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Effects of reforestation on the hydrological function of a small watershed in the Three Gorges Reservoir Area


Hydrological effects of forest litter and soil in the Simianshan Mountains in Chonging, China


A preliminary study of the hydrological effects of forest litter and soils in the Simianshan Mountains was carried out.


For the complexity and scale dependence of the influence of forest vegetation on runoff, forest hydrological functions based on regional scale or watershed scale were worthy of further studies.


The interception of rainfall by vegetation and the subsequent evaporation of intercepted water from the canopy surface play an important role in hydrological processes, and the water and energy balance of forest ecosystems.

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 This paper attempts to answer the following two questions: (1) Is it possible to derive the law of distribution of hydrological frequency theoretically(2) What type of distribution curve should be adopted as the model of hydrological frequency curve and how to determine their parameters? The results obtained may be summarized as follows: 1. Hydrological phenomena are time series with concealed periodic fluctuations. The results from statistical analysis based upon the current assumption that... This paper attempts to answer the following two questions: (1) Is it possible to derive the law of distribution of hydrological frequency theoretically(2) What type of distribution curve should be adopted as the model of hydrological frequency curve and how to determine their parameters? The results obtained may be summarized as follows: 1. Hydrological phenomena are time series with concealed periodic fluctuations. The results from statistical analysis based upon the current assumption that hydrological phenomena are independent stochastic variables should be accepted with due considerations. 2. In view of the regional nature of hydrological phenomena, the current parctice of analyzing samples taking from a single station only is, in effect, to narrow the sampling field arbitrarily from a larger area to a point, thus reducing the accuracy of the statistical results. Hence, the synthetic utilization of the data of all stations within the hydrologically homo geneous region is an important measure to increase the accuracy of statistical analysis. 3. The belief that the flood frequency obeys the binomial theorem or Poisson's theorem is but to mix up the priori with the empirical probability problem. The binomial theorem, being a powerful weapon to deal with the problems of priori probability, has not been adquately and properly utilized in the hydrologieal frequency analysis. 4. Analyses have been made of the nature of distribution of shydrologieal series on the basis of Kaptyen's derivation of the skew distribution, which indicate: (1) That the theoretical interpretation of the logprobability law of the hydrologic phenomena by V. T. Chow is not sound; (2) that hydrologic phenomena being results of very complicated meteorological and hydrological processes, it is impossible to derive theoretically the law of distribution for the hydrological series. 5. The view that the flood frequency obeys the Gumbel's distribution is theoretically not sound and also not verified by actual data. 6. According to the nature of the mathematical treatments applied, the method of description of the empirical probability can be classified into three systems: (1) The methods of the generalization of the characteristic factors of the distributions, such as Pearson's curves, Goodrich's curves, etc.; (2) The methods of the modification of a fundamental distribution by series and polynomials, such as GramCharlier curves. curves, etc.; (3) The methods of transformed functions, such as the logprobability law, curves, etc. It should be remarked that not only Pearson's and Goodrich's curves are frequency curves of empirical nature, but even the theoretical laws, such as the normal law and the logprobability law, will be aceepted as curves of empirical nature, when used as models for empirical probability problem. 7. Hydrological frequency analysis should not be mystified and made absolute. Instead of free selections, the models of hydrological frequency curve should be uniquely selected and specified. Statistical parameters should be determined not solely by the short period data of single station, but also by the synthetic utilization of the data of possible more stations. 8. It is recommended that one of the two types of distribution, i.e. the lognormal frequency curve with both sides limited and the Pearson's type Ⅲ curve, may be selected as unified models. The author suggests that the Kvalue corresponding to recurrence intervals of say 10~4, 10~5, or 10~6 years may be selected as the upper and lower limits for the lognormal curve. For Pearson's type III curves, C_s should be treated not as independent but as dependent variables of C_v. 9. The proper way to select and determine the model frequency curve is to see whether it fits well with the actual data of grouped stations (stations to be grouped by regions for rainfall data and by C_v for runoff data) and the reasonableness of the extrapolating part. 10. Suggestions on the method of determination of x and C_v: For point rainfall, isox map may be utilized, and the mean C_v for each hydrologicregion may be adopted in order to minimize the errors from single stations and to avoid the discrepancies in results obtained from the same region. With regard to flood frequency analysis, flood mark reconnaissance must be utilized to determine the magnitude and the recurrence interval of the unusual flood. The x and C_v values of the floods and runoffs of hydrologically similiar river basins may be compared. Besides, the reasonableness of the results of frequency calculations as well as of the statistical parameters adopted therein may be checked by comparing runoffs and pointrainfall values of the same frequency.  我国近期水文频率计算方法的研究工作在选择方法,经验频率公式,参数的误差和利用我国水文资料检验各种频率线型等方面有了一定的成果和实用的结论[1],但是下面两个问题还没有获得解决: (1)能否从机率理论证明水文频率属于何种分布律? (2)水文频率曲线应当采用什么线型?如何确定参数?本文试图解答以上两个问题。本文分析了水文系列的时序性质和区域性质,把机率问题按先验、极限和后验三种基本性质对水文频率问题进行了分析;利用开布屯推导偏态分布的方法分析了水文系列的分布性质,并从而批判了有关水文频率肯定属于对数正态律,耿贝尔极限律或二项式定理等等说法。认为属于后验机率性质的水文频率,不能从机率理论证明它属于何种分布律。最后提出联合利用各站水文资料来选择线型和确定参数的方法,并建议在两端有限对数正态和皮尔逊Ⅲ型两种线型中选择一种作为统一采用的线型,对两端有限曲线提出了简易可行的确定上下极限的方法,对皮尔逊Ⅲ型曲线认为应该把Cs作Cv的倚变参数。  A seale model investigation of surface runoff hydrographs for a small watershed with impermeable surface was carried out in a indoor laboratory. Hydrographs at the watershed outlet due to rainfalls of difforent durations and intensities were obtained experimentally. These results were used to check the unitgraph theory.The findings derived from experimental data are: 1.The duration of surface runoff for all uniformintonsity storms of the same length is not constant,but somewhat varies with the intensity of... A seale model investigation of surface runoff hydrographs for a small watershed with impermeable surface was carried out in a indoor laboratory. Hydrographs at the watershed outlet due to rainfalls of difforent durations and intensities were obtained experimentally. These results were used to check the unitgraph theory.The findings derived from experimental data are: 1.The duration of surface runoff for all uniformintonsity storms of the same length is not constant,but somewhat varies with the intensity of rainfall. 2.In cases,the rainfall duration is equal or longer than the time of concentration of the watershed,the configuration of unitgraphs remain unchanged in essential char acteristics. 3.In cases,the rainfall duration is shorter than the time of concentration,the re sultant unitgraphs are not similar in configuration;the unitgraph theory is not verified. 4.The stale model experiment method for hydrological investigation,although far from perfect in hydraulic simulation and experimental technique,is considered as a new and fruitful approach for further efforts.  为了研究表面径流过程线,我们采用一座象小流域表面不透水的比例模型,建造在室内实验室里。自记水位计安放在流域的出口处,合适地以不同的降雨历时和强度做试验,这种结果用来检验单位线理论。从试验的资料推论发现:1.所有一定强度的暴雨,地面径流历时的长短不是不变的,但是随降讯强度的变化不大。2.在降雨时间等于或大于流域的汇流时间的情况下,单位线的形状存在基本上不变的特征。3.在降雨时间短于汇流时间的情况下,结果单位线的形状不相似,单位线的理论不成立。4.为水文研究比例模型试验的方法,虽然在水力相似和试验技术不十分成熟,是新的事物,有待今后更进一步的努力。  In this peper, the author demonstrates the factors which affect the waterresistance of compacted soils, especially the degree of wetting by euviroments and the degree of compaction. It revealed the possibility, through laboratory test that at arid vegiuns (little possibility of wettiug or good hydrological conditions) the soil in embanbment could be compactell at the mois ture content below the optimum, and the wetstrength of compacted soil is higher than that at optimum. The author had also made the... In this peper, the author demonstrates the factors which affect the waterresistance of compacted soils, especially the degree of wetting by euviroments and the degree of compaction. It revealed the possibility, through laboratory test that at arid vegiuns (little possibility of wettiug or good hydrological conditions) the soil in embanbment could be compactell at the mois ture content below the optimum, and the wetstrength of compacted soil is higher than that at optimum. The author had also made the wetting and drying test of compacted. soil and found that the higher the degree of compaction, the larger the waterresistance of the compacted soil. The results of this research would be usefal to solve the compaction problems at arid regions.  压实士在润湿作用后的表现如何,要看润湿作用的强烈程度和路基土的压实程度而定。在西北缺水地区,由于湿源不足,路基土可以在低于最佳含水量时压实。此时,压实土在润湿后的强度反较在最佳含小量值时压实的小。借助于增加压实工作量而获得的高密实度的土,在反复干湿的作用下,是能保持较高的水稳定性的。因此,在缺水地区我们可以在较低的天然湿度下进行压实;同时也可以用较重的来压实工具压实,此时可获得高强度的土。   << 更多相关文摘 
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