Bucharest isn't flatROEN
The Colentina lakes as steps.

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  1. Measured from space · NASA's ICESat-2 and GEDI lasers

    Bucharest isn't flat

    Look up a street's heightor walk down the stairs: Mogoșoaia to Cernica

    The Colentina lakes, which cross the north and east of Bucharest, Romania's capital, do not sit at one level. From Mogoșoaia to Cernica the water comes down 37.6 m, lake by lake, in 11 drops. NASA's ICESat-2 satellite measured their surface from space: for the nine lakes with a published official level, within 0.4 m of it. Beneath them the whole city tilts the same way, and any street has a height you can look up here.

  2. The Colentina river, west to east

    Twelve lakes, twelve steps#

    The Colentina enters Bucharest from the north-west and leaves to the east through a chain of lakes: Mogoșoaia, Chitila, Străulești, Grivița, Băneasa, Herăstrău, Floreasca, Tei, Plumbuita, Fundeni, Pantelimon and Cernica. On a map they look like a necklace; in profile, they are a staircase.

    Each blue dot is a photon of the ICESat-2 laser that came back off the water. On a lake every photon gathers at one height, so each lake shows as a flat step. Between two lakes the water drops over a dam (between Fundeni and Pantelimon, over two: the Pantelimon I lake between them is not measured here). The vertical scale is greatly exaggerated: this stretch of river is 45 km long.

  3. The upper steps

    Mogoșoaia, 91.2 m above sea level#

    Lake Mogoșoaia is the highest of the twelve: 91.2 m. Then come Chitila (88.1 m), Străulești (85.6 m), Grivița (83.4 m) and Băneasa (80.4 m). The steps here are small, around 2–3 m each.

  4. The steps in the city

    Herăstrău sits 4.2 m above Floreasca#

    Herăstrău lake, at 78.9 m, and Floreasca lake, at 74.7 m, are separated by a dam. Over it the water drops 4.2 m in one go, about one and a half storeys of a block of flats.

    Tei lake is another 2.5 m lower. On every Colentina lake for which City Hall publishes a normal level, the laser read almost exactly that level: the largest difference is 0.4 m.

  5. The lower steps

    The last step is the tallest: 6.7 m, down to Cernica#

    After Plumbuita (68.2 m) and Fundeni (64.6 m), the river leaves the city. Between Pantelimon lake (60.3 m) and Cernica lake (53.6 m) is the biggest drop of the whole chain: 6.7 m.

    From Mogoșoaia to here the water has come down 37.6 m, about the height of a thirteen-storey block, over 45 km of river.

How high is a street#

Beneath the lakes, the city tilts the same way. Measured by the two lasers, the ground in Bucharest rises from 60 m in the east to 95 m in the north-west (leaving out the lowest and highest 1% of the city). Piața Unirii, the big square in the Dâmbovița valley, sits at about 70 m; Militari and Băneasa at about 92 m.

Type a street and number, or tap the map. You get the height of the ground, the difference from Piața Unirii and how sure the value is: the farther the nearest laser measurement, the larger the possible error.

Try:

The result appears here: the height, the difference from Piața Unirii and how sure it is.

Height of the ground in Bucharest, measured by laser

Dots are laser measurements; the faded colour between them is estimated. Tap anywhere on the map.

Why the lakes are a staircase#

Until the 1930s the Colentina wound through a floodplain of ponds and marshes. Works began in the mid-1930s (the Buftea dam opened in 1935; a 1936 book on the draining of the Colentina lakes lists the engineers N. G. Caranfil, Dorin Pavel and others as its authors): the channel was embanked and the ponds turned into reservoirs, each held back by an earth dam with a spillway. Bucharest City Hall now counts 15 reservoirs on the Colentina, from Buftea to Cernica; twelve are measured here (Buftea, Buciumeni and Pantelimon I are missing).

Each dam holds the lake above it at a set level, the normal retention level. That is why the water surface comes down in steps: the water lies flat on each lake, then drops suddenly over the dam.

How accurate is a laser from space on a lake#

For nine of the lakes, Bucharest City Hall publishes the normal level in metres above the Black Sea. Each time the laser gave a close value, at most 0.4 m lower:

Lake levels: official and measured by the laser
LakeNormal level (City Hall)LaserDifference
Străulești lake85.90 m85.58 m−0.32 m
Grivița lake83.55 m83.42 m−0.13 m
Băneasa lake80.40 m80.39 m−0.01 m
Herăstrău lake79.10 m78.86 m−0.24 m
Floreasca lake74.70 m74.68 m−0.02 m
Tei lake72.60 m72.20 m−0.40 m
Plumbuita lake68.50 m68.24 m−0.26 m
Fundeni lake65.00 m64.60 m−0.40 m
Pantelimon lake60.50 m60.26 m−0.24 m

The small gap has two causes: the laser and Romanian maps use slightly different height references, and in summer the lakes can sit a little below their normal level. Lacul Morii, on the Dâmbovița, sat 0.7–1.1 m below its normal level (84.50 m) in the three summers measured. That is an observation from three passes, not a trend.

How the ground was measured#

Two NASA lasers measured Bucharest's ground: ICESat-2, which flies at 496 km and draws lines of photons, and GEDI, on the International Space Station, which measures footprints about 25 m across. From ICESat-2 the page keeps the photons NASA classes as ground; from GEDI, only shots far from buildings with nothing tall in the circle. In all, 54,525 measurements of the ground in and around the city.

Between measurements, the height is estimated from the nearest points. As a check, one 600 m square at a time was removed and predicted from its neighbours: 300–500 m from the nearest measurement, the typical error was 0.7 m, and under 3.3 m in nine cases out of ten. On Strada Izvor the laser gives 71.2 m; the 1974 land-survey plan gives 71.0–71.3 m.

Two things stay hidden. The ground under large buildings: the Palace of Parliament stands on the plateau of Arsenal Hill, at about 88 m, and the laser cannot see the ground under it (its story is here). And small hills that no laser line crosses, such as Metropolitan Hill, which the map smooths over.

Sources#

  • NASA ICESat-2, ATL03 and ATL08, version 7, via SlideRule Earth nsidc.org
  • NASA GEDI L2A, version 2, via SlideRule Earth lpdaac.usgs.gov
  • OpenStreetMap: lakes, the Colentina river, buildings, addresses (ODbL) openstreetmap.org
  • Wikidata: Lacul Băneasa (Q3214777), for the lake's position wikidata.org
  • Bucharest City Hall, PAAR: normal retention levels of the lakes (mdMN75) doc.pmb.ro
  • Bucharest City Hall, risk plan: Lacul Morii, normal level 84.50 m doc.pmb.ro
  • Bucharest City Hall, HCGMB 294/2024: the 15 reservoirs on the Colentina and their history hcl.usr.ro
  • Euronews Romania: the Buftea dam, in service since 1935 euronews.ro
  • Asanarea lacurilor Colentinei, 1936 (Bucharest Digital Library) biblioteca-digitala.ro
  • Bucharest City Hall: the relief of Bucharest (maximum height 96.3 m) www2.pmb.ro
  • The EGM2008 geoid model (NGA), via PROJ cdn.proj.org

The same ICESat-2 data show, on another page, Bucharest photon by photon, and its trees. There Herăstrău reads 78.8 m: one pass, 9 July 2024; here the values are the median of every summer pass.