SI-3B (1/21/05 version)
Overview, "As Is" Stream Integrity Situation: Rural Stream Flow Research

Incremental Changes in Flashiness of Midwestern Streams and a New Flashiness Index
(David B. Baker, R. Peter Richards, Timothy T. Loftus and Jack W. Kramer2)

Abstract: The rate of flow increase and decrease during storm hydrographs, i.e. flashiness, is an important element of the natural flow regime of streams. Specifically, flashy streams are those for which intense rainfall inputs move rapidly across land surfaces into -- and through -- stream channels, generally resulting in spiky hydrographs and low baseflows. Departures from "natural" flashiness impair aquatic ecosystems and can be caused by many factors, including flow regulation, land use changes, agricultural drainage practices, urbanization, land management practices, and climate change, often to the detriment of aquatic life.

We have developed a new flashiness index based on mean daily flows from U.S. Geological Survey stream gages. The index consists of summing the absolute value of day-to-day changes in mean daily flow for a year and dividing that sum by the total annual discharge. This index has relatively small inter-annual variability, making it efficient in short-term trend detection.

We have applied this index to 78 stations in Ohio for the 27-year period from 1975 to 2001. The slope of the regression between the index and time (years) is positive for 77% of Ohio's streams and significant at the 95% level for 29% of the streams, suggesting that many Ohio streams are becoming more flashy. Significant increases occur in many rural streams. Only 4% of the Ohio streams have significant decreases in index values.

Significant increases in index values also occurred in 31% of 62 Michigan streams and in 38% of 104 Indiana streams. In contrast, 33% of 70 Iowa streams had significant decreases in index values. Means of index values for streams vary geographically, with Ohio's streams having the highest indices among six Midwestern states. These trends pose new challenges to agricultural water management in Ohio.

2Respectively, Director Emeritus, Senior Research Scientist, Director, and Laboratory Manager, Water Quality Laboratory, Heidelberg College, Tiffin, OH 44883 (e-mail /Baker:

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