Chapter 15 Ice Forecasting 15-1. General.pdf

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Chapter 15 Ice Forecasting 15-1. General

EM1110-2-1612 30 Oct 02 Chapter 15 Ice Forecasting 15-1. General Forecasting of ice conditions on inland waterways is based on the premise that, given forecasts of future meteorological conditions and forecasts of future hydraulic conditions, it is possible, through knowledge of thermodynamics, open channel hydraulics, ice physics, and an under- standing of the behavior of the various forms of river ice, to develop forecasts of the future ice conditions. The methodology described in this chapter produces ice forecasts that are unique to a specific river or basin for which an Ice Forecasting System is developed. a. The first goal of an Ice Forecasting System is to anticipate the period when ice formation is possible and, if possible, assign probabilities to the likelihood of formation. This type of forecast is known as a Long-Term Water Temperature Forecast. Such forecasts are made by a computer model of the overall heat balance of the river watershed, which indicates the long-term water temperature response to changes in air temperature. b. A second type of forecast is much more detailed in its results. The goals of this type of forecast are to predict the reaches of a river where ice will form, when that ice will form, the areal extent of stationary ice, the ice thickness, the time of breakup, and ice jams and other ex- treme ice conditions. This Mid-Winter Ice Forecast is very sensitive to day-to-day changes in meteorological conditions and flow conditions, making it apply to a much shorter time, generally 5 to 7 days. This short-term forecast requires the development of three closely interrelated mod- els: first, a dynamic flow model to simulate the channel hydraulics, including the influence of ice; second, a thermodynamic model to simulate the heat transfer between the waterway and the atmosphere; and third, an ice formation model to distribute the ice along the waterway and to calculate the ice thickness. c. In th

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