🔍 Key Concepts

• River gage zero definition on inland rivers like the Mississippi • Difference between a datum/reference plane and an actual water depth • How hydrographic and river engineers use a fixed vertical reference for all stage readings

💭 Think About

• Is gage zero based on a changing water condition (like highest/lowest depth) or on a fixed, engineered vertical reference? • Which choice sounds like something surveyors and chart-makers would use consistently over many years, regardless of floods or droughts? • Think about how you would compare river stages at different times—what kind of reference would give you a stable baseline?

✅ Before You Answer

• Make sure the option you pick is a fixed vertical reference, not something that changes every season • Ask: Can this reference be used the same way at every gage along the river? • Check which terms are commonly used in hydrographic surveying and river stage reporting for the Mississippi