Impacts of Varying Dam Outflow Elevations on Water Temperature, Dissolved Oxygen, and Nutrient Distributions in a Large Prairie Reservoir

Abstract

Dam operations are known to have significant impacts on reservoir hydrodynamics and solute transport processes. The Gardiner Dam, one of the structures that forms the Lake Diefenbaker reservoir located in the Canadian Prairies, is managed for hydropower generation and agricultural irrigation and is known to have widely altering temperature regimes and nutrient circulations. This study applies the hydrodynamic and nutrient CE-QUAL-W2 model to explore how various withdrawal depths (5, 15, 25, 35, 45, and 55 m) influence the concentrations and distribution of nutrients, temperature, and dissolved oxygen (DO) within the Lake Diefenbaker reservoir. As expected, the highest dissolved nutrient (phosphate, PO 3 À 4 -P and nitrate, NO À 3 -N) concentrations were associated with hypoxic depth horizons in both studied years. During summer high flow period spillway operations impact the distribution of nutrients, water temperatures, and DO as increased epilimnion flow velocities route the incoming water through the surface of the reservoir and reduce mixing and surface warming. This reduces reservoir concentrations but can lead to increased outflow nitrogen (N) and phosphorus (P) concentrations. Lower withdrawal elevations pull warmer surface water deeper within the reservoir and decrease reservoir DO during summer stratification. During fall turnover low outflow elevations increase water column mixing and draws warmer water deeper, leading to slightly higher temperatures and nutrient concentrations than shallow withdrawal elevations. The 15 m depth (540 m above sea level) outflow generally provided the best compromise for overall reservoir and outflow nutrient reduction.

Impact of Cedzyna Reservoir on Selected Physicochemical Parameters of River Water Quality (Swietokrzyskie Mountains, Poland)

“…Higher oxygen content in the river below the reservoir is connected with its turbulent flow from the dam and an adjacent artificial riffle. The differences in concentration of oxygen between the river inflow and outflow were greater during the growing season, which may result from the process of photosynthesis, particularly intense in surface layers of water [23,24]. From January to April the values were similar and slightly lower at the river outflow than the inflow.…”

Modeling reservoir surface temperatures for regional and global climate models: a multi-model study on the inflow and level variation effects

“…Overall, the results show that the water level variations are clearly related to surface water temperature simulation bias; besides, the outflow (deep abstraction) reduces the volume of hypolimnion and increases the volume of the epilimnion (mixed layer) by lowering the thermocline. Herewith, water level reduction increases the area-to-the-epilimnion volume ratio, which results in an increase in epilimnetic temperature (e.g., Carr et al, 2020). The hypolimnion water temperature (HWT) was generally higher in the W2 hydrology scenarios than in the W2 scenarios due to the heat transported by interflow and underflow currents.…”

Controlling blooms of Planktothrix rubescens by optimized metalimnetic water withdrawal: a modelling study on adaptive reservoir operation

“…It has been used to affect biogeochemical cycling (Weber et al, 2017) or to control vertical heat exchange (Mi et al, 2020b). Previous studies have illustrated that selective withdrawal can redistribute the dissolved oxygen in the water column (Carr et al, 2019), decrease nutrient concentrations (Dehbalaei and Javan, 2018), and change the dominant algal assemblages (Rigosi and Rueda, 2012). This body of research indicates that selective water withdrawal may also have potential to control P. rubescens blooms but this has never been explored so far.…”