🔍 Key Concepts

• Tidal datum used for charted depths (usually Mean Lower Low Water – MLLW) • How to use a tide table for a specific date, place, and time of low water • Whether the water level at that time is above or below the chart datum, and how that affects correction (add vs subtract)

💭 Think About

• Identify what vertical datum the charted depths are referenced to, then compare that datum to the predicted height of the PM low water on 18 December 1983 • Determine if the predicted low water height means there will be more or less water than the charted depth, and whether that means a positive or negative correction • Estimate which of the choices best matches the difference between the chart datum and the predicted PM low water height for Poquoson River at York Point

✅ Before You Answer

• Verify the tide station used (Poquoson River at York Point) and that you’re reading the PM low water for 18 December 1983 • Confirm whether charted soundings are based on Mean Lower Low Water (MLLW) and how to apply a tide height to those soundings • Double-check the sign of the correction: if the actual tide height is above the datum, the correction to the charted depth is usually positive (more water); if below, it is negative (less water)