Real-Time Water-Quality Methods

Real-time water-quality monitoring. In-stream water-quality monitors were installed at U.S. Geological Survey streamflow-gaging stations. Data collected by these monitors include: specific conductance, pH, water temperature, turbidity, dissolved oxygen, and total chlorophyll. These devices are connected to data-collection platforms at each stream-gaging station, and data are transmitted by satellite to a downlink site and to the computer at the U.S. Geological Survey office. Real-time water-quality monitor
Sample collection. Water samples are collected periodically at selected U.S. Geological Survey streamflow-gaging stations. These samples are collected throughout the range of expected hydrologic conditions and analyzed for selected constituents and properties. For example, consituent concentrations typically are determined for alkalinity, dissolved solids, total suspended solids, chloride, sulfate, atrazine (a pesticide), and fecal coliform bacteria. Collecting water sample at DeSoto
Regression analysis. The concentrations of constituents in surface water often are strongly related to physical properties of water and factors such as hydrologic conditions, season, and location. It is possible to express one constituent concentration in terms of another constituent or physical property using simple regression equations. To determine which independent variables to use in each regression equation, a stepwise procedure was used. The possible independent variables include each of the properties measured by the water-quality monitor (specific conductance, pH, water temperature, dissolved oxygen, and turbidity), streamflow, and time. Comparison of measured and estimated fecal coliform bacteria densities in Little Arkansas River at Highway 50 near Halstead, February 1995-December 1998.
Load Conversion. Once the constituent of concern is estimated with the regression equation, the concentration is multiplied by streamflow and an appropriate conversion factor to estimate the constituent load. Loads can be estimated every 15 minutes. Loads are useful because they give an indication of the total amount of a constituent being transported by a stream during a given period of time. These estimated loads may also be useful in the development of total maximum daily loads (TMDLs) Comparison of measured and estimated fecal coliform bacteria loads in Little Arkansas River at Highway 50 near Halstead, 1999.