摘要:

ABSTRACT:A hydrologic investigation to determine vertical and seasonal variation of atrazine, alachlor, cyanazine, and nitrate at one location and to relate the variation to ground‐water movement in the Iowa River alluvium was conducted in Iowa County, Iowa, from March 1986 to December 1987. Water samples were collected at discrete intervals through the alluvial sequence from the soil zone to the base of the aquifer. Alachlor, atrazine, and cyanazine were detected most frequently in the soil zone but also were present in the upper part of the alluvial aquifer. Alachlor was detected sporadically, whereas, atrazine, cyanazine, and nitrate were present throughout the year. In the alluvial aquifer, the herbicides generally were not detected during 1986 and were present in detectable concentrations for only a short period of time in the upper 1.6 meters of the aquifer during 1987. Nitrate was present throughout the alluvium and was stratified in the alluvial aquifer. The largest nitrate concentrations were detected in the middle part of the aquifer. Nitrate concentrations were variable only in the upper 2 meters of the aquifer. Vertical movement of herbicides and nitrate in the soil correlated with precipitation and degree of saturation. A clay layer retarded vertical movement of atrazine but not nitrate from the soil layer to the aquifer. Vertical movement could not account for the chemical variation in the alluvial aquife

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04012.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACT:CREAMS was applied to a field‐sized watershed planted to cotton in the Limestone Valley region of northern Alabama. The field was cultivated for three years with conventional tillage (CvT) followed by three years of conservation tillage (CsT). CREAMS is composed of three components: hydrology, erosion, and chemistry. Surface runoff and losses of sediment, N and P were simulated and results were compared with the observed data from the watershed. Curve numbers recommended in the CREAMS user's guide were not adequate for the watershed conditions. The hydrology submodel improved runoff simulation from CvT and CsT when field‐data based curve numbers were used. The erosion submodel demonstrated that CsT reduced sediment loss more than CvT, even though CsT had higher runoff than CvT. The nutrient submodel based on the simulated runoff and sediment underpredicted N loss for both CvT and CsT. This submodel, however, accurately predicted P loss for CvT, but underpredicted for CsT (50 percent lower than the observed). The results of CREAMS simulation generally matched the observed order of magnitude for higher runoff, lower sediment, and higher N and P losses from CsT than from

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04013.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACT:A numerical simulation model was developed to predict the vertical and lateral percolation losses from a ponded agricultural field. The two‐dimensional steady‐state unsaturated/ saturated flow equation was solved using the finite‐difference technique. A constant ponding depth was maintained at the soil surface with different water table conditions in an application of the model for rice fields bordered by bunds. Field experiments were conducted for two different water table depths to collect data on the spatial distribution of volumetric soil‐moisture content for model verification. The measured soil‐moisture content values were found to be in close agreement with those predicted by the model.The sensitivity analysis of the model with selected hydrologic conditions shows that the model is most sensitive to the values of saturated hydraulic conductivity, but relatively less sensitive to water table depth, ponding depth, and evaporation rate from the soil surface. It implies that, in a ponded rice field condition, the lateral and vertical percolation losses are mostly governed by the hydraulic conductivity of the soil. The vertical percolation losses were almost equal to the saturated hydraulic conductivity values and, in most cases, these losses increased with deeper water table depths. The lateral percolation losses also increased with deeper water table depths; however, these losses were relatively small in comparison to the vertical percolation losses. The vertical and lateral percolation losses increased with the increase in ponding depths. The lateral percolation losses through the bund decreased when the evaporation losses increased from the soil surface. The results of this study indicate that the percolation losses from a ponded field may be predicted accurately for a wide range of soil and hydrological conditions when the values of hydraulic conductivity, evaporation rate, depth of ponding, and water table depth are accurat

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04014.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACT:Many approaches are available for operation of a multipurpose reservoir during flood season; one of them is allocation of storage space for flood control. A methodology to determine a reservoir operation policy based on explicit risk consideration is presented. The objective of the formulation is to maximize the reservoir storage at the end of a flood season while ensuring that the risk of an overflow is within acceptable limits. The Dynamic Programming technique has been used to solve the problem. This approach has been applied to develop operation policies for an existing reservoir. The performance of the policy was evaluated through simulation and was found to be satisfactory.

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04015.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACT:We surveyed over 2000 lakes in the State of Massachusetts (1983–1984) to examine the spatial variations in their acid‐base chemistry. Our survey differed from previous surveys by including small lakes and nonpristine urban lakes. For samples collected in October 1983 and 1984, the median acid neutralizing capacity (ANC) was 184 μeq L−1and 5.9 percent were acidic (ANC≤O). Small lakes (<4 ha) were more likely to be acidic than large lakes. Generally, sulfate was the dominant acidifying agent, although organic anions were dominant in some of the lakes in the Cape Cod Region. The ionic composition of the lakes showed strong regional patterns which appear to be related to geology and human population density. An analysis of variance of ANC shows the six regional categories in the state explain 51 percent of the variance, while a combined general linear model of lake drainage type, color, elevation, size, silica, and hydrogen ion deposition could explain only 4.9 percent of the variation in ANC. Calcium rich, high ionic strength lakes were present in the marble bedrock in the west, and relatively dilute lakes dominated by sodium and chloride were found near the coast. Chloride concentrations were also related to population density, suggesting road salt as a likely contributin

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04016.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACT:The ability to predict extreme floods is an important part of the planning process for any water project for which failure will be very costly. The length of a gage record available for use in estimating extreme flows is generally much shorter than the recurrence interval of the desired flows, resulting in estimates having a high degree of uncertainty. Maximum likelihood estimators of the parameters of the three parameter lognormal (3PLN) distribution, which make use of historical data, are presented. A Monte Carlo study of extreme flows estimated from samples drawn from three hypothetical 3PLN populations showed that inclusion of historical flows with the gage record reduced the bias and variance of extreme flow estimates. Asymptotic theory approximations of parameter variances and covariances calculated using the second and mixed partial derivatives of the log likelihood function agreed well with Monte Carlo results. First order approximations of the standard deviations of the extreme flow estimates did not agree with the Monte Carlo results. An alternative method for calculating those standard deviations, the “asymptotic simulation” method, is described. The standard deviations calculated by asymptotic simulation agree well with the Monte Carlo resu

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04017.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACT:This paper presents a study which used a standard, hydraulic computer model to generate detailed design information to support conflict analysis of a water resource use issue. As an extension of previous studies, the conflict analysis in this case included several scenarios for stability analysis ‐ all of which reached the conclusion that compromising, shared access to the water resources available would result in the most benefits to society. This expected equilibrium outcome was found to maximize benefit‐cost estima

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04018.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACT:Records of hourly water temperatures for two streams in the Upper Mississippi River basin were used to find the error between instantaneous measurements of stream water temperatures and true daily averages. The instantaneous summer water temperature measurements were assumed to be collected during daylight hours, and measurement times were selected randomly. The absolute error at the 95 percent confidence level of randomly collected stream water temperatures was less than 0.9°C for a 1 to 5m deep large river, but as large as 3.6°C for a 0.3 to lm deep small stream. Temperature readings of morning samples were usually below daily average values, and afternoon readings were usually above. Daily mean water temperatures were obtained with less than 0.23°C standard deviation from true daily averages if the daily maximum and minimum water temperatures were averaged. Sample results were obtained for the open water (summer) season only, since diurnal water temperature fluctuations in ice covered streams are usually negligib

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04019.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACT:The Fairbanks Water Treatment Plant in Fairbanks, Alaska, processes approximately 3 MGD of drinking water using lime softening. Approximately 0.3 MGD of lime‐sludge from the treatment process is combined with effluent from a nearby power plant and discharged to the Chena River. There is little information available on the impact of water‐treatment sludge discharges, and virtually no information on the impacts of such discharges in polar environments. Concern surrounding the discharge of water treatment sludges have centered on alum‐sludge due to the potential toxic effects of aluminum. Because of the relatively benign composition of lime‐sludge, very little research has been published. However, there is the possibility that discharge of solids will result in sedimentation, accumulation of solids, and subsequent impacts on benthic organisms. This paper reports on the results of a study to determine if lime‐sludge discharge from the water treatment plant is adversely impacting the river environment. The results provide basic information on the important variables of concern in lime‐discharges to rivers.Samples from the discharge of the water treatment plant and combined water treatment plant/power plant effluent were collected weekly over a one‐year period, and in‐stream benthic and water column samples were collected biweekly during the fall and spring. Sediment and water quality data indicate that while significant accumulation of sludge solids is found downstream of the water treatment plant outfall, they are flushed out of the system by spring flows, which are significantly increased by snow melt. This process is most likely repeated on a yearly cycle.Hence, the data suggest that the FMUS water treatment plant's discharge of lime‐sludge is probably not adversely impacting the river. More generally, this may indicate that the natural flow variations and sediment‐laden characteristics of Arctic, glacier‐fed rivers may assimilate large quantities of nonputrescible solids without significant changes in the natural river environment. Further research in this area is required to v

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04020.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

ABSTRACT:As part of a major project to provide the Rhine delta protection from North Sea floods, the Dutch installed sluices at Haringvliet in the late 1960s and converted the Haringvliet‐Hollandsch Diep‐Biesbosch (HHB) estuary into a tidally‐damped, fresh‐water system. Two decades later, the Dutch Rijkswaterstaat commissioned a study of alternative policies for managing the sluices and removing contaminated bottom sediments, including policies which would at least partially restore estuarine conditions to the HHB. This paper describes the public policy analysis comprising that study, focusing on the role played by formal mullicriteria evaluation (MCE), including the Analytic Hierarchy Process. Through the tasks of value‐tree structuring, impact measurement, and criterion prioritization, the MCE influenced the entire structure of the analysis, became an integral part of it, and, despite initial skepticism among the participants about the utility of multicriteria analysis, was subsequently accepted and viewed favorably by the majorit

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1992.tb04021.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY