The unit hydrograph due to a storm may be obtained by dividing the ordinates of the direct runoff hydrograph by A. direct runoff volume B. period of storm C. total rainfall D. none of the above

The correct answer is: A. direct runoff volume.

A unit hydrograph is a hydrograph that represents the runoff from a unit storm of a specified duration and intensity. It is obtained by dividing the ordinates of the direct runoff hydrograph by the direct runoff volume.

The direct runoff hydrograph is a hydrograph that represents the runoff from a storm. It is obtained by subtracting the base flow from the total hydrograph.

The period of storm is the length of time that the storm lasted.

The total rainfall is the total amount of rain that fell during the storm.

None of the above options are correct because they do not represent the direct runoff volume.