Overview of an Instream Hydraulic Simulation Methodology
(Past Method for Instream Flow Modeling)

Go to Present Instream Flow Program

Hydraulic modeling is conducted to simulate the changing hydraulic characteristics of a stream study segment at various flow rates. Variations in hydraulic character may then be related to the species’ hydraulic preferences and used to assess species’ habitat availability. Since this type of study focuses on low flow conditions, hydraulic simulations are typically performed at several flow rates below the median flow (fifty percentile flow frequency).

Mathematical Model Hydraulic characteristics of the river segments are assessed using a two dimensional (2-D) depth-averaged finite-element model. A steady state numerical solution is developed for each flow rate of interest. SMS and RMA2 can be used for grid creation and simulation. This hydraulic simulation model is valid for shallow surface water flow problems such as for rivers and estuaries. The advantages of using this type of model are (1) ability to simulate complex 2-D flow conditions such as eddy currents and backwater flow, and (2) ability to handle complex bathymetry such as braided channels, tributary islands, and sand/gravel bars.

Model Boundary Conditions Hydraulic model boundary conditions are defined as the upper or up-stream discharge and the lower or down-stream water surface elevation. An example discharge versus water surface elevation relation (stage-discharge curve) is shown above.

Model Calibration In addition to the stage curves developed for the downstream boundary of the stream study segment, velocity and depth measurements are collected and compared to simulated values. In the figures shown below simulated water velocity and water surface elevation contour plots are presented for a typical study reach.

Simulated Velocity Contour Plot

Simulated Water Surface Elevation Contour Plot

Click here to download HYDROSTAT software.

SMS software is a product of:
Brigham Young University
Engineering Graphics Laboratory
368B CB
Provo, Utah 84602
(801)378-2812
FAX (801)378-2478
http://www.ecgl.byu.edu

For information on RMA2:
US Army Corps of Engineers
Waterways Experimental Station Hydraulics Laboratory
http://hlnet.wes.army.mil