Author : Ian M. Simpson
Publisher :
Page : 0 pages
File Size : 44,18 MB
Release : 2022
Category : Environmental engineering
ISBN :
While urban development provides many services to humanity, it also substantially impacts the environment and ecology of natural areas. Urbanization involves the conversion of forested and agricultural lands to impervious surfaces such as buildings, houses, roads, parking lots, and sidewalks. Stormwater runoff occurs when rainfall is not captured in depressional storage or is unable to infiltrate the soil surface. Land use changes may increase the generation and transport of pollutants and rate and volume of stormwater runoff, leading to increased pollutant load, flooding, in-stream erosion, and elevated stream temperatures. In urban areas developed prior to the Clean Water Act, stormwater is, in many cases, discharged without treatment. In recent decades, low impact development techniques, such as stormwater control measures (SCMs), have been increasingly adopted by municipalities to mitigate urban non-point source pollution. Efficacy of SCM retrofits run the gamut from success to failure. Thus, there is a need to fully understand the factors that affect stormwater quality and quantity to guide management. Urban land use and land cover (LULC) has been recognized as a strong influencer of stormwater quality and hydrology. Herein, I performed a meta-analysis utilizing stormwater quality data from the published literature spanning 360 unique urban watersheds. Furthermore, I monitored stormwater quality and hydrology from (urban and forested) watersheds in Ohio. Results indicate water quality can be further improved with a regionalization scheme. More specifically, regional climate substantially affected the quality of runoff. From the meta-analysis, it was observed that there is an absence of stormwater quality in certain regions of the world, one of which was the midwestern United States. Thus, stormwater models cannot be accurately calibrated or validated for this region. Analysis of local stormwater data (i.e., Dayton, Ohio metropolitan area) revealed LULC and rainfall patterns influenced the quality of runoff. Recent data also suggest stormwater quality is not temporally static (i.e., over years or decades), which opens various avenues for future research. Though design of SCMs is typically based on predicted runoff volume or peak flow rate, findings from water quality monitoring suggest placement of SCMs should also be considered in design (e.g., locate SCMs in hot spots for the generation of a pollutant of interest). Due to simplified hydrologic models, subjective parameter selection, and changing climatic patterns, the prediction of hydrologic responses contains large uncertainty. To bolster widely accepted models, I compared monitored hydrologic responses to predicted responses utilizing a variety of methodologies. Model performance varied with rainfall depth and watershed characteristics such and LULC and imperviousness. Thus, there was no one best model for every scenario, but the provided discussion will aide managers in selecting which model would provide the most accurate results under given circumstances. SCMs are often retrofitted with pollutants of concern in mind; however, these systems may provide treatment for other non-target pollutants. For example, stream temperature has been identified as the most important environmental cue to aquatic species behavior. Thermal impairments to receiving streams are commonly associated with impervious surfaces, yet ponds, wetlands, detention basins, and other noninfiltrating SCMs that are commonly retrofitted (or installed in new developments) further exacerbate stormwater temperature as they are subjected to solar radiation, often with little shading. Infiltrating SCMs such as bioretention and permeable pavements have shown promising reductions in stormwater temperature at the site-scale, but it is still unknown how a network of SCMs retrofitted at the watershed scale can ameliorate thermal impacts. My goal was to address this gap in knowledge to better inform other management strategies (e.g., riparian buffers, clustered imperviousness, underground storage/conveyance) that may need to be considered to protect cold-water ecosystems. Results indicate the best method of reducing thermal mass exported to receiving streams is through runoff volume mitigation, as runoff temperatures (monitored at watershed outlets) from watersheds with SCM retrofits were not different from watersheds without SCMs. It is commonly accepted in the literature that hydrologic mitigation is most critical for reducing the export of priority pollutants. In the final chapter of this dissertation, I addressed the effectiveness of five different maintenance techniques (two of which are new to the literature) to restore hydraulic function across five different permeable pavements by quantifying surface infiltration rates (SIRs) before and after maintenance activities. Three of the maintenance activities significantly improved SIRs, but results varied in effectiveness based on in-situ pavement conditions and operational factors. Thus, many maintenance take-aways were addressed such as performing maintenance during dry periods, topping up of joint aggregate after maintenance, and avoiding permeable pavement in high traffic/high speed areas.