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1

Electronic Resource

INTERPLAY BETWEEN PARAMETER UNCERTAINTY AND MODEL AGGREGATION ERROR (1989)

Warwick, John J.

Oxford, UK : Blackwell Publishing Ltd

Journal of the American Water Resources Association 25 (1989), S. 0

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ISSN: 1752-1688

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Architecture, Civil Engineering, Surveying , Geography

Notes: S: Modeling error can be divided into two basic components: use of an incorrect model and input parameter uncertainty. Incorrect model usage can be further subdivided into inappropriate model selection and inherent modeling error due to process aggregation. Total modeling error is a culmination of these various modeling error components, with overall optimization requiring reductions in all.A technique, utilizing Monte Carlo analysis, is employed to investigate the relative importance of input parameter uncertainty versus process aggregation error. An expanded form of the Streeter-Phelps dissolved oxygen equation is used to demonstrate the application of this technique. A variety of scenarios are analyzed to illustrate the relative obfuscation of each modeling error component. Under certain circumstances an aggregated model performs better than a more complex model, which perfectly simulates the real system. Alternately, process aggregation error dominates total modeling error for other situations. The ability to differentiate modeling error impact is a function of the desired or imposed model performance level (accuracy tolerance).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1752-1688.1989.tb03062.x

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2

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HYDRODYNAMIC MODELING OF THE CARSON RIVER AND LAHONTAN RESERVOIR, NEVADA (1995)

Warwick, John J. ; Heim, Kenneth J.

Oxford, UK : Blackwell Publishing Ltd

Journal of the American Water Resources Association 31 (1995), S. 0

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ISSN: 1752-1688

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Architecture, Civil Engineering, Surveying , Geography

Notes: : The RIVMOD hydrodynamic model was used to route upstream flows through a 115 km section of the Carson River and Lahontan Reservoir, Nevada. RIVMOD results will later be used to predict sediment movement and ultimately to determine mercury transport within the river/reservoir system. Significant modifications to the model computer code were necessary to represent the narrow, steeply sloping rectangular channel and relatively shallow sloping floodplain of the Carson River and its confluence with the Lahontan Reservoir. These changes include expansion of the continuity and momentum equations to account for rapidly changing channel widths along with the characterization of a complex cross-sectional shape. This modified version of the RIVMOD model can handle shallower side slopes and much more severe flood flow simulations than the original version. A 0.25 km spatial increment was required in the zone of confluence between the river and reservoir. Model predictions show excellent agreement with observed downstream flow and reservoir stage for the entire 1986 water year, which includes one of the most severe flood events of recent record. (KEY TERMS: hydraulics; modeling; simulation; surface water hydrology.)

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1752-1688.1995.tb03365.x

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3

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FUNDAMENTAL INVESTIGATION OF GRAVITY CURRENTS WITH VARYING DENSITY (1988)

Warwick, John J. ; Murray, Willard A.

Oxford, UK : Blackwell Publishing Ltd

Journal of the American Water Resources Association 24 (1988), S. 0

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ISSN: 1752-1688

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Architecture, Civil Engineering, Surveying , Geography

Notes: : A one-dimensional, gradually varying, non-uniform, flow equation is developed to describe the movement of a variable density gravity current through a reservoir. A linearly decreasing underflow density function is used to investigate the effect of in-reservoir density reduction on typical gravity current flow profiles. Only two types of flow profiles are found to exist for varying density underflows: Type I profiles where the underflow asymptotically approaches a horizontal surface, and Type III profiles where the underflow vertically approaches critical depth. Type I profiles pass through a transitional depth as the underflow density approaches that of the upper layer.Results indicate that a reservoir can be segmented into four distinct spatial regions with well defined flow profile characteristics. The location of these regions allows the sketching of interfacial flow profiles along with identifying the location of transitional depth conditions. Transitional depth conditions are utilized as the logical starting point for Type I flow profile numerical computation. (KEY WORDS: density; fluid flow; reservoirs; hydraulics.)

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1752-1688.1988.tb03020.x

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4

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USE OF FIRST-ORDER UNCERTAINTY ANALYSIS TO OPTIMIZE SUCCESSFUL STREAM WATER QUALITY SIMULATION (1997)

Warwick, John J.

Oxford, UK : Blackwell Publishing Ltd

Journal of the American Water Resources Association 33 (1997), S. 0

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ISSN: 1752-1688

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Architecture, Civil Engineering, Surveying , Geography

Notes: : A first-order uncertainty technique is developed to quantify the relationship between field data collection and a modeling exercise involving both calibration and subsequent verification. A simple statistic (LTOTAL) is used to quantify the total likelihood (probability) of successfully calibrating and verifying the model. Results from the first-order technique are compared with those from a traditional Monte Carlo simulation approach using a simple Streeter-Phelps dissolved oxygen model. The largest single difference is caused by the filtering or removal of unrealistic outcomes within the Monte Carlo framework. The amount of bias inherent in the first-order approach is also a function of the magnitude of input variability and sampling location. The minimum bias of the first-order technique is approximately 20 percent for a case involving relatively large uncertainties. However the bias is well behaved (consistent) so as to allow for correct decision making regarding the relative efficacy of various sampling strategies. The utility of the first-order technique is demonstrated by linking data collection costs with modeling performance. For a simple and inexpensive project, a wise and informed selection resulted in an LTOTAL value of 86 percent, while an uninformed selection could result in an LTOTAL value of only 55 percent.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1752-1688.1997.tb03544.x

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5

Electronic Resource

Mercury contamination in the Carson River, Nevada: A preliminary study of the impact of mining wastes (1996)

Wayne, David M. ; Warwick, John J. ; Lechler, Paul J. ; [et al.]

Springer

Water, air & soil pollution 92 (1996), S. 391-408

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ISSN: 1573-2932

Keywords: Mercury ; Carson River ; Nevada ; tailings ; cold vapor atomic fluorescence spectroscopy

Source: Springer Online Journal Archives 1860-2000

Topics: Energy, Environment Protection, Nuclear Power Engineering

Notes: Abstract From 1860 to 1890, approximately 7 100 metric tons of metallic mercury (Hg) were released into the Carson River-Lahontan Reservoir watershed as a by-product of Comstock Lode silver (Ag) and gold (Au) ore refining. Present-day Hg contamination is most severe in mine tailings, where total Hg concentrations can exceed several hundred µg/g. Hg-laden tailings were also dumped directly into the Carson River, and were subsequently transported downstream into the Lahontan Reservoir and the Stillwater Wildlife Management Area. The Hg, Ag and Au contents of sediments from the Carson River and the Lahontan Reservoir are well above local background levels, and both Ag and Au contents are positively correlated to Hg. Thus, tailings-derived Hg has been redistributed throughout the entire Carson-Lahontan watershed over the last century. Total Hg concentrations in water samples from the Carson River at seven localities show that: 1) elevated (e.g., 〉20 ng/L) Hg levels in Carson River waters first appear downstream from accumulations of mill tailings, 2) total Hg concentrations in unfiltered and filtered water from the Carson River increase downstream (i.e. away from the tailings piles), and 3) Hg concentrations in both the Carson River (downstream from the tailings piles) and the Lahontan Reservoir are among the highest known worldwide (100 to 1000 ng/L). Filtered water samples from the Carson-Lahontan system also have high Hg contents (up to 113 ng/L), and suggest that the 〉0.4 µm particle fraction constitutes over 60% of the total water-borne Hg.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00283569

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6

Electronic Resource

On the Errors Associated with Two-Dimensional Stochastic Solute Transport Models (2000)

Pohll, Gregory M. ; Warwick, John J. ; Benson, David

Springer

Transport in porous media 40 (2000), S. 281-293

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ISSN: 1573-1634

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Technology

Notes: Abstract Many subsurface solute transport studies employ numerical modeling techniques to estimate solute arrival times. Simplifying assumptions must be made to define the modeling domain within a mathematical framework. One common assumption is that the vertical flow is negligible such that the flow field can be simulated with a two-dimensional model. Reducing the vertical dimension reduces the number of flow paths that a solute can take. In a heterogenous medium, artificially removing the 3rd dimension may lead to erroneous results. We investigate the error in the simulated solute breakthrough associated with a two-dimensional model. We also use a stochastic solution of solute arrival time to derive a transform of a two-dimensional ln (k) field so that solute transport more closely resembles three-dimensional transport behavior. The moment equations for two- and three-dimensional domains were solved simultaneously to calculate this transform. The results indicate that the removal of the vertical variability (3D → 2D) introduces a 5–10% error in the predicted solute breakthrough. The error tends to increase with increased hydraulic conductivity variance. Numerical experiments confirm that the transform developed herein decreases the relative error of particle breakthrough curves.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1006786714947

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