Geography of Stockholm

thumb|350px|June 2017 aerial view of western Stockholm and Lake Mälaren.

alt=|thumb|350x350px|ESA satellite photo of Stockholm

The City of Stockholm is situated on fourteen islands and on the banks to the archipelago where Lake Mälaren meets the Baltic Sea. The city centre is virtually situated on the water.

The area of Stockholm is one of several places in Sweden with a joint valley terrain. In these landscapes erosion along geological joints has split the flattish upper surfaces into low-lying plateaus. In the case of Stockholm the plateau surfaces are remnants of the Sub-Cambrian peneplain.

Lakes and watercourses

{| class="wikitable" align="right"

|+ Highest values of water pollution registered in Stockholm (2002)

! Watercourse !! Value - (μg/g)

! colspan="2" | Lead - top sediments

| Beckholmen - Djurgården || 5,700

| Riddarfjärden || 940

| Liljeholmsviken || 610

! colspan="2" | Lead - deep sediments

| Liljeholmsviken - Reimersholme || 3,400

| Bällstaån - Bällstaviken || 1,900

| Riddarfjärden - south of Långholmen || 1,700

! colspan="2" | Cadmium - top sediments

| Brunnsviken - Bergianska trädgården || 15

| Saltsjön - Beckholmen || 10

| Brunnsviken - Haga Södra || 8,6

! colspan="2" | Cadmium - deep sediments

| Sicklasjön || 110

| Brunnsviken - southern part || 50

| Brunnsviken - northern part || 37

! colspan="2" | Copper - top sediments

| Bällstaviken - Ulvsundasjön || 4,590

| Saltsjön - south of Djurgården || 1,400

| Råcksta träsk || 1,200

! colspan="2" | Copper - deep sediments

| Bällstaån, outlet || 17,000

| Lake Mälaren, north - of Stora Essingen || 11,000

! colspan="2" | Mercury - top sediments

| Saltsjön - Beckholmen || 38

| Liljeholmsviken || 22

| Saltsjön - Beckholmssundet || 14

! colspan="2" | Mercury - deep sediments

| Bällstaån - outlet || 100

| Liljeholmsviken || 28

| Klara sjö || 17

The access to fresh water is excellent in Stockholm today. Historically, lakes and watercourses were used as refuse dumps and latrines, causing epidemic cholera and many other diseases. By the 1860s water was being drawn from Årstaviken, the waters south of Södermalm, and was treated in the first water-purifying plant at Skanstull and from there distributed through water mains.

As in other urban areas, the lakes of Stockholm are directly affected by the city's sewer system and pollution from settlements, traffic, and industry. Sewers often reduce the catchment areas of smaller lakes by redirecting surface water to Lake Mälaren or Lake Saltsjön. While nutritious substances such as phosphorus and nitrogen are mostly derived from agriculture, urban areas produce high amounts of metals and organic compounds. In Stockholm, this mostly applies to central bays – such as Klara sjö, Årstaviken, Ulvsundasjön, Riddarfjärden, and Hammarby Sjö - but also waters surrounded by bungalows and villas – like Långsjön in Älvsjö.

These first bridges were in no sense technically complicated or physically impressive, but rather simple wooden bridges, either floating bridges or beam bridges resting on poles or stone caissons, in either case with spans of no more than a few metres. The width probably corresponded to the directions for public roads, eight ell or 4,8 metres, which was probably more than enough for many centuries. The long and narrow bridges were easily demolished in case of siege, which besides the drawbridges, also necessary for the passing of ships, was an important defensive strategy. As the accounts of the city tells, spring floods and ice break-ups resulted in the frequent destruction of the bridges.

Not until the 20th century, Stockholm was able to surpass the straits and bays surrounding the city. Half of the about 30 bridges in central Stockholm were built 1920–50, most of them during the 1930s. This development was due to increasing traffic loads caused by a fivefold increase of vehicles in the 1920s. At Slussen, passing ships caused stationary rows of trams several hundreds metres long. The situation was solved when a traffic committee in 1930 could present the so-called "clover-leaf solution" of engineer Gösta Lundborg and architect Tage William-Olsson inaugurated in 1935. The modernity of the solution put Stockholm in a state of rapture and impressed even Le Corbusier, who praised the scale of the construction and invited the world to follow the example of Stockholm.

Meanwhile, across the Riddarfjärden bay, construction works had started on Västerbron, the large bridge offering a north–south passage west of the historical city centre. Designed by architects David Dahl and Paul Hedqvist and engineered by Ernst Nilsson and Salomon Kasarnowski, Västerbron became the first large bridge designed by this quartet. Tranebergsbron was inaugurated in 1934, with its span of 200 m, for a few years the world's longest span. These large-scale bridges not only tied various parts of the city together, but their mere size changed the cityscape permanently. Considerably smaller but during the decade equally praised was the small Riksbron designed by Ragnar Östberg.