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.

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 km 2 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.

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.

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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.