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排序方式: 共有119条查询结果,搜索用时 15 毫秒
91.
Eric W. Larsen Alexander K. Fremier Evan H. Girvetz 《Journal of the American Water Resources Association》2006,42(4):1063-1075
ABSTRACT: Flow regulation impacts the ecology of major rivers in various ways, including altering river channel migration patterns. Many current meander migration models employ a constant annual flow or dominant discharge value. To assess how flow regulation alters river function, variable annual flows ‐ based on an empirical relationship between bank erosion rates and cumulative effective stream power ‐ were added into an existing migration model. This enhanced model was used to evaluate the potential geomorphic and ecological consequences of four regulated flow scenarios (i.e., different hydrographs) currently being proposed on the Sacramento River in California. The observed rate of land reworked correlated significantly with observed cumulative effective stream power during seven time increments from 1956 to 1975 (r2= 0.74, p = 0.02). The river was observed to rework 3.0 ha/yr of land (a mean channel migration rate of 7.7 m/yr) with rates ranging from 0.8 ha/yr to 5.1 ha/yr (2.0 to 13.3 m/yr), during the analyzed time periods. Modeled rates of land reworked correlated significantly with observed rates of land reworked for the variable flow model (r2= 0.78, p = 0.009). The meander migration scenario modeling predicted a difference of 1 to 8 percent between the four flow management scenarios and the base scenario. 相似文献
92.
93.
湖北省宜都市岩溶地貌十分发育。在以王家畈乡为主体的面积约200km^2的岩溶地貌区域内.有天街、响水洞瀑布、古婆树、石塔、松乐山森林公园、石林生态、峡谷、天坑、溶洞、大岩屋、富硫泉水、陡崖、石巷、石林、古生物化石出露地等十五类以地质遗迹为主体的旅游景观。园区内55个自然景点组成了柳河景区、绿竹溪景区、毛湖淌景区、石羊河景区、大岩屋景区、潘家湾景区、仙女洞景区、老屋棚景区、松乐山景区、石塔景区、帽子尖景区等11个景区。宜都奥陶纪地质公园是以出露地层奥陶系地层为主体的岩溶地貌区域。建议在开发这些地质、地貌资源时.坚持以保护地质遗迹景观为前提。遵循开发与保护相结合的原则,严格保护自然与文化遗产。保护原有的景观特征和地方特色,维护生态环境的良性循环.防止污染和其它地质灾害.确保可持续发展。 相似文献
94.
南迦巴瓦峰地区自然变异强烈而频繁,地震、泥石流、崩塌与滑坡、雪害、洪水等自然灾害普遍。探讨了自然灾害的特征和规律、灾害的成因及其对社会经济的影响等问题,认为该地区自然灾害具有连锁性、群发性、突发性和频发性;强烈的新构造运动、高山深谷地貌及温热多雨的气候条件等是该地区灾害发生的最主要自然成因。灾害对该区人民生命财产安全、交通运输、山地农业及森林资源等造成严重影响。 相似文献
95.
Large lowland river valleys include a variety of floodplain environments that represent opportunities and constraints for
human activities. This study integrates extensive field observations and geomorphic data with analysis of satellite remote
sensing data to examine spatial relations between land use/land cover (LULC) and floodplain environments in the lower Pánuco
basin of eastern Mexico. The floodplain of the lower Pánuco basin was delineated by combining a digital elevation model with
a satellite image of a large flood event. The LULC was classified by combining a hybrid classification strategy with image
stratification, applied to 15-m-resolution ASTER data. A geomorphic classification of floodplain environments was performed
using a dry-stage image (ASTER data) and a 1993 Landsat image acquired during a large flood event. Accuracy assessment was
based on aerial photographs (1:38,000), global positioning satellite ground-truthing, and a Landsat 7ETM+ image from 2000, which resulted in an overall accuracy of 82.9% and a KHAT of 79.8% for the LULC classification. The geomorphic
classification yielded 83.5% overall accuracy, whereas the KHAT was 81.5%. LULC analysis was performed for the entire floodplain
and individually within four valley segments. The analysis indicates that the study area is primarily utilized for grazing
and farming. Agriculture is primarily associated with coarse-grained (sandy/silty) natural levee and point bar units close
to the river channel, whereas cattle grazing occurs in distal and lower-lying reaches dominated by cohesive fine-grained (clayey)
deposits, such as backswamps. In the Pánuco valley, wetlands and lakes occur within backswamp environments, whereas in the
Moctezuma segments, wetlands and lakes are associated with relict channels. This study reveals considerable variation in LULC
related to spatial differences in floodplain environments and illustrates the importance of considering older anthropogenic
influences on the landscape. The research design should be applicable for other large lowland coastal plain river valleys
where agriculture is a major component of the floodplain landscape. 相似文献
96.
Evaluating the BANCS Streambank Erosion Framework on the Northern Gulf of Mexico Coastal Plain 下载免费PDF全文
Mitchell McMillan Johan Liebens Christopher Metcalf 《Journal of the American Water Resources Association》2017,53(6):1393-1408
The Bank Assessment of Nonpoint source Consequences of Sediment (BANCS) framework allows river scientists to predict annual sediment yield from eroding streambanks within a hydrophysiographic region. BANCS involves field data collection and the calibration of an empirical model incorporating a bank erodibility hazard index (BEHI) and near‐bank shear stress (NBS) estimate. Here we evaluate the applicability of BANCS to the northern Gulf of Mexico coastal plain, a region that has not been previously studied in this context. Erosion rates averaged over two years expressed the highest variability of any existing BANCS study. As a result, four standard BANCS models did not yield statistically significant correlations to measured erosion rates. Modifications to two widely used NBS estimates improved their correlations (r2 = 0.31 and r2 = 0.33), but further grouping of the data by BEHI weakened these correlations. The high variability in measured erosion rates is partly due to the regional hydrologic and climatic characteristics of the Gulf coastal plains, which include large, infrequent precipitation events. Other sources of variability include variations in bank vegetation and the complex hydro‐ and morphodynamics of meandering, sand bed channels. We discuss directions for future research in developing a streambank erosion model for this and similar regions. 相似文献
97.
Michael W. Habberfield Stacey Sloan Blersch Sean J. Bennett Joseph F. Atkinson 《Journal of the American Water Resources Association》2014,50(4):1051-1062
Visual‐based rapid assessment techniques provide an efficient method for characterizing the restoration potential of streams, with many focusing on channel stability and instream habitat features. Few studies, however, have compared these techniques to see if they result in differing restoration priorities. Three rapid assessment techniques were contrasted at three wild trout streams in western New York with different amounts of channel disturbance. Two methods focused only on geomorphic stability, whereas the third addressed physical habitat condition. Habitat assessment scores were not correlated with scores for either geomorphic assessment method and they varied more between channels with different degrees of disturbance. A model based on dynamic equilibrium concepts best explains the variation among the streams and techniques because it accounts for a stream's capacity to maintain ecological integrity despite some inherent instability. Geomorphic indices can serve as effective proxies for biological indices in highly disturbed systems. Yet, this may not be the case in less disturbed systems, where geomorphic indices cannot differentiate channel adjustments that impact biota from those that do not. Dynamically stable streams can include both stable and unstable reaches locally as characterized by geomorphic methods and translating these results into restoration priorities may not be appropriate if interpretations are limited to the reach scale. 相似文献
98.
Dianna M. Hogan S. Taylor Jarnagin J.V. Loperfido Keith Van Ness 《Journal of the American Water Resources Association》2014,50(1):163-178
This collaborative study examined urbanization and impacts on area streams while using the best available sediment and erosion control (S&EC) practices in developing watersheds in Maryland, United States. During conversion of the agricultural and forested watersheds to urban land use, land surface topography was graded and vegetation was removed creating a high potential for sediment generation and release during storm events. The currently best available S&EC facilities were used during the development process to mitigate storm runoff water quality, quantity, and timing before entering area streams. Detailed Geographic Information System (GIS) maps were created to visualize changing land use and S&EC practices, five temporal collections of LiDAR (light detection and ranging) imagery were used to map the changing landscape topography, and streamflow, physical geomorphology, and habitat data were used to assess the ability of the S&EC facilities to protect receiving streams during development. Despite the use of the best available S&EC facilities, receiving streams experienced altered flow, geomorphology, and decreased biotic community health. These impacts on small streams during watershed development affect sediment and nutrient loads to larger downstream aquatic ecosystems such as the Chesapeake Bay. 相似文献
99.
Mathias J. Collins James C. Knox 《Journal of the American Water Resources Association》2003,39(2):487-500
ABSTRACT: Periodic surveys of the upper Mississippi River since 1866 and a discharge record of nearly equal length provided an opportunity to learn more about the magnitudes and rates of geomorphic processes at work in large stream systems. Furthermore, geomorphic and hydrologic adjustments could be evaluated in relation to watershed land use changes, small‐scale climate fluctuations, and considerable modifications to the channel and floodplain during the period of record. The present study uses GIS mapping to quantitatively compare historical changes in mapped land and water phenomena in the upper Mississippi River Pool 10, located along southwest Wisconsin's border. Modest channel widening and decreases in island area throughout the study reach during the last century are detectable. Flood magnitudes and frequencies also have varied during this time, and stages and low flow discharges have increased since the 1940s. The latter hydrologic change appears to be closely associated with the reach's geomorphic adjustments. Results are representative of a valley reach where a major tributary contributes a large sand bedload, forming an alluvial fan of considerable size in the floodplain. 相似文献
100.
Russell J. Anderson Brian P. Bledsoe W. Cully Hession 《Journal of the American Water Resources Association》2004,40(5):1159-1172
ABSTRACT: An extensive group of datasets was analyzed to examine factors affecting widths of streams and rivers. Results indicate that vegetative controls on channel size are scale dependent. In channels with watersheds greater than 10 to 100 km2, widths are narrower in channels with thick woody bank vegetation than in grass lined or nonforested banks. The converse is true in smaller streams apparently due to interactions between woody debris, shading, understory vegetation, rooting characteristics, and channel size. A tree based statistical method (regression tree) is introduced and tested as a tool for identifying thresholds of response and interpreting interactions between variables. The implications of scale dependent controls on channel width are discussed in the context of stable channel design methods and development of regional hydraulic geometry curves. 相似文献