Groundwater recharge estimation in arid hardrock‐alluvium aquifers using combined water‐table fluctuation and groundwater balance approaches

This paper proposes an approach to estimate groundwater recharge using an optimization‐based water‐table fluctuation method combined with a groundwater balance model in an arid hardrock‐alluvium region, located at the Oman–United Arab Emirates border. We introduce an “effective hardrock thickness” term to identify the percentage of the considered hardrock thickness in which effective groundwater flow takes place. The proposed method is based upon a Thiessen polygon zoning approach. The method includes subpolygons to represent specific geologic units and to enhance the confidence of the estimated groundwater recharge. Two linear and 1 nonlinear submodels were developed to evaluate the model components for the calibration (October 1996 to September 2008) and validation (October 2008 to September 2013) periods. Long‐term annual groundwater recharge from rainfall and return flow over the model domain are estimated as 24.62 and 5.71 Mm³, respectively, while the effective groundwater flow circulation is found to occur in the upper 7% of the known hardrock thickness (42 m), confirming conclusions of previous field studies. Considering a total difference in groundwater levels between eastern and western points of the study area of the order of 220 m and a 12‐year monthly calibration period, a weighted root mean squared error in predicted groundwater elevation of 2.75 m is considered quite reasonable for the study area characterized by remarkable geological and hydrogeological diversity. The proposed approach provides an efficient and robust method to estimate groundwater recharge in regions with a complex geological setting in which interaction between fractured and porous media cannot be easily assessed.     

Detrending methods for fluctuation analysis in hydrology: amendments and comparisons of methodologies

Detrending is a key step in the study of the scaling behaviors using Detrended Fluctuation Analysis (DFA) to explore the long‐range correlation of hydrological series. However, the irregular periodicity and various trends within hydrological series as a result of integrated influences of human activities such as construction of water reservoirs and human withdrawal of freshwater and climate changes such as alterations of precipitation changes in both space and time make difficult the selection of detrending methods. In this study, we attempt to address the detrending problem due to the important theoretical and practical merits of detrending in DFA‐based scaling analysis. In this case, with focus on the irregularity of the periodic trends, a modified DFA, varying parameter DFA (VPDFA), and its combination with adaptive detrending algorithm (ADA) are employed to eliminate the influences of irregular cycles on DFA‐based scaling results. The results indicate that, for streamflow series with no more than 20 cycles, VPDFA is recommended; otherwise, the combined method has to be employed. Comparison study indicates that the scaling behavior of the detrended observed streamflow series by average removed method, when compared to those by DFA, VPDFA, and ADA, is the one of the periodic residues around the averaged annual cycle for the entire series rather than that excluding all annual cycles. However, although the result by VPDFA for short observed streamflow record can well correspond to that for numerically simulated series, the scaling behavior obtained by combined method analyzing long record looks strange and is different from that by numerical analysis. We attribute this difference to the complicated hydrological structure and the possible hydrological alternation due to the increasing integrated impacts of human activities and human activities with the extending record. How to include the most of the important factors into the detrending procedure is still a challenging task for further study in the analysis of the scaling behavior of hydrological processes. Copyright © 2012 John Wiley & Sons, Ltd.     

Water uptake by saltcedar (Tamarix ramosissima) in a desert riparian forest: responses to intra‐annual water table fluctuation

There is considerable interest in naturalizing flow regime on managed rivers to slow the spread of saltcedar (Tamarix ramosissima) invasion in southwestern USA or to preserve riparian forests dominated by saltcedar and other species in northwestern China. However, little is known about the responses of established saltcedar in water sources to frequent intra‐annual fluctuation of water table resulting from this new, more dynamic flow regime. This study investigates how saltcedar at a riparian site in the middle reaches of the Heihe River, northwest China, responds in water sources use to intra‐annual water table fluctuations. Stable oxygen isotope was employed to determine accurate depth at which saltcedar obtains its water supply, and soil moisture monitoring was used to determine sources of plant‐available soil water. We found that the primary zone of water uptake by saltcedar were stable at 25–60 cm depth, but the water sources used by saltcedar switched between groundwater and soil moisture with the water table fluctuations. Saltcedar derived its water from groundwater when water table was at depth less than 60 cm but switched to soil moisture at 25–60 cm depth when water table declined. It is supposed that the well‐developed clay layer at 60–80 cm depth constrained lateral roots of saltcedar to the soil layers above 60 cm, while the fine‐textured soils at this site, which were periodically resaturated by rising groundwater before the stored soil moisture had become depleted, provided an important water reservoir for saltcedar when groundwater dropped below the primary zone of fine roots. The root distribution of saltcedar may also be related to local groundwater history. The quick decline in water table in the early 1980s when the riparian saltcedar had established may strand its roots in the shallow unsaturated zone. We suggested that raising the water table periodically instead of maintaining it invariably above the rooting depth could sustain desired facultative phreatophytes while maximizing water deliveries. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling of twin-turbine systems with vertical axis tidal current turbine: Part II—torque fluctuation

We recently showed the advantage of using a numerical system to extract energy from tidal currents by developing a new twin-turbine model (Li and Calisal, 2010a). Encouraged by this result, we decided to use this model to study another important characteristic of the turbine system, torque fluctuation. This effort is summarized in this paper. The torque fluctuation is expected to reduce the fatigue life of tidal current turbines, though potentially it also may deteriorate the power quality of tidal current turbines. In this paper, after reviewing the twin-turbine model, we use it to predict the torque fluctuation of the system with the same configurations as we used to study the power output in Li and Calisal (2010a). Specifically, we investigate the torque fluctuation of twin-turbine systems with various turbine parameters (e.g., relative distance between two turbines and incoming flow angle) and operational condition (e.g., tip speed ratio). The results suggest that the torque of an optimally configured twin-turbine system fluctuates much less than that of the corresponding stand-alone turbine, under the same operating conditions. We then extensively compare the hydrodynamic interaction’s impact on the torque fluctuation and the power output of the system. We conclude that the hydrodynamic interactions pose more constructive impacts on the torque fluctuation than on the power output. The findings indicate that the optimally configured counter-rotating system should be a side-by-side system, and that the optimally configured co-rotating system should have the downstream turbine partially in the wake of the upstream turbine depending on the detailed configuration of the turbines. Furthermore, one must balance the optimal torque fluctuation against the optimal power output.     

密集颗粒流中的速度波动及自扩散特征

 密集颗粒流是颗粒介质中非常重要的一种运动状态,其内部单个粒子的速度波动通常是导致系统出现输运、混合、分离等宏观过程的微观基础,因此,如何对其进行定量描述是颗粒介质研究中一个非常关键的问题。基于所建立的环形剪切颗粒流的离散元模型,首先分析了系统达到剪切稳定状态时不同局部区域内微观粒子速度波动的宏观统计特征;通过引入自扩散系数定量研究了剪切颗粒流内粒子扩散运动过程中的局部化和各向异性特征;最后讨论了局部剪切率、初始体积分数以及粒子间的摩擦系数对系统自扩散系数的影响规律。     

Application of the water table fluctuation method to characterize groundwater recharge in the Pampa plain,Argentina

Abstract

The water table fluctuation (WTF) method is based on accepting that rises of a water table are due to recharge water reaching the groundwater. To apply the method, an estimate of the specific yield of the zone of fluctuation of the groundwater level is required. In this paper, a method for estimation of the specific yield (S_y) is proposed; it consists of a graphical procedure which relates rises in groundwater level to the precipitation from which they originated. The method presents more reliable S_y values as the number of events measured increases. Eighteen years of daily measurements were analysed to obtain a S_y value of 0.09, which was used to apply the WTF method. The obtained recharge values show consistency with values calculated by other authors for the same region.

Editor D. Koutsoyiannis

Citation Varni, M., Comas, R., Weinzettel, P., and Dietrich, S., 2013. Application of water table fluctuation method to characterize the groundwater recharge in the Pampa plain, Argentina. Hydrological Sciences Journal, 58 (7), 1445–1455.     

An integrated water balance model for assessing water scarcity in a data-sparse interfluve in eastern India

Abstract

The objective of this study is to measure the balance of water demand versus water resource availability in an interfluve of West Bengal, India to support water resource planning, particularly of inter-basin transfers. Surface water availability was modelled using the US Soil Conservation Service curve number (SCS-CN) approach, whilst groundwater availability was modelled based on water-level fluctuations and the rainfall infiltration method. Water use was modelled separately for the agricultural, industrial, and domestic sectors using a predominantly normative approach and water use to availability ratios calculated for different administrative areas within the interfluve. Overall, the approach suggested that the interfluve receives 327 × 10⁶ m³ year^-1 of excess water after satisfying these sectoral demands, but that the eastern part of the study area is in deficit. However, a sensitivity analysis carried on the approach to several assumptions in the model suggested changed circumstances would produce surplus/deficit ranging from ?215 × 10⁶ to 435 × 10⁶ m³ year^-1 . The approach could have potential for localised water balance modelling in other Indian catchments.

Editor D. Koutsoyiannis; Associate editor D. Hughes     

湖北气温的3—5年周期振动及其与大气环流低频变化的联系

本文用月平均资料序列，提取湖北气温，北半球５００ｈＰａ高度和北太平洋海博温度的３－５年低频分量，分析研究了三者之间的联系，初步揭示了前期ＳＳＴ对湖北冬季气温影响的过程。     

低纬电离层TEC起伏与相位闪烁的统计特征

穿过电离层不规则体传播后的无线电波,其振幅和相位出现快速随机起伏,即电离层闪烁.为了量化电离层不规则体和相位闪烁的强度,本文提出用TEC起伏δTEC作为特征参量,并用δTEC的标准差构建一种新指数σ_tec.文中证明指数σ_tec与相位闪烁指数完全等效.在电离层强闪烁期间,经常出现信号短暂失锁和周跳,导致TEC值突跳和不连续.为此,本文设计了一种周跳检测与校正的批处理算法,用于消除TEC值突跳.在此基础上,利用位于我国中南部电离层闪烁监测台网2012-2015年的观测数据,考察了GPS信号相位闪烁和不规则体的统计特征.结果表明,我国低纬电离层不规则体和相位闪烁与振幅闪烁随地方时和月份变化的特征类似,一天之中主要出现在日落后至黎明前,一年之中,春季不规则体出现最频繁、秋季次之,呈现春秋不对称性,冬夏季出现很少.此外,我们还比较分析了指数S4与σ_tec的联系,两者之间显著正相关表明,小于第一菲涅尔带尺度的小尺度不规则体和大于第一菲涅尔带尺度的大尺度不规则体一般同时存在.

     

海相碳酸盐岩锶同位素及微量元素特征与海平面变化

以冀北坳陷中元古界高于庄组海相碳酸盐岩地层为研究对象,共采集94件碳酸盐岩样品,分析锶同位素及微量元素的化学特征,并结合高于庄组沉积特征,研究其与海平面变化的响应关系。结果表明,锶同位素、微量元素分析的古水深及海平面变化与岩石地层学分析的结论一致。高于庄初期为发育范围广泛的浅水碳酸盐潮坪,中期区域海平面上升,盆地水域增大,形成较深水碳酸盐台盆相沉积,晚期海平面下降,水体有相对变浅的趋势。87Sr/86Sr的变化与同期海平面的升降呈负相关关系,锶同位素可以作为海平面变化的指示剂,进而可应用于海相碳酸盐岩沉积层序的划分研究。代表陆源碎屑黏土矿物的微量元素K、Ti、V、Rb、Th和Sc对环境变化敏感,具有随沉积水深增大而增高的趋势,可用于海平面变化分析和古环境研究。