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| Titel |
Knickpoint retreat and channel profile evolution in bedrock rivers on the Isle of Jura, Scotland |
| VerfasserIn |
M. Castillo, P. Bishop, J. Jansen |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250019591
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| Zusammenfassung |
| The understanding of knickpoint (KP) migration in bedrock channels is fundamental to
understanding how long-profile disequilibrium is transmitted through the stream
network. There are few models that explain KP retreat on bedrock channels, and,
moreover, little attention has been paid to the morphological changes downstream of a
KP after it has propagated upstream (i.e., to the degree of long-profile adjustment
represented by the passage of a KP). We are studying the rivers of the Isle of Jura in
western Scotland to explore this issue. Jura consists largely of a single lithology
(quartzite) that dips more or less uniformly to the east along the length of the island.
Glacio-isostatic surface uplift of ~40 m since ~16 ka has triggered KPs that are
propagating headwards in the long-profiles above +40 m elevation; later KPs, triggered by
later base-level falls, are propagating into the long-profile. For smaller streams
these are mostly still located between +40 m and 0 m ASL, whereas in the larger
streams these later KPs have upstream of the +40 m shoreline. The distance of KP
propagation (D) in Jura, derived from long-profile analysis of high resolution DEM
and air-photo, is satisfactorily explained by Dr=cAb using the catchment area as
a proxy for discharge. We also found that channel lowering below the KP, using
a measure we call here the concavity area θa, is also a function of the discharge
in the form θa=cAd. Our results suggest that upstream propagation of a KP may
not achieve the full response of the long-profile to base-level fall, especially for
smaller streams with lower stream power. Intuitively, channel lowering below the KP
should be more complete for larger streams (i.e., the larger streams are more able to
achieve all the bed lowering triggered by the base-level fall), but in the case of
ongoing surface uplift, as on Jura, such adjustment may be delayed and/or complicated
by later KPs propagating headwards into the reach downstream of the first KP. |
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