Dissolved Oxygen Modeling of Lake Ogallala: A Midwest Hydropower Tailwater Reservoir Using CE-QUAL-W2, Version 3

The Lake Ogallala hydropower tailwater reservoir is subjected to wide fluctuations of the inflow water quality and quantity. These alterations impact lake temperatures, water stage, dissolved oxygen (DO) and nutrients. A two dimensional continuous simulation, hydrodynamic and water quality model, CE-QUAL-W2, was used to simulate the lake's dissolved oxygen. The elements modeled include surges of low DO and temperatures; high chemical oxygen demands and dissolved nutrients; in-lake algae, macrophytes, and epiphytes response; temperature and bathymetric induced circulation patterns; and weather impacts. The epiphyte routine was used to simulate macrophytes, and the model was able to emulate the diurnal DO and temperature fluctuations which ranged from 2 to 12 mg/L and 19.5 to 23 degrees C, respectively. The study found that the chemical demand resulted in an approximately 1.5 mg/L drop in DO across the lake but also found that macrophyte respiration causes approximately a 2 mg/L reduction in DO during dark respiration. Management alternatives were modeled based on controlling the inflow of DO and macrophyte harvesting.