Charlene LeBleu

Evaluation of Bioretention Nutrient Removal in a Rain Garden with an Internal Water Storage (IWS) Layer

Stormwater runoff has been identified as a major source of pollution in urban and suburban streams. There are several innovative stormwater practices that integrate stormwater infiltration and storage to improve the quality of runoff, including bioretention areas such as rain gardens. This paper reports first year results comparing two different bioretention (rain garden) designs constructed at the Donald E. Davis Arboretum on the Auburn University campus, one using conventional, aerobic treatment and the other incorporating an internal water storage (IWS) layer. Initial evaluation of outflow from the newly installed rain garden revealed several trends directly related to the chemical and physical properties of the fill media. Results support what is known in the literature about the linkage between outflow rain garden water quality and the inherent soil properties of the fill media. In addition, it was observed that settlement and consolidation of in-place rain garden media immediately following construction resulted in gradually reduced outflow peaks during the 6-month study period from July through December 2006. Significant removal of particulate phosphorus and total phosphorus constituents was found under both conventional and IWS operation of the rain garden and some beneficial nitrogen removal was also detected from the IWS layer towards the end of the study. Beneficial hydrologic effects of the rain garden included significantly reduced outflow hydrograph peaks and reduced total outflow volumes, both effects which would act to reduce total contaminant load to receiving waterways. In addition, within six months after construction, the peak outflow from the rain garden was seen to decrease until a near steady-state outflow was achieved.

Evaluation of Erosion and Sediment Control Cover Types for Long-term Vegetation Establishment on Disturbed Slopes

Study of erosion control techniques is necessary for the reduction of sediment loss from construction sites and other disturbed slopes. One of the most effective methods of reducing erosion is to establish a vegetative cover as soon as possible. This study evaluates six cover treatments and one bare soil treatment. The effectiveness of each cover type to reduce runoff and sediment yield was evaluated over an eight-month period on 10x25’ outdoor plots in Auburn, Alabama. Plots were constructed at 4:1 slope and instrumented with fabricated samplers capturing 1/20th of plot runoff volume and sediment yield during rain events. Along with standard covers such as wheat straw and erosion control blankets, four hydromulch treatments were tested, two of which had lime, fertilizer, and seed applied as a pre-mixed slurry. All other treatments had agronomic rates of lime and fertilizer incorporated into the soil before handseeding and cover placement. The establishment of a 75% bermudagrass cover took approximately 90 days from planting. Visual and photographic observation indicated three general stages of cover establishment, including: 1) 0% to 50% of vegetation cover, which occurred between May 24 and July 9, having the highest sediment yields; 2) 50% to 75% of vegetation cover from approximately July 16 to July 30, with decreasing sediment yields; and 3) 75% to 100% cover from approximately August 20 to December 26, with significantly decreased sediment yields. Preliminary results from the first year indicate that agronomic incorporation of fertilizer and lime before hydroseeding or other mechanical cover is an effective means of establishing vegetation on steep slopes, with over a 30-fold reduction in sediment yield over bare soil control plots. Preliminary results provide information for replicated follow-up treatments on 21 new plots, to include polyacrylamide addition with selected mechanical and biological covers.

Marine Spatial Planning: Exploring the Role of Planning Practice and Research

Marine spatial planning (MSP) is a tool for managing and improving marine environments. The field is dominated by natural scientists and has not been commonly associated with planning. This research analyzes the MSP literature to explore how planners can contribute to MSP research and practice. We organize the literature into eight themes, focusing on how planners may be able to contribute to MSP research and practice: ocean zoning, defining boundaries, planning in dynamic environments, stakeholder involvement, information needs, integrating ocean and land-use management, managing multiple and conflicting uses, and transboundary institutional structures. We conclude that planners have a lot to contribute in these eight areas.

Effects of Initial Abstraction Ratio in SCS-CN Method on Modeling the Impacts of Urbanization on Peak Flows

The initial abstraction ratio (λ) used in the SCS-CN method plays an important role in calculation of runoff volume and consequently hydrograph peak. The recommended value for λ in the SCS handbook is 0.2. However, recent studies suggest that λ varies between 0.05 and 0.2, closer to the lower bound. Yet, the SCS recommended value of 0.2 is still being widely used in many hydrologic models. In this study, we explored the effects of variation in λ on simulating urbanization impacts in a coastal Alabama watershed with HEC-HMS. The potential impacts of future development scenarios on peak flows were scrutinized for λ values of 0.2 and 0.05. Results showed that the use of λ = 0.05 provides superior results when model generated hydrographs and peak flows were compared to observed counterparts.

Evaluation of stormwater quality through pervious concrete pavement

This study focuses on a widely known but little studied stormwater mitigation technique, pervious concrete (PC) paving, which is used in place of an impervious paved surface to both reduce and potentially treat stormwater runoff flows from an urban surface. This construction technology is widely accepted as a beneficial urban stormwater mitigation practice, but has not been adequately evaluated with regard to pollutant removal efficiency, before, during, and after construction.