AEP, EY, and ARI Explained: Definitions, Formulas, & Misconceptions
AEP, ARI (Return Period), and EY are among the most commonly used terms in flood frequency analysis — yet they are often misunderstood and used interchangeably. In this video, I explain the true meanings of AEP, EY, and ARI, clarify their mathematical relationships, and highlight common misconceptions engineers may have when interpreting flood probabilities.
You’ll also learn how Annual Exceedance Probability (AEP) is used in real-world flood design, including recommended design standards for drainage systems, bridges, levees, and dams.
Whether you are a hydrology student, civil engineer, flood modeller, or water resources professional, understanding these concepts is essential for correct flood risk interpretation and infrastructure design.
Also watch our previous video on design storm and design flood:
Design Storm vs Design Flood – Key Differences & Common Mistakes Explained
• Design Storm vs Design Flood – Key Differe...
________________________________________
⏱️ Timestamps
00:00 Introduction
00:46 Why do hydrologists use probability?
01:28 What is Annual Exceedance Probability (AEP)?
02:17 What is ARI (Average Recurrence Interval / Return Period)?
02:45 What is EY (Exceedances per Year)?
03:06 Mathematical relationships between AEP, ARI, and EY
03:12 Common misconceptions engineers make
04:06 Recommended AEP for different infrastructure
• Minor drainage systems
• Major drainage systems
• Bridges and Levees
• Dams and critical infrastructure
05:05 Key takeaways
________________________________________
🎓 What you will learn
• The difference between AEP, ARI, and EY
• Why return period can be misleading
• How to convert between AEP and ARI
• The role of probability in hydrologic design
• Recommended design floods for infrastructure
________________________________________
🔎 Keywords
#aep #ARI #hydrologicalmodelling #floodfrequency #hydrologicprobability #returnperiod #floodrisk #floodprobability #civilengineering #hydrologytutorial #drainagedesign