Factors that Affect Flood Risk and How to Assess Them

When looking at buying property, your flood risk depends on at least ten factors. Unfortunately, people rarely consider most of them. Even if they do, they may not now how to assess them.

Harvey Flood. Photo by Sally Geis.

So, here’s a list of key factors that can increase or decrease your flood risk. I’ve also included examples and ways to explore their impact on your property or the property you’re considering buying:

  1. Geography and Topography: The natural landscape of an area plays a significant role in its flood susceptibility. Flat, low-lying areas, river valleys, coastal regions, and areas near lakes or other bodies of water are more prone to flooding because water naturally collects in these locations. To investigate a particular area, check out resources such as the USGS National Map and FEMA’s National Flood Hazard Layer Viewer.
  2. Proximity to Water Bodies: Areas near rivers, lakes, oceans, and other water bodies are at a higher risk of flooding. Riverine flooding, coastal flooding, and flash flooding can all occur in these regions. See any map or web sites such as RiskFactor.com.
  3. Rainfall and Precipitation Patterns: Areas that receive heavy or prolonged rainfall are more likely to experience flooding. Rainfall can lead to flash floods, riverine flooding, and urban flooding when drainage systems are overwhelmed. In Texas, generally the farther east and closer to the coast you go, the more rainfall increases. To see the likelihood of precipitation in any given area, check out NOAA’s Atlas-14 site then investigate local infrastructure standards to see if they meet Atlas-14 standards or something less (prior). Also understand that NOAA is revising Atlas-14 already to incorporate impacts of climate change (see Atlas-15).
  4. Climate and Weather Events: Areas prone to hurricanes, tropical storms, or other severe weather events are at risk of storm surges, heavy rainfall, and coastal flooding. Here are several sites that can help you find reliable climate data.
  5. Soil Type and Saturation: The type of soil in an area can impact its flood susceptibility. Soils with poor drainage or soils that are already saturated from previous rain events are more likely to contribute to flooding. Here’s a USDA national soil survey and how to determine whether flood mitigation projects in any given area properly account for the soil types in that area.
  6. Human Development: Urbanization and land development can increase flood risk. Paved surfaces and buildings can reduce natural drainage and increase runoff, overwhelming drainage systems. Harris County has proposed minimum drainage standards for areas draining into Harris County, but not all surrounding areas have adopted these standards yet.
  7. Deforestation and Land Use Changes: Changes in land use, such as deforestation or the construction of roads and buildings, can alter natural water flow patterns and increase flood risk. Think you’re protected? Unfortunately for homeowners, many wetlands are now being destroyed. The EPA and Army Corps amended the definition of protected “waters of the United States” in light of the decision in Sackett v. EPA in May. It narrowed the scope of the Clean Water Act and the EPA’s power to regulate waterways and wetlands.
  8. Infrastructure and Drainage Systems: The condition and capacity of drainage systems, including stormwater sewers and levees, can affect an area’s flood vulnerability. Inadequate or poorly maintained infrastructure can lead to flooding. After Harvey, Harris County Flood Control embarked on an ambitious expansion of flood-mitigation infrastructure, but recently spending has fallen. More in some areas than others. So stay alert to what’s happening in your area.
  9. Historical Flooding: Areas with a history of flooding are often at continued risk, as past floods can indicate a region’s susceptibility to future events. In Harris County, MAAPnext provides an excellent series of historical flood maps to help you understand your flood risk.
  10. Land-Use Planning and Floodplain Management: Effective land-use planning, zoning regulations, and floodplain management can help mitigate flood risk by restricting construction in flood-prone areas and implementing flood control measures. There’s no zoning in Houston and little in surrounding areas. We do have floodplain management regulations. When purchasing property, always look upstream to see if those regulations are effectively enforced.

Few things affect a property’s value more dramatically than flooding.

Yet flood risk can change over time – for better or worse. So buyer beware. Or buyer be wet.

Posted by Bob Rehak on 9/3/2023 with some help from ChatGPT

2196 Days since Hurricane Harvey

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.