摘要:

ABSTRACT:A groundwater quality modeling advisory system has been developed for the U.S. Air Force for use in investigating remediation alternatives for the cleanup of subsurface contamination. The system is capable of accounting for uncertainty, not only in the prediction of solute transport but also in the optimization of the remediation scheme through chance constraints. The system guides users in the selection of appropriate transport models through an algorithm independently tested with machine learning codes. An application to Hill Air Force Base, Utah, is presented for which different pump‐and‐treat strategies are considered: the results are evaluated in terms of the cumulative distribution of the contaminant concentration for each case and the tradeoff relationship between the cost of remediation and the probability that the remediation strategy exceeds an established maximum allowable contaminant concentrat

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03429.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:Accurate water balance calculations are essential for water resource and environmental management decisions, but many of the terms used in the equation are difficult to measure. In this study, a method for measuring rates of evapotranspiration and net seepage from a freshwater marsh in southwest Florida is described. The results are compared to evaporation pan estimates as well as to calculations that balanced all the terms in the hydrologic budget. The measured rates of evapotranspiration showed a. distinct seasonal trend ranging from an average high of 0.24 in/d during July 1992 to a low of 0.06 in/d in January 1993. Evapotranspiration rates were higher than Class A evaporation pan measurements during July and August, indicating transpiration by plants exceeded evaporation by pans. Net ground water seepage flowed out of the marsh except during periods of high water table conditions. When all terms in the hydrologic budget were evaluated, the equation balanced on a yearly basis with an error of 2 percent, on a seasonal basis with errors less than 7 percent, but on a monthly basis errors were as great as 30 percent. Total annual rainfall on the marsh was 45 percent of the total marsh hydrologic input and was approximately equal to the loss by evapotranspiration of 41 percent.

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03430.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:Low‐flow estimates, as determined by probabilistic modeling of observed data sequences, are commonly used to describe certain streamflow characteristics. Unfortunately, however, reliable low‐flow estimates can be difficult to come by, particularly for gaging sites with short record lengths. The shortness of records leads to uncertainties not only in the selection of a distribution for modeling purposes but also in the estimates of the parameters of a chosen model. In flood frequency analysis, the common approach to mitigation of some of these problems is through the regionalization of frequency behavior. The same general approach is applied here to the case of low‐flow estimation, with the general intent of not only improving low‐flow estimates but also illustrating the gains that might be attained in so doing. Data used for this study is that which has been systematically observed at 128 streamflow gaging sites across the State of Alabama. Our conclusions are that the log Pearson Type 3 distribution is a suitable candidate for modeling of Alabama low‐flows, and that the shape parameter of that distribution can be estimated on a regional basis. Low‐flow estimates based on the regional estimator are compared with estimates based on the use of only at‐site estimati

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03431.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:Determination of the boundary conditions for modeling ground water flow is a critical point especially in regional models. Normally the regional models require model areas that are greater than the given area of interest. This work focuses on the prediction of hydraulic heads in regional models using flux boundary conditions. The model uses flux boundary conditions that were estimated using a radial flow analog and Darcy's law. The regional model that is presented uses no parameter identification (inverse estimation) procedures. In the present work, the Houston area was used. The simulation of the hydrological conditions of the Chicot and Evangeline Aquifers that underlie the Houston area were made using the available information about the geological profile in the Houston region and the current information about the existing production wells. The regional model works as a forward problem. The system parameters such as hydraulic conductivity, specific storage, and hydrological stresses were specified, and the model predicts the hydraulic head. Actual data from piezometers operated by the U.S. Geological Survey (USGS) in many places throughout Houston were used as initial conditions. Some piezometric head data were generated using the regional variable theory called kriging to supply head estimates in areas where data were unavailable. The Modular Three Dimensional Finite Difference Groundwater Flow Model developed by the USGS was used to predict the hydraulic heads. The predicted ground water heads are compared to the actual data. The results show that the model performs well for locations where data were available.

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03432.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:The mean annual flow at a damsite during a water project yield study of several decades may differ considerably from the mean flow of several hundred years. The frequency of the most severe droughts of record may be much different than apparent from the historical record as well. Dendrohydrology and the Hurst Phenomenon provide means to evaluate the validity of the study period for project reliability analysis. The most severe hydrologic drought (1928–1934) affecting the watersheds of the Sacramento River and tributaries in Northern California during the 75‐year period 1906–1980 was also the worst drought in 421 years (1560–1980). In contrast, the most severe drought (1945–1951) in the Santa Ynez River watershed in Santa Barbara County, California, during the 62‐year period 1918–1979 was the ninth worst drought in 443 years (1537–1979). Thus, in one case the drought risk indicated by the dendrohydrologic time series would actually be less; in the other, actual risk would be greater than perceived from the historical record. In the absence of a dendrohydrologic prehistoric time series, Hurst Phenomena would have provided clues to this outcome. Hurstian plotting of the accumulated deviation from the mean for long time series facilitates observation of the wet‐dry regime of the examples and identification of characteristics that should be accounted for in water dev

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03433.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:A modeling framework was developed to determine phosphorus loadings to Lake Okeechobee from watersheds located north of the lake. This framework consists of the land‐based model CREAMS‐WT, the in‐stream transport model QUAL2E, and an interface procedure to format the land‐based model output for use by the in‐stream model. QUAL2E hydraulics and water quality routines were modified to account for flow routing and phosphorus retention in both wetlands and stream channels. Phosphorus loadings obtained from previous applications of CREAMS‐WT were used by QUAL2E, and calibration and verification showed that QUAL2E accurately simulated seasonal and annual phosphorus loadings from a watershed. Sensitivity and uncertainty analyses indicated that the accuracy of monthly loadings can be improved by using better estimates of in‐stream phosphorus decay rates, ground water phosphorus concentrations, and runoff phosphorus concentrations as in

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03434.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:For numerical modeling of ground water movement in a real aquifer system, the aquifer is usually divided into hydrogeologically defined zones, each with its own parameter values. The responses of the system, such as head or drawdown, are often available only in some of the zones. The estimated parameters of all the zones are based on the measured response in these limited zones. However, the estimates for some of the zones may be very uncertain, and these zones are therefore not justified by the data. In this paper, an approach is presented to understand which zone may produce uncertain parameter values and should be lumped with its neighbor. This approach is demonstrated using a regional numerical model for pumping test analysis in the Nottinghamshire aquifer, UK. A step‐by‐step process is used in identifying the aquifer zones and estimating their parameters based on the principle of using the smallest possible numbers of zones and parameters for adequate representation of the drawdown response. After the parameters of each zone are estimated, the sensitivity features of these parameters are examined. The results show that the parameters in one zone can be estimated properly by the drawdown in another zone only when there is significant sensitivity. For transmissivity, sensitivity between zones occurs when there is significant flow between them. For storativity, sufficient sensitivity can occur without large flows between the zones, provided that one zone causes significant drawdown in the other. This idea can be extended to the flow model for a large aquifer system. If the aquifer is divided in such a way that aquifer responses are not sensitive to the parameters in some of the zones, the parameters in those zones cannot be estimated properly and should be lumped into their neighboring zones. In this way, a simple but more reasonable model can be bu

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03435.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:Grazing can have a profound impact on infiltration and thus runoff and erosion. The objectives of this study were to quantify the effects of select grazing systems on rainfall and snowmelt induced runoff and sediment yield from sloped areas of the foothills fescue grasslands of Alberta, Canada. The effects of two grazing intensities (heavy and very heavy) for two durations (short duration and continuous throughout the growing season) were compared to an ungrazed control between June 1988 and April 1991. Runoff was measured using 1‐rn2runoff frames and collection bucket systems. Sediment yields were then determined on samples from the collected runoff.Snowmelt was the dominant source of runoff. Snowmelt runoff was higher from the heavily grazed areas than from the very heavily grazed areas, due to the higher standing vegetation which accumulated snow in the former areas. Sediment yields as a result of snowmelt were generally low in all areas. Only a few summer storms caused runoff. Runoff volumes and sediment yields from summer rainstorms were low, due to low rainfall and to generally dry antecedent soil moisture conditions. The greatest risk of summer runoff, and thus sediment yield, appears to occur in Augus

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03436.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:Pesticides were detected in ground‐water samples collected from 20 springs and nine wells in the Ozark Plateaus Province of Arkansas, Kansas, Missouri, and Oklahoma. From April through September 1993, water samples were collected from 50 shallow domestic wells and 50 springs in the Springfield Plateau and Ozark aquifers and analyzed for 47 pesticides and metabolites. Pesticides were detected in 17 water samples from the Springfield Plateau aquifer and 12 water samples from the Ozark aquifer. Fourteen pesticides were detected, with a maximum of four pesticides detected in any one sample. The most commonly detected pesticides were atrazine (14 detections), prometon (11 detections), and tebuthiuron (seven detections). P, P' DDE, a metabolite of DDT, was detected in water samples from three wells and one spring. The remaining pesticides were detected in three or less samples. The occurrence and distribution of pesticides probably are related to the local land use near a sampling site. Pesticide detections were significantly related to aquifer, site type, and discharge of spring

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03437.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT:Ground‐water level decline patterns in parts of Nebraska conform to the circular island concept of Bredehoeftet al. (1982), which indicates how water is derived by wells developed in a circular island. If elongated, the center of the island corresponds to a regional ground‐water divide while the shoreline corresponds to a regional river. In both versions, ground‐water table elevation is a function of recharge and transmissivity. A dynamic equilibrium exists such that the gradient of the water table will convey all recharge to discharge areas. Withdrawals of ground water result initially in mining, with a new equilibrium attained when pumping equals capture. During early development, capture is an important source of water in discharge areas, while mining is more significant in recharge areas. The pattern observed in many areas shows the greatest ground‐water level decline in the vicinity of ground‐water divides and the steepest gradient near regional rivers. A similar pattern has been observed adjacent to the Arkansas River in south‐central Kansas. Similar decline patterns can be modeled for a hypothetical ground‐water basin. This is of major importance to water‐resource managers because it dictates that management programs be applied to the entire hy

ISSN:1093-474X    

DOI:10.1111/j.1752-1688.1996.tb03438.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY