San Lorenzo River Floodplain Abandonment


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Owners: William A. L. Chapman
Type: Resource
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Created: Feb 25, 2021 at 8:20 p.m.
Last updated: Jan 27, 2022 at 11:01 p.m.
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Abstract

This resource contains relevant data and programs (.py and .ipynb) for the paper "River floodplain abandonment and channel deepening coincide with the onset of clear-cut logging in a coastal California redwood forest" (https://doi.org/10.1002/esp.5299) Programs are generalizable to other studies and may be used with proper citation.

Article abstract:

Changes in both land use and climate can alter the balance of transport capacity and sediment supply in rivers. Hence, the primary driver of recent incision or aggradation in alluvial channels is often unclear. The San Lorenzo River on the central coast of California is one location where both climate and land use—specifically, clear-cut forestry of coastal redwoods—could explain recent vertical incision and floodplain abandonment. At our field site on the San Lorenzo, we estimate the magnitude of recent incision using both the ratio of bankfull to critical Shields numbers (𝜏∗𝑏𝑓/𝜏∗𝑐) and the geomorphically effective discharge, calculated from historical gauge data. The Shields number ratio suggests that the normalized bankfull stress of the San Lorenzo River is in the upper 1–2% of West Coast rivers, and the effective discharge corresponds to flow depths ~2–4 m below current bankfull conditions. Radiocarbon ages from detrital charcoal in floodplain sediment reveal active floodplain deposition during the 1600s and possibly into the 1800s, constraining the timing of incision to the last few centuries. Multiple hanging tributaries above the mainstem San Lorenzo River, along with patterns in vegetation on terrace surfaces, corroborate our estimates of the magnitude and timing of incision. Taken together, our findings suggest that floodplain abandonment in this reach was mainly due to methods employed during logging that increased shear stress on the channel bed and reduced sediment storage capacity. We suggest that direct channel modifications in rivers can counterbalance increases in sediment delivery due to clear-cutting, resulting in channel incision rather than aggradation. Today, a young, lower surface appears to be forming adjacent to the San Lorenzo River, which we interpret as an incipient floodplain that is in equilibrium with modern sediment supply and transport capacity.

Coverage

Spatial

Coordinate System/Geographic Projection:
WGS 84 EPSG:4326
Coordinate Units:
Decimal degrees
Place/Area Name:
Big Trees USGS Gauge (#11160500; San Lorenzo River)
Longitude
-122.0719°
Latitude
37.0441°

Temporal

Start Date: 01/01/2019
End Date: 01/01/2022
Marker
Leaflet Map data © OpenStreetMap contributors

Content

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Related Resources

The content of this resource is derived from United States Geological Survey. (2020) USGS 11160500 San Lorenzo River at Big Trees, CA. USGS Current Conditions for the Nation [online]. Available at: https://nwis.waterdata.usgs.gov/usa/nwis/qwdata/?site_no=11160500 [Accessed 25 May 2021].

How to Cite

Chapman, W. A. L., N. Finnegan, A. Pfeiffer, S. L. Selle (2022). San Lorenzo River Floodplain Abandonment, HydroShare, http://www.hydroshare.org/resource/adab5574c2dd45d8bc12125fb47d1fa1

This resource is shared under the Creative Commons Attribution CC BY.

http://creativecommons.org/licenses/by/4.0/
CC-BY

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