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Kemi

BUREAU OF RECLAMATION LIBRARY Flow Regulation for Controlled River-Ice Formation Subash C. Jain, Robert Ettema an d Inbo Park May 1993 1° ^ [ULO 5 Abstract Results are presented of a study to determine appropriate methods of flow modification for mitigating ice jam formation in navigable rivers. Based on a review of alternative methods for flow modification, it is concluded that for many rivers, especially large ones, the most appropriate method involves controlled ice-cover formation through the regulation of river flow. Flow discharge and stages would be regulated by controlling the flow releases from reservoirs and flow stages at river dams, such that optimal flow conditions prevail for rapid formation, and subsequent maintenance, of an accumulation ice cover over river reaches in which potentially large amounts of frazil Ice may grow. Accumulation covers would be formed of frazil ice pans and floes and, if appropriate, broken ice conveyed from upstream. Existing dams, augmented where needed by navigable Ice booms, could serve as retention structures for the development of accumulation covers. A preliminary indication of the feasibility of this method for controlling ice-cover formation on stage-regulated pools of the Ohio River is assessed through the use of a numerical model that simulates ice-cover formation from frazil Ice. It is found thatthis approach holds promise for mitigating jam occurrence, although Its implementation necessarily entails management of flowthrough major portions of the Ohio River. The results of the study are, to a limited extent, generalized to other rivers. Cover: Severe ice accumulation upstream o f Locks and Dam 20, Mississippi River. For conversion of SI metric units to U.S./British customary units of measurement consult ASTM Standard E380-89a, Standard Practice for Useof the International System o f Units (SI), published by the American Society for Testing and Mater­ials, 1916 Race Sf„ Philadelphia, Pa. 19103. BUREAU OF RECLAMATIO

The objective of this study was to evaluate the effectiveness of movable-bed tidal inlet hydraulic models in predicting prototype behavior, by comparing model predictions with the observations made in the prototype, and to examine the scaling requirements for such models. Seven model studies were conducted by WES during the period 1939 to 1969. Calibrations of five of these models, as measured by bed topography changes, are evaluated by means of quantitative indicators, including correlation coefficients and root-mean-square (rms) error. The values of correlation coefficients, disregarding measurement errors in model and prototype soundings, were generally low and those of rms error high. Evaluation of data from the Galveston Harbor entrance model revealed that the shoaling rates and distribution along the navigation channel predicted by the model are not in good agreement with the prototype data. It was concluded that the model reproduction of details of bed topography was less accurate than that which might have been obtained had the proposed similitude criteria been used, and had more complete prototype data been available for calibration. Disagreement between model and prototype is believed to have been due to: scale effects introduced by nonsimilarity ofthe physical processes; insufficient prototype data for calibration and verification; oversimplification of the available prototype data for use in the model study; and experimental errors.

A laboratory model study of the mechanical draft cooling towers of Browns Ferry Nuclear Plant was conducted to determine plume recirculation and cooling-tower interference quantitatively, and to evaluate the effectiveness of various modifications, including removal of a nearby spoil hillock, rearrangement of the tower cells, and increase of stack height, on the cooling-tower performance. Two sectional models with a scale of 1:150, each consisting of two towers, were tested. The dynamic scaling was based on equality of the densimetric Froude number, F(D), (F(D) = V(j)/sq. root of delta (Rho sub o) gD, where V(j) is the stack exit velocity, D is the stack diameter, g is the gravitational constant, rho sub a is the ambient fluid density and delta (Rho sub o) is the density difference between the ambient and jet effluent and the velocity ratio K(K = V(j)/V(a), where V(a) is the cross-flow velocity at the stack height. It was found that the effect of the spoil hill and of the relocation of two cells per tower on the overall recirculation ratio of the towers is not significant. An increase in stack height from 14 ft to 42 ft significantly reduced tower recirculation. (Author)