53:171 Water Resources Engineering
Problem #5
Evaporation from a Lake

A meteorological station (located 2 m above the lake surface) collects the following data near a lake:

• Net Radiation: 275 W/m²
• Bowen's Ratio: 0.25
• Pan Evaporation: 0.40 in/day
• Pan Coefficient: 0.7
• Air Temperature: 82F
• Wind Speed: 15 mph
• Lake Area: 1250 acres
• Latent Heat of Vaporization: 2.5 x 10⁶ J/kg

Use the measurements to estimate the following:

1. Lake evaporation (in/day) using the pan evaporation method.
2. The power (W/m²) needed to evaporate water at the rate shown in part a.
3. The volume of water (m³) evaporated in 1 month (31 days) for the rate shown in part a.
4. Lake evaporation (in/day) using the (simplified) energy-budget method.
5. The power (W/m²) needed to evaporate water at the rate shown in part d.
6. The volume of water (m³) evaporated in 1 month (31 days) for the rate shown in part d.