Which statement best reflects the route choice for minimizing pumping effort in a water shuttle between fill and dump sites?

• A. A 5 mile circular route with downhill fill and uphill dumpsite
• B. A straight route with no elevation change
• C. A 10 mile loop with all uphill segments
• D. A route where both legs are downhill

Answer: (A)

Gravity-assisted routing is what this item tests: using elevation changes to cut pumping effort. The best route is the one where the fill leg is downhill and the dumpsite leg is uphill. The downhill portion lets water flow toward the dumpsite with less or no pumping, so gravity does part of the work for you. You still need to pump on the uphill leg to raise the water to the higher dumpsite, but the overall effort is reduced compared to routes with no elevation change or with all uphill segments. A straight route with no elevation change loses the gravity advantage entirely, making pumping more constant and higher. An all-uphill loop demands significant pumping on every leg. A route with both legs downhill isn’t practical for a shuttle because you’d still need to regain height to complete the cycle.