Rivermatics

USGS Streamgage 06479525

Big Sioux River near Castlewood, SD

Big Sioux River near Castlewood, SD is USGS streamgage 06479525 in South Dakota, monitoring river discharge in hydrologic subbasin 10170201. It sits on the Big Sioux River, alongside 16 other gauges Rivermatics tracks on the same river. It drains a watershed of about 1,096 square miles. Discharge records at this site go back to 1976. Typical flow runs near 56.9 cfs in July and 156.3 cfs in April, with the higher of the two arriving in April. Rivermatics issues a daily machine-learned flow outlook for this gauge, reaching 14 days ahead.

View live conditions & forecast →

Gauge details

State
South Dakota
Drainage area
1,096 sq mi
Gauge elevation
1,685 ft
Subbasin (HUC-8)
10170201
Coordinates
44.73158, -97.04431
USGS site number
06479525
Records begin
1976-10-01 (50 years)
Rivermatics forecast
14-day flow outlook

14-day flow forecast

Based on observations through for Big Sioux River near Castlewood, SD. Each day carries a median estimate and the band the model expects the flow to fall within — not a single number to plan against. Forecasts are re-issued daily; see the live screen for the current outlook.

Forecast daily mean discharge in cubic feet per second, by date
Date Low p10 Expected p50 High p90 Range
14.5 16 17.5
13.4 15.3 16.9
13 15 16.9
12.7 14.8 17.2
12.3 14.6 17.2
12.9 15.6 20.3
13.6 17.3 26.5
13.2 17.2 28.8
12.5 16.7 28.2
12.1 16.3 26.5
11.5 15.6 25.1
11.1 15.1 24.3
10.8 14.9 23.1
10.6 14.6 22.5

All values in cubic feet per second (cfs). Estimates only — do not use them for navigation or for any safety, rescue, or emergency decision.

Typical flow by month

Long-term daily discharge percentiles from the USGS record (up to 50 years of data), averaged within each month. These describe the historical normal range — they are not a forecast and not today's reading.

Historical monthly discharge percentiles in cubic feet per second
Month Low p10 Typical p50 High p90 Range
January 0.1 10.2 52.9
February 0.3 14.7 84.3
March 4.1 59.7 519.1
April 14.6 156.3 1,183.9
May 9.3 130 621.1
June 8.5 100.7 412
July 6.4 56.9 330
August 4.5 37.2 250.3
September 4 25.3 177.2
October 4.9 22.7 138.8
November 5.5 23.5 120.9
December 3.1 17.5 74.4

All values in cubic feet per second (cfs).

Common questions

When does Big Sioux River near Castlewood, SD normally run highest?
April, on the long-term record. The median daily flow that month is about 156.3 cfs, against 10.2 cfs in January, the lowest month. These are historical normals for the date, not a forecast and not today's reading.
What is a normal flow for Big Sioux River near Castlewood, SD?
It depends on the month. In January, half of days historically fall near 10.2 cfs, with the middle 80% of days between 0.1 and 52.9 cfs. The month-by-month table on this page gives the full range.
How long has Big Sioux River near Castlewood, SD been measured?
Discharge records at USGS site 06479525 begin in 1976, about 50 years, covering roughly 9,080 days of published daily values. The long record is what makes the monthly percentiles on this page meaningful.
Is there a flow forecast for Big Sioux River near Castlewood, SD?
Yes. Rivermatics trains a machine-learned model — a temporal-fusion transformer — on this basin's observed flows, weather, and snowpack, and issues a daily flow outlook reaching 14 days ahead: a median estimate inside a confidence band, not a single number to bet on. Every forecast is scored against days the model never trained on, and that track record is published on the live gauge screen. Open live conditions to see the current outlook.
Where is Big Sioux River near Castlewood, SD?
The gauge sits at 44.73158, -97.04431, in South Dakota, in hydrologic subbasin 10170201, at an elevation of about 1,685 feet, draining roughly 1,096 square miles.
Can I use Big Sioux River near Castlewood, SD data for flood or safety decisions?
No. Rivermatics provides estimates, not guarantees, and the readings and forecasts here may be delayed, inaccurate, or wrong. Do not use them for navigation or for any safety, rescue, or emergency decision. Check the National Weather Service and USGS directly, and use your own judgment.

Upstream and downstream on the Big Sioux River

Every gauge Rivermatics tracks on this river, ordered by drainage area — upstream first. See the Big Sioux River in full.

Other gauges in this subbasin