Morphologic and Morphometry Response to Channelization: The Case History of Big Pine Creek Ditch, Benton County, Indiana
Big Pine Creek in northwestern Indiana drains an extensive area of fertile prairie soils developed on Wisconsinan age till and alluvial deposits. The creek was channelized in 1932 to improve drainage; original channel geometry, slope, and sinuosity can be approximately restored from the engineering plans and design criteria. No organized or consistent maintenance has been performed on the stream, and by using time-sequential aerial photographs for the years 1938, 1963, and 1971, a topographic map prepared in 1962, and a field survey of selected reaches in 1975 it is possible to monitor progressive changes over a recovery interval of about 40 years. Principal adjustments include (a) an increase in sinuosity and initiation of new point bars and meanders accompanying lateral migration of the channel, (b) reestablishment of pool-riffle sequences through scour and fill in parts of the channelized reach, (c) bank erosion and slumping, (d) a decrease in gradient and other profile adjustments, and (e) reduction of channel drainage capacity with an increase in flood frequency and magnitude. These adjustments, however, are neither uniform nor consistent over the entire channel, probably because of interim maintenance undertaken by individual farmers along discrete segments.
Attempts to determine the principal cause of channel deterioration include an investigation of variations in bank material, distribution of spoil materials, and threshold values related to variations in sinuosity, slope, and stream power. The relationship between sinuosity and stream power seems most significant, and a stability envelope is developed for the natural, prechannelized stream. Assessment of this relationship from data available from aerial photographs and the field survey suggests that though instability continues there is a long-term adjustment trend toward the prechannelized state. This trend can also be used to predict recovery rates and cumulative recovery with time.
It is suggested that if stream power to sinuosity and other relationships are identified, quantified, and properly applied, engineering design error may be greatly minimized, and if geomorphic thresholds are not exceeded, a stable, effective drainage project may be constructed without significant loss of biotic, vegetational, or aesthetic qualities of the stream.