Extensive agricultural land use and intensive urban residential growth of the Calleguas Creek, California, watershed has increased chloride load and impaired beneficial uses. The hydrology of the watershed is typical of the semiarid U.S. West in that nearly all rainfall occurs in a
small number of discrete storm events that each produces peak discharges of a duration of several days or less; conversely, during the dry weather season, discharge has historically been near zero. Currently, a year-round flow is sustained by two factors: base line flow sustained by discharges
from publicly owned treatment works (POTWs) and increased groundwater discharge from a shallow water table elevated by intensive agricultural irrigation (deep groundwater basins used for water supply have declined into overdraft). Water quality impairment of Calleguas Creek increases during
low-flow days, but cannot be defined seasonally because days not influenced by storm discharge occur at substantial proportions during all months. Impairment is greatest not during lowest flows, which are dominated by POTW effluent, but when groundwater and other nonpoint sources are highest,
thereby contributing chloride load disproportionately to their flow. The highest nonstorm days are identified through cumulative frequency of mean daily discharge (MDD) as the transition from nonstorm conditions (described by normal distribution) to storm conditions (described by log-normal
distribution). Transition occurs at approximately the 80th to 85th percentile MDD at three Calleguas Creek locations. Critical conditions for chloride impairment are defined as volumetric flow at those percentiles of cumulative MDD distribution.
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CRITICAL FLOW FOR IMPAIRMENT;
NONPOINT SOURCE POLLUTION;
STATISTICAL DISTRIBUTION OF ENVIRONMENTAL DATA;
Document Type: Research Article
Publication date: 2003-01-01
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Water Environment Research (WER) is published monthly, including an annual Literature Review. A subscription to WER includes access to the latest content back to 1992, as well as access to fast track articles. An individual subscription is valid for 12 months from month of purchase.
Water Environment Research (WER) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year. Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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