Sayed-Farhad Mousavi, Ahmad Mohammad-Zadeh, Ahmad Jalalian, Hossein Samadi-Boroujeni,
Volume 1, Issue 2 (10-1997)
Abstract
One of the most vital problems in the storage and utilization of surface waters for drinking, flood control, hydropower, and agricultural purposes is that of sedimentation in reservoirs and subsequent decline of dam lifetime. The useful lifetime of a dam is defined as the time necessary for approximately 80% of the volume of its initial capacity to be filled by sediments washed in by water. It is a function of the volume of the incoming sediments, specific weight of sediments, and reservoir trap efficiency. Trap efficiency depends on sediment characteristics, life, shape, and rule curves of the reservoir as well as on the capacity-inflow ratio. It is the purpose of the present study to calculate sediment trap efficiency of small dams and also to determine the relationship(s) among the effective parameters in the Chaharmahal and Bakhtiary region. For our purposes, 14 small earth dams (with heights of less than 15 m and capacities of about 1 MCM) were selected around Shahrekord and Borougen. Since no data were available on the erosion and sedimentation for these dams, the MPSIAC empirical model was used to estimate the incoming sediment to the dams' reservoirs. The model considers nine factors effective on erosion and sediment production in each watershed. These factors were analyzed for the watershed of each dam under study and the annual sediment yield was calculated. The amount of sediments retained in the reservoirs as a result of the working life of the dams was estimated by reservoir surveying. The trap efficiency was calculated for all the reservoirs under study. The results obtained revealed that the trap efficiencies for these small dams ranged from 10.4 to 68.9%. New curves were developed and suggested for the trap efficiency of small dams based on these results.
Mehdi Naderi Khorasgani, Zahra Ghanavati Behbahani, Rohollah Fattahi, Hossein Samadi Brojeni,
Volume 30, Issue 2 (7-2026)
Abstract
Water erosion is a great issue in Iran, and due to a lack of reliable and sufficient data for the recognition of vulnerable areas, using models is inevitable. This study was designed for the evaluation of the MPSIAC model in the subbasin of Goharbaran in Chaharmahal va Bakhtiari province. The sediments of the reservoir were surveyed and measured after exhausting the water. Landsat-8 data were applied to study land use changes on soil erosion. During intensive fieldwork, 37 surficial (0-20 cm) soil samples were collected and, after pretreatment, were used for some soil physical and chemical analyses. For the determination of 9 MPSIAC factors, we used library, field, and laboratory data. Multitemporal analysis showed that the quality of rangelands has increased, and the surface area of orchards was doubled within 20 years (1994-2014). Sensitivity analysis indicated that the MPSIAC model was highly sensitive to the river erosion factor, while the least sensitive factor was soil. The sensitivity of the model to the runoff specific peak and soil silt percentage was also very high. Application of the MPSIAC model showed that 48% of soils were in moderate and 36% of soils were in severe sediment yield rate classes. Results of sediment measurements indicated that the specific sediment yield was 11.76 t.ha-1.y-1 during 26 years (1988-2014), while the forecasted value by the MPSIAC model was 5.97 t.ha-1.y-1 Despite others' findings, a lower estimation of the model revealed the need for MPSIAC model calibration before using it in similar environments.
