Evaluation of Groundwater Levels in Hydropedological Profiles in South Moravia, Czech Republic

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00020699%3A_____%2F20%3AN0000036" target="_blank" >RIV/00020699:_____/20:N0000036 - isvavai.cz</a>

Result on the web

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DOI - Digital Object Identifier

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Result language

angličtina

Original language name

Evaluation of Groundwater Levels in Hydropedological Profiles in South Moravia, Czech Republic

Original language description

The planned construction of Oder-Danube canal was one of the largest activities, which led to realization of research projects, which also included construction of boreholes for monitoring groundwater levels. The area of potential navigability of the rivers Morava and Oder (Odra) and route of the planned canal connecting Danube-Oder-Elbe has been protected since 1946 within zoning plans of larger territorial units. This would also fulfil the original goal of monitoring long-term time series of groundwater levels. Hydropedological profiles (HP) consist of boreholes, which are situated usually across the route of the canal and also across longitudinal axis of valleys or flat Moravian valleys. They belong to basins of Oder, Bečva, Thaya (Dyje) and Morava rivers. First observations began back in 1933 and 1934, subsequent followed after 1940. Nowadays these objects serve for general idea about the groundwater regime in valley profiles of these rivers. From geological perspective, they are HP profiles in an area of Quaternary sediments. Ladná, the profile of interest, is located north of Břeclav (south Moravia) and crosses the Thaya, Trkmanka and Včelínek rivers. It was build in 1948 and therefore has a 70-years long continuous monitoring series. Over time the location underwent several changes, most importantly the construction of the Nové Mlýny dam and modification of the Thaya riverbed. The current profile consisted of 16 probes which have automatized measuring system with daily values and one water gauge, the surface station Ladná on Thaya River. Hydropedological profile had an overall length of 4986.4 m and average elevation of 160.46 m above sea level in 1949. Dynamics of the groundwater level is assessed in the context of time and relationship with surface water levels, precipitation and geological profile during various reference periods. The obtained findings from the individual reference periods are analyzed and thoroughly assessed. One of the factors of interest is the impact of drought between 2014 and 2018 on the profile in relation to the distance from the watercourse and climatological conditions, including its effect on the entire historical series of groundwater level monitoring. Basic statistical methods have been used to analyze the data from the HP profile. The measurements were taken once per week until 2012 and since then in a daily step. After data verification and removal of outliers and biased data (anthropogenic effects, floods), weekly data were filtered out, so that the entire time series has a unified data interval. Subsequently, monthly averages were calculated as well as monthly minima and monthly maxima for the entire period of analysis. Cumulative frequency curves were constructed for the individual reference periods and from these, 50 % percentile, minimum and maximum found. The last parameter analyzed was the 85% percentile, which represents the drought threshold. Analysis of the long-term water level regime is problematic because it is difficult to decide the right length of the period of analysis and subsequently the associated suitable reference period for further analyses. Length of the period should obviously be related to the type of the groundwater cycle – in cases of structures where one can assume relatively significantly delayed response to meteorological parameters and which show long-term course, it is suitable to select the longest period possible. In order to compare the monthly characteristic with long-term values calculated for the reference period it is necessary to calculate monthly average values (usually in that year) and determine long-term monthly percentiles of the desired level for the reference period (or a real reference period with duration of observation of at least three subsequent years). Comparison of subsequent annual characteristics with long-term values forms the basis for the indication of long-term decreases in groundwater levels at the level of the individual objects as well as on the level of the entire hydrogeological structures. In order to assess the effect of water management at the Thaya River on groundwater levels two periods were selected. First, the period 1948-1972, only from the perspective of the Thaya River, i.e. in the absence of the Nové Mlýny dam and the period 1974-2018, i.e. after the construction of the Nové Mlýny dam and modifications of the Thaya River between Břeclav and Nové Mlýny. Also, based on long-term time series of groundwater level observations, an assessment was performed that looked at the course of groundwater levels during various time periods, in particular during the individual reference periods (as they were defined by the CHMI, i.e. 1931-1960, 1931-1980 and the current reference period 1981-2010). In addition, the period 1991-2018 was also included, which relates to the current situation. The entire 70-year period cannot be assessed as a whole because of the Nové Mlýny dam construction. Evaluation of the relationship between groundwater levels and surface water was performed using the data of monthly flow rates at the Thaya River during the period of analysis. Measurements were used from surface stations Dolní Věstonice, Nové Mlýny dam station and data from Ladná station, which lies directly in the HP profile. Evaluation of the groundwater level regime and its relationship to the surface water also requires the knowledge of critical years from the perspective of hydrology and meteorology. Four probes were selected for the assessment of the water management activities at the Thaya River and the mutual interactions with the surface flow – in particular the KB0689, KB0706 probes, which exist in the profile since 1948 and the probes KB0718 and KB0719, which started measuring later, in 1962. The following conclusions can be made from the data provided by the HP Ladná profile probes. Each probe in the profile is unique and several factors must be taken into account when analyzing data from them. This includes landscape type and vegetation in the vicinity of the station, geological profile, potential other important factors such as the effect of other watercourses, not just the main watercourse – the Thaya River. All probes interact with the surface water flow, however what is important is the distance from the flow, which determines the time it takes to restore the groundwater levels. Groundwater level monitoring at hydropedological profiles is important especially because of linking the profile to a particular watercourse and duration of the continuous monitoring (Fig. 1.). It can also be used for determination of hydraulic link between surface water and groundwater. These values would be very useful especially in determination of spread of potential groundwater pollutants via surface waters. Analyses of groundwater regime of the profile (during normal climatological and hydrological year) showed that groundwater level at all boreholes shows practically identical annual course of groundwater level in long-term, with minimum in October and maximum in April and gradual groundwater level fluctuation between these two extremes. Groundwater level at boreholes is affected by river discharges and only to a very minor extent by precipitation. Fluctuation of groundwater level is relatively large due to the overall extent of aquifer. The difference between maximum and minimum level is on average approximately 1 m. Largest differences are found at boreholes close to rivers, where they reach up to 2.5 m. Groundwater level in the Thaya basin decreased by about 0.5 m after the year 1972 and also the groundwater level fluctuation is smaller due to modifications of the Thaya riverbed.

Czech name

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Czech description

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Type

D - Article in proceedings

CEP classification

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OECD FORD branch

10501 - Hydrology

Project

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Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2020

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Article name in the collection

Abstract book - 6th IAHR Europe Congress

ISBN

978-83-66847-01-9

ISSN

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e-ISSN

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Number of pages

2

Pages from-to

221-222

Publisher name

IAHR

Place of publication

Varšava

Event location

Varšava

Event date

Jun 29, 2020

Type of event by nationality

EUR - Evropská akce

UT code for WoS article

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