The mond river is thelargest and most important river present in Bushehr province and carries a lot of sediments annually through the sea.Therefore, as a part of the studies, due to the presence of the river, the effects of the sediments caused by the Mondriver are of great importance. So, the rivers sediment and hydrologic studies have been implemented. The present report provides the achieved results.
The aim of hydrologic and sediment studies implementation of the Mond river is estimation of input sediment toward the sea in estuary, which inevitably makes us implement basic studies like physiographic, geologic, meteorologic and hydrologic studies of the river. In order to estimate the input sedimentation to the sea, due to the presence of the measuring sediment station of Pol-e-Ghantare and real observed sediment values, indirect methods was used based on suspended load samples of the river, which is due to the sampling time plan by extrapolation method with drawing the sediment measuring curve of daily current flow. In this regard, necessary tools for drawing the sediment measuring curve, are the current and corresponding sediment flow. To do this approach, the considered points, are the best fitting line which is used as the relation between current and sediment flow. Putting the daily flow in the statistical period, the annual average sedimentation rate will be obtained. But because the major part of sampling has been performed in non-flood period, while the most sediment values are carried in this period, an additive coefficient has been used which have been presented in the references as correction of the results of the sediment estimation by measuring curve. So, considering this coefficient, the annual suspended load of the Mond watershed basin, up to the location of Ghantare station equals to 11438426 ton per year.
Regarding the lack of the needed information to examine the moving sediments in the river beds, usually the bed load coefficient is considered between 20-30 percent of the suspended loads. Considering that close to the endof the Mond watershed basin, the river passes through large and mild slope flood plains, the value of 20 percent will be more reasonable and appropriate. So, considering 20% of the achieved value for adjusted suspended load, the bed load sediment weight also will be determined, hereby, this value is 2287685 ton year. Therefore, the total sediment load up to the location of Pole-Ghantare station will be equall to 13726112 ton per year.
Regarding that the area of the rest of the Mond watershed basin from Ghantare station up to the basin outlet equals to 3627.96 km2, the area’s sediment portion, must be added to the previous computations. In these cases by the determination of the special sediment, and by generalization it, the downsream basin sediment could be computed. considering the value of 13726112 ton per year and also the Mond basin area up to Ghantare station location (36500.4 km2), the special sediment of this basin is estimated as 376.05 ton per year. On the other hand, the downstream basin of Ghantare station up to the outlet end to the basin has the area of 3627.96 km2. Based on this value, the total sediment of the down stream basin, of Ghantare station up to the Khalig area, equals to 1364308 ton per year.
Therefore, the total sediment amount of the Mond basin equals to sum of the river upstream basin up to Ghantarehydrometry station total sediment and also total sediment of the down stream basin of Ghantare station up to the outlet end of the basin to Khalij which equals to 15090420 ton per year. If we consider the average density of the present sediments equals to 1.3 gr/cm3, the total output sediment volume of the basin will be 11608015 m3per year. Table (1) shows the computational values of the Mond basin sediments.
Table1.The results of the weight and volume calculation of the output sediment of the Mond basin
Now the sedimentation Cofficient or SDR is needed to determine the erosion rate in the Mond watershed basin. In order to estimate the sedimentation coefficient value in this study, one of the first category relations which have been designed based on the basin area was used.
where A and SDR are the basin area versus mile2 and sedimentation coefficient versus percent respectively.
Regarding theMond watershed basin area up to Ghantare station location which is 36500.4 km2 and from the station the area is 14092.8 mile2, the sedimentation coefficient value of this basin up to the station will be 18.12 percent. Based on this coefficient, the erosion value and special erosion of the whole basin up to Pole-Ghntare station, have been estimated, the results of which have been presented in table 2.
Table 2- The results of erosion and special erosion of the Mond basin up to Pole-Ghantare station location.