Soil-Water-Plant Relationships

• 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.

• NRCS-SCS Hydrologic Soil Groups (HSG) Classification:
• In the SCS Curve Number method, soils are categorized into four hydrologic groups based on minimum infiltration capacity and runoff potential:
• Group A (Low runoff potential): Deep sands, gravels with high infiltration rates ($\gt 7.6\text{ mm/h}$) and rapid water transmission.
• Group B (Moderately low runoff potential): Moderately deep to deep sandy loams and loams with moderate infiltration ($3.8 - 7.6\text{ mm/h}$).
• Group C (Moderately high runoff potential): Soils with low infiltration rates ($1.3 - 3.8\text{ mm/h}$) having shallow layers impeding downward drainage, clay loams, and shallow sandy clays.
• Group D (High runoff potential): Heavy clay soils with high swelling potential, claypans, and high water tables ($\lt 1.3\text{ mm/h}$).
• Conclusion: Group C represents Moderately high runoff potential (Option 3).

Correct option: (3) Moderately high runoff potential