摘要:

ABSTRACT:Channel incision is a pervasive problem that threatens infrastructure, destroys arable land, and degrades environmental resources. A program initiated in 1983 is developing technology for rehabilitation of watersheds with erosion and sedimentation problems caused by incision. Demonstration projects are located in 15 watersheds in the hills of northwest Mississippi. Watershed sizes range from 0.89 to 1,590 km2, and measured suspended sediment yields average about 1,100 t km‐2‐yr‐1. Water quality is generally adequate to support aquatic organisms, but physical habitat conditions are poor. Rehabilitation measures, which are selected and laid out using a subjective integration of hydraulic and geotechnical stability analyses, include grade controls, bank protection, and small reservoirs. Aquatic habitat studies indicate that stone‐protected stilling basins below grade‐control weirs and habitats associated with drop pipes and stone spur dikes are assets to erosion‐damaged streams. Additional recovery of habitat resources using modified stone stabilization designs, woody vegetation plantings, and reservoir outlets designed to provide non‐zero minimum flows is under

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03413.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACT:Following major floods in 1990 which resulted in widespread bank erosion in southern British Columbia, four streams typical of the region were evaluated for the effect which riparian vegetation played in reducing erosion. A total of 748 bends in the four stream reaches were assessed by comparing pre‐ and post‐flood aerial photography. Bends without riparian vegetation were found to be nearly five times as likely as vegetated bends to have undergone detectable erosion during the flood events. Major bank erosion was 30 times more prevalent on non‐vegetated bends as on vegetated bends. The likelihood of erosion on semi‐vegetated bends was between that of the vegetated and non‐vegetated categories

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03414.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACT:A fundamental problem in protecting surface drinking water supplies is the identification of sites highly susceptible to soil erosion and other forms of nonpoint source (NPS) pollution. The New York City Department of Environmental Protection is trying to identify erodible sites as part of a program aimed at avoiding costly filtration. New York City's 2,000 square mile watershed system is well suited for analysis with geographic information systems (GIS); an increasingly important tool to determine the spatial distribution of sensitive NPS pollution areas. This study used a GIS to compare three land cover sources for input into the Modified Universal Soil Loss Equation (MUSLE), a model estimating soil loss from rangeland and forests, for a tributary watershed within New York City's water supply system. Sources included both conventional data (aerial photography) and Landsat data (MSS and TM images). Although land cover classifications varied significantly across these sources, location‐specific and aggregate watershed predictions of the MUSLE were very similar. We conclude that using Landsat TM imagery with a hybrid classification algorithm provides a rapid, objective means of developing large area land cover databases for use in the MUSLE, thus presenting an attractive alternative to photo interpretatio

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03415.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTround water drought events were derived by taking a truncation level through the time series of daily ground water depth that are recorded elevation differences between the water table and land surface at a well site. Droughts of various truncation levels at 70, 80, 90, and 95 percent, were obtained, where a 70 percent truncation level means that 70 percent of ground water depth data are less than or equal to the truncated value. The conditional probability that a drought occurring at a certain truncation level will prolong and advance to that of the next higher level was estimated. The regionalization analysis was conducted assuming that conditional probabilities estimated at selected wells are regionalized variables. Contour lines of conditional probabilities for each truncation level were constructed to express their spatial variability in the region. Estimation errors associated with the regionalization were reasonably small.

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03416.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACT:This paper examines the relationship between best‐management practices, institutional needs, and improved water quality within the watersheds of Wisconsin's program for controlling rural nonpoint source pollution. The first section describes the federal requirements for state nonpoint source programs and the legislative and management methods the state of Wisconsin uses to put those requirements into practice. The emphasis of the paper, described in the second section, is the institutional difficulty in evaluating the success of a large, integrated water quality program. Measurements which are investigated include (1) watershed water quality before and after implementation of BMPs; (2) program participation as measured by eligible vs. participating landowners, BMPs considered necessary vs. BMPs implemented, or dollars allocated to the NPS program vs. dollars expended; and (3) institutional goal coordination and management effectiveness. It is found that, despite the size and sophistication of Wisconsin's NPS program, there is little if any improvement in ambient water quality in these watersheds, probably because of a general lack of adequate participation in this voluntary progra

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03417.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACT:Evaporative heat loss is an essential component of any heat budget used for the modeling of lake water temperatures. Seven evaporative heat loss equations were tested in a year‐round, physically‐based temperature and dissolved oxygen model for lakes. Deciding which equation to choose for use in the year‐round model was based on the goodness of fit of the simulated vs. measured surface temperatures, which were taken at a depth of 1 m below the water surface. An equation which includes free and forced convection components and which was previously used for cooling ponds gave the best fit between temperature simulations and measure

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03418.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACT:A streamflow duration curve illustrates the relationship between the frequency and magnitude of streamflow. Flow duration curves have a long history in the field of water‐resource engineering and have been used to solve problems in water‐quality management, hydropower, instream flow methodologies, water‐use planning, flood control, and river and reservoir sedimentation, and for scientific comparisons of streamflow characteristics across watersheds. This paper reviews traditional applications and provides extensions to some new applications, including water allocation, wasteload allocation, river and wetland inundation mapping, and the economic selection of a water‐resource

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03419.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACT:The effectiveness of urban Best Management Practices (BMPs) in achieving the No‐Net‐Increase Policy (NNTP), a policy designed to limit nonpoint nitrogen loading to Long Island Sound (US), is analyzed. A unit loading model is used to simulate annual nitrogen exported from the Norwalk River watershed (Connecticut) under current and future conditions. A probabilistic uncertainty analysis is used to incorporate uncertainty in nitrogen export coefficients and BMP nitrogen removal effectiveness. The inclusion of uncertainty in BMP effectiveness and nitrogen export coefficients implies that additional BMPs, or BMPs with a greater effectiveness in nitrogen removal, will be required to achieve the NNIP. Even though including uncertainty leads to an increase in BMP implementation rates or BMP effectiveness, this type of analysis provides the decision maker with a more realistic assessment of the likelihood that implementing BMPs as a management strategy will be successful. Monte Carlo simulation results indicate that applying BMPs to new urban developments alone will not be sufficient to achieve the NNIP since BMPs are not 100 percent effective in removing the increase in nitrogen caused by urbanization. BMPs must also be applied to selected existing urban areas. BMPs with a nitrogen removal effectiveness of 40–60 percent, probably the highest level of removal that can be expected over an entire watershed, must be applied to at least 75 percent of the existing urban area to achieve the NNIP This high rate of application is not likely to be achieved in urbanized watersheds in the LIS watershed; therefore, additional point source control will be necessary to achieve th

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03420.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACT:Geomorphic processes may partly determine channel geometry. Soil particle uplift during freezing and thawing cycles and bank sloughing during wetting and drying periods were observed. Soil properties and channel dimension were measured to determine the dominant processes controlling channel geometry in eight small (mean area 0.096 km2) drainages in Logan Canyon, Utah. Soil cohesion was low (plasticity index>15) for all but one of the drainages sampled. Basin scale geomorphic variables were examined to determine if they control channel dimension. Bankfull width was highly correlated to channel length and valley length with r2values of 0.85 and 0.84, respectively. A strong canonical correlation (0.64) showed that distance from the watershed divide, bank liquid limit, and bank sand content were effective predictor variables of bankfull width and depth. The interrelations between geomorphic and pedogenic processes were the strongest determinants of ephemeral channel dimension in this study.

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03421.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACT:A critical examination of the techniques used to assess and specify environmental instream flow requirements is provided. The strengths and weaknesses of individual techniques are evaluated on both an absolute and a comparative basis. Particular attention is given to the problem of specifying environmental flow requirements in Australia where the hydrology has distinctly different characteristics to those in countries where most of the models for prediction of instream flow requirements were developed. Broad recommendations as to the suitability and use of the different techniques for different conditions are provided.

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1995.tb03422.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY