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81.
Jeffrey J. Dose Brett B. Roper 《Journal of the American Water Resources Association》1994,30(6):993-1000
ABSTRACT: Recent stream survey data (1989–1993) from 31 stream segments of 21 streams within the upper South Umpqua Watershed Oregon were compared to 1937 stream survey data collected from these same stream segments. Current low-flow wetted stream widths of 22 of the 31 surveyed stream segments were significantly different than in 1937; 19 stream segments were significantly wider while the remaining three stream segments were significantly narrower. In only 1 of 8 tributaries to the South Umpqua River which had headwaters within land designated wilderness area did low-flow stream channel width increase since 1937. Conversely, 13 of the 14 tributaries to the South Umpqua River which originated from lands designated as timber emphasis were significantly wider than in 1937. The observed change in stream width was linearly related to timber harvest (r2= 0.44), road density (r2= 0.45), and the amount of large organic debris remaining within the active stream channel (r2= 0.43). These findings suggest that timber harvest and road construction may have resulted in changes in channel characteristics. These channel changes may also be a factor in the observed decline of three of the four populations of anadromous salmonids within the basin. 相似文献
82.
以上海市污水治理二期工程物理模型试验数据为基础,通过量纲分析的方法得出了污水排放口上升布置多个喷口时污水场宽度与各影响因素之间的关系式,根据污水场宽度可以确定出上升管理论间距,为实际工程中扩散器长度的确定提供理论依据。 相似文献
83.
84.
David R. DeWalle 《Journal of the American Water Resources Association》2010,46(2):323-333
DeWalle, David R., 2010. Modeling Stream Shade: Riparian Buffer Height and Density as Important as Buffer Width. Journal of the American Water Resources Association (JAWRA) 46(2):323-333. DOI: 10.1111/j.1752-1688.2010.00423.x Abstract: A theoretical model was developed to explore impacts of varying buffer zone characteristics on shading of small streams using a path-length form of Beer’s law to represent the transmission of direct beam solar radiation through vegetation. Impacts of varying buffer zone height, width, and radiation extinction coefficients (surrogate for buffer density) on shading were determined for E-W and N-S stream azimuths in infinitely long stream sections at 40°N on the summer solstice. Increases in buffer width produced little additional shading beyond buffer widths of 6-7 m for E-W streams due to shifts in solar beam pathway from the sides to the tops of the buffers. Buffers on the north bank of E-W streams produced 30% of daily shade, while the south-bank buffer produced 70% of total daily shade. For N-S streams an optimum buffer width was less-clearly defined, but a buffer width of about 18-20 m produced about 85-90% of total predicted shade. The model results supported past field studies showing buffer widths of 9-11 m were sufficient for stream temperature control. Regardless of stream azimuth, increases in buffer height and extinction coefficient (buffer density) were found to substantially increase shading up to the maximum tree height and stand density likely encountered in the field. Model results suggest that at least 80% shade on small streams up to 6-m wide can be achieved in mid-latitudes with relatively narrow 12-m wide buffers, regardless of stream azimuth, as long as buffers are tall (≈30 m) and dense (leaf area index ≈6). Although wide buffers may be preferred to provide other benefits, results suggest that increasing buffer widths beyond about 12 m will have a limited effect on stream shade at mid-latitudes and that greater emphasis should be placed on the creation of dense, tall buffers to maximize stream shading. 相似文献
85.
Jessie M. Doyle Ryan A. Hill Scott G. Leibowitz Joseph L. Ebersole 《Journal of the American Water Resources Association》2023,59(5):1099-1114
Channel dimensions (width and depth) at varying flows influence a host of instream ecological processes, as well as habitat and biotic features; they are a major consideration in stream habitat restoration and instream flow assessments. Models of widths and depths are often used to assess climate change vulnerability, develop endangered species recovery plans, and model water quality. However, development and application of such models require specific skillsets and resources. To facilitate acquisition of such estimates, we created a dataset of modeled channel dimensions for perennial stream segments across the conterminous United States. We used random forest models to predict wetted width, thalweg depth, bankfull width, and bankfull depth from several thousand field measurements of the National Rivers and Streams Assessment. Observed channel widths varied from <5 to >2000 m and depths varied from <2 to >125 m. Metrics of watershed area, runoff, slope, land use, and more were used as model predictors. The models had high pseudo R2 values (0.70–0.91) and median absolute errors within ±6% to ±21% of the interquartile range of measured values across 10 stream orders. Predicted channel dimensions can be joined to 1.1 million stream segments of the 1:100 K resolution National Hydrography Dataset Plus (version 2.1). These predictions, combined with a rapidly growing body of nationally available data, will further enhance our ability to study and protect aquatic resources. 相似文献
86.
87.
Kyle E. Juracek 《Journal of the American Water Resources Association》2000,36(3):633-645
ABSTRACT: The stability of the Neosho River channel downstream from John Redmond Dam, in southeast Kansas, was investigated using multiple‐date aerial photographs and stream‐gage information. Bankfull channel width was used as the primary indicator variable to assess pre‐ and post‐dam channel change. Five sin‐mile river reaches and four stream gages were used in the analysis. Results indicated that, aside from some localized channel widening, the overall channel change has been minor with little post‐dam change in bankfull channel width. The lack of a pronounced post‐dam channel change may be attributed to a substantial reduction in the magnitude of the post‐dam annual peak discharges in combination with the resistance to erosion of the bed and bank materials. Also, the channel may have been overwidened by a series of large floods that predated construction of the dam, including one with an estimated 500‐year recurrence interval. 相似文献
88.
Lawrence P. Smith Charles W. Stockton 《Journal of the American Water Resources Association》1981,17(6):939-947
ABSTRACT: The Salt and Verde Rivers of central Arizona provide the water supply for metropolitan Phoenix and a considerable acreage of irrigated agriculture. Rapid urbanization has caused concern over future water supply and aggravated flooding in the already flood-prone Salt River Valley. Tree-ring data were used as a proxy source to extend the annual and seasonal runoff records back to A.D. 1580 and thus to determine whether the period of record for annual discharge adequately represents the long term flow characteristics of the two rivers. Results show that several periods of extended low flow have occurred during the past 400 years, many of which were more severe then any comparable period since 1890. The low flow periods appear to have a recurrence interval of about 22 years. Also the gaged records contain an above average number of high seasonal and annual flows when compared to the entire 400 years. The reconstructions contain important implications for future water supply and flood potentials in the Salt River Valley. 相似文献
89.
通过分析当前常用干滩长度在线监测方法所适应的条件及其存在的问题,提出了一种可用于干滩长度在线监测的新方法——渗流反推法,其基本原理是通过在干滩面上依次布置一定数量的渗压计,以获取实时的浸润线,然后通过建立浸润线的库长-坝高坐标系,再结合库水位,通过解算浸润线与库水位方程组,计算出尾矿库的干滩长度。该方法具有适应性强,监测准确,费用低、操作与维护简单、抗雷电能力强等优点,为干滩长度在线监测新方法的探索提供了参考。 相似文献
90.
为研究煤柱宽度和煤层倾角对深部沿空巷道围岩的变形影响规律,采用数值模拟对沿空巷道煤柱宽度和煤层倾角的变化对围岩的变形影响规律进行分析,结果表明,煤柱宽度的变化对巷道围岩变形的影响十分明显。随着煤层倾角的增大,巷道围岩变形曲线呈现凹槽形状,表现出在煤层倾角中间值的巷道围岩变形值小于煤层小倾角和大倾角对应的巷道围岩变形值。然后,用模型试验验证数值模拟结果。验证结果表明,煤柱宽度和煤层倾角对应的巷道围岩变形较敏感期发生在开采深度600 m和900 m左右,开采深度在600~900 m之间时,巷道围岩变形与煤柱宽度和煤层倾角的大小基本上呈线性增长关系,而当开采深度超过900 m后,应适当加宽护巷煤柱宽度,以确保深部巷道围岩的稳定。 相似文献