A focus on river and stream morphology with a specific emphasis on how urbanization and human impacts affect river channels. In the study of rivers, specifically looking at how the channel geometry changes with time, there are five main physical factors described that affect the channel morphology: (1) bank and bar stability; (2) sediment size distribution; (3) sediment supply; (4) flow variability; and (5) downstream slope, width and height. Understanding how these five factors affect channel form is vital in constructing realistic and accurate models of rivers and how they change over time. It is also important to understand some of the limitations of the combined modeling of all these factors together for a general stream. Research studies are presented in order to further understand what knowledge has been acquired, and what areas are lacking in adequate understanding. Examples of cases where urbanization and land use change have a large impact and almost no impact are examined. It is important to understand what the limiting factors are in such cases, and whether it is possible to mitigate the effects or urbanization by any means other than natural channel phenomenon. A two-dimensional hydrodynamic and sediment transport model is thoroughly described. The model is evaluated and verified, and potential problems and limitations are then discussed. Then a one-dimensional sediment transport and bed variation model is examined and tested using parameter controlled cases. Urbanization increase near rivers and streams reduces the time frame over which certain natural events would have occurred in those channels. The affects of urbanization include but are not limited to changes in streamflow, sediment transport and deposition, channel bank stability, and increased channel widening. The magnitude of these affects will increase over time if careful steps are not taken to minimize the human influence within channels. / text

Downstream adjustment in stream channel morphology is examined in the context of stream channel confluences. Stream channel confluences represent areas of point specific increases in discharge, flow energy and potential erosion in a river system which will in turn affect the post-confluence downstream morphology. Analysis of 12 confluence junctions from southern Ontario streams, constituting 36 channel reaches in total, show an internally consistent hydraulic geometry relationship but with specific controls on channel morphology related to boundary conditions. Predictions of mainstem morphologies is possible using tributary attributes but reach specific channel confinement and material type add significant influence.

Downstream adjustment in stream channel morphology is examined in the context of stream channel confluences. Stream channel confluences represent areas of point specific increases in discharge, flow energy and potential erosion in a river system which will in turn affect the post-confluence downstream morphology. Analysis of 12 confluence junctions from southern Ontario streams, constituting 36 channel reaches in total, show an internally consistent hydraulic geometry relationship but with specific controls on channel morphology related to boundary conditions. Predictions of mainstem morphologies is possible using tributary attributes but reach specific channel confinement and material type add significant influence.

Fluvial channel geometry is controlled by the interaction of a number of geologic and hydraulic variables. The width of mixed alluvial-bedrock channels generally is a function of discharge, with variations due to local conditions. The aspect ratio (width/depth) of channels is heavily influenced by substrate size and erodibility. How channel width and aspect ratio vary as a function of other variables, such as structure, lithology, slope, large scale valley topography, and rock uplift, has not been fully quantified. The New River is ideal for examining these relationships because it shows considerable variability in width and aspect ratio and flows through three structurally and lithologically distinct geologic provinces. Through these provinces, the New River does not follow the expected trends of channel widening with increasing drainage area. Topographic maps show that channel width of the New River has a significant variation that far outscores an overall widening downstream. Aspect ratios for the New River are also large, approaching 500. We collected a field data set of 29 sites of the river's channel geometry, along with characteristics of bedrock, sediment, and confinement. Fifteen of the 29 sites are bedrock reaches. The data set allows empirical analysis of how width and aspect ratio of the New River are related to different variables, including slope, discharge, flow velocity, curvature, trend, bedrock type, and structure. Sediment characteristics and confinement of the channel do not affect channel morphology. Bedrock is shown to affect channel width directly through the percent of bedrock exposed in the channel and indirectly through the modified rock mass strength, rock hardness, obliquity to regional strike, dip orientation, and degree of joint intersection. / Master of Science

This dissertation examines the dynamics of sediment transport and channel morphology in the lower Mississippi River. The area of research includes the portion of the river where reach-averaged downstream flow velocity responds to the boundary condition imposed by the relatively uniform water-surface elevation of the receiving basin. Observational studies provided data that are used to identify channel-bed sediment composition, and measure bed-material sediment flux and the properties of the fluid-flow field over a variety of water-discharge conditions. The analyses demonstrate that a significant portion of the channel bed of the final 165 kilometers of the Mississippi River consists of exposed and eroding underlying relict sedimentary strata that qualify as surrogate bedrock. The exposed bedrock is confined to the channel thalweg, particularly in river-bend segments, and actively mobile bed-material sediments are positioned on subaqueous bars fixed by river planform. The analyses for sediment flux provides insight to the nature of sediment transport: during low- and moderate-water discharge, bed-material movement occurs primarily as minimal bedform flux, and so bed materials are not transferred between alluvial bars. During high-water discharge, bed-material transport increases one-hundred fold, and sands move as a part of both suspended and bedform transport. Physical models are used to show that skin-friction shear stress increases by a factor of ten for the measured water-discharge range. This change is not possible given conditions of uniform water flow, and therefore non-uniform flow in response to the Mississippi River approaching its outlet has a significant impact on the timing and magnitude of sediment flux through the lower river. In order to estimate the dynamics of bed material movement from the uniform to non-uniform segment of the river (lower 800 km), data for channel morphology are used to construct a model that predicts spatial changes in water-flow velocity and bed-material flux over a range of water-discharge conditions. The model demonstrates that non-uniform flow tends to produce a region of net channel-bed aggradation between 200-700 kilometers above the outlet, and a region of channel-bed degradation for the final 200. The implication for these results for the spatial variability of channel morphology and kinematics is explored. / text

Headwater streams provide diverse habitat for aquatic organisms, drinking water for downstream communities and abundant recreational activities. The addition of in-stream wood to headwater channels can influence the hydrology, morphology and ecology of the system. The recruitment of wood to the channel and the export mechanisms determine the wood load and structure types formed in-stream, thus altering the channel’s morphological response. This research examined the effects of in stream wood on channel morphology in two headwater streams along the eastern slopes of the Canadian Rocky Mountains; Lyons East (LE) and Corolla Creek (CC). Lyons East has natural and anthropogenic disturbance (burned and salvage-logged) in the watershed, while Corolla Creek has anthropogenic (grazing and recreation) disturbances in the watershed. An assessment of the longitudinal spatial distribution and a reach-scale geomorphic classification were conducted to investigate the impacts of in-stream wood on channel morphology, pool formation and sediment storage. The spatial distribution of in-stream wood was 1.49 sites/100m for both watersheds, results that are comparable to previously conducted studies in similar geographic watersheds. The types of structures found in both watersheds were predominately jam formations (LE - 43%, CC - 47%), which is consistent with the wood loading and spatial distribution conceptual model previously developed by Whol and Jaeger (2009) for in-stream wood accumulations in mountain streams. At the reach-scale level of analysis, in-stream wood was found to impact channel morphology and pool forming processes. The addition of wood to the stream caused half of the studied reaches to have forced pool-riffle morphology. For all six selected study reaches, there was a decrease in expected pool spacing and an increase in the diversity of pool types. The relationship between wood-affected pools and sediment storage was examined and the results show that more sediment was stored in the burned/salvage logged reaches. Cohesive sediment was stored only in pools influenced by wood structures for half of the studied reaches. V* was generally higher in wood-affected pools for five of the six study reaches. The weighted average (V*w), which provides information regarding the storage of cohesive at the reach scale, was greater in Lyons East than in Corolla Creek. The presence of both exposed bedrock in the channel as well as the amount of vegetation are possible reasons for the smaller amounts of sediment observed in Corolla Creek. The observations from this reach scale investigation led to the development of a conceptual model, which can be used to predict the location of cohesive sediment storage in headwater streams of the Oldman River Basin. This model highlights the relationship between simultaneous recruitment of in-stream wood and sediment from local sources as a mechanism for protecting and storing cohesive sediment deposits. This research examined channel responses to in-stream wood within the context of land-use planning and Alberta’s Water for Life Strategy. There was evidence of lateral channel migration in the floodplain of both watersheds. At some sites, the channel shifted up to 30 metres while in other sections of the watershed, the channel was confined within a narrow valley. Accordingly, it is recommended that the current salvage logging guidelines be changed to include a flexible riparian buffer that would more appropriately reflect the diversity in riparian widths throughout the watersheds. In addition the best management practice is to allow natural in-stream wood processes to evolve and not to remove in-stream wood from the channel. The in-stream wood provides diverse aquatic habitat and the cycle of wood being recruited and being in the stream is part of the natural ecosystem in forested environments.

Many deglaciated watersheds possess complex longitudinal profiles and spatially variable sediment sources derived from the last glaciation. Accordingly, downstream patterns in fluvial forms and characteristics of the channel and floodplain may diverge from conventional ‘graded’ watershed models where channel slope decreases downstream. Within a small, deglaciated watershed, five distinct fluvial forms were identified and it was found that the watershed is organized in a spatially variable, but generally inverted arrangement with stable, low-energy forms dominating the upper watershed and more dynamic, high-energy forms in the lower watershed. As a consequence of this inverted and variable downstream succession, and the spatially erratic organization of glacial sediment sources, downstream trends in channel and floodplain characteristics are poorly defined, and in many cases, deviate from expected trends. This is most true for sedimentological variables where multiple co-dominant controls exist, while morphological and hydrological variables better conform to expected downstream trends.

Many deglaciated watersheds possess complex longitudinal profiles and spatially variable sediment sources derived from the last glaciation. Accordingly, downstream patterns in fluvial forms and characteristics of the channel and floodplain may diverge from conventional ‘graded’ watershed models where channel slope decreases downstream. Within a small, deglaciated watershed, five distinct fluvial forms were identified and it was found that the watershed is organized in a spatially variable, but generally inverted arrangement with stable, low-energy forms dominating the upper watershed and more dynamic, high-energy forms in the lower watershed. As a consequence of this inverted and variable downstream succession, and the spatially erratic organization of glacial sediment sources, downstream trends in channel and floodplain characteristics are poorly defined, and in many cases, deviate from expected trends. This is most true for sedimentological variables where multiple co-dominant controls exist, while morphological and hydrological variables better conform to expected downstream trends.

Headwater streams provide diverse habitat for aquatic organisms, drinking water for downstream communities and abundant recreational activities. The addition of in-stream wood to headwater channels can influence the hydrology, morphology and ecology of the system. The recruitment of wood to the channel and the export mechanisms determine the wood load and structure types formed in-stream, thus altering the channel’s morphological response. This research examined the effects of in stream wood on channel morphology in two headwater streams along the eastern slopes of the Canadian Rocky Mountains; Lyons East (LE) and Corolla Creek (CC). Lyons East has natural and anthropogenic disturbance (burned and salvage-logged) in the watershed, while Corolla Creek has anthropogenic (grazing and recreation) disturbances in the watershed. An assessment of the longitudinal spatial distribution and a reach-scale geomorphic classification were conducted to investigate the impacts of in-stream wood on channel morphology, pool formation and sediment storage. The spatial distribution of in-stream wood was 1.49 sites/100m for both watersheds, results that are comparable to previously conducted studies in similar geographic watersheds. The types of structures found in both watersheds were predominately jam formations (LE - 43%, CC - 47%), which is consistent with the wood loading and spatial distribution conceptual model previously developed by Whol and Jaeger (2009) for in-stream wood accumulations in mountain streams. At the reach-scale level of analysis, in-stream wood was found to impact channel morphology and pool forming processes. The addition of wood to the stream caused half of the studied reaches to have forced pool-riffle morphology. For all six selected study reaches, there was a decrease in expected pool spacing and an increase in the diversity of pool types. The relationship between wood-affected pools and sediment storage was examined and the results show that more sediment was stored in the burned/salvage logged reaches. Cohesive sediment was stored only in pools influenced by wood structures for half of the studied reaches. V* was generally higher in wood-affected pools for five of the six study reaches. The weighted average (V*w), which provides information regarding the storage of cohesive at the reach scale, was greater in Lyons East than in Corolla Creek. The presence of both exposed bedrock in the channel as well as the amount of vegetation are possible reasons for the smaller amounts of sediment observed in Corolla Creek. The observations from this reach scale investigation led to the development of a conceptual model, which can be used to predict the location of cohesive sediment storage in headwater streams of the Oldman River Basin. This model highlights the relationship between simultaneous recruitment of in-stream wood and sediment from local sources as a mechanism for protecting and storing cohesive sediment deposits. This research examined channel responses to in-stream wood within the context of land-use planning and Alberta’s Water for Life Strategy. There was evidence of lateral channel migration in the floodplain of both watersheds. At some sites, the channel shifted up to 30 metres while in other sections of the watershed, the channel was confined within a narrow valley. Accordingly, it is recommended that the current salvage logging guidelines be changed to include a flexible riparian buffer that would more appropriately reflect the diversity in riparian widths throughout the watersheds. In addition the best management practice is to allow natural in-stream wood processes to evolve and not to remove in-stream wood from the channel. The in-stream wood provides diverse aquatic habitat and the cycle of wood being recruited and being in the stream is part of the natural ecosystem in forested environments.

Morphologic change of ephemeral stream cross-sections is a natural component of fluvial geomorphology but disruptions to natural erosion and deposition by anthropogenic disturbances has the potential for cascading impacts down the channel corridor. The proximal impact of a natural gas pipeline construction on ephemeral stream cross-section geometry in southern Arizona was evaluated from July 2014 (pre-construction) to July 2016 (two years post construction). Cross-sections at three locations (upstream the pipeline Right-Of-Way (ROW)), through the middle of the ROW, and downstream of the ROW) were measured using Light Detection And Ranging (LIDAR) and field methods for 16 ephemeral streams. Results of both the LIDAR and field measurements indicated insignificant difference in cross-sectional area change between upstream, across, and downstream-ROW cross-sections [(F 2,64) = 0.341, p = 0.73; (F2,18)= 0.980, p = 0.395]. Sediment generated during pipeline construction appeared to have moved beyond the physical confines of the study site, which limited the assessment of larger-scale geomorphic impacts. Furthermore, the 2014-2016 study period experienced only small (high-recurrence frequency) precipitation events, indicating the absence of large flows capable of significant morphologic change. To further explain differences in cross-section area change between LIDAR datasets, a linear regression model was used to assess the predictive value of nine variables: year of measurement, drainage area, drainage density, basin slope, upstream-, across-, downstream-ROW cross-section locations, percent bare soil in basin, percent mesquite in basin, total precipitation, and number of storms with average precipitation above 25 mm/hour. Though the amount of bare soil in the basin and the second study period (February 2015-July 2016) at least partially explained the changes in cross-section area, the model was not a strong predictor of morphologic change during the 2014-2016 study period. The majority of the variability in cross-sectional area change in the study basins remained unexplained.