If two rivers have drainage basins of about equal size, the river with higher discharge is explained by what factor?

• A. The basin receives more rain
• B. The basin has steeper gradient
• C. The basin has more downstream obstacles
• D. The basin is longer

Answer: (A)

Discharge is the amount of water moving past a point per unit time, which mostly reflects how much water enters the river system from precipitation. If two drainage basins are about the same size, the one that receives more rainfall produces more runoff and therefore a higher downstream discharge. Steeper gradient speeds up the water but doesn’t increase the total volume entering the river, so it affects timing and velocity rather than the overall discharge. Upslope obstacles or dams can delay flow and store water temporarily, altering when peak discharge arrives but not necessarily raising the total discharge. A longer basin can lose more water to evaporation and infiltration along its length, which can reduce discharge rather than increase it. So the higher discharge is best explained by more rainfall in that basin.