The Three Gorges Reservoir region suffers from severe soil erosion that leads to serious soil degradation and eutrophication. Interrill erosion models are commonly used in developing soil erosion control measures. Laboratory simulation experiments were conducted to investigate the relationship between interrill erosion rate and three commonly hydraulic parameters (flow velocity V, shear stress τ and stream power W). The slope gradients ranged from 17.6% to 36.4%, and the rainfall intensities varied from 0.6 to 2.54 mm·min–1. The results showed that surface runoff volume and soil loss rates varied greatly with the change of slope and rainfall intensity. Surface runoff accounted for 67.2–85.4% of the precipitation on average. Soil loss rates increased with increases of rainfall intensity and slope gradient, Regression analysis showed that interrill erosion rate could be calculated by a linear function of V and W. Predictions based on V (R2 = 0.843, ME = 0.843) and W (R2 = 0.862, ME = 0.862) were powerful. τ (R2 = 0.721, ME = 0.721) did not seem to be a good predictor for interrill erosion rates. Five ordinarily interrill erosion models were analyzed, the accuracy of the models in predicting soil loss rate was: Model 3 (ME = 0.977) > Model 4 (ME = 0.966) > Model 5 (ME = 0.963) > Model 2 (ME = 0.923) > Model 1 (ME = 0.852). The interrill erodibility used in the model 3 (WEPP) was calculated as 0.332×106 kg·s·m–4. The results can improve the precision of interrill erosion estimation on purple soil slopes in the Three Gorges Reservoir area.
Hydrological processes play important roles in soil erosion processes of the hillslopes. This study was conducted to investigate the hydrological processes and the associated erosional responses on the purple soil slope. Based on a comprehensive survey of the Wangjiaqiao watershed in the Three Gorges Reservoir, four typical slope gradients (5°, 10°, 15°and 20°) were applied to five rainfall intensities (0.6, 1.1, 1.61, 2.12 and 2.54 mm·min-1). The results showed that both surface and subsurface runoff varied greatly depending on the rainfall intensity and slope gradient. Surface runoff volume was 48.1 to 280.1 times of that for subsurface runoff. The critical slope gradient was about 10°. The sediment yield rate increased with increases in both rainfall intensity and slope gradient, while the effect of rainfall intensity on the sediment yield rate was greater than slope gradient. There was a good linear relationship between sediment yield rate and Reynolds numbers, flow velocity and stream power, while Froude numbers, Darcy-Weisbach and Manning friction coefficients were not good hydraulic indicators of the sediment yield rate of purple soil erosion. Among the three good indicators (Re, v and w), stream power was the best predictor of sediment yield rate (R2 = 0.884). Finally, based on the power regression relationship between sediment yield rate, runoff rate, slope gradient and rainfall intensity, an erosion model was proposed to predict the purple soil erosion (R2 = 0.897). The results can help us to understand the relationship between flow hydraulics and sediment generation of slope erosion and offer useful data for the building of erosion model in purple soil.
The aim of this study was to test the applicability of a simple scaling methodology for a regional estimation of intensity-duration-frequency (IDF) curves in Slovakia. The analysis is based on the regionalization process of Gaál (2006), which focused on the delineation of homogeneous regions for a regional frequency analysis of precipitation maxima. In order to examine the regionally estimated IDF curves, a region covering the western parts of Slovakia was chosen. The selected region, which encompasses 19 raingauging stations, may be characterized by the dominant influence of Atlantic circulation patterns. Three of the 19 stations belonging to the target region were set aside and flagged as verification stations. The regional dimensionless growth curve of 1-day precipitation maxima in the warm season was derived for the region, and the local T-year quantiles were estimated by the index value method for the stations. At the same time, a regionally averaged scaling exponent was derived using all the stations except for the three verification ones. The local IDF curves at the verification stations were estimated by downscaling the Tyear quantiles of the 1-day precipitation maxima using the regionally averaged scaling exponent. Finally, the IDF curves for these stations were compared with those defined by Šamaj, Valovič (1973). This study is the first step in assessing the applicability of a simple scaling theory for the regional estimation of IDF curves in Slovakia. and Cieľom tejto práce bolo otestovať možnosť použitia metódy jednoduchého škálovania zrážok pri regionálnom odhade návrhových hodnôt zrážkových intenzít na Slovensku. Pre analýzu bolo vybraných 19 zrážkomerných staníc vo vopred vyčlenenom regióne na území západného Slovenska, pričom tri stanice boli separované ako verifikačné stanice. Pre vybraný región sme odvodili bezrozmernú regionálnu čiaru prekročenia jednodenných maximálnych úhrnov zrážok v teplom polroku a následne sme pre verifikačné stanice metódou indexovej hodnoty odhadli lokálne návrhové hodnoty pre rôzne významné doby opakovania T (tzv. T-ročné kvantily). Vo vyčlenenom regióne sme určili priemerný regionálny škálovací koeficient. Návrhové zrážkové intenzity pre tri verifikačné stanice sa stanovili zoškálovaním T-ročných kvantilov jednodenných maximálnych zrážok pomocou regionálneho škálovacieho koeficientu. Určené návrhové hodnoty sme porovnali s výsledkami Šamaja, Valoviča (1973). Štúdia potvrdila možnosť využitia metódy jednoduchého škálovania na regionálny odhad návrhových hodnôt zrážkových intenzít na Slovensku.
Theoretical assumptions and practical approaches to temporal and spatial distribution of rainfall intensity in urban watersheds is still a research topic. The speed and direction of movement of rainfall events above urban watersheds are principal hydrologic parameters, which influence a rainfall-runoff process. This contribution reviews three methods, namely the Inverse Distance-Weighted Method (IDWM), Time Shift Method (TSM) and newly developed Geometrical Method (GM). The principal assumption of all three methods is based on the calculation of fictitious rainfall intensity at a particular location as weighted interpolation among the nearest real rain gauge stations. Any rainfall event above the urban watershed can be classified either as moving or non-moving storm. While the Inverse Distance-Weighted Method can be used for non-moving storms, the other two methods can describe the parameters of moving storms. Model RainGen, which was originally developed to create a basic source of rainfall data for rainfallrunoff mathematical models in urban watersheds, may be used not only for visualization but as well as for comparing of the measured and computed results. Case study for moving storms in Prague shows the results of TSM and GM methods. and Teoretické předpoklady a praktické přístupy k řešení časového a plošného rozložení srážek v urbanizovaných povodích jsou stále předmětem výzkumu. Rychlost a směr pohybu dešťových událostí nad urbanizovanými povodími představují hlavní hydrologické veličiny, které ovlivňují srážko-odtokový proces. Příspěvek se zabývá třemi metodami výpočtu, a to inverzní váhovou metodou, metodou časového posunu a nově navrženou geometrickou metodou. Hlavní předpoklad u všech tří metod je ve zvoleném místě založen na výpočtu fiktivní intenzity deště a to na základě interpolace s využitím váhové funkce mezi nejbližšími srážkoměrnými stanicemi. Každou srážkovou událost nad urbanizovaným povodím lze klasifikovat buď jako pohyblivou, nebo nepohyblivou. Zatímco inverzní váhová metoda může být použita pro nepohyblivé srážkové události, metodu časového posunu a geometrickou metodu lze doporučit pro pohyblivé srážkové události. Model RainGen, který byl původně vytvořen k tvorbě základních srážkových dat pro potřeby matematických modelů povrchového odtoku z urbanizovaných povodí, může být využit nejen k vizualizaci výsledků, ale rovněž k jejich vzájemnému porovnávání. Případová studie pohyblivých srážkových událostí v Praze ukazuje porovnání výsledků metody časového posunu a geometrické metody.