Determination of Some Paleohydraulic Parameters: ABSTRACT

Abstract

New river measurements combined with existing laboratory evidence show that, in a river reach where traction motion as well as net sediment deposition take place, the mean applied bed shear stress is equal to the critical shear stress required to move particles of median bed material size. Consequently, application of Shields' relation between shear stress and material size permits the determination of mean applied shear stress at an ancient depositional site from the grain-size distribution of the sediment. Furthermore, by applying laboratory values for the friction factor, determined for the appropriate bed configuration, we can calculate the paleoflow velocity by the Darcy-Weisbach relation. This method for the determination of paleoflow velocity is generally applicabl to any sedimentary deposit if a reasonable estimate of the friction factor can be made. For rock units containing climbing ripple cross-lamination, we can go one step farther and determine the rate at which the sediments were accumulated. The rate of bedload transport has a known functional relation to the mean velocity of the overlying column of water as determined in the first part of this study. Very high rates of sedimentation are found to exist in nature. Late Pleistocene deltaic sediments in the Truckee Canyon of Nevada, locally contain climbing ripple cross-laminated units indicating a local rate of aggradation of 0.1 mm/sec or 36 cm/hr. End_of_Article - Last_Page 797------------