Question

A 10 ha watershed experiences a rainfall of 15 mm, evapotranspiration of 5 mm, infiltration of 4.5 mm, deep percolation of 2.2 mm, detention storage of 0.5 mm, and other abstraction losses of 0.3 mm during the storm event. Neglecting other surface storages, the total overland flow generated from the watershed due to this storm event is _________m\(^3\) (Answer in integer).

Hint:

To calculate overland flow, subtract the losses from the total input. Ensure that the units are converted correctly (e.g., mm to meters or liters).

Answer 1

Given:

• Area of watershed, \( A = 10\, \text{ha} = 100{,}000\, \text{m}^2 \)
• Rainfall, \( P = 15\, \text{mm} = 0.015\, \text{m} \)
• Evapotranspiration = \( 5\, \text{mm} \)
• Infiltration (including deep percolation) = \( 4.5\, \text{mm} \)
• Detention storage = \( 0.5\, \text{mm} \)
• Other abstraction losses = \( 0.3\, \text{mm} \)

Step 1: Total Losses

\( \text{Total losses} = 5 + 4.5 + 0.5 + 0.3 = 10.3\, \text{mm} = 0.0103\, \text{m} \)

Step 2: Effective Rainfall (Runoff Depth)

\( \text{Runoff depth} = 0.015 - 0.0103 = 0.0047\, \text{m} \)

Step 3: Overland Flow Volume

\( Q = A \times \text{Runoff depth} = 100{,}000 \times 0.0047 = \boxed{470\, \text{m}^3} \)