Long-term variations and trends in a wide range of statistics for daily precipitation characteristics in terms of intensity, frequency and duration in Finland were analysed using precipitation records during 1908e2008...Long-term variations and trends in a wide range of statistics for daily precipitation characteristics in terms of intensity, frequency and duration in Finland were analysed using precipitation records during 1908e2008 from 3 meteorological stations in the south(Kaisaniemi),centre(Kajaani) and north(Sodankyl€a). Although precipitation days in northern part were more frequent than in central and southern parts, daily precipitation intensity in the south was generally higher than those in the centre and north of the country. Annual sum of very light precipitation(0 mm < daily precipitation long-term 50 th percentile of daily precipitation more than 0 mm) significantly( p < 0.05) decreased over time,with the highest rate in northern Finland. These decreasing trends might be the result of significant increases in frequency of days with very light precipitation at all the stations, with the highest and lowest rates in northern and southern Finland, respectively. Ratio of annual total precipitation to number of precipitation days also declined in Finland over 1908e2008, with a decreasing north to south gradient. However, annual duration indices of daily precipitation revealed no statistically significant trends at any station. Daily precipitation characteristics showed significant relationships with various well-known atmospheric circulation patterns(ACPs). In particular, the East Atlantic/West Russia(EA/WR)pattern in summer was the most influential ACP negatively associated with different daily precipitation intensity, frequency and duration indices at all three stations studied.展开更多
To verify the accuracy of weir and orifice formula and analyze the hydraulic characteristics of exchange flow in a manhole,a three-dimensional numerical model was proposed to assess the exchange flow rate between the ...To verify the accuracy of weir and orifice formula and analyze the hydraulic characteristics of exchange flow in a manhole,a three-dimensional numerical model was proposed to assess the exchange flow rate between the surface and sewer pipe systems based on the real-world scale model.The hydrodynamic model is based on the three-dimensional Navier-Stokes equations including the standard k-εmodel for turbulence processes,and the volume of fluid(VOF)method for capturing the free surface.The results of the computational fluid dynamics(CFD)simulation are compared with the conventional overflow equations,showing that the weir and orifice formula is appropriate to determine the exchange flow rate between two systems in this specific study case.Streamlines and velocity contours at the center profile under both the inflow and surcharge conditions show that the exchange flow is directly related to the water level on the surface and the junction area between the manhole and right pipe.The results demonstrate the potential application of CFD in analyzing the interaction of urban flood flows,which can provide much clearer details of the interaction process.展开更多
The Zoige wetland is the biggest alpine wetland in the world,and an important water resource of the Yellow River.Due to natural and human factors,the Zoige wetland has been seriously degraded.Existing studies on the Z...The Zoige wetland is the biggest alpine wetland in the world,and an important water resource of the Yellow River.Due to natural and human factors,the Zoige wetland has been seriously degraded.Existing studies on the Zoige wetland mainly focus on the macro features of the wetland,while the influence of the surrounding faults on the Zoige wetland degradation is rarely studied.This study uses terrain data to analyze the cover change and the water loss caused by the Wqie-Seji fault based on the distributed hydrological model.The simulated water loss demonstrates that the Normalized Difference Vegetation Index(NDVI) is the most important factor for inducing water loss.The fault is also a factor that cannot be neglected,which has caused 33% of the wetland water loss.Therefore,it is of importance to study the influence of the fault on the wetland degradation.展开更多
Beam dams are a highly effective and commonly used open-type check dam in debris-flow hazard mitigation. In this study, dimensional analysis was used to obtain empirical equations for quantitatively determining the se...Beam dams are a highly effective and commonly used open-type check dam in debris-flow hazard mitigation. In this study, dimensional analysis was used to obtain empirical equations for quantitatively determining the sediment-trapping and flow-regulating characteristics of a beam dam. To determine the coefficients of the empirical equations, flume experiments were conducted to simulate the trapping and regulating processes. The flow pattern, trapping, and regulating characteristics were investigated when debris flows passed through a beam dam. Debris-flow bulk density and peak discharge, and sediment-trapping ratios, were measured directly and indirectly. The results showed that three blocking actions occurred, and that blockage-breaking considerably influenced the trapping and regulating performance of the beam dam. The relative opening size and the sediment concentration were the two main factors affecting the performance of the beam dam. The ratio of trapping sediment decreased with relative opening, and increased with sediment concentration as well as reducing ratio of bulk density and reducing ratio of peak discharge. The sediment concentration and relative opening were the leading factors influencing the trapping and regulating sediment of a beam dam, followed by flume gradient. The results showed that the calculated values obtained using empirical equations were in good agreement with the values derived from the experiments, and that the deviation was acceptable. Finally, taking Zechawa Gully as an example, using the empirical equations we designed the opening size of a beam dam aimed to trap sediment and regulate peak discharge of debris flow in the main gully.展开更多
基金the Finnish Cultural Foundation and Maa-ja vesitekniikan tuki r.y. (MVTT, 29188) for funding this researchsupported by Swedish VR, BECC and MERGE programs
文摘Long-term variations and trends in a wide range of statistics for daily precipitation characteristics in terms of intensity, frequency and duration in Finland were analysed using precipitation records during 1908e2008 from 3 meteorological stations in the south(Kaisaniemi),centre(Kajaani) and north(Sodankyl€a). Although precipitation days in northern part were more frequent than in central and southern parts, daily precipitation intensity in the south was generally higher than those in the centre and north of the country. Annual sum of very light precipitation(0 mm < daily precipitation long-term 50 th percentile of daily precipitation more than 0 mm) significantly( p < 0.05) decreased over time,with the highest rate in northern Finland. These decreasing trends might be the result of significant increases in frequency of days with very light precipitation at all the stations, with the highest and lowest rates in northern and southern Finland, respectively. Ratio of annual total precipitation to number of precipitation days also declined in Finland over 1908e2008, with a decreasing north to south gradient. However, annual duration indices of daily precipitation revealed no statistically significant trends at any station. Daily precipitation characteristics showed significant relationships with various well-known atmospheric circulation patterns(ACPs). In particular, the East Atlantic/West Russia(EA/WR)pattern in summer was the most influential ACP negatively associated with different daily precipitation intensity, frequency and duration indices at all three stations studied.
基金The National Natural Science Foundation of China(No.51979040)。
文摘To verify the accuracy of weir and orifice formula and analyze the hydraulic characteristics of exchange flow in a manhole,a three-dimensional numerical model was proposed to assess the exchange flow rate between the surface and sewer pipe systems based on the real-world scale model.The hydrodynamic model is based on the three-dimensional Navier-Stokes equations including the standard k-εmodel for turbulence processes,and the volume of fluid(VOF)method for capturing the free surface.The results of the computational fluid dynamics(CFD)simulation are compared with the conventional overflow equations,showing that the weir and orifice formula is appropriate to determine the exchange flow rate between two systems in this specific study case.Streamlines and velocity contours at the center profile under both the inflow and surcharge conditions show that the exchange flow is directly related to the water level on the surface and the junction area between the manhole and right pipe.The results demonstrate the potential application of CFD in analyzing the interaction of urban flood flows,which can provide much clearer details of the interaction process.
基金supported by the National Key Project of Scientific and Technical Supporting Programs of the Ministry of Science&Technology of China(Grant No.2007BAC18B01)the Project of Ministry of Environmental Protection of China(Grant No.200809086),the Project of Ministry of Environmental Protection of China(Grant No.200909060)the Project of Scientific Research and Technological Development of Guangxi(Grant NO.GKG1140002-2-4)
文摘The Zoige wetland is the biggest alpine wetland in the world,and an important water resource of the Yellow River.Due to natural and human factors,the Zoige wetland has been seriously degraded.Existing studies on the Zoige wetland mainly focus on the macro features of the wetland,while the influence of the surrounding faults on the Zoige wetland degradation is rarely studied.This study uses terrain data to analyze the cover change and the water loss caused by the Wqie-Seji fault based on the distributed hydrological model.The simulated water loss demonstrates that the Normalized Difference Vegetation Index(NDVI) is the most important factor for inducing water loss.The fault is also a factor that cannot be neglected,which has caused 33% of the wetland water loss.Therefore,it is of importance to study the influence of the fault on the wetland degradation.
基金supported by the Chinese Academy of Sciences and Organization Department of Sichuan Provincial Party Committee“Light of West China”Program(the key control techniques of glacial debris flow along the Sichuan-Tibet Railway)the National Natural Science Foundation of China(Grant No.41772343)STS Project of the Chinese Academy of Sciences(KFJ-STS-ZDTP015)
文摘Beam dams are a highly effective and commonly used open-type check dam in debris-flow hazard mitigation. In this study, dimensional analysis was used to obtain empirical equations for quantitatively determining the sediment-trapping and flow-regulating characteristics of a beam dam. To determine the coefficients of the empirical equations, flume experiments were conducted to simulate the trapping and regulating processes. The flow pattern, trapping, and regulating characteristics were investigated when debris flows passed through a beam dam. Debris-flow bulk density and peak discharge, and sediment-trapping ratios, were measured directly and indirectly. The results showed that three blocking actions occurred, and that blockage-breaking considerably influenced the trapping and regulating performance of the beam dam. The relative opening size and the sediment concentration were the two main factors affecting the performance of the beam dam. The ratio of trapping sediment decreased with relative opening, and increased with sediment concentration as well as reducing ratio of bulk density and reducing ratio of peak discharge. The sediment concentration and relative opening were the leading factors influencing the trapping and regulating sediment of a beam dam, followed by flume gradient. The results showed that the calculated values obtained using empirical equations were in good agreement with the values derived from the experiments, and that the deviation was acceptable. Finally, taking Zechawa Gully as an example, using the empirical equations we designed the opening size of a beam dam aimed to trap sediment and regulate peak discharge of debris flow in the main gully.
