**2. Lake evolution and drainage basin**

During the final days of May 1872, an extensive area of southwestern and western Bohemia was affected by a massive incident of torrential rain, which according to historical reports lasted from noontime on 25 May until the morning of the following day. The Pilsen rain gauge recorded two thunderstorms on 25 May 1872, from which a total of 40 mm of precipitation was measured (Skrejšovsky 1872). However, a far greater sum of precipitation fell north of Pilsen, where no rain gauge was in operation at that time. Nevertheless, Karel Kořistka, a prominent cartographer, provided a detailed description of the meteorological situation (Kořistka 1872): "Observed in Mladotice, a standing empty vessel that was 9 inches or 237 mm tall was filled to the brim within one hour's time to the point that additional rain overflowed the vessel…".

This report of 237 mm of precipitation in one hour was for a long time considered to be unrealistic. Only with the measurement of torrential rain in southern Slovakia – i.e. in a similar Central European climate zone, recorded on 12 June 1957, when 225.5 mm of precipitation fell during 65 minutes at Skalka by Šturovo (southern Slovakia) – was the feasibility of these earlier data confirmed (see Štekl et al. 2001).

The extreme precipitation in May 1872 caused an extraordinarily destructive flood which devastated the catchment areas of the Střela and Blšanka Rivers as well as most of the Berounka River basin below Pilsen. On May 26, at 2 pm, the discharge of the Vltava in Prague was measured at 3300 m³/s, which represents the fifth largest flood observed since 1825 (Brazdil et al. 2005).

As a consequence of earthworks for a railway track at the footslope and the extreme rainfall event, large masses of rock slumped down from the western slope of the Potvorovsky Hill (546 m asl) into the Mladoticky valley during the night from 27 to 28 May, damming the creek with a massive dike (Fig. 1). Bedrock and mass accumulation mainly consist of

Fig. 1. Dammed valley immediately after the landslide in May 1872; the lake is emerging in the background. Print from Geografie (Sbornik ČSZ) 28, Praha 1912. Photo by C. Purkyně.

During the final days of May 1872, an extensive area of southwestern and western Bohemia was affected by a massive incident of torrential rain, which according to historical reports lasted from noontime on 25 May until the morning of the following day. The Pilsen rain gauge recorded two thunderstorms on 25 May 1872, from which a total of 40 mm of precipitation was measured (Skrejšovsky 1872). However, a far greater sum of precipitation fell north of Pilsen, where no rain gauge was in operation at that time. Nevertheless, Karel Kořistka, a prominent cartographer, provided a detailed description of the meteorological situation (Kořistka 1872): "Observed in Mladotice, a standing empty vessel that was 9 inches or 237 mm tall was filled to the brim within one hour's time to the point that additional rain

This report of 237 mm of precipitation in one hour was for a long time considered to be unrealistic. Only with the measurement of torrential rain in southern Slovakia – i.e. in a similar Central European climate zone, recorded on 12 June 1957, when 225.5 mm of precipitation fell during 65 minutes at Skalka by Šturovo (southern Slovakia) – was the

The extreme precipitation in May 1872 caused an extraordinarily destructive flood which devastated the catchment areas of the Střela and Blšanka Rivers as well as most of the Berounka River basin below Pilsen. On May 26, at 2 pm, the discharge of the Vltava in Prague was measured at 3300 m³/s, which represents the fifth largest flood observed since

As a consequence of earthworks for a railway track at the footslope and the extreme rainfall event, large masses of rock slumped down from the western slope of the Potvorovsky Hill (546 m asl) into the Mladoticky valley during the night from 27 to 28 May, damming the creek with a massive dike (Fig. 1). Bedrock and mass accumulation mainly consist of

Fig. 1. Dammed valley immediately after the landslide in May 1872; the lake is emerging in the background. Print from Geografie (Sbornik ČSZ) 28, Praha 1912. Photo by C. Purkyně.

feasibility of these earlier data confirmed (see Štekl et al. 2001).

**2. Lake evolution and drainage basin** 

overflowed the vessel…".

1825 (Brazdil et al. 2005).

Palaeozoic shale, sandstone and conglomerate, with some Proterozoic phyllite and spilite and Palaeozoic granite (Česky geologicky ustav 1996). The created lake is, up to the present day, the only example of such a genetic type of lake in the Bohemian Massif.

The preconditions for a landslide to occur on the slopes of the Potvorovsky Hill originated long before the catastrophic landslide of 1872. It is evident that there were multiple causes, and these should be viewed in the light of their mutual connections and not as isolated factors, owing to the fact that each of them contributed to a certain degree to disrupting the stability of the slope, as is discussed in detail by Jansky (1976, 1977).

Lake Mladotice still exists in the western Czech Republic about 30 km north of Pilsen. The receiving streams of the lake outflow are the Střela and Berounka Rivers; the latter drains into the Vltava River south of Prague. The erosion level of the lake is 413 m a.s.l.; its surface extends over 4.74 ha. The lake's drainage area is approx. 46.5 km², about 50% of which is being intensively farmed (Fig. 2). The lake's drainage basin – including the type of land use – is typical for a larger region of western Bohemia.

Fig. 2. Drainage basin of Lake Mladotice and location of the study area in the western Czech Republic.

Lake Mladotice in the Western Czech Republic – Sediments as a Geoarchive

for Flood Events and Pre- to Postcommunist Change in Land Use since 1872 311

Fig. 3. Map of Lake Mladotice showing locations of short and long cores. Core ML 18/03 is

Comparative analysis of bathymetric measurements from 1972 and 2003 yielded the following results (Jansky 2003). The maximum depth of the lake decreased from 7.7 m to 6.7 m (Fig. 4). The 7 m depth level disappeared entirely, and the area of all other depth levels decreased - the 6 m depth level to 61% of its initial area from 1972, the 5 m level to 43%, the 4 m level to 60%. The decline in the area of shallow water levels was somewhat less dramatic – the 3 m level decreased to 72% of its 1972 area, while the 2 m and 1 m levels decreased to

A decrease in the water level's surface area was measured, i.e. from an initial 5.85 ha (1972) to 4.73 ha (2003). This means a decrease of 1.12 ha in the lake's surface area, i.e. 19% of its initial area in 1972. The maximum water level fluctuation between 1972 and 2009 was recorded at around 55 cm. Moreover, the automatic limnigraph has measured a fluctuation of 26 cm in the last 12 months. After the bathymetric curves were elicited, the water volume of the lake basin was calculated. From an initial volume of 141,380 m³ in 1972, it decreased

**4.1 Sediment filling in the lake basin and fluctuations of lake water level** 

by 37,471 m³ to 103,910 m³; the water volume of the lake decreased by 26.5%.

located near the outflow with the maximum water depth.

**4. Results** 

69% and 76%, respectively.
