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• 1. [Article] Effects of Spatially Distributed Stream Power on Check Dam Function in Small Upland Watersheds: A Case Study of the Upper Laja Watershed, Guanajuato, Mexico

  Watershed restoration comes in a variety of forms depending on which set of problems are sought to be remedied. Severe soil erosion, in the form of gullying and/or headcutting, can be mitigated through ...

  Citation × Citation Citation Abstract Copy Title: Effects of Spatially Distributed Stream Power on Check Dam Function in Small Upland Watersheds: A Case Study of the Upper Laja Watershed, Guanajuato, Mexico Author: Herzfeld, Zachary Andrew Year: 2017 Watershed restoration comes in a variety of forms depending on which set of problems are sought to be remedied. Severe soil erosion, in the form of gullying and/or headcutting, can be mitigated through constructing check dams in well-selected locations. This practice has been used throughout the upland subwatersheds within the Upper Laja River watershed in Guanajuato, Mexico. The present study employed Wolman pebble counts to systematically assess the effectiveness of 21 check dams located near the city of San Miguel de Allende. Particle size distributions taken directly downstream and upstream of each check dam were differentiated, aggregated and compared--with the difference between median particle size of downstream and upstream distributions defined as DsD50-UsD50. Several subwatershed attributes were calculated in a GIS for comparison to DsD50-UsD50 values. Results indicate that, on aggregate, the check dams studied were moderately successful at retaining sediment that becomes entrained in concentrated flow (DsD50-UsD50 = 15.4 mm; p < 0.001). Individually, 18 of the 21 check dams surveyed had statistically significant differences between DsD50 and UsD50 (p < 0.05). The subwatershed variables of local channel slope (r = 0.55), mean subwatershed slope (r = 0.46), subwatershed area (r = 0.59), distance from channel head (r = 0.54), percent canopy cover (r = 0.46), Qmed (r = 0.46), total stream power (r = 0.58), and change in total stream power (r = -0.45) were found to be statistically significant when correlated with DsD50-UsD50 values (p < 0.05). Change in total stream power was used to classify stream reaches as either erosion or deposition-dominated. When compared, the DsD50-UsD50 values from check dams located in erosion and deposition-dominated reaches are statistically different (p < 0.05); higher performing check dams were predominantly found in deposition-dominated reaches. The results of this study suggest that spatially distributed stream power can be used as a variable for making decisions about future check dam locations. In particular, check dams are more likely to be effective if they are located within deposition-dominated areas (negative change in total stream power) and in areas of decreasing change in total stream power. In general, this study's findings also support locating check dams in second order streams. Title: Effects of Spatially Distributed Stream Power on Check Dam Function in Small Upland Watersheds: A Case Study of the Upper Laja Watershed, Guanajuato, Mexico Author: Herzfeld, Zachary Andrew Year: 2017 Watershed restoration comes in a variety of forms depending on which set of problems are sought to be remedied. Severe soil erosion, in the form of gullying and/or headcutting, can be mitigated through constructing check dams in well-selected locations. This practice has been used throughout the upland subwatersheds within the Upper Laja River watershed in Guanajuato, Mexico. The present study employed Wolman pebble counts to systematically assess the effectiveness of 21 check dams located near the city of San Miguel de Allende. Particle size distributions taken directly downstream and upstream of each check dam were differentiated, aggregated and compared--with the difference between median particle size of downstream and upstream distributions defined as DsD50-UsD50. Several subwatershed attributes were calculated in a GIS for comparison to DsD50-UsD50 values. Results indicate that, on aggregate, the check dams studied were moderately successful at retaining sediment that becomes entrained in concentrated flow (DsD50-UsD50 = 15.4 mm; p < 0.001). Individually, 18 of the 21 check dams surveyed had statistically significant differences between DsD50 and UsD50 (p < 0.05). The subwatershed variables of local channel slope (r = 0.55), mean subwatershed slope (r = 0.46), subwatershed area (r = 0.59), distance from channel head (r = 0.54), percent canopy cover (r = 0.46), Qmed (r = 0.46), total stream power (r = 0.58), and change in total stream power (r = -0.45) were found to be statistically significant when correlated with DsD50-UsD50 values (p < 0.05). Change in total stream power was used to classify stream reaches as either erosion or deposition-dominated. When compared, the DsD50-UsD50 values from check dams located in erosion and deposition-dominated reaches are statistically different (p < 0.05); higher performing check dams were predominantly found in deposition-dominated reaches. The results of this study suggest that spatially distributed stream power can be used as a variable for making decisions about future check dam locations. In particular, check dams are more likely to be effective if they are located within deposition-dominated areas (negative change in total stream power) and in areas of decreasing change in total stream power. In general, this study's findings also support locating check dams in second order streams. Close

• 2. [Article] The Influence of Floodplain Restoration on Flow and Sediment Dynamics in an Urban River

  A study of floodplain sedimentation on a recently restored floodplain is presented. This study uses a two-dimensional hydro-morphodynamic model for predicting flow and suspended-sediment dynamics in the ...

  Citation × Citation Citation Abstract Copy Title: The Influence of Floodplain Restoration on Flow and Sediment Dynamics in an Urban River Author: Ahilan, Sangaralingam, Guan, Mingfu, Sleigh, Andrew, Wright, Nigel G., Chang, Heejun Year: 2016 A study of floodplain sedimentation on a recently restored floodplain is presented. This study uses a two-dimensional hydro-morphodynamic model for predicting flow and suspended-sediment dynamics in the downstream of Johnson Creek, the East Lents reach, where the bank of the river has been reconfigured to reconnect to a restored floodplain on a 0.26 km2 (26-ha) site. The simulation scenarios include 10-, 50-, 100- and 500-year event-based deposition modelling of flood events and long-term modelling using the 64 historical flood events between 1941 and 2014. Simulation results showed that the restored floodplain significantly attenuates the upstream flood peak by up to 25% at the downstream. Results also indicated that approximately 20%–30% of sediment from the upstream is deposited on the East Lents floodplain. Furthermore, deposited sediment over the simulated period (1941–2014) is approximately 0.1% of the basin's flood storage capacity; however, the reduction in the storage does not offset the overall flood resilience impact of the flood basin. The sediment conservation at the East Lents flood basin as predicted by the model reduces the annual sediment loading of the Johnson Creek by 1% at the confluence with Willamette River, providing both improved water quality and flood resilience further downstream. Title: The Influence of Floodplain Restoration on Flow and Sediment Dynamics in an Urban River Author: Ahilan, Sangaralingam, Guan, Mingfu, Sleigh, Andrew, Wright, Nigel G., Chang, Heejun Year: 2016 A study of floodplain sedimentation on a recently restored floodplain is presented. This study uses a two-dimensional hydro-morphodynamic model for predicting flow and suspended-sediment dynamics in the downstream of Johnson Creek, the East Lents reach, where the bank of the river has been reconfigured to reconnect to a restored floodplain on a 0.26 km2 (26-ha) site. The simulation scenarios include 10-, 50-, 100- and 500-year event-based deposition modelling of flood events and long-term modelling using the 64 historical flood events between 1941 and 2014. Simulation results showed that the restored floodplain significantly attenuates the upstream flood peak by up to 25% at the downstream. Results also indicated that approximately 20%–30% of sediment from the upstream is deposited on the East Lents floodplain. Furthermore, deposited sediment over the simulated period (1941–2014) is approximately 0.1% of the basin's flood storage capacity; however, the reduction in the storage does not offset the overall flood resilience impact of the flood basin. The sediment conservation at the East Lents flood basin as predicted by the model reduces the annual sediment loading of the Johnson Creek by 1% at the confluence with Willamette River, providing both improved water quality and flood resilience further downstream. Close

• 3. [Article] Stacking Functions: Identifying Motivational Frames Guiding Urban Agriculture Organizations and Businesses in the United States and Canada

  While a growing body of scholarship identifies urban agriculture's broad suite of benefits and drivers, it remains unclear how motivations to engage in urban agriculture (UA) interrelate or how they differ ...

  Citation × Citation Citation Abstract Copy Title: Stacking Functions: Identifying Motivational Frames Guiding Urban Agriculture Organizations and Businesses in the United States and Canada Author: McClintock, Nathan, Simpson, Michael Year: 2017 While a growing body of scholarship identifies urban agriculture's broad suite of benefits and drivers, it remains unclear how motivations to engage in urban agriculture (UA) interrelate or how they differ across cities and types of organizations. In this paper, we draw on survey responses collected from more than 250 UA organizations and businesses from 84 cities across the United States and Canada. Synthesizing the results of our quantitative analysis of responses (including principal components analysis), qualitative analysis of textual data excerpted from open-ended responses, and a review of existing literature, we describe six motivational frames that appear to guide organizations and businesses in their UA practice: Entrepreneurial, Sustainable Development, Educational, Eco-Centric, DIY Secessionist, and Radical. Identifying how practitioners stack functions and frame their work is a first step in helping to differentiate the diverse and often contradictory efforts transforming urban food environments. We demonstrate that a wide range of objectives impact how urban agriculturalists practice UA and that political orientations and discourses differ across geographies, organizational type and size, and funding regime. These six paradigms provide a basic framework for understanding UA that can guide more in-depth studies of the gap between intentions and outcomes, while helping link historically and geographically specific insights to wider social and political economic processes. Title: Stacking Functions: Identifying Motivational Frames Guiding Urban Agriculture Organizations and Businesses in the United States and Canada Author: McClintock, Nathan, Simpson, Michael Year: 2017 While a growing body of scholarship identifies urban agriculture's broad suite of benefits and drivers, it remains unclear how motivations to engage in urban agriculture (UA) interrelate or how they differ across cities and types of organizations. In this paper, we draw on survey responses collected from more than 250 UA organizations and businesses from 84 cities across the United States and Canada. Synthesizing the results of our quantitative analysis of responses (including principal components analysis), qualitative analysis of textual data excerpted from open-ended responses, and a review of existing literature, we describe six motivational frames that appear to guide organizations and businesses in their UA practice: Entrepreneurial, Sustainable Development, Educational, Eco-Centric, DIY Secessionist, and Radical. Identifying how practitioners stack functions and frame their work is a first step in helping to differentiate the diverse and often contradictory efforts transforming urban food environments. We demonstrate that a wide range of objectives impact how urban agriculturalists practice UA and that political orientations and discourses differ across geographies, organizational type and size, and funding regime. These six paradigms provide a basic framework for understanding UA that can guide more in-depth studies of the gap between intentions and outcomes, while helping link historically and geographically specific insights to wider social and political economic processes. Close