Human Modification of the Geomorphically Unstable Salt River in Metropolitan Phoenix     

Martin Roberge 《The Professional geographer》2002,54(2):175-189

In‐stream gravel mining, massive bridge piers, and channelization have all contributed to the geomorphic instability of the Lower Salt River channel in Arizona. Dam closure, changing dam operating rules, and the frequent modification of the channel bed have decreased our ability to predict the Salt River hydrology. Engineering practice has adapted to this situation and to a public that is increasingly intolerant of service disruptions by constructing larger bridges and extending levees. Building these larger structures may be counterproductive; future construction should not constrict the channel and should re‐establish a braided river to decrease the energy available to the system.  相似文献   

Water discharge changes of the Changjiang River downstream Datong during dry season     

ZHANG Erfeng  CHEN Xiqing  WANG Xiaoli 《地理学报》2003,13(3):355-362

Based on hydrometric data and extensive investigations on water-extracting projects, this paper presents a preliminary study on water discharge changes between Datong and Xuliujing during dry season. The natural hydrological processes and human factors that influence the water discharge are analyzed with the help of GIS method. The investigations indicate that the water-extracting projects downstream from Datong to Xuliujing had amounted to 64 in number by the end of 2000, with a water-extracting capacity up to 4,626 m3/s averaged in a tidal cycle. The water extraction from the Changjiang River has become the most important factor influencing the water discharge downstream Datong during dry season. The potential magnitude in water discharge changes are estimated based on historical records of water extraction and a water balance model. The computational results were calibrated with the actual data. The future trend in changes of water discharge into the sea during dry season was discussed by taking into consideration of newly built hydro-engineering projects. The water extraction downstream Datong in dry season before 2000 had a great influence on discharges into the sea in the extremely dry year like 1978-1979. It produced a net decrease of more than 490 m3/s in monthly mean discharges from the Changjiang into the sea. It is expected that the water extraction will continually increase in the coming decades, especially in dry years, when the net decrease in monthly mean water discharge will increase to more than 1000 m3/s and will give a far-reaching effect on the changes of water discharge from the Changjiang into the sea.  相似文献   

Floodplain Residents' Preferences for Water Level Management Options in Flood Control Projects in Bangladesh     

Rasid  Harun  Haider  Wolfgang 《Natural Hazards》2003,28(1):101-129

A maximum difference conjoint (MDC) model was part of a questionnaire toassess floodplain residents' preferences for the outcomes of water level managementinside an enclosed embankment system on the left bank of the Dhaleswari River, calledthe Compartmentalization Pilot Project (CPP)-Tangail. The outcomes were described as(a) varied flood depths in the rice field, (b) incidence of flooding on the courtyard andinside homes, (c) changes in floodplain and culture fisheries, and (d) varied conditionsof drainage congestion. Following a standard survey, the respondents from inside andoutside a completed section of the compartment (Cluster 1b) were shown profiles of these flood management outcomes and were asked to indicate for each profile the one most preferred and the one least preferred item. The results of the study indicated that the respondents had a clear preference for preventing flooding of their homes and courtyards and for an ideal water depth of 2 ft in the aman rice fields. At the same time, they also showed a strong concern about malfunctioning of sluices and to a lesser extent about the changes in the fish habitat. The successful application of the MDC as an approach to model tradeoffs among rural residents of Bangladesh shows that a relatively complex quantitative survey method, incorporating choice cards as pictograms, can be applied successfully even in a developing country.  相似文献   

Book Reviews     

《The Professional geographer》1997,49(3):372-389

Aryeetey-Attoh, SamuelGeography of Sub-Saharan Africa Chew, Sing C. and Denemark, Robert A.(eds) The Underdevelopment of Development: Essays in Honor of Andre Gunder Frank Chinn, Jeff and Kaiser, RobertRussians as the New Minority: Ethnicity and Nationalism in the Soviet Successor States Curtis, Sarah and Taket, AnnHealth and Societies: Changing Perspectives Dudley, Nigel; Jeanrenaud, Jean-Paul and Sullivan, FrancisBad Harvest? The Timber Trade and the Degradation of the World's Forests Ellis, Steven and Mellor, AnthonySoils and Environment Gradus, Yehuda and Lithwick, Harvey (eds)Frontiers in Regional Development Green, Milford B. and McNaughton, Rod B. (eds)The Location of Foreign Direct Investment: Geographic and Business Approaches Greenberg, Michael and Schneider, DonaEnvironmentally Devastated Neighborhoods: Perceptions, Policies, and Realities Griffiths, Ieuan Ll.The African Inheritance Harrison, Lynn C. and Husbands, Winston (eds)Practicing Responsible Tourism: International Case Studies in Tourism Planning, Policy, and Development Jensen, John R.Introductory Digital Image Processing: A Remote Sensing Perspective Pacione, MichaelGlasgow: The Socio-Spatial Development of the City Platt, Rutherford H.Land Use and Society: Geography, Law, and Public Policy Rhodes, Martin (ed.)The Regions and the New Europe: Patterns in Core and Periphery Development Salant, Priscilla and Waller, Anita J.Guide to Rural Data Schnell, Izhak; Sofer, Michael and Drori, Israel Arab Industrialization in Israel: Ethnic Entrepreneurship in the Periphery Shelley, Fred M.; Archer, J. Clark; Davidson, Fiona M. and Brunn, Stanley D.Political Geography of the United States Taffe, Edward J.; Gauthier, Howard L. and O'Kelly, Morton E.Geography of Transportation  相似文献   

Small-scale vegetation dynamics in semi-arid steppe in Inner Mongolia     

Wei Zhang  Christina Skarpe 《Journal of Arid Environments》1996,34(4):421-439

Small-scale vegetation dynamics were followed for ecotones and in uniform stands inArtemisia-dominated steppe vegetation under grazing and when recovering from heavy grazing. Species composition was followed annually for 5 years in 1 m²and 0·25 m²plots for (1) presence–absence; (2) density; and (3) biomass.More rapid vegetation dynamics, in terms of change of type of vegetation and distance moved in DCA species space between sampling occasions, were observed in smaller plots and in early seral stages, where species were few and alpha diversity low. Only the plots recently protected from grazing showed a directional vegetation change; those protected for more than 3 years and those under continued grazing showed, at this scale, non-directional dynamics.  相似文献   

我国北方农牧交错带的环境演变   总被引：60，自引：2，他引：60  

张兰生  方修琦  任国玉  索秀芬 《地学前缘》1997,(Z1)

中国北方农牧交错带在１０～８．５ｋａＢ．Ｐ．经历了三次阶段性增暖后进入全新世暖期。８．５～８．０ｋａＢ．Ｐ．和４～３．５ｋａＢ．Ｐ．暖期的开始与结束事件中降水变化落后于温度变化３００～５００ａ；暖期盛期时的年均温较现代高２～３℃，降水多１００ｍｍ左右；暖期中存在多次短期寒冷事件，年均温最冷时较现代低３℃以上。３．５ｋａＢ．Ｐ．以来冷干趋势之上叠加着大致由３００ａ稳定与５００ａ波动构成的约８００ａ的周期性变化。全新世暖期原始农业文化的阶段性发展与暖期内环境波动相对应；暖期结束时发生了由农业向牧业文化转换的事件；暖期以后的冷干期为农牧交错文化时期，农业经济随冷干程度的变化而兴衰  相似文献   

Controlling factors of gullying in the Maracujá Catchment,southeastern Brazil     

L. de A. P. Bacellar  A. L. Coelho Netto  W. A. Lacerda 《地球表面变化过程与地形》2005,30(11):1369-1385

Hundreds of gullies (‘voçorocas’) of huge dimensions (up to 400–500 m long, 150 m wide and 50 m deep) are very common in the small Maracujá Catchment in southeastern Brazil. These erosional features, which occur with an uneven intensity throughout the area, started due to bad soil management practices at the beginning of European settlement, at the end of the 17th century, and nowadays are still evolving, but at a slower rate. As surface soils are usually very resistant to erosion, the outcrop of the more erodible basement saprolites seems to be an essential condition for their beginning. An analysis of well known erosion controlling factors was performed, aiming to explain the beginning and evolution of these gullies and to understand the reasons for their spatial distribution. Data shows that geology and, mainly, geomorphology are the main controlling factors, since gullies tend to be concentrated in basement rock areas with lower relief (domain 2) of Maracujá Catchment, mainly at the fringes of broad and flat interfluves. At the detailed scale (1:10 000), gullies are more common in amphitheatre‐like headwater hollows that frequently represent upper Quaternary gullies (paleogullies), which demonstrate the recurrence of channel erosion. So, gullies occur in areas of thicker saprolites (domain 2), in places with a natural concentration of surface and underground water (hollows). Saprolites of the preserved, non‐eroded hollows are usually pressurized (confined aquifer) due to a thick seal of Quaternary clay layer, in a similar configuration to the ones found in hollows of mass movement (mudflow) sites in southeastern Brazil. Therefore, the erosion of the resistant soils by human activities, such as road cuts and trenches (‘valos’), or their mobilization by mudflow movements, seem to be likely mechanisms of gullying initiation. Afterwards, gullies evolve by a combination of surface and underground processes, such as wash and tunnel erosion and falls and slumps of gully walls. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

A review of paired catchment studies for determining changes in water yield resulting from alterations in vegetation   总被引：21，自引：0，他引：21  

Alice E. Brown  Lu Zhang  Thomas A. McMahon  Andrew W. Western  Robert A. Vertessy   《Journal of Hydrology》2005,310(1-4):28-61

Paired catchment studies have been widely used as a means of determining the magnitude of water yield changes resulting from changes in vegetation. This review focuses on the use of paired catchment studies for determining the changes in water yield at various time scales resulting from permanent changes in vegetation. The review considers long term annual changes, adjustment time scales, the seasonal pattern of flows and changes in both annual and seasonal flow duration curves. The paired catchment studies reported in the literature have been divided into four broad categories: afforestation experiments, deforestation experiments, regrowth experiments and forest conversion experiments. Comparisons between paired catchment results and a mean annual water balance model are presented and show good agreement between the two methodologies. The results highlight the potential underestimation of water yield changes if regrowth experiments are used to predict the likely impact of permanent alterations to a catchment's vegetation. An analysis of annual water yield changes from afforestation, deforestation and regrowth experiments demonstrates that the time taken to reach a new equilibrium under permanent land use change varies considerably. Deforestation experiments reach a new equilibrium more quickly than afforestation experiments. The review of papers reporting seasonal changes in water yield highlights the proportionally larger impact on low flows. Flow duration curve comparison provides a potential means of gaining a greater understanding of the impact of vegetation on the distribution of daily flows.  相似文献   

ASSESSING THE SUITABILITY OF THE EPIC CROP MODEL FOR USE IN THE STUDY OF IMPACTS OF CLIMATE VARIABILITY AND CLIMATE CHANGE IN WEST AFRICA   总被引：1，自引：0，他引：1  

James Adejuwon 《Singapore journal of tropical geography》2005,26(1):44-60

The EPIC (Erosion Productivity Impact Calculator) crop model, developed by scientists of the United States Department of Agriculture (USDA), has been successfully applied to the study of erosion, water pollution, crop growth and production in the US but is yet to be introduced for serious research purposes in other countries or regions. This paper reports on the applicability of the EPIC 8120 crop model for the assessment of the potential impacts of climate variability and climate change on crop productivity in sub‐Saharan West Africa, using Nigeria as the case study. Among the crops whose productivity has been successfully simulated with this model are five of West Africa's staple food crops: maize, millet, sorghum (guinea corn), rice and cassava. Thus, using the model, the sensitivities of maize, sorghum and millet to seasonal rainfall were demonstrated with coefficients of correlation significant at over 98 per cent confidence limits. The validation tests were based on a comparison of the observed and the model‐generated yields of rice and maize. The main problems of validation relate to the multiplicity of crop varieties with contrasting performances under similar field conditions. There are also the difficulties in representing micro‐environments in the model. Thus, some gaps appear between the observed and the simulated yields, arising from data or model deficiencies, or both. Based on the results of the sensitivity and validation tests, the EPIC crop model could be satisfactorily employed in assessing the impacts of and adaptations to climate variability and climate change. Its use for the estimation of production and the assessment of vulnerabilities need to be pursued with further field surveys and field experimentation.  相似文献   

Using raw regional climate model outputs for quantifying climate change impacts on hydrology          下载免费PDF全文

Jie Chen  François P. Brissette  Pan Liu  Jun Xia 《水文研究》2017,31(24):4398-4413

General circulation model outputs are rarely used directly for quantifying climate change impacts on hydrology, due to their coarse resolution and inherent bias. Bias correction methods are usually applied to correct the statistical deviations of climate model outputs from the observed data. However, the use of bias correction methods for impact studies is often disputable, due to the lack of physical basis and the bias nonstationarity of climate model outputs. With the improvement in model resolution and reliability, it is now possible to investigate the direct use of regional climate model (RCM) outputs for impact studies. This study proposes an approach to use RCM simulations directly for quantifying the hydrological impacts of climate change over North America. With this method, a hydrological model (HSAMI) is specifically calibrated using the RCM simulations at the recent past period. The change in hydrological regimes for a future period (2041–2065) over the reference (1971–1995), simulated using bias‐corrected and nonbias‐corrected simulations, is compared using mean flow, spring high flow, and summer–autumn low flow as indicators. Three RCMs driven by three different general circulation models are used to investigate the uncertainty of hydrological simulations associated with the choice of a bias‐corrected or nonbias‐corrected RCM simulation. The results indicate that the uncertainty envelope is generally watershed and indicator dependent. It is difficult to draw a firm conclusion about whether one method is better than the other. In other words, the bias correction method could bring further uncertainty to future hydrological simulations, in addition to uncertainty related to the choice of a bias correction method. This implies that the nonbias‐corrected results should be provided to end users along with the bias‐corrected ones, along with a detailed explanation of the bias correction procedure. This information would be especially helpful to assist end users in making the most informed decisions.  相似文献