Thesis advisor: Noah P. Snyder / Substrate size and mobility are important to Atlantic salmon (Salmo salar) spawning and rearing success. Channel geometry is a control on bedload mobility in streams. It is believed that channel morphology in many Maine rivers has been altered by land use practices, creating wider and shallower channels, and lowering stream competence. If correct, these changes may be partially responsible for the limited number of returning salmon currently observed in Maine coastal rivers. To evaluate the magnitude of these changes, I performed a statistical comparison of channel morphology between two Atlantic coastal streams: the Narraguagus River in Downeast Maine and the Jacquet River in northern New Brunswick, Canada. Compared to the Narraguagus River, the Jacquet River has relatively healthy returns of adult salmon. Both watersheds have similar drainage areas (Narraguagus 588 km²; Jacquet 510 km²;) and mean annual precipitation (1244 mm; 1200 mm), but differing average channel gradients (0.16%; 0.51%) and longitudinal profiles. During the summer of 2007, I surveyed a 13.6-km section of the Narraguagus with a drainage area range of 129-247 km², and a 10.4-km section of the Jacquet with a drainage area range of 94-265 km². I made measurements of active and bankfull width and depth, and channel gradient at 100-m intervals, and performed grain-size counts at 200-m intervals. I also measured gradient and width in a GIS-based analysis. Results of my analysis show that channel gradient is likely the most influential factor on Atlantic salmon habitat as it relates to sediment size. The two rivers exhibit no significant difference in width-to-depth ratio, when low-gradient outliers in the Narraguagus River are removed. Predicted median riverbed grain sizes were calculated using two methods: (1) from the empirical relationship between basal shear stress and measured grain size; and (2) using the Shields parameter and remote sensing data only. Measured and predicted grain sizes reveal finer river-bed sediments on the Narraguagus River, however, Shields parameter calculations show that sediment should be mobile in both streams. I compare these predictions to field-based habitat mapping on the Narraguagus River. Based on predicted grain sizes, I expect nearly continuous Atlantic salmon spawning (28-95%) and rearing (95-100%) habitat on the Jacquet, and much less spawning (47-62%) and rearing (57-68%) habitat on the Narraguagus. This is likely because the Narraguagus River is segmented into reaches of steeper gradient (S < 0.002) with potentially good habitat, and flatter reaches (S < 0.0005) of poor habitat. The long flat reaches (several km) likely act as sediment sinks, preventing the continuity of downstream sediment transport and causing sediment to be sourced from localized glacial deposits. / Thesis (MS) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Thesis (M. Sc.)--Acadia University, 1999. / Includes bibliographical references (leaves 143-150). Also available on the Internet via the World Wide Web.

Thesis (M. Sc.)--Acadia University, 1999. / Includes bibliographical references (leaves 143-150). Also available on the Internet via the World Wide Web.

Lateral instability exerts considerable influence on the sedimentology, planform, and hydraulic characteristics of gravel-bed rivers. Because Atlantic salmon (Salmo salar) tolerate a narrow range of depths, velocities and substrate sizes, the quality and quantity of habitat available to salmon should vary with level of river instability. In the Riviere Nouvelle, a Gaspe river destabilized by deforestation and past channelization projects, the effect of lateral instability on habitat was variable. Fines content in riffle substrates did not show a significant relationship to local bank erosion rates, even where the rate was as high as 10 myr$ sp{-1}$ and the proportion of fines entering the channel was much higher than that found in riffles substrates (an excess of fines in potential spawning riffles reduces spawning success among salmonids). For juveniles, availability of hydraulically suitable habitat was largest where lateral instability resulted in aggradation of the river bed and development of a braided pattern. Hydraulic habitat availability was lowest where erosion patterns led to high planform curvature levels and to scouring of bed materials. In general, because of the relatively high power of the Riviere Nouvelle, structures or processes leading to diminishment of depths or velocities (e.g. aggradation) resulted in an increase in the amount of juvenile habitat available.

Although the watersheds of the Petite Cascapedia and Bonaventure Rivers, Gaspe Peninsula, have broadly similar geology and land use, their segment-scale river geomorphology is contrasted by subtle differences in valley characteristics that are a legacy of their individual geomorphic histories. These differences have consequences on the distribution of Atlantic salmon habitat such as boulder abundance (for parr rearing and overwintering habitats) and spawning substrate quality. Parr preference for boulder-rich river segments (1--5 km) was observed in the Bonaventure River. In the study systems redd distribution was sensitive to relatively small changes in the fines content of riffle substrate. River segments flowing through moderately narrow semi-alluvial valleys present better overall parr habitat (high boulder abundance) and better spawning substrate quality (percentage of sand) than wider valley sections. These differences are due to additional sources of coarse sediment, higher shear stresses, and lower bank erosion rates in such valleys.

Thesis (Ph.D.)--Memorial University of Newfoundland, 1999. / Bibliography: leaves 212-224.

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This thesis relates fluvial morphology to those hydraulic conditions identified as being ideal for the rearing of juvenile Atlantic salmon. The suitability of flow depths and velocities were obtained from published habitat preference curves in order to compute the percent area (percent usable area - PUA) and average width (average usable width - AUW) of reaches providing ideal rearing habitat for juvenile Atlantic salmon at 2 typical summer discharge levels, in the Ste. Marguerite River. / By dividing reaches into smaller, morphologic unit's, in order to make the conditions more uniform, it was noticed that the wetted width and the amplitude of the vertical oscillation of riffles and pools (riffle-pool amplitude) provided the strongest hydraulic and morphologic relationships with the amount of usable habitat at the morphologic unit scale. Two regression models were produced to estimate the AUW of morphologic as a function of hydraulics and morphology, respectively. / The historic flood in July 1996 also provided an opportunity to examine some of the impacts of a large magnitude flood on channel morphology: localized bed and bank erosion, the destruction of riparian vegetation, the enhancement and destruction of individual bars, and localized changes in the hydraulic and morphologic character (induced by large sediment inputs).

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