It is possible to calculate water losses by evaporation for specific SWR; however, more accurate data can be obtained by direct monitoring using an evaporimeter. TGM WRI has been dealing with direct evaporation monitoring since the 1950s [3]. In recent years, floating evaporimeters have been used to determine evaporation from water bodies; they are placed directly on the their surface, and thus can most precisely measure the meteorological conditions in a\u00a0reservoir.<\/p>\n
This article describes the results of evaporation measurement with a\u00a0floating evaporimeter from the Vav\u0159ineck\u00fd pond water surface between 2020 and 2023 and its effect on the overall hydrological balance. In the conclusion, the\u00a0pros and cons are discussed of using SWR as an adaptation measure supporting water retention in the landscape.<\/p>\n
METHODOLOGY<\/h2>\nProject \u201eThe influence of small water reservoirs on the groundwater level and hydrological balance with emphasis on dry periods\u201c (TITSMZP809)<\/h3>\n
The effect of evaporation from the water surface on the overall SWR hydrological balance was addressed between 2019 and 2022 within the programme of the\u00a0Technology Agency of the Czech Republic (TA CR) Beta2 \u201eThe influence of small water reservoirs on the groundwater level and hydrological balance with emphasis on dry periods\u201c for the Ministry of the Environment (MoE). The main goal of the\u00a0project was to assess the impact of SWR on the hydrological balance and its components at different spatial scales. The analysis was carried out in the SWR vicinity, in source catchments, and in catchments with systems of ponds and SWR. Hydrological balance was mainly assessed with regard to the influence of SWR on groundwater level, evaporation, and runoff. The activities were based on direct monitoring of selected hydrological quantities at\u00a0the\u00a0SWR, from analyses of the SWR vicinity through remote sensing data, estimation of the\u00a0components of the hydrological balance by hydrological models together with a\u00a0description of uncertainties, estimation of the physical-geographical characteristics of the SWR and affected basins, and from a\u00a0regional analysis of the SWR characteristics [4].<\/p>\n
Project \u201eWater centre\u201c (SS02030027)<\/h3>\n
After the completion of the above-mentioned project, the research on direct monitoring of evaporation from the water surface at Vav\u0159ineck\u00fd pond was transferred to the work package WP3 \u201eAdaptation measures on surface water and groundwater in deficit areas\u201c, which is part of the research project SS02030027 \u201eWater systems and water management in the Czech Republic in conditions of climate change (Water Centre)\u201c addressed within the Programme of applied research, experimental development and innovation in the field of the environment \u2013 Environment for life (Sub-programme 3 \u2013 Long-term environmental and climate perspectives) administered by the TA CR. The work package aims to assess possible adaptation measures for the deficit areas of the Czech Republic with regard to expected climate change scenarios. The investigated possible adaptation measures include water transfer, artificial infiltration, protection and support of groundwater sources, change in handling or increase of storage space of existing water\/dry reservoirs, construction or restoration of SWR, support of natural infiltration through water retention in the landscape, and establishing protected sites for surface water accumulation. Accurate determination of water surface evaporation plays a\u00a0role in designing or restoring SWR as an\u00a0adaptation measure.<\/p>\n
Vav\u0159ineck\u00fd pond<\/h3>\n
Vav\u0159ineck\u00fd pond is located in Central Bohemia upstream of the V\u00fdrovka (49.4\u00a0river km), about 3 km north of Uhl\u00ed\u0159sk\u00e9 Janovice in the Kutn\u00e1 Hora district. With a\u00a0surface area of about 71 ha and a\u00a0volume of over 1 million m3<\/sup>, it is one of the largest SWR in Central Bohemia as well as the whole of the Czech Republic. It is fed by the V\u00fdrovka stream flowing from Uhl\u00ed\u0159sk\u00e9 Janovice and the Osta\u0161ovsk\u00fd stream flowing from the southwest. The catchment area for the\u00a0dam is 60 km2<\/sup>.<\/p>\n The site is located in the hydrogeological district of 6531 Kutn\u00e1 Hora crystalline basement. It is a\u00a0typical environment of a\u00a0hydrogeological massif with occurrence of fissure-permeable rocks. Precipitation infiltration occurs almost on the whole area, with the exception of areas with loess, poorly permeable rocks, where infiltration is very limited. Natural sources of groundwater are below average; values of specific underground runoff are given by Kr\u00e1sn\u00fd et\u00a0al.\u00a0[5] around 1.5\u20132 l\/s\/km2<\/sup>, while the CGS balance calculations from 2006 give a\u00a0value of 2.19 l\/s\/km2<\/sup>, which corresponds to infiltration at the level of roughly 8\u00a0% of total precipitation. Long-term more recent values of natural resources for 1981\u20132019 are given by Ka\u0161p\u00e1rek et al. [6], whose calculations based on hydrological methods for hydrogeological region (HGR) 6531 correspond to a\u00a0value of 1.5 l\/s\/km2<\/sup>; therefore, in the given HGR, there is a\u00a0reduction of natural resources compared to older data, mainly due to the dry period 2014\u20132019.<\/p>\n An evaporimeter floating on a\u00a0water surface can best simulate the meteorological conditions of a\u00a0given water reservoir. It measures water temperature precisely compared to classic field evaporimeters, in which the water heat up faster in the\u00a0spring and cool down faster in the autumn. Due to their large volume, water bodies have a\u00a0certain inertia, thanks to which the temperature is more constant than in the measuring vessel itself. In the same way, the monitoring of evaporation directly on the water surface is more representative with regard to other conditions influencing this process, such as insolation and, above all, wind speed.<\/p>\n The floating evaporimeter used on the Vav\u0159ineck\u00fd pond (Fig. 1<\/em>) consists of a\u00a0supporting structure including floats and breakwaters, which includes a\u00a0measuring vessel with a\u00a0diameter of 620 mm. The device is powered by a\u00a0battery charged by 2 solar panels (20W each). The container is equipped with a\u00a0two-way pump that fills\/drains water into\/out of the evaporation measurement container in the event of a\u00a0level change from the reference value by 5 cm.<\/p>\n Sensor equipment:<\/p>\n Data is recorded at 10-minute intervals and sent to the server 3 times a\u00a0day (at\u00a01:00, 7:00, and 19:00) based on GSM data transmission. Evaporation and precipitation are measured on the basis of a\u00a01-minute recording of the water level in the evaporative container in combination with a\u00a0rain detector (in the case of rain detection, the level increase is caused by precipitation) and information about water intake\/discharge into\/out of the container. Average daily values of\u00a0meteorological quantities are calculated as an average of 10-minute measurements on a\u00a0given day. Evaporation and precipitation values are derived from 1-minute records.<\/p>\n Monitored meteorological quantities \u2013 evaporation [mm], precipitation\u00a0[mm], solar radiation [W\/m2<\/sup>], air temperature [\u00b0C], water temperature in the evaporimeter [\u00b0C], water temperature at depths 0.5\u20131\u20131.5\u20132\u20132.5 m [\u00b0C], wind speed [m\/s], instantaneous wind speed [m\/s], wind direction [0\u2013360\u00b0], relative humidity [%].<\/p>\n Meteorological data was recorded by a\u00a0floating evaporimeter; data from the\u00a0CHMI measurement network from station P3STAN01 Vav\u0159inec, \u017d\u00ed\u0161ov was used for verification. The gauging stations at the inflow and outflow (Fig. 2<\/em>) were established as part of the TITSMZP809 project in 2019 and record the water level at the tributary \u2013 Osta\u0161ovsk\u00fd stream, V\u00fdrovka, and the outflow \u2013 V\u00fdrovka below the dam of Vav\u0159ineck\u00fd rybn\u00edk in a\u00a0minute step. As part of the project, shallow (depth up to 9 m) monitoring wells were established to monitor the groundwater level in the vicinity of the pond (50\u2013300 m).<\/p>\n In the measuring season from 1st April to 30th September 2022, total evaporation from the water surface was measured at 678.4 mm, while precipitation total was 582.4 mm. Average air temperature was 15.81 \u00b0C. The changes in air temperature, solar radiation, evaporation from the water surface, and precipitation is shown in the graphs in Figs. 3<\/em> and 4<\/em>.<\/p>\n A\u00a0comparison of total evaporation and precipitation in the last three years, when the floating evaporimeter was used, is shown in Tab. 1<\/em> together with data on the difference between precipitation and evaporation. The representation of evaporation in mm and at the same time in m3<\/sup> in a\u00a0daily step between 2019 and 2022 is shown in Fig. 5<\/em>. The measured data clearly illustrate the fact that the\u00a0water area of 71 ha means a\u00a0significant loss of water from the watercourse in the summer months precisely due to evaporation. Every millimetre of vapour means a\u00a0loss of 710 m3<\/sup> of water. With an average daily evaporation of 3.7 mm in\u00a02022, this represents an average daily water loss of 2,627 m3<\/sup>. The highest daily evaporation over the past three years was measured at Vav\u0159ineck\u00fd pond on 19th\u00a0June 2022, namely 10 mm, which means a\u00a0daily loss of water due to evaporation from the surface of 7,100 m3<\/sup> in a\u00a0single day. It should be mentioned that the change in surface area during water loss, which is negligible for losses of several centimetres, was not taken into account.<\/p>\n Fig. 6<\/em> shows a\u00a0comparison of daily evaporation with current outflow from the\u00a0pond and also with the value of average long-term outflow Qa<\/sub>\u00a0=\u00a00.3\u00a0m3<\/sup>\/s\u00a0and with the value of Minimal Ecological Flow (MEF) = 0.047 m3<\/sup>\/s. In 2020, there was one case where the current outflow from the pond decreased below the\u00a0value of the minimum residual flow. This situation occurred at the end of the season (in September), when precipitation totals and inflow into the reservoir were missing. The outflow was increased by water supply in the pond. In 2022, several days were recorded when evaporation from the water surface exceeded the\u00a0value of minimum residual flow, and even the current value of outflow from the pond. This is best observed around 19th June 2022, when the water vapour was extreme.<\/p>\n Water surface evaporation is an important factor affecting the hydrological balance of a\u00a0basin. Vav\u0159ineck\u00fd pond is a\u00a0reservoir with a\u00a0relatively large water surface area, which increases loss of water through evaporation and, during dry periods, a\u00a0situation can arise when the influence of evaporation negatively affects the hydrological balance. During the monitored period, from April to September, total evaporation from the water surface ranged from 500 to 680\u00a0mm, with precipitation from 400 to 580 mm. In 2020, the water surface evaporation was higher then precipitation by 150 mm, and by 100 mm in 2021 and 2022; in terms of water volume, that is more than 70,000 m3<\/sup> of water.<\/p>\n During the monitoring, only exceptionally did the values of the outflow from the pond decreased below the value of the minimum residual flow. Outflow was replenished in periods of low water at the expense of water supply in the\u00a0pond. In 2022, there were also individual cases of water surface evaporation being greater than outflow from the pond.<\/p>\n This paper summarizes monitored evaporation data obtained by monitoring with a\u00a0floating evaporimeter, placed on the surface of Vav\u0159ineck\u00fd pond from 2020 to 2022. Floating evaporimeters can more accurately monitor conditions on water bodies, in particular water temperature, solar radiation, and wind speed. Evaporation from the water surface is a\u00a0negative factor from the\u00a0point of view of watercourse balance within the hydrological balance. However, only on the basis of evaluation of the amount of precipitation and evaporation, it cannot be claimed that SWR have a\u00a0negative impact on their surroundings. The\u00a0SWR influence on the hydrological regime is very complex, as well as the\u00a0influence of\u00a0SWR through individual hydrological processes. Although it negatively affects the watercourse balance, water loss by evaporation also has a\u00a0positive effect in the form of cooling the air due to the effect of energy consumed for the change in the state of matter during evaporation, which results in a\u00a0positive influence on the microclimate. Undoubtedly, the increase in underground water reserves due to backwater in reservoirs can be considered a\u00a0positive local influence of SWR. Last but not least, it is necessary to mention the possibility of the transformation of flood waves during significant rainfall-runoff events.<\/p>\n Positive and negative effects of SWR on the hydrological regime are described in the summary report of the project TITSMZP809 [4]. As the research carried out within the project shows, SWR influence the regime of both surface and sub-surface waters. The construction of SWR is often seen as a\u00a0possible element of protection against the impacts of climate change; however, it is important to remember that water management elements affect different processes in different ways, both positively and negatively. Therefore, when restoring or proposing new SWRs, all possible impacts should be properly assessed. In terms of the effect of evaporation, the location of SWR within the Czech Republic in areas with a\u00a0stable precipitation-evaporation balance is important, and the function of an SWR is also important. The methodological procedure for assessing the impacts of SWR on the hydrological balance and water resources deals with the procedure for designing or restoring SWR [7].<\/p>\n This paper was created as part of the projects TITSMZP809 \u201cThe influence of small water reservoirs on the groundwater level and hydrological balance with emphasis on dry periods\u201d and \u201cWater systems and water management in the Czech Republic under conditions of climate change (Water Centre)\u201d financed by the Technological Agency of the Czech Republic.<\/em><\/p>\n The authors thank the employees of Ryb\u00e1\u0159stv\u00ed Chlumec for their willingness and cooperation in monitoring the Vav\u0159ineck\u00fd pond with a\u00a0floating evaporimeter.<\/em><\/p>\n This paper was presented at the Rybn\u00edky 2023 conference on 15th June 2023.<\/em><\/p>\n This article was translated on\u00a0basis of\u00a0Czech peer-reviewed original by\u00a0Environmental Translation Ltd.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":" With increased average air temperature, there is an increase in water vapour from a water surface. Between 2020 and 2022, evaporation from the water surface was observed with a floating evaporimeter at Vav\u0159ineck\u00fd pond in the Central Bohemian region. A floating evaporimeter monitors evaporation from the water surface along with basic meteorological quantities directly on the surface of the water reservoir, so its results should be more accurate than calculations based on data from nearby meteorological stations. The results show that in all three years evaporation exceeded precipitation by more than 100 mm between April and September. However, the issue of the influence of small water reservoirs on the hydrological balance is a very complex topic, where the assessment of negative and positive effects is not always black and white and requires detailed investiga-tion.<\/p>\n","protected":false},"author":8,"featured_media":26449,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[86,92],"tags":[216,2045,106,3288,3289],"coauthors":[124,235,1824],"class_list":["post-26606","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-hydraulics-hydrology-and-hydrogeology","category-main","tag-evaporation","tag-floating-evaporimeter","tag-hydrological-balance","tag-vavrinecky-pond","tag-water-surface"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/26606","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/comments?post=26606"}],"version-history":[{"count":13,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/26606\/revisions"}],"predecessor-version":[{"id":26607,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/26606\/revisions\/26607"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media\/26449"}],"wp:attachment":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media?parent=26606"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/categories?post=26606"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/tags?post=26606"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/coauthors?post=26606"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Floating evaporimeter<\/h3>\n
\n
![\"\"](\"https:\/\/www.vtei.cz\/wp-content\/uploads\/2023\/10\/Beran-obr-1.jpg\")
<\/a>\nFig. 1. Floating evaporimeter (FIEDLER)<\/h6>\n
DATA<\/h2>\n
<\/a>\nFig. 2. Monitoring sensor location at Vav\u0159ineck\u00fd pond<\/h6>\n
RESULTS<\/h2>\n
<\/a>\nFig. 3. Air temperature and solar radiation at Vav\u0159ineck\u00fd pond, 1st April 2022 \u2013 30th September 2022<\/h6>\n
<\/a>\nFig. 4. Water surface evaporation and precipitation totals at Vav\u0159ineck\u00fd pond, 1st\u00a0April\u00a02022 \u2013 30th September 2022<\/h6>\n
<\/a>\nFig. 5. Water surface evaporation at Vav\u0159ineck\u00fd pond, 1st April 2020 \u2013 30th September\u00a02022<\/h6>\n
Tab. 1. Comparison of water level evaporation and precipitation in 2020\u20132022 (April\u2013October)<\/h5>\n
<\/a>\n<\/a>\nFig. 6. Volume of water level evaporation compared to the precipitation, inflow and\u00a0outflow characteristics at Vav\u0159ineck\u00fd pond, 1st April 2020 \u2013 30th September 2022<\/h6>\n
CONCLUSION<\/h2>\n
Acknowledgements<\/h3>\n