SEDIMENTATION ISSUES IN THE DEZ DAM RESERVOIR

摘要

The Dez Hydroelectric Power Project is located in the Zagros Mountains in Southwest Iran and was created by the construction, in 1963, of the 203-m high Dez Dam. The project is owned and operated by the Khuzestan Water and Power Authority (KWPA). An underground powerhouse contains eight 65 MW units for a total installed capacity of 520 MW which has generated an average of 2400 GWh/yr over an operating period of 40 years. The minimum reservoir level is elevation 300 m and the maximum controlled level is elevation 352 m. The original reservoir volume was 3315 million m~3, and over an operating period of 40 years the storage volume has been reduced to 2600 million m~3 by sedimentation which corresponded to a volume loss of about 19%. The incoming sediment has formed a delta, which has progressed about half-way down the 50-km long reservoir, as well as bottom set stratified beds near the dam. The sediment level near the dam has risen at a rate of about 2 m/yr over the operating period. As a result the reservoir bed at the face of the power intakes has increased from an original elevation of 180 m to 258 m in 2003, which is only 12 m below the invert level of the power intake at elevation 270 m. There is now concern that sediment will begin to be drawn into the power tunnels within a decade with potential damaging effects on the turbine runners and other water passage elements. In addition, this deposition adjacent to the dam is now about 30 m above the low level outlets within the dam body. This situation has an impact on the physical operations at the dam, including the irrigation outlets, power generation and reservoir operation. To address the project sedimentation issues, several general strategies have been identified, including: 1. Watershed management, such as terracing, tree planting, check structures or small dams. 2. Sediment flushing through upgraded low level outlets.