Module
River Hydromechanics Fundamentals
Flow, Velocity and Channel Characteristics
- Average river flow is calculated as: Width × Depth × Velocity.
- Water flow/volume is measured in cubic metres per second (m³/s).
- The greater the river slope, the greater the water velocity.
- Water speed is mainly determined by volume, gradient, nature of the channel bed and constrictions in channel.
- Water velocity is greatest in the middle of the river just beneath the water surface.
- Water flow in natural riverbeds is usually slower than in man-made channels.
- Laminar flow: the fastest water is closest to the surface and the slowest water is close to the river bed.
River Hazards and Formations
- More obstacles in the river pose a greater entrapment hazard.
- A hydraulic hole/stopper occurs when the river current flows over an obstacle submerged just at the right depth beneath the water surface.
- An eddy is a horizontal turn of the water flow where the water flows back towards the obstacle.
- Eddies occur behind obstacles in the river.
- A siphon is water running through a submerged hole, for example, a hole between two neighbouring rocks leaning against each other.
- On the upstream side of a mid-stream rock you will find a cushion wave.
- A greater mass of water stream increases the objective risk of accidents.
- Subjective risks include overestimation, bad anticipation, and underestimation of objective hazards.
River Navigation and Orientation
- The left bank is to our left when viewing downstream.
- The scale of river difficulty covers six levels.
- Difficulty level IV means Very difficult.