Isostatic uplift and 17th century military planning – causes for the flooding of a historic Swedish town

When an Asset Becomes a Curse

EAA Glasgow 2015 – Session LV 4

Claes Pettersson, archaeologistJönköpings County MuseumSwedenclaes.pettersson@jkpglm.se

Fredric Jonsson, Fire Protection EngineerFire and Rescue Services, Jönköping MunicipalitySwedenfredric.jonsson@jonkoping.se

Lake Vättern – an inland sea

…or rather an inland fjord?

Jönköping – pop. 123 000Founded in the 13th century / relocated in 1613Situated on the southern end of Lake VätternLength = 135 km / Width =

31 kmMax depth = 120 mVolume = 77,6 billion m3 water

Motala ström – the sole outlet

The Project – a Fortress Town in the Dutch Fashion

The New Jönköping – a 17th century State of the Art Design

A strategically important border fortressPlanned according to Simon Stevins’ principlesWater and wetland being its first line of defence

The town in 1690

Draft from 1619

The Problem – A Highly Unsuitable Place for a Town

Landfill made by private owners 1640 – 1800

Sand – landfill funded by the Crown in the 1610s

Where to build:“The Morass”- a peat bog…

Where to build:On timber caissons and landfill…

An estimated 20 000 wagon loads of landfill was needed before any of the houses in the new town could be built…

A constantly rising groundwater level

Casemates in the Carolus bastion; Jönköping Castle, built in the 1610s

Stone cellar built in 1618, issued with a number of floor levels due to rising ground water

The ground water level in the central part of historic Jönköping (the 17th century town) has risen with an estimated 40 cm due to the isostatic uplift. Thus drowning previously dry floor levels and other remains.

Issues that remain…

Jönköpings railway station during an ice-storm in 1928

A street in the 17th century town during the flood of 1920

In the 400 years that has passed since the fortress town was built numerous floods and severe storms have caused severe damage in Jönköping

Heavy rains & isostatic uplift – the present situation

No margins – a northerner hits town in the 1940s

Todays’ situation: Areas in the historic town that will be flooded if the water table rises with between 0,5 and 1 meter

The average water level in Lake Vättern:+ 88.52 meters above the sea level with a normal span of variation from + 87.92 to + 88.95 as seen on a yearly basis. (Source: SMHI)

But during heavy rainfall rapidly rising water levels in streams and lakes south of the historic town centre might spill over into the build up areas.

2013 – 63 mm in 30 minutes flooded the Ryhov hospital area…

Isostatic uplift – past and future Jönköping…

Jönköping valley today – after landfill A thousand years from nowFive hundred years ago

The isostatic uplift will slowly drown the historic city centre - Lake Vättern moves southwards

Measures to slow down the consequences:• Levees protecting the core area• Increased water-flow in the outlet, Motala Ström• New built-up areas planned in safe levels

(Source: SGU)

Plans for a new town – realistic or not?

Living very close to water – something essential?

Jönköping in 2030 – with a new district south of the lakes

The Vision:• 150 000 inhabitants in 2030• A new district south of the

lakes• …partly built on former

wetland• High speed railway+ 90,3 meters above sea level = the lowest safe level for

new housing

Motala ström – the Sole Outlet of Lake Vättern

Hydropower and fisheries share a long tradition in the Motala Ström River

Drainage area for Lake Vättern

Water level in Jönköping 1900 to 2006

Difference in water level between Motala and Jönköping 1900 to 2006

A more rapid isostatic uplift in the northern end of Lake Vättern results in a water level rising with 1,1 to 1,7 mm yearly in Jönköping

Submerged pre-history

A bronze age cairn in Huskvarna bay:• Diameter 20 meter• Height 2 meter• Today 5 meters below the

surfaceThe Huskvarna Bay offers a quite unique submerged inland landscape. A lagoon at the river mouth, an oak forest, a peat bog. Plus a number of man made features like cairns, poles and timber constructions. Finds include two swords and a torque from the bronze age, deposited in the bog.

The Erosion of History…

Mårup Church in Denmark – soon to fall off the edge

Rosenlundsbankarna – erosion and a changing coastline caused by isostatic uplift

Although far less spectacular than the rapidly retreating coastline in Danish Western Jutland, the erosion in the south Vättern basin continues with at least 20 – 30 meter in a century. Close to the Rosenlund Heights the Sanna parish church disappeared in the 16th century. Old place-names indicates that there might have been Pre-Christian cemeteries too, using the magnificent setting.

The Problem with Fortress Towns…

Kristianstad – built on a small island among lakes and marshes. A late 17th century map

Two medieval towns discontinued, being replaced by Kristianstad

The same conflict – The Kalmar War of 1611 – 1613The same causes – Old towns devastatedThe same solutions – Fortress towns in Dutch fashion…and the same problems – re-occurring floods!

It will happen again…

Kristianstad on the brink of disaster in 2002…

By rowboat in the city centre in 1928(+ 2.23 m above sea level)

Makeshift levee in the city centre 2002 (+ 2.15 m above sea level)

With a changing climate historic Kristianstad is even worse off than Jönköping, being situated between + 4 meter above and – 2.41 meter below sea level…

A permanent protection?

Normal water levels Worst case scenario today – with a rise of 2 meters + failing levees

New levees - safeguarding the city against seasonal floods

… but will that be sufficient in times of a changing climate?

Consequences of an Ice Age and Wars Long Forgotten

Strategic considerations makes lousy town planning…

Plans for the future

The paradox – fortress towns once protected by water …became civil towns threatened by that same fluid

Jönköping in the 21st century:• A historic city centre• Plagued by re-occurring floods since its foundation• Isostatic uplift makes things worse …and

unstoppable• Experiences from the past – a help in the present• Archaeological data combined with written sources

becomes an asset in todays planning!