Use of a 3D Hydrodynamic Model in an Incised Urban Channel with Woody Bank Vegetation to Evaluate Pool-Riffle Maintenance: Implications for Stream Restoration Design

The impacts of urbanization have modified natural watersheds and stream hydraulic, hydrologic, and geomorphic processes that have lead to geomorphic and ecological disturbances in natural stream systems. These alterations have resulted in channel incision and the loss of channel-scale hydraulic characteristics responsible for initiating and maintaining pool-riffle bedforms, which are capable of supporting diverse biological stream ecosystems. Through the use of FLOW-3D®, a 3-dimensional computational fluid dynamics model, three scenarios of an urban, incised, and channelized stream were simulated to characterize the turbulent, hydraulic structure during bank-full discharge. Simulations were conducted with trees inhibiting bank-full flow (representing the channels current state), trees removed from the channel, and a restoration design using three clusters of the original trees to initiate flow acceleration-deceleration patterns. The simulations suggested that hydraulic processes found to initiate and maintain pool-riffle sequences, may be restored to impaired urbanized channels for which these processes have been lost. This research can be applied to stream restoration design in hopes to establish less invasive procedures that can be implemented with a higher degree of permanent success.