🔍 Key Concepts

• Low Water Reference Plane (LWRP) and how bridge clearances on the Western Rivers are referenced to it • How to read the bridge clearance table on the river chart or in the Light List for Vicksburg, MS • What happens to clearance when the actual river stage equals the reference plane used for the published clearance

💭 Think About

• On Western Rivers, are published vertical clearances usually given at LWRP or at some other stage? How does that affect whether you must add or subtract anything when the river is exactly at LWRP? • If the gage reads the same as the reference plane (LWRP), what is the difference in height between the water surface and that reference? Does that change the published clearance? • Think about how you would adjust the clearance if the water were higher or lower than LWRP. What is that adjustment when the water level and LWRP are the same?

✅ Before You Answer

• Look carefully at how the vertical clearance is defined in the exam’s reference (river chart/bridge table) – is it “above LWRP” or “above gage zero” or something else? • Verify whether any correction for river stage is needed when the stage equals LWRP (difference between them is zero). • Confirm you are using the published clearance value for that specific bridge at LWRP, then decide whether any additional math is actually required.