Gomal Zam Dam Project Details and Structural Engineering

Introduction

The Gomal Zam Dam is a multi-purpose gravity-arch dam constructed on the Gomal River in the South Waziristan District of Khyber Pakhtunkhwa, Pakistan. Standing as a monument to modern roller-compacted concrete (RCC) engineering, the dam serves primary functions of flood control, irrigation, and hydroelectric power generation. In this article, we examine the structural features, design specifications, and engineering challenges encountered during its development.

Design Specifications and Geology

The dam is situated in a narrow, steep-sided gorge of the Gomal River. This geological layout is ideal for a gravity-arch configuration, where structural loads are shared between gravity action and arch action transferring forces directly into the solid rock abutments. The main structural parameters include:

• Dam Type: Roller-Compacted Concrete (RCC) Gravity-Arch.
• Height: 133 meters (436 feet) from the foundation.
• Crest Length: 231 meters (758 feet).
• Crest Width: 8 meters.
• Reservoir Capacity: Approximately 1.14 million acre-feet (1.41 billion cubic meters).

Roller-Compacted Concrete (RCC) Technology

Using RCC instead of conventional mass concrete significantly accelerated the construction timeline and lowered material costs. RCC is placed using earth-moving and compaction equipment in thin, horizontal layers. Due to the low water-cement ratio, strict thermal control measures were implemented to prevent mass cracking. Post-cooling pipes and fly-ash admixtures were utilized to control the hydration temperature peak.

Seismic and Hydraulic Safety

Located in a seismically active zone close to the Sulaiman Range, the dam was designed to withstand a Maximum Credible Earthquake (MCE) using finite element analysis (FEA) to simulate dynamic stresses. The spillway structure features an ungated overflow crest designed to handle extreme flood events (PMF – Probable Maximum Flood) safely, discharging water into a plunge pool below to dissipate kinetic energy and protect the river bed from erosion.