Runoff Calculation: Determining Infiltration Depth
This problem involves calculating the infiltration depth using the given storm and runoff data for a drainage basin. We need to find the total volume of rainfall and subtract the observed runoff volume to determine the infiltrated volume, then convert this volume back to depth (in mm) over the basin area.
Rainfall Volume Calculation
- Calculate Total Rainfall Depth: The rainfall intensity is uniform during the storm.
Total Rainfall Depth = Rainfall Intensity × Storm Duration
$ \text{Depth} = 16 \text{ mm/hr} \times 5 \text{ hr} = 80 \text{ mm} $
- Convert Units: Ensure consistent units for volume calculation. Convert basin area from km2 to m2 and rainfall depth from mm to m.
Basin Area = $400 \text{ km}^2 = 400 \times (1000 \text{ m})^2 = 400 \times 10^6 \text{ m}^2$
Total Rainfall Depth = $80 \text{ mm} = 0.080 \text{ m}$
- Calculate Total Rainfall Volume:
Total Rainfall Volume = Basin Area × Total Rainfall Depth
$ \text{Volume} = (400 \times 10^6 \text{ m}^2) \times (0.080 \text{ m}) = 32 \times 10^6 \text{ m}^3 $
Since $1 \text{ Mm}^3 = 1 \times 10^6 \text{ m}^3$, the total rainfall volume is $32 \text{ Mm}^3$.
Infiltration Volume and Depth
- Calculate Infiltrated Volume: The infiltrated volume is the difference between the total rainfall volume and the observed runoff volume.
Infiltrated Volume = Total Rainfall Volume - Observed Runoff Volume
$ \text{Volume}_{\text{infiltrated}} = 32 \text{ Mm}^3 - 20 \text{ Mm}^3 = 12 \text{ Mm}^3 $
- Calculate Infiltration Depth: Convert the infiltrated volume back into depth (mm) over the basin area.
Infiltration Depth = (Infiltrated Volume / Basin Area)
First, convert the infiltrated volume to m3: $12 \text{ Mm}^3 = 12 \times 10^6 \text{ m}^3$.
$ \text{Depth}_{\text{infiltration}} = \frac{12 \times 10^6 \text{ m}^3}{400 \times 10^6 \text{ m}^2} = 0.03 \text{ m} $
Convert the depth from meters to millimeters:
$ \text{Depth}_{\text{infiltration}} = 0.03 \text{ m} \times \frac{1000 \text{ mm}}{1 \text{ m}} = 30 \text{ mm} $
Therefore, the infiltration depth is $30 \text{ mm}$.
Important Questions from Hydrology And Water Resources
- A river with $2\text{ km}$ wide flood plain and $10\text{ m}$ channel depth flows with a velocity of $2\text{ ms}^{-1}$. What will be flow condition in the river?
Read the following statements and choose the CORRECT answer.
I. The suspended sediment concentration in rivers is supply-limited rather than hydraulically-limited, when
II. Much suspended material is contributed by overland flow from hillslope erosion
III. Suspended material is entirely derived by turbulent diffusion from the channel bed
- With reference to water in the hydrologic cycle, its residence time is the maximum in
Match the basin types A, B and C with the hydrograph patterns P, Q and R
Basin types Hydrograph pattern A. 
P. 
B. 
Q. 
C. 
R. 
Hydraulic gradient beneath A and B during rainy and dry seasons will
