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991.
B. J. M. Goes 《Hydrogeology Journal》1999,7(3):294-304
The Hadejia–Nguru Wetlands are annually inundated flood plains in semi-arid northeastern Nigeria. The area has a unique ecosystem
that forms a natural barrier against the encroachment of the Sahara desert. Both the rich wetland vegetation and local farmers
using shallow tube wells depend on a groundwater mound (with a water table less than 6 m below the surface) that is present
in the unconfined aquifer under the flood-plain area. Using well records (1991–97) and a hydrogeologic profile based on piezometers
that were monitored for two years, it is shown that recharge through the annually inundated flood plains is the source of
the groundwater mound. Maintenance of the groundwater-recharge function of the flood plains depends on wet-season releases
from two large upstream dams. On the basis of a water-budget method, the mean (1991–97) wet-season unconfined groundwater
recharge in the flood-plain area between Hadejia and Nguru and in the immediate vicinity (1250 km2) is estimated to be 132 mm (range, 73–197 mm). Outflow from the unconfined flood-plain aquifer to the unconfined upland aquifer
is approximately 10% of the wet-season flood-plain recharge. The unconfined groundwater outflow from the flood-plain area
can provide a significant contribution to the present-day rural water supply in the surrounding uplands, but it does not offer
much potential for additional groundwater abstraction. In addition to outflow to the upland aquifer (∼14 mm), the distribution
of the annually recharged water volume of the shallow flood-plain aquifer is (1) domestic uses (3 mm), (2) small-scale irrigation
(∼15 mm), and (3) evapotranspiration ( 1 100 mm). Along the hydrogeologic profile, the recharge in the upland (i.e., outflow
from the unconfined flood-plain aquifer and possibly diffuse rain-fed recharge) is in balance with the water uses (i.e., domestic
uses, groundwater outflow, and evapotranspiration). The absence of a seasonal water-level trend in the two piezometers in
the upland indicates that no rain-fed recharge occurs through preferential path-way (macropore) flow.
Received, June 1998 / Revised, November 1998, January 1999 / Accepted, January 1999 相似文献
992.
1998年5月29日皮山县发生6.2级地震,震中距皮山县城约39km,震源深度为32km,烈度分布区为北西-南东走向的椭圆形,极震区烈度为Ⅶ度,个别点为Ⅷ度,地震使皮山县县城,9个乡,2个镇,2个农场,墨玉县部分地区遭到不同程度的损失。共计受伤人数为26人,其中重伤为2人,无家可归者人数为5566人,1392户,牲畜死亡4454头。地震造成的直接经济损失达5486.75万元。 相似文献
993.
打桩对周围建筑物振动影响的研究与实例分析 总被引:5,自引:0,他引:5
研究了打桩过程中土层质点振动速度的监测方法,打桩振动对周围建筑物影响程度的评价标准,并结合工程实例探讨了有关因素对检测结果的影响,及施工中应采取的相应减振措施。 相似文献
994.
Geomorphic effects observed in the Barranco (creek) de Arás basin are used to characterize the flood. Sediment features allow to qualify the flood as essentially a water flow. Using the critical section method, the peak flood discharge is estimated to be between 400 and 600 m3 s−1. Similar results were obtained using a paleohydraulic formula based on the size of the largest mobilized clasts. Using the rational method with available rainfall data, the discharge for a recurrence interval of 500 years is estimated to be between 150 and 200 m3 s−1. These results agree with predictions obtained using curves of peak discharge versus basin area based on regional data. Several trenches dug on the fan showed that the size of boulders mobilized by the event is larger that those left by previous floods at the same place. When the estimated peak flood discharge is related to the basin area, values between 20 and 30 m3 s−1 km−2 are obtained, demonstrating that the Barranco de Arás flood was most unusual. 相似文献
995.
Omkar M. Shrestha Achyuta Koirala Jörg Hanisch Klaus Busch Martin Kerntke Stefan Jäger 《GeoJournal》1999,49(2):165-172
An engineering and environmental geological map of the Kathmandu Valley in Nepal has been elaborated within a project of German-Nepalese
cooperation. In the Kathmandu Valley, the major geo-environmental problems arise from haphazard exploitation of geologic resources,
local landslide zones, severe problems of garbage disposal, river flooding and a dramatic river pollution. The map was prepared
by the use of GIS techniques. It contains all basic geological and environmental data, as geotechnical risk zones (landslide-prone
areas or those of poor foundation conditions), areas for preferable extraction of construction material and those not to be
allowed to be exploited, areas of immediate need of reforestation in order to prevent landslide or badland development, groundwater
protection zones, and suitable garbage disposal sites.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
996.
997.
21世纪黄河下游防洪减灾对策 总被引:2,自引:0,他引:2
黄河是受人类活动强烈影响的河流,随着人类活动对流域环境的影响日趋增强,进入黄河下游的水沙条件发生了重大改变,防洪出现了许多新情况、新问题。黄河水资源进一步开发利用,下游牵断流及小水时间逐年延长,黄河将无有效输沙水量,如果来沙不能控制,现行河道的行洪能力和寿命将始终是中国的忧患。小浪底水库2001年投入运用后,对黄河下游又将强烈堆积。21世纪社会经济发展对黄河下游防洪减灾提出了更高要求,根据多年对黄 相似文献
998.
裂隙岩体非稳态渗流场与损伤场耦合分析模型 总被引:15,自引:0,他引:15
本文从流体扩散能量迭加原理,建立了裂隙岩体介质的渗流张量解析表达式,综合应用断裂力学与损伤理论,探讨了复杂应力状态下裂隙岩体的本构关系以及压裂裂纹的起裂准则,建立了裂隙岩体在压剪,拉剪应力状态下损伤演化方程,提出了渗透张量随裂隙损伤发展的关系以及裂隙岩体非稳态渗流场与与损伤场耦合模型。 相似文献
999.
lCOMPOSITIONOFTHE"92.8"FLOODThreerainstormsoccurredfrom7ththrough13,,,August,1992inShaanxiProvince,diStributingfromnorthtosouthinsequence.Therainfallareacoveredtheregionsofintensivesoilerosion,'wheretheaveragerateoferosionis10,000-15',000ton/kmZ'year.Fig.IshowsisohyetsofrainfallintensityinthecatchmentoftheMiddleYellowRiVerdepictingthedistributionoftherainstormsfrom7thto13,,,August,1992(thehydrologicalBureauYRCC,1992).ThecenterofthefirstrainstormwaslocatedattheYikezhaomengPrefec… 相似文献
1000.
Brad R. HALL 《国际泥沙研究》1999,(2)
ILOWERGUADALUPERIVER,SANJOSECALIFORNIATheLowerGuadalupeRiverProjectAreadoesnothavetheabilitytoconveytheflowofthe100-yearfloodevent.LocatedbetweentheSanrranciscoBayandDowntownSanJose,theLowerGuadalupeRiverProjectareaissubjecttomanynaturalandman-inducedagentsandnaturalphysicalprocessesthataffectthehydraulicandsedimenttransportcharacteristicsoftheRiver.Themostsignificantagentsandprocessesincludethelocalgeology,regionalseismicity,tidalprocesses,pastsubsidenceintheregion,risings… 相似文献