The sources of variation in storm runoff quantity and quality in the partially urbanized Leary's Brook basin, St. John's, Newfoundland

MacCallum, Ian Malcolm (1981) The sources of variation in storm runoff quantity and quality in the partially urbanized Leary's Brook basin, St. John's, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The known variation of water quality during storm runoff makes infrequent sampling unreliable. Though the variation of water quality from non-point source urban areas can be determined with frequent sampling, the extent of change due to the urbanization has been infrequently determined. Mixing of urban storm runoff with water from other source areas may be deleterious because of high yield rates of dissolved and suspended solids. The sampling programme of this research was designed for frequent sampling of three different urban and two non-urban sub-catchments and the outlet of Leary's Brook in St. John's, Newfoundland. Suburban residential, commercial/industrial, parking lot, rural and forested sub-catchments were sampled rotationally by hand on an hourly schedule for sixteen hours during the storm runoff period of November 13-14, 1979, and the outlet was automatically sampled hourly over 24 hours for the same rainfall event. Sampling of all sites for the same storm allowed comparison between the contributions in quantity and quality of storm runoff for the five land use types and the basin as a whole for effectively the same precipitation and antecedent moisture conditions. Temperature and conductivity of hand collected samples were determined in the field. Discharge was measured by stage and later calculated by the Manning equation or by rating with current meter measurements. Laboratory analysis was also carried out on all samples using spectro-photometric techniques for pH, turbidity, phosphate and nitrates. The response of Leary's Brook basin to the November 13-14 storm was dominated by the non-urbanized portions of the basin; although the urban high fast response in water, solute and suspended sediment yield rates produced a considerable short term effect on the outlet. The overall response of the basin was an aggregate of the urban and non-urban components. Although the outlet solute and sediment yield rates were considerably larger than those of the forested area, the outlet yield rates were not as high as many other urbanized areas. Parking lot runoff demonstrated that not all urban land use causes runoff deterioration. Planning and management may ameliorate urban runoff effects. This study demonstrated a variation in outlet response to non-uniform flood generation controlled by land use rather than precipitation distribution. Hourly rotational sampling proved useful for single storm sampling of five sites, but more frequent sampling of urban runoff would be an improvement. Dry weather sampling of 35 sites in the basin showed the choice of the representative sub-catchments to be reliable.

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