Glossary

Term

Definition

Acquisition module

The Acquisition module in HEC-RTS is the grouping of commands for data acquisition. These are commands for monitoring data acquired by HEC-RTS (and DSS files for gridded data), validating the quality of acquired data, and editing the data, as needed.

Arc shapefile

Arc shapefiles is the native data structure for the ArcGIS® software. Shapefiles store non-topological geometry and attribute information for the spatial features of a data set. A shapefile is a group of files that share a common base name and different extensions. At a minimum a shapefile has three component files: .dbf, .shp, and .shx. The .shp file contains the shapes (point, polylines, or polygons) that are displayed in the layer. Each shape has a record in the .dbf database file containing descriptive data called "attributes". The .shx file contains an index that links each shape to its record in the .dbf file.

Base data

Base data for an HEC-RTS study refers to the original set of data from which copies are made to create forecasts.

Baseflow method

The baseflow method is a model for calculating the subsurface flow contribution to total runoff flow in a subbasin.

Basin model

Basin models are one of the main components in an HEC-HMS project. Basin models are composed of subbasins, routing reaches, junctions, and other elements. Their principal purpose is to predict how meteorologic inputs are transformed into streamflow at specific locations in the watershed.

Cache

A cache is a temporary storage area where recently accessed watershed and data files are copied and stored.

Calibration

Calibration is the systematic adjustment of model parameters to produce model results that more accurately reflect watershed and channel behavior.

Common schematic

A common schematic consists of a stream alignment, map layers, time series icons, computation points, impact areas, and projects that allow sharing of common data between HEC software (e.g., HEC-HMS and HEC-ResSim) for a watershed. Use of a common schematic ensures consistency of computation nodes, routing reaches, and so on.

Computation point

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

Coordinated Universal Time (UTC)

UTC is a time scale that is the basis for the worldwide system of civil time. To provide a consistent method of assigning time to data, the HEC-RTS default time zone is UTC. No matter what time zone the data are originally measured in, the data will always be stored in UTC in the database. The time assigned to data can be converted to local time or another time zone when storing or retrieving data from the database.

Corps Water Management System
(CWMS)

CWMS is a real-time decision support system developed by HEC. CWMS makes readily available to USACE staff information about the current state of watersheds, likely future state of watersheds, and consequences of management actions. The information helps water managers make wise operation decisions.

Culvert

A culvert is a conduit that conveys stream flow through a roadway embankment or past some other type of flow obstruction.⁴

Data Storage System
(DSS)

DSS is a database system developed by HEC to store and retrieve efficiently scientific data that are typically sequential. Such data types include, but are not limited to, time series data, curve data, spatial-oriented gridded data, and others. HEC designed the system to make it easy for users and application programs to retrieve and store data. DSS is incorporated into most of HEC's major software applications.

Data Storage System
(DSS) Pathname

A DSS pathname is a unique reference to a record or time series in a DSS file. The pathname is structured so that it is easy to group related data together. A pathname is separated into six parts (separated by slashes) labeled "A" through "F", as follows: /A/B/C/D/E/F/.

Data Storage System
Visual Utility Engine
(HEC-DSSVue)

HEC-DSSVue is a software utility developed by HEC that provides a graphical user interface for viewing, editing, and manipulating data in DSS files.

Data validation

Data validation is the process of reviewing data and editing or deleting data that are erroneous.

Datum

Datum refers to the reference specifications of a measurement system, usually a system of coordinate positions on a surface (a horizontal datum), or heights above or below a surface (a vertical datum).³

Directory

A directory catalogs the computer files in a nested folder-like structure. Files are organized by storing related files in folders in the same directory.

Diversion

A diversion removes and redirects water from its normal course in a channel.

Domestic Satellite
Receive-Only Terminal
(DROT)

DROT is software that facilitates receipt of satellite data.

Easting

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

Flood Impact Analysis
(HEC-FIA)

HEC-FIA is an HEC analysis application that assesses consequences of flow or water surface elevations in the system. Inputs include computed or observed flows or water surface elevations at critical locations. Outputs include economic, life loss, or other measures of impact, or optionally, information on actions to be taken in response to flows or elevations that will be experienced.

Flow blending

Flow blending is the capability of CWMS to transition smoothly from observed flows during the "lookback period" to simulated flows during the forecast period. The lookback period is the period occurring prior to the time of forecast.

Forecast

A CWMS forecast is a simulation of watershed processes and consequences of flooding based on input data and hydrologic, reservoir operation, hydraulic, and impact analysis models configured in CWMS. Forecast results include flow and stage in the channel from watershed runoff, reservoir release schedules, floodplain inundation maps, floodplain consequence reports, and reports listing actions for emergency responders to take. These results inform water management decision making.

Forecast alternative

A forecast alternative is a single forecast scenario defined by a specific set of data and model alternatives. A second forecast alternative would be defined by different data or model alternatives.

Freeboard

Freeboard is the vertical distance from the water surface to the top of the channel, levee, or floodwall at design condition, and serves as a factor of safety for containing water in the stream without overtopping the channel, levee, or floodwall.¹

Geographic Information
System (GIS)

GIS is an integrated collection of software and data used to view and manage information about geographic places, analyze spatial relationships, and model spatial processes.³

Geo-referenced grid

A geo-referenced grid is a set of geographic data that are represented as a raster and have been linked to a coordinate system for viewing, querying, and analyzing with other geographic data.

Gridset

A gridset is a sequence or time series of georeferenced grids that describe properties or states of a watershed as they vary spatially and through time. Examples include sequences of precipitation or air temperature grids.

HEC-GridUtil

HEC-GridUtil is a software application developed by HEC that allows you to view, process, and analyze gridded data sets stored in DSS format.

Hydrograph

A hydrograph is a relationship of stage, discharge, velocity, or other state of water with respect to time at a certain location.

Hydrologic Engineering Center (HEC)

HEC is a USACE designated Center of Expertise in the technical areas of surface and groundwater hydrology, river hydraulics and sediment transport, hydrologic statistics and risk analysis, reservoir system analysis, planning analysis, real-time water control management, and a number of other closely associated technical subjects. HEC is the developer of CWMS.

Hydrologic Modeling
System (HEC-HMS)

HEC-HMS is an HEC analysis software application that simulates watershed response to precipitation. Inputs may include observed or forecasted precipitation, temperature, snowpack, and other environmental conditions. Outputs include flows throughout the watershed, including inflows to reservoirs.

Impact area

In HEC-RTS, an impact area is a distinct portion of a watershed in which rising stage in a stream, river, lake, or reservoir has a consequence that is to be assessed. The boundaries of an impact area are defined by a closed polygon. You characterize the effects of rising stage by describing the property and population at risk in the area bounded by the polygon as input to HEC-FIA.

Inundation

Inundation is a condition in which water covers normally dry land, primarily caused by severe events along rivers or the coast.⁶

Java Archive (JAR, .jar)

JAR is a platform-independent file format that aggregates many files into one. Multiple Java applets and their requisite components (.class files, images, and sounds) can be bundled in a JAR file. The JAR format also supports compression, which reduces file size.⁸

Layers

Layers in HEC-RTS are like transparencies laid one on top of the other. Each includes representations of static physical images such as roads, county and state boundaries, rivers, and subbasins. These are layered in the display area as color pictures. See Chapters 3, 4, and 5 for more information about layers.

Layer tree

A layer tree is a list representing the hierarchical arrangement of layers displayed in HEC-RTS.

Levee

A levee is a manmade barrier built along a stream to reduce flooding in the adjacent floodplain from rising water in the stream.

Log file

A log file is a file that holds messages produced by the HEC-RTS software. The types of messages include information-only messages and error messages.

Lookback period

The lookback period is the period occurring prior to the time of forecast.

Loss method

The loss method is a model for calculating infiltration and other abstractions of precipitation in a subbasin.

Map layer

A map layer is a digital map of watershed features that is configured to display in HEC-RTS. A map layer is displayed as a color picture. Map layers help you visualize your watershed.

Map projection

A map projection uses mathematical formulas to relate spherical coordinates on the globe to flat, planar coordinates.²

Map Window

The map window is the window in the HEC-RTS that displays the graphical (and usually georeferenced) representation of the watershed.

Meteorologic Forecast Processor (MFP)

MFP is an HEC analysis software application that processes meteorological forecasts for input to HEC-HMS. Inputs are forecasted meteorological data such as precipitation and temperature. Outputs are forecasted meteorological time series formatted for compatibility with HEC-HMS.

Meteorologic model

Meteorologic models are one of the main components in an HEC-HMS project. Their principal purpose is to prepare meteorologic boundary conditions for subbasin runoff computations.

Model alternative

A model alternative is a single model configuration with a specific set of input and parameters. A second model alternative would be defined by a different configuration or different input or parameters.

Modeling module

The Modeling module in the CAVI is the grouping of commands for model execution. These are commands for setting up and executing analysis applications and viewing results.

Module

Commands in the CAVI are organized by function: watershed setup, data acquisition, data visualization, and model execution. A module is the grouping of commands related to a function. The CAVI contains the Setup module for watershed setup, the Acquisition module for data acquisition, the Visualization module for data visualization, and the Modeling module for model execution. Each module has menus, tools, and a display area specific to its function.

Northing

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

National Weather Service (NWS)

NWS is a Federal agency that makes and issues meteorologic and hydrologic forecasts. NWS forecasts may be used as input for HEC-RTS simulations.

Off-channel storage area

In HEC-RAS, an off-channel storage area is a modeling element used to represent ponded water in interior areas, adjacent ponds and lakes, urban areas next to rivers, etc.

Parameter

A parameter is a representation of a watershed condition in a model of the watershed. You can set parameter values using HEC-RTS. Varying parameters may vary analysis results.

Precipitation grid

A precipitation grid is a spatial representation of precipitation over the whole watershed for an interval of time.

Project benefit

A project benefit is a reduction in adverse flood consequences attributable to a project or projects. Project benefit commonly is computed as the difference between the without- and with-project consequences.

Projects

Projects are man-made structures such as reservoirs or levees that are built to control water.

Quality color bar

The quality color bar is a thick, segmented line displayed in the HEC-RTS map window that represents the history of the data quality at a specific location within the time window you have established.

Quantitative precipitation forecast (QPF)

QPF is a spatial and temporal precipitation forecast for a specified region or area.⁷

Raw data

Raw data are data that are acquired, transmitted, and received, but not yet subjected to quality tests and revised. They are preserved in an HEC-RTS DSS file and are identified as raw data.

Regulated flow

Regulated flow is flow that has been changed from its natural state due to the influence of hydraulic constrictions or manmade influences.

Reservoir

A reservoir is a structure built to control water for uses such as flood control, hydropower generation, and water supply. Storing water in a reservoir can reduce flood consequences by regulating flow to reduce flood stages.

Reservoir System
Simulation
(HEC-ResSim)

HEC-ResSim is an HEC analysis software application that simulates behavior of reservoirs and linking channels, following user-specified operations for reservoir release decision making. Inputs include flows into reservoirs and unregulated flows downstream of reservoirs. Outputs include reservoir releases, downstream regulated flows, and reservoir storage conditions.

Revised data

Revised data are data that are validated and transformed for use in modeling. They are saved to the CWMS database and are identified as potentially revised data.

River Analysis System
(HEC-RAS)

HEC-RAS is an HEC analysis software application that simulates, in one-dimension, behavior of channels and adjacent floodplains. This permits determination of water surface elevations corresponding to flows computed by HEC-HMS or HEC-ResSim. Inputs include flows, and outputs include water surface elevations.

River Analysis System
Mapper (RAS Mapper)

RAS Mapper is tool that is 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 portion of a stream network. In HEC-HMS and HEC-ResSim, a routing reach is a modeling element used to compute behavior of flow in a channel.

Scripting

Scripting is the process of automating the actions of a program, so a prescribed sequence of actions can be executed with a single action.

Setup module

The Setup module in HEC-RTS contains the watershed setup commands. These are commands for configuring inputs, models, and outputs that describe a watershed's behavior.

Simulation

A simulation is a mathematical representation of the behavior of a system, given inputs and initial conditions.

Stage

Stage is the vertical distance of a water surface above or below a local or national datum.

Stream alignment

A stream alignment is a representation of the stream network in the watershed. The alignment shows routing reaches and indicates where confluences and bifurcations occur and provides a sense of distance and scale.

Stream element

A stream element is part of the representation of the stream network in the watershed. Specifically, a stream element is a segment of the stream alignment that is composed of vertex points (points with known coordinates). The beginning and ending vertex points of a stream element are stream nodes. Stream elements typically begin or end at a confluence, bifurcation, or at the boundary of the river system.

Stream junction

Stream junctions are part of the representation of the stream network in the watershed. Specifically, a stream junction is a point where two stream elements meet (two stream nodes at one location).

Stream node

Stream nodes are part of the representation of the stream network in the watershed. Specifically, stream nodes are the beginning and ending points for each stream element. Stream nodes are points where stream elements meet (stream junctions).

Stream stationing

Stream stationing is a reference system for locating features with distance along a stream. HEC-RTS creates and labels stream stations (or river stations) along each stream element. The station at the downstream end of an element is Station 0 (zero), and the stationing increases upstream along the element according to the linear distance between vertices on the stream element in the watershed coordinate system.

Subbasin

A division of a watershed typically delineated based on the terrain within the watershed. The entire precipitation within a subbasin drains to a common point.

Supplemental program

A supplemental program is a program or script that is not included with HEC-RTS. The program or script is developed by the user and may be added to the program order so it will be executed from HEC-RTS.

Threshold color bar

The threshold color bar is a thick, segmented line shown in an HEC-RTS map window that represents a linear histogram that compares current data against threshold values set for a location.

Time series

A time series is an ordered sequence of values of a property or state at equally spaced time intervals. DSS files also support time series composed of irregularly spaced increments.

Time series icon

A time series icon is a symbol in the display area that provides quick access to time-series data assigned to the icon. The location of the time series icon on the watershed map corresponds to the location to which the data pertains. Time series icons can be used to view data, images, web pages, scripts, and document files.

Time window

A time window is the duration that will be simulated. A time window is defined by starting and ending dates and times.

Transform method

The transform method is a model for calculating surface runoff from precipitation on a subbasin.

U.S. Army Corps of Engineers (USACE)

USACE is a Federal agency that operates about 700 water control projects in the U.S. as part of its water control management mission. These projects include reservoirs, navigation locks and dams, and levee and bypass systems with closure and diversion structures.

United States Geological Survey (USGS)

USGS is a Federal agency that collects hydrologic data with a network of gages and reports the data in real-time.

Validation list

A validation list is a way to organize data in HEC-RTS DSS files for editing or validation.

Vertex point

A vertex point is a point with known coordinates on a stream element in the stream alignment.

Visualization module

The Visualization module in HEC-RTS contains commands for data visualization. These are commands for displaying observed and forecast data to evaluate the hydrometeorological state of the watershed.

Watershed

In HEC-RTS, a watershed is a set of data, models, and images that represent watershed lands and the channels, gages, and water control features within the watershed.

Watershed pane

The watershed pane in the HEC-RTS refers to the set of Visualization, Acquisition, Modeling, and Setup module tabs (tabbed menus). Clicking a module tab opens that module in HEC-RTS.

World Coordinate System (WCS)

To maintain a geographic reference (also called a geo-reference), HEC-RTS uses a user-selected and customizable coordinate system, called the World Coordinate System. This superimposes a grid on layer features to establish x and y coordinates in WCS for each point on the layer. The x coordinate is referred to as "easting", and the y coordinate is referred to as "northing". Possible choices for the WCS include but are not limited to State Plane Coordinates and Universal Transverse Mercator (UTM) coordinates.

Zone

A set of subbasins in the watershed.