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| Titel |
Mapping erosion-accumulation forms using electromagnetic conductivity |
| VerfasserIn |
Aleš Létal, Libor Burian, Anna Smetanova |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046130
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| Zusammenfassung |
| The erosion-accumulation processes have become significant at times when most of
usable landscape is influenced by human activities. In the 20th century conventional
methods for analysing this phenomenon were discovered. It was found that common
geophysical methods are able to analyse erosion-accumulation forms in landscape as
a consequence of rainfall-runoff processes. Quantification of cubature of erosion and
accumulation forms using geophysical approach, mainly electromagnetic conductivity is the
main subject of the study. Huge amount of geophysical approaches are used for
such an analysis, but conductivity meter was recognised by us as an appropriate
method. However, the interpretation of geophysical measurement outputs is disputable
(based on proper operation of instrument). The previous approach was based on the
qualitative interpretation of the entities and discontinuities in electromagnetic record.
This method varies on operator abilities and experiences because it depends only
on abilities of operator. Traditional pedological-geomorphological research and
utilization geophysical methods are interconnected in our new approach. Thickness
of accumulation forms is calculated from their electromagnetic records. For this
purpose a specific equation for each measurement has to be derived. Data gained
from boreholes or excavations is compared with geophysical measurement using
statistical methods. There is no universal form defined for this equation, only general
formula:
r < M : h = f(E) V r -¥ M : h - f(E)
Where r is a coefficient of correlation ranging from 0 to 1, 0 represents week correlation,
M is maximum permitted coefficient of correlation, h is thickness of selected soil horizon or
thickness of accumulation form and E is a value of electromagnetic conductivity or resistivity.
This approach was tested in two study areas. The first represents buried gully, at the outlet of
small 1st order catchment, near village Voderady, Slovakia. Thickness and physical attributes
of buried gully infill was analyzed from the 15 boreholes and from an excavation trench. The
electromagnetic conductivity and susceptibility was measured. A coefficient of
correlation was close to 0,8, which means strong correlation, thus cubature of refilled
gully could be calculated from derived equation. Furthermore two paleomeanders
were identified from the electromagnetic conductivity records. Deep accumulation
has been found in the second study area at the outlet of a steep Y-shaped valley
system near the village Kostolné, Slovakia, the second study area. An estimated
hypothetical border between erosion dominating zone and accumulation dominating
zone was the point where vallies are connected to the major valley. One excavation
and 8 boreholes were made on the cross-section in the main valley. Analyses of
micromorfologic attributes were used for determining of soil horizons. The value of
a correlation coefficient was calculated to be near 0,5, meaning low correlation.
Based on electromagnetic image, some representative areas with constant value of
electromagnetic conductivity were chosen for further drilling and cores analysis.
Depth of accumulation was described from boreholes and extrapolated to the study
areas. Database for geomorphologic information system (GmIS) in a large scale was
constructed. Cubature of accumulation form was analysed as an output of GmIS.
Geophysical approach as a tool for quantification of accumulation forms is suggested to
become a common method in pedological-geomorphologic and agricultural studies. |
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