Mastering Dam-Break Modelling with HEC-RAS 2D | 2D Flood Simulation, Dam Breach Parameters

How to Perform Dam Modeling Using Latest Software

Introduction to Dam Failure

• The speaker introduces the topic of dam modeling, emphasizing its importance in understanding catastrophic structural failures characterized by rapid water release.

• Key causes of dam failure are outlined, including substandard construction materials, design errors, geological instability, and maintenance issues.

Approaches to Dam Modeling

• Two primary approaches for modeling dam break scenarios are discussed: piping and overtopping. Each method is illustrated with clear examples.

• Researchers have developed various equations for estimating critical parameters such as the bottom width of the bridge area and time required for completion.

Importance of Computer-Based Models

• The advancement of computer-based models like HECRAS has improved access to hydrodynamic simulations for dam modeling.

• The tutorial assumes prior knowledge of model simulation, focusing on practical steps rather than foundational explanations.

Setting Up the Model

• The speaker presents their imported digital elevation model and computational domain setup for simulation.

• Instructions are given on selecting tools within the software to create structures like bridges and dams effectively.

Mesh Creation and Geometry Saving

• Emphasis is placed on adjusting mesh cell size for better simulation accuracy; users can define appropriate values based on their project needs.

• After modifying geometry settings, users should save their work before proceeding with further configurations related to the dam structure.

Defining Dam Structure Parameters

• Users must input specific data regarding station elevation and other parameters essential for accurate modeling outcomes.

• Options for overflow computation methods are presented; users can choose between normal or equation domain methods based on their project's requirements.

Finalizing Bridge Simulation Settings

• It’s crucial to check bridge structure options in the software before importing additional inputs; this ensures proper simulation capabilities.

• The latest version of HEC-RAS simplifies parameter estimation directly within the model without needing external calculations.

Understanding Dam Failure Modes and Simulation Techniques

Minimum Elevation and Bridge Button Section

• The minimum elevation for the bridge button section is crucial; it should be determined based on the dam's bottom location.

• Users can find the minimum river elevation near the dam by checking the bridge plot tab, where station and elevation numbers change dynamically.

Types of Dam Failure Modes

• Two primary failure modes are discussed: overtopping (due to extreme inflow) and piping (often sudden failures due to material quality or earthquakes).

• The normal elevation of a dam is recommended as a key input for assessing potential failure scenarios.

Volume Calculations Related to Dam Failure

• The pool volume at failure correlates with normal water levels, which can be calculated using an elevation-volume curve specific to each dam.

Selecting Parameters for Simulation Models

• Various parameters must be selected, including dam type (e.g., rock fill or homogeneous), slope values, and material quality indicators.

• High-quality materials lead to lower risk classifications for dams, while low-quality materials increase risk assessments.

Flow Analysis and Hydrograph Definition

• Input hydrographs must be defined under boundary conditions; triangular flow hydrographs are suggested for simulations.

• After defining parameters, running flow analysis may require adjustments due to potential errors in numerical settings.

Time Step Adjustments in Simulations

• Two options exist for time step selection during simulations: fixed time steps or adjusted time steps based on Courant number. Adjusted time steps optimize simulation accuracy.

Simulation Setup and Parameters

Inputting Simulation Parameters

• Users can input maximum and minimum critical numbers for simulation, including the number of steps below the minimum before doubling.

• The diffusion wave option is recommended for quicker simulations compared to momentum equations, which take longer to solve.

Initial Conditions and Time Settings

• An appropriate initial condition time value is crucial; in this case, two hours was selected.

• Adjusting parameters like warm period and total simulation helps control model stability and accuracy. A practical range between 1.0 and 1.5 is suggested based on experience.

Output Configuration

Animation Creation

• Lower output intervals are necessary for creating detailed animations of the dam process.

• A one-hour time step is chosen for hydrograph outputs to enhance detail in results.

Running the Model

Execution and Error Handling

• After setting up, users should run the model while monitoring for errors related to dam elevation or other data issues.

• Saving progress before running simulations ensures that any changes are not lost if errors occur during computation.

Results Analysis

Reviewing Simulation Outcomes

• Upon completion, users should check geometric data by zooming into the dam structure to analyze flow hydrographs over time.

• Different options allow users to visualize water surface variations and flow rates post-simulation, highlighting peak values during flood events.

Flow Dynamics Visualization

Chart Customization

• Users can customize charts by selecting line styles and colors to better represent flow dynamics visually.

• Important data columns can be copied or utilized from charts for further analysis of flow characteristics.

Advanced Data Exploration

Special Information Retrieval

• Users can access more specific hydraulic information through mapping tools within the software interface.

Animation Playback

• Playing back animations allows observation of how flow reaches dam locations over time, providing insights into water surface elevation changes leading up to a breach event.

Peak Flow Analysis

Cross Sectional Studies

• Peak flow values at various locations can be plotted against time series data, illustrating how flows decrease downstream after reaching their peak at the dam.

Hydraulic Information Extraction

• The tutorial covers essential steps needed for extracting volume-elevation relationships using digital elevation models effectively.

Dam Elevation and Volume Calculation

Understanding Elevation vs. Volume

• The process of calculating elevation versus volume is introduced, emphasizing the importance of inputting correct data to compute necessary figures.

• The maximum elevation for a dam is discussed, with a specific reference to the top elevation number that can be entered to construct volume based on this elevation.

• Instructions are provided on how to select and navigate through the model to find volumes related to different elevations, highlighting user interface elements.

Creating Profiles and Analyzing Water Flow

• A demonstration of creating different profiles from riverbed parameters is presented, focusing on water depth and surface levels during processes.

• The flow dynamics from the dam are illustrated, showing how water surface levels change in response to flood conditions.

Observations on Flood Dynamics

• The impact of flooding on water surface elevation at the dam location is analyzed, noting an increase followed by a sudden decrease after a break occurs.

• A summary of model behavior regarding flow depth values downstream is provided, concluding with an invitation for questions about the tutorial's content.