This thesis integrates existing work on surface accretion rates with more recent advances in the understanding of creek hydrodynamics. Concepts drawn from various disciplines are formulated into a revised framework within which marsh sedimentation may be better understood. Channel flux studies that treat the marsh as a 'black box' contribute little to our understanding of marsh functioning, whatever the accuracy of their execution. Marshes are better conceptualised as complex bio-sedimentary systems, characterised not only by an intimate relationship with adjacent tidal waters, but also by numerous internal pathways along which transport of water and materials may take place. Data relating to surface sediments, surface sedimentation, channel and over-marsh hydrodynamics, and suspended sediment composition and settling behaviour have been obtained within a relatively mature back-barrier marsh, 54 ha in area, at Scolt Head Island, on the north Norfolk coast. Tidal range averages 3.2m at neaps and 6.4m at springs. The annual sediment input to the marsh surface is estimated at 675 tonnes, equivalent to a mean accretion rate of approximately 0.26 cm/year. The broad pattern in sedimentation reflects surface topography via its control over inundation frequency. Locally, however, proximity to the creek system as an intermediate sediment source determines the rate and nature of sedimentation. The formation of composite particles via the action of flocculation and organic binding agents determines the depositional behaviour of fine cohesive sediment introduced to the marsh. Particle fall velocities are thereby enhanced, with settling from over-marsh tidal flows being a continuous process and not confined to slack water. Reworking of newly deposited material by deposit feeding gastropods appears to be intense over much of the marsh, and may be an explanation for the paucity of sedimentary structures. The marsh surface acts as a topographic threshold separating markedly different spring and neap creek flow regimes. Morphological development of the creeks is effectively confined to ebb-dominated spring tides, when export of sand occurs. Though the creeks act as effective conduits for material transport, a large proportion of the total spring tidal prism may be exchanged directly over the marsh edge. These results may be viewed in the context of present concern over rising sea levels linked to human-induced global warming. Scenarios for future sea-level change vary widely, though most estimates put the present rate of eustatic rise at approximately 1-2 mm/year. Subsidence along this coast is around 1mm/year. Thus many marshes exist in delicate equilibrium with present relative sea level. A numerical model incorporating quasi-continuous deposition, annual tide data, and eustatic and crustal movements successfully simulates historic marsh sedimentation along the north Norfolk coast and provides an insight into the possible effects of future eustatic changes.

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This thesis aimed to provide improved understanding of the spatial and temporal variability of stream temperature, the influence of riparian woodlands on thermal regimes and examples of the ecological consequences of different thermal regimes.  First, the spatial and temporal variability of temperature within a large montane river basin at nested spatial scales was established.  It was from this analysis that (i) variation that can occur at all spatial scales was observed, (ii) different physical factors are controlling these variations at all scales, and (iii) greatest differences occur between different tributaries.  The extent of riparian forestry proved to be in important factor in determining river temperatures.  The results suggest that broadleaved tree species within the riparian zone are more able to reduced incoming solar radiation and consequently control stream temperature.  This highlights the potential of riparian plantings in mitigation efforts against high temperatures under future climate scenarios.  To complement these empirical assessments, the ecological significance of observed thermal variability was assessed in a laboratory study of the growth of juvenile Atlantic salmon.  The effects of the temperature regime on growth were in the range of about 3% reduction in final length in the variable regime compared to the constant one.  Relations between invertebrate growth, adult emergence patterns and thermal regime differences related to riparian cover were assessed in relation to the mayfly <i>Baetis rhodani.  </i>Statistically significant differences in mean size and size distribution of Baetis were found in the Girnock, between all sites separated by no more than 5 km.

Window constraints are mechanisms to bound the tuples processed by continuous queries specified over unbounded data streams. While sliding window queries move the constraint window upon the arrival of each individual tuple, hopping window queries instead move the window by a fixed amount after some period, thus periodically refreshing their results. We observe that for large hops, techniques liked delta result updating may not be efficient -- as large portions of the tuples in the current window will be different from the previous window and thus must be maintained. On the other hand, the complete result updating technique, which has been found to be less suitable for sliding windows queries. Compute the next result based on the complete current window now can be shown to be superior in performance for some hopping windows queries. A trade-off emerges between the complete result method which has a lower per tuple processes cost but potentially processing redundant results versus the delta result method which has no redundant processing but pays a higher per tuple processing cost. On top of that, strict non-monotonic operators such as difference operator, cause premature expiration due to operator semantics. Negative tuples are needed for this kind of special expiration. Such negative tuples added extra burden to the stream engine. Thus, in streaming processing, the difference operator is typically suggested to be placed on top of the query plan despite its potential ability to reduce cardinality of the stream. With this thesis, we introduce a whole solution for hopping window query processing which includes an optimizer for generalized hopping window query optimization that exploits both processing techniques within one integrated query plan alone with query plan rewriting. First, we design the query operators to be multi-mode, that is, to be able to take either a delta or a complete result as input, and produce either a delta result or complete result as output. Then we design a cost model to be able to chose the optimal mode for each operator. Thirdly, our optimizer targets to configure each operator within a query plan to work in the suitable mode to achieve minimum overall processing costs. Last but not least, two query optimization techniques have been adopted. One explores all possibilities of pushing the difference down past joins using dynamic programming and assigning optimal mode at the same time, the other applies heuristic difference push down rule. The proposed techniques has been implemented within the WPI stream query engine, called CAPE. Finally, we show the benefit of our solution with a vast number of experimental results.

Thesis (Ph. D.)--University of Wyoming, 2006. / Title from PDF title page (viewed on Dec. 15, 2007). Includes bibliographical references.

Although there has been extensive research on the geomorphic and ecologic role of large woody debris (LWD) in streams, the dynamics of LWD in streams are poorly known due to various measurement difficulties during floods. In this thesis I present the results of two flume experiments on the dynamics of wood in streams. The first experiment examined the effects of piece interaction on wood transport, while the second evaluated a theoretical model predicting the threshold of movement, and factors controlling the deposition of individual logs. Flume experiments allow us to model the wood movement under a variety of piece geometries, piece concentrations, and hydraulic conditions. The first experiment showed that logs moved in three distinct transport regimes; congested, semi-congested, and uncongested transport. During congested transport the logs move as a single mass and occupy > 33 % of the channel area. Uncongested transport occurs when the logs are moving as individuals and occupy < 10 % of the channel area. Semi-congested transport is intermediate between these two transport regimes and occurs when wood moves in clumps of 2-3 logs. Transport regime was dependent upon the ration of the volumetric input rate of pieces to the flow, and to a lesser degree, the ratios of the piece length to channel width and piece diameter to channel depth. The transport regime was reflected in the deposit. Congested transport deposits have a higher portion of their pieces oriented parallel to flow than uncongested and semi-congested transport. We expect that congested transport will occur in low-order channels where input rates are high and channel geometry is small relative to piece size. Uncongested transport will dominate large channels where input rates are lower relative to flow and channel geometry is large relative to piece size. Our theoretical model and these experiments indicate that the entrainment of individual logs was dependent upon the angle of the piece, and the presence/absence of rootwads. Although previously noted as a first-order control on piece movement, piece length had little effect on the entrainment threshold, but did affect the distance transported. The distance transported decreased with increases in the ratios of the piece length to average channel width (L[subscript log]/w[subscript av]), the piece length to the radius of curvature (L[subscript log]/R[subscript c]), and the piece diameter relative to average depth (D[subscript log]/D[subscript av]). These three ratios comprise the debris roughness. Increased debris roughness caused a general decrease in distance transported. Pieces with high debris roughness can travel further than predicted if they have high momentum, and over 50 % of their channel area deeper than the depth at which the piece floats. These results indicate that flume experiments and theoretical models, tools that have been extensively used to study sediment dynamics, are a useful in examining wood dynamics. / Graduation date: 1998