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.
   
Steep stream restoration model: Gravel bed-rivers are found in many parts of the world, typically existing in mountainous regions with high gradients and seasonally high flows.  These rivers are important in conveying flood waters from spring runoff in regions such as the Pacific Northwest, where heavy snows can be followed by equally heavy rains.  The combination of high stream gradient and high discharge can cause significant erosion of the bed and bank of the stream, in some cases moving large boulders with ease.  It is desirable to predict the hydraulic and geomorphologic interactions which can ultimately be used to minimize or prevent detrimental effects on stream ecology and infrastructure.  A study was carried out to investigate the scouring process which forms step-pool systems in high-gradient gravel bed streams. To quantify a relationship between streambed morphology and hydraulic parameters, a hydraulic model was constructed in a flume.  Several sediment gradations were utilized over a range of slopes and flow rates, and the change in the streambed elevation was surveyed after each test run.  Degradation of the bed was found to be related to flow rate, flow depth, and sediment size.  The results of this hydraulic model study were used to develop a predictive formula which allows computation of bed-height change due to a flow event.  This formula can be used in design of culvert structures and stream restoration in steep-sloped areas.