‘Local gradient’ and between-site variability of erosion rate on badlands in the Karoo, South Africa

David Favis-Mortlock, John Boardman, Ian D L Foster, Philip Greenwood

    Research output: Contribution to journalArticleResearchpeer-review

    Abstract

    Site-average values of local gradient, defined as the steepest slope angle measured at a point, are a powerful predictor of long-term rates of soil loss as measured by erosion pins on the non-channel floor portions of ten badland study sites in the Karoo area of South Africa. Local gradient may be easily measured using a smartphone clinometer. The successful use of local gradient here is in strong contrast to the previous failure of other site-specific attributes, including other measures of gradient and relief, to explain between-site variation in erosion rate on these study sites. Each measurement of local gradient may be thought of as a sample of the site’s microtopography. Microrelief is a strong determinant of the emergent patterns of inter-channel overland flow, and hence of the patterns of inter-channel erosion by flow. Local gradient changes most rapidly during the initial stages of channel incision. When channels are established, local gradient changes more slowly leading to almost-parallel retreat of channel sidewalls. A sensitivity analysis suggests that measurements of local gradient are not all equal with regard to prediction of long-term erosion rate. A greater share of predictive power is contributed by measurements made on very steep or vertical channel side wall areas, and a lesser share is contributed by measurements made on interfluves.
    Original languageEnglish
    Pages (from-to)871-883
    Number of pages13
    JournalEarth Surface Processes and Landforms
    Volume43
    Early online date22 Dec 2017
    DOIs
    Publication statusPublished - 30 Mar 2018

    Fingerprint

    badlands
    erosion rate
    erosion
    microrelief
    microtopography
    slope angle
    channel flow
    overland flow
    sensitivity analysis
    relief
    Africa
    prediction
    soil

    Keywords

    • Karoo
    • badlands
    • clinometer app
    • local gradient
    • microtopography
    • soil erosion

    Cite this

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    title = "‘Local gradient’ and between-site variability of erosion rate on badlands in the Karoo, South Africa",
    abstract = "Site-average values of local gradient, defined as the steepest slope angle measured at a point, are a powerful predictor of long-term rates of soil loss as measured by erosion pins on the non-channel floor portions of ten badland study sites in the Karoo area of South Africa. Local gradient may be easily measured using a smartphone clinometer. The successful use of local gradient here is in strong contrast to the previous failure of other site-specific attributes, including other measures of gradient and relief, to explain between-site variation in erosion rate on these study sites. Each measurement of local gradient may be thought of as a sample of the site’s microtopography. Microrelief is a strong determinant of the emergent patterns of inter-channel overland flow, and hence of the patterns of inter-channel erosion by flow. Local gradient changes most rapidly during the initial stages of channel incision. When channels are established, local gradient changes more slowly leading to almost-parallel retreat of channel sidewalls. A sensitivity analysis suggests that measurements of local gradient are not all equal with regard to prediction of long-term erosion rate. A greater share of predictive power is contributed by measurements made on very steep or vertical channel side wall areas, and a lesser share is contributed by measurements made on interfluves.",
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    ‘Local gradient’ and between-site variability of erosion rate on badlands in the Karoo, South Africa. / Favis-Mortlock, David; Boardman, John; Foster, Ian D L; Greenwood, Philip.

    In: Earth Surface Processes and Landforms, Vol. 43, 30.03.2018, p. 871-883.

    Research output: Contribution to journalArticleResearchpeer-review

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    AU - Greenwood, Philip

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    N2 - Site-average values of local gradient, defined as the steepest slope angle measured at a point, are a powerful predictor of long-term rates of soil loss as measured by erosion pins on the non-channel floor portions of ten badland study sites in the Karoo area of South Africa. Local gradient may be easily measured using a smartphone clinometer. The successful use of local gradient here is in strong contrast to the previous failure of other site-specific attributes, including other measures of gradient and relief, to explain between-site variation in erosion rate on these study sites. Each measurement of local gradient may be thought of as a sample of the site’s microtopography. Microrelief is a strong determinant of the emergent patterns of inter-channel overland flow, and hence of the patterns of inter-channel erosion by flow. Local gradient changes most rapidly during the initial stages of channel incision. When channels are established, local gradient changes more slowly leading to almost-parallel retreat of channel sidewalls. A sensitivity analysis suggests that measurements of local gradient are not all equal with regard to prediction of long-term erosion rate. A greater share of predictive power is contributed by measurements made on very steep or vertical channel side wall areas, and a lesser share is contributed by measurements made on interfluves.

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