Laserfiche WebLink
<br />7 <br /> <br />accreted deposits that result from channel migration across a flood plain, and <br />vertically accreted deposits that result from overbank deposition of sediment. <br />Flow hydraulics through laterally migrating meander bends have been studied <br />extensively (e.g., Dietrich and Smith, 1983; Bridge and Jarvis, 1976) and they <br />are relatively well understo~. The stratigraphy ~f point bar deposits that result <br />from lateral channel migration and create these floodplains also have been <br />studied by Jackson (1975) and Bridge and Diemer (1983). Conversely, the <br />processes involved in vertical accretion of sediment are largely undocumented, <br />due in part to the low rate of sediment deposition that is often associated with <br />overbank flow (Wolman and Leopold, 1957; Gomezet aI., 1995)oand the belief. <br />that this process is less widespread or of less geomorphic importance. <br />The basic theoretical model describing t~e rate of vertical accretion on <br />flood plains was proposed by Wolman and Leopold (1957), who showed that <br />the rate of vertical accretion must decrease with time if thalweg elevation does <br />not change (Fig. 2). The decreased rate of sediment deposition over time is <br />due to the decreasing frequency of overbank flow, because higher stages are <br />necessary to inundate an aggrading flood plain. Few field studies have <br />confirmed this model. <br />Nanson (1986) studied laterally stable and vertically aggrading streams <br />in southeastern Australia. He concluded that continued vertical accretion over <br />time and the associated fonnation of natural levees leads to a concentration of <br />flow energy in the main channel and in flood-plain backchannels. The energy <br />