A water balance study of the upper White Nile basin flows in the late nineteenth century

Abstract

A water balance model of the Nile is described, working in terms of dry season flows. The main use of the modelling studies was to extend flows back to the start of observations at Aswan in 1869, and hence to estimate the levels of Lake Victoria during the high flow event of the 1870s. New estimates of Lake Victoria levels and outflows for the period 1870–1895 are deduced, extending the length of the observed data for Lake Victoria by some 25%. Crucially, the analysis includes the major flood event of 1878, which historical evidence suggests was the highest since 1860 or earlier. The modelling results are compared with previous estimates and a detailed examination of historical evidence. Some prospects for future levels are considered, taking into account the reconstructed levels of the late nineteenth century.     

An automated routing methodology to enable direct rainfall in high resolution shallow water models

Recent high profile flood events have highlighted the need for hydraulic models capable of simulating pluvial flooding in urban areas. This paper presents a constant velocity rainfall routing scheme that provides this ability within the LISFLOOD‐FP hydraulic modelling code. The scheme operates in place of the shallow water equations within cells where the water depth is below a user‐defined threshold, enabling rainfall‐derived water to be moved from elevated features such as buildings or curbstones without causing instabilities in the solution whilst also yielding a reduction in the overall computational cost of the simulation. Benchmarking against commercial modelling packages using a pluvial and point‐source test case demonstrates that the scheme does not impede the ability of LISFLOOD‐FP to match both predicted depths and velocities of full shallow water models. The stability of the scheme in conditions unsuitable for traditional two‐dimensional hydraulic models is then demonstrated using a pluvial test case over a complex urban digital elevation model containing buildings. Deterministic single‐parameter sensitivity analyses undertaken using this test case show limited sensitivity of predicted water depths to both the chosen routing speed within a physically plausible range and values of the depth threshold parameter below 10 mm. Local instabilities can occur in the solution if the depth threshold is >10 mm, but such values are not required even when simulating extreme rainfall rates. The scheme yields a reduction in model runtime of ~25% due to the reduced number of cells for which the hydrodynamic equations have to be solved. Copyright © 2012 John Wiley & Sons, Ltd.     

Consensus among multiple trophic levels during high- and low-water stands over the last two millennia in a northwest Ontario lake

We investigated the modern distribution of fossil midges within a dimictic lake and explored downcore patterns of inferred lake depths over the last 2000 years from previously published proxies. Modern midge distribution within Gall Lake showed a consistent and predictable pattern related to the lake-depth gradient with recognizable assemblages characteristic of shallow-water, mid-depth and profundal environments. Interpretations of downcore changes in midge assemblages, in conjunction with quantitative lake-depth inferences across a priori defined (based on diatom data) ~ 500-yr wet and dry periods, demonstrated that both invertebrate and algal assemblages exhibited similar timing and nature of ecological responses. Midges were quantified by their relative abundance, concentrations and an index of Chaoborus to chironomids, and all showed the greatest differences between the wet and dry periods. During the low lake-level period of the Medieval Climate Anomaly (MCA: AD 900 to 1400), profundal chironomids declined, shallow-water and mid-depth chironomids increased, chironomid-inferred lake level declined and the Chaoborus-to-chironomid index decreased. The coherence between multiple trophic levels provides strong evidence of lower lake levels in Gall Lake during the MCA.     

Total and labile metals in surface sediments of the tropical river-estuary system of Marabasco (Pacific coast of Mexico): Influence of an iron mine

Marabasco is a tropical river-estuary system comprising the Marabasco river and the Barra de Navidad Lagoon. The river is impacted by the Pe?a Colorada iron mine, which produces 3.5 million tons of pellets per year. Thirteen surface sediment samples were collected in May 2005 (dry season) in order to establish background levels of Al, Cd, Co, Cu, Fe, Ni, Pb, and Zn in the system and to ascertain the potential mobility of metals in the sediments. Analyses were carried out in the fraction finer than 63 microm, and labile metals extracted according the BCR procedure. Certified reference materials were used for validation of methods. Total concentrations of Cd, Co, Cu, Ni, Pb, and Zn were in the range of 0.05-0.34, 6-95, 0.7-31, 9-26, 2-18, and 53-179 mgkg(-1), respectively; Al and Fe ranges of 24-127, and 26-69 mgg(-1) correspondingly. Cadmium was found to be significantly labile in the sediments (20-100%), followed by Co (0-35%), Ni (3-16%) and Zn (0-25%), whereas the labile fraction for Cu, Fe and Pb was almost negligible (<4%). According with the total metal concentrations, background levels and normalised enrichment factors (NEF) of the metals studied, the impact of the Pe?a Colorada iron mine on the Marabasco system is lower than expected when compared with other similar World systems influenced by mining activities.     

应用旅游地理学在中国的进展

应用旅游地理学是地理学变革时期的产物,是适应旅游业的发展需要,地理学与园林、建筑、旅游等学科相互交叉、渗透的结果。应用旅游地理学研究的中心是区域旅游开发。为了完成这一任务,地理工作者应投身旅游实践中去,发挥地理学的优势,联合其他学科,在旅游开发中做出贡献。     

The effect of tides and storms on the sediment transport across a Dutch barrier island

Under natural conditions, barrier islands might grow vertically and migrate onshore under the influence of long‐term sea level rise. Sediment is transported onshore during storm‐induced overwash and inundation. However, on many Dutch Wadden Islands, dune openings are closed off by artificial sand‐drift dikes that prevent the influx of sediment during storms. It has been argued that creating openings in the dune row to allow regular flooding on barrier islands can have a positive effect on the sediment budget, but the dominant hydrodynamic processes and their influence on sediment transport during overwash and inundation are unknown. Here, we present an XBeach model study to investigate how sediment transport during overwash and inundation across the beach of a typical mesotidal Wadden Sea barrier island is influenced by wave, tide and storm surge conditions. Firstly, we validated the model XBeach with field data on waves and currents during island inundation. In general, the XBeach model performed well. Secondly, we studied the long‐term sediment transport across the barrier island. We distinguished six representative inundation classes, ranging from frequently occurring, low‐energy events to infrequent, high‐energy events, and simulated the hydrodynamics and sediment transport during these events. An analysis of the model simulations shows that larger storm events cause larger cross‐shore sediment transport, but the net sediment exchange during a storm levels off or even becomes smaller for the largest inundation classes because it is counteracted by larger mean water levels in the Wadden Sea that oppose or even reverse sediment transport during inundation. When taking into account the frequency of occurrence of storms we conclude that the cumulative effect of relatively mild storms on long‐term cross‐shore sediment transport is much larger than that of the large storm events. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

三峡工程蓄水对洞庭湖水情的影响格局及其作用机制

三峡工程建成投入运行后,汛末蓄水将使坝下河湖水情发生变化,长江中下游秋季来水减少成为常态.为客观分析三峡蓄水对洞庭湖水情的影响分量、空间格局及其作用机制,选取三峡工程典型的蓄水过程,运用长江中游江湖耦合水动力学模型计算了因上游来水变化引起的洞庭湖水情时空变化.结果表明:1)三峡汛末蓄水对洞庭湖水位影响具有明显的"北高南低,东强西弱"的格局,即东洞庭湖最为显著、南洞庭湖东部和西洞庭湖北部次之,南洞庭湖西部和西洞庭湖南部最小.2)洲滩湿地受蓄水影响最明显的主要为东洞庭湖、南洞庭湖和湖泊洪道两侧的条带状洲滩.3)三峡蓄水对洞庭湖水位的影响机制有二:长江干流水位快速消落加速湖泊水体下泄以及削减长江三口分流补给湖泊的水量.     

湖南中强地震活动地区Ⅱ类场地放大效应研究

利用工程场地地震安全性评价工作中大量实际钻孔和土工实验资料,建立了实际工程场地模型,在50年超越概率为63%、10%、2%共3种地震动输入下,采用SHAKE91和ELSSRA两种等效线性化方法,研究了湖南省Ⅱ类场地土层的放大效应.计算结果表明:湖南省50年超越概率10%的场地效应放大因子为1.30,若使用<中国地震动参数区划图(GB18306-2001)>认定的1.25系数,将低估湖南中强地震活动地区的场地放大效应.湖南省50年超越概率63%、10%、2%这3个设定水准的场地效应放大因子满足1.10:1.00:0.95的关系.这些结果有益于为湖南省提供更为合理的抗震设防标准.     

东天山香山铜镍矿区构造特征与成岩成矿

香山铜镍矿床属典型的岩浆型铜镍硫化物矿床，产于东天山东段黄山-镜儿泉铜镍成矿带中，矿床形成主要受岩浆作用和构造作用控制．岩浆作用为矿床的形成提供了物质来源及成矿元素的熔离富集，构造作用为成矿物质提供了上侵通道和容矿空间．矿区断裂构造以韧性剪切带为主，具多级构造组合特点，共划分出4级构造层次，各级构造与成岩成矿有密切关系．I级构造控制基性。超基性岩带的分布；Ⅱ级构造控制基性—超基性岩体群的分布；Ⅲ级构造控制基性—超基性岩体或矿体的形态、产状；Ⅳ级构造控制岩相带或矿体的产出．     

Productivity, trophic levels and size spectra of zooplankton in northern Norwegian shelf regions

Many studies have been conducted in northern Norwegian shelf regions to assess distributions and abundances of zooplankton in the last decade using towed Scanfish-conductivity, temperature and depth sensors (CTD)–optical plankton counter (OPC), and plankton nets. Significant progresses have been made in understanding dominant species, life histories and behavior, and in using size-structured data to identify dominant species in a certain size range. Using these Scanfish–CTD–OPC data, the analysis of zooplankton community size structures, compositions and their relationships with water types is made along the shelf region from Lofoten, North Cape to Varangerfjorden. From the relationships between the water types and zooplankton communities, the transports and exchanges of zooplankton communities between the Norwegian Coastal and Norwegian Atlantic Waters in regions near Malangsgrunnen and Nordvestbanken are examined. The biovolume (biomass) spectra are further analyzed for the productivity, trophic levels and seasonality of communities in these regions, indicating a steeper slope of the biovolume spectrum for a community dominated by herbivorous species in spring and a flatter slope for a community dominated by carnivorous–omnivorous species in winter. The comparison with the zooplankton biovolume spectra obtained in areas west of Antarctic Peninsula is made to examine and understand the differences in the zooplankton biovolume spectra, their trophic dynamics and potential human impacts between different regions.