice-Jam Flood Risk Due to the Future Climate**

Observational data show that extreme precipitation is becoming more extreme, nearly on a global scale [5]. Observed connections between heavy precipitation and air temperature broadly agree with the Clausius–Clapeyron law, foreseeing an increase in the vapor-holding capacity of the atmosphere at a rate of approximately 6–7% per 1 ◦C warm-

ing. This sensitivity may be much higher for precipitation on a subdaily scale, i.e., close to 14% per degree of warming for hourly precipitation [6,7].

However, this increase in extreme rainfall does not reflect higher discharges in rivers and decreases are observed at many stations. Globally, the number of stations with significant decreasing trends prevails over the number of stations with significant increasing trends [8].

In the future, along with the warming climate, atmospheric water vapor content is likely to increase, hence the potential for the occurrence of heavy precipitation is on the rise. According to Huo et al. [9], short-duration extreme precipitation may prevail over longduration extremes. Extreme precipitation events with intensity exceeding the infiltration capacity and the conveyance capacity of the system will very likely result in urban and flash floods of increasing frequency and magnitude. Strong increases in the frequencies of extreme precipitation events (from the 95th to the 99.97th percentile) based on an analysis of observations was presented by Myhre et al. [10]. The total precipitation from these intense events almost doubles per degree of warming, mainly due to changes in frequency. As shown by Hettiarachchi et al. [11] such extremely intense short-duration events will cause flooding in most areas.

The frequency and magnitude of fluvial (river) floods is expected to increase in many regions, but the statement that these kinds of floods are on the rise has not been substantiated. However, projections for the future indicate a greater increase in land areas where river floods become more frequent, compared to the fraction of areas for which fluvial floods will decrease.

At this time there is a lack of consistency between the trends observed in river discharges, which do not indicate an increase, and the model-based projections for the future, which show increasing trends. However, climate change has accelerated, and some changes may yet reveal themselves, so the change expected for the far future could be considerably different from the trend that is now observed [3].
