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Hydrograph River at a Glance Download
Big Sioux River near Castlewood Stage (ft)Flow (cfs)USGS--Water Resources of the United StatesCSWS2(plotting HGIRG) Graph Created (8:00AM Feb 26, 2021)Flood Stage is 9 ft
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Datum: NAVD88
NOTE: River forecasts for this location take into account past precipitation and the precipitation amounts expected approximately 48 hours into the future from the forecast issuance time.

NOTE: Forecasts for the Big Sioux River near Castlewood are issued as needed during times of high water, but are not routinely available.

Vertical Datum updated from NGVD29 to NAVD88 by gauge owner.

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Upstream Gauge - below Watertown Upstream Gauge Downstream Gauge Downstream Locations
Flood Categories (in feet)
Major Flood Stage: 16
Moderate Flood Stage: 11
Flood Stage: 9
Action Stage: 8
Low Stage (in feet): -9999

Historic Crests
(1) 13.19 ft on 04/07/1997
(2) 12.39 ft on 03/28/2019
(3) 12.29 ft on 03/23/2011
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(P): Preliminary values subject to further review.

Recent Crests
(1) 12.39 ft on 03/28/2019
(2) 10.93 ft on 04/23/2018
(3) 8.60 ft on 02/20/2017
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(P): Preliminary values subject to further review.

Low Water Records
Currently none available.

For more information on your flood risk go to

Zoom Level:14
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Latitude/Longitude Disclaimer: The gauge location shown in the above map is the approximate location based on the latitude/longitude coordinates provided to the NWS by the gauge owner.
Flood Impacts & Photos Collapse
If you notice any errors in the below information, please contact our Webmaster
16 The bridge at the gaging location is overtopped the big sioux river will be about 1 mile wide and many farm buildings around Castlewood will be flooded
15 The water reaches the bottom of the bridge 1 mile south of Castlewood
12.9 The water reaches the bottom of the bridge at the gauge
11.73 Significant amounts of pasture and other agricultural land will be flooded
11 Significant amounts of pasture and other agricultural lands will be flooded
10 The roads on both sides of the river are overtopped.
9.2 The road on the southwest side of Castlewood is overtopped
8 Minor flooding of low-lying agricultural lands along the river will begin
7.5 The water level is above the top of the culverts on the southwest side of Castlewood
About This Location Collapse

Latitude: 44.731667° N, Longitude: 97.044444° W, Horizontal Datum: NAD83/WGS84

River Stage
Reference Frame
Gauge Height Flood Stage Uses
NWS stage 0 ft 9 ft Interpreting hydrographs and NWS watch, warnings, and forecasts, and inundation maps
Vertical Datum Elevation
(gauge height = 0)
(gauge height = flood stage)
Elevation information source
NAVD88 1668.47 1677.47 Survey grade GPS equipment, FEMA flood plain maps, newer USGS topographic maps
NGVD 29 Not Available Not Available Older USGS topographic maps, NGVD29 benchmarks
MSL Not Available Not Available Older USGS topographic maps, MSL benchmarks
Other Not Available Not Available  

Current/Historical Observations:

Additional Information Collapse
Effective on Friday, June 1 2012, the Minor Flood Stage has been changed to 9.0 feet, and the Moderate Flood Stage changed to 11.0 feet.
How low could the river get?
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The National Weather Service prepares its forecasts and other services in collaboration with agencies like the US Geological Survey, US Bureau of Reclamation, US Army Corps of Engineers, Natural Resource Conservation Service, National Park Service, ALERT Users Group, Bureau of Indian Affairs, and many state and local emergency managers across the country. For details, please click here.
NWS Information
National Weather Service
Aberdeen Weather Forecast Office
824 Brown County 14 South
Aberdeen, SD 57401
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Page last modified: 2-Nov-2020 7:29 PM
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