Ebrahim Borooshke; Mahmood Arabkhedri
Abstract
Soil erosion and sediment transport is an important issue in many Iranian watersheds. Watershed planning without accurate estimates of erosion and sediment yield with appropriate models is not possible. The objective of this study was evaluating of two common empirical models of MPSIAC and EPM. First, ...
Read More
Soil erosion and sediment transport is an important issue in many Iranian watersheds. Watershed planning without accurate estimates of erosion and sediment yield with appropriate models is not possible. The objective of this study was evaluating of two common empirical models of MPSIAC and EPM. First, 10 small watersheds were selected in Western Azerbaijan Province, with several consecutive check dams on their streams implemented under watershed management projects. No flow over the last downstream check dam was considered as the main criterion in each selected basin. In addition to the direct measurement of sediment deposited behind the dams, sediment yield of watersheds were estimated using the models. Comparison of means using (Mann-Whithney) did not show any significant difference at 0.05 percent level between measured and estimated data. At final step, both models were tested by MAE and MBE statistics. The MPSIAC showed better performance than EPM with MAE=1.34 and MBE =-0.12.
Mahmood Arabkhedri
Abstract
River bed load is usually estimated as a ratio of suspended load due to difficulty in direct measurement. The ratio of bed load to suspended load can be determined more accurately using reservoir sediment bathymetric information. In this research, two successive top bathymetric maps from reservoirs of ...
Read More
River bed load is usually estimated as a ratio of suspended load due to difficulty in direct measurement. The ratio of bed load to suspended load can be determined more accurately using reservoir sediment bathymetric information. In this research, two successive top bathymetric maps from reservoirs of Dez dam (1983 and 1997), and Minab dam (1985 and 1998) as well as suspended sediment data measured at the inflow were analyzed. After determining the position of delta crest and dividing deltaic and lacustrine parts in each reservoir, the volume of sediment were estimated followed by weight calculation based on sediment bulk density. Then, the influence of factors such as the temporal compactness of deposits, the dam sediment trap efficiency, and the contribution of upstream basin and the sub basins adjacent to the reservoir in sediment production was determined. On the other hand, the suspended sediment yield was estimated in Telehzang and Barantyn gauging stations (at reservoirs inflow) using USBR method. In the next step, the ratio of bed load to suspended load was estimated with two scenarios A) by considering the deltaic and lacustrine sediments as bed load and suspended load respectively and B) calculating the bed load by subtracting suspended sediment estimated in reservoir inflow gauge from total deposited sediment. The BLSLR was overestimated as much as 251 and 348 percent in Dez and Minab dams respectively under the Scenario "B" due to underestimation error of suspended load. Under the Scenario "A", the BLSLRs of Dez and Minab were 45 and 56 percent respectively. Two very important uncertainty factors in this method are the dam trap efficiency and bulk density of deposits particularly the deltaic coarse sediment. By changing the trap efficiency from approximately, 95 percent to 60 percent the BLSLRs were decreased from 42 percent to 23 percent in Dez River and from 53 percent to 27 percent in Minab River. A 14 percent cut in bulk density of deltaic deposit in Minab reservoir causes a reduction of seven percent in the BLSLR. Although, large differences are observed among the results of different scenarios, even the minimum ratios are much higher than 15-20 percent BLSLR that are commonly used in water resources studies.
Ebrahim Boroshkeh; Mahmoud Arabkhedri
Abstract
Sediment yield estimation for small basins is essential in watershed management planning projects. However, almost all of these basins are ungauged. In this study, in order to determine a range for specific sediment yield and to develop a regression model for estimating annual sediment yield, sedimentation ...
Read More
Sediment yield estimation for small basins is essential in watershed management planning projects. However, almost all of these basins are ungauged. In this study, in order to determine a range for specific sediment yield and to develop a regression model for estimating annual sediment yield, sedimentation behind small dams within 25 basins in Western Azerbaijan province, were measured. The selected basins with an area ranged 29 to 1200 ha, cover a range of lithology, land uses and climates and all of the sediments had been trapped behind the check dams. The specific sediment yields showed a two digit differences ranged 0.12 and 12 . However, the weighted average of specific sediment yield for all basins was calculated a low value of 1.3. Study of relationship between annual sediment yield and 18 characteristics of watersheds using correlation matrix showed that the sediment yield is significantly affected by geologic erodibility, basin area and land use factors. From several regression models which were developed, an equation including two independent variables, geologic erodibility and basin area, with a high determination coefficient (R2=0.899) was chosen.
Seyed Ali Asghar Hashemi; Mahmood Arabkhedri
Volume 2, Issue 1 , May 2010, , Pages 25-34
Abstract
Evaluation of empirical models for sediment yield in watersheds is a necessity. One of the conventional models in Iran is MPSIAC that has been used extensively. Sediment measurement of small dam's reservoirs is one of the methods for evaluation of these models. In this research, 9 small watersheds were ...
Read More
Evaluation of empirical models for sediment yield in watersheds is a necessity. One of the conventional models in Iran is MPSIAC that has been used extensively. Sediment measurement of small dam's reservoirs is one of the methods for evaluation of these models. In this research, 9 small watersheds were selected in Semnan Province. There is an earth small dam at the outlet of each watershed built in the past 10 years. These dams have not spilled since they were built. Therefore total sediment volume discharged from each watershed was entrapped behind the dams. The amount of deposited sediments in these reservoirs was measured by surveying and estimation of apparent Specific Weight which then compared with estimating values of MPSIAC model by paired t-test. The results showed that the difference between the means for estimated volumes of sediment yield by use of MPSIAC model at the level of 5% had no significant difference while the difference between mean weights of sediments at the level of 5% was significant. Also determination of performance and relative root mean square error showed that MPSIAC model has no appropriate efficiency for application in the region.
