Hydraulic Simulations include calibration of water surface levels and cell velocities over a range of known and simulated flows.
The HYDSIM module of RHABSIM incorporates a powerful set of WSL and vel modeling algorithms, including IFG4 Log-log Regression, Channel Conveyance (or ManSQ), and Step-backwater (or WSP) models for water surface levels. Direct entry of FLows and WSLs is also available.
For velocities, the user can model using 1-vel, Regression and Depth calibration methods. A variety of options allow full control over velocity calibrations.
WSL and Velocity calibrations can both be customized for each cross-section. For example, pools and riffles can be treated separately, and if one or a few cross-sections have only one set of raw velocity data and thus require the 1-vel calibration model, other cross-sections with more raw data sets can implement the regression model.
Water Surface Level Calibrations
The screen below shows the IFG4 Log-log regression model interactive graph with the Dual-Stage method turned on. The user can easly see the data, the extrapolated regression line, and the interaction of the lines. Full regression statistics (A and B coefficients, mean error, variance and standard deviation) can be viewed in a report.
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The Channel Conveyance (MSQ) model uses a worksheet and an interactive graph to set WSLs. A variety of options are available: including Manning and Chezy equations; Discharge, Hydraulic Radius and Substrate Size Beta Adjustments; the user can subtract the Hydraulic Radius from the HyRad at the Stage-of-zero Flow (useful in pools) and use (or not) the Weighted Area method. The user also has full control over which cross-sections to calculate, and which calibration set (if more than one) to use.
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The screen below shows the Reach Manning worksheet. RHABSIM allows Reach Manning values to be entered directly (and then locked) or calculated using either of the "Between" or "At" methods. Because of this feature, the user can work up the reach by calulating Reach Mannings, then making minor changes (which improve calculations upstream), then locking that Mannings, and continuing upstream.
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Velocity Calibrations
The Velocity Calibration Parameter Worksheet sets up most global and cross-section parameters. For each cross-section, the user can select one of three methods: 1-Vel, when you have only a single set of raw velocity data or have multiple sets and want to choose the best (usually corresponding to the highest flow and WSL); The Regression method when 2 or more raw velocity sets are available; and the Cell Depth method, used most often when no raw velocity data is available.
The Velocity Algorithm can be Roughness (Manning's N) or Velocity Distribution Factors, and users can set the global variables of Roughness Coefficient, Regression B-maximum, and Beta Control options in the same manner as PHABSIM.
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The next screen below shows the Roughness Worksheet, where the user controls the actions of the Manning N (or Velocity Distribution Factor) for individual cells. The worksheet has all of the functions of the Velocity Calibration Parameter Worksheet (Calculation Method, global Algorithm, CalVelSet to use, BETA, B-Max, N-Min/max) as well the ability to enter Given Ns and toggle use of either Given or Calculated Ns.
At the bottom of the worksheet is information on the Given Flow, the Calculated Flow based on the *Given* Vels and the Calculated Flow based upon the Calculated Vels and Calculated (or Given) N's. The Velocity Adjustment Factor (VAF) is the Given Flow divided by the CalcVel Flow.
The user can also view a graph of Calculated Vels superimposed on Given Vels. This graph can help users judge the adequacy of choice of method and individual cell N's. If there are illogical spikes or dips in velocities across the cross-section, the user can adjust the N at individual cells.
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The next screen below is the Velocity Adjustment Factor graph showing the VAF's for all cross-sections in a data file. When many cross-sections are available, the user can select groups to display.
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RHABSIM has extensive graphs and reports for showing the results of hydraulic calibrations. Users can view graphs of Rating Curves (WSLs vs. Flows), Long-profile graphs of WSLs, a Long-profile graph showing a single calibration flow, the Velocity Adjustment Factor graph (as above), and finally a fully configurable graph of cross-section bottom profile with calibrated WSLs and Velocities.
The graph below shows the cross-section graph with information on a single flow. The user may view a single flow or all flows, turn WSLs and Vels on or off, and even instantly view the difference when vels are modeled as centered or offset (averaged to right.)
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