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.
   
 

Culvert design: An experimental study was conducted in a recirculating flume to determine the optimal design for culverts that are passable to salmon and remain stable under various hydraulic conditions.  The flume was filled with rocks of 2- to 8 inch in diameter and tested under a wide range of flow conditions.  Equilibrium, critical, and scour conditions were observed.  It was found that the best culvert is the one that most closely matches the streambed above and below it.  Data from the flume yielded nondimensional relationships that predict, for any given flow, the depth at which rocks are eroded.  The scour depth data was used to properly size culverts to avoid erosion.  It was concluded that maximum rock diameter in the culvert should not exceed 25 % of the culvert diameter.  Rocks larger than 25 % of the pipe diameter will trap trash and debris.  This will degrade the culvert’s fish-passage characteristics and will contribute to blockages, flooding and washouts. Thus, a culvert with 12 ft diameter should contain rocks smaller than 3 ft.  About 35 % of the culvert pipe must be submerged in the rocks.  In stream structures, called sills, must be built to stabilize the gravel, especially on steep slopes.