Erosion characteristics and horizontal variability for small erosion depths in the SacramentoSan Joaquin River Delta, California, USA
Erosion characteristics and horizontal variability for small erosion depths in the SacramentoSan Joaquin River Delta, California, USA. Schoellhamer, D.and Manning, A.J. and Work, P. Ocean Dynamics, 67 (6). pp. 799811. (2017) Full text not available from this repository. Official URL:  https://link.springer.com/article/10.1007/s1023601710472 

Abstract:  Erodibility of cohesive sediment in the SacramentoSan Joaquin River Delta (Delta) was investigated with an erosion microcosm. Erosion depths in the Delta and in the microcosm were estimated to be about one floc diameter over a range of shear stresses and times comparable to half of a typical tidal cycle. Using the conventional assumption of horizontally homogeneous bed sediment, data from 27 of 34 microcosm experiments indicate that the erosion rate coefficient increased as eroded mass increased, contrary to theory. We believe that small erosion depths, erosion rate coefficient deviation from theory, and visual observation of horizontally varying biota and texture at the sediment surface indicate that erosion cannot solely be a function of depth but must also vary horizontally. We test this hypothesis by developing a simple numerical model that includes horizontal heterogeneity, use it to develop an artificial time series of suspendedsediment concentration (SSC) in an erosion microcosm, then analyze that time series assuming horizontal homogeneity. A shear vane was used to estimate that the horizontal standard deviation of critical shear stress was about 30% of the mean value at a site in the Delta. The numerical model of the erosion microcosm included a normal distribution of initial critical shear stress, a linear increase in critical shear stress with eroded mass, an exponential decrease of erosion rate coefficient with eroded mass, and a stepped increase in applied shear stress. The maximum SSC for each step increased gradually, thus confounding identification of a single welldefined critical shear stress as encountered with the empirical data. Analysis of the artificial SSC time series with the assumption of a homogeneous bed reproduced the original profile of critical shear stress, but the erosion rate coefficient increased with eroded mass, similar to the empirical data. Thus, the numerical experiment confirms the smalldepth erosion hypothesis. A linear model of critical shear stress and eroded mass is proposed to simulate smalldepth erosion, assuming that the applied and critical shear stresses quickly reach equilibrium. 

Item Type:  Article 

Uncontrolled Keywords:  Erosion; Cohesive sediment; SacramentoSan Joaquin River Delta; Erosion microcosm; Critical shear stress; Estuary; Estuarine; Sediment bed 

Subjects:  Floods > General 

ID Code:  1429 

Deposited On:  25 Sep 2017 09:33 

Last Modified:  25 Sep 2017 09:34 

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