How does drainage density affect the speed and magnitude of runoff in a basin?

How does drainage density affect the speed and magnitude of runoff in a basin?

• A. Lower drainage density increases peak discharge.
• B. Higher drainage density provides more channels to convey water, reducing travel time and increasing peak discharge.
• C. Drainage density does not influence runoff characteristics.
• D. Higher drainage density reduces channel network length and runoff velocity.

Answer: (B)

Drainage density is a measure of how many channels exist per unit area, so a basin with many streams is highly dissected. When drainage density is high, water from rainfall has many nearby paths to reach the outlet, shortening the travel time to the stream network. This quick concentration of flow makes the runoff respond rapidly, producing a steeper hydrograph with a higher peak discharge for a given rainfall event. In contrast, low drainage density means fewer channels and longer distances for water to travel, which slows the response and typically yields a lower, more protracted peak. Therefore, the statement that more channels convey water, reduce travel time, and increase peak discharge best describes how drainage density affects runoff speed and magnitude.

Drainage density is a measure of how many channels exist per unit area, so a basin with many streams is highly dissected. When drainage density is high, water from rainfall has many nearby paths to reach the outlet, shortening the travel time to the stream network. This quick concentration of flow makes the runoff respond rapidly, producing a steeper hydrograph with a higher peak discharge for a given rainfall event. In contrast, low drainage density means fewer channels and longer distances for water to travel, which slows the response and typically yields a lower, more protracted peak. Therefore, the statement that more channels convey water, reduce travel time, and increase peak discharge best describes how drainage density affects runoff speed and magnitude.