كليدواژه :
دانهبندي , رسوبات سيلابي , سيستان , فرسايش بادي , فرسايشپذيري
چكيده لاتين :
1-Introduction
The purpose of this research was evaluating the effect of the 120 -day's winds on flood flow entering
deposit to Sistan region. At first, it became clear that flood flow path to Sistan area after the floods and
droughts, according to the file work is randomly sampled from the flood deposits accumulated for a
period of 3 years. Also, high deposit was measured with filed work in two periods before and after the
begining of 120-days winds. In order to study the graded sediment samples and granulometry, the
parameters were determined middle (D50), Mid-average, Kurtosis, Skewness and sorting. For analyzing
the winds of the region WRplot view 8 and the harvest sand rose Software were used. In statistics study
parameters of graded flood flow deposit entering to Sistan shows that the average particle size of
sediment is 88 microns and mainly were fine-grained sediment. By determining the threshold of peak
flow deposits, the frequency of prevailing winds and also draw sand rose of stations points of study,
data shows that the high cumulative flow of sediment erosion affected by winds of 120 days of Sistan
region. As the frequency of winds over speed threshold is 100 percentages to study station. In study of
sediments height, the results showed significant differences at 0.01 levels (p < 0.01) between the
heights average of sediment before and after the beginning of 120 days winds in Sistan region.
Therefore, according to analyzing Granulometry of Sediments transported by floods, determined
threshold and the capability of carrying particles by local winds as well as field measurements, these
deposits are the main resources harvested with starting 120- days winds along with flood flows intering
Sistan region each year, eroding and causing a lot of problems in that region.
2- Methodology
In this research we have provided data about the direction of rivers in Afghanistan country watershed.
We used accessible images of Google Earth for determining peak flow path in the Sistan area and
according to the luck ontinuity of flow in the region, areas that have been affected by flood flow was
determined. In the following, it was found rods of Sistan region. After the floods and droughts, during
field operations, accumulated flood sediments samples were collected randomly. Also, the sediment
level in scale (Sediments transported by floods and depth of drilled by wind sediments carried by wind)
of the 14 points were measured. The above steps have been done during each incoming flow to the
Sistan region during 3 years (2016-2018). To evaluate the constituent particles of sediment in
granulometry, 60 samples were selected and analyzed in Sistan Agricultural, Natural Resources
Research and Education Center lab. In the study of granulometry of sediments taken with respect to
deposits collected by 20 sieves. The estimation depth of accumulated flood sediments for two stages
before and after the 120-day winds flood in summer. Selected by accumulated flood sediments and high
measured sediments. In order to study the graded sediment samples and granulometry, parameters were
determined middle (D50), Mid-average, Kurtosis, Skewness and sorting. For winds of region analysis,
we used WRplot view 8 and the harvest sand rose Software. In statistics study parameters of graded
flood flow deposit entering to Sistan shows that the average particle size of sediment is 88 microns and
mainly were fine-grained sediment.
3- Results
By determining the sediment in granulometry, frequency curve of particle was drowning for
each of the study samples. Drawing on sediment size distribution for each sample, the results of the
study analysis parameters, were estimated the peak flow of sediment into the Sistan region. Based on
the results, the median and mean values of accumulated sediment on the bed river (Sistan River) and
Hamon wetland were phi 6.2 and 6.4, respectively. Changes in these parameters are almost identical,
but in some areas, the median value is greater than the average value which is due to finer grain
particles. The general trend changes two parameters; the mean and median separable in study terms. In
the first year, medians index was more than the average value of the samples taken which indicates that
the presence of fine particles is more than coarse particles percent (the average size of silt). Whereas in
the second year, the average of sediment samples taken increased the size of the fine silt particles
coarser grain and reduced the fine silt particles in much finer grain. In the third year, the mean and
median values are almost identical and fine silt was deposited as sediment size. The result shows that
the tilting parameter values of sediment samples of peak flow was from very good tilting (0.22) until
very weak tilting (2.86). Study of parameter values tilting this parameter indicates the rate of change
between 0.14-0.76.
4- Discussion & Conclusions
In this study, for the first time has survey graded sediment input peak flow in Sistan. Then determine
particle size and analyze the wind of the region, was estimated attrition of the sediments. In examining
sediment samples in granulometry, during study period and the overall changes under the influence of
mean and median and existence fine and coarse particles was perceptible in the overall trend analysis of
these two parameters. Fluctuations in hydrological and hydraulic conditions prevailing in the bed of
peak flow to Sistan area includes Sistan and Frahe rivers are determining particle transport in flood
deposits. In support of this important Morphometry properties including sorting that reflects that the
energy levels in sedimentary environments and energy situation is stable over time shows that the
natural sediment sorting peak flow is not formed under the influence of hydraulic and dynamic
conditions governing the flow of the river. In the other hand, because the rivers are seasonal and alluvial
transmitter rivers transfer flood flows in the Sistan region, decrease the sediments have been sorted
turbulent flow conditions along the river and rapid changes in river flow and erosion phenomenon over
time. The results showed that sediment in granulometry of sediments transported during peak flow is
always fine which has a low threshold velocity and due to the frequency and intensity of wind in the
region, this has eroded sediments which effects of like phenomena dust and endangering the health of
residents. Therefore, according to the analysis in granulometry of sediments transported by the floods
and determined threshold, capability of carrying particles by local winds and field measurement, these
deposits are the main sources of harvest starting with 120 days winds
