Final answer:
Impermeable rock affects river discharge by blocking the movement of water, leading to lower discharge. Rocks that are impermeable act as confining layers, preventing water from entering the river through groundwater seepage.
Step-by-step explanation:
Impermeable rock affects river discharge by preventing the flow of water. Rocks that are impermeable act as confining layers, blocking the movement of water through them. This can have a significant impact on river discharge because it reduces the amount of water that can enter the river from groundwater seepage. As a result, the river may have lower discharge compared to if the rocks were permeable.