The main difference between a dam and a run-of-river hydropower plant lies in the way water is managed and utilized for electricity generation:

Dam: A dam is a structure built across a river or waterway to create a reservoir by impounding water. It involves the construction of a large barrier to hold back water, resulting in the formation of a reservoir behind the dam. The stored water is then released in a controlled manner through turbines to generate electricity. Dam-based hydropower plants are often referred to as conventional or reservoir-based hydropower plants.

Pros: Dams can provide a significant amount of stored water, allowing for dispatchable power generation, grid stability, and the ability to respond to fluctuating electricity demand. They can also help with flood control, water storage for irrigation, and recreation activities in the reservoir.

Cons: Building a dam involves significant environmental impacts, such as habitat alteration, loss of ecosystems due to flooding, and potential displacement of communities living in the flooded areas. The construction of large dams can be costly and time-consuming, and they may have a significant ecological and social footprint.

Run-of-River Hydropower Plant: A run-of-river hydropower plant does not involve significant water storage or the creation of a large reservoir. Instead, it utilizes the natural flow of a river or stream to generate electricity. A portion of the flowing water is diverted from the river through a canal or penstock and directed to the turbines, where it generates electricity. The diverted water is then returned to the river downstream.

Pros: Run-of-river plants have a smaller environmental footprint compared to dam-based plants as they do not require the construction of large dams or reservoirs. They generally have lower impacts on water flow, sedimentation, and ecosystem disruption. Run-of-river plants can be more suitable in locations with limited water storage potential.

Cons: Since run-of-river plants rely on the natural flow of the river, their electricity generation capacity can be affected by seasonal variations and changes in river flow. They may have less flexibility in adjusting power generation according to demand compared to dam-based plants with reservoir storage.

In summary, dams are associated with large-scale hydropower plants that involve the construction of a barrier and reservoir, allowing for water storage and controlled release for power generation. On the other hand, run-of-river hydropower plants utilize the natural flow of a river without significant water storage, resulting in smaller environmental impacts but potentially less flexibility in power generation.