Stream Gauge Finder

Open Stream Gauge Finder

Locate DWS and USGS stream-gauging stations near a point of interest and download their observation records in minutes. This guide covers the four search modes (point, polygon, watercourse, watershed), the filtering options (drainage region, station type, catchment area, record length), the DWS station-naming convention, the 22 primary drainage regions, station-type codes, and how to feed annual peak-flow data directly into Flood Frequency Analysis.

Overview

The Stream Gauge Finder provides direct access to 2 896 DWS (Department of Water and Sanitation) stream gauging stations across South Africa, together with USGS gauges in the United States. Unlike the DWS website, the tool offers an intuitive map interface with powerful filtering, spatial search, and direct links to download station data.

Each station record includes the drainage region, station type, catchment area, observation period, and direct links to the DWS station page, monthly peak-flow CSV, and annual peak-flow CSV files. The annual peak CSV is the standard input for statistical Flood Frequency Analysis using LP3, GEV, Gumbel, or other distributions.

The tool supports four search modes and rich filtering by drainage region, station type, catchment area, record length, and station name — making it significantly faster and easier to find relevant gauge data than navigating the DWS website directly.

Search modes

Four complementary search modes cover the most common use cases in a hydrological desk study.

Point search

Click on the map or enter coordinates to find the $N$ nearest gauges sorted by distance. Use the slider to control results (1 – 50). The distance metric is the great-circle distance from the point of interest to each gauge location.

When to use point search

Ideal for initial desk studies — quickly see what gauge data is available near your project site. Start with 20 – 30 results to get a broad picture, then narrow down with filters once you have a feel for the gauge density in the area.

Polygon upload

Upload a catchment boundary as GeoJSON. Gauges inside the polygon are listed first, then the nearest gauges outside the polygon are added to fill the results count. Distances are measured from the polygon centroid. This mode is the right choice when you have a delineated catchment and want to find every gauge that lies within the contributing area.

Watercourse search

Upload a river centreline (GeoJSON LineString). The tool finds gauges within a configurable buffer distance of the watercourse — ideal for finding gauges on the same river system, including downstream and upstream of the point of interest.

Buffer distance

For major rivers use 5 – 10 km. For smaller tributaries, 1 – 3 km is more appropriate. The buffer should be large enough to catch gauges on the mainstem but small enough to exclude gauges on parallel rivers.

Watershed search

Select a saved watershed delineation — the polygon is loaded automatically and the polygon search is applied. This is the most seamless workflow when the gauge search is part of a larger design-flood analysis that already has a delineated catchment.

Filtering results

Filters can be combined to narrow 2 896 DWS stations down to the handful that are actually usable for your analysis.

• Search by name or station number — type to filter, e.g. “A2H” or “Krokodil”.
• Active gauges only — exclude stations that stopped recording before 2024.
• Drainage region — select one or more of the 22 primary drainage regions (A through X).
• Station type — filter by River, Reservoir, Eye (spring), Canal, Meteorological, Lake/Pan, etc.
• Catchment area range — set min/max catchment area in km² (available for ~56% of stations).
• Minimum record years — only show gauges with sufficient observation history for flood frequency analysis (typically 25 – 30 years minimum).
• Maximum distance — limit results to a search radius in km.

Understanding results

Results appear on the map (green = active, orange = inactive) and in a sortable table:

Field	Description
Station No	DWS station identifier (e.g. A2H019)
Place	River name @ location (e.g. “Krokodil River @ Hartbeespoort”)
Distance	Distance in km from search point or polygon centroid
Region	Primary drainage region (A – X)
Type	Station type (River, Reservoir, Eye, Canal, etc.)
Area (km²)	Upstream catchment area (where available)
Record	Length of observation record in years
Status	Active (green) or Closed with year (grey)
Links	DWS station page, monthly peaks CSV, annual peaks CSV

Hover to highlight

Hover over table rows to highlight the corresponding gauge on the map. Click map markers for full station details with clickable data links.

DWS data links

Each gauge provides three direct links to DWS data, accessible from both the map popups and the results table.

DWS station page

Opens the DWS Hydrology Verified Data page for the station — view verified hydrological datasets, metadata, rating curves, and additional station information. Use this as the authoritative source when you need to confirm record completeness or download sub-hourly data not available as a pre-packaged CSV.

Monthly peak flows CSV

Downloads a CSV file of monthly peak instantaneous flows — useful for flow-duration curves, seasonality analysis, and monthly rainfall-runoff calibration.

Annual peak flows CSV

Downloads a CSV of annual maximum peak flows — the primary input for statistical Flood Frequency Analysis (LP3, GEV, Gumbel, Log-Normal, etc.). This is the fastest path from “I need design floods” to a fitted quantile table.

DWS data availability

Not all stations have complete data for their full observation period. The CSV files may contain gaps, and some years may be flagged as unreliable. Always verify data quality before using for design purposes — run homogeneity and trend tests in the Flood Frequency Analysis tool before fitting.

Station naming convention

DWS station numbers follow a consistent four-part format. For example, A2H019:

• A — Primary drainage region (A to X, see Drainage regions below).
• 2 — Secondary drainage region number (1 – 9) within the primary region.
• H — Station type: H = hydrological (flow), R = reservoir, M = meteorological.
• 019 — Sequential station number within the secondary region.

So A2H019 is the 19th hydrological flow station in secondary region 2 of primary region A (Limpopo).

Drainage regions

South Africa is divided into 22 primary drainage regions, identified by letters A through X (I and O are skipped).

Code	Region name
A	Limpopo
B	Olifants
C	Vaal
D	Orange
E	Olifants/Doorn
F	Buffels
G	Berg
H	Breede
J	Gouritz
K	Coastal Rivers
L	Gamtoos
M	Swartkops
N	Sondags
P	Boesmans
Q	Fish
R	Nahoon/Keiskamma
S	Great Kei
T	Mzimvubu/Umbashe
U	Mvoti/Mgeni/Mkomazi
V	Tugela
W	Usutu/Phongolo/Mfolozi
X	Sabie/Krokodil/Komati

Station types

Type	Code	Description
River	RIV	Flow measurement on a natural river or stream
Reservoir	RES	Dam reservoir and associated components
Eye (Spring)	EYE	Natural spring or groundwater emergence point
Canal	CNL	Artificial canal or water transfer scheme
Meteorological	MET	Weather and rainfall monitoring station
Lake/Pan	LAK	Natural lake, pan, or wetland monitoring
Closed Conduit	DC	Pipe or tunnel flow measurement
Downstream Components	DC	Downstream river components of a dam system

For flood frequency analysis, River (RIV) stations are the primary target. Reservoir stations record stage and can provide inflow only after a water-balance adjustment, and canal or closed-conduit stations reflect regulated flow rather than natural hydrology.

Exporting data

Click Export CSV to download results including all station metadata, coordinates, distances, and DWS data URLs — ready for import into Excel, GIS, or your analysis tools. The exported file can also be re-uploaded into the Flood Frequency Analysis tool when paired with the annual peak CSV from each chosen station.

Tips and best practices

Start broad, then filter

Begin with 20 – 30 max results and no filters, then use drainage region, station type, and minimum record length to narrow down to the best-quality data for your analysis. A gauge with 60 years of continuous active record will almost always beat a closer gauge with 10 discontinuous years.

Use the Annual Peak CSV

For flood frequency analysis, the Annual Peak Flows CSV is your primary input. Download it directly from the results table without navigating the DWS website. Paste the peaks into the Flood Frequency Analysis tool to fit LP3, GEV, Gumbel, and the other supported distributions.

Check catchment areas

When comparing gauges, use the catchment area to understand scale. A gauge with 100 km² catchment is not directly comparable to one with 10 000 km² — regional transfer of flood estimates requires an area-scaling law such as the index-flood growth curve in the Index Flood Calculator.

Integration with other tools

Use the Watershed Delineation tool first, then use Watershed mode to automatically find gauges within your delineated catchment. Combine with the RMF Calculator for upper-bound checks, the Index Flood Calculator for regional quantiles, and the Flood Frequency Analysis tool for at-site LP3/GEV fitting. Daily Rainfall Data complements flow records when a rainfall-runoff cross-check is needed.

Record-length guidance

Reliable statistical inference places real lower bounds on the record length needed for a given return period. Typical guidance for flood frequency analysis:

Target return period	Minimum record (years)	Preferred record
1:10	15	25
1:50	25	40
1:100	30	50+
1:200	40	60+

Shorter records can still be used with regional methods (Index Flood Calculator) where the effective sample size is multiplied by the number of sites in the homogeneous cluster. For sites with no usable nearby gauges, fall back on fully regional methods and the RMF Calculator as a sanity check.

Limitations

• Data gaps — DWS records are not always continuous; apparent record length can overstate the usable sample size.
• Rating-curve extrapolation — the largest observed peaks are often derived from stage readings beyond the measured rating range, introducing additional uncertainty.
• Station drift — river morphology can change over decades (bed scour, encroachment, dam construction upstream), breaking the assumption of stationarity.
• USGS vs DWS coverage — USGS coverage is currently limited to the United States. For other countries, use the appropriate national hydrological service directly.

References

• Department of Water and Sanitation (DWS). Hydrology Verified Data. Government of South Africa. https://www.dws.gov.za/Hydrology/
• USGS. National Water Information System (NWIS). U.S. Geological Survey. https://waterdata.usgs.gov/
• WMO. (2009). Guide to Hydrological Practices, Volume II: Management of Water Resources and Application of Hydrological Practices (6th ed., WMO-No. 168). World Meteorological Organization.
• Midgley, D.C., Pitman, W.V. & Middleton, B.J. (1994). Surface Water Resources of South Africa 1990 (WR90). Water Research Commission Report 298/1/94.

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Open Stream Gauge Finder