WSP01119 - Laserfiche WebLink

Home Browse Search

.' oj ong S8 recent years. Yet a 11 attest that ice jams, such as those ooserved in 1983-84 and 1984-85, were never commonplace prior to completion of the Blue Mesa Reservoir. This study has thus oeen directed towards examlnlng closely the effects of the operation of the Blue Mesa Reservoir on icing action in the Gunnison River. 2.0 GENERAL ICING MECHANICS 2.1 General There have oeen a number of research studies conducted regarding the production of ice on rivers and streams. Although it is oeyond the scope of this study to present and evaluate the extensive research that has occurred, it is important that those reading this report first have a basic understanding of some key factors regarding the production of ice in or over streams and rivers. In this section, a orief explanation and summary of river icing mechanics will oe presented as a preface to the site-specific analysis that was carried out on the Gunnison River. 2.2 Ice Cover As noted in the introduction, it is not uncommon in the Gunnison Valley for streams and rivers, especially in slow-moving reaches, to oecome completely frozen over on the surface. This formation of an ice cover results from the surface freezing progressively inward from the banks toward the center. Eventually, the whole surface becomes covered with ice and the stream continues to flow underneath. The formation of the ice cover is more likely to occur in reaches of the stream where the velocities are low and the surface relatively quiet. Rarely does this kind of icing action result in restriction of the flow, to the extent that overoank flooding occurs. A good example of this type of action is the ice cover formation on a tributary to the Gunnison River located south of the City of Gunnison (Tomichi Creek). The stream gradient is not steep, as evidenced oy the -3-