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Assessment Database
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Tools for Georeferencing to NHD

Hydrography Event Management (HEM) Tool

The Hydrography Event Management (HEM) Tool is now available to create NHD events for various EPA programs. The Hydrography Event Management (HEM) tool is a set of ArcGIS tools that can be used to create National Hydrography Dataset (NHD) events for both state and EPA programs. Click to learn more about the HEM Tool.


The ADBv2-RIT is an ArcView 3.x extension that works with the Reach Indexing Tool (RIT) for the National Hydrography Dataset (NHD). The NHD-RIT is a graphic information system (GIS) tool that allows users to delineate 305(b) waterbody segments in NHD and create event tables that store the location information for these waterbody segments. These event tables can be displayed in ArcView and used to make maps of the water quality assessment data in the Assessment Database (ADB). The NHD-RIT is part of the NHD ArcView Toolkit. The Toolkit, as well as associated documentation and tutorials can be downloaded from

While it is possible to use the ADB v.2 and Reach Indexing data together, users in the past have been required to update the database and the Reach Indexing data separately. The purpose of the ADBv2-RIT utility is to provide an interface in ArcView where information available from the NHD (assessment unit size and name) can be used to enter or update data directly in the ADB.

The Users Guide for the ADBv2-RIT is available in the Reference section. You can download the ADBv2-RIT from the Tools section.


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