NAWQA Study Unit Boundaries for National Water-Quality Assessment

57 Study Units within the conterminous United States are represented by this GIS coverage from the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program. It contains boundaries, names, starting dates, and standard abbreviations for each unit, compiled from hydrologic and state boundary sources. The data was developed for a program initiated in fiscal year 1991 to assess national water resources.

Use Cases

• Display the geographic location of all 57 NAWQA Study Units using their boundary polygons.
• Analyze national-scale water quality trends by grouping data based on Study Unit names or standard abbreviations.
• Correlate water quality sampling site data (e.g., from NAWQA_TE or NAWQA_NU coverages) with their parent Study Unit boundaries.
• Track the phased implementation of the NAWQA program by filtering Study Units based on their documented starting dates.

Strengths

• Contains boundaries for 57 distinct Study Units within the conterminous United States.
• Integrates multiple data sources, including 1:2,000,000-scale hydrologic unit boundaries and state boundaries.
• Designed specifically for national-scale analysis of water-quality data.

Limitations

• Not recommended for local or regional analysis due to the small scale of most boundary features.
• The number of Study Units was reduced from an originally planned 60, and some units have delayed or unscheduled starts.
• Boundaries are subject to modification as the NAWQA project progresses, which may affect data consistency.

Provenance

Source

U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program.

Collection Method

Boundaries composed from 1:2,000,000-scale hydrologic unit boundaries and state boundaries, with subsequent modifications.

Time Range

Program studies began in fiscal year 1991 (October 1990).

Geography

Conterminous United States (excluding the High Plains Regional Ground-Water Study).