This study presents a flood frequency analysis for the Vltava River catchment
using a major profile in Prague. The estimates of peak discharges for the
pre-instrumental period of 1118–1824 based on documentary sources were
carried out using different approaches. 187 flood peak discharges derived for
the pre-instrumental period augmented 150 records for the instrumental period
of 1825–2013. Flood selection was based on
Research of historic floods significantly enhances our ability to better understand the behaviour of recent flood events in the context of global environmental change. Numerous studies have focused on this issue in the last 2 decades (e.g., Brázdil et al., 2006b; Glaser et al., 2010). The augmentation of systematic hydrological series by interpreted historic records to provide a better and more accurate estimation of hydrological parameters is an important task. Flood frequency analysis (FFA) appears to be a real challenge, particularly for limited data sets as indicated for example by Mudelsee et al. (2003) and Stedinger and Cohn (1986). In this study, the estimated flood discharges are used for identification of flood-rich periods.
In the Czech Republic, four extreme summer floods were recorded within the
last 15 years (1997, 2002, 2010, and 2013). Two of these were classified as
500-year or even 1000-year events (Blöschl et al., 2013; Hladný et
al., 2004); two out of the four stroke the Vltava River catchment. Taking
into account the entire region of central Europe, further extreme summer
floods can be added: in the Alps in 2005, and in Slovakia and Poland in 2010.
An interesting question thus emerges as to whether there is an analogy with a
similar frequency of important or extreme floods in the past. The aim of this
contribution is to answer two scientific questions:
Has the territory of the present Czech Republic experienced four summer
extreme flood events within a mere 15-year period earlier in history? Did the region of central Europe record extreme large-scale floods during
the last 500 years more often when compared to the present? The methodical
approach used in this study was inspired by Bayliss and Reed (2001).
Important data on floods in the Elbe catchment. Values for major profiles are in bold.
A: catchment area.
The Vltava River catchment. The major tributaries and sites with records of historic floods and flood marks are highlighted.
Prague is, with respect to floods, a key point for central Europe. It
represents a closing profile of the Vltava River, the most important
tributary of the Elbe River. As compared to other major Elbe tributaries,
such as the Saale, Spree, and the Mulde, with respect to the catchment area, average discharge and
For the Vltava River catchment, 161 flood cases for the period between 1118 and 1824, when the regular daily water level measurements began, are available in Brázdil et al. (2005), denoted as set B further in this study.
The most reliable 18 cases associated with summer floods are related to the flood marks and original Prague water gauge denoted as “the Bearded Man”, used since 1481 (Elleder, 2003).
Novotný (1963) presented an additional 121 peak discharges (1825–1953)
for the period before the Vltava River Cascade construction. The peak
discharges from 1825 to 1880 were assessed earlier, with an assumption of the
1880–1890 rating curve validity (Richter, 1893). Water levels and peak
discharges for Prague after 1954 are in the Czech Hydrometeorological
Institute database, concurrently in simulation without the influence of the
Vltava River dams (Hladný et al., 2004). The 2012 flood, with peak
discharge of 5160
Regarding the specific conditions of the Vltava River catchment, particularly in Prague, it was advantageous to use the estimated peak discharges. This approach enabled the author to use simple hydrological balance for filling and checking the final data set.
The major Vltava River profile for Prague until 1824 was the monastery of the Knights of the Cross with the Red Star past the Charles Bridge; after 1824 with the beginning of the systematic water level measurements it was the Old Town Mills profile upstream of the Charles Bridge. An overview of the most important changes of floodplain and documentary sources available was presented by Elleder et al. (2013). The entire period under review, 1118–2013, has been divided into seven periods of more or less homogenous topography, with respect to both the reliability of input data and changes in the area near the major profile (Historical Urbanization Stage, HUS further in the text). The least reliable data are those relating to 1118–1350 (HUS1). After the construction of the new city walls (1250–1300) and reconstruction of the city, the Old Town terrain was more or less stabilized (Hrdlička, 2000). In 1351–1480 (HUS2) some floods are recorded as related to important town buildings (Table 2). During this period, the number and height of Prague weirs were fixed. In 1481–1780 (HUS3) the records of water levels are available. Since 1481 these are related to the “Bearded Man” water gauge (Elleder, 2003, 2010b, 2013). Since 1501 flood marks started to appear, but those from 1501 and 1655 were destroyed, and currently flood marks since 1675 are preserved (Brázdil et al., 2005). Changes in floodplain between the 16th and the mid 19th century were minor (Elleder et al., 2013). The first modern water gauge in Prague was set up in 1781 (Brázdil et al., 2005; Elleder, 2010b). Systematic records date back to 1825. The next 60-year period of 1781–1843 (HUS4) until the construction of the Vltava River embankment is used for calibration of the relation between measured water stages during flood events and flood impacts, such as the flooded area (Elleder, 2010b). For similar relations applicable for the HUS3 period it is possible to derive for flood damages and the Vltava River behaviour during ice-jamming. For the next period of 1844–1904 (HUS5), when the Vltava River embankment construction was undertaken, a rating curve is available. In 1904–1926 (HUS6a) the inundated area of the Old Town was raised to the embankment. In the next period 1927–1953 (HUS6b) no major changes occurred until construction of the Vltava River cascade dam. Construction of the Vltava River dam cascade in 1954–1961 resulted in a crucial change of the hydrological regime (Kašpárek and Bušek, 1990). The current period 1954–2013 (HUS7) has been affected by implementation of the cascade. Until mobile dikes were put into operation (2000–2013), no major changes were undertaken in Prague.
Selected important sites (water level indicators) with relations between water levels and peak discharges.
Reliable records of 18 summer floods from 1481–1825 were assessed using a
hydraulic approach, similar to that applied by Herget and Meurs (2010) for
German Cologne (the Rhine). Herget et al. (2014) recommended support of the
hydraulic approach with detailed knowledge of river cross-section and flood
plain, and use of the Manning equation (Chow, 1959). The results of this
approach for Prague including detailed information on cross-section of chosen
Vltava profile were published earlier by Elleder et al. (2013). This
evaluation, however, did not include winter floods, or flood events with less
reliable or roughly estimated water-level records. The objective of this
study was the utilization of most of the data with an acceptable level of
reliability for flood seasonality analysis. Some 90 % of all data (B set)
from the pre-instrumental period met the reliability or authenticity criteria
according to Bayllis and Reed (2001). This applies mostly for evidence of
major floods equal or higher to
Relations between water stage or peak discharge and impacts relevant for HUS5 and HUS6 periods (Elleder, 2010b) were applied for the interpretation of historic floods. The rating curve for 1880–1890 (Richter, 1893) was used for HUS3 floods – events with a fairly reliable documented water level. The map presenting isolines for different water levels in Prague (Elleder, 2010a) was used for interpretation of flooding of different sites or buildings in floodplain of Prague.
For winter floods, a problematic relation between water level and discharge
due to ice jamming is to be accounted for. It is necessary to distinguish
between the flood caused by ice jam making a barrier, and the flood caused by
an increase of discharge (Beltaos, 2008). No case, nevertheless, with a higher
water level due to ice jamming, as compared to subsequent water level due to
flood discharge, is known for Prague. For discharge higher than or equal to
Supporting profiles in the upper Vltava River (České Budějovice, Beroun, Písek) as mentioned for example by Elleder (2008) were used for providing a balance of estimated discharges in the upper Vltava River, while supporting profiles downstream (Litoměřice, Děčín, Pirna, Dresden, Meissen) were used for regression estimates published earlier by Elleder et al. (2013). This approach enabled the checking and specification of not only estimated discharges, but also the time of flooding in Prague. In some cases, this approach facilitated even the filling in of the missing values as an for example for 1434, 1531, 1775.
The credibility of discharges estimated by this approach above is undoubtedly lower than discharges derived from authentic description and records of floods in Prague.
In the framework of the analysis, two approaches are to be distinguished: annual maximum flood (AMF further in the text), and peaks over threshold (POT further in the text) approach.
The original B set including 161 recorded Vltava floods was augmented by 23
flood events. The results of my hydrological interpretation of the augmented
B set are presented for all floods during 1118–2013 (Fig. 2). For further
FFA only values higher or equal to
Set of estimated maximal water levels and peak discharges (equal or greater
then
A perception threshold for recognizing an event as a flood, and for drawing a
flood mark, a discharge around
Figure 2 summarizes the frequency of floods over the centuries. The high
variability in
Frequency of floods in Prague over the centuries.
Final time series presenting running 31-year frequencies in summer and winter floods in Prague with identification of flood-rich periods, the extreme floods are in bold.
Figure 3 presents an overview of about 300 maximal annual peak discharges in
Prague (AMF, according to Elleder, 2010b). For more accurate identification
of periods with high flood frequencies, a 31-year running sum was used. The
exceedance of POTQ10 defines flood-rich periods (FRP, further in the text).
Six periods FRP1–6 with two sub-periods (FRP4a, b and FRP5a, b), with
minimal overlap with respect to
Some significant floods in HUS1 (1118, 1272, 1273), and HUS2 (1432) are not included in the above periods. This fact is most likely a consequence of the lack of documentary sources for HUS1 and HUS2 periods. It holds, however, also for the beginning of the HUS3 period with the extreme flood of 1501.
Selected important impacts with relations between water levels and peak discharges.
Some of the POTQ10 floods recorded in the Vltava River in Prague were part of more extensive events affecting a major part of central Europe as well. If at least two or three major catchments out of five (the Elbe, Danube, Oder, Wesser, Warta) were simultaneously struck, these events can be labelled as Central European Floods (CEF, further in the text). An example of such a CEF is the 1374 flood (FRP1), which is recorded, apart from the Vltava River, also in the Saale catchment (Deutsch and Portge, 2003), Danube catchment (Kiss, 2011) and the Rhine catchment (Herget and Meurs, 2010). More additional information is needed for the winter flood of 1367 in Transylvania (Kiss, 2011) or in the Hornád River basin in 1568 (Pekárová et al., 2011). Synchronic winter floods (1655, 1682, 1784, 1799, 1862, 1876) were recorded by flood mark on the Main (Eibelstadt, Frankfurt am Main, etc.), the Danube (1682, 1784, 1799, 1830, 1862), and the Rhine (1651, 1784, 1799). For summer floods, an association with the Danube and Oder catchments is more common. Frequently, the Alpine tributaries of the Danube – the Inn, Enns, Traun – or the Danube itself between Passau and Vienna (1501, 1569, 1598, 1890, 2002, 2013) are involved. Flood marks of these are found at numerous sites (Linz, Schärding, Burghausen, Steyer). Synchronic floods with the Vltava River for some Oder tributaries (Nysa Łużycka [Lausitzer Neiße], Kwisa, Bóbr, Kaczawa, and Nysa Klodzka) for 1359, 1387, 1432, 1501, 1563, 1564, 1567, 1569 are presented by Girgus and Strupczewski (1965).
In cases when other catchments (the Seine, Loire, Maas) were also affected, the acronym WCEF (West-Central European flood) is used. These are, for example, 1651, 1658, 1740, 1784, and 1799 winter floods, as commented in detail earlier by Elleder (2010a) for Cologne, Dresden, Paris, and Vienna.
The overview of the identified periods with high flood frequencies with relevant flood events is presented below.
It includes summer floods of 1359 (CEF), 1370, and 1387 (CEF) and winter floods of 1367, 1364, 1373, and 1374 (CEF).
Summer floods prevail in 1564, 1567, 1568, 1569 (CEF), 1575, 1582, 1587, and 1598 (CEF). Winter floods in 1570, and 1566 (CEF). The type of the 1575 flood is not known.
Winter floods prevail in 1651 (WCEF), 1655 (CEF), and 1682 (CEF). Flood in 1658 (WCEF) was recorded for Dresden and Paris (Elleder, 2010a). It is unclear, however, if the high peak discharge was not due to ice jamming. Summer floods in 1651 and 1675 have not been mentioned so far outside of the Czech lands.
Winter floods prevail in 1770, 1771, 1782, 1784 (WCEF), 1786, 1799 (WCEF).
Winter floods in 1809, 1810, 1827, 1830 (CEF), and summer floods in 1804 and 1824.
Winter floods prevail in 1845 (CEF), 1862 (CEF), 1865, and 1876 (CEF). The summer flood of 1872 was a flash flood with extreme intensity. This flood is related to the floods on the upper Rhine and Po tributaries. This period includes a catastrophic flood on the Elbe River in February 1846, and a no less deleterious flood in August 1858.
Summer floods dominate in 1890 (CEF), 1896, and 1915. In the Czech lands,
there were simultaneous catastrophic floods, particularly in the Elbe
catchment, in August and September 1888, 1897 (CEF), and 1899 (CEF), that
reached a mere
So far summer floods have prevailed in 2002 (CEF) and 2013 (CEF), after
simulation (removing of the Vltava dam cascade influence), also the 2006
flood can be included
(
The flood periods identified correspond, more or less, with similar periods for central Europe published earlier. The period corresponding with FRP1 was reported, for example, for the Isar River (Böhm and Wetzel, 2006), the Pegnitz, and the Rhine downstream of the confluence with the Mosela (Glaser et al., 2004).
Schmocker-Fackel and Naef (2010) assessed the flood frequency in 14 catchments across Switzerland. This was further extended by Böhm et al. (2014), who studied in more detail Bavarian Fore-Alps. Flood-rich periods in central European catchments (Glaser and Stangl, 2003) correspond with FRP2–FRP4. This is not a surprising result, as the major floods in the Vltava River catchment were obviously part of extended CEF (likely more often than stated above), rarely of WCEF. The records are mostly lacking, however.
Results of this study show a minor peak around 1440–1450, which was recorded also in the Pegnitz River catchment (Glaser et al., 2004). This peak in Prague is associated particularly with three extreme floods in 1432, and with 1434. Interestingly, one of these, the flood of August 1432 is comparable with the extreme 2002 flood (Brázdil et al., 2006a; Elleder, 2010b).
There are also some discrepancies between the results of the presented study and results published for other catchments. Surprisingly, one of the most prominent flood-rich periods in the second half of the 16th century (FRP2) differs from the Isar and Lech rivers catchments (Böhm and Wetzel, 2006), which are, with respect to geography, very similar to the Vltava River catchment. Nevertheless, in the very next Danube tributaries – the Traun and Enns River catchments – flood events parallel to the Vltava River catchment were identified (Rohr, 2007).
Identified flood-rich periods correspond with decadal frequencies for Prague
(Brázdil et al., 2005), except for the period around 1750. This
discrepancy is closely related to POTQ10 selection. If the criteria for
selection are strictly adhered to, only floods from 1712, 1734, and 1736 may
be identified. For this reason, the peak around 1750 is reduced.
Nevertheless, in this period also a fairly high number of summer floods with
estimated peak discharge of
With regard to flood frequency across the entire area of Central Europe, the present flood-rich period began around 1994. Major floods were recorded in 1994, and 1995 (the Rhine River: Engel, 1997), 1997 (the Oder River: Kundzewicz, 1999), 2002 (the Elbe and Danube Rivers: Hladný et al., 2004), 2005 (Upper Rhine and Danube tributaries: Beniston, 2006), 2010 (the Oder and Vistula Rivers) and 2013 (the Elbe, Danube, and Oder Rivers: Blöschl et al., 2013). This makes six or seven major floods over 20 years, including one large-scale event in the vast region between the Rhine and Vistula Rivers. For such events, however, no comparable period was found in the last 100–200 years of the instrumental period. This reason further enhances an interest in examining the pre-instrumental period in search for an analogy with recent records.
The presented set of estimated flood peak discharges for Prague
specifies results of previous studies. Peak discharge estimates made it
possible to utilize also the data from the tributaries, and profiles situated
downstream of the examined river profile. In contrast, some discharges lower
than
In total, five historical periods with higher than POTQ10 flood frequency were identified. The time span for each of these five periods was some 35–40 years. Results of this study clearly show that POTQ10 flood is likely to occur 6–12 times in a period of higher flood frequency, which means every third (in the 16th century) to eighth (in the 19th century) year on average. Additionally, during the current period, in the Vltava River catchment we have recorded three major floods within 12 years (2002, 2006, and 2013), which means one in 4 years on average.
To summarize: the results of the presented analysis indicate that the territory of the present Czech Republic might have experienced in the past extreme floods comparable, with regard to peak discharge (POTQ10) and frequency, to flood events recorded recently. With respect to Central Europe considered as a whole, the existence of a similar period can be fairly reasonably assumed at least for the 16th century. It cannot be excluded, however, that one or even several more periods of extreme floods over a relatively short time span, occurred in the past. As a matter of fact, the historical data available presently do not allow an unambiguous conclusion on this issue.
The results of this study clearly show that currently available historical data do not allow for deriving detailed conclusions on flood frequency in Central Europe. Further analysis of single flood events for the whole affected area (such as in Brázdil et al., 2010; Munzar et al., 2008, 2010) are urgently needed to be more certain in this aspect.
The author thanks his colleague Jolana Šírová for preparing Fig. 1. The valuable comments of the three reviewers and proofreading by Sharon King are highly appreciated. Edited by: G. Blöschl