An Investigation into the Role of Plant Health Status in Flow-vegetation Interactions: A Case Study on Potamogeton Crispus

Live vegetation is widely used in flume facilities for investigating flow-vegetation interactions because it guarantees a more faithful reproduction of natural systems. However, use of live vegetation introduces a series of questions regarding how to make sure that vegetation behaviour in a laboratory setting is representative of what happens in the natural environment. This is relevant to hydraulic research because environmental conditions typical of flume facilities can affect plant health status, leading to physiological responses that may change biomechanical properties of vegetation and, as a consequence, its hydrodynamics. The objectives of the present study are: (i) to assess the effects of a range of mean flow velocities on the health status of vegetation, and (ii) to assess if the health status of vegetation can have an effect on its hydrodynamic performance.

Experimental investigation was conducted in a laboratory open channel flume at Loughborough University, with focus on a freshwater macrophyte (Potamogeton crispus). Synchronous measurements of instantaneous flow velocities and plant positions were made. Flow velocities were quantified by a pair of Nortek Vectrino+ Acoustic Doppler Velocimeters (ADVs), while plant positions were recorded by a full HD digital camera. Plant health status was assessed by using a chlorophyll fluorometer and measuring the maximum quantum yield of photosystem II on eight leaves. This technique is well established in the botanical literature to study plant photosynthetic activity and obtain information about plant health status.

Preliminary results indicate that mean flow velocities exceeding 0.3 m/s negatively impacted plant health status and higher velocities were associated with stronger impact. Hydrodynamic performance of plants was assessed with focus on static reconfiguration by measuring plant deflected height and by analysing the centroids (or mean vertical positions) along plants. As expected, all plants became more prone as the flow velocity increased. Preliminary results reveal that healthier plants were more efficient at reducing their height exposed to the flow, therefore employing a more streamlined posture.