Glossary

Base Data

The original set of files (such as model files) that serve as the foundation for creating forecast scenarios. Copies of this base data are used to generate forecasts without altering the original data.

Basin Model

A core component of an HEC-HMS project that consist of elements such as subbasins, routing reaches, and junctions. Their main purpose is to simulate how meteorological inputs, like rainfall, are converted into streamflow at key points within a watershed.

Cache

A temporary location used to store copies of recently accessed watershed and data files for quicker access.

Calibration

The process of adjusting model parameters to ensure the model’s results closely match observed data from a gage within the watershed.

CDA

CWMS Data API. A REST API developed by the US Army Corps of Engineers that serves as the critical interface for transferring water management data to and from the cloud environment. (previously known as RADAR)

Collections

A group of time-series datasets that share the same location (A & B Parts), parameter (C Part), and time step (E Part). In HEC-DSS, collections are identified by a C:000000 value in the F Part, with each individual dataset in the collection assigned a unique number, such as C:000001, C:000002, and so on. Collections used for ensemble forecasting must span a common time window.

Common Schematic

A group of elements such as stream alignments, map layers, time series icons, computation points, and projects. It facilitates the sharing of common data between HEC software applications (e.g., HEC-HMS and HEC-ResSim) for a watershed. Using a common schematic ensures consistency across computation nodes, routing reaches, and other components.

Coordinate System

Cumulus

CWMS-Vue

Corps Water Management System Visual Utility Engine. A software tool developed by HEC that offers a graphical user interface for viewing, editing, and managing data in HEC-DSS files and the CWMS database.

DSS Pathname

A unique identifier for a record or time series within an HEC-DSS file. The pathname is organized to make it easy to group related data. It is divided into six parts, labeled A through F, with each part separated by a slash: /A/B/C/D/E/F/. For more details refer to the HEC-DSS documentation.

Dashboard

A customizable interface for displaying key watershed information and forecast data at a glance.

Data Validation

The process of reviewing data to identify and correct any errors.

Data Validation Editor

A tool within the Acquisition Module for reviewing, editing, and validating time-series data.

Datum

The reference system used for measurements, typically either a system of coordinate positions on a surface (horizontal datum) or heights above or below a surface (vertical datum).

EFP

Ensemble Forecast Processor. A plugin that enables the processing of various statistical metrics from ensemble flows at specific locations within the watershed. These metrics can then be used to influence other model alternatives in the forecast.

Ensemble

A collection of time series data, where each series represents a different possible outcome for a specific location and parameter.

Ensemble Member

A single time series data set that represents one possible outcome for a specific location and parameter.

Extract

The process of retrieving time-series or gridded data from external sources for use in a forecast.

Extract Group

A group that specifies the data source, the method for extracting the data into the forecast.dss file, and the name the data will have once it is stored in the file.

FIRO

Forecast-Informed Reservoir Operations. An approach use by USACE and other agencies to improve how reservoirs are managed, especially for flood risk reduction and water supply, by incorporating advanced weather and water forecasts, including uncertainty meteorology and hydrology, into operational decision-making. FIRO uses modern forecasting tools to make more dynamic, flexible decisions about when to store or release water from reservoirs.

Forecast

A simulation of watershed processes and the potential consequences of flooding based on input data and various models, including hydrologic, reservoir operation, hydraulic, and impact analysis models configured in HEC-RTS. The forecast results include channel flow and stage from watershed runoff, reservoir release schedules, floodplain inundation maps, consequence reports, and recommendations for emergency responders. These results support water management decision-making.

Forecast Alternative

A forecast scenario defined by a specific combination of input data and model alternatives.

Forecast Time

The time at which a forecast is initiated, marking the transition from observed (lookback) data to forecasted data.

Forecast Run

A predefined sequence of model alternatives executed in a specific order during a forecast.

Forecast Run Key

A unique alphanumeric identifier composed of model alternative keys that represents a specific forecast run configuration.

Grid Set

A grid set is a series of georeferenced grids that represent the changing properties or conditions of a watershed over time and space. Examples include sequences of grids showing precipitation or air temperature.

Hydrograph

A graphical representation of the rate of water flow (discharge) versus time at a specific location within a river, channel, or conduit. It may also display stage (elevation) versus time data for the same location.

Hyetograph

A graphical representation of rainfall intensity over time for a specific location, typically represented as a bar chart. It plots rainfall depth or intensity on the vertical axis against time on the horizontal axis.

HEC

Hydrologic Engineering Center. USACE's Center of Expertise in areas such as surface and groundwater hydrology, river hydraulics, sediment transport, hydrologic statistics, risk analysis, reservoir system analysis, planning analysis, real-time water control management, and other related technical fields. HEC is the developer of HEC-RTS and it's integrated software packages.

HEC-DSS

Data Storage System. A database system developed by HEC to efficiently store and retrieve sequential scientific data. This includes, but is not limited to, time series data, curve data, and spatially oriented gridded data. The system is designed for easy access, allowing both users and application programs to quickly store and retrieve data.

HEC-DSSVue

Data Storage System Visual Utility Engine. A software application developed by HEC that offers a graphical user interface for viewing, editing, and managing data stored in HEC-DSS files.

HEC-FIA

Flood Impact Analysis. A software application developed by HEC designed to assess the consequences of flow or water surface elevations within a watershed. It uses input data such as observed or calculated flow rates and water surface elevations at key locations. The outputs include measures of impact, such as economic loss, loss of life, or other relevant factors. Additionally, it can provide recommendations for actions to take in response to anticipated flow levels or water elevations.

HEC-HMS

Hydrologic Modeling System. A software application developed by HEC that simulates how a watershed responds to precipitation. Input data can include observed or forecasted precipitation, temperature, snowpack, and other environmental conditions. The outputs include flow data throughout the watershed, including inflows to reservoirs.

HEC-MetVue

Meteorological Visualization Utility Engine. A software application developed by HEC that allows you to view and manipulate meteorological datasets. It also performs various computations and analyses, such as temporal and spatial aggregation of datasets and areal average calculations.

HEC-RAS

River Analysis System. A software application developed by HEC that simulates the behavior of channels and surrounding floodplains. It calculates water surface elevations based on flows provided by HEC-HMS or HEC-ResSim. The inputs include flow data, and the outputs include water surface profiles and depth grids.

HEC-ResSim

Reservoir System Simulation. A software application that simulates the behavior of reservoirs and connected channels based on user-defined operations for reservoir release decisions. It takes inputs such as inflows into reservoirs and unregulated flows downstream. The outputs include reservoir releases, downstream regulated flows, and reservoir storage levels.

HEC-RTS

Real Time Simulation. An integrated software package for real-time water management that supports short-term decision-making for water control operations. It includes tools for data collection, validation, transformation, storage, visualization, real-time hydrologic modeling, and information dissemination.

Inundation Map

A map showing areas that would be flooded under specified flow or stage conditions.

JAR File

Java Archive File. A platform-independent file format that combines multiple files into one. It can bundle Java applets along with their necessary components (such as .class files, images, and sounds). The JAR format also supports compression, which helps reduce file size.

Layers

In HEC-RTS, layers function like transparencies stacked on top of each other. Each layer contains static physical features, such as roads, county and state boundaries, rivers, and subbasins, which are displayed as colored images in the viewing area. There are two types of layers: Map Layers and Primary Layers.

Layer Tree

A list that shows the hierarchical structure of the layers displayed in the map window.

Lookback Period

The time period before the time of forecast (i.e., the start of the simulation until the time of forecast).

Map Layer

A digital representation of watershed features. It appears as an image and helps visualize the characteristics of the watershed.

Map Window

The window displaying the graphical representation of a watershed, including both map layers and primary layers.

Master Watershed

In team modeling, the authoritative version of the watershed configuration stored in a shared location.

Message Pane

A scrolling display at the bottom of the main window showing system messages and activity logs.

Meteorologic Model

Meteorologic models are a key component of an HEC-HMS project. Their primary purpose is to generate meteorological boundary conditions for calculating subbasin runoff.

Model Alternative

A specific configuration of a model, defined by a particular set of inputs and parameters.

Model Alternative Key

A unique alphanumeric identifier assigned to each model alternative within a specific model type.

Model Linking

The process of connecting model alternatives within a forecast run so that each model receives necessary input data from other models or an Extract Group.

Model Schematic

A visual representation of computational model elements displayed in the map window.

Modeling Module

The module that consists of commands for running forecasts. These commands are used to set up and execute analysis applications, as well as to view the results.

Module

A module is a group of commands related to a specific function. HEC-RTS contains four modules: Setup, Acquisition, Visualization, and Modeling. Each module includes menus, tools, and a display area tailored to its function.

NWS

National Weather Service. The federal agency responsible for making and issuing meteorological and hydrological forecasts. These forecasts can be used as input for HEC-RTS simulations.

Parameter

A variable or input value that defines specific conditions or characteristics within a model. These parameters influence the model's behavior and output, helping to simulate real-world processes or systems accurately. 

Post

The process of saving or storing modeling results from a forecast to a database or HEC-DSS file.

Post Group

A group that specifies the pathnames from the forecast.dss file, the destination (database or HEC-DSS file), and the name the data will have once it is posted.

Precipitation Grid

A precipitation grid is a spatial representation of precipitation across the coverage area for a specific time period.

Primary Layer

A layer automatically created as part of watershed configuration, including Time Series Icons, Stream Alignment, Gridded Data, and Model Schematic layers.

Program Order

The sequence in which models are executed during a forecast.

Projects

Man-made structures, such as reservoirs or levees, designed to manage water.

Quality Color Bar

A thick, segmented line, representing the data quality history at a specific location within the defined time window.

QPE

Quantitative Precipitation Estimation. An estimate of the observed, accumulated precipitation over a specific area and time period. It is typically derived using radar data and sometimes corrected with rain gage data.

QPF

Quantitative Precipitation Forecast. The expected amount of liquid precipitation (rain, melted snow, etc.) accumulated over a specified time period for a future time period.

Raw Data

Data that has been collected, transmitted, and received but has not yet undergone quality checks or revisions. 

Regulated Flow

Flow that has been altered from its natural state due to the impact of hydraulic structures or human-made interventions.

Replace from Base

A feature within HEC-RTS that allows you to replace a model in a forecast with a copy of the base watershed model. 

Reservoir

A structure designed to manage water for purposes such as flood control, hydropower generation, recreation, and water supply.

Revised Data

Data that has been validated and transformed for use in modeling.

RAS Mapper

The geospatial interface within HEC-RAS used for managing and visualizing spatial data for hydraulic modeling. It allows you to perform tasks such as importing and manipulating terrain data, displaying model inputs and results, and creating inundation maps of floodplains.

Routing Reach

A routing reach is a section of a stream or river network used in models like HEC-HMS and HEC-ResSim to simulate how water flows through a channel.

Save to Base

A feature in HEC-RTS that allows you to save changes made to a model in a forecast back to the original base watershed model.

Script

A sequence of instructions or commands written in a programming language that is used to automate repetitive tasks, manage system operations, or control the behavior of other applications. 

Setup Module

The module that organizes commands used to configure a watershed, allowing you to define the inputs, models, and outputs that represent how the watershed behaves.

Shapefile

An Esri vector data storage format used to store the geographic location, shape, and attribute data of spatial features (points, lines, or polygons). It is stored as a collection of related files that must be kept together in the same directory. A minimum valid shapefile requires at least three files: .shp (geometry), .shx (index), and .dbf (attributes) files, often accompanied by a .prj file (coordinate system).

Simulation

A mathematical model that predicts how a system will behave based on given inputs and starting conditions.

Stage

The height of the water surface at a given location measured relative to a specific reference point, called a datum.

Stream Alignment

Represents the layout of the stream network within a watershed. It displays routing reaches, shows where streams meet (confluences), and gives a sense of distance and scale.

Stream Element

A part of the stream alignment defined by a series of vertex points with known coordinates. It starts and ends at stream nodes, which are usually located at confluences or the boundaries of the river system.

Stream Junction

A point where two stream elements meet.

Stream Node

The starting or ending point of a stream element. It also serves as a junction where multiple stream elements meet.

Stream Stationing

A system used to reference locations along a stream based on distance. In HEC-RTS, stream stations (or river stations) are assigned along each stream element. The station at the downstream end is labeled as Station 0, and the station number increases as you move upstream, based on the linear distance between vertices in the watershed’s coordinate system.

Subbasin

A subbasin is a smaller, distinct area within a watershed, separated based on natural features like terrain or topography. It is a portion of the larger watershed where all the water from precipitation, runoff, and streams drains to a common outlet or point.

SWE

Snow Water Equivalent. The amount of water contained in snow, recorded in inches or centimeters. It’s calculated by determining how much water would be produced if the snow were melted.

Team Modeling/Team Forecasting

A collaborative approach where multiple forecasters work with the same watershed and forecast files, with version control and conflict resolution.

Threshold Color Bar

A thick, segmented line displayed in the map window that acts as a linear histogram, comparing current data with predefined threshold values for a specific location within the defined time window.

Thumbnail Plot

A small preview plot in the map window showing data trends at a time series icon location.

Time Series

A time series is a sequence of values for a specific property or state, recorded at specified time intervals.

Time Series Icon

A symbol in the map window that allows quick access to time series data linked to it. The icon’s location on the watershed map usually corresponds to the place where the data was collected.

Time Series Icon Layer

A sub-layer within the Time Series Icons primary layer, organizing icons by data type or function.

Time Window

The period simulated during a forecast, defined by a specific start and end date and time. It can also refer to the time range used to display data in the Acquisition or Validation map windows.

USACE

U.S. Army Corps of Engineers. A federal agency that provides engineering services for a wide range of projects, including water resources management, civil works, environmental restoration, infrastructure development, and military engineering. It plays a critical role in managing the nation's infrastructure and natural resources, helping with disaster response, and providing engineering solutions for both military and civilian needs. 

USGS

United States Geological Survey. The federal agency that is responsible for monitoring the nation's water resources by operating a vast network of stream gages across the U.S., often in partnership with state and local agencies. The data from these gages is used for flood forecasting and warning, water resources management, environmental studies, and research. 

UTC

Coordinated Universal Time. The primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones.

Validation List

A method used to organize time series records for the purposes of data editing and validation.

Visualization Module

The module that provides an interface for displaying data, allowing you to view both observed and forecast information.

Watershed

A collection of data, models, and images that represent the land area, channels, gages, and water control features within its boundaries.

Watershed Pane

The collection of Visualization, Acquisition, Modeling, and Setup tabs within HEC-RTS.

Watershed Tree

A hierarchical display in the Setup Module showing all watershed components, including models, model alternatives, forecast runs, and stream alignments.

WCS

World Coordinate System. A global reference system used to define locations on the Earth's surface. It provides a standard framework for mapping, spatial analysis, and geospatial data management. The WCS typically uses geographic or projected coordinate systems to describe the positions of points in a two-dimensional space.

Workflow

The sequence of tasks and models executed to complete a forecast, displayed in the Workflow tab of the Modeling Module.

Zone

A zone is a grouping of model elements (subbasins, reaches, etc.) used to assist in calibration of an HEC-HMS model.