Mapping and SSessment of wind Erosion in central

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Mohammed Ahmed, Hussien
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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 v 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. vi - 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.