Stormwater management is an essential aspect of urban hydrology. Urbanized areas have large amounts of impervious surface cover (ISC) and well developed sewer and drainage networks which rapidly channel water and pollutants off of streets and into local streams. This research evaluates the use of vegetated roofs as mechanisms to reduce ISC and stormwater runoff in downtown Atlanta. A 3-D model of the study site was created so that runoff rates could be measured for various rooftop scenarios under different size storm events. The results revealed a reduction in peak runoff and an increase in both the lag time and duration of response time. The results were most significant for the smallest storm event with 2/3 of the rooftops vegetated. As these experiments use a scale model for a section of downtown Atlanta, results are likely to be applicable to similar urban environments and may provide guidance for stormwater engineers.

Around the world, many forested areas have been and continue to be cleared for expanding agriculture. Canada’s remaining forested lands account for around 9% of the world’s forest cover. Although only a fraction is lost to deforestation annually (0.02%, 2013), Statistics Canada reports that conversion to agriculture is the most significant driver of forest loss. As climate changes and agricultural demand expands, this trend is expected to continue, and ecosystems will continue to be impacted by resulting habitat loss and hydrological changes that can impact infrastructure and communities. Additionally, changes to sediment and nutrient loadings can harm ecosystems and affect the downstream usability of freshwater supplies. The impact of increased sediment and nutrient concentrations in freshwater systems has been extensively documented in the literature. In some extreme cases, it can lead to anoxic ‘dead zones’ in riverine, lacustrine, and marine habitats. Many river systems in Canada have shown elevated nutrient levels in recent years, often tied to the expansion of agricultural land use and destruction of natural forests to increasing nutrient levels in downstream rivers, lakes, and oceans. This study applies numerical modelling to quantify the influence of forest loss, agricultural expansion and the application of best management practices (BMPs) on water quality and quantity in the South Nation Watershed in eastern Ontario, Canada. The land use in the watershed is mainly agricultural (over 60%) with forest (27%) that is unevenly distributed in the basin. Aerial photography surveys from 2008 and 2014 show a steady decline in forest cover. Recent water quality monitoring has shown nutrient concentrations at or above Canadian water quality standards in many parts of the basin. The Soil and Water Assessment Tool (SWAT) was used to model the watershed because of its capacity to simulate comprehensive land management scenarios and assess their impact on a variety of water quantity and parameters quickly and effectively. The work was performed in four steps: 1. Recent land use configurations (2008-2014) in the watershed were acquired, and simplified land use projections based on the direct substitution of cropland for forest land were developed. 2. A numerical model was calibrated and validated for the initial land use scenario. 3. These land use scenarios, as well as more hypothetical scenarios representing more extensive deforestation and reforestation, were used as the basis for hydrological modelling using 31 years of real-world meteorological observations. 4. Idealized vegetated filter strips (VFSs) and grassed waterways (GWWs) were added to the cropped land packages to study the potential of these practices to contribute to the management of water quality. Analysis of the 33 output datasets derived from simulations of the suite of land use scenarios with and without VFSs and GWWs leads to several conclusions, while also raising some questions. Generally, forests significantly reduce sediment, nitrate and phosphorus outputs to streams as well as slightly reducing water yield compared to cropped areas due to an increase in surface runoff, groundwater and lateral flow combined with the absence of tile drainage. Across subbasins, this translates to significant reductions in sediment, nitrate and total phosphorus loadings entering the river reaches and a slight increase in water yield. At the basin outlet near Plantagenet, Ontario, streamflow and sediment loading show to have little sensitivity to changes in forest and crop cover, while increased forest cover leads to significantly reduced nutrient loadings, particularly in late spring and early winter. It is clear from this work that continued deforestation will continue to drive further nutrient enrichment in the South Nation River, while VFSs seems to have a significant potential for offsetting some of this enrichment. Streamflow and sediment loadings, however, are not significantly impacted by foreseeable deforestation. The influence of land use change and BMPs was much more significant in the runoff than in exports from the basin, suggesting there would be value in further examination of water quality and quantity at a higher spatial density to expand on assumptions of in-stream processes made here.

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13262号 / 論農博第2875号 / 新制||農||1071(附属図書館) / 学位論文||R1||N5217(農学部図書室) / (主査)教授 山下 洋, 教授 澤山 茂樹, 教授 吉岡 崇仁 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

The 42-kilometer beach in Harrison County, Mississippi necessitates continual re-nourishment projects to ensure its survival due to constant erosion events. The stability that the root structures of vegetated beaches provide have been shown to be a countermeasure to these erosion events. It has also been shown that the public will utilize landscapes that they find to be attractive. Therefore, the purpose of this thesis is to ascertain whether beach users find vegetated beaches more attractive than un-vegetated beaches. In several Harrison County communities, beach users were surveyed through the use of a Visual Preference Survey and an accompanying questionnaire to determine their opinions on the design of the beach, its design elements, and the purpose of those elements. Results were mixed, however it was determined that beach users found beaches vegetated with multiple types of florae to be more attractive than non-vegetated beaches.

Green roofs are increasingly being used in the United States to mitigate the negative effects of impervious surfaces on aquatic ecosystems. Though performance of these systems varies with climate, little research has been conducted in the Southeastern U.S., and no prior research has been conducted in Mississippi. An experiment was conducted to determine the effect of soil depth and roof slope on the stormwater retention of green roofs in Mississippi’s hot, humid climate. Simulated roof platforms were constructed to investigate two soil depths and two slopes, each replicated three times and planted with four species of Sedum. The green roof platforms significantly reduced runoff depth when compared with total rainfall depth. Soil depth and slope both significantly affected retention, with higher retention seen with increasing soil depth and lower retention seen with increasing slope. These results indicate that green roofs can be an effective tool to reduce runoff in Mississippi.

Yes / Simulation of the suspended sediment concentration (SSC) has great significance in predicting the sediment transport rate, vegetation growth and the river ecosystem in the vegetated open channel flows. The present study focuses on investigating the vertical SSC profile in the vegetated open channel flows. To this end, a model of the dispersive flux is proposed in which the dispersive coefficient is expressed as partitioned linear profile above or below the half height of vegetation. The double-averaging method, i.e. time-spatial average, is applied to improve the prediction accuracy of the vertical SSC profile in the vegetated open channel flows. The analytical solution of SSC in both the submerged and the emergent vegetated open channel flows is obtained by solving the vertical double-averaging sediment advection-diffusion equation. The morphological coefficient, a key factor of the dispersive coefficient, is obtained by fitting the existing experimental data. The analytically predicted SSC agrees well with the experimental measurements, indicating that the proposed model can be used to accurately predict the SSC in the vegetated open channel flows. Results show that the dispersive term can be ignored in the region without vegetation, while the dispersive term has significant effect on the vertical SSC profile within the region of vegetation. The present study demonstrates that the dispersive coefficient is closely related to the vegetation density, the vegetation structure and the stem Reynolds number, but has little relation to the flow depth. With a few exceptions, the absolute value of the dispersive coefficient decreases with the increase of the vegetation density and increases with the increase of the stem Reynolds number in the submerged vegetated open channel flows. / Natural Science Foundation of China (Nos. 11872285 and 11672213), The UK Royal Society – International Exchanges Program (IES\R2\181122) and the Open Funding of State Key Laboratory of Water Resources and Hydropower Engineering Science (WRHES), Wuhan University (Project No: 2018HLG01).

Yes / Simulation of the suspended sediment concentration (SSC) has great significance in predicting the sediment transport rate, vegetation growth and the river ecosystem in the vegetated open channel flows. The present study focuses on investigating the vertical SSC profile in the vegetated open channel flows. To this end, a model of the dispersive flux is proposed in which the dispersive coefficient is expressed as partitioned linear profile above or below the half height of vegetation. The double-averaging method, i.e. time-spatial average, is applied to improve the prediction accuracy of the vertical SSC profile in the vegetated open channel flows. The analytical solution of SSC in both the submerged and the emergent vegetated open channel flows is obtained by solving the vertical double-averaging sediment advection-diffusion equation. The morphological coefficient, a key factor of the dispersive coefficient, is obtained by fitting the existing experimental data. The analytically predicted SSC agrees well with the experimental measurements, indicating that the proposed model can be used to accurately predict the SSC in the vegetated open channel flows. Results show that the dispersive term can be ignored in the region without vegetation, while the dispersive term has significant effect on the vertical SSC profile within the region of vegetation. The present study demonstrates that the dispersive coefficient is closely related to the vegetation density, the vegetation structure and the stem Reynolds number, but has little relation to the flow depth. With a few exceptions, the absolute value of the dispersive coefficient decreases with the increase of the vegetation density and increases with the increase of the stem Reynolds number in the submerged vegetated open channel flows. / the Natural Science Foundation of China (Nos. 11872285 and 11672213), The UK Royal Society – International Exchanges Program (IES\R2\181122) and the Open Funding of State Key Laboratory of Water Resources and Hydropower Engineering Science (WRHES), Wuhan University (Project No: 2018HLG01)

No description available.

Coastal ecosystems comprise a relatively small area of the ocean, yet they play a disproportionate role in greenhouse gas (carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)) and nutrient cycling. Vegetated coastal ecosystems (e.g., mangroves, salt marshes, and seagrasses) are key drivers of coastal greenhouse gas and nutrient cycling because of their environmental characteristics (e.g., shallow depths, organic matter rich sediments, etc.). My dissertation addresses the role of vegetated coastal ecosystems in greenhouse gas budgets and biogeochemical cycling. In Chapter 1, I conducted a meta-analysis to quantify the global emissions of CH4 from mangrove, salt marsh, and seagrass ecosystems. Here I show that mangrove ecosystems contribute the most CH4 out of these vegetated areas to the global marine CH4 budget. Further, while a well-known negative relationship between salinity and CH4 fluxes exists for salt marshes globally, this relationship does not hold for mangrove or seagrass meadows, suggesting that other environmental drivers are more important for predicting CH4 fluxes in these ecosystems. In Chapter 2, I present in situ fluxes of CH4 and N2O across the sediment-water interface as well as air-sea fluxes in seagrass meadows and adjacent non-vegetated sediments in two temperate coastal lagoons. Here I demonstrate that seagrass meadows can be sources or sinks of CH4 and that N2O uptake can enhance carbon sequestration in seagrass meadows by ~10%. In Chapter 3, I quantify fluxes of dissolved inorganic carbon, nitrogen, and phosphorous across the sediment-water interface in seagrass meadows and adjacent non-vegetated sediments in the same two coastal lagoons. I found that both seagrass and non-vegetated sediments exhibited dissolved inorganic carbon emission and denitrification, and that dissolved inorganic phosphorous fluxes varied by site and not with vegetation presence. This dissertation highlights the dynamic role coastal ecosystems play in biogeochemical cycling and the importance of vegetated coastal ecosystems in coastal greenhouse gas budgets. / 2024-10-03T00:00:00Z

This research is intended to determine the role of riparian vegetation in stream morphology. This experiment examined the effects of riparian vegetation on boundary shear stress (BSS) by completing the following objectives: (1) evaluating the effects of streambank vegetation on near-bank velocity and turbulence; (2) determining a method for measuring BSS; and, (3) examining the effects of streambank vegetation on BSS using an existing model. A second order prototype stream, with individual reaches dominated by the three vegetation types (trees, shrubs, and grass) was modeled using a fixed-bed Froude-scale modeling technique. One model streambank of the prototype stream was constructed for each vegetation type in addition to one bank with only grain roughness. Velocity profiles were measured using an acoustic Doppler velocimeter (ADV) and a miniature propeller (MP). A flush-mounted Dantec MiniCTA system was used to measure shear stress at the streambank wall. The addition of vegetation on a sloping streambank increased the streamwise free stream velocity and decreased the near-bank streamwise velocity. The turbulence caused by the upright shrub treatment increased turbulent kinetic energy and Reynolds stresses near the streambank toe, an area susceptible to fluvial erosion. The presence of dense, semi-rigid vegetation may encourage the formation of a wider channel with a vertical streambank. The small range of CTA shear stress measurements (0.02—2.14 Pa) suggested that one estimate can describe a streambank. The law of the wall technique is not appropriate because the velocity profiles did not follow the necessary logarithmic shape. Vegetative roughness present in channels created secondary flow; turbulence characteristics more appropriately estimated BSS. The BSS model predicted velocity fields in similar distribution to that measured by the ADV and MP. BSS calculated using the ray-isovel method for both velocity measurement devices were different than the measured BSS values, likely due to distortions in the measured velocity field. In general, the predicted BSS distribution increased with water depth and decreased with increasing vegetation density. The predicted BSS at the shrub toe indicated a spike in shear stress consistent with TKE estimates. / Ph. D.