Galveston (Galveston County), TX Flood Zone & Drainage Map

Address
Overview

Where does rainwater drain in Galveston County? This interactive map shows surface drainage patterns across Galveston Island, League City, Texas City, and surrounding areas based on terrain shape - where gravity directs rainwater based on elevation and slope. For official flood risk information, see the FEMA flood zone layer on the Hazards tab.

Galveston County's extremely low elevation - averaging just 15 feet above sea level - makes surface drainage a critical concern. The county faces both riverine flooding from Clear Creek and Dickinson Bayou and coastal storm surge from Galveston Bay. The barrier island geography limits natural drainage outlets. Choose a location to see surface drainage analysis and water flow direction based on terrain shape. The first three locations are free.

Interpretation

Select a location on the map or enter an address to see terrain analysis.

3D Terrain Visualization
Where does rainwater flow based on terrain shape? Blue areas show where water collects and drains downhill.
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Terrain drainage map of Galveston County, TX: modeled paths where rainwater runs and collects, from USGS 3DEP elevation data, with the county boundary Click any spot on the map to analyze it
4.0× Horizontal:Vertical
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Galveston County flood history

FEMA records 60,620 flood insurance claims in Galveston County since 1978, with about $2.4 billion paid. 31% of the claims with a rated flood zone came from moderate- or low-risk zones (X, B or C), outside the high-risk areas on FEMA’s flood maps.

Bar chart of FEMA flood insurance claims per year in Galveston County, TX, 1978 to 2026, highest in 2008 (Hurricane Ike) with 22,606 claims.

Biggest flood years

  1. 2008 · Hurricane Ike · 22,606 claims
  2. 2017 · Hurricane Harvey · 8,853 claims
  3. 1983 · Hurricane Alicia · 7,483 claims
  4. 1979 · Tropical Storm Claudette · 5,461 claims
  5. 1989 · Hurricane Chantel · 2,801 claims

ZIP codes with the most claims

ZIPClaimsShare
775398,37313.8%
775508,11613.4%
775546,96211.5%
775516,50210.7%
775734,3787.2%
775464,1606.9%
775634,0236.6%
776503,4365.7%

How to read this. These are National Flood Insurance Program claims, so they count only insured buildings and miss flooding where owners had no flood insurance. FEMA publishes them without names or addresses: they show which years and areas flooded, never whether a particular house did. ZIP codes are as reported on the claims, and a ZIP code can extend beyond the county. The “rated” flood zone is the one used to price the policy and may come from an older map. Data as of 2026-09-08, from FEMA OpenFEMA.

Next: look up the flood zone for an address · how to check whether a specific house has flooded · why Zone X can still flood · how to read the drainage map

Sunlight and soil in Galveston County

Sunlight. Ground here gets about 4.9 kWh of sunlight per square meter per day on average (4.8 to 5.0 across the map), above the middle of the lower 48 (4.5). South-facing slopes get more, north-facing ones less.

Soil. The ground is mostly swelling clay (Vertisols 96%). Rain soaks in slowly, so more of it runs off. Swelling clay also shrinks and cracks as it dries, which can move slabs and foundations.

The Solar and Soil tabs on the map above show both for any address. Read more: how much sun does my property get? · what soil type is my property, and how it affects drainage

Sunlight: long-term average on flat ground from the National Solar Radiation Database (National Laboratory of the Rockies, formerly NREL). Soil: most likely soil types from ISRIC SoilGrids, a 250 m model, not a survey of any lot. Both cover the map area above.

Explore more flood and drainage maps

Browse all 64 flood and drainage maps · Flood insurance claims in the 50 largest cities · How Terreflow uses terrain and FEMA data