Publication Date:
2020-02-12
Description:
Knickpoints are a reliable indicator of stream channel incision. How these features impact a drainage basin as a whole as they migrate upstream however is less clear. To address this question, we have studied drainage basins in the Swiss Mitteland that have differing histories with respect to knickpoints and knickpoint migration. The Grosse Fontanne is a bedrock stream that drains the Molasse conglomerates of the Napf region. The system has been described as an actively incising rejuvenated landscape. Incised valleys and knickpoints are present on the trunk stream and many tributaries. Seven basinaveraged erosion rates varying from 330 to 640 mm/ky, derived from cosmogenic nuclides, were calculated for the watershed. The highest rates were recorded for the trunk stream near the confluence with the Kleine Emme River, while the lowest rates are found in small headwater basins. Of the samples, three were collected upstream of visible knickpoints, and two were collected downstream of visible knickpoints. The two remaining samples were collected on tributaries that had no visible knickpoints. The upstream erosion rates are lower, 350 mm/ky vs. 560 mm/ky, than the downstream erosion rates. The watersheds with no visible knickpoints are similar to the downstream samples, eroding at 500 mm/ky, suggesting that the knickpoint has already propagated through these catchments. The basins with active or presumed relict knickpoints also tend to have higher average relief than the basins which the knickpoints have not yet reached. The timing of initial formation, based on the volume of incision and a calculated erosion rate for the areas experiencing rapid downcutting, appears to be post-glacial. The cause of the knickpoint formation appears to be stream piracy by the Kleine Emme.
Keywords:
550 - Earth sciences
Type:
info:eu-repo/semantics/conferenceObject
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