Hydroelectric power uses falling or fast-flowing water to turn turbines. Pakistan’s northern relief and Indus river system provide major opportunities, especially where steep gradients and large seasonal flows combine. Large dams are often multipurpose, supplying irrigation storage, flood regulation and electricity.

How hydel power is generated

Water stored behind a dam has gravitational potential energy. It flows through an intake and penstock, turns a turbine and drives a generator. A transformer raises voltage for transmission. Run-of-river schemes use river flow with less storage, while reservoir schemes regulate output more strongly.

Output depends on water discharge and head, the vertical drop through which water falls.

Physical conditions

Suitable sites need reliable river flow, a steep gradient or narrow valley, strong stable rock and a catchment capable of supplying water. High sediment load can reduce reservoir capacity and damage turbines. Earthquake risk and landslides must be assessed.

Pakistan’s northern and north-western highlands offer steep relief, while the Indus and tributaries provide large flows.

Human conditions

Large schemes need capital, engineering, roads, transmission lines, resettlement planning and long construction periods. Political agreement over water allocation and benefit sharing is important. Demand must justify the project.

Small and micro-hydel plants can serve remote valleys where grid extension is expensive, but they need local maintenance and reliable seasonal flow.

Multipurpose benefits

Tarbela and Mangla are major examples of multipurpose storage. Reservoirs can provide irrigation water, hydel electricity and some flood control. They may support fisheries, tourism and water supply.

However, one objective may conflict with another. Keeping space for flood control may reduce stored water; irrigation timing may differ from peak electricity demand.

Limitations and impacts

Construction can displace settlements, flood farmland and habitats, interrupt fish movement and change downstream sediment. Reservoirs lose capacity through siltation and lose water by evaporation. Drought reduces output.

Catchment management, sediment control, fair compensation, environmental flow and coordinated reservoir operation reduce but do not remove impacts.