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Water Quality Input Datasets
Developing a water quality model in ResSim requires several types of input data, which are organized into datasets. These datasets include: WQ Geometry, WQ Constituents, WQ Parameters, Meteorological Data, Boundary Conditions, Initial Conditions, Mass Injections if additional mass is added into the system, Mixing Coefficients, and Observed WQ Data for model calibration and validation. Additionally, water quality stations include both meteorological stations and observed water quality stations, which provide essential time series data for meteorological parameters and observed constituents. Observed WQ Data is crucial for calibrating and validating the water quality model. The HEC-ResSim Water Quality Input Data table provides a description of each of these datasets.
Input Dataset | Description |
WQ Geometry | This dataset is a fundamental component for all water quality models and defines the water quality (WQ) domain, which includes river-reservoir network connectivity and discretization details. The geographic extent of the geometry dataset can be subdivided into regions, which group watershed elements that share water quality parameters. Additionally, the geometry dataset is built upon an ResSim network, an HEC-RAS geometry shapefile, and the output from a steady flow model, which is used when simulating river reaches. For temperature modeling, the geometry dataset is also connected to meteorological data. Geometry |
WQ Constituents | This dataset is required input for all water quality models. Users can choose constituents of interest from a list of available water quality libraries (DLLs), with each library simulating a specific set of constituents. A complete list of the available constituents by library can be found in the WQ Constituent Set Editor – Table Overview. Additionally, users have the option to include global reference values. Water Quality Constituents |
WQ Parameters | This dataset is generated using the geometry and constituent datasets. When the linked geometry dataset contains defined regions, users have the option to input separate water quality parameter values for each individual region. Alternatively, they can apply the same parameters across the entire geographic extent of the water quality model domain. This flexibility allows for more precise modeling of water quality variations across different regions of the watershed. Water Quality Parameters |
Meteorological Data | Meteorological data is optional for general water quality modeling but is required specifically for temperature modeling. The meteorological station data includes essential atmospheric parameters such as atmospheric pressure, air temperature, humidity, shortwave radiation, cloud cover, and wind speed. Meteorological Data |
Observed WQ Data | Observed water quality data includes time series or profile measurements. While this data is not required to run an ResSim water quality model, it is used for model calibration and/or validation. Observed WQ Dataset |
Boundary Conditions | Boundary conditions represent the water quality conditions for inflows and simulated constituents, and are required for all water quality models. Boundary Conditions |
Initial Conditions | Initial conditions represent the water quality status at the beginning of the simulation and are required for all water quality models. Initial Conditions |
Mass Injections | Mass injections refer to additional masses of simulated constituents that are introduced into the water quality model domain. This data is optional for water quality modeling and is typically used when users want to simulate the impact of specific sources of contamination. Mass Injections |
Mixing Coefficients | Mixing coefficients are required transport parameters that describe the rates of longitudinal or vertical mixing within the water body. Dispersion Coefficients |
Units of Water Quality Measure
In a ResSim watershed, the units of measure are determined when the watershed is created, as outlined in the HEC-ResSim User's Manual (Chapter 3, Section 3.3). All modeling data, such as time series data, geometric and reservoir information, model parameters, and flow, elevation, and stage time series data, must be saved using the same unit system.
However, water quality input data may come in various units. To accommodate this, the ResSim GUI offers dropdown menus that allow users to convert and match the imported water quality data to the units used in the water quality libraries. These unit menus are independent of the unit system set for the watershed (see HEC-ResSim User's Manual, Chapter 1, Section 1.1). For instance, Relative Elevation (refer to Section 2.2.3 of the manual) can be displayed in either feet (ft) or meters (m), depending on the watershed's set units of measure and display units.
It is important for users to pay close attention to the units associated with water quality data and input parameters during the water quality simulation setup to ensure correct input and accurate model results.