# The 3D National Topography Model Call for Action Part 1 - The 3D Hydrography Program

The implementation of 3D National Hydrography Program marks the beginning of a new era of water data. The public and private sectors that depend on high-quality water data have expressed the need for better information to answer the most demanding water resource management questions. Community-wide coordinated investments contribute toward consistent set of national water data.

3D NATIONAL TOPOGRAPHY MODEL  | INTRODUCING THE 3D HYDROGRAPHY PROGRAM  | DESIGNING THE PROGRAM  | BUILDING THE PROGRAM | NEXT STEPS  | CONCLUSION  REFERENCES CITED

## 3D NATIONAL TOPOGRAPHY MODEL

Topography is defined by terrain and water, each influencing and shaping the other. The 3D National Topography Model (3DNTM) is a new initiative that updates USGS elevation and hydrography data and integrates these interdependent topographic relationships into a 3D model to deliver higher-quality data and support improved geospatial analysis. The 3DNTM, including 3DHP and the next generation of the 3D Elevation Program (3DEP), will provide foundational data to meet the most demanding scientific requirements and enable data-driven decisions across user communities.

Key elements of the 3DNTM are in place or under development, such as completing nationwide 3DEP and High Resolution NHDPlus baseline datasets, piloting the integration of hydrography and elevation datasets, and developing this Call for Action Part 1 focused on hydrography and a Call for Action Part 2 focused on the next generation of 3DEP. Later development phases of the 3DNTM will include construction of and a transition to a 3D data model that will include additional topographic datasets of The National Map managed by the USGS National Geospatial Program

### A Legacy of Surface Water Mapping

For more than 20 years, the USGS and partners have developed and maintained the National Hydrography Datasets as the authoritative mapping of the Nation’s surface water network and watersheds (OMB, 2002). The National Hydrography Datasets have been integral to a wide range of business uses and mission-critical activities undertaken and managed by government entities, nonprofit organizations, Tribes, and private companies including water quality monitoring, flood risk prediction, infrastructure development, ecosystem management, agricultural resources, and many more. These hydrography data, which are regularly used to depict the stream network on maps by a broad variety of users, provide a consistent framework for geographic analyses and hydrologic modeling and support scientific research by connecting information from the landscape to the stream network.

The National Hydrography Requirements and Benefits Study (HRBS; Dewberry, 2016) was conducted to document and understand current and emerging requirements and future potential benefits for hydrography data. The participants included Federal, State, Tribal, Territorial, and local government associations, private companies, associations, and non-profit organizations. Data users identified \$538.5 million in annual benefits from the current National Hydrography Datasets. An additional \$602.4 million in annual benefits could be realized if all unmet needs are satisfied, for a total of over 1.14 billion in potential annual benefits. HRBS identified requirements to link to other water datasets such as the National Wetlands Inventory (NWI) and also signaled that hydrography data need to be more spatially accurate, better aligned to elevation data, and kept more current, among other findings. ## INTRODUCING THE 3D HYDROGRAPHY PROGRAM ### A New Approach to Water Data Building on the decades of experience developing and managing the National Hydrography Datasets, the USGS is establishing the 3D Hydrography Program (3DHP) initiative to completely refresh the Nation’s hydrography data and improve discovery and sharing of water-related data. When fully implemented, 3DHP is estimated to provide more than1 billion in benefits every year, in addition to myriad societal benefits. Additionally, decisions that directly affect water would be better informed. The next generation of surface water mapping under the new 3DHP will incorporate the most relevant and impactful components of the existing hydrography data and accomplish major spatial accuracy improvements. The resulting products and services will be freely available and openly accessible.

The 3DHP will significantly improve the level of detail, currency, and inclusion of hydrography data by deriving a 3D stream network and hydrologic units from accurate, high-quality 3D Elevation Program (3DEP) data, as well as hydrologically enhanced digital elevation and other surfaces to support applications like hydrologic and hydraulic modeling. 3DHP will improve information such as streamflow permanence and vastly improve the ability to account for the hydrologic cycle by connecting to wetland, engineered hydrologic systems, and groundwater data.

3DHP will establish an information infrastructure, or “infostructure”, to support sharing and discovering water-related data in the context of the improved stream network. USGS will develop and implement an operational system, including a modernized data model to support this vision. In line with the Geospatial Data Act of 2018 and Federal Geographic Data Council (FGDC) guidance (FGDC 2021), 3DHP Datasets and Infostructure will emphasize being FAIR – findable, accessible, interoperable, and reusable.

3DHP data and capabilities will allow scientists to more fully model the hydrologic cycle, engineers to make better development decisions, water suppliers to improve water quality and availability, disaster response planners to mitigate natural disasters, and natural resource managers to better protect the environment. When 3DHP data are widely available, further private sector and government innovations will follow for years to come.

### 3DHP Datasets

3DHP Datasets will include a 3D hydrography network generated from 3DEP data including waterbodies, hydrologic units, hydrologically enhanced elevation and other surfaces, and related attributes that bring a new level of consistency and accuracy. Using 3DEP data will ensure that 3DHP Datasets are built on a high-quality, standardized national data source to ensure spatial and temporal consistency in derived products for reporting, modeling, and scientific research. This direct relationship of hydrography to the elevation surface will create a cohesive set of hydrographic information, increasing its usability for applications like flood modeling and prediction, culvert and bridge engineering design, and stormwater management.

3DHP Datasets will be a vertically integrated data stack that includes:

•    A stream network derived from high quality 3DEP elevation data;
•    Multiple levels of nested hydrologic units derived using the stream network and elevation data;
•    Hydrologically enhanced elevation and other surfaces that align with the stream network and hydrologic units; and
•    Additional attributes that assist with hydrologic and stream network routing and analysis

3DHP Datasets will inherit key attributes of the NHD, WBD, and NHDPlus HR, preserving the components of those datasets that have evolved and improved throughout their history. 3DHP Datasets will include new attributes and connections to other data such as the USFWS National Wetland Inventory, groundwater, and engineered hydrologic systems like stormwater networks.

The modernized 3DHP data model will include both the stream network and hydrologic units with topological rules enforcing their geometries. The model will store the highest level of detail available for derived stream network features, with processes for generalizing the stream network and hydrologic units. The new 3DHP features are expected to be within one meter vertically, and within two meters horizontally, of the bottom of a channel depicted in a high accuracy elevation surface, greatly improving the positional accuracy of features. The stream network will be connected such that flow models will work correctly across the entire network. Improved spatial accuracy will also make the new hydrography data more compatible with other data such as surficial geology, soils, landcover, transportation networks, and other infrastructure.

A snapshot of all 3DHP data will be available annually as a national dataset release with a persistent web location to support citations in scientific research. The most current data will be available as individual data layer downloads and accessible as map services between annual data releases. Open data standards will be considered in developing 3DHP Datasets.

## Enhancements included in the 3D Hydrography Program

##### 3D stream network
The stream network will be derived from 3DEP 1-meter standard product digital elevation models (DEMs) created from lidar (5-meter DEMs from IfSAR in Alaska), and will include elevation values on each vertex to enable 3D analysis of the data.
##### Hydrologically enhanced elevation and other surfaces
Hydrologically enhanced raster DEMs will be created as a part of the stream network derivation process such that the flow of water across the surface is represented accurately. Other surfaces that are created during the derivation process, such as geomorphic classifications, flow accumulation, and flow direction surfaces, may also be distributed.
##### Topobathymetry
USGS is researching how to create a continuous topobathymetric surface derived from high-resolution elevation and bathymetry. Plans to operationalize inland bathymetry will be addressed in the program plan for the next generation of 3DEP.
##### 3D hydrologic units
Hydrologic units will be derived using the stream network and elevation data, while retaining and utilizing important outlet point information from the Watershed Boundary Dataset.
##### Groundwater connections
Connection between surface and groundwater features will be supported, for example, by identifying gaining and losing stream reaches or providing estimates of groundwater contributions to streamflow, where known.
##### Wetlands
Collaborative mapping of the stream network and the NWI will enable the two datasets to function together as a whole and to accurately depict the inland waters of the U.S.
##### Engineered Hydrologic Systems
3DHP will include information on engineered hydrologic systems, with a concerted effort to integrate connection points to, or generalized representations of, stormwater systems in urban areas.
##### Culverts
Culvert data acquired during the process of deriving hydrography from elevation will be made available.

### 3DHP Infostructure

The 3DHP Infostructure will be co-designed with 3DHP Datasets to provide a set of open and interoperable web-based tools, maps, and data catalogs housed at USGS, creating a robust system for users to reference their information about water to support discovery of data in the context of the stream network – everything from water levels at stream gages to water temperature to the health of fish and aquatic life in a stream. The 3DHP Infostructure will provide the geospatial underpinning for the Internet of Water (IoW), which seeks to advance the transformation and modernization of water data infostructure in the U.S. The 3DHP Infostructure will be collaboratively built and open and available to everyone.

3DHP hydrographic addressing tools will enable users to link water data to the 3DHP Datasets and create and share the information as authoritatively managed web-based maps. 3DHP hydrographic addressing tools will provide reference locations on the stream network, similar to street addresses, that can be attached to a user’s data records. 3DHP search and discovery tools will be available to analyze addressed data within the stream network to understand relationships between different records or observations, such as the distance between water quality observations or the downstream relationship of a fish population to a dam. Any kind of water-related information can be addressed including hydrology, geomorphology, water quality, biology, regulations, etc.

### 3DHP Lifecycle

Due to the complexity of meeting data specifications and the need for a consistent data product, it is anticipated that much of the work to delineate the stream network from elevation will be completed by the private sector for the USGS or partner organizations. All data must meet specifications published by USGS to support derivation of hydrography features from 3DEP 1-meter standard product lidar-derived DEMs, or a 5-meter elevation grid created from IfSAR in Alaska. USGS will be responsible for data validation prior to accepting data into national data holdings. Once in national data holdings, errors within the 3DHP datasets either discovered by USGS or reported by users will be corrected by USGS staff, with a 3DHP maintenance goal of correcting errors in 1-2 months after they are reported. The stream network will be reviewed on approximately a 4-5 year cycle with updates applied as needed (dependent on 3DEP data availability). In the future, change detection based on either the elevation data or hydrography may trigger updates to 3DHP data.

USGS will also be responsible for producing data such as hydrologic units and some attributes, as well as the general management and delivery of data to the public. USGS will maintain an enterprise system to manage 3DHP Datasets and Infostructure. The 3DHP Infostructure must be developed, tested, and operationalized to use the 3DHP Datasets as the geospatial foundation. These actions will be addressed fully in internal USGS 3DHP Operational Plans.

## DESIGNING THE PROGRAM

### Program Scenarios

HRBS highlighted the need for a modernized, 3D-enabled hydrography program to support emergent user and stakeholder applications and provide additional benefits. To help define a modernized program, three scenarios created from HRBS were considered.

Scenario 1 (status quo) retains the current hydrography data with minimal incremental improvements. While USGS would make general progress to update the NHD using current technologies, continued local maintenance programs with varied  funding and priorities would continue to decrease national consistency of the datasets over time.

Scenario 2 strives to replace all existing hydrography over a nine-year period with data derived from 1 meter DEMs created from Quality Level* 2 (QL2) or better 3DEP lidar data, as well as improvements supported by HRBS such as improved accuracy, accounting for more of the hydrologic cycle, and more effective maintenance of data.

Scenario 3 is similar to Scenario 2, except the source data would be 0.5 meter DEMs created from Quality Level 1 (QL1) or better 3DEP lidar data. QL1 data are not readily available across the country, making this scenario currently difficult to achieve, but may be a viable program in the future.

### Research Requirements

The 3DHP planning process identified numerous issues or questions for which additional assessments, evaluations, or research is required. Research will be undertaken by the USGS National Geospatial Program (NGP), National Geospatial Technical Operations Center (NGTOC) for operational development activities, the USGS Center of Excellence for Geospatial Information Science (CEGIS) for primary GIS and hydrography-related research, and USGS Water Resources Mission Area, and the broader community of researchers for basic water data and hydrology-related research. The near-term and immediate requirements have been identified, and the research agenda will be managed as a cohesive activity within the USGS NGP.

To address emerging needs and to test leading technologies, the development strategy for the 3DHP Infostructure calls for an evolution of products and services. Development teams will advance a core functionality, and through feedback from the community the 3DHP Infostructure will be improved. User community input and collaboration will also be provided by the 3DHP Working Group. Over time, the 3DHP Infostructure will evolve to improve functionality and grow additional partnerships through the community.

## CONCLUSION

In 1884, Congress authorized the U.S. Geological Survey to begin systematic topographic mapping of the United States. The implementation of 3D National Hydrography Program marks the beginning of a new era of water data. The public and private sectors that depend on high-quality water data have expressed the need for much better information to answer the most demanding water resource management questions. USGS proposes to work with partners to share the costs of a new program that will address these needs in as little as nine years, assuming the community-wide funds are available to complete the work. Federal, State, Tribal, and local governments are making independent investments to improve their water information, and without a coordinated effort their investments are not contributing to a consistent set of national water data. Government agencies need to respond to this Call for Action to implement the 3DHP Datasets and Infostructure as the universal geospatial underpinnings for water information. The return on investment is significant. The need to support better water resources decisions cannot be overstated. Together, the community can achieve 3D Hydrography Program.

## REFERENCES CITED

Dewberry, 2016, National Hydrography Requirements and Benefits Study―Preliminary results: Fairfax, Va., Dewberry, May 20, 2016, 139 p. plus appendixes, accessed January 28, 2022, at https://www.dewberry.com/services/geospatial/national-hydrography-requirements-and-benefits-study.

Federal Geographic Data Committee, 2021, FGDC Technical Guidance: Data.gov and The GeoPlatform Metadata Recommendations Including Guidelines for National Geospatial Data Assets (NGDA), accessed January 28, 2022, at https://www.fgdc.gov/technical-guidance/metadata/fgdc-technical-guidance-datagov-geoplatform-ngda.pdf.