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121.
Selection of regional historical rainfall time series as input to urban drainage simulations at ungauged locations 总被引:1,自引:0,他引:1
P.S. Mikkelsen H. Madsen K. Arnbjerg-Nielsen D. Rosbjerg P. Harremoës 《Atmospheric Research》2005,77(1-4):4
It has become established practice during the past 20 years to use high-resolution historical rainfall time series as input to hydrological model packages for detailed simulation of urban drainage systems. However, sufficiently long rain series are rarely available from the exact catchment in question and simulations are hence often based on available rain series from other locations. Extreme rainfall properties of importance to the performance of urban storm drainage systems vary significantly even in regions with only minor physiographic differences. Part of this variation can be explained by regional variations of the mean annual rainfall and the remaining statistical residue can be interpreted as statistical uncertainty.In Denmark, more than 75 high-resolution rain gauges are installed across a total area of 43,000 m. About 40 gauges had sufficiently long records to be included in a comprehensive national investigation where newly developed statistical regionalisation procedures were used to model the regional variation of extreme rainfalls. On this basis, a spreadsheet model was made available for estimation of extreme design rainfalls and the associated uncertainty at any location in the country. Statistics were furthermore computed to classify historical rainfall time series according to the developed regional model, and this makes it possible to assess the uncertainty related with using different historical rain series for simulations at ungauged locations.This research indicates that use of historical point rainfall data at ungauged locations introduces a significant uncertainty that is largely overlooked in today's practice. The engineering recommendation is to select historical rain series based on an evaluation of the local physiographic characteristics (e.g., the mean annual rainfall) and a (pre-defined) desired safety level of the simulations. 相似文献
122.
1980年以来我国城市商业区位研究述评 总被引:2,自引:0,他引:2
总结了1980年以来我国城市商业区位研究的进展。将我国商业区位研究大致划分为3个阶段,即以商业地理学及城市商业区位为主的宏观研究阶段,以城市商业网点区位及商业活动空间结构为主的中观研究阶段,以大型购物中心、百货店、零售店区位等为主的微观研究阶段,分析了各个阶段对应的研究主要内容与研究方法,对近年来城市商业区位研究新领域:信息化背景下商业区位、轨道交通影响下的商业区位、微区位理论、外资零售企业区位、社区商业布局等进行了概述,总结出我国商业区位研究存在的重实证、轻理论等问题,并对未来商业区位的研究提出几点思路。 相似文献
123.
广州城市旅游竞争力研究及其发展战略 总被引:7,自引:0,他引:7
随着经济的发展和产业升级的不断推进,旅游业作为第三产业的重要组成部分受到高度重视,国际旅游市场竞争也日益激烈。基于国际旅游竞争力理论,选取18项旅游竞争力评价指标,采用主成分分析法对我国15个大城市进行了旅游竞争力计算与排序,并将广州与各主要城市进行对比分析。结果表明,在城市旅游综合竞争力方面,广州仅次于北京、上海位于第3位,广州在旅游市场、设施、企业等方面有竞争优势,但在旅游文化、城市环境质量、旅游意识等方面存在明湿差距。据此从营销导向、产品升级、品牌带动、持续发展和区域联动等5个方面对广州旅游发展战略选择进行了详细探讨。 相似文献
124.
Vulnerability of groundwater in Quaternary aquifers to organic contaminants: a case study in Wuhan City,China 总被引:5,自引:0,他引:5
Yanxin Wang Broder J. Merkel Yilian Li Hui Ye Surong Fu Dana Ihm 《Environmental Geology》2007,53(3):479-484
More than 30 organic contaminants were detected in shallow groundwaters at Wuhan, the largest city in central China. Seriously
contaminated groundwaters were from densely populated, industrial and commercial areas. Abnormal concentrations were found
in groundwater from Hankou, downtown Wuhan: trimethylbenzene up to 29 μg/L, tetramethylbenzene up to 866 μg/L, and trichloroethene
up to 9.5 μg/L. Benzene, Toluene, Ethylene and Xylene (BTEX) contamination of groundwater is serious and widespread at Wuhan,
ranging between 0.14 and 25.0 μg/L. Considering the hydrogeological conditions of most Chinese cities, DRAMIC, a modified
version of the widely used DRASTIC model, was proposed by the authors for assessing vulnerability of groundwater to contamination.
The factors D, R, A and I in DRAMIC model are the same as in DRASTIC. The factor topography is ignored. The factor soil media is substituted by a new factor aquifer thickness (M) and the factor hydraulic conductivity of the aquifer by a new factor impact of contaminant (C). The equation for determining the DRAMIC Index is: DRAMIC = 5D
R + 3R
R + 4A
R + 2M
R + 5I
R + 1C
R. The calculated DRAMIC Index can be used to identify areas that are more likely to be susceptible to groundwater contamination
relative to each other. The higher the DRAMIC Index is, the greater the groundwater pollution potential. Applying DRAMIC,
a GIS-based vulnerability map for Wuhan city was prepared. Interestingly, places such as downtown Hankou, where enhanced concentrations
of BTEX have been detected, correspond quite well with those with higher DRAMIC ratings. 相似文献
125.
A study on two closed salt lake basins, Tal Chapar and Parihara in the eastern margin of the Thar Desert, Rajasthan, was carried
out to unravel late Quaternary geomorphic evolution of these saline lakes. Both lakes are elliptical in shape bordered by
stabilised dunes, and are oriented in a NE-SW direction, i.e., in the direction of the prevailing summer monsoon wind. Both
lakes have been formed in the wind-shadow zones of isolated hills of Precambrian quartzite. Our study indicates that the late
Quaternary sediments in the lakes began with the cyclic deposition of laminated fine silt layers (0.5 m thick), rich in organic
matter, alternating with ripple cross-bedded sand layers (each ∼1.5–2 m thick). Sand layers that are moderately sorted are
separated by laminated silt-clay layers with gypsum/calcite and this unit occurs in the upper most 4 m sequence in deeper
sections. The presence of gypsum crystals within the laminated sediments suggests a high concentration of Ca in the inflowing
water.
At Parihara Lake the organic carbon-rich sediments at 95 cm depth was dated to 7,375 + 155/−150 year BP. At Tal Chapar radiocarbon
dates of 7,190 + 155/−150 and 9,903 + 360/−350 was obtained from the sediments rich in organic carbon occurring at a depth
of 1.35 m and 1.80 m, respectively. The study reveals strong hydrologic oscillations during the past ∼14,000 year BP (13,090 + 310/−300 year
BP).
Quaternary geomorphic processes, especially the strong aeolian processes during dry climatic phases, played a major role in
the formation of the lake basins, as well as the fringing linear dunes. Geochemical and mineralogical analyses of the lacustrine
sediments, supported by radiocarbon dates indicate the existence of an ephemeral lake earlier than ∼13,000 year BP as sediments
began to be deposited in a lacustrine environment implying sustained runoff in the catchments. A freshwater lake formed between
9,000 year and 7,000 year BP. The lake dried periodically and this strong fluctuating regime continued until about ∼7,000 year
BP. Mid-Holocene was wet and this was possibly due to higher winter rains A saline lake existed between 6,000 year and 1,300 year
BP and finally present day semi arid conditions set in since 1,200 year BP. Remnants of a habitation site (hearth and charred
bones) on stabilised dune at Devani near Tal Chapar were dated to 240 ± 120 year, while that at Gopalpura was dated to 335 ± 90 year.
These historical sites on stabilised dunes were, according to the local accounts, settlements of people who used the lake
brine for manufacturing salt. 相似文献
126.
Three cores from two connected lakes in Central Ireland (Lough Kinale and Derragh Lough) were investigated using diatom analysis
to establish the Holocene development of the lacustrine system, any local variations within the lakes and any anthropogenic
influences. The study area was situated in a lowland location and the lakes were shallow, unstratified and interconnected.
Litho-and bio-stratigraphical analyses of the lake cores and deposits beneath a mire separating the two lakes showed the changing
spatial configuration of the lake system in the early Holocene and the separation of the initial lake into three basins (cf.
lacustrine cells) and finally into two interlinked lakes. The evolution of the lake system is conceptualised as the development
of distinct lacustrine cells, and its sediments have recorded changes in the physical (geography, depth and sedimentation)
and chemical (water chemistry) properties of the lakes inferred through diatom analyses. The longest sequence, from the early
Holocene, records fluctuating lake levels and these are correlated with geomorphological mapping and surveying of palaeoshorelines.
The diatom assemblages of the upper 2 m of the three cores, covering approximately the last 2000–3000 radiocarbon years show
considerable difference in trophic status and life-form categories. This is related to the location of the cores in the lake
and also the distance from human settlement with particular reference to proximity to crannog (artificial island) construction
and use. The most central core from the deepest part of Lough Kinale has the least representation of the human settlement
and agricultural activity in the catchment and on the fringes of the lake, whereas the core taken from the edge of a crannog
is able to identify when construction and use of the crannog occurred. The local nature of the palaeoecological response to
human activity due to incomplete water mixing has the advantage of allowing the lake sediment cores to be used to determine
spatially discrete settlement patterns. 相似文献
127.
K. W. Keatings I. Hawkes J. A. Holmes R. J. Flower M. J. Leng R. H. Abu-Zied A. R. Lord 《Journal of Paleolimnology》2007,38(2):261-283
The utility of ostracod-based palaeoenvironmental reconstruction was evaluated using instrumental data for Lake Qarun, Egypt.
The euryhaline ostracod Cyprideis torosa was the only species found in the lake’s recent sediment record. This species is known to tolerate salinity levels and water
solute compositions that may prevent colonisation by other species. Oxygen and carbon isotope ratios of ostracod carbonate
from lake sediments covary with changes in instrumental values for lake level and salinity for the period 1890–1974. δ13C-values correlate negatively with lake water salinity (r
2 = 0.87) and δ18O-values correlate negatively with measured lake level changes (r
2 = 0.41). Other ostracod proxy data provide qualitative information on lake level trends. Fossil assemblage data (juvenile/adult
and valve/carapace ratios and valve preservation) provide information on wave energy. Ecophenotypic variation of C. torosa valves provided some useful palaeolimnological information. Sr/Ca and Mg/Ca ratios in ostracods were not found to reflect
water composition, due to the uncoupling of these ratios with salinity in Lake Qarun. Overall, our results highlight the need
to calibrate ostracod proxy data in modern systems prior to their use for palaeoenvironmental reconstruction. 相似文献
128.
梅州城市空间形态演化及其成因分析 总被引:1,自引:0,他引:1
在把握梅州城市近千年的形成与发展历史的基础上,总结梅州城市空间形态的演化特征,剖析其空间形态演化的成因。受河流的阻碍与切割、行政建制的变迁与政府导向、城市规划的引导与控制、城市的职能转变与规模扩张等多因素的作用和影响,梅州城市空间形态呈"块状-星状-纺锤形-圈层状"演化。梅州城市空间形态的嬗变要满足历史文化名城保护的要求,分散组团状空间形态将是梅州城市空间形态的演化方向。 相似文献
129.
The Chilean lake district includes diverse lentic ecosystems along ca. 700 km of the country (36°–43°S), including the “Nahuelbutan lakes”, “Araucanian lakes” and “Chiloe lakes”. This area is recognized as an important “hot spot” of benthic freshwater biodiversity in Southern South America. In Chilean temperate lakes, increased nutrient loads of P and N caused eutrophication, particularly in the Nahuelbutan Lakes. The freshwater Hyriidae mussel Diplodon chilensis (Gray, 1828) which is one of the most abundant species in Chilean temperate lakes, is known to be very susceptible to eutrophication. This species presents a clear reduction in its geographic ranges and is considered to be a threatened species in many Chilean lakes. In this study, we used a correlative approach to determine how eutrophication-driven changes in the food supply and in geographical parameters of different Chilean lakes affected the shell growth rates of D. chilensis. The results obtained from sclerochronological analyses of the mussel shells suggest an association with a group of environmental variables, including geographical types (negative), such as latitude and altitude, and limnological types (positive), especially phosphorous and turbidity. However, the D. chilensis populations under extreme conditions of turbidity in eutrophic and hypertrophic lakes are extinct or nearly so. The high positive correlation of the mean D. chilensis growth rates with orthophosphate (R=0.76; P<0.05), in relation to dissolved inorganic nitrogen, suggests that P is the major limiting factor of the primary productivity in Chilean temperate lakes. We discuss some implications of our results in terms of the conservation of biodiversity in temperate lake ecosystems at different taxonomic levels. 相似文献
130.