Mapping and SSessment of wind Erosion in central
Mapping and SSessment of wind Erosion in central
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Date
2015-04-27
Authors
Mohammed Ahmed, Hussien
Journal Title
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Publisher
UOFK
Abstract
This study has been conducted in central Northern State of Sudan which is
situated in the South eastern boundary of the Sahara desert. A brief account
on the environmental setting including climate, geomorphology, sand
sources, and wind was given. The main objective of the study is to assess
and map wind erosion in the Northern State, specify its magnitude and
impact on socio-economic activities and propose some measures for its
mitigation.
Relevant landsat imageries were interpreted and the data acquired coupled
with field measurements of drifting sand rates by the method of sand traps
were used. This combination furnished the base for conducting mapping
and further assessing wind erosion hazards. The final results of this
undertaken is the production of wind erosion hazard map Fig.(4.12),which
indicates that:
- The study area is barren.
- Main terrain types of the study area are dunes, sand sheet and desert
pavement.
- Rates of sand drift varied widely from site to site during any given
period, depending upon terrain type; generally the average mean rates
drift was 16.7m3/m-w/yr (cubic meter per meter width per year) in the
sites located at the right bank of the River Nile and between 3.6–4.2
m3/m-w/yr in the sites located at the left bank of the river. Pronounced
transport of drifting sand was observed during the months February to
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May and from August to September, while minimum transport was
observed during November to December.
- Average mean drifts sand from (S + SW + W) directions accounted for
37 % for the site at the left bank and 12% for Elkhawie dune field right
bank site for season 2005/2006.
- The amount of sand encroaching into the Nile course was measured to
be 0.0454 m3/m-w/day (45.5m3/km-width/day).
- Rates of dune advance range was between 6 – 23 m/yr.
- Field measurement revealed that nearly 80% saltating sand
accumulations occurred within 0-30 cm from soil surface and then
decrease with the height.
- The winds which are causing the greatest sand movement are the
Northerly or North-north easterly winds blowing from October to May
and being worst from February to May.
- Reversal of wind direction primarily occurring during khareef months
cause small Northward facing slipfaces on top of the dune.Fig.3.3.d
- The percentage of sand accumulation decreased with increasing sand
trap height, nearly 80% occurred within the depth 0-30cm
- Grain size analysis showed that values of median M50 and mean
diameter Mz are similar for each sample that belong to the samples
under investigation.
- On the basis of grain size it was possible to differentiate between sand
plain (Al Baja), dune fields (Al khowie) and drifting sands.
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- Data on inclusive standard deviation (σ1) defined as a measure of the
spread about the mean, or sorting in Table 2.3 showed sorting values
indicative of very well sorting.
- Mean average of inclusive graphic kurtosis (Kg); defined as the
peakedness of distribution in Table 2.3 showed mesokurtic distribution,
meaning that most of the sand samples are closely reassembled a
normal frequency distribution.
- Due to the continuous incidence of el Shamal winds blowing from the
northerly direction, new dunes are formed and old ones became
enlarged due to the increase in the amount of sand available for
transport .These dunes encroach on roads, building , and the River Nile
course. Consequently, there is a need for mapping and monitoring the
process so that remedial actions can be taken.
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