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91.
Gary B. Kappesser 《Journal of the American Water Resources Association》2002,38(4):1069-1081
ABSTRACT: Riffles in moderately entrenched stream reaches with gradients of 2 percent to 4 percent that have received excessive sediment from upstream have a distinctly different and higher proportion of smaller mobile particles than riffles in systems that are in dynamic equilibrium. The mobile fraction on the riffle can be estimated by comparing the relative abundance of various particle sizes present on the riffle with the dominant large particles on an adjacent bar. Riffle particles smaller than the dominant large particles on the bar are interpreted as mobile. The mobile percentile of particles on the riffle is termed “Riffle Stability Index” (RSI) and provides a useful estimate of the degree of increased sediment supply to riffles in mountain streams. The RSI addresses situations in which increases in gravel bedload from headwaters activities is depositing material on riffles and filling pools, and it reflects qualitative differences between reference and managed watersheds. The RSI correlates well with other measures of stream channel physical condition, such as V and the results of fish habitat surveys. Thus, it can be used as an indicator of stream reach and watershed condition and also of aquatic habitat quality. 相似文献
92.
Robert G. Traver Arthur C. Miller 《Journal of the American Water Resources Association》1993,29(5):767-776
ABSTRACT: This paper confirms the use of interpolated data to refine water surface profiles. Sources of error within these computations are due to truncation error, inaccuracies in geometric data, and improper modeling. Confirmation includes the development of an equation that models the effect of data measurement error on the computed water surface profile. A review of interpolation procedures includes a proposed method based upon geometric properties. 相似文献
93.
方至 《中国环境管理干部学院学报》1999,(3)
本文分析了洞庭湖流域生态环境破坏对洪涝造成的影响,指出流域生态环境受到破坏主要是人类违背自然规律、破坏森林植被、盲目围湖造田、生产及建设性破坏河道及湖滩所致。文章还就根治洞庭水患的关键性措施——搞好生态恢复,提出了几点意见。 相似文献
94.
95.
Modeling the Suitability of Potential Wetland Mitigation Sites with a Geographic Information System 总被引:1,自引:0,他引:1
Wetland mitigation is frequently required to compensate for unavoidable impacts to wetlands. Site conditions and landscape context are critical factors influencing the functions that created wetlands perform. We developed a spatial model and used a geographic information system (GIS) to identify suitable locations for wetland mitigation sites. The model used six variables to characterize site conditions: hydrology, soils, historic condition, vegetation cover, adjacent vegetation, and land use. For each variable, a set of suitability scores was developed that indicated the wetland establishment potential for different variable states. Composite suitability scores for individual points on the landscape were determined from the weighted geometric mean of suitability scores for each variable at each point. These composite scores were grouped into five classes and mapped as a wetland mitigation suitability surface with a GIS. Sites with high suitability scores were further evaluated using information on the feasibility of site modification and project cost. This modeling approach could be adapted by planners for use in identifying the suitability of locations as wetland mitigation sites at any site or region. 相似文献
96.
Resource managers require objective methodologies to optimize decisions related to forest road deactivation and other aspects of road management, especially in steep terrain, where road-related slope failures inflict extensive environmental damage. Decision analysis represents a systematic framework that clearly identifies real options and critical decision points. This framework links current decisions with expected future outcomes and provides advantages such as a common currency to systematically explore the liability consequences of limited budget expenditures to road deactivation and other road-related activities. Furthermore, the decision framework prevents the analysis from becoming hopelessly entangled by the vast number of possibilities generated by the alternative occurrences, magnitudes, and consequences of landslide/debris flow events and provides the information required for the first step of an adaptive management process. Here, a structured analysis of potential environmental risks for a road deactivation project in coastal British Columbia, Canada is presented. The application of decision analysis generates a ranking of the expected benefits of proposed deactivation activities on various road sections. The ranking distinguishes between road sections that offer high expected benefit from those that offer moderate to low expected benefit. Seventeen of 171, 100–m road segments accounted for 18% of the cumulative cost and 98% of the cumulative expected net benefits from road deactivation. Furthermore, the cost of deactivating a section of road is related to the expected benefit from such deactivation, thus providing the basis for more effective resource allocation and budgeting decisions. 相似文献
97.
Vellidis G Smith MC Leibowitz SG Ainslie WB Pruitt BA 《Environmental management》2003,31(2):0301-0312
In a climate of limited resources, it is often necessary to prioritize restoration efforts geographically. The synoptic approach
is an ecologically based tool for geographic prioritization of wetland protection and restoration efforts. The approach was
specifically designed to incorporate best professional judgment in cases where information and resources are otherwise limited.
Synoptic assessments calculate indices for functional criteria in subunits (watersheds, counties, etc.) of a region and then
rank the subunits. Ranks can be visualized in region-scale maps which enable managers to identify areas where efforts optimize
functional performance on a regional scale. In this paper, we develop a conceptual model for prioritizing watersheds whose
wetlands can be restored to reduce total sediment yield at the watershed outlet. The conceptual model is designed to rank
watersheds but not individual wetlands within a watershed. The synoptic approach is valid for applying the sediment yield
reduction model because there is high demand for prioritizing disturbed wetlands for restoration, but there is limited, quantitative,
accurate information available with which to make decisions. Furthermore, the cost of creating a comprehensive database is
prohibitively high. Finally, because the model will be used for planning purposes, and, specifically, for prioritizing based
on multiple decisions rather than optimizing a single decision, the consequence of prioritization errors is low. Model results
cannot be treated as scientific findings. The conclusions of an assessment are based on judgement, but this judgement is guided
by scientific principles and a general understanding of relevant ecological processes. The conceptual model was developed
as the first step towards prioritizing of wetland restoration for sediment yield reduction in US EPA Region 4. 相似文献
98.
Human impacts on the stream-groundwater exchange zone 总被引:13,自引:0,他引:13
Hancock PJ 《Environmental management》2002,29(6):763-781
Active exchanges of water and dissolved material between the stream and groundwater in many porous sand- and gravel-bed rivers
create a dynamic ecotone called the hyporheic zone. Because it lies between two heavily exploited freshwater resources—rivers
and groundwater—the hyporheic zone is vulnerable to impacts coming to it through both of these habitats. This review focuses
on the direct and indirect effects of human activity on ecosystem functions of the hyporheic zone. River regulation, mining,
agriculture, urban, and industrial activities all have the potential to impair interstitial bacterial and invertebrate biota
and disrupt the hydrological connections between the hyporheic zone and stream, groundwater, riparian, and floodplain ecosystems.
Until recently, our scientific ignorance of hyporheic processes has perhaps excused the inclusion of this ecotone in river
management policy. However, this no longer is the case as we become increasingly aware of the central role that the hyporheic
zone plays in the maintenance of water quality and as a habitat and refuge for fauna. To fully understand the impacts of human
activity on the hyporheic zone, river managers need to work with scientists to conduct long-term studies over large stretches
of river. River rehabilitation and protection strategies need to prevent the degradation of linkages between the hyporheic
zone and surrounding habitats while ensuring that it remains isolated from toxicants. Strategies that prevent anthropogenic
restriction of exchanges may include the periodic release of environmental flows to flush silt and reoxygenate sediments,
maintenance of riparian buffers, effective land use practices, and suitable groundwater and surface water extraction policies. 相似文献
99.
Graf WL 《Environmental management》2000,25(3):321-335
/ Data from historical aerial photographs analyzed with a GIS show that river channel change on the Salt River in the Phoenix metropolitan area of central Arizona has been driven by large-scale regional flood events and local human activities. Mapping of functional surfaces such as low-flow channels, high-flow channels, islands, bars attached to channel banks, and engineered surfaces shows that during the period from 1935 to 1997, the relative areal coverage of these surfaces has changed. Flood events have caused general changes in sinuosity of the low-flow channel, but islands have remained remarkably consistent in location and size, while channel-side bars have waxed and waned. The most important determinant of local channel form and process is sand and gravel mining, which in some reaches occupies more than 70% of the active channel area. The general location of mining is closely related to the location of the moving urban fringe, which serves as a market for sand and gravel during construction. Quantitative spatial analysis of imagery supplemented by field mapping shows that for each location within the general channel area, it is possible to specify a probability of encountering a low-flow channel or other fluvial features. Maps showing the distribution of these probabilities of occurrence reveal the most probable location and configuration of the channel as it occurred in the past. Some reaches have the low-flow channel located persistently within a limited area as a result of bedrock or sinuosity controls, but other reaches dominated by flow separation or shallow gradient have almost no persistence in channel location from one flood to another. 相似文献
100.