Glossary

Arc Shapefile

An Arc shapefile is the native data format used by ArcGIS®. It stores spatial features along with associated attribute data, using a non-topological structure. A shapefile is a group of files that share the same base name but have different extensions. At a minimum, a shapefile includes the following three components:

• *.shp – Contains the geometric shapes (points, polylines, or polygons) that make up the map features.
• *.dbf – A database file that stores attribute data (descriptive information) for each shape.
• *.shx – An index file that links each shape in the .shp file to its corresponding record in the .dbf file.

Together, these files enable the display and analysis of spatial data in GIS applications.

Base Data

Base data for a watershed refers to 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.

Baseflow Method

The baseflow method, used in HEC-HMS, is a model that estimates the portion of total runoff in a subbasin that comes from subsurface (groundwater) flow.

Basin model

Basin models are a core component of an HEC-HMS project. They 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 cache is a temporary storage location used to store copies of recently accessed watershed and data files for quicker access.

Calibration

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

Collections

A collection in HEC-DSS refers to 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.

Common Schematic

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

Computation Point

A computation point is a location where time series data are transferred between different analysis applications.

Coordinated Universal Time (UTC)

UTC is the standard time scale used worldwide for civil time. To maintain consistency in time assignments, the CWMS database uses UTC as its default time zone. Regardless of the time zone in which data is originally measured, it will always be stored in UTC in the CWMS database. When storing or retrieving data, the time can be converted to local time or another time zone as needed.

Corps Water Management System Visual Utility Engine (CWMS-Vue)

CWMS-Vue is 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.

Cumulus

CWMS Data API (CDA)

CDA is a tool that allows users to collect data on current operations and historical events from US Army Corps of Engineers districts (previously known as RADAR).

Data Storage System (HEC-DSS)

HEC-DSS is 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-DSS is integrated into most of HEC's major software applications.

Data Storage System (HEC-DSS) Pathname

An HEC-DSS pathname is 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/.

Data Storage System Visual Utility Engine
(HEC-DSSVue)

HEC-DSSVue is a software tool developed by HEC that offers a graphical user interface for viewing, editing, and managing data stored in HEC-DSS files.

Data Validation

Data validation is the process of reviewing data to identify and correct any errors.

Datum

A datum refers to 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).

Directory

A directory organizes computer files in a hierarchical structure, similar to nested folders. Related files are stored together in folders within the same directory.

Diversion

A diversion is an element in HEC-HMS that redirects water from its normal path in a channel.

Easting

Easting is the x-coordinate of a location in the chosen World Coordinate System.

Ensemble

Ensembles are collections of time series data, where each series represents a different possible outcome for a specific location and parameter.

Ensemble Forecast Processor (EFP)

The EFP is 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 Member

An ensemble member is a single time series data set that represents one possible outcome for a specific location and parameter.

Extract List

An Extract List 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.

Flood Impact Analysis (HEC-FIA)

HEC-FIA is a software application 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.

Flow Blending

Flow blending in HEC-HMS allows for a smooth transition from observed flows during the lookback period to simulated flows during the forecast period.

Forecast

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

Forecast Informed Reservoir Operations (FIRO)

FIRO is 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.

Geographic Information System (GIS)

GIS is a system of software and data used to view, manage, and analyze information about geographic locations, spatial relationships, and spatial processes.

Georeferenced Grid

A georeferenced grid is a set of geographic data represented as a raster, which has been linked to a coordinate system. This allows the data to be viewed, queried, and analyzed in conjunction with other geographic data.

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 hydrograph is a graph that visualizes the rate of water flow (discharge) over time at a specific location, like a river or stream.

Hydrologic Engineering Center (HEC)

HEC is the developer of HEC-RTS and serves as 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.

Hydrologic Modeling System (HEC-HMS)

HEC-HMS is a software application 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.

Emergency Planning Zone

An Emergency Planning Zone is a specific area within a watershed where rising water levels in a stream, river, lake, or reservoir could have significant consequences. The boundaries of this zone are defined by a closed polygon. The potential impacts of rising water levels are assessed by describing the properties and population at risk within the polygon, which is then used as input to HEC-FIA.

Inundation

Inundation occurs when water covers areas that are typically dry, usually as a result of severe events along rivers or coastlines.

Java Archive (JAR, .jar)

A JAR is 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.

Layer Tree

A layer tree is a list that shows the hierarchical structure of the layers displayed in HEC-RTS.

Log File

A log file is a file that stores messages generated by HEC-RTS, including informational messages and error messages.

Lookback Period

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

Loss Method

The loss method is a model used to calculate infiltration and other forms of precipitation loss in a subbasin.

Map Layer

A map layer is a digital representation of watershed features designed to be displayed in HEC-RTS. It appears as a colored image and helps visualize the characteristics of the watershed.

Map Projection

A map projection uses mathematical formulas to convert spherical coordinates on the globe into flat, planar coordinates.

Map Window

The map window in HEC-RTS displays a graphical representation of the watershed, including both map layers and primary layers.

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.

Meteorological Visualization Utility Engine (HEC-MetVue)

HEC-MetVue is a software application that allows users 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.

Model Alternative

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

Modeling Module

The Modeling module (or Modeling tab) consists of commands for running models. 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.

Northing

Northing is the y-coordinate of a location in the chosen World Coordinate System.

National Weather Service (NWS)

The NWS is a federal agency responsible for making and issuing meteorological and hydrological forecasts. These forecasts can be used as input for HEC-RTS simulations.

Parameter

A parameter is 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. 

Precipitation Grid

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

Projects

Projects are man-made structures, such as reservoirs or levees, designed to control water.

Quality Color Bar

The quality color bar is a thick, segmented line, representing the data quality history at a specific location within the set time window.

Quantitative Precipitation Forecast (QPF)

The QPF is the expected amount of liquid precipitation (rain, melted snow, etc.) accumulated over a specified time period over a specified area.

Quantitative Precipitation Estimation (QPE)

The QPE is a method of approximating the amount of precipitation that has fallen at a specific location or across a region, typically utilizing data from weather radar, satellites, and rain gauges to generate maps showing estimated precipitation amounts over a given period of time.

Raw Data

Raw data refers to data that has been collected, transmitted, and received but has not yet undergone quality checks or revisions. 

Real Time Simulation (HEC-RTS)

HEC-RTS is an integrated system 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.

Regulated Flow

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

Replace from Base

Replace from Base is a feature that allows the user to replace a model in a forecast with a copy of the base watershed model. 

Reservoir

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

Reservoir System Simulation
(HEC-ResSim)

HEC-ResSim is 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.

Revised Data

Revised data refers to data that has been validated and transformed for use in modeling.

River Analysis System (HEC-RAS)

HEC-RAS is a software application 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.

River Analysis System Mapper (RAS Mapper)

RAS Mapper is tool included in the HEC-RAS software application that allows you to use and visualize floodplain geospatial information along with HEC-RAS analysis results.

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

Save to Base is a feature that lets users save changes made to a model in a forecast back to the original base watershed model.

Scripting

Scripting is the process of automating a program's tasks, allowing a specific sequence of actions to be carried out with a single command.

Setup Module

The Setup module (or Setup tab) organizes commands used to configure a watershed. These commands define the inputs, models, and outputs that represent how the watershed behaves.

Simulation

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

Stage

Stage is the height of the water surface measured relative to a specific reference point, called a datum.

Stream Alignment

A 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 stream element is 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 stream junction is a point where two stream elements meet.

Stream Node

A stream node is the starting or ending point of a stream element. It also serves as a junction where multiple stream elements meet.

Stream Stationing

Stream stationing is 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.

Supplemental Program

A supplemental program is a user-developed program or script that is not included with HEC-RTS. It can be added to the program sequence, allowing it to be executed within a forecast.

Snow Water Equivalent (SWE)

SWE measures 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.

Threshold Color Bar

The threshold color bar is a thick, segmented line displayed in the map window. It acts as a linear histogram, comparing current data with predefined threshold values for a specific location.

Time Series

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

Time Series Icon

A time series icon is 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 Window

A time window refers to 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.

Transform Method

The transform method is a model used to calculate surface runoff from precipitation within a subbasin in HEC-HMS.

U.S. Army Corps of Engineers (USACE)

The USACE is a federal agency within the U.S. Department of Defense 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. 

United States Geological Survey (USGS)

The USGS plays a vital role in monitoring and managing 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. 

Validation List

A validation list is a method used to organize time series records for the purposes of editing or validation.

Vertex Point

A vertex point is a location along the stream alignment with specified coordinates.

Visualization Module

The Visualization module (or Visualization tab) offers commands for displaying data, allowing users to view both observed and forecast information. These tools support the evaluation of the hydrometeorological conditions within the watershed.

Watershed

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

Watershed Pane

The watershed pane refers to the collection of Visualization, Acquisition, Modeling, and Setup tabs within HEC-RTS.

World Coordinate System (WCS)

The WCS is 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, where the x coordinate is referred to as "easting" and the y coordinate is referred to as "northing".

Zone

A zone is a grouping of subbasins used to assist in calibrating an HEC-HMS model.