Author : Tobias Raphael Hasse
Publisher :
ISBN 13 :
Total Pages : 499 pages
Book Rating : 4.7/5 (86 download)
Book Synopsis Storage Time Dynamics of Meandering River Floodplain Sediments by : Tobias Raphael Hasse
Download or read book Storage Time Dynamics of Meandering River Floodplain Sediments written by Tobias Raphael Hasse and published by . This book was released on 2022 with total page 499 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using numerical simulations of meandering rivers and adjacent sediments, I develop new length, velocity, and time scales based on planform dynamics of meandering rivers, allowing researchers to estimate the storage time of sediments in the absence of simulation or geochronologic measurements. I derive an equation which fits the sediment storage time distribution remarkably well and combines aspects of an exponential distribution with a truncated Pareto distribution. The truncation of the Pareto distribution is obscured if the oldest few percent of sediments are omitted. Storage time distributions have heavier tails in wider valleys. Storage time distributions are not at steady state: a) because the timescale to reach steady state in a broad floodplain exceeds the land use or climate timescale of constant external forcing, and b) due to heterogeneity in alluvial deposit ages and removal, even in a simulation under constant forcing conditions. Median storage times range from 330 to 750 years with an average of 497 years, while mean storage times (residence times) range from 540 to 20,300 years with an average of 2,490 years. 'Flood' deposits (deposited on top of point bars) are stored 1.2-2x longer than point bar deposits. The highest fraction (5.7%) of eroding point bar sediment has been stored for 90 years which is how long it takes for the channel to migrate 2.5 channel widths. There is significant variability in storage time distributions: Correlations between the median storage times decreases quickly through time, for distributions 180 years apart R2 is only 0.5. Most of the time, the oldest eroding sediment is younger than 10 kyr; occasionally, 20% of eroding sediment is older than 25 kyr. Flood deposits have less variability and preserve significantly more temporal signal than point bar deposits, but older deposits of both types are rarely included in the 'sampled' eroding sediment. Visually apparent patterns in the graphical presentation of the distributions suggest that variability is occurring at longer time scales than individual bend dynamics. Storage time distributions of sediment eroded today are poor estimates for the eventual storage time distribution of sediment deposited today.