New Jersey StreamStats: Flood and Low-Flow Estimates for Any Stream

StreamStats is a free, interactive, map-based USGS web application that gives streamflow statistics and watershed characteristics for both gaged and ungaged sites on streams across New Jersey, developed with the New Jersey Department of Environmental Protection. Click a point on a stream to get estimates for that spot, or click a streamgage for its published statistics. It is available for most states and some river basins through one portal, streamstats.usgs.gov.

What it's for

• Flood planning: the 1-percent annual chance flood (the "100-year" peak flow) that defines flood plains.
• Low flows: the monthly 7-day, 10-year low flow (M7D10Y), used for water supply, recreation, wildlife conservation and wastewater dilution.
• Basin characteristics: drainage area, percent forested, average percent impervious, and more — widely used in land-use planning and environmental assessments.

It can: delineate basins automatically, compute basin characteristics, generate peak-flow and low-flow statistics, build reports with tables and maps, export GIS and spreadsheet files, and link to published USGS reports and data.

Using it

The home page links to the application (Version 4), user instructions, a fact sheet, FAQs, a batch processing tool, web services and contacts. For an ungaged site in New Jersey:

1. Identify a study area: zoom to the location and select New Jersey.
2. Delineate the basin: it appears in yellow on the map.
3. Select scenarios and basin characteristics.
4. Build a report of flow statistics and basin characteristics — the characteristics are the explanatory variables in the regression equations.

Streamgages: the USGS collects continuous stage (water-surface elevation) at streamgages, converting it to discharge, the volume of water passing per unit of time. Partial-record stations get periodic high- or low-flow measurements specifically to support flow statistics. Stations show as colored triangles; use the Exploration Tools (toolbox) button, then Query Streamgages, to see a station's data. The About button leads to New Jersey's State/Regional Info page: which statistics are available, the reports behind the equations, how basin characteristics are computed, state notes, and cooperating agencies.

Basin characteristics used in New Jersey

What it computes

• Floods: peak discharges for seven annual exceedance probabilities (AEP) — 0.5, 0.2, 0.1, 0.04, 0.02, 0.01 and 0.002, i.e. the 2-, 5-, 10-, 25-, 50-, 100- and 500-year floods — for ungaged, unregulated or slightly regulated, non-tidal streams. An AEP of 0.01 means a 1-percent chance each year; the recurrence interval is 1 divided by the AEP.
• Low flows: 87 statistics for the Coastal Plain and non-coastal regions under baseline and current land- and water-use — monthly flow-durations of the minimum 1-day flow (99th to 25th percentiles), August–September minimum 1-day flows, and the monthly 7-day, 10-year low flow.

Peak flows at different kinds of sites

Recent improvements

• Sharper terrain: a new state-built digital elevation model with 10-foot horizontal resolution and 1.1-foot vertical accuracy replaced a 32.8-foot grid with 5.4-foot relative accuracy, improving basin characteristics and flow estimates.
• Version 4: one seamless interface for all states and selected basins, step by step from study area to report.

Use it carefully

The New Jersey equations apply to sites on ungaged, unregulated or slightly regulated, non-tidal streams whose basin characteristics fall within the published ranges. Read the documentation and the underlying reports first, and always:

1. check the basin delineation;
2. understand the error of each estimate;
3. consider other methods if the uncertainty is too large for your purpose.

Sources

Based on New Jersey StreamStats: A Web Application for Streamflow Statistics and Basin Characteristics, by Kara M. Watson and Jon A. Janowicz, USGS Fact Sheet 2017–3057, prepared with the New Jersey Department of Environmental Protection, U.S. Geological Survey (DOI), citing Watson and Schopp (2009), Watson and McHugh (2014) and the U.S. Water Resources Council (1981); a work of the United States government in the public domain. Table 1 comes from the fact sheet's PDF; its screenshots of the application are left out. Contact: USGS New Jersey Water Science Center, Lawrenceville.