Thanos Papanicolaou
IIHR - Hydroscience & Engineering, The University of Iowa

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Application Note: Watershed Studies
 
Watershed dynamics: Many watershed simulations today work in the batch world; an event is simulated based on a static set of field data.  If newer data become available, the simulation is simply rerun. For example, hydrodynamic and sediment transport simulations to predict geomorphologic changes within a stream and the impact of these changes to the aquatic life are conducted by considering a constant sediment input value from terrestrial sources such as roads, floodplains, and other natural occurring disturbances (i.e., landslides, fires).  As a result perturbations that exist in the system due to the spatial and temporal variability in the terrestrial sediment input are not accounted.  Very few applications use real time data even if the capability to do so is available.  A great effort has been recently devoted to run simulations faster than real time based on static data sets.  However, this is highly inefficient and leads to multiple sediment predictions that are conflicting when major events are predicted.  This lack of ability to dynamically inject data into simulations and other applications, as these applications execute, limits the analysis and the predictive capabilities of these applications.  The novel capabilities to be sought here are application simulations that can dynamically accept and respond to on-line field data and measurements and/or control such measurements.  This synergistic and symbiotic feedback control-loop between simulations and measurements is a novel technical direction that can open domains in the capabilities of simulations within watersheds that can facilitate the “capturing” of episodic catastrophic events. 
   
Microtopography: Bedforms, clusters, step and pools are few examples of complicated microtopography in watersheds. These bed features are produced by the interaction of flow structure and entrainable sediment.  Once developed, it is believed that they influence sediment transport and the surrounding flow field.  A study was conducted on clusters to identify the bed shear stress range in which clusters form from a non-clustered bed and subsequently the stress values at which clusters disintegrate.  The spacing characteristics and orientation of clusters with respect to flow characteristics were examined.  The study also examined the effects of clusters on mean bedload rate in unsteady flow conditions and on the pulsating nature of bedload.