The influence of effective rainfall on modeled runoff hydrograph

Influence of the pattern of effective rainfall on modeled hydrograph was investigated in the study. The\ud modelling was performed with the U.S. Army Corps of Engineers hydrograph package HEC-HMS 3.2 and\ud calibrated and validated on measured hydrographs of Glinscica watershed. Six different models of rainfall\ud loss were applied and their effect on modeled hydrograph was evaluated. Peak discharge, time of peak\ud discharge and runoff volume were compared. The best results with the lowest RMSE in the study was\ud obtained with the SCS curve number loss method. Also synthetic hyetographs of different probability and\ud duration were used. Three positions of the maximum rainfall intensity at 25, 50 and 75 % of the rainfall\ud duration were applied. The results showed essential differences in simulated time to peak and also\ud differences in peak discharge. The differences in time to peak increases considerably with the increasing of\ud the rainfall duration. Finally, the results of constant intensity distribution of rainfall of different durations\ud were compared with those obtained with typical rainfall distribution with the position of the maximum\ud intensity at 50 %. Results showed considerable differences in peak discharge and time to peak by longer\ud durations of the rainfall

Rainfall interception by two deciduous Mediterranean forests of contrasting stature in Slovenia

Measurements of precipitation above the canopy, throughfall and stemflow were\ud made on the south and north-facing slopes of a deciduous forest on the experimental\ud watershed of the Dragonja river in SW Slovenia. The Dragonja watershed was\ud chosen for the experimental watershed, being of interest because of intensive natural\ud reforestation in the last decades that caused a decrease in minimum and maximum\ud flows. At the same time no noticeable precipitation and temperature changes were\ud observed. Two forest plots were selected. One is located on the north-facing slope\ud (1419 m2) and the other on the south-facing slope (615 m2). Analyses and modelling\ud were made for a one-year period from October 2000 to September 2001. The leaf\ud area index (LAI) was estimated by three methods, one direct and two indirect ones.\ud The obtained values of LAI with the direct method were 6.6 and 6.9 for the south and\ud north slopes, respectively. Measurements and regression analyses gave the mean\ud annual throughfall value (± standard error) on the south plot 67.1 (± 9.6) % of gross\ud precipitation, and 71.5 (± 11.6) % on the north plot. The average stemflow values\ud were 4.5 (± 0.8) % of gross precipitation in the south plot and 2.9 (± 0.6) % in the\ud north plot. The average annual interception losses amount to 28.4 (± 4.1) and 25.4 (±\ud 4.0) % for the south and north slopes, respectively. In the study a significant influence\ud of the south-east wind was proven. With regression analyses and the classification\ud decision tree model it was established that at the events with more than 7 mm of\ud precipitation and south-east wind with a speed higher than 4 m/s an unusually low\ud amount of throughfall occurred and thus high interception losses. The analytical\ud Gash model of rainfall interception (Gash, 1979; Gash et al., 1995) was successfully\ud applied. The results of the modelling corresponded well to the observed values and\ud were within the limits of the standard error of the observed values

Estimating leaf area index of the deciduous forest in the Dragonja watershed. Part 2: Results and discussion

Measurements and estimation of leaf area index (LAI) were carried out in the deciduous forest in the experimental watershed of the Dragonja River. At the same time precise measurements and analysis relevant to single elements of the forest hydrological cycle and other vegetational\ud parameters with modern measuring equipment were made. In Part 1 of the paper (Šraj, 2003b) the methods of delineation of the leaf area index and measurements of LAI were discussed. An accurate description of characteristical features of trees on both chosen plots was also given. In this part of the paper, results of measurements, LAI estimation and analysis are given. The measurements\ud commenced in autumn 2000. The specific leaf area (SLA) was estimated for the most abundant tree species (for example oak, ash, hornbeam, maple, cornelian cherry dogwood). Leaf area index was estimated according to three methods: direct method of litterfall collection, method of hemispherical photography, and method of measuring photosynthetically active radiation (PAR). The analyses revealed that the methods of hemispherical photography and of photosynthetically active radiation (PAR) underestimated the value of LAI in the full-leaf period. LAI estimated\ud according to the litterfall collection method was 6.7 on the south plot and 7.3 on the north plot. The lower value of LAI on the south plot was expected, since the forest on the south plot has a more open character than the one on the north plot

Analysis of the possibility of\ud using the distributed two-dimensional model Flo-2D for hydrological modelling

The paper presents a hydrological model of the Glinščica watershed with the program \ud Flo-2D. The aim of \ud the research was to analyze the applicability of the two-dimensional mathematical model Flo-2D for \ud hydrological modeling and to compare the results with the one-dimensional HEC-HMS model. Flo-2D is \ud a commercial, physically based model with distributed parameters. lts main purpose is \ud modeling river hydraulics. lt continuously computes the rainfall runoff from the watershed according to the \ud topography or a\ud digital elevation model (DEM), the quantity and intensity of precipitation, the land use and soil \ud type. On the other hand, HEC-HMS is freely available software that enables to create a simple and \ud sufficiently detailed hydrologic model on the basis of precipitation, discharge and some watershed \ud characteristics. ln both cases precipitation losses were computed with SCS (Soil Conservation \ud Service) Curve Number loss method. Flo-\ud 2D model was calibrated by varying input and modeling parameters including grid size, roughness \ud coefficients and SCS Curve Numbers. The results of 10-year and 100-year events and 2, 12 and \ud 24-hour storms are also compared. The results of runoff volumes are comparable, but the shape of \ud runoff hydrograph computed with HEC-HMS model is much better. ln the Flo-2D model assessing the \ud Manning roughness coefficient and selecting the size of the grid cells are the most problematic, \ud whereas in the HEC-HMS model it is the assessment of the time of concentration. Calibration of the \ud model with distributed parameters is difficult and time-consuming. The results have shown that the \ud Flo-2D model can be used in hydrological\ud practice only in cases where good input data are available for the model and its calibration.\u

Measurements and Analysis of Intercepted Precipitation of Silver Birch (Betula pendula Roth.) and Scots Pine (Pinus sylvestris L.) in Urban Area

Study presents measurements, comparation and analysis of intercepted precipitation of\ud coniferous and deciduous trees. Measurements were made on experimental plot in the urban\ud part of the city Ljubljana on two groups of trees: Betula pendula and Pinus sylvestris.\ud Analyses and comparations of throughfall and stemflow were made for the period from June\ud 2004 till December 2006 which was devided onto four vegetation periods. Rainfall above the\ud canopy was measured automatically with a tipping bucket rain gauge with digital recording of\ud results every 10 minutes in combination with manual Helman's rain gauge for control.\ud Throughfall was measured using a combination of fixed gauges with digital recording of\ud results every 10 minutes and manual roving gauges. Stemflow was measured manually on one\ud tree of each specie. The results of the measurements showed that the throughfall for Betula\ud pendula was 57-70 % of precipitation and for Pinus sylvestris 35-49 % which is comparable\ud with the results of other similar studies around the world. The stemflow fraction for Betula\ud pendula amounted 1,1-6,7 % of precipitation and it was practically negligible for Pinus\ud sylvestris

Določanje kazalnikov nizkih pretokov – prikaz na primeru vodomerne postaje Kokra I na reki Kokri

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Vpliv podnebne spremenljivosti na rezultate verjetnostnih analiz visokovodnih konic: primer vodomerne postaje Litija na reki Savi

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Coincident frequency analysis of flood waves at the confluence of the Soča and the Vipava rivers

In this paper the methodology of the coincident frequency analysis is presented. Using the HEC-SSP program the coincident frequency analysis of flood waves at the confluence of the Soča and Vipava rivers \ud was performed. \ud The probability distribution of water level of the Vipava River in Sovodnje was assessed on the basis of measured discharge data of the Vipava River in Miren and calculated discharge data of the Soča River at the confluence with the Vipava River. In order to obtain the response curves of the water level of the Vipava River at Sovodnje, simulations using a one -dimensional hydraulic model HEC\ud -RAS were performed. \ud The water level of the Vipava River in its lower reach near the confluence is highly influenced by increased discharge of the Soča River at the confluence with the Vipava River, which causes backwater of the Vipava River. In order to reduce the probability of flooding of the Vipava River at its lower reach near the confluence, the backwater effect should be reduced first

The influence of the choice of method on the results of frequency analysis of peaks, volumes and durations of flood waves of the Sava river in Litija

Complex hydrological events such as floods always appear as a consequence of several correlated random\ud variables (peak, volume, duration). Therefore single-variable frequency analysis can only provide limited\ud assessment of these events. To fully understand all three variables and their relationship, a multivariate\ud statistical approach is necessary. A precondition for such an approach is a complete analysis of all individual\ud variables. 58 years of data from gauging station Litija on the Sava River were analyzed. Peaks, volumes and\ud durations of flood waves were considered in the flood frequency analysis. Statistical and graphical tests were\ud used to assess performance of the most commonly used distribution functions and parameter estimation\ud techniques. Log-Pearson III distribution gave the best results in case of peaks and durations of flood waves\ud and Pearson III distribution in case of volumes. Method of L-moments, which has not yet been used in\ud Slovenian hydrological practice, gave the best estimation of parameters for most distributions

Izdelava Huffovih krivulj in njihova analiza za izbrane\ud padavinske postaje v Sloveniji

Prispevek predstavlja izdelavo, rezultate in analizo Huffovih krivulj za izbrane meteorološke postaje: Ljubljana, Murska Sobota, Novo Mesto in Portorož. Za meteorološko postajo Ljubljana smo obdelali podatke od leta 1948 do 2010 in za ostale meteorološke postaje od leta 1970 do 2011. Pri primerjavirezultatov smo ugotovili razlike v obliki Huffovih krivulj in tudi vštevilu neviht, ki so ustrezale definiciji neodvisnega padavinskega dogodka. Razlike med postajami so bile dovolj velike, da lahko zaključimo, da ne moremopredpostaviti ene same oblike Huffovih krivulj za celotno Slovenijo, karnarekuje izdelavo Huffovih krivulj tudi za ostale meteorološke postaje