Question

In the context of the effect of drainage density on the run-off generation and the hydrograph at the catchment outlet, all other factors remaining the same, pick one or more CORRECT statement(s):
 

• A. Lower drainage density results in higher peak in flood hydrograph compared to that when the drainage density is higher.
• B. Lower drainage density results in lower peak in flood hydrograph compared to that when the drainage density is higher.
• C. Lower drainage density results in a flood hydrograph with a longer time base compared to that when the drainage density is higher.
• D. Lower drainage density results in a flood hydrograph with a shorter time base compared to that when the drainage density is higher.

Hint:

High drainage density results in faster, sharper hydrographs; low drainage density causes slower, flatter hydrographs with longer duration.

Answer 1

The Correct Option is B, C

Drainage density is defined as the total length of streams per unit area of the watershed. It significantly influences the shape of the flood hydrograph:

- Lower drainage density indicates fewer channels and longer flow paths. As a result: - Runoff takes longer to reach the outlet,
- Peak discharge is lower,
- Time base of the hydrograph is longer.
Hence: - Option (B) is correct — lower drainage density leads to lower peak discharge.
- Option (C) is correct — lower drainage density leads to longer duration of flow.
- Option (A) is incorrect — lower drainage density causes a lower, not higher, peak.
- Option (D) is incorrect — it reverses the effect on time base.