A river is high in winter and low in August. A city wants to store its own wet-season river water for use in late summer. What intervention directly provides that storage?

A reservoir is kept partly empty before the rainy season. During a major storm, what benefit does that unused capacity provide downstream?

Water falls through a dam from a high-elevation reservoir. Which facility converts that moving water into electricity?

An irrigation district needs to deliver water to farms after the river's spring runoff has ended. Which dam operation provides that benefit?

A reservoir stores 24 million liters of water for a dry season. If a town withdraws 3 million liters each month, for how many months can the stored water meet that demand?

A dam blocks a navigable river used by cargo barges. Which structure lets barges move from the water level below the dam to the reservoir above it?

A county builds a dam that floods a valley and forms a large lake. Besides water storage, what new human use does the impoundment directly provide?

A large dam traps sediment that once reached a river delta each year. What is the likely long-term downstream effect?

A dam without fish passage is built across a river where salmon swim upstream each year to spawn. What is the most direct effect on the salmon?

In a hot, dry watershed, a new reservoir has a much larger water surface than the original river channel. Which cost is likely to increase?

A reservoir is filled over a forested river valley. What environmental cost occurs in the flooded area?

A dam reduces the seasonal floods that used to spread across a downstream floodplain. What change is most likely on that floodplain?

Over decades, sediment accumulates behind a dam. How does this affect the reservoir's water-supply function?

A dam releases unusually cold bottom water into a river during summer. What ecological cost can result for native fish?

A hydropower dam releases bottom water with low dissolved oxygen. Which downstream condition is the most immediate concern?

What does reverse osmosis do in a desalination plant?

A coastal desalination plant discharges concentrated brine near its ocean outfall. What environmental concern does this create?

Why does seawater reverse-osmosis desalination have substantial operating energy costs?

Compared with modern membrane desalination, why is thermal desalination generally more energy-intensive?

Saltwater intrusion has made a coastal community's groundwater brackish. What trade-off describes desalinating that groundwater?

A drought-prone coastal city considers seawater desalination. What benefit and cost are correctly paired?

A rural community has very limited electricity capacity for a new water-supply project. Which option is least suited because of its heavy reliance on energy input?

An inland town has a sustainable freshwater aquifer and no access to seawater or brackish water. Why is desalination a poor fit compared with a groundwater well?

A farm district must move river water 40 kilometers to fields. Which option directly accomplishes delivery, and what is its key environmental trade-off?

A coastal metro must add drinking water without withdrawing freshwater from any river. Which option meets that condition, and what cost accompanies it?