In open channel flow, when the actual depth of water is greater than the critical depth, the flow is classified as sub-critical. In this state, the flow velocity is relatively low, and the Froude number is less than one.

Specific gravity is defined as the ratio of the density of a substance to the density of a reference substance, which is pure water. Since the density of water is used as the standard reference, the specific gravity of water itself is exactly 1.0 at standard temperature and pressure conditions.

The hydrostatic force on a vertical surface is calculated by multiplying the pressure at the centroid by the area. For a vertical wall of height H, the pressure distribution is triangular, resulting in a total force of F = (1/2) * w * H^2, where w is the specific weight of water. The provided option C represents this mathematical relationship.

A hydraulic jump is a phenomenon in open channel flow where liquid at high velocity discharges into a zone of lower velocity, resulting in a sudden rise in the liquid surface. This transition typically occurs when flow changes from supercritical to subcritical (streaming) flow, effectively dissipating kinetic energy through turbulence and preventing downstream erosion in irrigation structures.

Chezy's formula, expressed as Q = Ac√(RS), is a foundational equation in fluid mechanics used to estimate the velocity and discharge of water in open channels. In this formula, 'A' represents the cross-sectional area, 'c' is the Chezy coefficient reflecting channel roughness, 'R' is the hydraulic radius, and 'S' is the slope of the energy line.

A venturimeter is a highly efficient flow measurement device. Due to its gradual convergence and divergence design, it minimizes energy losses, resulting in a high coefficient of discharge, typically ranging between 0.95 and 0.99, indicating very low frictional resistance.

In sanitary engineering, maintaining a specific velocity range is crucial. A minimum velocity of approximately 0.6 to 1.0 m/s is typically required to prevent the deposition of solids (self-cleansing velocity), while the upper limit is set to prevent excessive scouring or erosion of the sewer pipe material. The range of 1 to 3 m/s is a standard design guideline for gravity sewers to ensure efficient transport of wastewater.

Unlike liquids, where viscosity decreases as temperature rises, the viscosity of gases increases with temperature. This occurs because higher temperatures increase the kinetic energy of gas molecules, leading to more frequent and energetic collisions between them, which effectively increases the internal friction or resistance to flow within the gas.

The Darcy-Weisbach equation is a fundamental formula used to calculate the loss of head due to friction in a pipe. The formula is expressed as hf = (f * L * v^2) / (2 * g * d), where f is the friction factor, L is length, v is velocity, g is gravity, and d is diameter.

The meandering pattern of a river is shaped by the dominant discharge, which is the flow rate that performs the most geomorphic work over time. While extreme floods occur, the dominant discharge is the most effective at transporting sediment and shaping the channel morphology.