Glossary

The following are definitions of terms used in this manual. The terms are defined in context with CWMS.

Term	Definition
Acquisition module	The Acquisition module in the CAVI is the grouping of commands for data acquisition. These are commands for monitoring receipt of data by the CWMS database (and DSS files for gridded data), validating the quality of incoming data, and editing the data when required.
Arc shapefile	The Arc shapefile is the native data structure for the ArcGIS® software (GIS stands for Geographic Information System). 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 a CWMS watershed 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. (HEC-HMS)
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 meteorological 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 observed readings from a gage within the watershed.
Collections	A group or set of HEC-DSS time-series datasets that share a common location (A & B Parts), parameter (C Part), and time-step (E Part). Collections are defined in DSS with C:000000 contained in the F-Part, with each individual member assigned a unique number. IE C:000001, C:000002, etc.
Common schematic	A common schematic consists of a stream alignment, map layers, time series icons, computation points, Emergency Planning Zone 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.
Control and Visualization Interface (CAVI)	The CAVI is the graphical user interface (GUI) of CWMS. You command CWMS with graphical menus and tools available in the CAVI. With the CAVI you configure watersheds, view and edit data, setup and run forecasts, and view results.
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 CWMS database 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.
Corps Water Management System Visual Utility Engine (CWMS-Vue)	CWMS-Vue is a software utility developed by HEC that provides a graphical user interface for viewing, editing, and manipulating data in HEC-DSS files and the CWMS database. It is the CWMS version of HEC-DSSVue.
Culvert	A culvert is a conduit that conveys stream flow through a roadway embankment or past some other type of flow obstruction.
Cumulus	Cumulus is a WMES-CWMS web service that offers a one stop shop for meteorological data access for the U.S. Army Corps of Engineers Water Management and Hydrology and Hydraulics Communities of Practice. Cumulus is primarily meant to serve real-time hydrologic and hydraulic forecast modeling, model development and calibration for CWMS applications, and planning and dam safety applications.
CWMS Data API (CDA)	The Corps Water Management System (CWMS) Data API (CDA) is a tool for anyone to gather data about current operations status and historical events from US Army Corps of Engineers districts across the United States. This tool was formerly known as RADAR.
Data Storage System (HEC-DSS)	HEC-DSS is a database system developed by HEC to efficiently store and retrieve 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. HEC-DSS is incorporated into most of HEC's major software applications.
Data Storage System (HEC-DSS) Pathname	An HEC-DSS pathname is a unique reference to a record or time series in an HEC-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 HEC-DSS files.
Data stream	A CWMS data stream is a group of processes that receive real- time data from remote sources and provide those data to the CWMS database and other files and processes. The primary CWMS processing components are DataSender, DataReceiver, DataCapture, and DataReader, which can be combined to process any type of data, but are generally used to capture, decode, and load SHEF data and National Weather Service (NWS) gridded data products into CWMS. CWMS data stream components typically run together on a CWMS Solaris server, but can be configured to operate in a Wide Area Network (WAN) of dispersed Solaris servers and PCs. A typical office using CWMS will have several CWMS data streams, allowing the office to separate the data load by data source, type of data, or region.
Data validation	Data validation is the process of reviewing data and editing or deleting erroneous data.
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).
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. They are elements found in HEC-HMS.
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.
Ensemble	Ensembles are sets of time series data, where each member of the data set represents a different “possibility” for a given location and parameter.
Ensemble Forecast Processor (EFP)	A plugin that allows you to process various statistical metrics from ensemble flows at specified locations in the watershed, and then use those metrics to influence other model alternatives in the forecast.
Ensemble Member	A single set of time series data that represents a single possibility for a given location/ parameter.
Extract List	The Extract List tells the CAVI where to get data from, how to extract it into the forecast.dss file, and what it will be named once it is in the forecast.dss file.
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 HEC-HMS to transition smoothly from observed flows during the "lookback period" to simulated flows during the forecast period. The lookback period is the period of time 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.
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.
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 temporally. Examples include sequences of precipitation or air temperature grids.
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 USACE's 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.
Emergency Planning Zone	In CWMS, an Emergency Planning Zone 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 Emergency Planning Zone are defined by a closed polygon. The effects of rising stage is characterized 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.
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.
Layers	Layers in the CAVI 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.
Layer tree	A layer tree is a list representing the hierarchical arrangement of layers displayed in the CAVI.
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 CWMS program. The types of messages include information-only messages and error messages.
Lookback period	The lookback period is the period of time 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 the CAVI. 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.
Map Window	The map window is the window in the CAVI 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. Note: This software is depreciated and will no longer be supported or available after CWMS 3.4.
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.
Meteorological Visualization Utility Engine (HEC-MetVue)	HEC-MetVue facilitates viewing and manipulation of meteorological datasets as well as performing a variety of computations and analyses, including temporal and spatial aggregation of datasets and areal average 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)	The NWS is a Federal agency that makes and issues meteorologic and hydrologic forecasts. NWS forecasts may be used as input for CWMS 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 the CAVI. Varying parameters may vary analysis results.
Precipitation grid	A precipitation grid is a spatial representation of precipitation over the enitre 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 shown in the CAVI display area 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 weather forecast that predicts the expected amount of liquid precipitation (rain, melted snow, etc.) that will fall over a specified area during a specific time period.
Quantitative Precipitation Estimation (QPE)	QPE is a method used to approximate 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; essentially, it's a way to calculate how much rain has fallen in a particular area based on various data sources.
Raw data	Raw data are data that are collected, transmitted and received, but not yet subjected to quality tests and revised. They are preserved in the CWMS database 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.
Replace from Base	A CAVI feature that allows the user to re-base their current unsaved models in a forecast run by replacing that model from the base watershed model.
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 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 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.
Save to Base	A CAVI feature that allows the user to save an Forecast run altered model to the Base watershed. Replacing the previous base model in that watershed.
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 the CAVI is the grouping of 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 also points where stream elements meet (stream junctions).
Stream stationing	Stream stationing is a reference system for locating features with distance along a stream. CWMS 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 CWMS. The program or script is developed by the user and may be added to the program order so it will be executed from CWMS.
Snow water equivalent (SWE)	SWE is a measurement of the amount of water in snow, and is recorded in inches or centimeters. It's calculated by determining how much water would result if the snow were melted.
Threshold color bar	The threshold color bar is a thick, segmented line shown in the CAVI display area 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. HEC-DSS and the CWMS database 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 and 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 approximately 740 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 the CWMS database for editing or validation.
Vertex point	A vertex point is a point with known coordinates for an element in the stream alignment.
Visualization module	The Visualization module in the CAVI is the grouping of commands for data visualization. These are commands for displaying observed and forecast data to evaluate the hydrometeorological state of the watershed.
Watershed	In CWMS, 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 CAVI refers to the set of Visualization, Acquisition, Modeling, and Setup module tabs (tabbed menus). Clicking a module tab opens that module in the CAVI.
World Coordinate System (WCS)	To maintain a geographic reference (also called a georeference), CWMS 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 zone is a grouping of subbasins used during calibration of the HEC-HMS model.