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

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Application Note: Hydraulic Structures
 
Design and evaluation: Hydraulic structures are typically used for flood control, flood conveyance, irrigation purposes, fish passage, banks protection, navigation, recreation and ecological restoration.   A hydraulic structure must meet the safety, functional and aesthetic goals for its purpose.  Thus, valuation studies must be carried out before and after the construction of the structure to assess its impacts. The structure must be of sufficient size that natural flooding is not worsened and to ensure that the structure can withstand the design flood and remain traversable.  This is required in order to protect the property and residents upstream and downstream of a structure.  In the hydraulic design, one main thing to remember is that water is dynamic.
   
 

Shallow water habitat in the Missouri River: From the early 19th century to the present, the Missouri River has been transformed from a complex multi-channel system with highly variable width and depth into a much more uniform, single-thread channel that is narrower, deeper, shorter, and characterized by much more uniform flow.  This transformation process has caused the reduction of the overall length of the Missouri by 10% and decreased the channel surface area by as much as 80% in some reaches.  A study was conducted to examine the assertion that placement of hydraulic structures such as dikes and chevrons in the Missouri could enhance Shallow Water Habitat (SWH) availability by redirecting flow from the main channel towards the banks.  The study also examined the effects that notching of dikes may have on increasing SWH.  A channel surface area qualifies as a SWH when the flow depth is less than 5ft and the depth-averaged velocity is less than 2.5 ft/s.  The hydraulic performance of the aforementioned structures was evaluated via detailed field monitoring studies for a range of flow conditions and for different locations within the stream.  In addition, a 2-D hydrodynamic model was used to describe the flow patterns around the hydraulics structures.  The code provided for different flow conditions the flow depth and velocity variation introduced by the structures.  Analysis of historic and current information through aerial photography, field work and numerical modeling clearly showed that dikes have overall led to the development of additional channel surface area, on an average 0.6 acres per dike.  It is shown that in the spring period as flow increases the SWH available for Pallid Sturgeon reduces.  During Fall the surface area that qualifies as SWH increases.  Finally, the model results and analysis indicated that notching of the dikes has zero contributions in increasing SWH.  This was a very complex problem that required interagency-based collaborative research in order to identify new hydraulic structures and other related approaches that may enhance SWH.