Thesis advisor: Noah P. Snyder / Thesis advisor: Gail C. Kineke / Maine coastal rivers host the last remaining runs of endangered anadromous Atlantic salmon in the United States, whose populations have decline from ~500,000 returning adults in the 1880s to only ~1000 in 2000. Restoration projects have focused on these coastal river systems to bring natural populations back to the area, and recent efforts involve adding large woody debris (LWD) to small tributaries to improve salmon rearing habitat. Large woody debris actively changes the hydraulics and geomorphology of small streams by acting as a barrier to flow and creating decreased velocity zones, scour pools, and sediment storage and sorting. I study the effects of LWD additions in early August 2008 on hydraulics and substrate in Baker Brook, a west-flowing tributary of the Narraguagus River. Hydraulically, I focus on the treatment reach nearest the confluence with the Narraguagus River (Baker1), and I also study changes in substrate in Baker1 and the upstream treatment location (Baker3). Both study locations are divided into two reaches, treatment (Baker1-T and Baker3-T) and control (Baker1-C and Baker3-C). In Baker1, the treatment and control reaches are further divided into four 50 m sub-reaches based on channel gradient (~1% in Baker1-C-Flat and Baker1-T-Flat; >2% in Baker1-C-Steep and Baker1-T-Steep). In Baker3, we use two 50 m sub-reaches of similar gradient (ranges from ~1% to 2%) to determine substrate changes. Significant post-LWD addition changes are determined by comparison with the control sub-reaches. Changes in the treatment sub-reaches must be larger than those in the control sub-reaches to be deemed significant. I seek to answer three research questions: (1) how much does mean velocity through the study sub-reaches change as a result of additions; (2) how much does hydraulic roughness change; and (3) does sediment storage and spatial sorting result from the LWD additions? I measured reach-average velocities (Ureach) in Baker1 using the salt dilution method in May, July and August 2008 and May 2009. I use rating curves to compare the post-treatment to the pre-treatment Ureach-stage relationship. A temporary decrease in Ureach occurred in October 2008 in Baker1-T-Flat, whereas the other sub-reaches experienced no change in Ureach. A localized change in cross-sectionally averaged velocity (U) measured with a flow meter, is also evident at Baker1-T-Flat, but this is because an added tree lies directly in the downstream cross-section where measurements are recorded. I assessed channel roughness changes by comparing roughness rating curves created using the Manning roughness parameter, n (back-calculated from velocity measurements) for each sub-reach. Because of the short-term decrease in Ureach, roughness increased in Baker1-T-Flat in October 2008 as well. No change in roughness is evident in the other sub-reaches because post-treatment values of n plot on the same decreasing trend with respect to stage as pre-treatment values. I quantified pre- and post-treatment sub-reach substrate median grain size (D50) with intensive clast counts in July 2008 and May 2009. In Baker1, analysis of pre-treatment substrate size show that the flat sub-reaches have a finer substrate size (34-38 mm) than the steep sub-reaches (88-134 mm). Baker3 pre-treatment grain size is similar to that of the flat Baker1 sub-reaches, with a median grain size of 38 mm in Baker3-T and 28 mm in Baker3-C. Two of the three treatment sub-reaches exhibited significant fining (D50 decreased by 37-54%) between the surveys, and the third changed less than measurement uncertainty. One of the three control sub-reaches coarsened significantly (D50 increased by 29%), one fined significantly (-42%), and one coarsened less than measurement uncertainty. In summary, I find that LWD additions in Baker Brook had little effect on reach-scale hydraulics during the flows we observed, but did influence bed-grain size during the 10-month study interval, underscoring the importance of floods on channel change. / Thesis (MS) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

The extreme flooding event that occurred in 2013 in Alberta, Canada was at time the most costly natural hazard event in the nation’s history with damages exceeding $5 billion. Due to this event, an increased effort for flood mitigation strategies began and resulted in the proposal of the Springbank Off-Stream Storage Reservoir to divert and detain Elbow River flow upstream of the City of Calgary. In order to validate the design of the flow diversion structures, a large (1:16) scale physical model was constructed. The model tested among other things, the impact of large woody debris (LWD) on the flow diversion structures. The LWD modelling included a comparison of LWD manufactured from smooth cylindrical dowels versus natural tree limbs of the same dimensions. The results from the physical model led to a series of design changes for the diversion structures that likely would not have been identified without physical modelling. The LWD material comparison demonstrated significantly different behaviours between LWD types. Specifically, LWD manufactured from natural tree limbs was significantly more likely to accumulate in debris dams on the diversion structures. The impact of root wad was also investigated and proved to play a major role in the damming characteristics and blocking probability of debris. Following the physical model investigations, a numerical simulation was completed in order to examine further the hydrodynamic results obtained from the Springbank project. Using TELEMAC MASCARET’s open source free surface flow program TELEMAC 2D, a two dimensional simulation was completed using data from the physical model. Flowrates and velocities from both models were compared and discrepancies between the two are identified. Reasoning for these differences as well as future works for the numerical model are presented.

Classical approaches to evaluate the stability of large woody debris (LWD) introduced in streams for habitat restoration or flood management purposes are usually based on inappropriate assumptions and hydraulic equations. Results suggest that the physics of small cylindrical elements located in large channels cannot be transferred to the case of a large roughness elements placed in small channels. The introduction of LWD in a small channel can generate a significant modification of the upstream hydraulic conditions. This modification has direct implications on the stability of the LWD. Experiments were performed in a controlled environment: a small stream section was represented by a low roughness rectangular flume and LWD were modeled with smooth PVC cylinders. Direct force measurements were performed with a load cell and results were used to identify an equation that evaluates the drag force acting on a large cylindrical element place in a rectangular channel. This equation does not depend on a drag coefficient. Water depths were also measured during the experiments and results were used to develop an approach that evaluates the upstream hydraulic impacts of a large cylinder introduced in a rectangular channel. The effect of the variation of the unit discharge (discharge per unit of width), cylinder size, cylinder elevation from the channel bed, and downstream hydraulic conditions, could be related to the upstream hydraulic conditions with relative success. Dimensionless parameters were developed to increase the versatility of the approach. The application of this approach to field cases is expected to require adjustments, mainly because of the roughness of natural environments differs from the smoothness of the controlled environment described in this work.

This thesis explores the geomorphic implications of large woody debris (LWD) residing in the backshore of beach-dune systems along the northeastern coasts of Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada. Detailed topographic surveys were employed to quantify seasonal mass balance of the beach-dune systems along two distinctly different coastlines. Erosion and accretion potential models were applied to characterize sediment transport conditions. Holman’s (1986) R2% wave runup model was superimposed on total water levels, to model wave runup exceedence of the beach-dune junction elevation (6.5 m aCD). Modelled ‘erosion potential’ hours were demonstrated to correspond with observed erosion including removal of the LWD zone, resulting in decreased mass balance. Similarly, Fryberger and Dean’s (1979) Drift Potential model was used to model accretion potential hours. Modelled accretion potential hours were also able to effectively describe conditions when actual accretion occurred. The presence of LWD in the backshore offered two functions to the above processes: it acted effectively as an ‘accretion anchor’, promoting increased mass balance and rebuilding of the incipient foredune; and, it offered a mass of sediment fronting the foredune to protect the beach-dune system from storm wave attack and subsequent erosion.

Classical approaches to evaluate the stability of large woody debris (LWD) introduced in streams for habitat restoration or flood management purposes are usually based on inappropriate assumptions and hydraulic equations. Results suggest that the physics of small cylindrical elements located in large channels cannot be transferred to the case of a large roughness elements placed in small channels. The introduction of LWD in a small channel can generate a significant modification of the upstream hydraulic conditions. This modification has direct implications on the stability of the LWD. Experiments were performed in a controlled environment: a small stream section was represented by a low roughness rectangular flume and LWD were modeled with smooth PVC cylinders. Direct force measurements were performed with a load cell and results were used to identify an equation that evaluates the drag force acting on a large cylindrical element place in a rectangular channel. This equation does not depend on a drag coefficient. Water depths were also measured during the experiments and results were used to develop an approach that evaluates the upstream hydraulic impacts of a large cylinder introduced in a rectangular channel. The effect of the variation of the unit discharge (discharge per unit of width), cylinder size, cylinder elevation from the channel bed, and downstream hydraulic conditions, could be related to the upstream hydraulic conditions with relative success. Dimensionless parameters were developed to increase the versatility of the approach. The application of this approach to field cases is expected to require adjustments, mainly because of the roughness of natural environments differs from the smoothness of the controlled environment described in this work.

Classical approaches to evaluate the stability of large woody debris (LWD) introduced in streams for habitat restoration or flood management purposes are usually based on inappropriate assumptions and hydraulic equations. Results suggest that the physics of small cylindrical elements located in large channels cannot be transferred to the case of a large roughness elements placed in small channels. The introduction of LWD in a small channel can generate a significant modification of the upstream hydraulic conditions. This modification has direct implications on the stability of the LWD. Experiments were performed in a controlled environment: a small stream section was represented by a low roughness rectangular flume and LWD were modeled with smooth PVC cylinders. Direct force measurements were performed with a load cell and results were used to identify an equation that evaluates the drag force acting on a large cylindrical element place in a rectangular channel. This equation does not depend on a drag coefficient. Water depths were also measured during the experiments and results were used to develop an approach that evaluates the upstream hydraulic impacts of a large cylinder introduced in a rectangular channel. The effect of the variation of the unit discharge (discharge per unit of width), cylinder size, cylinder elevation from the channel bed, and downstream hydraulic conditions, could be related to the upstream hydraulic conditions with relative success. Dimensionless parameters were developed to increase the versatility of the approach. The application of this approach to field cases is expected to require adjustments, mainly because of the roughness of natural environments differs from the smoothness of the controlled environment described in this work. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Five hundred eighty red alder along a 2.16 km portion of the Little Creek riparian zone were assessed for mortality following the 2009 Lockheed Fire near Davenport, California. The study area was divided into burn severity zones and every red alder within the riparian zone was observed and assessed for mortality. Height, diameter at breast height (DBH), and age were collected on selected trees. An estimation of red alder large woody debris (LWD) input to Little Creek since a 2010 LWD survey (Smith, 2010) was calculated using average red alder tree dimensions applied to Smalian’s formula (MLNRO, 2011). The mean proportion of dead red alder in the non-burn zone and burn-zone was .11 and .45 respectively. Volume of red alder LWD in Little Creek is estimated to have increased approximately 245% since the fire. Given other factors may have played a role in red alder mortality in Little Creek, the analysis reported here supports fire also contributed to accelerated mortality of red alder established following the catastrophic debris torrent in 1955 in Little Creek. This study provides useful information regarding fire and red alder and establishes baseline conditions of the Little Creek riparian zone following the 2009 Lockheed Fire.

Those who frequent the coastline may be accustomed to seeing driftwood washed onshore, some of it having seemingly found a home there for many years, others having been freshly deposited during the last set of storms; However, if a passerby were to take a closer look at the driftwood on the coastline, they may notice that some of these logs – also known as Large Woody Debris (LWD) – are anchored in place, a practice which is generally used for the purpose of stabilizing the shoreline or reducing wave-induced flooding. Records of existing anchored LWD project sites date back to 1997 and anecdotal evidence suggests that the technique has been used since the mid-1900’s in coastal British Columbia (BC), Canada, and Washington State, USA. Now, with an increased demand for natural and nature-based solutions, the technique is again gaining popularity. Despite this, the design of anchored LWD has largely been based on anecdotal observations and experience, as well as a continuity of design practices from the river engineering field. To date, there is no known peer-reviewed literature on the design or efficacy of LWD protection systems in a coastal environment. In 2019, the “Efficacy and Design of Coastal Protection using Large Woody Debris” research project was initiated to determine if LWD are effective at stabilizing the shoreline under wave action, if they are effective at reducing wave run-up, and if they are durable enough to meet engineering requirements for shore protection. In addition, the project aimed to determine the optimum configuration of LWD for design purposes. To meet these objectives, this study included the following work: (1) field studies of existing LWD installations, (2) experimental modeling of beach morphology with and without LWD structures, (3) experimental modeling of wave run-up with and without LWD structures, and (4) development of preliminary design guidance. The first phase of the project included field investigations at 15 existing anchored LWD sites in coastal BC and Washington State. Site characteristics, design techniques, and durability indicators were examined and correlated to a new design life parameter: ‘Effective Life’. Six primary installation techniques were observed: Single, Multiple, Benched, Stacked, Matrix, and Groyne. Observed durability and/or performance issues included: missing LWD, erosion, arson, wood decay, and anchor corrosion/damage. The Effective Life of anchored LWD was found to be strongly correlated to the tidal range and the upper beach slope for all installation types, and the LWD placement elevation relative to the beach crest elevation for single, shore-parallel structures. The many noted durability issues and ineffectiveness as mitigating erosion indicates that existing design methods for anchored LWD have not generally been effective at providing coastal protection and meeting engineering design life requirements. A comprehensive set of over 60 experimental tests were completed as part of the overall research program. Thirty-two (32) tests were analyzed as part of this study relating to the morphological response of a gravel beach with and without various LWD configurations. The tests were conducted within a wave flume at the National Research Council’s Ocean, Coastal and River Engineering Research Centre (NRC-OCRE), at a large scale (5:1) based on site characteristics and LWD design characteristics made during the previous field investigations. Tests were also conducted to assess experiment repeatability, sensitivity to test duration, sensitivity to wave height, wave period, and relative water level, influence of regular waves, and influence of log roughness. The position of the most seaward LWD (whether considering distance or elevation) was found to be strongly linked to morphological response. A theoretical relationship was developed between LWD elevation and sediment volume change. Configurations which included LWD placement below the still water level, such as the Benched configuration, were found to be most effective at stabilizing the beach profile. As part of the experimental modeling program, 24 tests were also conducted for the purpose of estimating the effect of LWD design configuration on wave run-up. In total, six different beach and LWD configurations were tested under a base set of four regular wave conditions. The study findings indicated that anchored LWD may increase wave run-up relative to a gravel beach with no structures. In particular, configurations with more logs tended to result in higher wave run-up. However, additional research is needed on the effect of LWD on wave run-up to confirm and expand these findings. There are a number of potential engineering, ecological, social, and economic benefits associated with anchored LWD installations if designed, installed, and monitored appropriately for the site conditions and user needs. To realize these potential benefits, significant additional research is needed on the topic. One of the most significant barriers to usage is a lack of information on how to effectively anchor LWD structures. However, this research project provides a baseline for future comprehensive studies on the effect and design of coastal protection using LWD. The project provides preliminary design considerations for the usage of LWD as coastal protection and contributes to the growing body of literature on nature-based solutions.

The forestry is the main use of forests in Sweden which results in a number of positive aspects but also a number of negative effects on our nature. Aquatic ecosystems are specifically exposed to land use by the forest industry. The problem areas that arise are mainly discharge of nutrients, mercury, change in hydromorphology and local environment, sludge transport, absence of dead wood in streams and altered solar radiation. In order to reduce negative impact and protect natural populations of species but also to protect important ecosystems, there are a number of national prospective objectives and laws. From the year 2014, a number of prospective aims have been introduced to get a common view of the problem factors, but also to get a common representation of how the forestry measures should be carried out.  This work evaluated the width of the riparian buffer zone left along the 138 streams at final clearcutting in the Vindelälven catchment, comparing three periods: period 1 (year 2001-2007), period 2 (year 2008-2013) and period 3 (year 2014-2018).  The work also included a count of the number of dead wood objects that occur in 16 of the 138 streams in the study area. The method of the study is based on remote sensing using ArcGIS software, along with a field inventory to verify the remote sensing with reality. The results found from the study were that a significant increase in average minimum-width was shown between periods 1 and 3 (ANOVA, n = 138, df = 2, F = 5.083 and p = 0.007). The results from the average width were not significantly different but suggest a positive correlation between lower age of final clearcutting and the average width of the riparian zone. The density of dead wood in the streams of the study site did not give any significant differences or correlations depending on time period. What could be explained from the result was that the presence of beaver (Castor fiber) positively affected the amount of dead wood. To conclude, positive effects of the introduction of new objectives for riparian buffer zone management were indicated.  This is a sign that the forestry industry is moving towards implementing more sustainable methods. In addition, a method based on remote sensing for measuring riparian buffer zone widths was found to provide reliable estimates in the Vindelälven catchment, Västerbotten County. / Grip on Life IP

Coastal foredune evolution involves complex processes and controls. Although a great deal is known about the effects of vegetation cover, moisture, and fetch distance on sediment supply, and of topographic forcing on airflow dynamics, the role of large woody debris (LWD) as a modulator of sediment supply and a control on foredune growth is understudied. Large assemblages of LWD are common on beaches near forested watersheds and collectively have a degree of porosity that increases aerodynamic roughness and provides substantial sand trapping volume. To date, no research has attempted to understand the geomorphic role that LWD matrices, as a whole, have as roughness elements affecting airflow and sediment transport across a beach-dune system, or, what the long-term implications of these impacts are on beach and foredune erosion recovery and evolution. This four-year research initiative investigated the role of a LWD matrix on beach-dune morphodynamics on West Beach, Calvert Island on the central coast of British Columbia, Canada. This study integrated data from research that spanned three temporal scales, 1) event-scale (10 min) flow and sediment transport patterns, 2) daily frequency and relative magnitude of landscape changing events, 3) seasonal to interannual-scale volumetric and LWD changes. An event-scale experiment to characterise airflow dynamics and related sand transport patterns showed that LWD distinctly alters wind flow patterns and turbulence levels from that of incoming flow over a flat beach. Overall, mean wind speed and fluctuating flow properties declined as wind transitioned across the LWD. Streamwise mean energy was converted to turbulent energy, however, the reductions in mean flow properties were too great for the increased streamwise turbulence to have an effect on transport. In response to these flow alterations and more limited sand transport pathways to the foredune, sediment flux was reduced by 99% in the LWD compared to the open beach, thereby reducing sand supply to the foredune. Sand grains rebounding off of the LWD were carried higher into the flow field resulting in greater mass flux recorded at 20-50 cm in the LWD as opposed to the flat beach. This effect was only recorded 6 m into the LWD. As such, LWD has the potential to modulate rates of foredune recovery, growth, and evolution. Time-lapse photography collected at 15 min intervals during the study revealed that storm events lead to wave-induced erosion of the backshore and reworking of the LWD matrix. The exposed LWD matrix subsequently traps aeolian sediment that leads to rapid burial of the LWD and building of a raised platform for emergent vegetation. However, infilling of the accommodation space within the LWD matrix is so rapid, that sediment starvation of the foredune is short-lived. While the LWD at this site does trap sediment in the backshore, helping to protect the dune from scarping, LWD at this study site maintains an overall lower impact on transport to the foredune. Critical to this relationship is the frequency and magnitude of nearshore events that erode the beach periodically and re-organize the LWD matrix, which directly impacts the ability of LWD to store sediment and modulate transport to the foredune. A conceptual model exploring these relationships is presented. / Graduate