Overview
The lecture reviews flood mitigation strategies, flood risk assessment, and the challenges faced by developed and developing countries in managing flood hazards.
Flood Control Challenges
- Flood control is costly, often unaffordable for poorer and developing communities.
- Developed countries invest in flood mitigation, but this can transfer risks downstream.
- Poor or failed levees have caused catastrophic flooding (e.g., Mississippi 1927, Katrina 2005).
Key Flood Mitigation Methods
- Levees and flood walls prevent river overflow onto floodplains but require maintenance and can fail.
- Dams and reservoirs store excess water and release it safely; dam failures can be catastrophic.
- Channelization involves straightening, deepening, or lining stream channels but disrupts ecosystems.
- Relocation, zoning, wetland restoration, and building codes are non-structural mitigation strategies.
Flood Risk Assessment & Mapping
- Flood risk maps use hydrologic (stream gauge) data to show hazard zones.
- Recurrence interval: the average time between floods of a particular size (e.g., 100-year flood = 1% chance/year).
- Insurance, regulation, and building restrictions are based on flood risk maps (e.g., 100-year and 500-year flood zones).
Statistical Flood Risk Concepts
- 100-year flood: 1% probability in any given year; 2-year flood: 50% chance/year.
- The occurrence of a major flood does not reduce the chance of recurrence in the near future.
- Peak discharge data helps identify flood thresholds for different recurrence intervals.
Case Studies & Examples
- Bangladesh is highly flood-prone due to low elevation and dense population, experiencing worsening floods due to climate change.
- The US benefits from better flood control infrastructure, but property damage and flash floods still occur.
Key Terms & Definitions
- Levee — a raised embankment built to prevent river overflow.
- Floodwall — a vertical barrier designed to temporarily contain high water levels.
- Dam — a barrier that stores and controls river water flow.
- Channelization — modifying a river channel to control flow and reduce flooding.
- Recurrence interval — average number of years between floods of a certain size.
- 100-year flood — flood event with a 1% chance of occurring in any year.
Action Items / Next Steps
- Review and understand flood hazard maps for interpreting flood risks.
- Complete assigned activity/quiz on calculating annual flood probabilities.
- Check flood risk when purchasing property using official hazard maps.