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Overview |
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Crop Pattern |
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Irrigation |
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Relevant Products |
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The sediment yield potential estimation of Fariabad and Kordian watersheds using MPSIAC model in the GIS framework
Then based on the table 2 and 3,the erosion and sediment yield maps were classified and vectorized and at last polygons with area less than one hectare because these polygons is not executive, were eliminated and their area was added to their adjacent polygons .To providing suspended load and bed load maps and to calculate suspended load and bed load in each subbasin and work units, at first considering the bed load is twenty percent of suspended load,the sediment yield map was divided by 1.2 and at last suspended load map of basin was obtained and then by subtracting suspended load from total load , bed load was obtained in each pixel . At final step by Spatial Analyst module facilities in Arc View software and by introducing work units map and hydrologic units map as the background theme, the amount of sediment total load , erosion , suspended load and bed load was obtained in each pixel .
The providing of work units and erosion shapes maps
To providing work units, only we used the intersection of geology , geomorphology and hydrologic units (sub-basins ) maps and at last 28 work unit in the Fariabad basin and 19 work unit in the Kordian basin were obtained . By interpretation of aerial photographs and the field surveying, 2 erosion form in the Fariabad and 5 erosion form in the Kordian basins were obtained .
Results and discussion
With due attention to the studies and surveying of this watershed, the main reason of erosion in these basins is overgrazing . Thus, with applying the reformatory programs, exclosuring and grazing management, and considering the basin formation, is not sensitive to erosion , we can decrease the basin erosion .The erosion quantity of Kordian basin is higher than Fariabad basin because the sensitive formation and high runoff. In this study to increasing the precision of maps overlaying, more speed in the operation, to prevent increasing of files volume and working with data tables of the maps databases, seven factor (X1 , X2 , X3, X6 , X7 , X8 , X9 ) of nine factors of PSIAC model, were overlayed vectorically .In the rasteric mode to decreasing of files volume , best speed and precision, a best size (5*5) for pixels was defined . with due attention to the obtained results and studied basin conditions, obtained sediment has good accuracy .
Acknowledgement
The authors thanks Mr. Ali Ershadi, the expert of Toosab Company, for his valuable guidances and comments.
Table1.Effective factors on the erosion in the MPSIAC model
| Description |
Equation |
Effective factors |
No |
| X1=Stones sensivity to erosion(0-10) |
Y1=X1 |
Surface geology |
1 |
| K=soil erodibility |
X2=16.67K |
Soil |
2 |
| P2=6-hour rainfall with 2-year return period |
X3=0.2P2 |
Climate |
3 |
| R=runoff heightQp=1-year specific pick discharge |
X4=0.006R+10Qp |
Runoff |
4 |
| S=slope(%) |
X5=0.33s |
Topography |
5 |
| Pb=bare ground percent |
X6=0.2Pb |
Land cover |
6 |
| Pc=crop canopy percent |
X7=20-0.2Pc |
Land use |
7 |
| SSF=the score of soil surface erosion in the BLM method |
X8=0.25SSF |
Surface erosion |
8 |
| SSFg=the score of gully erosion in the BLM method |
X9=1.67SSFg |
Gully erosion |
9 |
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