Flooding at Karlshamnsverket

Master Thesis TVVR 19/5011

Analysis and Recommendations

______Daniel Wirtz

Division of Water Resources Engineering

Department of Building and Environmental Technology Lund University

Flooding at Karlshamnsverket

Analysis and Recommendations

By: Daniel Wirtz

Source: Mynewsdesk (2019)

Master Thesis

Division of Water Resources Engineering Department of Building & Environmental Technology Lund University Box 118 221 00 Lund, Sweden

Water Resources Engineering TVVR-19/5011 ISSN 1101–9824

Lund 2019 www.tvrl.lth.se

Master Thesis Division of Water Resources Engineering Department of Building & Environmental Technology Lund University

Title: Flooding at Karlshamnsverket - Analysis and Recommendations Author: Daniel Wirtz Supervisor: Magnus Larson Assistant supervisors: Bo Martinsson & Johan Thomsson Examiner: Rolf Larsson Language English Year: 2019 Keywords: Karlshamnsverket, Blekinge, flooding, drainage pipe system, mitigation measures, extreme value analysis

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Acknowledgements

This work would not have been possible without the help of a large number of persons. Thus, i would like to thank: My father and my mother for always supporting and believing in me. My supervisor, Prof. Dr. Magnus Larson, for his guidance and advices throughout the thesis project, around the clock when needed. Without his invaluable support and input this study would not have been half as good. My assistant supervisor, Bo Martinsson, for his patience, support and essential inputs throughout the thesis project, providing me with whichever information I needed about the area as long as it was available. Everybody at Karlshamnsverket, notably: • The employees in the maintenance department for their continuous support, may it be help when i needed it, additional information or working material. Special thanks are given to Henrik Pagels for enabling me to do this master thesis and to Johan Thomsson for his organizational guidance, as well as to Benny Thuresson for his help with the pipe systems investigation. • The employees in the laboratory for helping me out with Conductivity and pH measurements. • The employees in the operation department for helping me whenever needed, especially Torbjörn Ericson for providing me with groundwater data and information about the rock caverns. Caroline Hallin and Johanna Sörensen at the Department of Water Resources Engineering, Lund University, for guiding me through necessary statistics and deepening my understanding of coastal processes. Jan-Erik Rosberg at the Department of Technical Geology, Lund University, for his guidance concerning the construction of boreholes, as well as Gerhard Barmen for his insights in groundwater questions. Additionally, I would like to thank Peter Jonsson and Conny Svensson for their additional input concerning specific questions I had. Per Nyström, visiting lecturer at the Department of Biology, Lund University, for identifying a frog and clarifying at which salt concentrations it can survive. Per Johan Gustafsson, Professor at the Department of Construction Sciences, Lund University, for his advice on determining the instability of fill. iii iv

Abstract

Karlshamnsverket is a power plant located at the Baltic Sea in southern Sweden. Due to the coastal location this important infrastructure already experienced flooding in its basement in the past. The objective of this study is to conduct an initial analysis to determine the underlying reasons for the flooding and to provide suitable measures to increase the resilience of the power plant, also with regards to the future. For that reason, an initial analysis of sea water levels and rainfall data was performed and altered for a prospective climate scenario. Further information was gathered from measurements, original construction documents and literature to obtain a better understanding of the hydro(geo- )logical situation in the area. Based on this information suggestions were developed. Recommendations also include a maintenance plan for the drainage pipe system, developed after international standards. Flooding in the basement mostly stems from the stormwater pipe system, which is susceptible to high water levels in the surge basins and downpour events. Flooding is to be expected frequently and thus it is recommended to alter the current pipe system layout. Significant surface flooding of the power plant area, that constitutes a fill made of friction soil and blast rock, is unlikely. Most of the fill surface is located 265 cm above mean sea level, while the highest water level to be expected is 233 cm in the year 2100. Sea water is instead thought to enter the fill through a permeable seawall, which needs to be confirmed by constructing observation wells.

Sammanfattning

Karlshamnsverket är ett kraftverk som ligger vid Östersjön i södra Sverige. På grund av placeringen vid kusten har denna viktiga infrastruktur redan tidigare varit utsatt för översvämningar i källaren. Syftet med föreliggande studie är att genomföra en första analys för att fastställa de bakomliggande orsakerna till översvämningarna och att föreslå lämpliga åtgärder för att öka kraftverkets motståndskraft, även när det gäller framtida förändringar i olika påverkansfaktorer. Av den anledningen utfördes en första analys av havsvattennivåer och nederbördsdata med hänsyn till möjliga förändringar vid olika framtida klimatscenario. Bakgrundsinformation samlades in från mätningar, ursprungliga konstruktionsdokument och litteratur för att få en bättre förståelse för den hydro(geo-)logiska situationen i området. Baserat på denna information utvecklades förslag till åtgärder. Dessa rekommendationer inkluderar också en underhållsplan för dräneringssystemet, utvecklat efter internationella standarder. Översvämningarna i källaren härrör mestadels från dagvattensystemet i samband med skyfall; detta system påverkas också av höga vattennivåer i svallbassängerna som i sin tur bestäms av havsvattennivån. Översvämningar kan förväntas ske oftare i framtiden och därför rekommenderas det att ändra den aktuella layouten av rörsystemet. Betydande översvämning av kraftverkets område, som utgör en fyllnad av friktionsjord och sprängsten, är osannolik. Det mesta av fyllningsytan ligger 265 cm över medelvattenytan, medan den högsta vattennivån som kan förväntas är 233 cm år 2100. Havsvattnet antas istället komma in i fyllnaden genom en permeabel jordvall, vilket dock måste bekräftas genom att konstruera observationsbrunnar och genomföra mätningar.

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Table of contents

Acknowledgements ...... iii Abstract ...... v Sammanfattning...... vii Table of contents ...... ix 1. Introduction ...... 1 1.1 Background and Problem Formulation ...... 1 1.2 Goals and objectives ...... 3 1.3 Limitations...... 3 2. Methodology ...... 5 2.1 Literature Study ...... 5 2.2 Review of available site documentation ...... 5 2.3 Data compilation and analysis ...... 5 2.4 Field measurements and tests ...... 6 2.4.1 Field measurements and inspections ...... 6 2.4.2 Tracer test ...... 6 3. Overview over the power plant ...... 9 3.1 General ...... 9 3.2 Description of the power plant ...... 10 3.3 Description of the basement ...... 12 3.4 Flooding problem ...... 15 4. Drainage systems for near-coastal large-scale installations ...... 19 4.1 Coastal flooding and landward inflow ...... 19 4.2 Evaluating and coping with flooding and inflow ...... 21 4.2.1 Evaluation ...... 21 4.2.2 Coping with flooding...... 22 4.3 Construction and Maintenance of drainage systems ...... 22 4.3.1 Construction of near coastal drainage systems...... 22 ix

4.3.2 Maintenance of drainage system ...... 23 5. Study area ...... 27 5.1 Geography ...... 27 5.2 Topography ...... 27 5.3 Geology ...... 28 5.3.1 Bedrock ...... 28 5.3.2 Fracture Systems and bedrock properties ...... 29 5.3.3 Depth to bedrock ...... 30 5.3.4 Soil...... 30 5.3.5 Geological and geotechnical investigations ...... 32 5.4 Excavation and Fill ...... 33 5.4.1 Excavation ...... 33 5.4.2 Basement construction ...... 34 5.4.3 Fill in the power plant area ...... 35 5.4.4 Seawalls ...... 36 6. Sea Level Variation ...... 39 6.1 General ...... 39 6.1.1 Introduction to sea level variation ...... 39 6.1.2 Land uplift and future sea level rise ...... 40 6.2 Data series and basic properties ...... 42 6.3 Statistical analysis and extreme events ...... 43 6.3.1 Theoretical aspects ...... 43 6.3.2 Extreme sea levels ...... 46 6.3.3 Duration ...... 48 6.4 Implications ...... 50 6.4.1 Power plant ...... 51 6.4.2 Gas turbine plant ...... 52 7. Precipitation and runoff ...... 53 7.1 General ...... 53 7.2 Data series and basic properties ...... 54 x

7.3 Statistical analysis and extreme events ...... 56 7.3.1 Correlation analysis ...... 56 7.3.2 Extreme rainfall ...... 57 7.3.3 Runoff ...... 59 7.4 Implications ...... 61 7.4.1 Power plant ...... 61 7.4.2 Gas turbine plant ...... 62 7.4.3 Runoff ...... 63 8. Groundwater ...... 65 8.1 General ...... 65 8.2 Data series properties ...... 65 8.2.1 Limitations ...... 65 8.2.2 Measuring Procedure ...... 66 8.3 Analysis ...... 66 9. Field Measurements ...... 71 9.1 Introduction ...... 71 9.2 Water levels in the basement ...... 72 9.2.1 Methodology ...... 72 9.2.2 Results ...... 72 9.3 Conductivity ...... 74 9.3.1 Introduction ...... 74 9.3.2 Methodology ...... 75 9.3.3 Limitations...... 76 9.3.4 Findings ...... 77 9.4 Conclusions ...... 79 10. Suggestion for measures ...... 80 10.1 Measures for the fill area ...... 80 10.2 Measures for the basement ...... 82 10.2.1 Long-term measures ...... 82 10.2.2 Quick fix solutions and urgent measures ...... 83 xi

11. Discussion and Outlook...... 85 12. Conclusions ...... 86 References ...... 89 Appendices ...... 94 A1: Sea level extremes ...... 94 A2: Precipitation extremes ...... 96 A3: Groundwater levels...... 97 A4: Field Measurements ...... 98 A5: General bearing capacity equation (Per Johan Gustafsson, Personal Communication): ...... 100 A6: Soil definitions ...... 102

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1. Introduction Residential areas, important infrastructure and habitats in coastal regions around the world are more or less at risk of being flooded due to extreme high sea water levels today and even more so in the near future due to the prognosed sea-level rise (IPCC, 2014). To decrease this risk several protective measures can be taken into consideration, albeit they should fit the area to be protected. As a design and consideration basis for these measures usually extreme sea water levels and wave conditions are combined (Fredriksson et al., 2016), although the latter can be omitted if the area is sheltered and no large waves were observed in the past. Coastal regions are furthermore susceptible to high rainfall and groundwater tables. Generally, more rain tends to fall in coastal areas than in inland areas (Hill et al., 2010), although it is influenced by the local topography (Länsstyrelsen Blekinge län, 2012). The rainwater then either flows overland or infiltrates into the ground and flows as groundwater towards the coast and into the sea. Further, as groundwater is less saline and thus has a lower density then seawater it floats above it (Fetter, 2000). This leads to high groundwater tables in coastal areas. Flooding of coastal infrastructure can occur as a result of only one of these three factors or due to their combined action and needs to be thoroughly analysed so that appropriate actions can be taken.

1.1 Background and Problem Formulation Karlshamnsverket is an important oil-driven reserve power station near Karlshamn, Sweden, located at the Baltic Sea. Thus, it is prone to high sea water levels that have led to substantial flooding of the power plant basement, located at a height of 0.3 m above mean sea level (msl), in the past (Jönsson and Marcusson, 2008). The basement contains important pipe systems and electrical cables essential for the operability of the power plant and thus any flooding should be avoided. Additionally, rainwater enters the basement through a storm water pipe system which might not function as designed. It is projected that the mean water level in Baltic Sea increases at a rate higher than today over the next decades (Luoma & Okkonen, 2004), which increases also the risk of flooding of the basement. In addition, there is a projected increase in local precipitation, as well as storm intensity and duration (Länsstyrelsen Blekinge län, 2012).

This makes it important to find fast implementable solutions to the flooding problems and related issues, such as potential ground instability in some parts of the area and uncertainty in the effectiveness of drainage pipes, in order to avoid even higher expenses in the future to overcome these problems. A Master thesis study was conducted in 2008 regarding the flooding problems at Karlshamnsverket, delineating the areas with the highest risk of flooding. This study has already proposed some solutions (Jönsson & Marcusson, 2008). In Figure 1 the situation before the construction of Karlshamnsverket is depicted. It shows that where the power plant stands today the Kölö strait was located. Already in the year 1923 it was possible to cross this strait and access the island of Kölön by means of a bridge that connected it to the Stärnö peninsula outside Karlshamn. This bridge, that was constructed on top of a dam made of an impermeable soil core, has been incorporated into the later fill area by backfilling the entire strait up to 2.65 m above msl with excavated material from the construction site.

Figure 1: Map of Karlshamn and surroundings approximately in the year 1923 with the area of Karlshamnsverket before construction marked in red and coastal areas in shaded grey. Changed after: Lind (2019). 2

1.2 Goals and objectives The goal of this study is to help determine the speed and principle direction of the unwanted water flow into the area of the power station and the basement. This requires the development of suitable measurement methods to map the flow pattern and magnitude. In conjunction with this, worldwide procedures of maintaining drainage systems are investigated that are applicable to the present situation at Karlshamnsverket. An additional objective is to investigate available information on the properties of the sediment fill, which dominates most of the area, to possibly determine the risk of instability when it is subject to flooding. Furthermore, by examining available sea level, precipitation, and groundwater data and extrapolating the data properties to describe conditions considering a changing climate, it should be possible to obtain a clearer picture of the hydro(geo-)logical situation in the area. As such, the impact of flooding in the near future can be estimated, which enables to develop suitable countermeasures.

1.3 Limitations This study was conducted over a period of a few months. As such an in-depth investigation was not possible. Rather, this report is to be regarded as an initial study that has to be followed by additional research as described in chapter 11. Discussion and Outlook. One example is the determination of water inflows into the area and their velocity. Recommendations to determine these are given in the report, but the research itself was not possible to be fully conducted. The same applies to the possibility of instability of the fill when it is subject to high water tables. Here, insufficient data is available to receive a realistic result from which actions could be derived. Instead, the report focusses more on the determination of water inflows into the basement. Also, several parts of the power plant layout still remain unclear and were not able to be determined, both because of inaccessibility and due to missing technical drawings. Additionally, it cannot be out ruled that significant changes have been made from the original design drawings that have been used as an assessment basis in this report. The analysis of sea water level was moreover limited to 50, 100 and 200-year events today, as well as in the years 2050 and 2100. Events that statistically happen less than once in 200 years could lead to worse flooding than 3 discussed here. Similarly, the rainfall analysis was only conducted with a maximum 20-year event due to a shorter data record being available. Also, the quoted estimates for the future sea level rise and future rainfall might be either under or overestimating the future conditions. Both datasets are also to be regarded with some reservations due to their properties as described in chapters 6. Sea Level Variation and 7. Precipitation and runoff. An analysis of wind strength and wave heights was omitted in this study due to time concerns and the proposedly low risk for large waves and thus wave overtopping of the seawalls. This is due to the relatively sheltered position of the power plant, as seen in Figure 1. The largest possible waves would require the wind to be coming from 186-193° South, which is a small corridor starting around 250 km away in the German-Polish border region. Lastly, climate change and its underlying factors are not discussed in this study. Instead, only some estimates as calculated by other studies are utilized here to determine possible future impacts on the power plant.

2. Methodology This chapter briefly describes the methodology that was followed throughout the project. A more thorough description of the methodology can be found at the beginning of most chapters.

2.1 Literature Study First, a literature study was conducted to compile existing knowledge on landward inflows to coastal areas, measures that can be taken to control these flows and the typical design and maintenance of drainage systems for near- coastal buildings and infrastructure.

2.2 Review of available site documentation A total of 20 folders of information were investigated to gain an understanding of how the buildings had been constructed and how the preparatory work was conducted. As these folders contained confidential information a separate discussion of these findings is not possible. Some information, however, was included throughout the text after an approval by company representatives.

2.3 Data compilation and analysis Data compilation and analysis was conducted for sea water level data, rainfall data and groundwater data. While the latter was provided by the company, freely available sea water level data and rainfall data have been downloaded from the Swedish Meteorological and Hydrological Institute (SMHI) website. Information about the data and its properties are noted in the respective chapters 6.2 Data series and basic properties, 7.2 Data series and basic properties and 8.2 Data series properties. The raw data that was used can be found in Appendices A1, A2 and A3. Categorial data on bedrock and soil properties was also compiled using the Swedish Geological Survey (SGU) map database (SGU, 2019a). Information has been further visualized by using ESRI’s ArcGIS Desktop 10.5.1 and Autodesk’s AutoCAD 2018.2, as well as the online service SCALGO Live. Analysis of numerical data was conducted by using the programmes Microsoft Excel, as well as R 3.5.3 (R Core Team, 2019) within RStudio 1.2.1335 with the package extRemes 2.0 (Gilleland & Katz, 2016) and in2extRemes (Gilleland & Katz, 2013).

2.4 Field measurements and tests 2.4.1 Field measurements and inspections As it became apparent that available data was not sufficient enough to determine the water inflows into the basement, a 6 weeklong study of water levels and conductivities was conducted in conjunction with a closer investigation of the basement (see Appendix A4). Measurements were made in three drainage wells, as well as one point each influenced by the storm water pipe system or cooling water system. These points were chosen due to their relative ease of access, their diversity within the pipe systems and their location. The number was limited to due to time concerns, as one round of measurements takes around 35 minutes. Additionally, after realizing that desalinated process water is emptied into the surge basins, also in this point conductivities were measured on an irregular basis. This would add another 10 minutes to one measurement round.

2.4.2 Tracer test 2.4.2.1 Introduction It was tested whether a fluorescent tracer can be applied in the present pipe systems in order to determine breakages or leaks in them and to see how the pipes are connected, as well as to determine the flow velocity in them. For this test, the pH of the water was determined first. This is due to the dependence of most fluorescent tracers on pH and temperature (Jones, 2012). The subsequent laboratory test for two samples, one from the surge basin and one from the storm water pipe system, yielded a pH of 7.3 and 7.8, which is almost neutral.

Thus, PyraGreen™, Pyranin with 120% intensity, was able to be applied in this test. It has the colour index 59040, otherwise known as Solvent Green 7, and the chemical formula C16H7Na3O10S3. Other dyes are also available on the market, of which the most common ones are listed in Jones (2012). For this particular area, however, only one other (fluorescent) dye is recommendable: Sodium Fluorescein, otherwise also known as Uranine, with the colour index 45350 (Acid Yellow 73). This is because both Pyranine and Uranine are, amongst others, not toxic to the environment, colorize the water, are relatively stable, detectable at low concentrations and not common in the environment. 2.4.2.2 Procedure

A simplified test with the tracer was conducted on a day without precipitation in the storm water system of block 3, using about 30 ml of fluorescent dye solution. This had a long-lasting colouring effect over several hours. Moreover, the tracer visualized the interaction between the surge basin and the storm water system by showing the water flow patterns into and out of the pipes. Figure 2: Stormwater access well during the Following the water flow with tracer test, displaying sediment transport. open hatches it took about 15 minutes for water in the southernmost access well in Block 3 to first flow into the surge basin. It was only after 45 minutes, however, that the dye spread out in the surge basin until it was not visible anymore. An additional observation was that about half an hour after adding the dye as a point source it was diluted enough to lose its strong green colour and instead displayed the sediment transport with a yellowish tint. Hence, tracer tests can also be applied here to determine if a lot of sediment is in the system (see Figure 2). 2.4.2.3 Recommendations Based on the experience the tracer should be added to the system by using a dosage pump or lower quantities than 30 mL When buying an additional tracer in powder form the amount should be controlled by diluting it in water first before adding it to the pipe system that is to be tested. Excessive usage should be avoided in any case to avert the alarming of government agencies and also due to economic reasons. An initial estimate of tracer quantities can be calculated by formulas provided in Field (2003), but generally the quantity of tracer to be used depends on two factors: One factor is the amount of water to be coloured, as smaller pipe systems with smaller quantities of water require less tracer than larger pipe systems. Another factor is the reason why the tracer test is applied, as this influences the choice of the methodology and the amount of work required. Jones (2012) distinguishes two types of tests with tracers: 7

Qualitative testing Qualitative testing can be used to determine whether pipe sections are connected. Several small packets with activated carbon granules are normally used during a qualitative test to capture the dye and analyse it in the laboratory (Jones, 2012). Compared to monitoring by eye this has the advantage that maintenance employees are able to do other tasks in the meantime and that less tracer can be used. This method also requires less tracer dye than quantitative testing. Quantitative testing Quantitative tests include the sampling of water in short intervals and analysis of the samples by a fluorometer. As a fluorometer is available in the local laboratory such a test could also be applied at Karlshamnsverket. The large advantage of quantitative tracing is that it is suitable to determine the flow velocity by analysing the tracer concentration over time (Jones, 2012). However, it requires automatic water samplers at different wells that collect water in glass bottles in intervals of a few minutes over a day and is thus more expensive and labour intensive. When manual or simplified testing is done all wells should be opened, and another person should stand by to be able to follow the tracer. A sample should be taken before the tracer test to allow for a comparable background fluorescence in relation to a sample with tracer. As such, background data is already available if one of the two above testing methods is followed later. For all tracer tests, the tracer should be introduced upstream so that it can flow according to gravitational flow. If testing is planned to be done in dry wells a tank trunk with trained contractors is required as then the amount of tracer needs to be adjusted.

3. Overview over the power plant 3.1 General Karlshamnsverket is an oil powered peak load and reserve power plant operated by Sydkraft Thermal Power Aktiebolag (AB) within the multinational parent company Uniper SE. In such a function the power plant is used to secure the supply of electricity. Thus, it is in operation when the main producers of electricity in Sweden, namely hydro, nuclear and wind power, cannot produce enough electricity, are undergoing maintenance or experience any other type of disruption, i.e. due to the lack of wind or water. Within one to two hours it can then be started and feeds a maximum capacity of around 662 MW into the national powerlines (Uniper, 2019). Additionally, it is used to smooth peak loads and to increase the transmission capacity when electricity is transported throughout Sweden or to other countries (Jönsson & Marcusson, 2008). Its location can be seen in Figure 3.

Figure 3: The location of Karlshamnsverket in the Karlshamn greater area and in Sweden. Changed after: TUBS (2012), Sveriges Radio (2012), Mynewsdesk (2019). Planned in the year 1956, block 1 first produced electricity in 1969 when demand for electricity was greater than the supply in Sweden (Uniper, 2019). In 1971 block 2 and in 1973 block 3 were taken into operation so that over 4 TWh were able to be produced just a year later. After 1974, however, the nuclear power capacity in Sweden was increased, while also the price for oil increased, making the power plant less profitable and less important. 9

This ultimately led to the shutdown of Block 1 in the year 2015 and a reduction in capacity from 1000 MW to 662 MW. Today, of three independent turbine blocks mostly just block 3 is operated. This is due to its advanced exhaust gas cleaning process using a desulphurisation plant, an electric filter and a catalysator (Uniper, 2019), enabling the plant to operate even with strict environmental laws in place.

3.2 Description of the power plant This chapter describes only those parts of the power plant which are discussed throughout the text. For a more complete description (in Swedish) Jönsson & Marcusson (2008) is recommended, who also describe how electricity is generated in this power plant. As discussed in chapter 5, the power plant is located in an area that was backfilled and is surrounded by two seawalls that are at minimum designed to avoid fill material to be dispersed into the sea. In Figure 4 the original design of the seawalls, which encompass the fill area, have been drawn in yellow. It is unknown if after construction this design was fulfilled in extent, but if it did it shows a significant erosion of the southern dam by weather and wave action. In comparison, the much more sheltered northern dike nearly fits the design. A detailed discussion of the dams can be found in chapter 5.4. In blue the cut and fill line during the basement construction has been marked. It denotes the border between the excavation of bedrock down to 0.15 m to the right of the line and fill up to 0.15 m to the left of the line. Thus, it gives an indication what kind of ground can be found under the basement floor.

Figure 4: Satellite image of Karlshamnsverket with the cut and fill line in blue and the dams in yellow, as well as discussed parts of the power plant. Additionally, in Figure 4, parts of the power plant have been marked with numbers, which are shortly described in the following: 1 - Turbine hall. Here the three turbines, one per block, are located. 2 - Boiler house of block 1; the respective transformer is denoted as 2a. 3 - Boiler house of block 2; the respective transformer is denoted as 3a. 4 - Boiler house of block 3; the respective transformer is denoted as 4a. These building parts, with the exception of the transformers, have a basement which is further described in the next subchapter 3.3.

5 - two of a total seven small daily service oil fuel tanks. These have been founded in the fill. Thus, one concern is that they are instable, especially when the water level in the fill rises, i.e. due to seeping sea water. This is discussed in chapter 5.4. 6 - Oil separator plant. Here the oil is separated from the oil-contaminated water (OFA) before the water is led into the oil dam. It is part of the OFA pipe system. 7 - Oil dam. Any other contamination is supposed to sediment here before the clean water is discharged into the Baltic sea. It is part of the OFA pipe system. 8 - Gas turbine plant. It is not officially part of Karlshamnsverket but was included in the analysis upon request.

3.3 Description of the basement Depicted in Figure 6 is the basement of the power plant, outlined in brown. It also features several pipe systems that partially extend outside of the basement. The figure was created in AutoCAD by combining several technical drawings and adding own observations. The basement is located approximately at a height of 0.3 m above msl (see Figure 5) and hosts diverse electrical and data cables, as well as important technical infrastructure which requires the basement to be dry. For this reason, a drainage system, drawn in green, was constructed. Additionally, a storm water pipe system, drawn in blue, is also running below the basement.

Figure 5: East-West Sections through the basements of blocks 1 and 3. Block 1 is completely founded on bedrock while half of block 3 is founded on fill.

Figure 6: Basement of the power plant with relevant pipe systems and connected objects. Rain/Storm water combined means here Drainage and Rainwater pipe systems being combined outside of the basement. In Figure 6 it can be seen that every block has its independent drainage system that is designed to be leading into two collection wells, each. From there water is transported by means of one pump per block into the nearest surge basin, drawn in magenta, via a pipe. In blocks 2 and 3 this pipe is further equipped with a check valve that stops water from flowing back into the collection wells. Additionally, presumably drainage water flows to one other pump sump per block where the water is pumped into the OFA pipe system. However, it is unclear how the drainage systems and the respective pump sump are connected and thus the pipes are drawn in red. Furthermore, the pump sumps could instead be connected to the storm water system since in some technical drawings they are denoted as collection wells for this type of water. Another observation that was made on site concerning the drainage system comprises changes of the drainage system layout that have not been marked in the technical drawings. As such, a pipe has been added that leads drainage water under the office building, located to the left of block 1 in Figure 6. Also, the well denoted as point 3 has been increased in height so that it can store more water than the identical wells in blocks 1 and 2. The drainage system is theoretically accessible by 19 wells in block 1, 12 wells in block 2 and 20 wells in block 3. In practice, however, most access 13 wells are located under or behind several stacked cable ladders and cannot be opened. Further, the drainage mostly consists of two horizontally parallel 4” clay pipes, which have open joints. An example of such a pipe is shown in Figure 7, but it is unclear if this layout is representable for the whole basement. 6” single concrete pipes have also been used extensively, while 2” galvanized steel pipes have only been used for a Figure 7: Installed drainage pipes few locations. For example, in block 1 made of clay and with open joints. 170 m double clay pipes, 70 m single agricultural concrete pipes and 10 m galvanized steel pipes have been laid. Concerning the storm water pipe system there is one main pipeline that is thought to be continuously leading throughout the entire turbine hall in a NNE-SSW direction. It is only interrupted by five access wells, of which one each is located in blocks 1 & 2. The other three access wells are located in block 3. In blocks 1 and 2 the main pipeline consists of concrete pipes which are 500 mm in diameter and are held together by rubber ring joints. Then, the diameter decreases to 400 mm between the access well in block 2 and the first access well in block 3 and continues with 300 mm pipes throughout the rest of block 3 until the pipeline presumably ends in the filled area. Judging from the technical design drawings the storm water, coming both from the northern and eastern parts of the power plant, is designed to flow via Figure 8: Stormwater pipe access a 800 mm diameter concrete pipe into well. To the right and ahead rainwater the surge basin of block 1 (Figure 8). enters the basement, to the left it flows From the western power plant area into the surge basin of block 1. another 800 mm pipe enters the surge basin from the opposite side. In block 3 the storm water main pipe is instead coupled to the surge basin via a 400 mm

14 diameter pipe and another 500 mm diameter pipe leads storm water from west of the power plant into the surge basin. This flow direction is however not always the case, as discussed in chapter 9. Additionally, three downspouts per block are directly connected to the main storm water pipe to lead rainwater from the roof. These are galvanized steel pipes that have been moulded to the concrete main pipe and are one reason for the flooding of the basement (see chapter 3.4). The inflow and outflow tunnels used to transport cooling water to and from the power plant have also been included in Figure 6 and are drawn in yellow. They are located at a depth ranging from -12 to -22 m under the msl where the power plant is located above (see Figure 9). Both tunnels are not directly connected, as first the water has to be pumped above the msl so that it can be used in Figure 9: Section through the surge the power generation process. After that basin, restricted orifice and outflow the water is emptied into the two surge tunnel in block 1. Heights in meters basins from which the water flows out under mean sea level (msl). into the Baltic sea. The surge basins and the outflow tunnel are further connected by a restricted orifice, as depicted in Figure 9. This is used prominently in hydropower plants to avoid water hammers, assure a steady flow to the turbines and to achieve maximum friction losses to alleviate any excess pressures (Ramadan & Mustafa, 2013). In the case of Karlshamnsverket it was instead constructed to buffer the hydrologic effects when the discharge of the used process water stops.

3.4 Flooding problem Upon starting the project, an incident list was created where water related problems have been observed in the basement. In the following, each problem, that was not examined in Chapter 9, is thoroughly described and probable causes are named. Possible solutions and suitable recommendations to all flooding related problems are named in Chapter 11. 1 - Pipes with electrical cables to operate the fine particle cleaning plant

In the northernmost outer wall of the basement two holes were made to lead electrical cables from outside into the basement. These lead through a series of specifically built access wells to the fine particle cleaning plant which strips the incoming sea water from unwanted particles. Deviating from the design drawing, a weir has been constructed that presumably was built to assure the operability of the cleaning plant even during high sea water levels. However, this water then enters into the first cable well and then cascades down Figure 10: Water flowing into the until it flows into the basement, as basement through cable pipes during depicted in Figure 10. January 2, 2019. 2 - Rainwater pipes from the turbine hall roof

As can be seen in Figure 11, cast iron downspouts were constructed vertically from the roof down to the basement level at +0.3 msl. There, they were casted, by means of asphalt sealant, on a concrete pipe that leads into the storm water main at a -5° angle relative to the ground. The problem here is the cast, which probably hasn’t been executed correctly or has become broken. Thus, when the sea water level is high, water flows from the surge basin into the storm water system and rises in the main pipe until it also flows contrary to the design into these rainwater pipes and exits the pipe when it reaches the cast. Figure 11: Downspout made of cast iron connected to a concrete pipe. Rust indicates that water stands or stood in the pipe.

3 - Storm water pipe system Along the whole length of the storm water main the mostly grey ground is often green, which either indicates that water stood over the surface there or that the ground was wet or still is wet. This must then mean that pipes are leaking. Thus, either pipes sections are broken, which could have happened if the filling material was compressed too much, or the rubber ring joints are in a bad shape, either due to fatigue or due to the brackish sea water. Additionally, sedimentation was found in one of the access wells, as can be seen in the Figure 12, to block most of the flow. Also, what will be discussed more in detail in chapter 9, water movements from the surge basin translate even to the wells that are located upstream (see Figure 12). This provides evidence that the surge basin and storm water pipe system are linked even at the low sea water levels observed.

Figure 12: left: sedimentation in an access well for the storm water pipe system, middle: water movement in an access well for the storm water pipe system on a dry day, right: water movement in a rainwater well outside of the basement on a dry day. 4 - Animals

Although not directly a problem, a symptom of the basement being flooded is the attraction of unwanted animals like the common toad (Bufo bufo), as depicted in Figure 13, and fishes, especially the common roach (Rutilus rutilus). They find their way into the basement most probably through the storm water pipe system. Both species are tolerating variable salt concentrations (Per Nystrom; personal Figure 13: Common toad (Bufo communication) that are to be found in the bufo) in the basement of block 3. local pipe systems (see Chapter 9).

5 - Surge basin gate to block 4

In preparation for the - never constructed - block 4, a gate has been placed in the southern side of the surge basin of block 3 (see Figure 14). It is in a bad shape, but it is yet unclear what is situated behind the gate and whether water leaks from the surge basin into the fill area or not.

Figure 14: Closed gate in the surge basin of block 3, viewed from above. 6 - Leaking pipes

Throughout the basement several waterpipes are leaking, either because they have cracks, or because the joints are no longer tight. The leaking effect can best be seen in Figure 15 where the pipe that leads drainage water from block 2 into the surge basin of block 1 is depicted. Instead of flowing into the surge basin, a lot of water flows down the surge Figure 15: Leaking pipe that should lead basin wall and is collected by the drainage water from block 2 into the surge drainage system of block 1, putting basin of block 1. additional strain on that system.

Besides these problems it is to be noted that water marks can be observed up to 20 cm above the ground in the basement.

4. Drainage systems for near-coastal large-scale installations 4.1 Coastal flooding and landward inflow Around the world several examples exist of power plants that are situated in the vicinity of the coastline and which were impacted by extreme sea water levels and/or downpour events (i.e. Wang et al., 2019; Pisharady et al., 2015; Lacerda et al., 2014). Examples in the vicinity of Karlshamn include the almost closure of the Loviisa Nuclear Power Plant in Finland in January 2005, as seawater levels were extremely high at the cooling water outflow tunnel exit (Geological Survey of Finland, 2006). Further, the Gdynia Heat and Power Station suffered from flooding of its basement which required the reconstruction of the whole drainage pipe system (Uponor, 2016). Besides extreme sea levels or rainfall, also other phenomena can lead to flooding in coastal areas, such as wave action and high groundwater tables (ASN, 2013). More possible flood sources are displayed in Figure 16.

Figure 16: Possible sources for flooding at Karlshamnsverket. Especially groundwater plays an important role in landward inflows. As will be explained in chapter 5, groundwater flow in crystalline bedrock is limited to fractures. In coastal environments this leads to limited amounts of inflowing sea water during normal sea levels (see Figure 17). Due to the density differences between fresh groundwater and seawater, groundwater flows on top of sea water. Since groundwater flows into the sea and sea water tends to flow inland, an interface between both types of water is existent near the coastline where both forces cancel out. Also, in fill the saltwater interface is not located far inland, as the fill acts as an aquifer where 19 groundwater is stored in larger quantities than before filling (Guo & Jiao, 2007).

Figure 17: Model of saltwater intrusion in a fractured crystalline aquifer. Source: Lorentz (2005). Due to sea level rise there will be a higher pressure from the sea, leading to increased inflow of sea water landwards. This forces the groundwater upwards and, in the worst case, leads to flooding besides sea water inundation (see Figure 18). It is to be noted though, that the groundwater level change because of sea level rise is generally thought to be slow (Masterson et al., 2013).

Figure 18: Sea level rise is expected to lead to both surface flooding and increase in groundwater that itself leads to flooding. Source: Masterson et al. (2013). 20

4.2 Evaluating and coping with flooding and inflow 4.2.1 Evaluation Several approaches are available in literature to evaluate flooding and related problems. For example, guides from several authorities are available, of which specifically ASN (2013) is recommended for further reading. Wang et al. (2019) describe the setup of a model to simulate flooding scenarios based on wave overtopping and downpour events and quote even more examples to model several other flooding scenarios. Pisharady et al. (2015) state a methodology to analyse the probabilities of certain events and their influence on the safety of a power plant. That methodology is more detailed than the one applied in this report since it, amongst others, involves the development of fault trees and assessing how much flooding is tolerable. This type of analysis could be done by the employees at Karlshamnsverket, since they should be familiar with the water related fragilities of the electrical, mechanical, data and communication systems in the basement. As a result, it could be determined up to which flood water level in the basement it is safe to operate the plant (Pisharady et al., 2015). It is defined here as that water level where damage to critical equipment inside the basement begins. If flooding is considered non-critical to the structural integrity of the building it can be thought of elevating equipment or floodproofing (FEMA, 2013) so that the power plant can even operate at higher flood water levels. It is considered more effective, though, to avoid flooding of the basement in the first place and large scale floodproofing is not recommended locally. Evaluation of basement flooding risk When a building has a basement near a body of water and is located in fill the risk of being flooded is significantly greater in relation to other foundations. Thus, it is not advisable to construct basements in such environments, especially when it is located below the expected extreme level elevation of that water body (FEMA, 2001). If a basement is still built, several aspects need to be considered to determine the flooding risk. Generally speaking, the risk of flooding decreases with an increase in basement height and increase in distance from a body of water. Additionally, it is recommended that fill surrounding the basement walls has a low conductivity and that a drainage layer is placed outside the building, 21 away from the basement walls (FEMA, 2001) to reduce the flooding risk. If this was not done the flooding risk is significantly greater. Basement walls and floors have further to be evaluated whether they can cope with crushing pressures and buoyant forces during flooding and/or high groundwater tables (FEMA, 2013), as well as with seepage of water. These forces can be determined according to formulas in literature, i.e. FEMA (2001, 2013). 4.2.2 Coping with flooding Based on the results gained from an analysis or evaluation of the most probable reasons of flooding, solutions can be developed. Most often these include structural measures at the shoreline, such as building a seawall or protecting existing slopes (Lacerda et al., 2013). As a second line of protection, a drainage system is usually installed to avoid flooding near buildings. It is to be noted, though, that even structures that were designed and built according to best practice were observed to have problems with the drainage system during an extreme event (ASCE, 2015). Flooding can even happen during an average event when the drainage is blocked (IAEA, 2011). When the drainage is not functioning as designed or if the design flow is exceeded due to a changing climate, recurring damage is also to be expected (FEMA, 2007). Thus, great care needs to be taken when designing, constructing or maintaining a drainage system (ASCE, 2013). If these protection measures fail pumping is often utilized, especially in basements. It is to be regarded as a last option, though, as especially rapid pumping can lead to the collapse of basement walls (FEMA, 2001) and create higher costs than maintaining a drainage system.

4.3 Construction and Maintenance of drainage systems 4.3.1 Construction of near coastal drainage systems It is recommended to lead rainwater away from structures that are located near the coast (IAEA, 2011). This is achieved by constructing a drainage/storm water pipe system outside the infrastructure, that is to be protected from e.g. extreme rainfall, and leading the runoff away from it. For instance, at the new Hong Kong International Site culverts were constructed in the fill and through the seawalls, so that this water can enter the sea (Plant & Hughes, 1998).

4.3.2 Maintenance of drainage system This chapter compiles existing procedures for maintaining a drainage system. These were obtained from the American Society of Civil Engineers (ASCE, 2013) standard and ASN (2013) unless quoted otherwise and which were adjusted and expanded to local conditions using own observations. Background Maintaining drainage systems is regularly overlooked as most parts of these systems are under the surface and thus not visible, but also because they are developed to sustain up to 100 years. Deterioration of the system hence progresses moderately and may only be identified years after the initial incident. From an economical viewpoint it is, however, cheaper to implement a preventive maintenance routine instead of reconstructing the system after a serious failure, also known as corrective maintenance, and should be the preferred option. Furthermore, flow capacity minimization is common over long time periods. To keep the original design flow, a maintenance plan has to be established that includes cleaning, checking on the structural integrity of the system and avoid soil to enter the pipe system. This requires regular scheduled inspections of the whole pipe system to determine the need for maintenance. Employees All employees should be trained to have a basic understanding of the local drainage system and its components above and under the surface as to recognize deviations from normal operation as soon as possible. Qualified employees shall be appointed to be responsible for the maintenance tasks or training of suitable employees ought to be provided. Security Local health safety security environment (HSSE) schemes must be followed by maintenance employees, as well as other safety measures that are in place for other maintenance tasks at the power plant. Some special precautions ought to be taken additionally, such as ventilation of closed rooms, like manholes, before entering them. Even then caution is advised as deadly gases like methane may be produced by decay of organic material or may be created by maintenance work. Also, fast flow conditions can persist, making it important that employees is secured by means of a safety harness and safety west, as well as lighting, when entering a manhole.

When working on one of the pumps its valves must be closed and should preferably not be in operation. Only limited repair or lubrication as outlined in the manufacturer maintenance manual is tolerable when it is in operation. Maintenance plan A power plant wide system for reporting and registering flooding incidents should be established. This includes noting the date, time, sea water level height as measured at Karlshamn harbour and the flooding height in the basement in the five observation points as denoted in chapter 9, as well as other affected parts of the basement. Also, a thorough maintenance plan shall be developed and implemented. The plan should be divided at least by turbine block and include all system components, that is pipes, trenches, maintenance wells and their construction type. Maintenance documentation provided by manufacturers of the drainage system parts, if found in the company archive, should be consulted and included in the maintenance plan. It should also include a checklist for manholes and pipes, that is to be completed on a scheduled basis. This checklist should have enough space to note possible damages and whether the system has a restricted capacity. If repair is needed it should be reported in the already implemented intranet maintenance system and discussed in the weekly meeting. Also, keeping a record of the conducted inspections and repairs is important to comprehend the current system status, making it important to keep the original inspection documents in the company archive. Yearly inspection and maintenance A general system inspection and maintenance is recommended to be executed minimum once per year by a min. of two people (Pisharady et al., 2015). The optimum time for it would be sometime in summer when the sea water level is low, and the power plant is not in operation. More frequent or intensive inspections and maintenance might be necessary for some parts of the system and should be scheduled as knowledge about the pipe system is acquired. For example, in the beginning the pipe system should be cleaned from debris once a year. This has to be adjusted with growing knowledge through observations. Normal operation inspection If the pipe system is working as designed only scheduled inspection is required. Inspections are important to work out the persisting system status and any developing problems. Typically, during a regular inspection the following should be conducted:

• Controlling the wells inside and outside the power plant for sediment or other material that does not belong in the system, as well as for damages. This includes gutter wells, infiltration wells and manholes. • Controlling the pipes inside and outside the power plant for sediment or other material that does not belong in the system, as well as for damages, by means of a television camera for pipe systems. Damages could be cracks and misalignments for example. • Controlling connected structures, such as culverts, gutters and ditches for sediment or other material that does not belong in the system, as well as for damages. • Check ground surfaces for leakage of water. Usually this indicated by a green surface, topsoil saturation or vegetation. • Evaluation of the inlet areas for soil erosion that leads to sedimentation in the upstream wells. Planting grass can significantly reduce this erosion, which otherwise can result in undermining and thus reduced performance of the pipe system if not dealt with. • Control of the inlet areas for standing water which could be a sign of blockage. • Optionally, usage of a tracer to determine if sediment or other debris is entering the collection wells and surge basins. Regular maintenance This type of maintenance includes most actions that follow after a problem has been found during regular inspections. It should follow the original construction procedures as close as possible. For example, when a pipe segment needs to be exchanged it should be replaced by a pipe made of the same material, that is either concrete, clay or galvanized steel. If a substitute material is used it should be ensured that the capacity is retained and that the change is marked in technical drawings. Regular maintenance can also include the realignment of some pipe sections, the repair of manholes, outlining the pipe system with a filter to avoid sediment entering the pipe system or the enlargement of said system. This has to be determined after a technical analysis and cost comparison. Then the latest construction methods and safety procedures should be followed. Emergency maintenance For serious disruptions, such as the breakdown of pumps, an action plan should be developed by responsible employees. This type of disruption requires corrective maintenance and should follow the suggestions of the manufacturer.

A rather common, yet critical, disruption is line blockage. Drainage system pipe diameters are normally chosen according to a minimum flow design, making the system sensitive to blockages. This blockage can be resolved using several approaches of which the most common ones are jetting, hydraulic flushing and hydraulic drain cleaners. Considering that most drainage pipes consist out of clay, have open joints and that most debris is sediment, jetting should be utilized. For those parts that consist out of concrete pipes, hydraulic drain cleaners can be used instead. These are more effective and do not damage the concrete. During cleaning operations, the downstream manhole should be observed to determine what the cause of the blockage was. No chemical cleaning agents should be utilized unless iron deposits are found and even then, provisions need to be made to avoid damage to the pipes and the environment.

5. Study area 5.1 Geography Karlshamnsverket is situated in the northern part of Pukavik bay at the Baltic Sea, as can be seen in Figure 19. More precisely, it stands on the Stärnö peninsula which is part of Karlshamn municipality in southern Sweden. The power plant is located 2,5 km southwest from the city centre of Karlshamn and 1 km east of the port of Karlshamn, as well as 47 km west from the capital city of Blekinge county, Karlskrona.

Figure 19: (Topographical) map of Blekinge county with larger towns and islands. Changed after Länsstyrelsen Blekinge län (2012), which used Lantmäteriet and SMHI data.

5.2 Topography The power plant can be described to be located in a valley, as it stands within a topological low at 2.65 m above msl (+0.07 m; see chapter 6.1.2), to be seen in Figure 20. To the west it is bounded by the up to 14 m high former island Kölön, which is only cut by a street to the harbour located at around +3 m. To the north bedrock rises up to 15 m and to the east bedrock rises up to 27 m above msl. South of Karlshamnsverket a seawall with a height of around 4 m is situated

(see chapter 5.4.4), while the seawall located northwest of the power plant has the same height as the power plant area. Thus, the area northwest of the power plant is the most susceptible to high sea water levels. Additionally, as both groundwater and rainwater tend to follow the topography it is important to determine their implications on the power plant. This is done in chapters 7 and 8.

Figure 20: Map obtained from SCALGO Live, showing the slopes of the area using the Lantmäteriet GSD height grid 2+ as of March 23, 2017. Structures and buildings are drawn in green. 5.3 Geology This chapter, intended for an engineering geologist reader, constitutes a short summary of information found in the tender documents and relevant literature, of which Ahlbom et al. (1992) is recommended for further reading. 5.3.1 Bedrock The bedrock in the area is mainly a fine to medium grained grey(-red) gneiss (Ahlbom et al., 1992) with some granite and pegmatite paths/veins, as well as amphibolite veins which are black and contain a lot of hornblende. It is also known as the Blekinge coastal gneiss due to its abundance in the coastal region of Blekinge (SGU, 2019b). 28

Besides the gneiss, granite can be found in the southern part of the power plant (see Figure 21). This granite is termed Karlshamnsgranite and has a mineralogic composition of quartz, feldspathoids, hornblende and some mica. Both types of bedrock belong to the Blekinge-Bornholm Province. 5.3.2 Fracture Systems and bedrock properties Fractures occurrence in the bedrock is moderate to low at the surface and decreases with depth (Ahlbom et al. 1992). In that report it was further agreed upon one fracture system that is orientated north-south throughout the power plant area and assumed to be vertical (see Figure 21). Another study conducted by a contractor states two other vertical fracture systems orientated N 60° W and N 10° E. Local Groundwater flow is limited to these fractures and their intersections, as well as to the homogenous rock mass (Ahlbom et al., 1992). Thus, the bedrock is reasonably impermeable and does not support high groundwater carrying capacities, having a maximum hydraulic conductivity of 10-8 m/s.

Figure 21: Local bedrock map showing bedrock types and fracture systems. Changed after: SGU (2019a).

5.3.3 Depth to bedrock The maximum depth to bedrock found on an interpolated map, that is based on borehole data before filling the area, was -16 m inside the Kölö straight. A later study for block 3, however, found a maximum depth of -23 m under the msl until impermeable bedrock was reached.

Figure 22: Local map showing the estimated depth to bedrock. Changed after: SGU (2019a).

5.3.4 Soil Above the bedrock, soil of varying thickness can be found. It mostly consists of varved clay, while the upper meter is often a different soil and consist of either dy (see Appendix A6), gyttja, peat, sand or till. This information is based on 24 boreholes that were drilled in the vicinity of the power plant and for which also the soil type was determined, as can be seen in Figure 23. In particular, in the Kölö straight the soil consisted of a 0-2 m thick top layer of amorphous peat and/or a sand layer with silt, as well as partly gyttja. Only below that top layer loose, varved, sometimes sandy, clay is to be found lying above bedrock. Due to the thick soil layer the water depth in the Kölö straight was just -3 m, while in the northwestern area it was max. -8 m deep before backfilling it. Even more boreholes were drilled around the marked area in Figure 23 but were not included, as only the area at +2.65 m was of interest in this study. Other information, for example, includes that at the 120 kV electrical substation the clay was solid and occasionally topped by sand and silt with a

30 depth of 1 to 6.5 m, while at the office building and turbine hall site the clay had a variable solidity, included a layer of sand and had a thickness of 1-5 m.

Figure 23: Interpolated depths (upper boundary) of soil based on data of 24 boreholes that also described the soil type. Boreholes were made before excavation and filling the area, but it was accounted for by adjusting values above a threshold. The marine sediment around the area has a total thickness of 1-15 m. It generally consists of a thin loose top layer of gyttja and vegetation. This layer is located above a layer of either solid dry crust clay or sand/silt situated over loose clay under which till, or bedrock is located. Where the bedrock is located at shallow depth the loose clay is often missing. The Harbour area has/had soil of loose varved clay of maximum 10 m thickness and includes some silt. This layer is on top of friction soil of till character that is situated over bedrock. Today, most of the power plant area is covered by fill (see Figure 24). To the north and east of the power plant also sandy till with an estimated depth of up to 3 m can be found (see Figure 22), as well as a minor area of glacial clay near the oil tanks. Otherwise the visible surrounding area is best described by bedrock under a thin layer of soil. 31

Figure 24: Local quaternary map showing soil types and boulders. Changed after: SGU (2019a).

5.3.5 Geological and geotechnical investigations Boreholes have been made in a large number. It included: • weight sounding tests in the Kölö strait, Harbour, 120 kV electrical substation, outflow tunnel and office building areas to receive information about soil properties. • hammer drilling and driving tests in the Kölö strait, Harbour and cooling water inlet areas to determine the bedrock depth. • piston and spoon sampling, as well as vane tests in the Kölö straight and in the Harbour area to receive information on the bearing capacity and consolidation properties of the clay. • Trial pits around Kölön to classify the soil for street building purposes and thickness needed for construction grounds. • 10 core rock drills of 20-50 m length in the area of the bedrock caverns, as well as 5 others southeast to northeast of the plant with 577-807 m length, each (Ahlbom et al., 1992).

Lab measurements included density (t/m3), water content, sensitivity (H quo.), shear strength (t/m3), strain and consolidation coefficients.

For example, a natural water content of 35-50% for gravely, silty sand and 45-55% up to 90% for clay was determined, while fall cone tests yielded 8- 25% more.

5.4 Excavation and Fill 5.4.1 Excavation Bedrock and soil were excavated to a uniform level of 2.25 m above msl for the control room, office, workshop and storage areas. The same was done for the turbine hall, boiler houses and the electrical substations, but here to 0.15 m above msl. All other areas were generally excavated until +2.35 m. Excavation extended 1 m beyond the buildings with slopes of 1:1.5 (soil) and 10:1 (bedrock) or alternatively sheet piles when the bedrock was too deep. Excavation of bedrock was done by blasting. Blasting consisted of blasting in the plane (until 1 m under the rock surface), trench blasting (trenches with a bottom width of less than 1 m) and blasting in open shaft (all other blasting). The latter also includes blasting of closed rooms, which encompasses caverns in bedrock, tunnels and descend facilities, as well as for arches/securing facilities. Care was taken to limit unnecessary cracks in the bedrock so that it remained as impermeable as possible. Grounding was then done on scraped and cleansed bedrock surface, but where no grounding was done the rocks were left if deemed stable. To be noted is that stones >5 m3 were denoted as bedrock during excavation. In general, more rock was excavated than soil. One exception to this was the office building and turbine hall area where more soil was excavated than rock masses. Most of this material was deposited in the gas turbine area along with rock masses. A general section for this can be seen in Figure 25.

Figure 25: W-E section through the power plant area, showing the depths (relative to msl) of bedrock, soil and fill, based on geotechnical investigations and planning. 33

5.4.2 Basement construction This chapter focuses only on those parts of the basement construction that were deemed essential to determine the reason for the flooding and how flooding affects the basement besides the equipment situated in it. 5.4.2.1 Fill Filling inside buildings was supposed to be done with a max. 50 cm thick till layer of former bedrock, including stones of max. 0.03 m3 size. That this is not always the case can be seen in Figure 26. As an example, the turbine hall basement of block 1 was calculated to be filled up with 700 m3 of blasted rock inside and 1250 m3 around the building, while in pipe trenches 60 m3 were to be used. This corresponds to a Figure 26: Fill in the basement consisting of 10 cm thick fine macadam layer several kinds of material (heterogenous). of 6-32 mm grain size with a top coating of 5 cm stable gravel.

In addition, concrete was laid in minor parts of the basement, i.e. 950 m2 in block 1, while 2500 m2 were laid out with fill material. Where concrete was laid, 5 cm fine macadam was used as a base, which was then coated with 5 cm stable gravel before the concrete was poured. If the ground consisted of clay the uppermost 10 cm were replaced with till first. Furthermore, Figure 5 in Chapter 3.3 shows that block 1 is grounded entirely on bedrock, while the boiler house of block 3 sits on top of pillars and thus is surrounded by fill that is described in chapter 5.4.3. 5.4.2.2 Basement walls Between block 1 and 2, as well as 2 and 3, the wall was temporarily equipped with steel sheet piles. These were secured by means of a small dam of compressed dense soil and anchors to fix them in place in the fill before the respective next block was built. No evidence was found that this was also done at the southern end of block 3 in preparation of block 4. Thus, today all outer walls in the basement are made of either concrete, clay, sheet metal or concrete masonry units. These walls were all envisaged to function as a barrier against groundwater pressure / high groundwater levels, 34 but it is unclear whether they really are impermeable. This can either be because of incorrect construction, developing failure over time or because water flows beneath them. In Figure 27 it can be seen that the outer walls are grounded on bedrock rather than in bedrock. Thus, if fractures were introduced into the impermeable bedrock by blasting, groundwater could enter the basement. Possibly this is the reason why such an extensive drainage system, as outlined in chapter 2.3, was constructed. 5.4.2.3 Drainage trench design Figure 27 shows further that the pipe trenches in bedrock were filled with 10 cm gravel. In fill areas instead 10 cm of compressed 16-32 mm macadam was used. In general, 3 different types for the drainage trench layouts were utilized as described below: Type A: Here, the drainage pipes are located in a trench in the fill, next to the outer wall. The outer wall sits on top of bedrock, while the pipe trench Figure 27: The drainage trench and material, macadam, is located on top outer wall designs used in the of a thin layer of gravel fill over basement. bedrock. Type B: The pipes and the outer wall are located in an excavated trench in bedrock. Hence, there is only the packing material, gravel, between the pipes and bedrock, which is topped by macadam. Type C: Here, the outer wall sits on top of bedrock. The drainage pipes are located further away in a pipe trench in bedrock, filled up with gravel and topped with macadam. 5.4.3 Fill in the power plant area 5.4.3.1 Fill Filling of the area was done in two stages, due to some zones where the clay had less bearing capacity. Only when the clay layer was very thin, or where harder materials were assumed below it was filled up in one stage. Thus, most of the area was initially filled up to 0.5 m above msl and then, in the next stage, to 2.65 above msl.

Friction soil and blast rock masses were used as primary filling masses. Friction soil was thereby defined as soil with gravel, sand and till fractions. After the initial settling the fill was refilled with blasted rock and then finalized with fine macadam. Three exemptions to this procedure were named, though: • If buildings were to be constructed on top, mixed crushed gravel was laid as a reinforcement layer before topping it with fine macadam. • When the soil below was clay or other loose soil, a min. 10 cm tick isolation layer of sand, sandy gravel or similar material was applied first. • Some parts were additionally laid with 15 cm topsoil for vegetation. In some areas it was further deviated from the general fill: • For the electrical substations, the filling consists of a max. 1 m thick layer of blasted rock, topped with 25 cm gravel and 5 cm topsoil. Possibly, a 30 cm thick transition layer of sandy gravel was applied first in areas where fine-grained soils were found. • In some locations additionally impermeable soil and friction soil has been laid. The impermeable soil used was defined as being of till size with a max. permeability of 10-6 m/s. 20-40% grains had to be <0.075 mm, while max. 35% of the grains were between 2-16 mm large. 5.4.3.2 Drainage and Trenches Drainage trenches that contain buried pipes were constructed with a slope of 1:200. In bedrock the trenches were laid out with 10 cm compressed gravel, while in other soils 10 cm fine macadam was used. Utilized pipes are either clay pipes or non-reinforced concrete pipes with branches of 3” clay pipes. The trenches were then filled up with 20 cm unsorted gravel. Where a bank was blocking water from being drained, 150 mm concrete pipes with a 0.05 % slope were laid as culverts. Electric cables were placed in trenches located 70 cm below ground in soil or 50 cm in bedrock and topped with a minimum 5 cm sand layer before topping it with macadam. 5.4.4 Seawalls As explained in chapter 3.2, the fill area is surrounded by two seawalls, one in the northwest and one in the south of the power plant area. Judging from three different technical drawings, the northern seawall consists only of blasted rock topped with stone blocks. However, it remains unclear 36 whether the seawall was outlined with a filter to keep fine soil contained as it was only discussed as an option. Underwater the seawall is connected to clay that is located at a depth of -11 to -16 m and below the seawall impermeable friction soil has been laid that consists of gravel, sand and till. This friction soil layer is situated above impermeable bedrock. Thus, no water can infiltrate below the seawall. However, the purpose of the seawall is possibly to keep the fill contained in the area rather than to keep water from flowing into said area. This is because it misses protective layers or impermeable soils that would have a preventive effect on water inflow. Thus, as the situation is at the moment, the groundwater level in the fill is assumed to follow the sea water level due to nearly unhindered water inflow and outflow through this seawall.

Figure 28: North-South Section through the southern seawall. In contrast, the southern seawall has been constructed more elaboratively, as can be seen in Figure 28. Before its construction, blasting was done to impermeable material or bedrock. Then, an unsorted blast rock core was constructed on top of a stony gravel bed. This core serves the purpose to support the main core. Thus, in the next step a stony gravel layer was applied on the southern slope of the core before constructing the main core. This main core was made out of impermeable soil consisting mostly out of dy and reaches up to a height of 1.5 m above msl. Next, a coating of stony gravel was applied on the main core before both cores were buried in unsorted blast rock in such a way that a slope of 1:10 was attained towards the power plant. Lastly, blocks of blasted rock, weighting 0.5 - 2 tons and on average 1.2 t, were laid some meters south from both cores as a protection against waves.

These blocks were laid in two courses with a slope of 1:2 and 1:3 until a depth of -4.5 m or to bedrock when it was located at shallower depth. The southern seawall thus effectively blocks water from entering the fill area as long as the sea water level is below 1.5 (+0.07 m; see chapter 6.1.2) m and provides protection against waves up to a combined sea water level and wave height of around 4 (+0.07) m above msl.

6. Sea Level Variation 6.1 General 6.1.1 Introduction to sea level variation In Figure 29 below, one can see both the average and the highest sea level per year (January to December) at Kungsholmsfort, using the RH 2000 dataset from SMHI. This data is uncorrected for land uplift and sea level rise. To account for both effects, all other results in this chapter will be using the mean water level (MW) dataset from SMHI, as explained in chapter 6.2. The purpose of Figure 29 is to show the significant variation of the sea levels between the years, as well as that the mean and extreme sea levels usually vary together, although not with the same magnitude. To be noted is that the pattern of the variation is erratic, however, as for example years with moderately high sea water levels can either be succeeded by a year with an even higher sea level or by a year with a lower sea level. Thus, no clear reoccurring trend is visible that would allow to forecast in which year and how extreme an extreme sea level is going to be. Rather, the height of an extreme sea level depends on a number of factors, such as the sea water level before a storm, the wind direction and speed (Länsstyrelsen Blekinge län, 2014). As a result, one has to work with statistical return periods that are further explained in chapter 6.3.1. This is a standard practice, followed i.e. by SMHI (2018).

150 140 130 120

) 110

m c

( 100

e 90

v e

L 80 Extreme High

e 70 t Average

a 60

a 50 e

S 40 30 20 10 0 18801890 19001910192019301940195019601970 1980 1990200020102020 Year

Figure 29: Average and highest sea water levels per year using the RH2000 dataset for Kungsholmsfort, that is uncorrected for land uplift and sea level rise. 39

6.1.2 Land uplift and future sea level rise 6.1.2.1 Land uplift A discussion about future sea level rise in the Nordics must also include a discussion about land uplift. This uplift is attributable to the isostatic, postglacial, rebound process which started after the end of the last ice age. More precise, it started after the melting of the large Fennoscandian ice sheet (Grinsted, 2015) that had pushed the continental crust down due to its weight. The land uplift varies from -10 mm/year in southernmost Sweden up to 90 mm/year in northernmost Sweden (Ekman, 1996). For Karlshamn, the land uplift measured at Kungsholmsfort, 1.4 mm/year (Länsstyrelsen Blekinge län, 2014), is reasonable to assume. Thus, since the construction of Karlshamnsverket in the year 1965, the area located at +265 cm should have risen by at least 7.56 cm. However, it is not clear if this was compensated by the movement of the fill, so that in the rest of this paper the +2.65 m above msl ground level is used for simplicity.

Figure 30: Global mean sea level rise estimation from 2006 to 2100 relative to 1986-2005 as determined by the IPCC. Display of projections with uncertainties displayed as shaded areas for the RCP 2.6 (blue) and RCP 8.5 (red) scenarios. To the right, means and their uncertainties are displayed for all RCP scenarios as vertical bars. Source: IPCC (2014). 6.1.2.2 Sea Level Rise In its Assessment Report (AR) 5 the Intergovernmental Panel on Climate Change (IPCC, 2014), whose results are commonly quoted for sea level rise 40 estimates, has determined an upper border of 98 cm global sea level rise until the year 2100, as well as 32 cm until the year 2050. This can be seen in Figure 30. These values are based on the Representative Concentration Pathway (RCP) 8.5 scenario, which would constitute a ‘business as usual’ case. SMHI considers these values also in their sea level rise projections for the Baltic Sea (Länsstyrelsen Blekinge län, 2014; SMHI, 2018). Thus, also in this report a sea level rise of 98 cm until the year 2100 and 32 cm until the year 2050 will be utilized for further analysis. It is to be noted though that recent studies, such as the one by Bamber et al. (2019), estimate higher sea levels than reported by the IPCC. They come to the conclusion that the global sea level likely rises 34 cm (21-61 cm; 95% confidence intervals) by the year 2050 and 111 cm (62-238 cm; 95% confidence intervals) by the year 2100. Corrected for local land uplift this yields an estimate of +25.6 cm sea level rise until the year 2050 and +95.6 cm for the year 2100. A sea level rise of 95.6 cm would not be critical, as explained in chapter 6.4. However, considering the upper 95% confidence interval for the year 2100, a sea level rise of 223 cm would be critical for the power plant if the sea water level would be 56 cm above msl. In recent years water levels that exceed the msl by +50 cm have been commonly observed, as explained in chapter 6.3.3. This is expected to continue in the near future and thus the power plant would be at risk under such a scenario. Future reports, such as the IPCC AR 6 that is scheduled for 2021, should yield better estimates how the sea level rise is likely to develop until the year 2100, which would still leave enough time to implement long term preventive measures. Thus, as noted above, the IPCC AR 5 estimates will be utilized in the analysis below. 6.1.2.3 Implications The already occurred net sea level rise from the reference period 1986-2005, simplified by using the year 1990, until today can be considered to be negligible at the analysed location (Länsstyrelsen Blekinge län, 2014) even though it currently increases by 3 mm/year in a global perspective (Bamber et al., 2019). Thus, the sea level rise beginning at the reference period 1990 can be utilized. Combining both land uplift and sea level rise, a net sea level increase as depicted in Figure 31 is yielded. Looking at the year 2100 this would mean

41 an increase of the msl of 82.6 cm compared to the reference year 1990. For the year 2050 the respective value is +23.6 cm.

Figure 31: Net sea level rise (green line) for the period 1990-2100 assuming a 98 cm sea level rise and a land uplift of 15.4 cm until the year 2100. Changed after: Länsstyrelsen Blekinge län (2014).

6.2 Data series and basic properties To determine various extreme water levels at Karlshamnsverket, trend corrected (MW) hourly sea water level data from Kungsholmsfort was used. It is provided at no cost by SMHI (2019d). This station, which is located around 47 km east of Karlshamnsverket, is in operation since December 1, 1886 and provides almost continuous data (SMHI, 2018). Thus, the full data record comprising of 133 years was used in the analysis of chapter 6.3.2. The station has further been chosen as the coastal locations are similar. It provides more appropriate data than the other SMHI station in the vicinity, which is located in Simrishamn (SMHI, 2018). The coastline at Simrishamn is open and is thus prone to more wave action. The similarity can be proven with SMHI (2019a), where the sea water level at Sjöfartsverkets station, located at Karlshamn harbour, is compared to the SMHI measurement station Kungsholmsfort. Both stations either display the same sea level or are a few cm apart. Sjöfartsverket does not provide open access to their sea water level data records that are older than a week and thus it was not able to be analysed in this chapter. Real time data will be used in chapter 9, though. To be noted is that the gross of the data values have been denoted with the colour code orange, meaning that these values are not controlled. It is only from 2001 that data started to be controlled, thus yielding the colour code green. One exception to this is some data collected in November 2018. This data has the colour code yellow, which describes suspicious or aggregated 42 values. The yearly maximum of the year 2018 was in October, though, and has no implications.

6.3 Statistical analysis and extreme events 6.3.1 Theoretical aspects 6.3.1.1 Introduction A major part in the process to determine extreme sea water levels includes the extreme value analysis (EVA). EVA is, amongst others, applied to estimate the extent of events with return periods that exceed the observed data record (Fredriksson et al., 2016). Thus, the longer the observed data record is the better estimates can be made. For example, a storm that occurs on average once in 200 years can be reasonably estimated with just 100 years of observed data (Länsstyrelsen Blekinge län, 2014). Using EVA, the sea level height corresponding to such a storm event can be determined and is thus named return level. When it comes to the determination of risk, the probabilities of certain events are related to the potential consequences to create a reasonable action plan with mitigation measures. 6.3.1.2 Probability of Exceedance and return period P, the probability of exceedance, is defined as a 1 in T year’s event, where T is the return period. As such the result is a fraction or decimal that can be converted into a percentage: 푃 = 1⁄푇 Equation 1 Here, the initial analysis will be limited to 1 in 100 year, or simplified 100- year, events. In this case these events are sea water levels that have a statistical return period of 100 years, but in fact have a probability of 1% to occur in any given year according to equation 1. If accounting for the cumulative effect, this event has a 63% probability of exceedance if one assumes that the power plant has a lifetime n of 100 years. This is calculated with the following accumulative probability of exceedance formula (Fredriksson et al., 2016):

1 푛 푃 = 1 − (1 − ) Equation 2 푇 Thus, 50-year events have a probability of 2% and 200-year events a probability of 0.5% to occur in any year, while cumulated over n = 100 years

43 these events have an 87%, respective 39% probability of exceedance according to equation 2. A summary of this accumulation is given in Table 1. Table 1: Probabilities for different return periods and lifetimes calculated by using equations 1 and 2.

Return period Probability per Probability after Probability after year 50 years 100 years 2 years 50 % 100 % 100 % 5 years 20 % 100 % 100 % 10 years 10 % 99 % 100 % 20 years 5 % 92 % 99 % 50 years 2 % 64 % 87 % 100 years 1 % 39 % 63 % 200 years 0,5 % 22 % 39 %

6.3.1.3 Probability distribution function The theory behind EVA is mainly dependent on the choice of the probability distribution function. For extreme events the chosen function is normally an extreme value distribution instead of a normal distribution. This is because most of the data is not located evenly around the mean (Gumbel & Lieblein, 1954). Rather, the data displays a skewed curve with a data specific tail towards higher values, meaning that smaller values tend to occur Figure 32: Theoretical distribution of an more frequently than larger values extreme-value probability function (see Figure 32). (changed after Gumbel & Lieblein, 1954). Several extreme value distribution functions have been developed on the basis of a number of assumptions (Fredriksson et al., 2016). Thus, a distribution that suits the random data, in this case comprising of the maximum sea water level per year, needs to be selected and tested for suitability. 44

According to Fredriksson et al. (2016) it is assumed that the used type of maxima, also termed block maxima, follow the Generalized Extreme Value (GEV) distribution if they are independent. Generally, events are only considered independent when they are separated by time, at minimum a number of days. Thus, not only yearly maxima from January to December were analysed but also oceanographic maxima from July-June, as sea level maxima never occur during these months. As such it is ensured that these events are independent. The GEV distribution function, as described in Coles (2001), delineates the distribution of block maxima, termed Mn. n is here equal to 365.25*24 per block due to the selection of yearly maxima from hourly values. Mn is equal to max (X1, ..., Xn), where Xn describes a block maximum, in this case a year. These block maxima are then fitted on a GEV family distribution:

푥 −휇 −1⁄휉 퐺(푥) = 푒푥푝 {− [1 + 휉 ( 푝 )] } Equation 3 휎

, where 휉 is the shape parameter, µ is the location parameter, 휎 is the scale parameter of the distribution function and xp is the return level. When ξ > 0, the GEV distribution function is said being of Fréchet type, while when ξ < 0 it is said to be of Weibull type (Fredriksson et al., 2016). A simplified version of this is the Gumbel type distribution function, also known as double exponential, that was developed by Emil J. Gumbel. Here, the shape parameter is equal to 0 and thus the function is only dependent on the location and scale parameters: 푥 −휇 퐺(푥) = 푒푥푝 {−푒푥푝 [− ( 푝 )]} Equation 4 휎 By fitting the block maxima to the Gumbel distribution these two parameters are estimated, which makes it possible to determine the return level for a chosen return period according to:

푥푝 = 휇 − 휎 푙푛{−푙푛(1 − 푃)} Equation 5 Similarly, for the GEV distribution function the return level for a chosen return period is determined according to: 휎 푥 = 휇 − [1 − {−푙푛 (1 − 푃)}−휉] Equation 6 푝 휉 For future conditions, it is reasonable to assume that the storm frequency does not change (Länsstyrelsen Blekinge län, 2014). Thus, the return periods

45 for observed data can be utilized to estimate future return levels. This is done by adding future sea level rise estimates to the calculated return levels without altering the distribution function.

6.3.2 Extreme sea levels Initially both, Gumbel and GEV, distribution functions were fitted to the two chosen periods by estimating the parameters with the help of the maximum likelihood method in the program R, according to Fredriksson et al. (2016). To test whether the simpler Gumbel distribution function or the GEV distribution function should be used, the Likelihood-Ratio test was then applied with a 95% significance level. Its theory is beyond the scope of this study, but a short summary is given in Gilleland & Katz (2013). The result for the January to December period yields no significant improvement using the GEV distribution function, so the easier Gumbel distribution function can be utilized. However, for the July to June period the GEV distribution function yields a better fit. A comparison of the different estimated water levels was also carried out in the beginning and can be seen in Table 2. It shows that, depending on the chosen yearly period and the method, the obtained water level for a 100-year return period varies significantly from 122 to 139 cm. Table 2: Maximum likelihood estimation of parameters for the GEV and Gumbel (ξ=0) distribution functions (with standard error in brackets). Estimated 100-years return levels (in cm) are relative to the msl (with the 95 % confidence interval in brackets).

Period Method Location, Scale, σ Shape, ξ Estimated µ water level 100 years return period Jan. - Gumbel 67.0 (1.4) 14.9 (1.0) 0 136 (126-147) Dec. GEV 67.9 (1.5) 15.3 (1.1) -0.1 (0.06) 124 (115-142) Jul. - GEV 64.5 (1.7) 17.1 (1.2) -0.15 (0.06) 122 (113-139) Jun. Gumbel 63.2 (1.5) 16.5 (1.1) 0 139 (129-151)

Ultimately, it was decided to continue the analysis only with the maxima from the July to June period as here it is ensured that the yearly maxima are independent. This yields a data set comprising of 132 data points starting from July 1887. The GEV distribution function was selected for this data set as the likelihood ratio test indicated a significant improvement of the fit using the GEV function instead of the Gumbel distribution. This is confirmed when looking at the diagnostic plots of the fit in Figure 33, which show a very good fit. Thus, the return levels for return periods of 50, 100 and 200 years for today and the years 2050 & 2100 can be estimated according to the methodology described in chapter 6.3.1.3. The results are depicted in Table 3, yielding a sea water level of 2.33 above msl in the worst case. Table 3: Estimated return levels (relative to the mean sea level) for events with return periods of 50, 100 and 200 years today and in the years 2050 & 2100. 95 % confidence intervals are given within brackets. Estimated future land uplift and sea level rise are included.

Return Estimated water Estimated water Estimated water period level (cm) today level (cm) Year level (cm) Year (years) 2050 2100 50 115 (108-129) 139 (132-152) 198 (191-211) 100 122 (113-139) 145 (137-163) 204 (196-222) 200 127 (118-150) 151 (141-174) 210 (201-233)

Table 3 shows that the uncertainty of the different return levels increase with an increasing return period. This is expected to continue with larger return periods. The return levels themselves are comparable to other studies, such as Länsstyrelsen Blekinge Län (2014). In that study the obtained water levels are generally a few cm higher, while the 95% confidence intervals are a few cm higher here. The former can be related to a slightly different methodology, while the latter can be associated to the 5 years of additional data that were available for this study. The extreme sea water levels in the years 2016 and 2019 have been amongst the 10 highest in the 133 years of measurements, thus possibly raising the confidence interval. On the other hand, SMHI (2018) comes to the conclusion that the 100-year return level for Karlshamn today is 114 cm (107-122; 95% confidence interval) and the 200-year return level is 118 cm (109-126; 95% confidence 47 interval). These values are based on a comparison of data from Karlshamn and Kungsholmsfort over 15 days that revealed a 15 cm lower water level at Karlshamn harbour, as well as a correlation analysis for the yearly maxima over eight years. Due to the short time period analysed these return levels are regarded as an underestimation in this report, though. With more data available in the future this analysis should be repeated to receive a better estimate for extreme sea levels in Karlshamn. Even when the sea water level in Karlshamn is then determined to be lower, the discrepancy still serves as a reasonable security, also known as freeboard.

Figure 33: Diagnostics plots for the fit of the GEV distribution function on 132 years of oceanographic block maxima (July-June period) obtained in R.

6.3.3 Duration Furthermore, the duration of higher sea levels was analysed to estimate how long possibly installed pumps in the basement (see chapter 11) would need to be operated to avoid a flooding of the basement. For this reason, the number of hours where the seawater exceeded levels of +0.3, 0.5, 0.7 and 1 m above msl were determined per year. The result of this analysis can be seen in Figure 34. Average values are stated in Table 4, where these are compared to values of an earlier study by Bergsten (1950).

Table 4: Average time of exceedance for different water levels compared to a study from the year 1950 (in days/year).

Days >0.3 m Days >0.5 m Days >0.7 m Days >1 m Own calculation 21.7 3.7 0.9 0.3 days/year Bergsten (1950) 21.2 3 0.5 days/year In Figure 34 it can be seen that water levels of 30 cm above msl or more occur every year since the start of the measurements. On average, the duration of these water levels increases by 2 hours every year. Thus, while on average for all years (Table 4) this water level is exceeded for 520 hours or 21.7 days, nowadays it occurs rather 648 hours or 27 days during a year. Equivalently, water levels of 50 cm or more above msl persist on average 89 hours or 3.7 days during a year, while today it is more likely to be exceeded for 116 hours or 4.8 days, increasing on average by about half an hour every year. The last time this threshold sea water level was not exceed was in the year 1996. Sea water levels above 70 cm were increasingly observed since the year 2001, with the exception of the years 2010, 2014 and 2016. A clear trend is not observable here but on average these water levels occur for 22 hours during years where this water level was exceeded. Similarly, sea water levels in exceedance of 1 m above the mean sea level occur seldomly, but more frequently again since 1983. Water levels of this magnitude last on average about 6 hours in years where they occur. Thus, these water levels are attained only during the course of one day of a year in comparison to all other discussed water level thresholds. In conclusion, this means that not only the extreme sea water levels will increase, but also their duration.

100 y = 0.0842x - 142.79 R² = 0.0569

>0.3 m

>0.5 m

s y

a 1 >0.7 m D >1 m Linear (>0.3 m)

0.1

0.01 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year

Figure 34: Exceedance of different extreme sea water levels in days per year at Kungsholmsfort.

6.4 Implications This chapter discusses sea water levels higher than estimated in the foregoing subchapters of chapter 6 for the simple reason to add another safety margin for small scale waves on top of the 95% confidence intervals. For this reason, the 155 cm sea water level calculated by SMHI (Schöld et al., 2017) has been utilized as a design scenario for the present. It is a combination of the highest observed net increase of the sea water level at Kungsholmsfort (100 cm; during the 1914 storm) and the highest sea level before a storm for all oceanographic measurement stations in southern Sweden (55 cm at Skanör). At least one other study also utilized this sea water level to evaluate implications (Karlsson, 2006). That study also includes the design scenario of 240 cm for the year 2100 which was also utilized here, and which was calculated by SMHI (2019b) based on the 155 cm scenario for today. Investigating the sea water levels during the 1914 storm, however, it was not apparent that the sea level increased by as much as 100 cm. In general, the value is an overestimation due to the inclusion of data from Skanör where higher sea water levels should be observed frequently. Thus, this event is an overestimation that can be utilized for designing coastal protections as it is unlikely to occur. 50

6.4.1 Power plant In Figure 35 the implications of extreme sea water levels on the power plant area both today and at the end of the century can be seen. Already today, to be seen on the left, some smaller areas would be flooded when the design event would occur. However, this only involves unused parts of the power plant area. Some infrastructure is at risk of being flooded, though. This includes the street to the breakwater and the oil dam. Considering the design event in the year 2100 these two structures would be flooded. Additionally, the breakwater would have an impeded function and would also be at risk of being flooded. The power plant would still be protected, though, since the critical sea level is 2.79 m above msl. A more likely critical sea level can be said to be 167 cm, since then the oil dam is at risk of being flooded. This event could already happen around 2050. Other surface flooding based on the sea level alone is not be expected in the short term. Solutions to these problems are not provided here, as these already had been subject to discussion in Jönsson & Marcusson (2008). They state that increasing the oil dam and breakwater height is a viable solution. Considering the street to the breakwater this could also be done, although it is not regarded necessary as it is a non-essential street. Other, non-visible problems are more probable to occur. For instance, the southern dam is only impermeable up to a water level height of 1,5 (+0.07; see chapter 5.4.4) m today, meaning that more water will enter the fill area at higher water levels. This will increase the groundwater table in the fill which could for instance lead to higher than designed water flows into the storm water system or higher than designed groundwater pressure on the basement walls. This is already probable to occur around the year 2050. Higher water levels are also probable to be present in the surge basins during an extreme event. This leaves the basement more vulnerable to flooding as will be explained in detail in chapter 9.

Figure 35: Power plant area in SCALGO Live. Left: Design sea level today (155 cm); right: Design sea level in the year 2100 (240 cm).

6.4.2 Gas turbine plant As can be seen in Figure 36, the gas turbine plant is sufficiently protected when applying the design sea water levels. Only a minor unused area in the south-east is at risk of being flooded using the chosen design event for today. Even when one considers the design event in the year 2100 the northern dam will still be high enough. Only when the sea water level rises above 2.66 m it will reach the gas turbine plant. This, however, is unlikely to occur in the near future.

Figure 36: Gas turbine area in SCALGO Live. Left: Design sea level today (155 cm); middle: Design sea level in the year 2100 (240 cm); right: critical sea level height (266 cm). Black line: chosen modelling boundary. Buildings are marked in green. 52

7. Precipitation and runoff 7.1 General Similar to high sea water levels also downpour events can damage infrastructure and housing properties. The amount of damage thereby depends on the area where the event occurs (Svenskt vatten, 2016). In urbanized city areas impermeable concrete surfaces are common which lead to more water flowing on the surface. This is termed as overland flow and is the main source for runoff, which is the main cause of rainfall induced damages. In the countryside water can infiltrate the soil easily, leading to less or no overland flow and hence less risk for property damage due to smaller runoff intensities over longer time periods compared to the city. The general pattern for a rainfall induced runoff can be seen in Figure 37. In the figure, the intensity of the runoff is less than the rain intensity but therefore runoff lasts longer than the rain event.

Figure 37: Visualized relation of a design runoff intensity QR, max derived from a chosen or determined maximum rainfall intensity imax that is assumed to be constant over time over a chosen area A. As such it is ensured that the storm water pipe system is designed large enough. Changed after Gujer (2007). Already in the past 20 years the abundance of downpour events increased, of which the most prominent one in southern Sweden is the Malmö downpour event (Svenskt vatten, 2016). On August 31, 2014 more than 120 mm fell within 6 hours in parts of the city. This exceeded the available pipe system volume by a factor of 5, leading to widespread flooding throughout the city. 53

When it comes to the estimation of future cloudburst events several projections have been made for Sweden. Länsstyrelsen Blekinge län (2012) i.e. states a maximum 47% increase of daily rainfall for a 20-year event in the period 2068-2097 in relation to 1961-1990. SMHI (2015) reports an estimated 16% stronger 10-year storm with a duration of one hour for the period 2021-2050 relative to 1961-2000. For the period 2069-2098 this rises by 34% compared to 1961-2000. Consultant companies usually use a climate factor of 1.25 as a reasonable approximation (Svenskt vatten, 2016), thus increasing the observed rainfall intensities by 25% (i.e. Sweco, 2017). This was also applied in the analysis of chapter 7.3.2.

7.2 Data series and basic properties For the runoff calculation, gauge data from the island of Hanö rather than Karlshamn was utilized, which is reasoned below. The station on Hanö is located 15.5 km south of the power plant, while the weather station in Karlshamn is situated 6 km northeast at the motorway E22 (see Figure 38). Thus, the station on Hanö accounts somewhat better for the coastal climate, which is likely to be different from the inland climate (Hill et al., 2010), due to effects of i.e. the sea breeze that persist only a few km inland. Further, for Karlshamn only daily rainfall values are distributed via open access by SMHI, while 15-minute values and hourly values are accessible for Hanö since December 1, 1995 (SMHI, 2019c). Having a better time resolution is essential to receive a more realistic result of the runoff amount. It makes a difference for the runoff calculation if 24 mm/day, thus on average 1 mm/hour, are measured or 24 mm/hour. Also, to be noted is that the interstation difference in mean monthly precipitation is not very large, as one can see in Figure 39. While it rains on average 563 mm/year in Karlshamn the respective value for Hanö is 496 mm/year. An analysis of both datasets further revealed that both daily precipitation and yearly maxima on Hanö have on average a 1.7% higher intensity than the respective precipitation in Karlshamn. Thus, on Hanö it tends to rain less but some precipitation events are slightly more intensive than in Karlshamn. Using the extremes of Hanö hence constitutes a better evaluation and design basis for the storm water pipe system. The full capacity of a pipe system 54 should not be utilized (Svenskt Vatten, 2016). Thus, usually a security factor for the peak flow calculation is added to design a sufficiently large pipe system, which can be omitted by using the data from Hanö. The best option would be to utilize weather radar data from the radar station in Karlskrona since this provides local rainfall intensity. It is, however, a time intensive task that involves the analysis of radar imagery. Thus, this analysis could be performed during another study in the near future but was omitted here due to time issues.

Figure 38: Locations of Karlshamnsverket (red pin) in relation to the two the rain gauges (yellow pins) in Karlshamn and on Hanö. Map Source: Google Earth. It is to be noted that of a total of 203.784 possible observations between December 1, 1995 and February 28, 2019 6660 observations or about 3% of the data is missing as the station was out of service. Of the rest of the data about 75% is marked with the colour code yellow, labelling these as suspicious or aggregated values, while the other 25% are marked as approved values.

This makes the following analysis and discussion of results weak, as the risk is high that the most extreme rain events are missing in the data and that the data itself is wrong. However, due to the lack of suitable alternative rain gauges in the vicinity, it was still chosen to work with this data in order to receive a better time resolution.

)

a d

/ 40

m Karlshamn

m ( Hanö

n 30

a R 20

0 Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec.

Figure 39: Mean monthly precipitation (in mm/day), normalized using data from the years 1961-1990 for the weather stations in Karlshamn and on Hanö. Data source: SMHI.

7.3 Statistical analysis and extreme events

The methodology to determine extreme rainfall/storm events is based on the same principles and follows initially the same methodology as described in chapter 6.3.1.3 and the beginning of chapter 6.3.2. Thus, these are not repeated here and instead the determination of a possible correlation is discussed first, followed by the results of the statistical analysis and the methodology to determine the runoff from a precipitation event. 7.3.1 Correlation analysis Hourly data that has been simultaneously observed at Kungsholmsfort (sea water levels) and on Hanö (precipitation) was used for this analysis. First, missing and 0 mm precipitation data, as well as sea water levels measured at the same time as the excluded precipitation data, were excluded from further analysis.

Then, the graph depicted in Figure 40 was created to determine whether sea water level and precipitation maxima are correlated. On the y-axis therefore the sea water levels are drawn, while on the x-axis the natural logarithm of the precipitation height ln(p) is plotted against the number of observations on the z-axis. Figure 40 shows that extreme sea water levels and extreme storm events are not correlated to each other, thus making it possible to discuss the results independently from extreme sea water levels. Even in the future it is unlikely that extremes of both parameters will occur simultaneously. An analysis of the extreme events yielded that the highest rainfall usually occurs sometime in the months June to September, while the highest sea water level usually occurs in the months of October to February.

Figure 40: Correlation analysis using simultaneous sea water levels (y-axis) and precipitation data (x-axis; in the form of ln(p)). The z-axis describes the amount of observations. No correlation of the extreme events can be observed (see corner to the right).

7.3.2 Extreme rainfall Like for the extreme sea levels, the GEV distribution function was determined to fit the extreme rainfall data significantly better compared to the Gumbel method. This was tested by means of the Likelihood-Ratio test that is explained in chapter 6.3.2. The obtained distribution parameter values for the GEV distribution function can be seen below in Table 5.

Table 5: Maximum likelihood estimation of parameters for the GEV distribution function on extreme rainfall data (with standard error in brackets).

Method Location, µ Scale, σ Shape, ξ GEV 9.87 (0.76) 3.20 (0.65) 0.34 (0.18)

In Table 6 the return levels for common return periods today and for a future climate are summarized, while Figure 41 shows the return level plot for present conditions only. Usually, a 5 to 10-year rainfall event is taken into consideration when evaluating or building rain/storm water systems (Svenskt vatten, 2016). Thus, a rainfall intensity of 20.6 respective 25.8 mm/h will be used as an assessment basis for the runoff calculation in chapter 7.4.3. However, to visualize the impact of an extreme rain on the area, a storm with a 20-year return period was chosen for chapters 7.4.1 and 7.4.2. Table 6: Estimated return levels (relative to the mean sea level) for return periods of 2, 5, 10 and 20 years today and for a future climate. 95 % confidence intervals are given within brackets.

Return period Estimated rainfall Estimated future (years) intensity (mm/h) today rainfall intensity (mm/h) 2 11.1 (9.5-13.3) 13.9 (11.9-16.6) 5 16.1 (13.1-22.8) 20.1 (16.4-28.5) 10 20.6 (16.2-36.3) 25.8 (20.2-45.3) 20 26.2 (18.8-51.1) 32.7 (23.5-63.9)

Figure 41: Return level plot for Hanö, showing the return level (in mm/h) in relation to a return period (in years).

7.3.3 Runoff To determine the implications of rain events two general approaches are thinkable. One is to visualize how the rain events would fill topographical depressions in the area and thus create small ponds by water flowing over land only. This was achieved with the help of SCALGO Live (SCALGO, 2019). The other approach involves the calculation of the runoff flow to determine whether or not the current storm water system is dimensioned large enough. The simplest approximation is thereby done with the help of the so termed rational method (Svenskt vatten, 2016): 푄 = 퐶 ∗ 𝑖 ∗ 퐴 Equation 7 where Q is the runoff (in l/s), C (or φ) is the mean runoff coefficient (-) for the area A (hectares; ha) and i is the intensity of the chosen rainfall event (l/(s*ha)). A rainfall intensity given in mm/h can be transformed to l/(s*ha) by multiplying with 2.78, while multiplying with 0.38 is valid for the opposite transformation.

C is calculated according to:

퐶 = (퐴1 ∗ 퐶1 + ⋯ + 퐴푛 ∗ 퐶푛)⁄퐴푡표푡 Equation 8

, where An is the area of a subcatchment and Cn is the respective runoff coefficient for that subcatchment. Atot is the total catchment area. The runoff coefficient is applied to associate the amount of overland runoff to the amount of precipitation and is dependent on factors such as slope, surface type or land use and permeability. Higher runoff coefficients account for higher runoff amounts and less infiltration, while the opposite is the case for low runoff coefficients. Suitable runoff coefficients for subcatchments were obtained from Table 6.10 in Svenskt vatten (2004), which was translated into Table 7. Table 7: Runoff Coefficients for various types of surfaces. Changed after: Svenskt vatten (2004).

Type of surface Runoff Coefficient, C Roof 0.9 Concrete and asphalt surface; surface bedrock with 0.8 steep slope Paved surface with gravel joints 0.7 Gravelled street; steep sloping mountainous park 0.4 area without significant vegetation Surface bedrock without a steep slope 0.3 Gravel surface and gravelled walkway; 0.2 undeveloped building land Park with rich vegetation and hilly mountainous 0.1 woodland Cultured land, lawn, meadow land etc. 0 - 0.1 Flat, densely grown woodland 0 - 0.1

7.4 Implications In the chapters 7.4.1 and 7.4.2 the implications of foremost a 20-year storm event on the area are discussed and problematic parts are named by utilizing maps created with SCALGO Live. In chapter 6.4.3 the results of the runoff calculation are discussed using a 10-year storm event. 100-year or 200-year events were not considered here due to the short data record and the large uncertainty related to these events (see Figure 41). 7.4.1 Power plant Generally, one can say that the power plant area is protected for storm events, as most areas coincide with the already installed storm water system. This can be seen in Figure 42. For instance, the largest affected area by a 20-year storm of 26.2 mm/h would be to the west of blocks 2 and 3. The northern part of this affected area is used as a storage space and thus it was important to install a storm water system there. The southern part was used as a basin for water but now has been deconstructed, leaving the space unused. It yet has to be observed how this will impact the infiltration capacity of the fill there during a rain event. Other prominently marked areas include the side slopes of the streets, the area between the boiler houses of block 2 and 3 and the area behind the storage to the east of the office building. These, however, all are connected to the storm water system. Several smaller areas near infrastructure as well as some non-utilized areas are also affected by a 20-year storm event, however not to such an extent that actions would be necessary. Considering a future climate, and also when using the upper 95% confidence intervals, the results would be very similar compared to the results for the current climate. Just the depth and extend of the rainwater ponds would increase to a minor degree.

Figure 42: Accumulation of rain in depressions after a 20-year rain today (left) and in the future (right), if there would be no infiltration and no storm water pipe system. Areas marked in red display resulting water bodies with a minimum depth of 30 cm. Buildings are drawn in green; black lines are contour lines that represent the local topography. Obtained by using SCALGO Live.

7.4.2 Gas turbine plant As can be seen in Figure 43, a 20-year storm event, both today and in the future, leads to the creation of a pond behind the main building, which is even the case for a 10-year storm. The extent of the pond is thereby dependent on the water depth chosen, which in that figure is 50 cm. Thus, at this point an evaluation should be made to determine if a rainwater system should be established.

Figure 43: Accumulation of a 50 cm deep pond after a 26.2 mm/hour rain (left) and after a 32.7 mm/hour rain (right). 62

7.4.3 Runoff

Figure 44: Map of the catchment area, divided into 38 subcatchments by land usage. The legend displays the selected runoff coefficients C for the subcatchments and the numbers in the polygons display the subcatchment area in hectar (ha). For the runoff analysis a shapefile containing depression-free flow watersheds in the form of polygons was downloaded from SCALGO Live. It was chosen due to simplicity and because the flash flood watersheds, which account for depressions, seemed incorrect. Thus, the area and runoff amount will probably be overestimated in this analysis since in reality not all water will reach the storm water system. This serves as an additional safety margin. Then, all but the largest watershed polygon were deleted in ArcGIS, since this the only one where storm water will reach the power plant and the rainwater system (see Figure 44). This watershed has a total area of 39.61 ha or 0.3961 km2. It was further divided into 38 smaller polygons to account for the current land usage as to apply the runoff coefficients of Table 7. 63

This yielded an average runoff coefficient of 0.353 for the analysed area using equation 8. Thus, according equation 7, the runoff flow is Q = 0.353*2.78*20.62*39.61 = 801 l/s

, or 0.8 m3/s, when assuming a 10-year event for today’s climate. This is about double as much as was estimated by Scandiaconsult AB (1980) in an unpublished report for an unspecified downpour event and an area around 2 km away from the power plant. Normally, a storm duration is then selected, and the respective intensity is determined from intensity-duration-frequency (IDF) curves to be able to calculate the flow volume in m3 (Svenskt vatten, 2016). This then yields the situation as depicted in Figure 37, by assuming a constant rainfall over that time period. For example, if it is assumed that the rain intensity remains constant for 10 minutes a flow volume of 481 m3 is obtained for a 10-year event today. Using the upper 95% confidence interval the runoff flow, instead, amounts to 1409 l/s or 1.41 m3/s and thus to a volume of 846 m3 over 10 minutes. For a future climate the upper value of the 95% confidence interval yields 1762 l/s, respective 1.76 m3/s and thus 1057 m3 over 10 minutes. In this report, however, it was refrained from establishing IDF curves due to time concerns and no suitable IDF curves were able to be found in the literature. Thus, no reasonable estimates for runoff volumes can be made here and it is referred to the results as in Table 8.

Table 8: Estimated runoff flows (m3/s) today and for a future climate using a 10- year event and it's upper 95% confidence interval.

Estimated runoff Estimated future flow (m3/s) today runoff flow (m3/s) 10-year event 0.80 1.02 Upper 95% confidence 1.41 1.76 interval Worth noting here is that the storm water pipe system, without wells and only in the basement, has a capacity of around 66 m3. This value is based on calculations done for this study. It yet has to be determined how large the total system capacity is to determine the implications of the calculated flows.

8. Groundwater This chapter is to be seen as a continuation on information provided in chapter 5. It focuses on groundwater table data collected between January 1988 and April 2019 in 6 of 8 measuring points. Groundwater levels (gwl) have been measured since 1970 in all 8 points, but it was decided not to use all available gwl records. The reasons for this are given in chapter 8.2.1.

8.1 General The measurements points, or wells, are located south-east to east of the power plant. All points have in common that they are located at a height of 20-30 m above msl and more or less near bedrock caverns that have been specifically designed to hold oil that is lighter than water. For this reason, groundwater is measured as to ensure that constant surrounding pressure is available. Point 1 is located in an artificial fill area of a few m thickness, while the others are located in a forest next to a nature reserve. The soil thickness in the forest varies from a few mm (observed) up to around 3 m where till has accumulated (see Figure 22). Two points, points 6 and 7, are located in such till areas, whilst the other 5 points are situated in bedrock covered by soil. Also, important to note is that the well openings are located somewhat over the ground, as the water table in the wells can be above the ground level. The opening of Point 1 is about 0.3 m above ground level, while the openings of the wells 2-8 are located 0.95 m, 0.87 m, 1.6 m, 1.18 m, 1.12 m, 1.08 m and 1 m above ground, respectively.

8.2 Data series properties 8.2.1 Limitations The data provided has a number of limitations which are explained in the following. First, the data is only available in paper format. Thus, it took a considerable amount of time to digitize the data and it was considered sufficient to utilize a period of 30 years in an attempt to normalize yearly fluctuations, which is also done to determine the climate of a location.

Furthermore, data collection in these years varied from 2 times a year to 3 times a month, yielding a total of 224 observation days. While for the month of December only 12 data points are available, 25 observations are available for the months of January, August and October, each. As the monthly values have been averaged over the years to obtain Figure 45, this means that the quality of the averaged value varies considerably. Additionally, the measurement points 3 and 8 have been excluded from analysis due to the apparent influence of the oil caverns on the groundwater level there, explained by extremely low groundwater levels. In general, for all 8 data points an in-depth analysis is not possible because of the influence of the oil level in the oil caverns and groundwater pumping on the groundwater level. To determine this influence and possible leakages, however, is outside the scope of this study. The following analysis is thus only made to obtain initial indications for further investigations and the results are not to be considered representative for the whole power plant area. 8.2.2 Measuring Procedure First, the measuring point is located, and the opening of the well is unlocked and unscrewed. Then, a floater attached to a tape measure (error of +/- 0.1 m) is lowered to the gwl. The tape measure is lifted one or two times to confirm acoustically that the groundwater surface is found, and the value is read of the tape measure at the pipe opening height. To this value the distance between the floater bottom and the start of the tape measure is then added. After the collection of the floater, the groundwater table is recorded and lastly the well is locked again.

8.3 Analysis In Figure 45 the heights of the well openings (above msl) are marked with a dotted line, each. These have been added for reference only. The other lines are interpolations between monthly groundwater values and display the groundwater table variation in m above msl. These values were averaged over 30 years for each measurement point, as described above.

Measurement Point 1

l 25 Measurement Point 2

v e

l Measurement Point 4

e Measurement Point 5

s 20

n Measurement Point 6 a

e Measurement Point 7

e 15

v Tube Top Point 1 o

b Tube Top Point 2

m 10 Tube Top Point 4 Tube Top Point 5 Tube Top Point 6 5 Tube Top Point 7

0 Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Month

Figure 45: Averaged (1988-2019) monthly groundwater tables in 6 wells with the well opening heights drawn as dotted lines. Considering the characteristics of the bedrock, as outlined in chapter 5, it is reasonable to assume that the wells are located in a confined bedrock aquifer. This means that the water carrying layer, the aquifer, is characterized by saturated conditions and stands under pressure. Thus, when a well is installed, water can rise above the aquifer (Fetter, 2000). This can even lead to artesian conditions when the pressure is great enough. In Point 4 this is the case, as water is standing above the surface in the pipe with the exception of the months June to October. Even in August the gwl is on average just 0.8 m below ground.

Figure 46: Upper: Groundwater level (gwl) variation as measured in the confined bedrock aquifer near Fjälkinge. Max. depth of well: -80 m. Lower: averaged gwl variation in the unconfined till and bedrock aquifer near Sänneshult. Max. depth of well: -5.1 m. All values are in m below ground for the period September 2016 to September 2017. Source: SGU (2019a). Compared to another confined bedrock aquifer that is located in Fjälkinge, about 37 km from Karlshamnsverket, it is apparent that the groundwater variation is at most 4 times greater at Karlshamnsverket (see Figure 46). Also, to be noted is that the local time series follows a more gradual pattern compared to the more erratic variation in the Fjälkinge aquifer, although it could also be attributed to the significantly smaller sample size at Karlshamnsverket. The time series is instead seemingly similar to the pattern of an unconfined till and bedrock aquifer as depicted in Figure 46, although the magnitude of the yearly variation is about 25 times greater in the local

68 aquifer. This disqualifies the local aquifer being a unconfined aquifer since the yearly fluctuation in unconfined aquifers is small. Rather, the local gwl variation is to be explained by the operation of oil caverns in the direct vicinity of the wells. It is one of 80 locations throughout Sweden where oil is stored in unlined rock caverns (Werner et al., 2012). As can be seen in Figure 47, the oil is stored on a stationary water cushion. This requires the pumping of groundwater, that is cleaned by the OFA system before being discharged into the sea. Thus, similar to a groundwater well, the groundwater level is significantly lower in the direct vicinity of the cavern than around it. Further, the groundwater level in the direct vicinity is influenced by the oil level in the oil cavern. Since the exact oil levels in the oil caverns during the measurements are not known here, no viable analysis of the gwl variation can Figure 47: Principle of storing oil products be made to determine the in an oil cavern on a stationary water implications on the power plant. cushion. Grey: stationary waterbed; black: This could be done in a later oil; dotted line: groundwater gradient. study. Source: Werner et al. (2012).

Thus, a careful analysis is that the groundwater tables in the analysed area are usually the lowest in July to September depending on the well location on the site. Complimentary, the highest groundwater tables are to be found in the months December to February, which is earlier in the year compared with other aquifers in the region (see Figure 46).

This coincides with the yearly pattern of the sea water level variation, as explained in chapter 6, and it is to be expected that when extreme sea water levels occur also the groundwater table is high. As a result, there is additional stress on the combined drainage and stormwater system and the basement walls when sea water enters the fill area (see chapter 5.5.4), which might create a higher force than designed for. This could lead to the failure of the storm water system and/or the basement walls and needs to be further investigated in later studies. Recommendations regarding future groundwater measurements are listed in Chapter 10.

9. Field Measurements 9.1 Introduction This chapter describes and discusses the results obtained from conducted field experiments within this work. It consists out of water level and conductivity measurements that were conducted in the basement in five points, of which three are access wells (see Figures 48 & 6). Additionally, on an irregular basis the conductivity in the surge basin of block 3 was measured.

Figure 48: upper left: Point 1, Drainage well in block 1; upper right: Point 2, Drainage well in block 2; middle left: Point 3, Drainage well in block 3; middle right: Outer basement wall in block 3 above the storm water system; lower left: Pillar in block 1 above the cooling water culvert, lower right: flooding in the basement of block 3 during January 2, 2019. 71

Besides the reasons named in chapter 2.4.1, these field measurements were conducted to better understand the underlying reasons for the basement flooding as it occurred on January 2, 2019 (see Figure 48) during a sea water level of 107.1 cm above msl.

9.2 Water levels in the basement 9.2.1 Methodology The water levels were measured by using a folding meterstick made of wood. This yielded an error of ±0.001 m to ±0.005 m depending on the depth of the well or the measurement point. As such, point 1 has the lowest error (±0.001 m) as this well is just 35 cm deep so that the meter stick can be read precisely. In contrast, point 2 has the highest error (±0.005 m) as the well is 1.35 m deep and also had the lowest water levels. Thus, the water level had to be derived from the water that stuck on the meter stick when taking it out of the well. Additionally, water level measurements were repeated 2 times in this well due to the uneven ground produced by stones in the well. The same high error is applicable to Point 4 as it is located behind three horizontally stacked pipes so that a view is only possible from a height of around 1.5 m down to the ground. The error for the points 3 and 5 are approximately ±0.003 m due to their intermediate accessibility, depth and insecurity of measurement. To determine the water levels, the base height of the wells was determined first. This was done by applying the meterstick from the ground level (+2.65 m) to the base of the well and for Points 4 and 5 until the concrete/metal protrusion (see Figure 48). Further, real time sea water level data from Karlshamn harbour (Sjöfartsverket, 2019) was used as a comparison. 9.2.2 Results As can be seen in Figure 49, the observed sea water level (swl) at Karlshamn harbour varied from +25 cm to -36 cm in the observation period. Thus, it is only a fraction of the observed swl at Kungsholmsfort in the past, which ranged from -93.5 cm to 132.7 cm relative to the msl. Hence, assumptions for water levels in the basement have to be made for higher or lower swl. This is important to be noted, as in Figure 49 it can be seen that the water levels in the selected points generally follow the swl to a certain extent. That could be attributed to the setup of the pipe systems as explained below. 72

0.3 -1.160

0.2 -1.164

0.1 -1.168 )

(

)

m v

( Point 1

l 0 -1.172

v Point 3

r Point 4

W t

-0.1 -1.176 a

2 Point 5

W n

i Sea Level o -0.2 -1.180 P Point 2

-0.3 -1.184

-0.4 -1.188 25.03. 1.04. 8.04. 15.04. 22.04. 29.04. 6.05. Date (d.mm.2019)

Figure 49: Daily water levels in the measurement points and in the sea. One notable exception is Point 2, which however is not representative due to its connection to a pump and a very small observed variation of 2 cm within the 6 weeks of study. Additionally, due to the small observed water levels the error of the data is quite large, as explained above. Despite the fact that higher water levels are not unusual in this point, indicated by the wet walls of the access well, these were not able to be observed. To be noted here, however, is that the water level does sometimes seem to correlate with the swl, such as in week 1, while for example in week 2 the opposite is the case. This correlation is not significant enough to be attributed to a specific cause as it could be caused by the large measurement errors. On the other hand, the water level in point 4 follows the swl the closest and even matches it on March 28 at 16 cm above msl. This interaction seems only to stop when the swl is 22 cm below the msl as, then, the water level in Point 4 stays constant. The same was observed with the water level in point 3 and also the corresponding Figure 50: Water stands in a well in block 2 judging from own drainage well as the pipe has been observations (see Figure 50). constructed at a too high elevation.

It is unclear if this is also the case in block 1 as this well is not accessible due to cable ladders lying above it. Reasons for this behaviour are given in the next chapter. The water levels in points 1, 3 and 5 also follow the swl, albeit are not as impacted by it. This is to be seen by the smaller variation in water level height compared to the water level in point 4 and the swl. To be highlighted with these measurement points is that no water can be observed in Point 1 when the swl drops below -5 cm, as well as in Point 5 when the swl drops to -12 cm or more under the msl. However, even when this swl threshold is exceeded again it takes a considerably higher swl so that water can be detected again, as can be seen with Point 5 for example. After Point 2, Point 1 usually had the lowest water levels compared to the swl, followed by Point 5, then Points 3 and 4. This indicates that block 3 is much more susceptible to having high water levels in the basement when the swl is high compared to block 1. Flooding in block 3 starts at a swl of 14 cm or higher above msl judging from these observations. It is, however, only expected during a swl 1 m above msl, possibly also 70 cm or 50 cm, that widespread, critical flooding will occur. This has to be confirmed by investigations of the water level in the basement during such a high sea water level. Suggestions to solve these problems are given in chapter 10.2.

9.3 Conductivity 9.3.1 Introduction Conductivity measurements are, amongst others, made to figure out how saline a given water sample is by determining its conductivity. In aqueous solutions the conductivity is dependent on the number of ions, their velocity and their properties. Normally, this means that conductivities are higher when the ion concentration in the sample is higher, as electrical currents then pass easier through the sample (Thermo Fisher Scientific, 2019). This can be utilized to determine the type of water that was analysed. Conductivity is specified as the conductance measured in a sample over a designated distance (cm-1). When using a conductivity meter, however, a measuring cell with a specific geometry (distance/area; cm/cm2) is used. This geometry defines the cell constant K of the utilized cell, which is standardized using a standard solution (Thermo Fisher Scientific, 2019). Thus, conductivity is the product of K and the conductance when using a conductivity meter. 74

Conductance is the inverse of resistance and thus indicates how effortless an ion can move through the water. It is measured in Siemens (S), giving conductivity a unit of S/cm (Thermo Fisher Scientific, 2019). More common, conductivity is stated in milliSiemens/cm (mS/cm) or microSiemens/cm (μS/cm), though. This can be seen in Figure 51 below, where conductivity ranges for different types of water are stated.

Figure 51: Conductivity ranges for different types of water. Changed after: https://www.thermofisher.com/de/de/home/life-science/lab-equipment/ph- electrochemistry /conductivity-measurement-testing/conductivity-probes accessories/jcr:content/MainParsys/ well_7a0d/uipar/textimage_ae6d/image.img.full.high.jpg/1522083491848.jpg

9.3.2 Methodology The conductivities were mostly measured using a Knick Portavo 902 COND portable conductivity meter equipped with a SE202 sensor. This device has a measurement error of <0.5% of the measurement value and the sensor has an error of 0.4 (µS) multiplied by the cell constant of 0.098 (/cm). However, in comparison to the Radiometer Copenhagen CDM 92 Conductivity Meter used in the laboratory, it yields an additional error of -1.4 mS/cm (see Table 9). The portable conductivity meter was still utilized due to the reasons given in the chapter below. Usually, the sensor was therefore introduced into the 75 chosen body of water, which limited the measuring depth to a maximum of 10 cm under the water surface. After pressing the ‘measure’ button, the sensor was left in the water until a stable value of both temperature and conductivity was achieved. This required to monitor if any change happened within 15 seconds and was repeated until stable conditions were attained. For both Point 2 and the surge basin a different approach was chosen. Due to the difficulty to directly access the water in these points it was first sampled with a small plastic bottle. This bottle was during this time fastened in a telescopic sampler that could be extended to 5 m in length. For water in Point 2 the portable conductivity meter was then used to determine the sample conductivity. Afterwards, the bottle was cleaned thoroughly with deionised water and the sample bottle was used again to sample water in the surge basin. That sample was then analysed in the laboratory. 9.3.3 Limitations The conductivity measurements were mostly conducted with a handheld device as explained in Chapter 9.3.2. This yielded a deviation, or error, of up to 1.4 mS/cm compared to more precise conductivity measurements in the laboratory, as can be seen in Table 9. This is due to several reasons. One reason is that the utilized sensor is designed to be operated in solutions with a conductivity of 0.01-200 µS/cm. Another reason is the temperature compensation (TC) to the reference temperature of 25 °C applied by the device in dependence of the chosen anion cation pair sodium chloride (NaCl). While sodium and chloride are the most abundant ions in sea water, they constitute only one part in a mix of different ions in water. Still, this method was applied due to a number of reasons: First, this method is less time consuming and less employee intensive. It suited the goal sufficiently well to determine whether sea water or water from other sources is present in the system. Secondly, the used handheld device is only able to measure conductivities up to 7.8 mS/cm. The conductivity of the Baltic sea water, which was measured by the laboratory on one occasion during this study, is around 13 mS/cm. In contrast, the conductivities in the selected points varied between 0.5 to 4.5 mS/cm (+1.4 mS/cm) with notable exceptions on April 15, as well as May 2 and 3 in Point 4, where a sea water like concentration was found.

Lastly, the sample amount is greater as the conductivity meter simply needs to be held into a body of water, while for the analysis in the lab a small bottle is filled with sample water. This yields a better average value if the conductivity is varying within the measurement point. As an example, the surge basin was once sampled at three different locations, yielding conductivities of 1.515, 1.650 and 1.615 mS/cm with laboratory instrumentation. Table 9: Comparison of conductivities measured by using a portable device and a laboratory device, obtained by analyzing the same sample. The handheld device shows a significant underestimation of the conductivity.

Knick Portavo 902 COND Radiometer Copenhagen CDM 92 2.40 mS/cm 3.59 mS/cm 2.19 mS/cm 3.56 mS/cm 2.20 mS/cm 3.19 mS/cm

9.3.4 Findings Considering these limitations, Figure 52 shows that the salinity in point 4 closely follows the salinity of the surge basin in block 3. One exception to this is the last study week where it rained the weekend before, thus yielding very low conductivities in the storm water pipe system.

14 0.3

12 0.2

10 0.1

)

c /

) Point 1

( m

8 0 l

( Point 2

v t

i Point 3

t a

c 6 -0.1 Point 4

S d

n Point 5 o

C Surge basin 4 -0.2 Sea level

2 -0.3

0 -0.4 25.03. 1.04. 8.04. 15.04. 22.04. 29.04. 6.05. Date (d.mm.2019)

Figure 52: Daily conductivities in the measurement points with the conductivity of the surge basin of block 3 and the sea water level as a reference. 77

9.3.4.1 Background Referring to chapter 3.3, the surge basin is coupled to the Baltic sea via a restricted orifice connecting it to the outflow tunnel that leads into the sea. As water from different sources within the power plant is emptied into the surge basins, water inside these does not have to have the salinity of Baltic sea water. Thus, probably stratified conditions persist where lighter process water floats on top of denser sea water. This is valid to assume as the pumps, that transport fresh sea water into the power plant and subsequently to the surge basin, are only in operation when the plant is in operation. The experiments were mostly conducted during a non-operation period. The water level in the surge basins is thought to be additionally influenced by the swl. 9.3.4.2 Results In accordance with the observations in Figure 49, the water originates from the surge basin and flows contrary to the building design into the storm water system to Point 4, which is confirmed by the observation of a fish in this point. From Point 4, as well as the last access well in block 3, water is leaking into the ground, so that it is picked up by the drainage system. This is backed by the fact that at Point 3 water has nearly the same conductivity as water at Point 4. Only when the swl is 10 cm below msl conductivity measurements are not possible anymore at Point 4 because of the small amount of water above the surface. At that swl water in Point 3 stagnates just as discussed for Figure 49. Thus, even when conductivities of 12 or 13 mS/cm are found in the surge basin they do not translate to points 3 and 4 at low swl. This is only the case when the swl is above -10 cm relative to the msl, as the observation on May 3 shows. Points 1, 2 and 5 (see Figure 6) do not seem to be influenced by water in the surge basin in block 3 judging from the conductivity measurements. This is plausible as, during the examination of the storm water pipe access wells, one access well in block 3 was found to be nearly filled with sediment. As such only minor exchange of water between block 3 and the other two blocks is possible (see Figure 12). Additionally, an investigation of the conductivities in the surge basin of block 1 was omitted in this study due to time concerns. These could differ from the conductivities obtained in the investigated surge basin and thus these points may be influenced by the surge basin of block 1 instead.

9.3.4.3 Discussion The Points 1, 2 and 5 seem to be influenced by the swl only to a low degree, indicating that the water is mostly moving up and down in the pipe systems instead of flowing laterally. This could, however, also be an effect of the applied methodology, as at most only the first 10 cm under the water surface were able to be sampled. Additionally, to be noted here is that the water in the drainage and storm water pipe systems may not solely come from the surge basin and rainfall, but also from groundwater that might itself be a mix of former rainwater and sea water seeping into the area. This can be the case if the outer basement walls are not groundwater tight as explained in chapter 5.4.2.2. Lastly, even though the series of surge basin conductivities is incomplete it does show a trend that when the swl is above the msl, conductivities, and thus the salinity of the water, are lower compared to when the swl is low. However, due to the fact that water is emptied into the surge basins on a fluctuating level it is not valid to assume that this is always the case.

9.4 Conclusions The analysis of the water levels and conductivities in the drainage and storm water pipe systems in the basement have revealed that block 3 is at the greatest risk of being flooded. Minor flooding starts there at 14 cm above msl, although critical flooding is only expected to occur at swl above 0.7 or 1 m. Flooding there most probably stems from surge basin water entering the faulty storm water pipe system, which is then designed to be picked up by the drainage system. Evidently, however, the drainage does not seem to completely function as designed so that flooding occurs. This requires an investigation as outlined in chapter 4.

10. Suggestion for measures Several measures are thinkable in order to minimise or to alleviate the flooding risk and related problems of the described area. These measures should be considered separately, as an action to solve one problem can in the worst case create or worsen another problem. It is thus advisable to prioritize those problems with the worst effects on the operability of the power plant. This chapter is divided into measures that can be taken outside, as well as inside the buildings. Additionally, it will be distinguished between quick fix, also otherwise known as end of pipe solutions, and long-term measures. While the latter measures are initially coupled to high costs, these solutions are cheaper and more effective over longer time scales compared to the quick fix solutions.

10.1 Measures for the fill area In the earlier chapters it was shown that water most probably can be found in the filled area due to the permeable northern dam, as well as due to groundwater inflow and because of infiltrating rainwater. Assuming that the outer walls of the power plant basement are impermeable, as it is stated in the construction documents, this water might only affect the stability of the daily service oil fuel tanks. These have been founded in the fill. Research Due to missing properties of the fill material, and also because of its high grade of heterogeneity, it was not possible to solve the bearing capacity equation, which is stated in the appendix A5. Thus, further research is needed to determine whether the fill is an unstable ground at higher water levels. This is achievable by taking and analysing samples of the fill material and the installation of wells in the fill. These wells would also allow for the determination of the water velocity in the fill, using i.e. the Darcy velocity (Fetter, 2000): 퐾 푣 = 𝑔푟푎푑 ℎ = 퐾 ∗ 퐼/푛 Equation 9 푛 , where v is the velocity of advective transport, K is the horizontal hydraulic conductivity, n is the effective porosity and h, or I, is the horizontal hydraulic gradient. K and n are determined either using samples that are analysed in the laboratory or are roughly estimated using tables that are to be found in 80 literature, i.e. in Fetter (2000). The hydraulic gradient I is determined by measuring the gwl in the wells and is defined by the difference of the gwl (head; h) between two wells separated by a distance l. Thus, I = dh/dl. These wells could even be used for tracer tests to determine the water flow direction if a number of wells are installed. A minimum of eight wells should be built to fulfil all these criteria. A map with suggested sites and a possible section of a well can be seen in Figures 53 and 54. The wells should be made by percussion drilling and outfitted with stainless-steel casings to stabilize them. Further, they should be large enough so that samples can be taken. Measurements of the groundwater level can either be made automatically by means of divers, pressure sensors, piezometers or by hand and should be done frequently and over several years. At the same time the observed sea water level should be noted as a comparison value. Measures When it is determined that the fill is an instable building ground, several measures can be undertaken. These could either be the deconstruction of the daily service oil fuel tanks, the construction of a new foundation and the subsequent relocation of these tanks, or the construction of sheet piling in the fill down to the clay soil. The last measure is also applicable if it is found out that water enters the basement below the basement walls. It is thereby considered more economically feasible than the refitting of the dams in order to make them impermeable also at high sea water levels. Also, the latter would require a temporary construction of a coffer dam which is subject to municipal approval and conditions. In either case, provisions should then be made to lead rain and groundwater into the sea in order to avoid a critical collection of that water in the former strait.

Figure 53: Simplified section of a well if it would be installed in the area.

Figure 54: Recommended sites for monitoring wells in the fill.

10.2 Measures for the basement 10.2.1 Long-term measures In general, the main problem seems to be the storm water pipe system in the basement. As such, it is thinkable to elevate the pipe system to a higher ground level where water from the surge basin cannot enter the rainwater system easily. Currently, surge basin water enters the storm water pipes when the water level in the surge basins is above -1.4 to -0.54 m, depending on the location. Alternatively, one could close the connection between the surge basins and the rainwater pipes. Then, the current pipe system could either be extended south so that the rainwater can be directly discharged into the sea or a pump sump could be built similar to the drainage system collection wells. Even the whole storm water system in the basement could be closed down, which would then make it necessary to find solutions how to lead rainwater into the sea in order to avoid high groundwater levels in the fill. At the new Hong Kong International Airport site this was achieved by constructing culverts in the fill. These lead through the seawalls, where the water is discharged into the sea (Plant et al., 1998). 82

In all these scenarios the outflow tunnel should be closed off and the water level in the surge basins should to be lowered to allow these reconstructions. The same applies during maintenance procedures, such as cleaning or filming the pipes, as only the surge basin of block 3 is equipped with gates that can be shut. It should be preferably done in summer when the sea water level is low, and the power plant is not in operation. Alternatively, a way must be found to shut the connection of the rainwater system and the surge basin of block 1. One example for this is installing temporary inflatable pipe plugs that are commercially available from a large number of manufacturers. This approach, however, does not allow for complete cleaning of the pipes since suction instead of flushing needs to be applied, which is further limited by the capacity of the cleaning truck used. If instead it is feared that the volume of the surge basins is not large enough, the storm water system could be utilized as a backup. However, this would require a thorough inspection and possible exchange of all rubber ring joints and sections of pipes, as well as increased maintenance work. 10.2.2 Quick fix solutions and urgent measures In the basement, the last section of the rainwater main pipe leading to block 4 should be removed or filled with an impermeable material such as concrete. In both cases it must then be ensured that both the basement wall and the southernmost access well are made impermeable. This can be done by filling the space between the pipe and the respective structure it leads through with concrete. Similarly, the space between the electrical cables and the cable access wells to the fine particle cleaning plant should be stuffed to avoid water entering the wells through the gaps. A quick fix to solve the problem with the water standing in the drainage system is the utilization of pumps to lead water from there into other systems, such as the OFA system. This, however, can only be done until the design capacity is reached, which would then require the enlargement of these systems. Additionally, a maintenance plan for the drainage system should be established, as outlined in chapter 4. The importance of maintaining a pipe system can be seen in Figure 55, where sediment or debris fills nearly half the stormwater pipe. This diminishes the available space for water flow in the pipe and, as a result, water is not as quickly transported away. Thus, the pipe system is rendered ineffective when it is subject to large inflows. 83

In conjunction with the maintenance plan, the cable ladders should be moved in such a way that all 51 drainage wells can be accessed. A thorough inspection of the drainage system is important to determine the next necessary actions. Some other possible necessary actions, as noted in chapter 4, include outlining the drainage pipes with a membrane to avoid sedimentation in them or the readjustment of the pipe depths. Also, the measurements of chapter 9 should be continued at high swl to determine their implications on the degree of flooding in the basement. A solution should also be found for the gate in the surge basin that leads to block 4. Filming by a remote operated vehicle (ROV) revealed that there are gaps between the sides and the gate, as well as that the gate itself is in a bad shape. It yet has to be determined what type of surface is behind the gate to be able to decide if the installation of a new gate is required or, in the case of a concrete wall, the gate can be permanently removed.

Figure 55: Picture made by a remote operated vehicle (ROV) at a water depth of 0.9 m. It depicts the west-north-west orientated rain / storm water pipe entering the surge basin of block 1, which is half filled with sediment and debris. Lastly, until it is decided on a long-term strategy for the storm water pipe system, the pipe joints connecting the downspouts with the main storm water pipe should be reconstructed to avoid water leaking from them. It could also be thought about exchanging the cast iron pipes for stainless steel pipes.

11. Discussion and Outlook Utilizing the information collected from literature, original construction documents, technical drawings and own observations enabled to develop an initial analysis and understanding of the processes underlying the local flooding problems. This approach is not only applicable to the examined area but in fact to similar problems worldwide. Based on this knowledge, appropriate measures were proposed that have either been already utilized in similar situations worldwide or which are based on common technical knowledge. It should be noted, though, that an in-depth analysis was not possible, and that further research is needed to increase the resilience of the power plant with regard to climate change impacts. For example, regarding the maximum sea water level height, an analysis of possible wave heights based on measured wind data should follow. Then, it should be combined with the maximum sea water level analysis to obtain the maximum sea water level height thinkable. Further, to determine the approximate runoff volume from rainwater, an analysis of radar data might be better suited and would also require the development of IDF curves. This could also be used as data in a computer model like MIKE Urban if an analysis of the storm water pipe system is considered necessary. With regards to groundwater and the instability of the fill, the construction of wells and measurements of the groundwater levels in the fill area needs to be awaited. Other climate factors, such as temperature, lightning, snow and ice are also probable to change in the near future and might also affect the power plant, although in other ways than water related climate factors. Thus, this study is to be considered as a continuation of the investigation that started with the work of Jönsson & Marcusson (2008) and which should be expanded even more in the future. Nonetheless, it is hoped that with the implementation of proposed measures the employees at Karlshamnsverket have the possibility to cope better with the flooding until it is alleviated by solving the underlying problems that lead water into the basement.

12. Conclusions The aim of this study was to help determine the flow velocity and principle direction of the unwanted water inflow into the area of the power plant and its basement. This was, amongst others, achieved by developing suitable measurement methods to map the flow pattern and magnitude, as well as gathering and analysing (available) information. In addition, worldwide standards for maintaining near coastal drainage systems were investigated that are applicable to the present situation at Karlshamnsverket. These include in particular the implementation of maintenance plans and inspection routines, as well as the setup of a flooding report system to determine the need for further actions. Also, available information on the properties of the sediment fill, which dominates most of the area and which consists out of blast rock and soil, was gathered. This ought to serve as initial information for a future study to determine the risk of instability when the fill is subject to flooding. Available sea level, precipitation, and groundwater data was also examined. Further, the properties of the former two were extrapolated to describe conditions considering a changing climate. The result of both analyses can be seen in Table 10. Thus, a clearer picture of the hydro(geo-)logical situation in the area and the risk of flooding in the near future was obtained so that suitable countermeasures can be implemented. It should be noted, though, that the worst-case scenario as known today was utilized and that the weather and climate could develop very differently in the future. Table 10: Summary of calculated extreme sea water levels and extreme rainfall intensities today and in the near future.

Return Estimated sea Estimated sea Estimated sea period water level (cm) water level (cm) water level (cm) (years) today Year 2050 Year 2100 50 115 (108-129) 139 (132-152) 198 (191-211) 100 122 (113-139) 145 (137-163) 204 (196-222) 200 127 (118-150) 151 (141-174) 210 (201-233) 86

Estimated Estimated future rainfall intensity rainfall intensity (mm/h) today (mm/h) 2 11.1 (9.5-13.3) 13.9 (11.9-16.6) 5 16.1 (13.1-22.8) 20.1 (16.4-28.5) 10 20.6 (16.2-36.3) 25.8 (20.2-45.3) 20 26.2 (18.8-51.1) 32.7 (23.5-63.9) Water inflow into the power plant area presumably consist of seawater flowing through the permeable northern dam and groundwater, that flows towards the low-lying area where the power plant is located. In addition, rainwater infiltrates the permeable fill, also by means of specifically built infiltration wells. The velocity of the water inflow in the power plant area can be determined after observation wells have been installed in the fill and the hydraulic conductivity of the fill material was measured or approximated. Then, water levels, that should be measured in these wells on a regular basis, can be used to calculate the groundwater flow velocity. Water inflow into the basement, in connection to the inflow into the power plant area, is certainly related to a faulty storm water pipe system, as well as to other pipe systems that lead into the two surge basins of the power plant. It yet has to be determined whether large amounts of water can also enter below the outer walls, though. The velocity of the water inside the basement can be determined by means of tracer tests, if needed. The directly visible surface impacts of extreme high sea water levels or extreme rainfall, as they were estimated in this study, are expected to be rather small. It is unlikely that large or important parts of the power plant area will be subject to surface flooding because of these factors. Rather, these factors will affect the underground, that is the fill on one side and the basement on the other side. That is because the stability of the fill depends, amongst others, on the groundwater level, which rises with an increasing swl. If the ground below the outer walls has blast induced fractures this will also lead to larger water inflows in the basement due to the higher surrounding groundwater pressure. Higher water levels in the basement are, however, rather expected because of higher water levels in the surge basins due to high swl. This results in a 87 counter design flow into the faulty storm water pipe system and thus it is recommended to change the current design of it. Also, more water will enter the storm water system from the power plant area due to increased sea water inflow with high sea water levels. As of now, flooding in the basement is to be expected to first occur at sea water levels of 14 cm above msl in block 3. This, however, is not regarded as critical. Widespread and thus critical flooding in the basement is rather to be expected during sea water levels of +1 m above msl, possibly also +0.7 m or even +0.5 m. This should be investigated when such extreme sea levels occur in the near future. Water levels +0.5 m above msl are to be expected every year, while a water level of +0.7 m above msl is exceeded at least every other year and +1 m above msl is expected to happen at least twice per decade judging from observations. Flooding of the basement is also expected as a result of downpour events. It is, however, unclear what the critical rainfall amount for the current pipe system is. In general, flooding is to be expected due to a combination of bad maintenance in the past and natural factors.

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Appendices A1: Sea level extremes Table 11: Input data for the extreme value analysis in R to determine sea level extremes. Max per year denotes the period January-December for the given year and Meteo year the period July-June. Data from Kungsholmsfort, relative to the mean sea level (MW) provided by SMHI.

Year Max per Meteo Year Max Meteo Year Max Meteo year year per year per year year year 1887 89.5 89.5 1910 86.7 86.7 1933 37.9 71.9 1888 57.5 66.5 1911 65.7 64.7 1934 71.9 60 1889 66.5 41.5 1912 66.7 66.7 1935 83 83 1890 93.5 93.5 1913 116.7 132.7 1936 74 72 1891 56.5 65.5 1914 132.7 66.7 1937 72 72 1892 65.5 49.5 1915 55.8 66.8 1938 72 76 1893 63.5 83.5 1916 66.8 63.8 1939 76 44 1894 83.5 78.5 1917 99.8 99.8 1940 72 72 1895 64.6 90.6 1918 70.8 46.8 1941 59 59 1896 90.6 43.6 1919 44.8 44.8 1942 76 88 1897 54.6 69.6 1920 51.8 81.8 1943 88 60 1898 107.6 107.6 1921 81.8 86.8 1944 60 70.1 1899 101.6 101.6 1922 86.8 58.8 1945 70.1 82.1 1900 66.6 68.6 1923 90.8 90.8 1946 82.1 48.1 1901 73.6 73.6 1924 69.8 65.9 1947 44.1 44.1 1902 69.6 77.6 1925 65.9 59.9 1948 60.1 93.1 1903 77.6 63.6 1926 49.9 49.9 1949 93.1 53.1 1904 110.6 113.7 1927 51.9 51.9 1950 54.1 54.1 1905 113.7 76.7 1928 49.9 49.9 1951 69.1 69.1 1906 87.7 87.7 1929 53.9 53.9 1952 66.1 52.1 1907 58.7 80.7 1930 65.9 65.9 1953 58.1 73.1 1908 80.7 47.7 1931 65.9 77.9 1954 73.1 62.1 1909 64.7 64.7 1932 77.9 49.9 1955 73.2 73.2

Year Max per Meteo Year Max Meteo Year Max Meteo year year per year per year year year 1956 52.2 44.2 1979 60.4 60.4 2002 90.6 61.8 1957 62.2 62.2 1980 69.4 69.4 2003 83.5 83.5 1958 52.2 52.2 1981 71.4 71.4 2004 89 89 1959 52.2 36.2 1982 58.4 105.4 2005 74.5 50.7 1960 60.2 70.2 1983 105.4 88.4 2006 86.9 105.2 1961 70.2 110.2 1984 76.4 46.4 2007 105.2 65.4 1962 110.2 50.2 1985 66.5 66.5 2008 70.3 70.3 1963 71.2 86.2 1986 86.5 86.5 2009 78.9 78.9 1964 86.2 63.3 1987 64.5 64.5 2010 58.2 76 1965 63.3 43.3 1988 100.5 100.5 2011 76 103.8 1966 49.3 58.3 1989 92.5 93.5 2012 103.8 52.7 1967 98.3 98.3 1990 93.5 56.5 2013 81.6 81.6 1968 65.3 33.3 1991 68.5 107.5 2014 68.4 74.4 1969 68.3 68.3 1992 107.5 82.5 2015 74.4 68.2 1970 76.3 76.3 1993 82.5 63.5 2016 65.4 108.4 1971 78.3 78.3 1994 62.5 97.6 2017 108.4 68.8 1972 63.3 63.3 1995 97.6 77.6 2018 75.4 107.1 1973 90.3 90.3 1996 46.6 86.6 2019 107.1 1974 82.3 88.4 1997 86.6 75.6 1975 88.4 91.4 1998 58.6 58.6 1976 91.4 54.4 1999 65.6 65.6 1977 67.4 71.4 2000 65.6 45.6 1978 76.4 76.4 2001 104.6 104.6

A2: Precipitation extremes Table 12: Input data for the extreme value analysis in R to determine precipitation extremes. Max. precipitation (mm/h) today refers to the highest hourly precipitation observed during the given year. Max. precipitation (mm/h) future is the same value as today, multiplied by a factor of 1.25 to account for a future climate. Data from Hanö provided by SMHI.

Year Max. precipitation (mm/h) today Max. precipitation (mm/h) future 2002 46.4 58 2016 22.6 28.3 2006 19.6 24.5 1999 18.5 23.1 2011 16.2 20.3 2010 13.3 16.6 2014 12.4 15.5 2005 12.1 15.1 2007 11.9 14.9 2009 11.8 14.8 2013 11.6 14.5 2001 11.5 14.4 2000 11.4 14.3 2017 10.9 13.6 1996 10.2 12.8 2012 10.2 12.8 1997 9.5 11.9 2008 9.3 11.6 2003 9.1 11.4 2018 7.8 9.8 1998 7.2 9.0 2015 6.9 8.6 2004 6.3 7.9

A3: Groundwater levels Table 13: Groundwater levels (in meters above mean sea level) averaged over 30 years by month in 6 of 8 observation wells.

A4: Field Measurements Table 14: Water level, conductivity and visual observations made during field measurements in five 5 access points and in the surge basin of block 3 in relation to the sea water level, wind and precipitation approximately at the same time or

averaged over the measurement period as measured at Karlshamn Harbour.

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A5: General bearing capacity equation (Per Johan Gustafsson, Personal Communication):

′ qb = cNcscdcicgc + qNqsqdqiqgq + (1⁄2)γ̅ bN훾푠훾푑훾𝑖훾𝑔훾 Equation 10

, where:

푞푏 is the bearing carrying capacity (force/area) c is the soil cohesion

Nc, Nq and Nγ are functions of ∅, according to the table below sc and 푠푞 are calculated according to: 1 + 0.2 푏⁄퐿

푑푐 and 푑푞 are calculated according to: min(1 + 0.35 푑푓⁄푏 , 1.7), where 푑푓 is the grounding depth

𝑖푐 is calculated by: 1 − 2퐻/(푏퐿푐푁푐) if ∅ = 0 or 𝑖푞 − (1 − 𝑖푞)/(푁푞 − 1) if ∅ > 0. H is the horizontal load component.

𝑔푐 = 1 − 훽⁄147° if ∅ = 0. 훽 is the slope of the ground in degrees q is the effective overlay pressure 3 𝑖푞 = (1 − 0.7퐻⁄(푉 + 푏퐿푐 푐표푡∅)) ; V is the vertical load component. 3 𝑔푞 and 𝑔훾 are calculated by: (1 − 0.7 tan 훽) 푦̅′ is the mean of the effective density of the soil layer from the grounding ′ level down a distance b. It is = 훾푑 if ℎ푔 ≥ 푏 or = 훾′ + (ℎ푔⁄푏)(훾푑 − 훾 ) if 푏 ≥ ℎ푔 ≥ 0. ℎ푔 is the groundwater level under the grounding level. b and L are the width and the length of the grounding area with 푏 ≤ 퐿

푠훾 = 1 − 0.4푏⁄퐿

푑훾= 1 3 𝑖훾 = (1 − 퐻⁄(푉 + 푏퐿푐 cot ∅)) Buoyancy functions according to Prandtl:

∅ Nc N푞 Nγ ∅ Nc N푞 Nγ ∅ Nc N푞 Nγ 0 5.14 1.00 0 ------16 11.6 4.34 1.42 26 22.3 11.9 7.64 36 50.6 37.8 41.1 17 12.3 4.77 1.70 27 23.9 13.2 8.99 37 55.6 42.9 49.1 18 13.1 5.26 2.02 28 25.8 14.7 10.6 38 61.4 48.9 58.9 19 13.9 5.80 2.40 29 27.9 16.4 12.5 39 67.9 56.0 70.9 20 14.8 6.40 2.84 30 30.1 18.4 14.7 40 75.3 64.2 85.6

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21 15.8 7.07 3.36 31 32.7 20.6 17.4 41 83.9 73.9 104.0 22 16.9 7.82 3.96 32 35.5 23.2 20.6 42 93.7 85.4 126.0 23 18.1 8.66 4.67 33 38.6 26.1 24.4 43 105.1 99.0 154.0 24 19.3 9.60 5.51 34 42.2 29.4 29.0 44 118.4 115.0 190.0 25 20.7 10.7 6.48 35 46.1 33.3 34.4 45 134 135.0 234.0

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A6: Soil definitions Dy and gyttja are less known soil types, which is why a short definition is given here using the description as given by Ismail-Meyer et al. (2018). Both are formed under water and contain a lot of organic matter.

Dy: is also known as peat mud. It consists of humus layers that sedimented in acidic water with few nutrients.

Gyttja: is also known as eutrophic mud. It displays different properties depending on the degree of wetness. It consists of larger organic particles that are rich in nutrients.

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