Friday, August 7, 2009

PS 89-150: A review of instream flow models with recommendations

Philip Harrison, C3


This will be a review and synthesis of Instream Flow Models.  Recommendation for the best models will be made for different model applications. This will enable researchers’ and practitioners’ to choose a model for their study or project. The three models I am most familiar with are PHABSIM, SALMOD and Individual Based Models (IBMs). These models relate discharge to fish habitat (indirectly carrying capacity and population).  This allows the user to run various “what if” and simulations to gain a better understanding of limiting factors and underlying ecosystem interactions’.

PHABSIM is the gold standard of agency model used by USFWS, USGS and some state agencies to manage streamflow (discharge=Q) for competing uses.  PHABSIM determines Weighted Usable Area of stream habitat for you parameter of interest, traditionally for Salmonid Species. In other words how much water can we divert from the stream and maintain a wild trout fishery as opposed to a sport (put and take fishery).

SALMOD was derived from the PHABSIM model and incorporates more of the life history template of the trout species of interest, generally Rainbow, Brown, Brook or Cutthroat trout species. It assumes the Habitat determines the population level of trout based on available modeled habitat (WUA).

IBMs are the most data intensive and complex models of all, but unlike PHABSIM which is largely a hydrologic model, it follows the life cycle of each individual in the model.  This allows for more realistic modeling of limiting factors to come into play such as biological interactions such as competition, predation and there ilk.

We can model what we know and make predictions; this enables us the find gaps in our understanding of the system at hand. We have been studying Salmonids for over 100 years, but how much do we really know about their life history template and what can we reliably predict?  

Results/Conclusions Depending on the study streams' limiting factors and your research question or managment goal a model will be recommended.