Abstract

The accurate prediction of water quality is essential for management of reservoirs used for drinking water supply. Since algae are a major source of taste and odor problems in drinking water, understanding and controlling algal growth and production is an important task. Deer Creek Reservoir supplies drinking water for over one million people in northern Utah and has been highly eutrophic in the past. Despite major reductions in external nutrient loading, including phosphorus, seasonal algal blooms in Deer Creek have not decreased to desired levels. Resuspension of sediment has been suggested as a potential source of internal nutrient loading for water bodies (including reservoirs in the Utah/Wyoming area) and may be responsible for delays in water quality improvement. I investigated sediment deposition and resuspension rates at the upper end of the reservoir and evaluated these sediments as a possible internal source of phosphorus. Sonar and GPS systems were used to make measurements of recently deposited sediment in the submerged Provo River delta of Deer Creek Reservoir during the period of May, June, July, and August 2011. ArcGIS 10 was used to interpolate survey points and calculate sediment volume changes, including areas of deposition and erosion. These data were used to develop approximate sedimentation rates for the soft sediment – which is most susceptible to resuspension during reservoir drawdown. I used previously measured field phosphorous concentrations in the sediment to estimate if these processes could affect reservoir phosphorous concentrations. The study used two survey areas, a small area near the Provo River inlet early in the year, and an extended larger area starting on June 23rd. I found that sediment volume in the smaller study area was increasing at a rate of 27-109 m3/day during the spring season. Data show that rates are slightly correlated with flow and reservoir elevation. Typically by August, Deer Creek reservoir would have been drawn down 2 to 4 m. However, due to a heavy snow pack in 2011, Deer Creek reservoir was not drawn down. When the reservoir is drawn down, the sediments in the upper region of the delta, where the survey was conducted, will be resuspended and deposited lower in the reservoir. These processes will likely result in releasing the phosphates currently bound to the sediment into the water column. Based on previous measurements of readily soluble phosphates bound to the sediment, this resuspension could release between 80 and 230 kg of phosphorus from the study area into the water column during critical times during the warm months–conditions well suited for algal growth. This amount of phosphorus, while an upper bound of what could be expected under actual field conditions, could raise phosphorus concentrations in the survey area by as much as 0.38 mg/L. The potential P (80-230 kg) release could account for 14%-42% of the TMDL. This is a potentially significant amount, especially if released during the critical late-summer period, and warrants more detailed study.

Degree

MS

College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2011-10-18

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd4797

Keywords

GPS, GIS, sonar, water quality, sediment resuspension, phosphorus, TMDL, Deer Creek Reservoir, algae

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