The Effects Of Channel Modification On Characteristics Of Streams During Low Flow PDF Download

Fluorescent dye was used to assess summer low flow hydraulic retention and transient storage (dead zone) associated with fish habitat structures at Camp Creek, Drift Creek, and the East Fork of Lobster Creek within the central Coast Range of Oregon. Utilizing channel units to stratify stream reaches, the effect of instream structures upon the hydraulic retention of pools was evaluated. The cycling time of water into and out of storage was also estimated by calculating an exchange coefficient. Camp creek had a pre- and post-treatment design that included unaltered, low, medium, and high levels of coarse woody debris loading. Except for one Camp Creek channel unit (CC21), major alterations to low flow channel unit dimensions did not occur after treatment and the volume of water in transient storage in the other treated channel units was probably not altered. Intensive debris loading increased the length of channel unit CC21 by 6 meters and the average cross-sectional depth by 0.04 meters. An "additional sums of squares" test was used to evaluate whether there was a statistically significant difference existing between Camp Creek pre- and posttreatment simple linear regressions of transit time versus debris loading and the average cross-sectional area, depth, width, and velocity. The additional sums of squares comparison did show that an increase in posttreatment transit time was statistically significant (p 0.10) when compared against debris additions that were located within the low flow wetted perimeter of the stream (wood influence Zone I). Statistically significant (p 0.10) results for dye plume and geomorphic variables for Drift Creek and Lobster Creek are not presented as major conclusions because of a lack of pretreatment control data. Qualitatively, however, one-tailed t-test indicate that during summer discharges, flow velocities and peak concentrations may significantly decrease in treated channel units, compared to the channel units that were assumed to be controls. Intensive debris loading may enhance low flow channel complexity by increasing turbulent mixing and increasing the transit time of water. However, in this study the largest amount of debris volume was located in the cross-section of channel existing between low flow and bankfull flow (wood influence Zone II). Thus, hydraulic interaction with debris primarily occurs during winter flows and storm flows when streampower is at its highest.