Date of Award:

3-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Civil and Environmental Engineering

Advisor/Chair:

Darwin L. Sorensen

Abstract

Pineview Reservoir, near Utah's populous Wasatch Front, could play an important role in modulating water supply as water demands and water uses change in response to increasing population densities. The reservoir is currently mesotrophic but threatens to become eutrophic. Ground water in the shallow water table aquifer that surrounds the reservoir contributes a large proportion of the reservoir's inflows in summer and fall because most of the stream flow is diverted for irrigation. Ground water flow and its subsequent nutrient loading to the reservoir were studied from February 2010 through November 2011. The objectives were to: 1) characterize nutrient transport from the water table aquifer to the reservoir; 2) quantify and characterize the spatial variability of ground water flow and nutrient loading in a mountainous irrigated valley; and 3) estimate nitrate leaching to ground water from cropland, lawns and septic drain fields. The first objective was achieved by monitoring stream flows, and modeling ground water flow and nutrient loading towards Pineview Reservoir. Ground water from the water table aquifer contributed 22 percent and 2.6 percent nitrate + nitrite nitrogen and total dissolved phosphorus, respectively, to the annual reservoir loads. The aquifer contributed a total inflow of 3.4 x 106 m3 yr-1 (2 percent of the total inflows) to the reservoir. Large variations in both ground water nutrient concentrations (6 - 310 µg P L-1 as total dissolved phosphorus and 3.3 - 21 mg N L-1 as nitrate + nitrite) and ground water flows among aquifer subdivisions were observed. Study of the second objective employed GIS-based interpolation techniques in analyzing the spatial distribution of ground water flow and nutrient loading towards the reservoir. Large spatial variations in ground water flows and nutrient loadings were observed. The 67 percent confidence intervals (geometric mean ± 1 standard deviation) for total dissolved phosphorus ranged from 0.014 - 0.400 kg P d-1. Nitrate + nitrite nitrogen had a 67 percent confidence interval of 0.954 - 39.1 kg N d-1. The variations were attributed to agricultural and domestic non-point sources. Under the third objective, ground water nitrate loadings in the near-reservoir drainage area of the reservoir's major tributary, the South Fork of the Ogden River, were simulated in the GIS-based Nitrogen Loss and Environmental Assessment Package. Annual leaching rates (kg N ha-1 yr-1) from drain-fields and the lawns were, respectively, more than 2.6- and 1.1-fold higher than the croplands. However, differences in the spatial extent of contributing sources resulted in 70- and 50-fold higher total leaching losses from croplands and lawns, respectively, than drain-fields. The findings would help water managers, town planners, and stakeholders in their decisions relative to land use, water distribution and use to protect and/or improve water quality in the reservoir.

Share

COinS