WATERSHED RESPONSE TO STORM EVENTS

During May 11-13, 1998 and July 21-22, 1998, two storm events passed across north-central and central Indiana dropping as much as 6-8” of rain in a 24-36 hour period. During this time the Fixed Station Monitoring Program of the Indiana Department of Environmental Management (IDEM) collected water samples that included total metals. Increased rainwater and runoff to river systems decreases water hardness and increases total metal concentrations, which leads to increased toxicity. The Indiana Environmental Rules for Water state that the Acute Aquatic Criterion (AAC) levels should never be exceeded. The Acute Aquatic Criterion was exceeded four times during these events, twice for Copper and once each for Cadmium and Zinc. Data results that exceed the AAC can be plotted on a hydrograph of the storm events to determine the point in time a watershed exceeded its AAC. The Wabash River at Logansport exceeded the AAC for Zinc as the hydrograph peaked for the May 11-13, 1998 event, and exceeded the AAC for Copper as the hydrograph peaked during the July 21-22, 1998 event. The Big Monon Creek near Monticello exceeded the AAC for Cadmium on the downswing of the hydrograph during the May 11-13, 1998 event approximately four days after the peak. The Salamonie River at Portland exceeded the AAC for Copper on the upswing of the July 21-22, 1998 event. This model approach to watershed analysis could be useful in determining the instance and duration of AAC toxicity in a stream, which in turn can assist in improving watershed management planning.