CONFIGURATION AND PROPERTIES OF A BREAKUP JAM

Favorable weather conditions in January, 1986, resulted in a breakup jam on the Thames River that froze in place. This afforded safe access and performance of detailed thickness measurements that are normally not possible to obtain. Approximate assessment of the absolute roughness of the jam indicated fair agreement with earlier deductions based on hydraulic resistance data. Using existing theoretical concepts, it was deduced that the downstream portion of the jam was likely formed by 'shoves' or internal collapse ('wide') whereas the upstream portion was likely formed by frontal progression ('narrow') and juxtaposition. For the former reach, the present data enabled approximate evaluation of coefficients utilized in pertinent theories. The 'wide' jam theory was adapted to describe a jam overlain by solid ice cover. This enabled approximate determination of the friction coefficient between the jam and the cover.