Evolution of undercut slopes on abandoned incised meanders in the Eastern Highland Rim of Tennessee, USA

Field surveys, location-for-time reasoning, and computer modeling were used to study the evolution of slopes on valley walls of abandoned bedrock meanders on the Eastern Highland Rim, Tennessee. Hillslopes on the undercut slopes of cutoff incised meanders were ordered as to relative age by the height of their meander floors above the modern stream level. The assumption is that the undercut slope is actively eroded by the stream until abandonment of the meander, at which time the slope begins to evolve to a different form. More-advanced stages of evolution occur on walls of higher meanders that were abandoned earlier. The most rapid change in this initial form is the elimination of a free face, which occurs soon after the meander is abandoned. In addition, the hillslopes associated with even the lowest (youngest) cutoff meanders show somewhat gentler overall gradients than the actively undercut slopes. Hillslopes associated with meanders 3 to about 20 m above modern stream level maintain straight segments with angles showing only a slight decrease from the 36–38° associated with the lowest cutoffs; overall angles decrease, however, as the straight segment becomes shorter. The oldest slopes, those on cutoffs 30 m or greater above modern stream level, have developed into convex–concave slopes with maximum slopes of 15°.A hillslope evolution model based on previously published algorithms was used to simulate the transition of actively undercut hillslopes into hillslopes on abandoned meanders. Hillslope modeling is particularly useful in this setting. If the valley incision rate is known, an age can be estimated for the cutoff and hence for the hillslope. Alternatively, if hillslope process rates are known, a model age obtained for the hillslope can be used to estimate an incision rate. Even where both incision rates and hillslope process rates are poorly constrained, as in the present setting, modeling allows assumptions about specific rates to be evaluated by determining their implications for other rates. For example, for three cutoff meanders along one stream, best-fit criteria were used to select process rates for the model. Model ages of hillslopes were then obtained and compared with those calculated from a valley-incision rate measured elsewhere in the same physiographic province. For two of the hillslopes, model ages were found to be much younger than those calculated from the incision rate. In order to make the two ages agree, unreasonably low process rates had to be used in the model, thus implying that the incision rate probably underestimates the actual incision rate in this valley.Experimentation with heights of initial profiles, again using best-fit criteria, suggests that since abandonment of the highest cutoff, the plateau has been downwasting at a rate about one-fourth that of the valley incision rate, a finding in agreement with published rates of chemical denudation in the area.     

Seismic Anisotropy Observations in the Mexicali Valley,Baja California,México

A study of seismic anisotropy was performed using data from earthquakes of the Mexicali Valley. The investigated region encompasses the Cerro Prieto Geothermal Field (CPGF), one of the most important fields in the world. The results showed that at most of our stations the average polarization directions of the fast S waves range from N14°W to N17°E. A N-S polarization direction was obtained for the whole area by averaging the polarization directions from all stations used. In terms of the EDA hypothesis, this average trend agrees with the postulated state of stress for southern California, and with fault plane solutions for events of the Mexicali Valley. Notorious deviations from the N-S global trend were found southeast of the CPGF, with polarization trends between N25°E and N67°E, and in the geothermal field, with polarization directions between N7°W and N14°W. The polarization results for these zones indicated stress conditions that are different from the more regional stress pattern. The delay times that were measured between the fast and slow shear waves reached values of up to 0.6 sec, with a mean value of 0.35 sec. Consistent with our polarization results, the larger delay times (0.2–0.6 sec) were found in the CPGF. Smaller or null values were observed at the periphery of the study area. No temporal trends in the delay times were apparent, as shown by data from the two stations that recorded the larger number of events. Overall, we conclude that the splitting effects of this study result from a shallow anisotropy volume. The splitting results are thus interpreted as caused by the preferred orientation of vertical fluid-filled microcracks aligned in a direction that is parallel to the regional stress field. The stronger splitting effects that were observed in the area of the CPGF were found consistent with the geothermal reservoir that is embedded in the sedimentary cover of the zone, at depths of 1 to 4–5 km from the surface. We thus believe that such marked splitting effects have a direct relation with the reservoir of the CPGF.We are grateful to Miguel Navarro, Tito Valdez, and Manuel Luna for their contribution in the operation of RANM and for processing and cataloguing the strong-motion data. Ignacio Méndez and Francisco Farfán helped us with data from the RESNOM system. The study benefited from funding provided by CICESE and from grants awarded by CONACYT to Luis Munguía (Grants F195T and PCCNCNA-031339).     

Comparative Accuracy in Four Civil War Maps of the Shenandoah Valley: A GIS Analysis*

This study compares the accuracy of four maps available to Union and Confederate officers during the 1862 Shenandoah Valley campaign of the American Civil War. It examines historical maps of the Valley of Virginia by the following cartographers: James W. Abert, Hermann Böÿe and Lewis von Buchholtz, Jedediah Hotchkiss, and Franz Kappner. Both simple and three‐tiered sinuosity measures are derived for reference points along study map representations of the Shenandoah river system. These data are then statistically compared to corresponding sinuosity data from USGS topographic quadrangles to identify the relative accuracies of the historical maps. This article offers evidence to refute the common historical assumption that Hotchkiss provided Maj. Gen. Thomas “Stonewall” Jackson with terrain intelligence that was far superior to that available to his Union opponents. Evidence indicates that maps by Union cartographers as well as the prewar Böÿe‐Buchholtz map were at least as accurate, or superior to, the work of Hotchkiss.     

长波辐射对大气变化的敏感性和在WRF模式中的应用检验

用RRTM长波辐射 (LWR)参数化方案测试了LWR对大气变化的敏感性。结果表明 :高云对向外长波辐射(OLR)、30 0和 5 0 0hPa净LWR通量的减弱作用较中、低云大 ;低云对 85 0hPa和地表净LWR通量的减弱作用较中、高云大。在云层中 ,LWR冷却率受云影响最大 ;在云层下方 ,云对LWR的影响迅速减小 ;而在云层上方 ,冷却率几乎不受云的影响。当水汽含量减少或增加时 ,地表向下LWR受到相应减弱或增强 ,而净LWR则在一定程度上受到相应增强或减弱 ,并且越接近地面 ,受到水汽变化的影响就越大。O3 对LWR的影响相对云和水汽来说是比较小的。文中介绍了在WRF模式中应用RRTM方案预报LWR不同季节的 2个个例 ,给出了应用NCEP/AVN分析资料预报和验证中国范围 2d之内LWR通量的模拟结果。试验表明 ,OLR和 5 0 0hPa净LWR通量与高度形势场有较好的对应关系 ,而地表净LWR很大程度上还受到地形的影响。     

Assessment of downstream trends in channel gradient, total and specific stream power: a GIS approach

Geographic Information Systems (GIS) analyses of Digital Elevation Models (DEMs) coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient, total stream power, and in riverscapes conducive to regime analysis, also specific stream power. For a small, high relief, coastal catchment in SE Australia, good agreement was obtained between channel gradients derived from a 25 m cell-size DEM and field survey equivalents over distances of several kilometres, indicating that channel gradients derived from DEMs can have a reasonable degree of absolute as well as relative accuracy over multi-kilometre reach scales. Assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream. Modelling of downstream trends in channel gradient, total and specific stream power from catchment-wide DEMs has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient, stream power and the form and dynamics of river systems.     

Irrigated agriculture and place‐making in the East Kimberley

This paper explores the way in which lived experiences of farmers in the Ord Valley have intersected with representations of the Ord Valley over time. I contrast the development of Stage 1 of the Ord River Irrigation Scheme in the 1960s with a proposal put forward in the late 1990s for greatly expanding the area of irrigated agriculture as Stage 2 of the scheme. I examine the rhetoric employed in planning documents and public media coverage of the first and proposed second stages of the Ord Irrigation Scheme and explore its connections with social identifications of farmers in the Ord Valley since the 1960s. I then argue the value of this approach for understanding the dynamic relationship between the spatial practices and social identifications of farmers and representations of place and land use in public media and planning processes.     

从清江流域瓦屋场滑坡复活看人类对坡体的利用

居住在山区的人们主要活动空间是斜坡。人们对斜坡利用的有效与否是由人们对斜坡认识充分与否决定的。倘若人们对斜坡认识不足，就可能遭受因斜坡失稳所带来的损失。因此，对这类斜坡的稳定状况的正确认识很有必要。以清江流域典型滑坡——瓦屋场滑坡的复活为例，通过介绍清江流域瓦屋场滑坡人类活动与该滑坡产生的变形情况，根据滑坡体工程地质条件，针对变形原因用萨尔玛法及不平衡推力法进行了稳定分析，同时对复活机制进行分析。在此基础上按照顺应性准则和协调性原则，提出相应的工程治理措施。鉴于该滑坡为该地区的典型滑坡，从灾害学角度说明人类在利用坡体前，对坡体稳定状况认识的重要性并给出人们合理利用该地区自然边坡的建议。     

四川大九寨国际旅游区生态功能保护研究

大九寨国际旅游区位于四川阿坝州东北部，包括九寨沟、松潘、若尔盖和红原四县范围。集中了以九寨沟层湖瀑叠景观、黄龙边石坝彩池景观、高寒湿地景观等为代表的中国西部旅游资源优势。但随着旅游业的快速发展，生态功能受到了较为严重的威胁，部分景观开始退化、消亡。为此，本文对其生态环境现状、生态功能进行剖析，探讨保护目标和对策，做到合理利用和可持续发展。     

The Potential for Rural Heritage Tourism in the Clarence Valley of Northern New South Wales

In the past, heritage tourism has been associated with urban sites but there is now an acceptance of the application of this concept to rural areas. In the Clarence Valley in northern New South Wales there is potential for an extension of agritourism associated with working dairy farms to include safari tours to clusters of dairy heritage sites which are scattered throughout the area. Remnants of the old dairy industry, which began in the Clarence River Valley of New South Wales in the late nineteenth century, are scattered throughout the landscape. Over 300 dairy milking bails remain—ghosts of the former thriving industry when over 2000 dairy farms were operating. Concrete foundations of some creameries built in the 1890s can still be found, and three factory buildings still stand. These relics are disappearing quite rapidly and if the importance of the industry is to be recognised by future generations then it seems that some heritage conservation is overdue. At the same time, in order to survive in a post-deregulated economic environment, the remaining 10 dairy farmers in the Clarence Valley are diversifying their activities, with one form of pluriactivity being agritourism. Currently few of these farmers have entered this field but most of them see its potential to broaden their income base. Associated with agritourism at the farm level, the local government authorities see heritage tourism as a way of increasing employment in the region.