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湿润地区的流域汇流计算，常常以不同水源分别的进行汇流计算，需将总径流量划分为直接径流量和地下径流量两部分，流域稳定下渗率ＦＣ是划分径流量的重要参数，通常用试错法确定，对固定流域取为常数。本文考虑流域各处透水性能并不均一，设想类似于流域蓄水容量曲线，在下渗面上存在着流域稳渗率分布曲线，并表达为少数参数方便，以便于地区综合，提高划分水源，流域汇流计算的精度。 相似文献
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下渗强度的计算是干旱半干旱地区超渗产流计算的关键环节。河北雨洪模型中的流域下渗强度计算公式由两部分组成,一部分为由张力引起的下渗强度,另一部分为由重力引起的下渗强度(稳定下渗能力)。计算以上两部分下渗强度时,公式所用的雨量有重复,致使总下渗强度普遍偏大,从而导致模型模拟的洪水过程的洪量及洪峰偏小。提出一个改进的流域下渗强度计算公式,计算张力引起的下渗时所用雨强为总雨强与稳定下渗能力的差值。利用改进前后的计算公式,分别对2mm/h到10mm/h雨强及0mm到140mm表层土湿条件下的下渗强度进行计算,并对结果进行对比分析。大阁流域的实例应用结果表明,改进后的下渗强度计算公式,对模拟洪水过程的洪量和洪峰流量的增加效果明显,增加值分别为实测值的14.14%和10.08%。 相似文献
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提出了一个基于统计理论的产流模型,该模型考虑了降雨、土壤下渗能力及土壤蓄水容量的空间变异性。假定每个时段的降雨量在空间上可以用概率密度函数或分布函数描述,根据实测降雨资料通过统计拟合优度途径估计各时段降雨的空间概率分布;采用抛物线型函数分别描述土壤下渗能力和土壤蓄水容量的空间分布。按照超渗产流机制计算地表产流量,通过降雨量和土壤下渗能力的联合分布推导得到地表径流量的统计分布,进而得到平均产流量的解析表达式。下渗水量补充土壤含水量,假定满足田间持水量后形成地下径流,其产流量根据下渗量和土壤蓄水容量的空间分配曲线进行计算。以半湿润的黄河支流伊河东湾流域为例,对模型进行了验证和应用,并与新安江模型的结果进行了对比。结果表明,模型对所研究的半湿润区的洪水模拟预报有较好的模拟效果。 相似文献
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包气带土壤性质具有强烈的空间变异性,显著影响包气带水的分布特征和运移过程,在巴丹吉林沙漠这种包气带巨厚而观测困难的地区尤其值得重视.通过收集包气带不同深度水分观测资料和水力参数测试成果,采用前人提出的水分特征曲线参数的对数正态分布模型和互相关模型,对巴丹吉林沙漠风积砂的变异特征进行了Monte-Carlo模拟,发现稳定下渗带能够自由流动的水分体积含量低于5%.在此基础上重建土水势的垂向分布,发现稳定下渗带的水力梯度接近于1,基本满足重力作用控制的自由下渗条件.以残余含水率为独立随机变量,基于Richards方程对不同下渗强度条件的包气带含水率分布进行了Monte-Carlo模拟,通过与观测统计特征对比得到下渗强度的合理取值范围.结果表明,包气带水下渗强度最有可能取值范围是30～41 mm/a,且低于10 mm/a和高于50 mm/a的可能性都很小.包气带水的随机模拟方法为研究巴丹吉林沙漠地下水补给提供了新的视角. 相似文献
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西北干旱地区水资源现状、问题及对策 总被引：10，自引：0，他引：10
通过对西北干旱地区的水资源现状分析,得出西北干旱区水资源存在着水资源量不足、分布不均、严重浪费、水环境恶化等问题;解决该地区水资源问题的相应对策,即:强化管理,科技兴水,合理配置,高效利用,优化环境,加大投入和持续利用等。 相似文献
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利用间接边界元方法,在频域内求解了层状场地中局部不均体对平面P波的散射。利用精确的土层动力刚度矩阵进行自由场反应分析,求得位移和应力响应。通过计算虚拟分布荷载的格林影响函数,求得相应位移和应力;根据边界条件确定虚拟分布荷载,最终得到问题的解答。研究了入射P波时,不均体宽度、埋深、厚度、入射角、入射频率度等参数对地表位移幅值的影响,并与相应自由场的结果进行了比较。不均体对P波散射有重要影响,在工程场地地震安全性评价中,应合理考虑局部不均体对场地设计地震动参数确定的影响。 相似文献
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Christopher Uche Ezeh Michael Chukwuma Obeta Raymond N. C. Anyadike 《Arabian Journal of Geosciences》2016,9(16):681
The study compared the sequences of daily rainfall over coastal southern and semi-arid northern Nigeria. Daily rainfall occurrences for 41 years (1971–2011) over four meteorological stations in Lagos, Rivers, Borno, and Katsina were analyzed using frequency analysis and Markov chain model. Findings indicate that the coastal area had a predominance of 2–4-day wet spells while the semi-arid area showed a wet spell distribution that is geometric in nature with 1-day spell predominance. The dry spell behavior was nearly the opposite of the wet spell occurrence. The coastal region showed a dry spell of 1–4-day spell predominance while the semi-arid region showed a predominance of higher dry spells of 2–6 days. Accumulation of the amount of rainfall in each spell also showed that much rainfall from the coastal area was obtained from rains of spells of 3 days and above while the semi-arid had more of its rain from spells of 1–3 days. The mean annual rainfall was 1423.75 mm (Lagos), 2173.56 mm (Rivers), 517.50 mm (Katsina), and 578.34 mm (Borno). The wettest month was June (274.08 mm) in Lagos, September (378.18 mm) in Rivers, and August in Katsina and Borno (172.98 and 184.81 mm, respectively). The driest months were January for Lagos and Rivers (15.77 and 18.96 mm, respectively) and November–February for Katsina and Borno (0–0.06 mm). This showed that the coastal areas had nearly three times the volume of rain in the semi-arid area. The study further showed that onset of rain for the coastal area was March/April while the cessation of rainy season was October/November. On the other hand, the onset of rainy season in the semi-arid area was May/June and cessation of rainy season was September. Findings portend drier days for the semi-arid area due to dry spell persistence and hence, the consequent challenges of providing artificial water supply for agriculture and other purposes especially from October to May. 相似文献
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Tyson P. D. 《GeoJournal》1981,2(2):3-10
Short-term changes in the general circulation of the atmosphere, which may lead to prolonged periods of drought, are catalysts for producing accelerated desertification. In southern Africa the northeastward thrust of desertification from the western and central arid and semi-arid areas (the Karoo) has long been recognised, but up til 1970 research failed to demonstrate a clear-cut relationship between the process of desertification and long term rainfall data. The application of sophisticated analytical techniques to regional rainfall data showed, however, that spatial and temporal variations in the Southern African rainfall pattern have a striking degree of organization. The summer rainfall region of the northeastern part of the subcontinent experiences 16–20 year fluctuations, in contrast with 10–12 year fluctuations in the all-season rainfall region along the southern Cape coast. Concentrating on regionally averaged data for the summer rainfall region, the author used Fourier analysis to confirm the persistence of the quasi 20-year fluctuations since 1840. The wet spell of the late 1970s is expected to die out by 1982 and may be followed by a dry spell running from 1983 to 1992. Policy and management practices should be geared to prevent further desertification during this period. 相似文献
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In order to improve the spatial uniformity of rainfall generator to natural rainfall uniformity, according to the rotation of the test platform, a rotary test platform was designed and developed, and the slip-ring was used to solve the problem of signal transmission in the process of the rotation. Besides, the relationship between rotational speed and spatial uniformity of rainfall generator was established. The results of tipping-bucket rain gauge tested in rainfall field and flow type rainfall intensity standard device testing demonstrated that rainfall generator as the rainfall accumulation and rainfall intensity of the test environment was feasible. Results showed that with the increase of the rotate speed, spatial uniformity first increased, and then decreases, and with the decrease of the test area, different speed presented different trends. When the rotational speed was 1 RPM, test area was 1.6 m×1.6 m and 1.2 m×1.2 m, its uniformity of rainfall generator reached maximum which was bigger than 95%; with the increase of the rotate speed, tipping-bucket rain gauge of RA and RI were of good consistency under the RPM 1 and RPM 2 and the RA maximum deviation reached minimum, 0.2 mm; the average of RA under flow type rainfall intensity standard device test consisted well with rotating test platform at speed RPM 1 and 2, which illustrated the rotary testing platform was consistent with the flow type rainfall intensity standard device. It showed that the method to improve the space uniformity of rainfall generator is feasible and it could find the dynamic difference of RA. 相似文献
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Russell S. Crosbie James L. McCallum Glen R. Walker Francis H. S. Chiew 《Hydrogeology Journal》2012,20(2):245-261
In semi-arid areas, episodic recharge can form a significant part of overall recharge, dependant upon infrequent rainfall events. With climate change projections suggesting changes in future rainfall magnitude and intensity, groundwater recharge in semi-arid areas is likely to be affected disproportionately by climate change. This study sought to investigate projected changes in episodic recharge in arid areas of the Murray-Darling Basin, Australia, using three global warming scenarios from 15 different global climate models (GCMs) for a 2030 climate. Two metrics were used to investigate episodic recharge: at the annual scale the coefficient of variation was used, and at the daily scale the proportion of recharge in the highest 1% of daily recharge. The metrics were proportional to each other but were inconclusive as to whether episodic recharge was to increase or decrease in this environment; this is not a surprising result considering the spread in recharge projections from the 45 scenarios. The results showed that the change in the low probability of exceedance rainfall events was a better predictor of the change in total recharge than the change in total rainfall, which has implications for the selection of GCMs used in impact studies and the way GCM results are downscaled. 相似文献
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Hamza Varikoden Hilal Sulthan Ali Al-shukaili C. A. Babu A. A. Samah 《Arabian Journal of Geosciences》2016,9(8):520
The Sultanate of Oman is located in the south-eastern part of the Arabian Peninsula and covers the larger part of the southern coasts of the Arabian Peninsula in both arid and semi-arid environments except for the southern part which is swept by the monsoon affecting the Arabian Sea during the period from June to September. The summer rainfall over Oman shows year-to-year variability, and this is caused by oceanic and atmospheric influences. In the present study, we tried to explore the influence of El Niño on the rainfall over Oman using different data sets. The empirical orthogonal function (EOF) technique employed to the zonal wind at 850 hPa for the 30-year period shows that the second and third modes of EOF are showing high variability over the Oman regions. The corresponding PCs were subjected to FFT analysis, and it showed a peak about 5–6 years. In addition to this, the zonal wind over the Oman regions is correlated with the global zonal wind and found a significant correlation (1 % significant level). It has already been proved that the wind and rainfall during summer monsoon is in phase. Moreover, the spectral analysis of rainfall at Masirah station and the Niño3.4 index show the similar mode of variability indicating a direct relationship. The correlation between rainfall and the Niño3.4 index is also showing a positive significant value, and therefore, it can be concluded that the El Niño in the Pacific favours rainfall over the Oman region. 相似文献
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I. B. Goni 《Hydrogeology Journal》2006,14(5):742-752
The southwestern Chad basin is a semi-arid region with annual rainfall that is generally less than 500 mm and over 2,000 mm of evapotranspiration. Surface water in rivers is seasonal, and therefore groundwater is the perennial source of water supply for domestic and other purposes. Stable isotope has been measured for rainwater, surface water and groundwater samples in this region. The stable isotope data have been used to understand the inter-relationships between the rainwater, surface water, shallow and deep groundwater of this region. This is being used in a qualitative sense to demonstrate present day recharge to the groundwater. Stable isotope in rainwater for the region has an average value of –4‰ δ18O and –20‰ δ2H. Surface water samples from rivers and Lake Chad fall on the evaporation line of this average value. The Upper Zone aquifer water samples show stable isotope signal with a wide range of values indicating the complex character of the aquifer Zone with three distinguishable units. The wide range of values is attributable to waters from individual unit and/or mixture of waters of different units. The Middle and Lower aquifers Zones’ waters show similar stable isotopes values, probably indicating similarity in timing and/or mechanism of recharge. These are palaeowaters probably recharged under a climate that is different from today. The Upper Zone aquifer is presently being recharged as some of its waters show stable isotope compositions similar to those of average rainfall waters of the region. 相似文献
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B. Siva Soumya M. Sekhar J. Riotte Amlan Banerjee Jean-Jacques Braun 《Environmental Earth Sciences》2013,69(7):2311-2335
Hydrogeological and climatic effect on chemical behavior of groundwater along a climatic gradient is studied along a river basin. ‘Semi-arid’ (500–800 mm of mean annual rainfall), ‘sub-humid’ (800–1,200 mm/year) and ‘humid’ (1,200–1,500 mm/year) are the climatic zones chosen along the granito-gneissic plains of Kabini basin in South India for the present analysis. Data on groundwater chemistry is initially checked for its quality using NICB ratio (<±5 %), EC versus TZ+ (~0.85 correlation), EC versus TDS and EC versus TH analysis. Groundwater in the three climatic zones is ‘hard’ to ‘very hard’ in terms of Ca–Mg hardness. Polluted wells are identified (>40 % of pollution) and eliminated for the characterization. Piper’s diagram with mean concentrations indicates the evolution of CaNaHCO3 (semi-arid) from CaHCO3 (humid zone) along the climatic gradient. Carbonates dominate other anions and strong acids exceeded weak acids in the region. Mule Hole SEW, an experimental watershed in sub-humid zone, is characterized initially using hydrogeochemistry and is observed to be a replica of entire sub-humid zone (with 25 wells). Extension of the studies for the entire basin (120 wells) showed a chemical gradient along the climatic gradient with sub-humid zone bridging semi-arid and humid zones. Ca/Na molar ratio varies by more than 100 times from semi-arid to humid zones. Semi-arid zone is more silicaceous than sub-humid while humid zone is more carbonaceous (Ca/Cl ~14). Along the climatic gradient, groundwater is undersaturated (humid), saturated (sub-humid) and slightly supersaturated (semi-arid) with calcite and dolomite. Concentration–depth profiles are in support of the geological stratification i.e., ~18 m of saprolite and ~25 m of fracture rock with parent gneiss beneath. All the wells are classified into four groups based on groundwater fluctuations and further into ‘deep’ and ‘shallow’ based on the depth to groundwater. Higher the fluctuations, larger is its impact on groundwater chemistry. Actual seasonal patterns are identified using ‘recharge–discharge’ concept based on rainfall intensity instead of traditional monsoon–non-monsoon concept. Non-pumped wells have low Na/Cl and Ca/Cl ratios in recharge period than in discharge period (Dilution). Few other wells, which are subjected to pumping, still exhibit dilution chemistry though water level fluctuations are high due to annual recharge. Other wells which do not receive sufficient rainfall and are constantly pumped showed high concentrations in recharge period rather than in discharge period (Anti-dilution). In summary, recharge–discharge concept demarcates the pumped wells from natural deep wells thus, characterizing the basin. 相似文献