Modeling Stream Channel Characteristics From Drainage‐Enforced DEMs in Puget Sound,Washington, USA1

Abstract: Mapping stream channels and their geomorphic attributes is an important step in many watershed research and management projects. Often insufficient field data exist to map hydromorphologic attributes across entire drainage basins, necessitating the application of hydrologic modeling tools to digital elevation models (DEMs) via a geographic information system (GIS). In this article, we demonstrate methods for deriving synthetic stream networks via GIS across large and diverse basins using drainage‐enforced DEMs, along with techniques for estimating channel widths and gradient on the reach scale. The two‐step drainage enforcement method we used produced synthetic stream networks that displayed a high degree of positional accuracy relative to the input streams. The accuracies of our estimated channel parameters were assessed with field data, and predictions of bankfull width, wetted width and gradient were strongly correlated with measured values (r² = 0.92, r² = 0.95, r² = 0.88, respectively). Classification accuracies of binned channel attributes were also high. Our methodology allows for the relatively rapid mapping of stream channels and associated morphological attributes across large geographic areas. Although initially developed to provide salmon recovery planners with important salmon habitat information, we suggest these methodologies are relevant to a variety of research and management questions.     

Predicting River Floodplain and Lateral Channel Migration for Salmon Habitat Conservation1

Abstract: In this article, we describe a method for predicting floodplain locations and potential lateral channel migration across 82,900 km (491 km² by bankfull area) of streams in the Columbia River basin. Predictions are based on channel confinement, channel slope, bankfull width, and bankfull depth derived from digital elevation and precipitation data. Half of the 367 km² (47,900 km by length) of low‐gradient channels (≤ 4% channel slope) were classified as floodplain channels with a high likelihood of lateral channel migration (182 km², 50%). Classification agreement between modeled and field‐measured floodplain confinement was 85% (κ = 0.46, p < 0.001) with the largest source of error being the misclassification of unconfined channels as confined (55% omission error). Classification agreement between predicted channel migration and lateral migration determined from aerial photographs was 76% (κ = 0.53, p < 0.001) with the largest source of error being the misclassification of laterally migrating channels as non‐migrating (35% omission error). On average, more salmon populations were associated with laterally migrating channels and floodplains than with confined or nonmigrating channels. These data are useful for many river basin planning applications, including identification of land use impacts to floodplain habitats and locations with restoration potential for listed salmonids or other species of concern.     

GIS Methodology for Quantifying Channel Change in Las Vegas,Nevada1

Abstract:  This study applies spatial analyses to examine the consequences of accelerated urban expansion on a hydrologic system over a period of 24 years. Three sets of historical aerial photos are used in a GIS analysis to document the geomorphic history of Las Vegas Wash, which drains the rapidly growing Las Vegas urban area in southern Nevada. New spatial techniques are introduced to make quantitative measurements of the erosion at three specific time intervals in the hydrologic evolution of the channel and floodplain. Unlike other erosion studies that use two different elevation surfaces to assess erosion, this study used a single elevation surface to remove systematic and nonsystemic elevation errors. The spatial analysis quantifies channel changes for discrete time periods, calculates erosion volumes, and provides a foundation to examine how the specific mechanisms related to urban expansion have affected Las Vegas Wash. The erosion calculated over 24 years is the largest documented sediment loss attributed to the effect of rapid urban growth.     

Enhancing Hyrdological Simulation Program – FORTRAN Model Channel Hydraulic Representation1

Abstract: The hydrological simulation program – FORTRAN (HSPF) is a comprehensive watershed model that employs depth‐area‐volume‐flow relationships known as the hydraulic function table (FTABLE) to represent the hydraulic characteristics of stream channel cross‐sections and reservoirs. An accurate FTABLE determination for a stream cross‐section site requires an accurate determination of mean flow depth, mean flow width, roughness coefficient, longitudinal bed slope, and length of stream reach. A method that uses regional regression equations to estimate mean flow depth, mean flow width, and roughness coefficient is presented herein. FTABLES generated by the proposed method (Alternative Method) and FTABLES generated by Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) were compared. As a result, the Alternative Method was judged to be an enhancement over the BASINS method. First, the Alternative Method employs a spatially variable roughness coefficient, whereas BASINS employs an arbitrarily selected spatially uniform roughness coefficient. Second, the Alternative Method uses mean flow width and mean flow depth estimated from regional regression equations whereas BASINS uses mean flow width and depth extracted from the National Hydrography Dataset (NHD). Third, the Alternative Method offers an option to use separate roughness coefficients for the in‐channel and floodplain sections of compound channels. Fourth, the Alternative Method has higher resolution in the sense that area, volume, and flow data are calculated at smaller depth intervals than the BASINS method. To test whether the Alternative Method enhances channel hydraulic representation over the BASINS method, comparisons of observed and simulated streamflow, flow velocity, and suspended sediment were made for four test watersheds. These comparisons revealed that the method used to estimate the FTABLE has little influence on hydrologic calibration, but greatly influences hydraulic and suspended sediment calibration. The hydrologic calibration results showed that observed versus simulated daily streamflow comparisons had Nash‐Sutcliffe efficiencies ranging from 0.50 to 0.61 and monthly comparisons had efficiencies ranging from 0.61 to 0.84. Comparisons of observed and simulated suspended sediments concentrations had model efficiencies ranging from 0.48 to 0.56 for the daily, and 0.28 to 0.70 for the monthly comparisons. The overall results of the hydrological, hydraulic, and suspended sediment concentration comparisons show that the Alternative Method yielded a relatively more accurate FTABLE than the BASINS method. This study concludes that hydraulic calibration enhances suspended sediment simulation performance, but even greater improvement in suspended sediment calibration can be achieved when hydrological simulation performance is improved. Any improvements in hydrological simulation performance are subject to improvements in the temporal and spatial representation of the precipitation data.     

区间盾构隧道联络道施工对隧道结构和周围地层安全性影响的研究

在建成的区间盾构隧道基础上,采用矿山法构筑联络通道是地铁工程施工的难点。由于盾构隧道联络通道的施工需要拆除区间隧道的部分管片,极易导致盾构管片发生过大的变形,使得隧道结构受损。笔者采用3DFLAC数值分析软件对区间盾构隧道之间的联络道施工进行了三维弹塑性仿真分析,分析了联络道施工对盾构隧道变形、盾构管片受力及联络通道地表沉降的影响,数值模拟得出的结论为制定施工辅助安全措施提供了依据。     

MODELING THE LONG TERM IMPACTS OF USING RIGID STRUCTURES IN STREAM CHANNEL RESTORATION1

Abstract: Natural channel designs often incorporate rigid instream structures to protect channel banks, provide grade control, promote flow deflection, or otherwise improve channel stability. The long term impact of rigid structures on natural stream processes is relatively unknown. The objective of this study was to use long term alluvial channel modeling to evaluate the effect of rigid structures on channel processes and assess current and future stream channel stability. The study was conducted on Oliver Run, a small stream in Pennsylvania relocated due to highway construction. Field data were collected for one year along the 107 m reach to characterize the stream and provide model input, calibration, and verification data. FLUVIAL-12 was used to evaluate the long term impacts of rigid structures on natural channel adjustment, overall channel stability, and changing form and processes. Based on a consideration of model limitations and results, it was concluded that the presence of rigid structures reduced channel width-to-depth ratios, minimized bed elevation changes due to long term aggradation and degradation, limited lateral channel migration, and increased the mean bed material particle size throughout the reach. Results also showed how alluvial channel modeling can be used to improve the stream restoration design effort.     

河流横向混合系数的室内试验

本文在实验室矩形平直明渠内,对横向混合系数的公式结构进行了探讨.在室内模型内做大量的示踪试验,获得63组实验数据,在此基础上确定了关于横向混合系数的准数关系式,并对该式作了分析.由室内模型所归纳的公式和结论,可为天然顺直河流横向混合系数的确定提供参考.     

Evaluating the Slope‐Area Method to Accurately Identify Stream Channel Heads in Three Physiographic Regions

Estimation of stream channel heads is an important task since ephemeral channels play a significant role in the transport of sediment and materials to perennial streams. The slope‐area method utilizes digital elevation model (DEM) and related information to develop slope‐area threshold relationships used to estimate the position of channel heads in the watershed. A total of 162 stream channel heads were mapped across the three physiographic regions of Alabama, including the Southwestern Appalachians (51), Piedmont/Ridge and Valley (61), and Coastal Plains (51). Using Geographic Information System and DEM, the local slope and drainage area for each mapped channel head was calculated and region‐specific models were developed and evaluated. Results demonstrated the local slope and drainage area had an inverse and strong correlation in the Piedmont/Ridge and Valley region (r² = 0.71) and the Southwestern Appalachian region (r² = 0.61). Among three physiographic regions, the weakest correlation was observed in the Coastal Plain region (r² = 0.45). By comparing the locations of modeled channel heads to those located in the field, calculated reliability and sensitivity indices indicated model accuracy and reliance were weak to moderate. However, the slope‐area method helped define the upstream boundaries of a more detailed channel network than that derived from the 1:24,000‐scale National Hydrography Dataset, which is commonly used for planning and regulatory purposes.     

长输油气管道河沟道水毁灾害气象风险预警系统的设计与实现

以长输油气管道沿线河沟道水毁灾害调查为基础,详细叙述了管道河沟道水毁灾害的发育及危害特征,拟定了河沟道水毁冲刷深度计算方法;构建半定量评价指标体系,建立长输油气管道河沟道水毁灾害的气象风险预警模型,设计了基于WebGIS的长输油气管道河沟道水毁灾害气象风险预警系统.该风险预警系统基于B-S架构计算机程序,实现了最少人机...     

中国矿山环境保护投融资渠道研究

矿产资源的大规模开发,在带来巨大经济效益的同时也产生了一系列的社会和环境问题。在市场经济条件下,资金问题是制约矿山环境保护的最大瓶颈。长期以来,受我国经济水平和矿山环境保护自身特点的限制,庞大的资金需求和有限的供给之间的矛盾成为制约矿山环境保护的主要障碍。为了改善我国矿山环境保护巨大资金缺口的局面,探索我国矿山环境保护的投融资渠道,就显得十分重要和迫切。本文从我国矿山环境保护的投融资现状入手,在分析我国现行矿山环境保护投融资渠道的基础上,对我国矿山环境保护投融资渠道进行了创新。