Quantifying the effect of riparian forest versus agricultural vegetation on river meander migration rates, central Sacramento River, California, USA

Abstract

Riparian forest vegetation is widely believed to protect riverbanks from erosion, but few studies have quantified the effect of riparian vegetation removal on rates of river channel migration. Measured historical changes in a river channel centreline, combined with mapped changes in floodplain vegetation, provide an opportunity to test how riparian vegetation cover affects the erodibility of riverbanks. We analysed meander migration patterns from 1896 to 1997 for the central reach of the Sacramento River between Red Bluff and Colusa, using channel planform and vegetation cover data compiled from maps and aerial photography. We used a numerical model of meander migration to back-calculate local values for bank erodibility (i.e. the susceptibility of bank materials to erosion via lateral channel migration, normalized for variations in near-bank flow velocities due to channel curvature). A comparison of migration rates for approximately 50 years before and after the construction of Shasta dam suggests that bank migration rates and erodibility increased roughly 50%, despite significant flow regulation, as riparian floodplains were progressively converted to agriculture. A comparison of migration rates and bank erodibilities between 1949 and 1997, for reaches bordered by riparian forest versus agriculture, shows that agricultural floodplains are 80 to 150% more erodible than riparian forest floodplains. An improved understanding of the effect of floodplain vegetation on river channel migration will aid efforts to predict future patterns of meander migration for different river management and restoration scenarios.

Modification of river meandering by tropical deforestation

“…2A). This is consistent with previous studies that have assessed the role of vegetation in riverbank erosion (Beeson and Doyle, 1995;Micheli et al, 2004). Increases in M R following deforestation can be attributed to increases in riverbank erodibility, at least as reflected in the differences in ε.…”

“…3). At least one other study, from the Sacramento River in California, USA, has quantified riverbank erosion as a function of planform curvature following deforestation, highlighting that erosion by curvature-driven forcing of river flow predominates only along sections of floodplain where the natural riparian cover was replaced by agriculture (Micheli et al, 2004). We hypothesize that the increase in riverbank erosion sensitivity to curvature-driven forcing of river flows occurs because clearing riparian forest improves the ability of near-bank flows to remove riverbank materials (both intact and failed) and, by reducing riverbank shear strength, facilitates smaller, more frequent mass-failure events.…”

“…channel centerlines by interpolating through digitized points located halfway between channel margins at 100 m intervals. Values of M R were then calculated after Constantine et al (2009) and Micheli et al (2004), in which superposed centerlines from successive Landsat images created polygons that represented the total area of eroded bank material. Mean erosion rates for river sections spanning individual meanders were then defined as the sum of the polygon areas within each section divided by the average streamwise length of the section.…”

Alluvial plain dynamics in the southern Amazonian foreland basin

“…Images have been transformed into 2 bit (black and white) data sets and channel centrelines have been digitalized using the ArcScan extension of ArcGis software. Meander migration rates have been calculated as in Micheli et al (2004) and Constantine et al (2014). Values of the Multivariate ENSO Index (MEI) (Wolter and Timlin, 2011) have been downloaded from http://www.esrl.noaa.gov/psd/enso/mei/rank.html.…”

Modelación matemática de la interacción entre la vegetación de ribera y el régimen hídrico del río en condiciones semiáridas

“…Para ello, se puede explorar el campo de conocimiento de la hidráulica bidimensional o tridimensional del flujo de materia y energía en las riberas; es recomendable seguir la base conceptual de los trabajos de Fathi-Maghadam y Kouwen (1997), Glenz et al (2003), Järvelä (2002Järvelä ( y 2004, Kouwen (2003), Kummu (2002), Mason (2003), Micheli et al (2004), Simon y Collison (2002). Para esta interacción con la dimensión longitudinal será necesario adecuar los procesos fluviales y ecológicos de mayor interés a la escala espacial y temporal más conveniente.…”