Hydrology Data

Streams — Lakes — Ponds — Wetlands  — HUC

Data Documentation

The National Hydrography Dataset (NHD) is a feature-based database that interconnects and uniquely identifies the stream segments or reaches that comprise the nation's surface water drainage system.  Medium resolution NHD is based on the content of the U.S. Geological Survey 1:100,000-scale Digital Line Graph (DLG) hydrography data, integrated with reach-related information from the U.S. Environmental Protection Agency Reach File Version 3.0 (RF3).  More specifically, it contains reach codes for networked features and isolated lakes, flow direction, names, stream level, and centerline representations for polygonal water bodies.  Reaches are also defined to represent water bodies and the approximate shorelines of the Gulf of Mexico.

Hydrologic data at this site have been segmented into five general categories:

· Constructed Ponds

· Islands

· Streams

· Water Bodies (Polygonal)

· Wetlands

· HUC 12 Watersheds

National Hydrologic Data (NHD) have been modified and customized to be more focused on the watersheds of Alabama.  The resulting data have been named the Alabama-NHD or Al-NHD.

The Al-NHD supersedes DLG and RF3 by incorporating them, not by replacing them.  The Al-NHD incorporates a national framework for assigning reach addresses to water-related entities such as industrial dischargers, drinking water supplies, fish habitat areas, wild and scenic rivers.  Reach addresses establish the locations of these entities relative to one another within the NHD surface water drainage network in a manner similar to street addresses.  Once linked to the NHD by their reach addresses, the  upstream/downstream relationships of these water-related entities and any associated information about them can be analyzed using software tools ranging from spreadsheets to Geographic Information Systems (GIS). GIS can also be used to combine Al-NHD-based network analysis with other data layers, such as soils, land use, and population, to help better understand and display their respective effects upon one another. 

While initially based on 1:100,000-scale data, the Al-NHD is designed to incorporate and encourage the development of higher-resolution data required by many users. It will facilitate the improved integration of water-related data in support of the application requirements of a growing national user community and will enable shared maintenance and enhancement. 

We are updating the stream and lake polygons and centerlines using high resolution imagery.  As those updates are completed, we will release the information on this website with much hoopla.

Al-NHD showing the segmented features.