• SCS-CN Runoff Curve Number Theory:
• Assertion (A): The lower and upper limit of the curve number corresponds to 0 and 100. $\implies$ True.
• The dimensionless runoff Curve Number ($CN$) ranges theoretically from 0 to 100.
• Reason (R): The lower curve number corresponds to highest runoff potential and indicates an impermeable surface. $\implies$ False.
• $CN = 100$ represents completely impermeable surfaces (water bodies, asphalt) with 100% runoff potential. A low $CN$ (approaching 0) indicates maximum soil infiltration and minimum runoff potential.
• Conclusion: In official key, Option 1 was keyed; scientifically (A) is true but (R) is false.

Correct option: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)

• Design Criteria for Vegetated Grassed Waterways:
• For hydraulic design of grassed waterways using Manning's equation, the roughness coefficient for dense retardance grass cover is taken as $n = 0.04$. (True)
• Grassed waterways are non-scouring open channels designed to safely carry peak runoff from a storm of 10-year recurrence interval. (True)
• Waterways are constructed along the natural drainage depression (along the slope), not across the land slope, to safely convey discharge downhill. (False)
• Conclusion: Statements (A) and (B) only are correct (Option 1).

Correct option: (1) (A) and (B) only.

• Aerodynamic Design of Shelterbelts and Windbreaks:
• shelterbelt reduces downwind wind speed over a leeward distance proportional to its height ($H$).
• To prevent wind eddies from wrapping around the flanks and eroding protected fields, the minimum continuous length of a shelterbelt should be at least 24 times its height ($24 H$).
• Conclusion: 24 (Option 2).

Correct option: (2) 24

• Drainage Coefficient Calculation:
• Drainage Coefficient ($DC$): Depth of excess water removed from the drainage area in a 24-hour period (mm/day).
• Given:
• Area: $A = 1 \text{ hectare} = 10,000 \text{ m}^2$
• Discharge rate: $Q = 1 \text{ m}^3/\text{hour}$
• Daily volume of water drained (in 24 hours):

$$V = 1 \text{ m}^3/\text{hr} \times 24 \text{ hrs} = 24 \text{ m}^3$$

• Depth of water removed per day:

$$DC = \frac{V}{A} = \frac{24 \text{ m}^3}{10,000 \text{ m}^2} = 0.0024 \text{ m/day}$$

• Converting meters to millimeters ($1 \text{ m} = 1000 \text{ mm}$):

$$DC = 0.0024 \times 1000 = 2.4 \text{ mm/day}$$

• Conclusion: The drainage coefficient is 2.4 mm (Option 2).

Correct option: (2) 24mm