The Seagrass Ecology Lab, located at Kristineberg marine station in Sweden, houses a hydraulic flume for studying the flow of water in a simple channel. The flume is capable of generating waves and currents to replicate conditions present in shallow coastal environments. It is a valuable tool for investigating the interactions between hydrodynamics and organisms, as well as sediment dynamics, wave propagation and turbulence.

The flume is constructed from PVC and plexiglass and is open-topped, measuring 8 m in length, 0.5 m in width, and 0.5 m in height. A test section box, 2 m in length and located at the bottom of the tank, is filled with sediment (eg, mud, sand, gravel, rocks, etc).

One unique feature of the flume is its ability to be filled with sea water from the fjord, as well as fresh water from the tap or a mix of seawater and tap to simulate brackish environments. The water temperature can be increased with resistances or reduced with a chiller. In addition, CO₂ gas can be pumped in the water to reduce the pH, if required. The flume can hold up to 1500 L of water, where the filling height is 20-30 cm.

A wooden frame beneath the plastic and plexiglass construction elevates the flume and improves accessibility. A large pipe runs between the rack, creating currents within the flume. This design allows water to flow continuously without reflecting back to the end. The pipe also features a valve for draining the water, which is beneficial when working with sensitive organisms and requiring specific water temperature and salinity.

Currents

The hydraulic flume is capable of generating unidirectional flow or currents, which can be adjusted by controlling the motor revolutions per minute (RPM) that determine the flow velocity of the water. The motor is connected to a propeller located at the end of the flume, which creates the currents that flow through the pipe below the flume. To ensure a laminar flow, two elements consisting of tubes and straws are positioned at the beginning of the flume.

Waves

Oscillatory flow or waves in the flume are generated using an electric piston, which is mounted on a rolling cart. The length and speed of each piston stroke can be controlled electronically to modify the paddle speed and paddle stroke, thereby allowing for the creation of waves with different characteristics. The wave frequency is also controlled from a computer that regulates the forward and backward stroke velocity of the wave paddle. To reduce reflections of wave energy, a beach is located at the opposite end of the flume, which is designed to dissipate wave energy using a thick porous mat placed at a 15-degree angle. This design effectively damps wave energy, reducing the impact of reflections and enabling more accurate studies of wave dynamics.

An Acoustic Doppler Velocimeter (ADV) Nortek Vectrino is available in the lab and is a highly useful tool for measuring fluid velocities and turbulence in a hydraulic flume. ADVs can be used to precisely measure the velocity and direction of water flow, which can provide valuable information for a wide range of scientific and engineering applications. For example:

• Measuring water velocity and turbulence in hydraulic flumes or other flow systems
• Studying the behavior and physiology of marine organisms in relation to water flow patterns
• Investigating how marine organisms interact with different flow environments (e.g. bottom roughness)
• Developing models and simulations of flow-organism interactions (e.g. transport, feeding, swimming)
  
• Monitoring the effects of anthropogenic disturbances (e.g. ocean acidification, climate change, pollution) on flow patterns and organism behavior
• Evaluating the effectiveness of artificial structures (e.g. breakwaters, reefs) in altering flow patterns and providing habitat for marine organisms
• Assessing the impact of hydrokinetic energy devices (e.g. tidal turbines) on water flow and marine ecosystems
• Characterizing the flow of sediment and other particles in aquatic environments
• Studying the dynamics of rivers and other natural water systems.

Wave gauge (HR Wallingford) are availabe in the lab  to measure the height and frequency of waves in a flume or other body of water. There are different types of wave gauges available, but most work by detecting changes in water pressure caused by the passage of waves. The data collected by wave gauges can provide important information about wave behavior and the effects of waves on structures and marine ecosystems. In hydraulic flumes, wave gauges can be used to study the effects of wave energy on sediment transport, coastal erosion, and other processes, and to test the performance of coastal engineering structures such as seawalls or breakwaters.