Coastal and Freshwater


Ecohydraulics is a comparatively recent discipline that merges hydraulic engineering and ecology.

It is the science of how aquatic organisms respond to flowing water, with emphasis on predictive modelling. It builds on purely physical hydraulic models pioneered by engineers, with models of the ecological response of aquatic organisms to hydraulic variables (e.g., depth, velocity, shear stress, etc.).

These models are now key tools in water allocation management. Cawthron is actively involved in model development and applying models to assess the effects of flow change on aquatic organisms (mainly fish, aquatic invertebrates and periphyton).

Cawthron's capability includes:

  • One- and two-dimensional Instream Flow Incremental Methodology (IFIM) and instream hydraulic-habitat modelling (e.g. RHYHABSIM and River2D)
  • Fish drift foraging bioenergetics modelling – linking physical habitat, drift food supply and foraging behaviour to predict net rate of energy intake (NREI) and reach scale carrying capacity
  • Benthic Invertebrate Habitat Time series Simulation (BITHabSim) – for assessing the effects of flow change (especially to mid-range flows) in the context of natural flow disturbance
  • Expert evidence on effects assessment of flow change

Cawthron has been a world leader in the development and application of trout bioenergetics growth models and process-based, flow-related NREI models responding to long-held stakeholder calls for more biologically meaningful models than simple physical habitat models.

Most recently, Cawthron, with assistance from NIWA, developed BITHabSim – which again responded to stakeholders' need for more biologically realistic habitat models taking account of physical and ecological processes.

For more information, contact John Hayes.

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+64 3 548 2319