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Comparing the accuracy of several field methods for measuring gully erosion

Research output: Contribution to journalJournal article

Published

Journal publication date07/2012
JournalSoil Science Society of America Journal
Volume76
Number of pages14
Pages1319-1332
Original languageEnglish

Abstract

Most fi eld erosion studies in agricultural areas provide little information on
the probable errors involved. Here, for the fi rst time, we compare the accuracy,
time and cost of conventional and new methodologies for gully surveying,
and provide a model to estimate the effort required to achieve a specifi ed
accuracy. Using a terrestrial LiDAR survey of a 7.1-m-long gully reach as a
benchmark data set, the accuracies of different measurement methods (a
new 3D photo-reconstruction technique, total station, laser profi lemeter,
and pole) are assessed for estimating gully erosion at a reach scale. Based
on further fi eld measurements performed over nine gullies (>100 m long), a
simulation approach is derived to model the expected volume errors when
2D methods are used at the gully scale. All gullies considered were located
near Cordoba, Spain. At the reach scale, the fi eld measurements using 3D
photo-reconstruction and total station techniques produced cross-sectional
area error values smaller than 4%, with other 2D methods exceeding 10%.
For volume estimation, photo-reconstruction proved similar to LiDAR data,
but 2D methods generated large negative volume error (EV) values (<–13%
for laser profi lemeter and pole). We show that the proposed error expressions
derived from the model are in line with the reach-scale fi eld results. A measurement distance factor (MDF) is defi ned that represents the ratio between
cross-section distance and the gully length, and thus refl ects relative survey
effort. We calculate the required MDF for specifi ed values of EV, illustrating
how MDF decreases with increasing gully length and sinuosity.