A StreamStats alternative for sites outside the United States

What StreamStats is and who it suits

StreamStats is a USGS web application for water-resources planning and engineering design. You click a site on a stream, it delineates the drainage basin from USGS 3D Elevation Program (3DEP) data and the high-resolution National Hydrography Dataset, measures basin characteristics, and passes them to the National Streamflow Statistics (NSS) service, which holds the USGS regression equations for flood-frequency statistics across the country. Depending on the state, the statistics include peak flows, low flows, flow durations and bankfull dimensions.

StreamStats was implemented state by state. The USGS notes that some states are not implemented because the local Water Science Centers could not obtain cooperative funding, and the statistics on offer vary from state to state. Inside a covered state it is the reference tool for an ungauged US site.

What the USGS suggests when StreamStats is not available

The USGS has an FAQ page titled “StreamStats not available where I need information — are there any alternatives?” Its answer lists four options: Esri’s Watershed Explorer (an ArcGIS Online account is needed), hand delineation in The National Map Viewer for basins under about 1.5 square miles, an EPA web service that needs a web developer to use, and The National Map Downloader for ArcGIS users. Each one is a US dataset or an Esri product. Apart from the Esri tool, which needs an ArcGIS Online account, none of them helps with a bridge in Kenya, a culvert in Chile or a dam in Vietnam, and none of them returns a flow statistic. That is the gap this page is about.

Where StreamStats is the better choice

• Inside a covered US state, use StreamStats. Its terrain is finer than a 90 m global grid, and its flow statistics come from the published USGS regression equations for that state, with their regression regions and limits.
• Statistics Studio does not produce. Low-flow statistics, flow durations and bankfull dimensions from NSS have no equivalent in Studio’s delineation.
• Basin characteristics. StreamStats returns the state’s own set of parameters, such as soils and land cover, ready for the state’s equations. Studio’s delineation returns geometry: area, perimeter, stream network and the longest flowpath.
• Regulatory familiarity. Many US agencies expect a StreamStats report in a submission.

Studio does not try to replace StreamStats in the US. Its USGS Flood Estimate tool calls the StreamStats delineation and the NSS equations for a US pin, shows peak flow against return period in ft³/s or m³/s with the interval bounds the service returns, and saves the result to a project. The StreamStats and USGS NLDI backends are also selectable in the Watershed Delineator for US outlets.

What Studio does outside the US

Delineation anywhere from 60°S to 85°N. The default engine outside South Africa is the Global Watersheds service (Heberger, 2022), which unions pre-computed MERIT-Basins unit catchments upstream and delineates the last unit on the MERIT-Hydro flow grid at about 90 m. High precision follows the raster all the way to the outlet; catchments over 50 000 km² revert to the faster low-precision mode. An Esri backend built on HydroSHEDS gives an independent cross-check. In South Africa the Copernicus GLO-30 DEM, hydrologically corrected at 30 m, resolves a 1 km² culvert catchment that a 90 m grid cannot.

Outlet snapping. Outside South Africa, the Global Watersheds service snaps your click to the nearest cell on the MERIT-Hydro flow-accumulation grid, so a click near a visible river lands on it. In South Africa the tool goes further: it lists the channels near your click, says how far the outlet moved, and lets you choose the branch. Near a confluence this matters everywhere, because an engine that snaps to the highest flow accumulation can put a click on a small tributary onto the larger river.

What comes back. A catchment polygon with geodesic area and perimeter on the WGS-84 ellipsoid, a river network with Strahler order on every segment, and the longest flowpath with its length, drop, average slope and 10-85 slope. Exports are GeoJSON, Shapefile and KML, plus an EPA SWMM file. Delineation is free on every plan.

Flow statistics: the honest gap. Outside the US and South Africa, Studio has no regional regression equivalent to NSS. You have two routes. With a gauge record nearby, fit a flood frequency analysis: annual peaks import by station number from USGS, DWS in South Africa and the Australian Bureau of Meteorology, or upload a CSV from any national agency. Without one, use a rainfall-runoff method such as the TR-55 calculator, with depths from Design Rainfall (NOAA Atlas 14 for the US, BoM IFD for Australia, the K5_1060 grid for South Africa, or a table you enter).

StreamStats and Studio side by side

How to move a job across

1. Coordinates. Click the map or type latitude and longitude in WGS-84 decimal degrees. A surveyed structure position goes in as typed.
2. Snap deliberately. Click on the channel you are designing for, clear of any confluence, and check where the snapped outlet landed. If the area jumps when you move the point a short way, you have crossed onto another branch or over a divide.
3. Choose high precision for design work, and leave Beautify off when the area goes into a calculation.
4. Check the area against a gauge’s published catchment area or an earlier study. A difference above about 10% usually means the outlet is a little upstream or downstream of where you meant.
5. Know the resolution limit. Below about 1 km², or in flat coastal and pan country, check the boundary against imagery and use a local DEM if you have one.
6. Carry the result forward. Send the watershed to the Tc, Rational and TR-55 calculators, open its longest flowpath in the Watercourse Profile for a long section with 10-85, equal-area and Taylor-Schwarz slopes, and use the polygon for area-weighted design rainfall.

Where to start

Begin with Watershed Delineation for the catchment, then the Watercourse Profile for length and slope. For flows, use Flood Frequency Analysis when a gauge record exists and Design Rainfall with a rainfall-runoff method when it does not.