Flooding in Southeast Texas

Overview

• Last lecture for Unit 3
• Focus on flooding following severe weather discussion
• Flooding in Southeast Texas impacted by several variables

Key Factors Contributing to Flooding

1. Intensity of Rainfall

   • Example: 2 in/hour vs. 6 in/hour
   • Higher intensity = higher flooding risk

2. Duration of Rainfall

   • Extended periods (e.g., Hurricane Harvey) lead to higher flooding due to saturation

3. Infiltration Rate of Soils

   • Speed at which soil absorbs water
   • Impacted by soil type and condition

4. Land Use and Land Cover

   • Urban areas exacerbate flooding (concrete, roofs, etc.)
   • Natural areas (forests, wetlands) reduce flood risk

5. River Size and Capacity

   • Smaller creeks vs. larger rivers (Buffalo Bayou, San Jacinto River)
   • Larger rivers accommodate more floodwater

6. Topography

   • Houston's flat terrain vs. steeper slopes out west
   • Flat areas collect water, increasing flood risk

Rainfall and Flooding

• 100-year storms: 1% chance of occurring any given year
  • Gulf Coast: Significantly higher rainfall vs. interior US
  • Influenced by moist, warm air masses

Soil Composition and Flooding

• Soil Types
  • Clay: Small particles, slow water absorption
  • High clay content in Texas contributes to flooding

Urbanization and Its Effects

• Development increases runoff and flood risks
• Example: The Woodlands area pre- and post-Hurricane Harvey
• Urbanized areas show higher and faster peak water flow in rivers

Flooding Statistics and Probability

• 100-year flood: 1% annual chance
• Misconception: Frequent events can occur back-to-back
• Flood events are predictable over longer periods (e.g., mortgage terms)
• Banks require flood insurance in designated flood-prone areas

Impact of Major Events like Hurricane Harvey

• Redefined flood probabilities and statistical measures
• Increased risk due to more water and higher river stages

Floodplain Management

• National Flood Insurance Program (NFIP)
  • Established in 1968
  • Requires flood insurance for high-risk areas
• Strategies for reducing flood risk:
  • Buyouts of high-risk homes
  • Infrastructure improvements (e.g., deeper channels, levees)

Flood Prevention Measures

• Learning from the Netherlands: Room for the River plan
• Practical applications in areas like Dallas (Trinity River)
• Continued development and buyout programs in Houston

Recommendations for Home Buyers

• Use county floodplain viewers to check property flood risk
• Be aware of potential inaccuracies in outdated maps
• Consider future changes in precipitation and infrastructure enhancements