Flooding at Karlshamnsverket - Analysis and Recommendations

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.

Abstract (Swedish)

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.

Popular Abstract

Flooding of coastal housing and infrastructure is a worldwide problem that creates a lot of damage. It leads to costs that amount to hundreds of millions of Swedish crowns per year in Sweden alone! In the future this flooding problem is about to get much worse because of our human actions and the wish to live near the coastline. Karlshamnsverket, a coastal power plant, is an example of an infrastructure affected by coastal flooding.

The results of this study show that flooding of the power plant itself is unlikely, also in the near future. The main problem is the basement under the power plant. Here, longer and more flooding than already today must be expected with time. This is critical because it contains important pipes and electrical cables that are important to run the power plant. These are either damaged or cannot be operated during flooding. Thus, doing nothing cannot be an option for economic reasons alone.

A cause that likely contributes to the basement flooding is a poorly maintained and insufficient functioning drainage system. As a result, a maintenance plan was set up in this study.
The greatest cause of flooding was determined to be the storm water pipe system, though, and as result has to be altered. As this pipe collects both drainage/groundwater and rain water, but is also connected to sea water, it is influenced by all three types of water. This required an independent analysis of these three water types.
Due to ground and rain water data limitations, the sea water level was established to be the greatest factor leading to basement flooding. Sea water proposedly enters the storm water pipe system in a number of ways, of which the most problematic is through the soil surrounding the power plant, in which also this pipe system begins. The cause for this inflow is a dam to the north-west of the power plant that structurally does not prevent water inflow. To confirm this educated guess, observation wells must be installed in this soil. If sea water is found, the construction of sheet piles, vertical steel walls, should be considered. These also serve to reduce the risk for potential ground instability of the soil surrounding the power plant during high water levels. An unstable ground could otherwise damage structures founded in the soil.

To get these results, this study used worldwide literature and site documentation. Also, data were collected and analyzed, and field measurements were made. This approach is applicable to similar problems worldwide. The recommendations given here can be used as a starting point for future actions to reduce or even prevent future flooding not only at the analyzed location.

• author: Wirtz, Daniel
• supervisor: Magnus Larson
• organization: Division of Water Resources Engineering
• course: VVRM01 20191
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• publication/series: TVVR 19/5011
• report number: 19/5011
• ISSN: 1101-9824
• language: English
• additional info: Examiner: Rolf Larsson
• id: 8995350
• date added to LUP: 2019-09-19 14:27:31
• date last changed: 2019-09-20 03:45:55