Irrigation Engineering MCQ Questions & Answers | Civil Engineering

A fall is a structure constructed across a canal to lower the water level and dissipate surplus energy caused by a difference in bed levels.

A low weir fall is specifically designed to maintain the depth of flow in the canal. It allows water to flow smoothly over a broad-crested weir while keeping the upstream depth nearly constant.

This type of fall helps in energy dissipation and prevents scouring and erosion downstream by stabilizing the flow conditions.

Trapezoidal notch fall and rectangular notch fall are primarily used for measuring discharge and controlling flow rather than maintaining depth.

Hence, among the given options, the fall that maintains its depth is the low weir fall.

Therefore, the correct answer as per exam and technical standards is Option B: A low weir fall.

The correct answer is Option A: 0.2 x 10⁶
The question involves understanding S-curve hydrographs and their relationship to unit hydrographs.
An S-curve hydrograph is created by summing an infinite series of unit hydrographs, each lagged by a duration equal to the unit hydrograph duration.
In this case, we have a 6-hour unit hydrograph.
The equilibrium discharge of the S-curve represents the constant rate of runoff when the rainfall continues indefinitely at a rate of 1 cm (or 1 unit) over the basin for the duration of the unit hydrograph.
The equilibrium discharge (Q_eq) is calculated as:
Q_eq = (Area of catchment x Rainfall depth) / Duration of Unit Hydrograph
Where, Area = 120 km² = 120 x 10⁶ m²
Rainfall depth = 1 cm = 0.01 m
Duration = 6 hours
Q_eq = (120 x 10⁶ m² x 0.01 m) / 6 hours
Q_eq = (1.2 x 10⁶ m³) / 6 hours
Q_eq = 0.2 x 10⁶ m³/hour
Therefore, the equilibrium discharge of the S-curve is 0.2 x 10⁶ m³/hour.