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Existing knowledge of the flow in a river past a groyne is inadequate to explain fully the siltation and scour that take place around such a structure. A survey of published material reveals controversy over the choice of pertinent flow parameters affecting the maximum scour depth.

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The use of catchment areas for the study of elemental mobilities is discussed with particular reference to two catchments in north-east Scotland. Underlying geology has considerable influence on their respective stream water compositions, although total annual solute output ultimately depends on the quantity of stream runoff. Tremendous fluctuations in stream water chemistry occur during storms which, it has been suggested, are due to the pathways taken by storm water through chemically contrasting soil horizons. Field sampling of this soil throughflow storm component and laboratory studies involving the leaching of undisturbed soil cores (taken at various depths down the profile) support this conclusion. Relationships between iron, aluminium and organic matter in stream water are discussed in detail. Full use of the available analytical facilities has been made with modifications to existing methods and development of new methods undertaken where necessary.

Thesis advisor: Noah P. Snyder / The Souhegan River is a tributary of the Merrimack River that drains a 443 km<super>2</super> watershed in southern New Hampshire. The lowermost barrier on the Souhegan River, the Merrimack Village Dam (MVD), was demolished and removed in August and September 2008. The modern MVD impoundment contained at least 62,000 m<super>3</super> of sediment, mostly sand. Analysis of topographic and historical maps, and photographs suggests that approximately twice the area of what is now the modern impoundment has been affected by over 200 years of damming at the site. I use repeat surveys of cross sections and the river longitudinal profile, and sediment samples, to document the response of the Souhegan River to the MVD removal. A base level drop of 3.9 m caused immediate incision of the sand-sized sediment and channel widening. The impoundment later segmented into a non-alluvial, bedrock and boulder controlled reach; and a quasi-alluvial sand and gravel reach with erosion and deposition modulated by the presence of vegetation on the channel banks. One year after the removal, the Souhegan River has excavated 38,100 m<super>3</super> (65%) of the sediment in the modern impoundment. The response of the Souhegan River was rapid and the channel and floodplain continue to evolve toward a quasi-equilibrium configuration. Continued response will be substantially influenced by the establishment of vegetation within the former impoundment and the magnitude and frequency of high discharge events. / Thesis (MS) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

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