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DHazard risk
Natural hazards in Big Sioux Township · FEMA

FEMA puts Big Sioux Township’s expected hazard damage per building above that of 91% of U.S. towns, mostly from river and rain flooding

On FEMA’s National Risk Index, Big Sioux Township gets a D for hazard risk: higher expected damage per building than 91% of U.S. towns. Most of that expected damage is river and rain flooding (78%), then tornadoes (13%). Flood insurance has paid 27 claims here since 2011.

River and rain flooding 78%Tornadoes 13%Wildfire 4%

Graded on FEMA’s expected yearly building damage per dollar of building value (NRI v1.20, December 2025), weighted by where residents live; flood claims are shown, not graded. How hazard risk is graded

more than 91%of U.S. townsLess damageMoreExpected yearly damage per dollar of building, vs. the 21,298 U.S. towns we grade
Hazard risk
D#34 of 35
in South Dakota · higher than 91% of U.S. towns
Main hazard
River and rain flooding
78% of expected building damage
Flood claims
27
paid since 2011 · $1.1M
Flood claims per home
14 per 1,000
more than 79% of U.S. towns
By hazard

What Big Sioux Township faces

Each hazard’s share of the building damage FEMA expects here, and how its rate compares with the rest of the country.

River and rain flooding

78%of expected building damage
Well above average · in the top 6% of U.S. census tracts
Recorded about 4 times a year in the area

Tornadoes

13%of expected building damage
Well above average · in the top 1% of U.S. census tracts
Smaller shares here
 Wildfire Hail Winter storms top 1% Strong wind Lightning top 0% Ice storms Earthquakes Cold waves Heat waves top 2% Landslides
FEMA models no building damage here
Coastal floodingHurricanesAvalanchesTsunamisVolcanic activity

Shares are of FEMA’s expected building damage, the measure the grade uses; ranks compare each hazard’s building-damage rate with all 85,154 U.S. census tracts. In FEMA’s terms, river and rain flooding is FEMA’s “Inland Flooding” (rivers and streams overflowing their banks, or rain overwhelming drainage). FEMA defines coastal flooding as high or rising tides and storm surge, so surge damage is counted there. Drought isn’t listed: FEMA counts its losses in crops only.

Flood risk changes street by street. Check a specific address on FEMA’s flood map, and ask about flood insurance before you buy.
Hazard risk grade

What’s behind Big Sioux Township’s grade

River and rain flooding is 78% of the building damage FEMA expects in Big Sioux Township, and Big Sioux Township’s rate of river and rain flooding damage is in the top 6% of U.S. census tracts. Tornadoes add 13%, at a rate in the top 1% of U.S. census tracts.

Where Big Sioux Township sits
Big Sioux Township
Least damageMiddleMost damage

D #34 of 35 in South Dakota; higher expected damage per building than 91% of U.S. towns (21,298).

Big Sioux Township’s residents live in 2 census tracts; FEMA’s figures are combined by where they live.

What drives the damage to buildings
River and rain flooding78%Tornadoes13%Wildfire4%Everything else5%

The typical South Dakota town has higher expected damage than 58% of U.S. towns; within the state, Big Sioux Township has more expected damage per building than 97% of South Dakota towns.

In dollars, FEMA expects about $5.3M a year in losses across Big Sioux Township: $4.4M to buildings, the rest to people and crops.

A small-area figure. Big Sioux Township covers 2 census tracts, combined by where residents live. FEMA’s model is an average year for today’s buildings, not a record: the claims and disasters below are the record.

How TownRatings grades hazard risk →

Flood insurance claims

Does Big Sioux Township flood? Sometimes: 27 flood claims since 2011

Every paid claim on a federal flood insurance policy in Big Sioux Township, from FEMA’s records: 14.1 per 1,000 homes, more than 79% of the 13,809 U.S. towns with a flood insurance record.

Paid flood claims, by year
2011: 20 claims2012: 0 claims2013: 0 claims2014: 0 claims2015: 0 claims2016: 0 claims2017: 0 claims2018: 0 claims2019: 3 claims2020: 0 claims2021: 0 claims2022: 0 claims2023: 1 claim2024: 3 claims2025: 0 claims2026: 0 claims201120192024
20112026
Biggest named events
  • The Late spring storms19 claims · $782K
  • The June Midwest Flooding3 claims · $260K
27
paid claims since 2011
$1.1M
paid to owners
0
homes flooded more than once
$42K
average claim
of homes in flood zones are insured
of all homes are insured
No community discount

Big Sioux Township isn’t in FEMA’s Community Rating System, which cuts flood insurance up to 45% in towns that do extra flood-proofing.

Insurance rates: Union County.
Disasters

The storms Big Sioux Township remembers

None of the 16 disasters declared for Union County shows FEMA aid or repair money reaching Big Sioux Township itself in FEMA’s records, so these are its biggest flood-claim years.

  1. 201120 flood claims paidThe year of Flooding, declared for Union County
  2. 20193 flood claims paidThe year of Severe Storms, Tornadoes, and Flooding, declared for Union County
  3. 20243 flood claims paidThe year of Severe Storms, Straight-line Winds, and Flooding, declared for Union County
Disasters declared, by decade
Paid out in Big Sioux TownshipUnion County only

Union County has had 16 natural disasters declared by the President since 1953, most often floods, then severe storms. Not counted: the 2005 Hurricane Katrina evacuee emergency, which covered counties that took in evacuees.

Were you here?

Old photos of Big Sioux Township after a storm or flood belong in the town’s history. Add one, or share what you remember below.

Add to the Big Sioux Township archive →
Next door

Big Sioux Township and its neighbors

Big Sioux Township is 4th of the 5 graded towns here, from least expected damage per building to most. Tap a town to see its hazards.

North Sioux City: hazard risk DSioux City: hazard risk C+Dakota Dunes: hazard risk DJefferson Township: hazard risk DNorth Sioux CitySioux CityDakota DunesJefferson TownshipBig Sioux Township
Lowest fifthSecondMiddleFourthHighest fifth
TownHazard riskMostly (buildings)Flood claims
Sioux CityC+more damage than 58%river and rain flooding152
Jefferson TownshipDmore damage than 88%river and rain flooding9
North Sioux CityDmore damage than 89%river and rain flooding12
Big Sioux TownshipDmore damage than 91%river and rain flooding27
Dakota DunesDmore damage than 91%river and rain flooding—

Hazard risk = FEMA’s expected yearly building damage per dollar of building value, vs. the 21,298 U.S. towns we grade; the map is shaded by fifths of the same scale. Flood claims = paid federal flood insurance claims on record.

Be ready

Get ready for what Big Sioux Township faces

A short kit for the hazards that drive the building damage here, what to check before you buy, and where neighbors get alerts.

When the river rises
  • Turn around at flooded roads: a foot of moving water can carry off a car.
  • Flood insurance usually takes 30 days to start, so buy it before the forecast.
  • Keep papers and medicines up high, in a grab-and-go bag.
More from Ready.gov ↗
Tornado warnings
  • Pick your spot now: the lowest floor, an inside room, no windows.
  • A watch means be ready; a warning means take cover now.
  • Keep shoes and a flashlight by the bed.
More from Ready.gov ↗
Before you buy or rent
  • Look up the address on FEMA’s flood map.
  • Ask the seller or landlord whether it has ever flooded, and what flood insurance costs there.
  • Get a flood insurance quote early: policies usually start 30 days after you buy.
When a storm is coming
Forecast and alertsWeather →911, the nearest ERSafety →

Know where neighbors sign up for alerts? Add it to the Handbook so everyone has it.

Questions about natural hazards in Big Sioux Township

Is Big Sioux Township at risk for natural disasters?

On FEMA’s National Risk Index, Big Sioux Township has higher expected damage per building than 91% of U.S. towns: D for hazard risk. Most of the expected damage is river and rain flooding (78%) and tornadoes (13%). This is FEMA’s model of an average year for today’s buildings, not a forecast.

Does Big Sioux Township flood?

Flood insurance has paid 27 claims in Big Sioux Township since 2011, $1.1M in all, or 14.1 per 1,000 homes, more than 79% of U.S. towns with a flood insurance record. The most claims came from Late spring storms (19).

Is Big Sioux Township in a flood zone?

Flood zones are drawn street by street, so the answer depends on the address: look it up on FEMA’s flood map. In Union County, 26% of homes in mapped flood zones carry federal flood insurance, and 2.5% of all homes do.

How much is flood insurance in Big Sioux Township?

FEMA’s Community Rating System list shows no discount for Big Sioux Township’s flood program. Premiums depend on the building; policies usually start 30 days after you buy, so get a quote early.

What was the biggest storm in Big Sioux Township?

By flood claims, Late spring storms: 19 paid, $782K.

Is Big Sioux Township at risk from river and rain flooding?

It is the largest share of the building damage FEMA expects here (78%), and Big Sioux Township’s rate for it is in the top 6% of U.S. census tracts.

Storm stories

Memories, warnings and help from neighbors in Big Sioux Township.

Town Square →
Start the conversation

Sources: FEMA National Risk Index v1.20 (December 2025), census-tract table, combined by where Big Sioux Township’s residents lived in the 2020 census; OpenFEMA: NFIP redacted claims, multiple-loss properties, community status book and residential penetration rates, housing assistance (owners and renters), public assistance funded projects, hazard mitigation properties and disaster declarations. Homes: Census ACS 2020–24. Preparedness tips: Ready.gov. FEMA’s model is an average of expected damage, not a forecast. How hazard risk is graded.