P. Kovář

Use of terraces to mitigate the impacts of overland flow and erosion on a catchment.

The paper presents the impact of a historical system of terraces constructed centuries ago to mitigate the effect of a steep slope on overland flow. Systems of this type were constructed in past centuries by land owners, who then ploughed the land and grew crops on it. They used stones collected from the local agricultural fields as their terracing material. The influence of terraces on overland flow was simulated using the KINFIL. The overland flow is therefore reduced by greater infiltration of extreme rainfall excess flows on the terraces, and the KINFIL model shows to what extent the system of terraces can mitigate the resultant flood and soil erosion. The Knínice locality in North-Western Bohemia, with seven terraces and six field belts between them, was selected as the experimental catchment area. The results compare hydrographs with N-year recurrence of rainfall-runoff time, where N = 10, 20, 50, and 100 years, and the hydraulic variables, e.g. overland flow discharges of a design rainfall, hydraulic depths, flowing water velocity, and shear stress. The comparison provides hydraulic results with terraces and without terraces. The contrast between the results with and without terraces shows the positive role of the system of terraces in protecting the field belts.

Impact of evapotranspiration on discharge in small catchments

Abstract We apply the Linear Storage Model (LSM) to simulate the influence of the evapotranspiration on discharges. High resolution discharge data from two small catchments in the Czech Republic, the Teply Brook and the Starosuchdolsky Brook catchment are used. The results show the runoff process is simpler in a deeper valley of the Starosuchdolsky catchment where the soil zone is deeper and the valley bottom recharges runoff even during very dry periods. Two-soil zone model is adequate to simulate the diurnal runoff variability. Three-soil zone model is needed in the Teply Brook catchment due to the absence of water transport in the most-upper soil zone. Time delays between minimum and maximum discharge during the day reach up to about 20 hours. Evapotranspiration and hydraulic resistances are as high as 14% of catchment daily runoff in the urbanized Starosuchdolsky Brook catchment and 25% of catchment daily runoff in the forested, less impacted Teply Brook catchment

Impact of evapotranspiration on diurnal discharge fluctuation determined by the Fourier series model in dry periods.

Kovař P., Bacinova H. (2015): Impact of evapotranspiration on diurnal discharge fluctuation determined by the Fourier series model in dry periods. Soil & Water Res., 10: 210–217. Precise measurements of discharges at the outlet of a small catchment, using high resolution sensing equipment, can currently be done without difficulty. In particular, measurements can take place even during dry periods, when high temperatures increase actual evapotranspiration on the catchment and diurnal streamflow fluctuation changes occur in a harmonic wave at any time of the day. Some 10–15 years ago, a current runoff measurement record based on a high resolution equipment clearly recognizing a diurnal wave-shape fluctuation could hardly be available. The measurement of discharge ordinates from the catchment, and from free water pan evaporation, showed an undulating fluctuation tendency. However, the discharge minima appeared at day time and their maxima at night. The measured discharge data are represented not only by a fluctuating form, but also by a mild form, an even straight line, or by a flat depletion curve. For the purpose of analyzing the wave shape of discharge we implemented the Fourier series model, simulating the measured data through the Fourier input, output, and transformation coefficients. The purpose of this analysis was to use the Fourier equations in order to substitute the missing data (when the discharge or evaporation measurements collapsed). Due to very sensitive data, when the measured discharge series are jagged, the equation can be smoothed by the harmonic approximation or by the polynomial approximation. Our study was carried out on the small experimental catchment of the Starosuchdolsky Brook, in the vicinity of the campus of the Czech University of Life Sciences Prague. The harmonic analysis provided an interesting outcome, as well as innovative methodology.

The influence of woven geotextiles on ponding time and overland flow

Kořínek J., Nekardová O., Kovář P. (2016): The influence of woven geotextiles on ponding time and overland flow. Soil & Water Res., 11: 244−249. Nowadays, both synthetic and natural geotextiles are used to mitigate water erosion processes on hillslopes. Jute and coir are most suitable materials for the production of woven geotextiles. They are used for a variety of purposes – from natural fibre composite building materials to a soil protective agent. They were tested under laboratory conditions, without soil. This enabled us to focus on the reaction of the woven geotextiles to simulated rainfall. ECC 700 (coir), ECC 400 (coir), and ECJ 500 (jute) were tested. The Norton Ladder Rainfall Simulator was selected for spraying. Each simulated rainfall event lasted 15 min. An artificial hillslope with a gradient of 7.2 degrees was used. Jute absorbed water more effectively than both types of coir, and ECC 400 was more effective than ECC 700. The measured values were entered into the KINFIL hydrological model, which confirmed a positive impact of jute on delaying the ponding time and on reducing the total discharge. In practice, it can be suggested that jute prevents drying of the soil better than coir, and thus promotes better vegetation growth. The results also demonstrated that jute material is suitable for erosion control of hillslope surface for a short time (the time of the grass cover reinforcement), because it has good adhesion and reduces the total overland flow in an effective manner.

Stakeholder group consensus based on multi-aspect hydrology decision making / Skupinový konsensus zainteresovaných subjektů založený na multikriteriální metodě rozhodování. j. hydrol. hydromech., 60, 2012, 4; 22 lit, 6 obr., 8 tab.

Catastrophic impact of floods is the result of an interaction between extreme hydrologic events and environmental, social and economic processes. Therefore, an integrated approach to flood management plays an important role in sustainable development. Such an approach requires a team comprising experts from the fields of hydrology and water resources, nature protection, risk management, human security, municipalities, economics and land use. The estimations of experts can serve for finding a solution to specific YES/NO problems and for estimating the value of specific attributes or parameters. In order to measure and evaluate the level of agreement between experts, a newly developed method for assessing the level of agreement and the value of τ-agreement, based on the Shannon theory of entropy, was applied. The use of such fuzzy-group-agreement decision making procedure, involving a broad range of stakeholders, is illustrated by the Flood Control Case Study, Zarosice, Czech Republic. In the case study of the Zdrava Voda catchment, where a part of the urbanised territory of the Zarosice village suffered from periodical flooding, a group of experts analysed the catchment data, focusing particularly on designed rainfall data. The KINFIL model was subsequently applied. Katastrofální dopad povodní je výsledkem vzájemné interakce extrémních hydrologických událostí a environmentálních, sociálních a ekonomických procesů. Z tohoto důvodu je integrovaný přístup k řešení protipovodňové ochrany důležitou součástí trvale udržitelného rozvoje. Tento přístup vyžaduje tým odborníků z oborů hydrologie a vodního hospodářství, ochrany přírody, řízení rizik (risk managementu), bezpečnosti osob, samosprávy, ekonomiky a hospodářského využití půdy. Názory těchto odborníků slouží k nalezení odpovědi na specifické otázky typu ano/ne, případně ke stanovení přesných hodnot parametrů. Pro měření a vyhodnocení konsenzu odborníků je použita nová metoda pro stanovení míry souhlasu a hodnoty τ-agreement vycházející z Shannonovy teorie entropie. Metoda je popsána na případové studii prováděné v části katastru obce Žarošice, která je často zaplavována. Tým expertů, zahrnující široké spektrum zainteresovaných subjektů, se zaměřil na dostupné informace o povodí, zejména na návrhové srážky, které byly následně vstupem do matematického srážko-odtokového modelu KINFIL.

Comparison of water regimes of two dump catchments in the Krušné hory Mts. (Czech Republic) in dry years using a hydrological balance

Gregar J., Kovář P., Bačinová H., Bažatová T. (2017): Comparison of water regimes of two dump catchments in the Krušné hory Mts. (Czech Republic) in dry years using a hydrological balance. Soil & Water Res., 12: 137−143. The dump catchments water regime optimization is one of fundamental recultivation operations in areas devastated after surface coal mining. Two dump catchments (at Radovesice and Loket in the Krušné hory Mts., Czech Republic) were selected to study whether their hydrological balance allows to keep life in them on a sufficiently natural level. The WBCM-6 water balance model was implemented. Different hydrological conditions of the mentioned dump catchments located ca. 90 km apart were compared. The Radovesice catchment lies in a precipitation shadow and suffers from a much greater precipitation deficiency than the Loket one. Its long-term annual precipitation deficit makes about 100 mm. Based on the analysis of the dry year 2003 growing season, biotechnical hydrological measures, in particular cascades of small reservoirs, were proposed.

Use of terraces to reduce overland flow and soil erosion, comparison of the HEC-HMS model and the KINFIL model application

Fedorová D., Bačinová H., Kovář P. (2017): Use of terraces to reduce overland flow and soil erosion, comparison of the HEC-HMS model and the KINFIL model application. Soil & Water Res., 12: 195−201. In our study, a system of seven natural terraces interspersed with six field belts situated at the Knínice locality (the Ore Mts., North-West Bohemia) was selected as the experimental catchment area. Overland flow was computed using two different methods: the kinematic wave method and the SCS dimensionless Unit hydrograph (UH). For the kinematic wave method calculations the KINFIL software was used; for SCS dimensionless hydrograph the HEC-HMS software was applied. The results compare hydrographs with N-year recurrence of rainfall-runoff time, where N = 10, 20, 50, and 100 years. The comparison provides hydraulic results with terraces and without terraces computed using both mentioned software products. Although two different methods of overland flow computation were performed, the input data obtained from geodetic and hydrological measurements were identical. Results of the comparison are presented and discussed.

Impact of overland flow on soil characteristics in Třebsín experimental plots

Bačinová H., Kovář P. (2017): Impact of overland flow on soil characteristics in Třebsín experimental plots. Soil & Water Res., 12: 187−193. This paper describes the continuation of simulated outcomes from the plots No. 4 and No. 5 with two different soils, using the KINFIL model to assess the runoff from extreme rainfall. The KINFIL model is a physicallybased, parameter-distributed 3D model that has been applied to the Třebsín experimental station in the Czech Republic. This model was used for the first time in 2012 to simulate the impact of overland flow caused by natural or sprinkler-made intensive rains on four of the nine experimental plots. This measurement of a rain simulator producing a high-intensity rainfall involves also hydraulic conductivity, soil sorptivity, plot geometry and granulometric curves to be used for the present analysis. However, since 2012, the KINFIL model has been amended to provide a more effective comparison of the measured and computed results using the values of new parameters such as storage suction factor and field capacity on plot 4 and plot 5. The KINFIL model uses all input data mentioned above, and it produces the output data such as gross rainfall, effective rainfall, runoff discharge hydraulic depths, hydraulic velocities and shear velocities as well as shear stress values depending on the soil particle distribution. These processes are innovative, physically based, and both the measured and the computed results fit reliably.

Choosing an appropriate hydrological model for rainfall-runoff extremes in small catchments.

Kovář P., Hrabalíková M., Neruda M., Neruda R., Šrejber J., Jelínková A., Bačinová H. (2015): Choosing an appropriate hydrological model for rainfall-runoff extremes in small catchments. Soil & Water Res., 10: 137–146. Real and scenario prognosis in engineering hydrology often involves using simulation techniques of mathematical modelling the rainfall-runoff processes in small catchments. These catchments are often up to 50 km2 in area, their character is torrential, and the type of water flow is super-critical. Many of them are ungauged. The damage in the catchments is enormous, and the length of the torrents is about 23% of the total length of small rivers in the Czech Republic. The Smědá experimental mountainous catchment (with the Bílý potok downstream gauge) in the Jizerské hory Mts. was chosen as a model area for simulating extreme rainfall-runoff processes using two different models. For the purposes of evaluating and simulating significant rainfall-runoff episodes, we chose the KINFIL physically-based 2D hydrological model, and ANN, an artificial neural network mathematical “learning” model. A neural network is a model of the non-linear functional dependence between inputs and outputs with free parameters (weights), which are created by iterative gradient learning algorithms utilizing calibration data. The two models are entirely different. They are based on different principles, but both require the same time series (rainfall-runoff ) data. However, the parameters of the models are fully different, without any physical comparison. The strength of KINFIL is that there are physically clear parameters corresponding to adequate hydrological process equations, while the strength of ANN lies in the “learning procedure”. Their common property is the rule that the greater the number of measured rainfall-runoff events (pairs), the better fitted the simulation results can be expected.