摘要:

The impact of irrigated agriculture on regional economies is a subject of continuing interest and debate. A cross‐sectional analysis of 1978–1980 U.S. Census data for 104 counties in the northern High Plains is formulated. A recursive system of equations is estimated and used to derive multipliers of irrigated acreage on employment. Effects of irrigation on local employment are statistically very significant but not substantively large in the context of a developed econ

ISSN:0043-1397    

DOI:10.1029/WR023i009p01711

年代:1987

数据来源: WILEY

摘要:

For regional aquifer modeling it is often necessary to produce maps of the distribution of the transmissivity in the aquifer, for example, as initial input for the calibration phase of the model, either by automatic or by trial and error procedures. Such estimations must be based on all possible information available in the field; in many instances, direct transmissivity measurements from pumping tests are scarce, whereas indirect estimations based on specific capacity data are more numerous. It is, however, possible to use jointly both types of data when a geostatistical estimation technique is used. Four such methods will be compared here: (1) kriging combined with linear regression, (2) cokriging, (3) kriging with an external drift, and (4) kriging with a guess field. This comparison is made both on a set of real field data and on a theoretical case, where the “true” solution is kn

ISSN:0043-1397    

DOI:10.1029/WR023i009p01717

年代:1987

数据来源: WILEY

摘要:

We develop a stochastic model for the transport of stored sediment down a river channel. The model is based on probabilities of transition of particles among four different sediment storage reservoirs, called active (often mobilized), semiactive, inactive, and stable (hardly ever mobilized). The probabilities are derived from computed sediment residence times. Two aspects of sediment storage are investigated: flushing times of sediment out of a storage reservoir and changes in the quantity of sediment stored in different reservoirs due to seasonal sediment transport into, and out of, a reach. We apply the model to Redwood Creek, a gravel bed river in northern California. Although the Redwood Creek data set is incomplete, the application serves as an example of the sorts of analyses that can be done with the method. The application also provides insights into the sediment storage process. Sediment flushing times are highly dependent on the degree of interaction of the stable reservoir with the more mobile sediment reservoirs. The most infrequent and highest intensity storm events, which mobilize the stable reservoir, are responsible for the long‐term shifts in sediment storage. Turnover times of channel sediment in all but the stable reservoir are on the order of 750 years, suggesting this is all the time needed for thorough interchange between these sediment compartments and cycling of most sediment particles from the initial reservoir to the ocean. Finally, the Markov model has adequately characterized sediment storage changes in Redwood Creek for 1947–1982, especially for the active reservoir. The model replicates field observation of the passage of a slug of sediment through the active reservoir of the middle reach of Redwood Creek in the 18 years following a major storm in 1964 that introduced large quantities of landslide debris to the chan

ISSN:0043-1397    

DOI:10.1029/WR023i009p01738

年代:1987

数据来源: WILEY

摘要:

Flows in the unregulated Great Lakes connecting channels, the St. Clair and Detroit Rivers, are normally determined using mathematical flow models with calibration based on periodic discharge measurements taken during the open‐water seasons. Consequently, the calculated flows normally exhibit good accuracy during ice‐free periods, but may contain large errors during winter months with extensive ice cover. The St. Clair River is particularly prone to large ice jams because of practically unlimited ice flow supply provided by Lake Huron and an extensive river delta that retards the passage of these ice flows. This study describes the experimental results of continuous flow measurements using electro magnetic (EM) current meters and an acoustic Doppler current profiler (ADCP) meter during the 1983–1985 period. A record ice jam in the St. Clair River occurred in April 1984 and provided an excellent opportunity for testing the current meter program. Verification of current meter results was provided by flows transferred from the Detroit River, which was ice‐free and permitted accurate flow simulation. The current meter flow measurement program illustrated high consistency of exponential (logarithmic) vertical distribution of velocities. Results indicate that accurate estimates of mean river flows can be obtained with a single well‐placed current meter. However, the EM current meters are direct contact single‐point sensors that are affected by frazil ice during winter and weed effects during most of the year. The ADCP meter is a remote sensor of velocities in the overhead water column and is not affected by the frazil ice and we

ISSN:0043-1397    

DOI:10.1029/WR023i009p01751

年代:1987

数据来源: WILEY

摘要:

Seventy lakes in the Mt. Zirkel Wilderness Area, Colorado, were sampled for alkalinity, and 20 of these lakes were sampled for major anions. Analysis of the data indicates that most of the lakes are extremely sensitive to acidification; about half of the lakes have alkalinities less than 100 μeq/L. A linear regression of alkalinity against lake altitude accounts for 55% of the variance in alkalinity among the lakes, whereas a regression of alkalinity against dominant geologic unit (exclusive of altitude) accounts for 63% of the alkalinity variance. A conceptual model of lake acidification allows estimation of the quantity of acidification that may have occurred. Acidity associated with strong acid anions probably neutralized no more than 9 μeq/L of alkalinity. This estimate is much smaller than a previous estimate for nearby Colorado lake

ISSN:0043-1397    

DOI:10.1029/WR023i009p01757

年代:1987

数据来源: WILEY

摘要:

Local pressure variations of the order of 100–1000 N/m2can be observed between the upstream and downstream faces of the typically triangular‐shaped dunelike sediment structures that form at the sediment‐water interface of rivers. Laboratory experiments were conducted examining the influence of this localized pressure variation on contaminant transport processes within the sediment. Numerical modeling of the in‐bed flow via boundary element methods was also undertaken in order to predict convective transport under typical field conditions. The laboratory experiments and numerical simulation of the in‐bed flow in several rivers verified that the pressure distribution observed on the sediment surface and the resulting interstitial fluid convection can control transport of chemically inert, nonsorbed contaminants in stable sediments. In‐bed Peclet numbers were of the order of 100–1000, indicating the negligible influence of diffusion under the condit

ISSN:0043-1397    

DOI:10.1029/WR023i009p01763

年代:1987

数据来源: WILEY

摘要:

Evaporation from a saline water body is less than that from a freshwater body because of two factors: a decrease in saturation vapor pressure and a partially compensating increase in water surface temperature. These factors are quantified by analyzing field data for eight evaporation pans containing solutions with different salinities and ionic compositions (extending the analysis of Salhotra et al. (1985)). A large saline lake (Dead Sea) is also analyzed using a one‐dimensional numerical model with coupled heat, salt, water, and mechanical energy balances. Further, the use of experiments involving evaporation pans, to study the effect of salinity on lake evaporation, is discussed in light of the fact that the two water bodies have different wind speed functions and hence different temperature feedback effects. Finally, data on the direct measurement of the saturation vapor pressure from mixtures of Mediterranean and Dead Sea waters are presented and compared with results from the analyses of the evaporation pan dat

ISSN:0043-1397    

DOI:10.1029/WR023i009p01769

年代:1987

数据来源: WILEY

摘要:

A method for determining the validity of the Local Equilibrium Assumption (LEA) for multicomponent contamination models is presented. The LEA may be justified only when interaction rate coefficients are large enough to force solutions of kinetic models to be indistinguishable from their pointwise equilibrium counterparts. When rate constants are not sufficiently large, LEA models can yield large prediction errors. A pulse error method is presented that offers more easily interpreted and less functionally complex measures of LEA error than existing procedures. Pulse error measures are also well conditioned for the questions most often asked of groundwater contamination models (arrival times and arrival concentrations at strategic downstream points). Nondimensional results for 1:1 ion exchange are presented to illustrate how pulse error analysis may be used to establish critical Damkohler number constraints for classes of interaction mechanisms. For the example problem discussed the Damkohler number constraint (Dar>100) appears to be more stringent than previously reported.

ISSN:0043-1397    

DOI:10.1029/WR023i009p01775

年代:1987

数据来源: WILEY

摘要:

The transport of two conservative tracers, bromide and chloride, was studied in a stony field soil under natural soil, vegetative, and climatic conditions. Small tracer pulses were applied evenly over the 94‐m2plot area in April 1982 (bromide) and October 1982 (chloride). A 15‐m‐long, 3‐m‐deep transect through the plot area was extensively sampled in May 1983, approximately 400 days after the bromide and 200 days after the chloride was applied. Tracer concentrations were obtained from 842 samples taken at 61 locations along the transect. Two‐dimensional contour plots of the data showed a relatively uniform displacement in the vertical direction, as well as a significant horizontal redistribution during the study period. The data were analyzed with the classical convection‐dispersion equation (CDE) and with a regional stochastic model that assumes logarithmic distributions of the pore water velocity and the dispersion coefficient across the field. Both models successfully described momentary field‐averaged concentration distributions but failed to predict observed concentration data in October 1984 when another, less intensive sampling was carried out. Pore water velocities could be estimated reasonably well with as few as five vertical sampling lines, whereas dispersion coefficients and solute loads required numerous additional samplings. A field scale dispersivity of about 8 cm was obtained for the CDE model. Between 75 and 130% of the applied tracers were recovered in 1982. The effects of sampling size (0.3 versus 3 kg dry soil weight) were found to be r

ISSN:0043-1397    

DOI:10.1029/WR023i009p01785

年代:1987

数据来源: WILEY

ISSN:0043-1397    

DOI:10.1029/WR023i009p01795

年代:1987

数据来源: WILEY