An Assessment of an Unsuccessful Restoration Project for Lake Sturgeon Using Three‐Dimensional Numerical Modelling

Abstract

AbstractDespite a widespread acknowledgment that river restoration projects sometimes fail due to a poor understanding of geomorphology and hydrology, there are relatively few published case studies reporting failures, particularly for nonsalmonid species such as Lake Sturgeon Acipencer fulvescens. We used a three‐dimensional hydrodynamic model to retroactively assess a restoration project in the 80‐m‐wide Ouareau River, Quebec which did not meet its objective of providing additional spawning habitat for Lake Sturgeon. Virtual modifications of the bathymetry allowed for the flow field to be simulated with and without instream structures (boulder weirs) constructed in 2007 for four discharges representing flow conditions during spawning. Simulated velocities and flow depths were used to determine the suitability of the site and to assess the impact of the instream structures. Results revealed that instream structures did not meet the expectation of raising water levels and had no significant impact on river velocity. Furthermore, there was sufficient good quality habitat within the study area before restoration, and artificial spawning sites were placed in locations with nonoptimal velocities for spawning Lake Sturgeon. A comparison with a successful Lake Sturgeon restoration project in the St. Clair–Detroit River system revealed marked differences in restoration strategies, which likely explain the different outcomes of these two projects. These results point to the need for (1) adaptive management protocols that include an iterative decision‐making process to allow for adjustments in hypotheses and strategies to improve the management process, (2) multidisciplinary input, including hydrogeomorphology, and (3) a more systematic use of two‐dimensional or three‐dimensional numerical models prior to the implementation of instream structures in river restoration projects.