Civil and Environmental Engineering

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This is the collection for the University of Waterloo's Department of Civil and Environmental Engineering.

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

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Now showing 1 - 6 of 6

Assessing The Erodibility of Cohesive Media in Southwestern Ontario With In-Situ Mini-JET Methodology
(University of Waterloo, 2023-09-25) Jefferies, Caleb; Annable, William
Despite research indicating that the resistance of cohesive sediments to fluvial erosion is related to the geologic media, regulators and industry in Southern Ontario do not typically consider the diversity in geologic landscapes when assessing the erosion potential of streams with cohesive boundaries. The development of the mini-Jet Erosion Test (JET) methodology has facilitated in-situ data collection of the resistance of cohesive media to erosion, however, it has not been widely applied in Ontario and there remain knowledge gaps in the interpretation of the test results. This research collected a miniJET dataset of 245 in-situ tests spanning 13 sites and 10 distinct geologic units. To address the gradient of weathered material within JET scour holes, a method of test segmentation is proposed where each JET is separated into a segment representing a surficial (weathered) layer and an underlying (unweathered) layer. This method of analysis results in three output parameters per JET; the depth of the first segment, a critical shear stress and an erodibility coefficient. To estimate the critical shear stress and erodibility parameters the JET dataset is analyzed using three methods of JET solution techniques (Scour Depth Method (SD), Blaisdell Method (BM), and Linear Regression Method (LR)) and the sensitivity of these solution techniques to JET duration and measurement frequency is assessed. It is demonstrated that BM is the most sensitive to test duration and LR is the most sensitive to measurement frequency. The estimation of critical shear stress is robust to JET duration and measurement frequency on a site scale, however, the estimation of the erodibility coefficient can be skewed on a site scale when JETs longer than 120 minutes are compared to tests shorter than 60 minutes. Using the depth of the first segment as a surrogate for the presence of weathered material, subaerial tests are shown to have a higher presence of weathered material compared to submerged tests, and tests higher on banks have a greater presence of weathered material compared to tests lower on banks or along the streambed. No differences in the presence of weathered material are detected between geologic units. SD and LR have close agreement on the estimates of critical shear stress imparting greater confidence in its representativeness, but they diverge substantially on estimates of the erodibility coefficient inserting uncertainty into the representativeness of that parameter. Halton Till is shown to have a statistically lower mean critical shear stress compared to the grouped results of all the geologic units investigated, however, the difference in mean of 2.8 Pa may have limited implications given the range in critical shear stress at individual sites. Comparing tests from summer and early spring at the same site indicates that seasonal processes significantly increase the presence of the surficial weathered layer but do not influence the critical shear stress of the underlying unweathered material. The higher availability of readily erodible weathered material corresponding to seasonal freshet flows suggests that late winter/early spring may be responsible for an outsized amount of erosion in streams with cohesive boundaries, particularly in headwater systems with shorter, more frequent hydrographs. This suggests that regulators and industry should place higher importance on considering how modifications to watersheds alter the frequency of detrition and regeneration of the surficial weathered material. Future research should focus on relating the importance of weathering processes on fluvial erosion rates in cohesive soils to watershed size, land use, and stormwater management techniques.
The effects of vegetation on the estimation of low flows: a high-resolution study in natural streams featuring novel techniques
(University of Waterloo, 2018-07-12) Brignoli, Lorenzo; Annable, William
Accurate measurement of stream discharge under low-flow conditions is of utmost importance to many water resources practitioners. In most of the world, discharge is estimated at gauging stations using rating curves. These relate observed water level to field measured discharge, under the assumption that a direct proportionality exists between the two. However, if seasonal aquatic vegetation growth occurs, water levels (or stages) will rise as macrophytes increase flow resistance. Consequently, if this effect is not accounted for, the increase in water levels may be mistaken as an increase in discharge. Current methods to correct these errors in flow calculations can be time-consuming and do not always perform consistently, as they rely on sporadic discharge measurements and qualitative observations. As such, it is not uncommon for flow records to be discontinued during the summer, a period often coinciding with the low flow season in many climatic regions. During these months, incorrectly estimated flow values, or lack of flow records can have problematic consequences. For instance, reliable flow estimations are required to provide adequate water apportionments between parties, while avoiding water scarcity issues in downstream communities. Furthermore, the assessment of ecological low flow requirements for fish and benthic communities often depends on available flow records. As such, methods to aid in the estimation of flow records are warranted, especially at a time when climate change is being proven to exacerbate the severity of low flow extremes. There has been extensive research regarding the general relationship between aquatic vegetation and flow resistance. However, a lack of standardization has resulted in different methods of data collection and results, thus preventing universal comparison and the achievement of conclusive results. Consequently, reliable methods of quantifying vegetative flow resistance have not been established. This thesis is aimed at obtaining a thorough understanding of the effects of vegetation on flow resistance and using this knowledge to provide reliable methods to estimate low flow rates at gauging stations during the macrophytes growing season. To achieve this, it was paramount that the methods developed were capable of assessing vegetative flow resistance reliably and consistently. This was done by thoroughly quantifying the parameters often found proportional to channel roughness, such as plants stiffness and density, while flow and water level conditions were continuously monitored. A simple image processing technique was developed to map aquatic plants at the reach scale by analyzing aerial photogrammetry data, obtained using an Unmanned Aerial Vehicle (UAV). The data collection and processing methods presented are simple, reproducible, and allow for the high-resolution mapping of aquatic plants in a time-efficient manner. Results showed that the algorithm presented here consistently out-performed conventional manual post-processing techniques and in-stream surveys. Post-processed data were also used to estimate how ground data resolution affects the accuracy of flow resistance formulae, which in turn was used to assess the sensitivity of discharge estimates on vegetation mapping. A simple and cost-effective test, and associated testing apparatus, were developed to measure plants biomechanical properties (stiffness and density). Different than most methods found in literature, the test is not disruptive and can be undertaken on both submerged and emergent vegetation. It was first calibrated with artificial vegetation, of known biomechanical properties, and then tested on natural plants. Results showed that plants biomechanics evolve temporally following the growth and decay cycle of macrophytes. Therefore, these findings have useful implications for understanding seasonal changes in vegetative flow resistance which can impair rating curves during the low flow season. To gain a thorough insight on how vegetation can affect stage-discharge relationships, a three-year investigation was undertaken at two separate reaches (~100 m in length) located on a Southern Ontario stream. Here, it was determined that using conventional rating curves, average daily discharge can be overestimated up to 100%. Published equations to determine flow resistance were not capable of correcting these estimates. Different to most published studies, flow resistance was not found proportional to the average spatial density of vegetation, rather it was correlated to the distribution of macrophytes in the most densely vegetated parts of the reach. By characterizing the spatial distribution of vegetation, it was then possible to successfully correct flow estimates at the study reaches for the period of record affected by macrophyte growth. The developed correction procedure was also validated on three additional streams, with successful results. Therefore, these findings can be applied to other gauged sites affected by aquatic plant growth to provide accurate low flow records. Results from this thesis were obtained through a large dataset, both in terms of temporal and spatial resolution, and significantly expand previous findings regarding vegetative flow resistance. The methods presented herein can be readily applied to correct rating curves affected by vegetation growth in a time and cost-efficient manner. This can improve the estimation of environmental flows to aid in important water management decisions, such as water allocations for agricultural or potable water use. Further, more accurate aquatic habitat sustainability assessments can be achieved by using improved flow records. In turn, as these would reflect actual low flow conditions, they can be used to develop appropriate water taking targets that will not impact the environment negatively.
High Resolution Investigation of Thermal Spatial Variability of Two Cobble Bed Rivers, and the Correlation to Salmonid Spawning Preferences
(University of Waterloo, 2016-01-22) McCutcheon, Cailey; Annable, William
This thesis introduces and demonstrates the application of a recently designed mobile streambed temperature measurement system. The apparatus, called the High Resolution Temperature Mapping Device (henceforth HI-RES TMD) was built to increase the resolution of established temperature sampling methods and instantaneously acquire 32 equally distributed temperature measurements within 3 m2 (0.3 m grid spacing) at the streambed interface. Sampling is done under wadable flow conditions, and can be completed every 4-5 minutes. This allows sampling of any spatial extent such as full morphological units or the reach scale within hours or days respectively. The HI-RES TMD is able to overcome many of the short comings of previous sampling methods such as the range of investigation of a given study, or require the insertion of temperature probes into the substrate which considerably increased sampling time. The HI-RES TMD has been field tested in two mountain streams located along the western slope of the Rocky Mountains, in southeastern British Columbia, Canada to examine temporal repeatability of thermal streambed patterns. A dataset of more than 80,000 individual streambed temperature measurements was obtained using the HI-RES TMD. A series of analysis were then completed to determine whether the spatial variability of streambed temperature plays a role in the choice of spawning locations for fish. Both rivers are characterized by intense spawning of two salmonid species: cutthroat trout (oncorhynchus clarkia) and bull trout (salvelinus confluentus). This was confirmed during three consecutive seasons of spawning site surveys completed between 2012 and 2014 with the help of expert fisheries biologists at which time the precise locations of all the spawning locations (i.e., redds) within the study areas were surveyed. Analysis of streambed temperature patterns on the morphological features presented correlations between the average thermal distributions and spawning density and repeatability. Spatial autocorrelation analysis was completed to identify hot spots and cold spots within the study areas. It was found that bull trout redd density and repeatability were significantly correlated to the cold spots. As presence of colder areas on the streambed may be related to hyporheic flow or groundwater emergence, recommendations for improvements of the HI-RES TMD present an opportunity to determine if the bull trout redds are also correlated to groundwater emergence.
How Large Immobile Particles Impact Sediment Transport and Bed Morphology in Gravel Bed Rivers
(University of Waterloo, 2019-05-29) McKie, Christopher; Annable, William
Large particles can be deposited in natural stream channels as a result of failed erosion protection measures or geological deposits. The impacts these large particles have on the natural systems have been studied, however the previous literature that has been completed either has a very narrow scope applicable only to alpine rivers or are simpliﬁed and do not fully capture the processes that occur in a natural channel system. Additionally, the results often contradict each other, and give an unclear understanding of the eﬀects these large particles have on bed morphology and sediment transport. This thesis utilizes a laboratory experiment to evaluate the eﬀects that varying densities of large immobile particles in a gravel-bed channel have on sediment transport and bed morphology. The objective of this study is to gain further understanding and to consolidate existing literature to provide a more holistic overview of the eﬀects of these large particles on a channel bed. It was expected that large immobile particles would cause an increase in channel roughness, and that the impacts to sediment transport and bed morphology would reﬂect this. The laboratory experiment consisted of 5 test cases with varying densities of large immobile particles, and one base case with no large particles present. In each case, the ﬂume bed was composed of a poorly sorted gravel mixture with a bi-modal distribution of sand and gravel meant to be representative of a natural gravel-bed channel. The large particles were sized to be representative of common engineering principles by applying a factor of safety to a minimum stable particle size. Each experimental case consisted of a single hydrograph with continuous sediment input scaled to the ﬂow rate. The results of the test cases and the base case proved that relating the large particle density to an increase in channel roughness was too simplistic to explain the trends found within this study. At low densities of large immobile particles, the transported material and the bed material both became coarser. At medium densities of large immobile particles, the bed material size and erosion reached a maximum, and the system also approached equal mobility. Finally, at high densities of large immobile particles, the size of transported material and bed material sizes were similar to that of the base case, and the sediment transport also had the strongest clockwise hysteresis trend. These results indicate the diﬃcult of relating large immobile particle density to channel roughness to explain the eﬀects on sediment transport and bed morphology. In an eﬀort to provide a more holistic explanation, and to consolidate the existing lit- erature, a more complex explanation was developed using the ﬁndings of previous research and relating it to the results found within this study. This complex model is made up of 3 main points: 1. Isolated large immobile particles create localized areas of increased erosive forces, and localized protected areas (Brayshaw et al., 1983). 2. At a narrow range of large immobile particle spacings, ﬂow structures build upon each other and amplify their erosive forces (Tan and Curran, 2012). 3. Densely spaced large immobile particles causes high energy skimming ﬂow that is able to create powerful eddies in gaps between the large particles (Hassan and Reid, 1990). This complex model explains the trends and results found within this study. Addi- tionally, the results of this research were used to form the framework for predicting or understanding the impacts to a natural channel system caused by the introduction of large immobile material. Finally, the results of this study can be used to further research and develop design criteria for engineered in-channel structures to remedy imbalanced channel processes.
Impacts of Hydromodification and Sediment Supply Alterations on Bedload Transport and Bed Morphology in Urbanizing Gravel-bed Rivers
(University of Waterloo, 2017-08-18) Plumb, Benjamin; Annable, William
Urbanization is known to change the hydrologic and sediment supply regimes of rivers, causing more frequent, flashier flood events (hydromodification) and a reduction and redistribution of sediment sources. Presently, the impact that these changes have on bedload transport in gravel-bed channels and the resulting impact on bed morphology remains largely unknown due to a lack of process based studies. A better understanding of how riverbed form and processes evolve with urbanization is critical as they are a primary factor in controlling stream stability, providing habitat for aquatic species and influencing flood elevations. Additionally, stream rehabilitation is becoming increasingly common in urban rivers and an understanding of how sediment transport dynamics change with the alterations common to urbanization is critical for a successful design. This thesis explores the impact of urbanization, which is the combination of hydromodification and alterations to sediment supply, on the morphodynamics (linkages between channel form and process) of bedforms in gravel-bed rivers. Specific objectives are: 1) to determine if detectable differences in bed morphology exist between rural and urban rivers in the same hydrophysiographic region; 2) to characterize the sediment transport dynamics of a highly urbanized channel; 3) to investigate the differences in geomorphically significant flows and sediment transport characteristics for different levels of watershed urbanization; and 4) to generalize field specific results using a mobile-bed laboratory flume to investigate the sediment transport characteristics for different levels of watershed hydromodification. Longitudinal profiles of 11 rural and 9 urban watercourses with pool-riffle dominated morphologies in the same hydrophysiographic region (Southern Ontario, Canada) were investigated using three objective bedform identification methods; zero-crossing analysis, bedform differencing technique and residual pool depth analysis, as well as visual field identification. Results indicate that urban rivers possess deeper pools and a more topographically variable bed. A field investigation was undertaken to characterize event-based sediment transport dynamics of a highly urbanized gravel-bed river over a three year period. Mimico Creek, located in Toronto, Ontario, Canada, is nearly fully urbanized and lacks significant stormwater management controls, therefore making it a representative study reach. Bedload transport was measured using both active and passive sampling methods to characterize the mobility and transport dynamics of the entire range of surface particles. During this time, over 10 floods were sampled ranging from the approximate threshold discharge to well over the bankfull discharge. Coarse particle mobility differed from that previously reported in literature for rivers with more natural flow regimes. A strong link was found between coarse particle mobility and the transport dynamics of finer material which tends to dominate the bedload. The measured bedload transport data were also used to calibrate a fractional sediment transport model which was combined with hydrometric data corresponding to different levels of watershed urbanization to perform a geomorphic work analysis. Urbanization is increasing the frequency, volume and time of competent discharge events (capable of performing work on the channel). Greater increases of intermediate discharge events were observed. Less urban streams are more influenced by larger discharge events, while urbanization is shifting the geomorphic significance to lower (but still competent) discharges. Inspired from the field observations, an unsteady flow laboratory experiment was conducted to provide more generalized results. Three land-use scenarios representing different levels of watershed urbanization were developed from measured hydrometric data. Results show that both unsteady bedload transport dynamics and resulting bed morphology change with different levels of urbanization. Shorter duration hydrographs (corresponding to urban conditions) possess higher transport rates, less pronounced bedload hysteresis loops and more topographic variability of the bed. A proposed parameter for evaluating the degree of hysteresis shows sediment transport is closely linked with falling limb dynamics. The key conclusion from the field, modeling and laboratory studies is that bedforms in gravel-bed rivers appear to be evolving to a state with more topographic variability. This variability is hypothesized to be additional form roughness to dissipate energy introduced due to hydromodification. These results are unique in literature and further our understanding of urban river processes.
Thresholds and Sediment Transport Dynamics in an Interbedded Shale and Limestone Controlled Urban Watercourse
(University of Waterloo, 2017-02-13) Hivonen, Jeffrey; Annable, William
Sediment transport is a fundamental component of research into river morphology and related engineering practices. The relationship between flow and sediment particle entrainment underpins many of the empirical models used to estimate sediment transport dynamics. The scientific literature reports a research gap specific to the thresholds of mobility of different sized particles in non-gravel bed systems, including those in bedrock channels. Particle tracer technology was used to study coarse sediment entrainment and transport dynamics in an urban, bedrock controlled stream channel in Toronto, Ontario, Canada. Passive integrated transponders were inserted in constrained and unconstrained particles within an incised reach of stream. The distribution of particles transport distances conformed to a two-parameter gamma distribution model, which assumes integrations of the travelled series of steps and rests. Size selective dependency of path length was found to increase for coarser clasts, as compared to observed conditions for gravel-bed systems. Coarser particles were also found to transport in an unconstrained mode, as compared to finer grains. A force exceedance model was applied to further test the performance of reported size selective transport relationships for the study site. Many particles were found to transport at critical shear ratios less than 1, when assuming a modified Shields’s based model for entrainment. Field data was then used to determine a reference shear based on the smallest magnitude competent storm. The results show that, when compared to alluvial gravel-bed conditions, finer particles require larger thresholds to mobilize and the inverse is true for coarser particles. Using the reference shear conditions, rates of sediment transport were calculated and compared to common models for coarse particle transport. The results confirm size selectivity by grain class and indicate differentiations between fine and coarse transport relationships for the site. This research confirms non-conformity of particle entrainment and transport relationships for the study site, when compared to common empirical model for gravel-bed rivers. The results may be used to obtain critical entrainment parameters and sediment transport relationships, which can then be used to inform design criteria for regional watercourses having like lithology and morphology.

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