Karun-3 Dam: Iran's Tallest Dam in the Zagros Mountains

**Karun-3 Dam** on the Karun River in Khuzestan Province, southwestern Iran, is the tallest dam in Iran at **205 meters** and one of the tallest double-curvature arch dams in the world. Completed in **2005**, it generates **2,000 MW** of hydroelectric power from eight turbines, making it the most powerful hydroelectric station in the country.

Introduction

The dam is part of a cascade of dams on the Karun River, Iran's most voluminous river, which descends from the snow-capped Zagros Mountains through a series of dramatic gorges before reaching the lowland plains of Khuzestan and emptying into the Shatt al-Arab waterway near the Persian Gulf. The Karun cascade is the backbone of Iran's hydroelectric system, generating roughly 70 percent of the nation's hydroelectric power.

Engineering & Structure

• Type: Double-curvature arch dam
• Height: 205 meters
• Crest Length: 462 meters
• Concrete Volume: 1.55 million m³

Karun-3's slender arch spans 462 meters across a narrow limestone gorge in the Zagros Mountains. The double-curvature design efficiently transfers the reservoir's pressure into the competent limestone abutments, requiring only 1.55 million cubic meters of concrete. The dam's maximum base thickness is about 29 meters, tapering to approximately 5.5 meters at the crest.

The underground powerhouse contains eight 250 MW Francis turbines, accessed through tunnels bored into the mountain. The dam's spillway system includes two chute spillways capable of discharging 5,800 cubic meters per second, designed to handle the Karun's extreme spring flood flows generated by snowmelt in the Zagros highlands.

Geographic Setting

• River: Karun River
• Location: Izeh County, Khuzestan Province, Iran
• Coordinates: 31.98°N, 49.93°E
• Reservoir Area: 48 km²

The Karun River originates in the Bakhtiari Mountains of the central Zagros range, at elevations exceeding 3,500 meters, and flows approximately 950 kilometers to the Persian Gulf lowlands. The dam site is located in a dramatic limestone gorge where the river has cut through folded Cretaceous and Tertiary rock formations, creating walls that rise steeply on both sides.

The Zagros Mountains, stretching 1,600 kilometers across western Iran, receive substantial precipitation — 500 to 1,000 millimeters annually — mostly as winter rain and snow. This precipitation feeds the Karun and makes it the most voluminous river in Iran, with an average annual discharge of approximately 14.8 cubic kilometers. The reservoir extends 60 kilometers into the mountain valleys, surrounded by oak forests and nomadic pasturelands.

Hydroelectric Power

• Installed Capacity: 2,000 MW
• Annual Output: ~4.1 TWh
• Turbines: 8 × 250 MW Francis turbines
• Karun Cascade: ~4,500 MW total across four major dams

Karun-3's eight turbines generate approximately 4.1 terawatt-hours per year, making it the single largest hydroelectric contributor to Iran's grid. The dam operates as part of a four-dam cascade on the Karun — including Karun-1 (1,000 MW), Karun-3 (2,000 MW), Karun-4 (1,000 MW), and the older Masjed Soleyman Dam — that collectively produce roughly 4,500 MW.

Iran's electricity grid is dominated by natural gas-fired thermal plants, but the Karun cascade provides critical peaking and load-following capacity, ramping up quickly during demand surges. The hydroelectric output also helps Iran manage its natural gas consumption during hot summer months when both electricity demand and gas use for cooling peak simultaneously.

Environmental & Social Impact

• People Displaced: ~4,000
• Bakhtiari Nomads: Seasonal migration routes disrupted
• Sedimentation: Karun carries heavy sediment loads from Zagros erosion

The Karun-3 reservoir displaced approximately 4,000 people, primarily from small farming and nomadic communities in the mountain valleys. The Bakhtiari people, Iran's largest nomadic pastoral tribe, have historically used the Zagros valleys and mountain passes for seasonal migration with their livestock. The reservoir and associated roads disrupted some of these ancient migration corridors.

Sedimentation is a significant challenge for the Karun cascade. The Zagros Mountains are geologically young and actively eroding, sending large volumes of fine sediment into the river. This sediment accumulates in the reservoirs, gradually reducing their storage capacity and potentially clogging intake structures. Managing sedimentation is a long-term operational concern for all dams on the Karun system.

Key Facts

• Karun-3 is the tallest dam in Iran at 205 meters.
• Its 2,000 MW capacity is the largest of any hydroelectric station in Iran.
• The dam is part of a four-station cascade on the Karun generating ~4,500 MW total.
• The Karun is Iran's most voluminous river, originating in the Zagros Mountains.
• The Zagros limestone gorge provides excellent rock abutments for the arch design.

Fun Facts

• The Zagros Mountains are home to the oldest known evidence of winemaking, dating back over 7,000 years, found in the valleys upstream of the Karun dams.
• The Bakhtiari nomads, whose migration routes were affected by the dam, are famous for their annual migration across the Zagros — one of the most grueling pastoral journeys in the world.
• Karun-3's reservoir is strikingly turquoise-colored, a result of the dissolved limestone minerals in the water.

Final Thoughts

Karun-3 Dam harnesses the power of Iran's mightiest river in one of the world's most geologically dramatic mountain ranges. As the tallest and most powerful dam in a critical cascade system, it is central to Iran's electricity supply — though sedimentation and climate-driven changes to snowpack in the Zagros Mountains pose growing challenges.