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Glossary

Concepts and Terms​

Catchment​

A specific, contiguous geographic area. In hydrologic modeling, larger regions are divided into catchments to allow for localized modeling and outputs.

Note that catchment IDs may not be persistent across hydrofabrics. Instead, points of interest should be used as persistent identifiers.

Calibration​

The process of tuning a hydrologic model's parameters to more accurately match observed outcomes.

The NGIAB ecosystem offers the NGIAB Calibration utility to streamline this process.

Evaluation​

The process of assessing the quality and performance of a hydrologic model.

The NGIAB ecosystem offers integration with the TEEHR toolkit to streamline this process.

Forcing​

Values provided as inputs for a hydrologic model. The term comes from the practice of experimentally "forcing" certain input values by overriding the usual flow of data into a model.

Formulation​

Some set of defined links between modules within the NextGen Framework.

Gage​

Short for a stream gauge or streamgage. Fixed locations where streamflow properties such as water level and streamflow are measured and recorded.

Hydrofabric​

Broadly speaking, a hydrofabric defines the physical hydrology of a region, allowing for the region to be modeled. These hydrofabrics are defined by physical attributes and the links between those attributes.

For the R library, see "Hydrofabric (R library)".
For the hydrofabric used as a baseline by most NextGen models, see "USGS-NOAA Reference Fabric".

Nexus​

A point of data exchange within a NextGen network. Nexuses are placed at endpoint locations where water flows to within a catchment, such as along its borders.

Note that nexus IDs may not be persistent across hydrofabrics. Instead, points of interest should be used as persistent identifiers.

Point of Interest​

A physical position that is being used in a model or hydrofabric, such as a gage location. Points of interest are tracked by a wide variety of sources, including the Army Corp National Inventory of Dams and the USGS Gages III database.

Within the USGS-NOAA reference fabric, points of interest are given a persistent POI identifier to allow for tracking across hydrofabric versions.

Realization​

The instructions that tell the NextGen Framework how to run a simulation.

Realizations are stored in model realization files. These files contain formulations of modules, along with the order in which those modules should be run.

Subsetting​

The practice of taking a subset of a larger dataset. Subsetting is both common and highly recommended for model runs, as it can greatly reduce the computational load required.

Both GUI and command-line utilities for subsetting the NextGen reference fabric are available within the Data Preprocess utility.

Vector Processing Unit (VPU)​

Regional discretizations used by the USGS-NOAA reference fabric. These VPUs designate fixed regions for model runs and data collections.

Somewhat related to catchments, though VPUs are significantly larger and act as collections of contiguous catchments.

File Formats​

Geopackage (.gpkg)​

An open, non-proprietary data format for geographic inforamtion systems. NextGen uses geopackages to contain hydrofabrics.

JSON (.json)​

Short for "JavaScript Object Notation", JSON files are used to store objects consisting of name-value pairs. Despite the name, JSON sees wide use in non-JavaScript contexts.

NextGen uses JSON to store its model realization files (ngen-run/config/realization.json), which tell the NextGen engine how to execute a model run.

NetCDF (.nc)​

An open standard for arrays of scientific data. NextGen uses the netCDF-4 standard to contain model variable metadata.

Tarball (.tar.gz)​

A common archive format among Linux users. Analogously to formats like .zip and .rar, it allows for folders of content to be shared as a downloadable file.

YAML (.yaml/.yml)​

Short for "Yet Another Markup Language", YAML files are typically used to store metadata. NextGen uses a YAML file to store run configurations (ngen-run/config/ngen.yaml).

Tools and Software​

Basic Modeling Interface (BMI)​

A standardized set of function and parameter bindings that allow models to interact with external components in a predictable, modular way.

BMI has been adopted as the standard for models compatible with the NextGen framework. Documentation for BMI is available here.

Hydrofabric (R library)​

A standard library maintained by NOAA-OWP for processing and updating hydrofabrics in R.

Information on Hydrofabric is available here.

National Hydrography Dataset Plus (NHDPlus)​

A comprehensive reference hydrofabric for the United States, maintained by the EPA and USGS. NHDPlusV2 is the most current and relevant version.

Relevant to NextGen due to its use as a base for the USGS-NOAA reference fabric. As such, many tools and utilities designed for the NHD and its descendents will also work for NextGen hydrofabrics.

TEEHR​

Short for "Tools for Exploratory Evolution in Hydrologic Research", TEEHR is a Python library that provides comprehensive tooling for model evaluation. TEEHR is included as a part of the NGIAB ecosystem.

Information on TEEHR is available here.

Tethys Platform​

Tethys is a Python-based platform for building geospatial web apps. It forms the core of NGIAB's Data Visualizer, alongside many other CIROH applications.

Information on the Tethys Platform is available here.

t-route​

A dynamic channel routing model using in determining routing for river networks. T-route is BMI-compliant and is used to prepare hydrofabrics for both the National Water Model and NGIAB.

Information on t-route is available here.

USGS-NOAA Reference Fabric​

A hydrofabric jointly developed by the NOAA, USGS, and Lynker Spatial, which provides a shared baseline for NextGen models.

Implementation and usage information for this fabric is available here.