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| Titel |
Field measurement of infiltration rate using an oscillating nozzle rainfall simulator in the cold semiarid grassland of Mongolia |
| VerfasserIn |
Hiroaki Kato, Yuichi Onda, Yukiya Tanaka, Maki Asano |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038641
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| Zusammenfassung |
| In arid and semiarid rangelands, the process of desertification due to overgrazing has been
described in terms of changes in surface vegetation cover and reduction in infiltration rate.
Infiltration rate is one of the key indicators of overland flow generation and soil erosion;
therefore, detecting reduction in infiltration rate is essential to assess land degradation of
rangeland. Mongolia is located in northeastern Asia, and approximately 75 percent of its total
land area consists of cold, semiarid grassland that is subjected to grazing throughout the year.
Recent intensive grazing in Mongolia may be significantly reducing the infiltration rate of
rangeland; however, very few data on the infiltration rate are currently available in this
region.
In this study, a new light-weight oscillating nozzle rainfall simulator was developed to
generate the simulated rainfall with large raindrops and raindrop kinetic energy based on the
design of existing rainfall simulators. We carried out a series of field infiltration tests for
various surface cover conditions using the modified rainfall simulator and small plots (1 m2)
in Mongolia. The objectives of this study were to elucidate the fundamental relationships
between surface vegetation cover and infiltration rate in cold semiarid grassland. The results
of field infiltration tests indicated that dense surface vegetation cover increased the infiltration
rate significantly; however, a statistically significant correlation was found between the total
surface cover (including rock fragment cover) and steady state infiltration rate, suggesting
that surface cover by rock fragments also increased the infiltration rate to some
extent.
In general, steady state infiltration rate observed in the simulated rainfall experiment
increases with increasing rainfall intensity until all parts of the plot are saturated (Murai and
Iwasaki, 1975; Hawkins, 1982). The infiltration rates observed in simulated rainfall
experiment is apparent infiltration rate under certain rainfall intensity experimental condition,
and the maximum spatially averaged infiltration rate for the whole plot attained can be
observed when the entire plot is contributing surface runoff (Dunne et al., 1991). We used the
mathematical relationships between rainfall intensity and infiltration rate represented by
using hyperbolic tangent curve (Tanaka and Tokioka, 2007) to estimate the maximum
spatially averaged infiltration rate for the observed steady state infiltration rates.
The relationships between surface cover and the calculated maximum spatially
averaged infiltration rate for the Mongolian grassland were compared to those in
various other regions. The relationships between the surface vegetation cover and the
infiltration rate showed approximate correspondence to the different grassy hillslopes.
The high consistency in these relationships suggested rather common effects of
surface cover on the infiltration rate throughout grass-covered hillslopes in semiarid
environments.
References: Dunne, T., Zhang, W., Aubry, B.F., 1991. Effects of rainfall, vegetation, and
microtopography on infiltration and runoff. Water Resources Research, 27(9), 2271-2285.
Hawkins, R.H., 1982. Interpretation of source-area variability in rainfall-runoff relationships.
In Rainfall-Runoff Relationships edited by Singh V.P., pp.303-324. Water Resources
Publications, Fort Collins, Colorado. Murai, H., Iwasaki, Y., 1975. Studies on function of
water and soil conservation based on forest land (1) –Influence of difference in forest
condition upon water run-off, infiltration and soil erosion-. Bull. Gov. For. Exp. Sta., 274,
23-84 (in Japanese with English abstract). Tanaka, S., Tokioka, T., 2007. The 62th Annual
Proceeding of Japanese Society of Civil Engineers (CD-ROM), 2-003, pp.5-6 (in Japanese). |
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