Urban development significantly increases water temperatures within watersheds, primarily from the construction of impervious surfaces for buildings and pavement. While thermally enriched runoff can be harmful to aquatic life, available research and guidance on predicting these effects is limited. The goal of this assessment is to provide guidance on how to achieve necessary temperature regimes that meet aquatic health criteria for sensitive species such as trout. To address this need, the Minnesota Urban Heat Export Tool (MINUHET) and U.S. Environmental Protection Agency's Storm Water Management Model (SWMM) models were utilized to simulate hourly streamflow, water temperature, and heat flux in an urban watershed in Blacksburg, VA for typical summer periods using continuous-based simulation. SWMM and MINUHET were combined in a unique, hybrid approach that emphasized each model's strengths, i.e., SWMM for runoff and streamflow, and MINUHET for water temperature. The watershed is 14.1 km², and is portion of Stroubles Creek located near downtown Blackburg, Virginia and the main campus of Virginia Tech. Streamflow, water temperature, and climate data were acquired from Virginia Tech StREAM Lab (Stream Research, Education, and Management) monitoring stations. SWMM and MINUHET were calibrated manually for the summers of 2016, and were validated for the summer of 2015. Model sensitivity analyses revealed that simulations were especially sensitive to imperviousness (SWMM predicted streamflow as outputs) and dew point temperature (MINUHET predicted water temperatures as outputs), both resulted in increased outputs of SWMM and MINUHET models, respectively. Model performance in simulating streamflow was evaluated using Nash-Sutcliffe Efficiency (NSE) and correlation (R²). NSE and R² values were 0.65 and 0.7 for the SWMM Model and 0.57 and 0.55 for the MINUHET model during the validation period, indicating that SWMM performed better than MINUHET in streamflow simulation. Streamflow temperatures were simulated using MINUHET with a NSE and R² statistical values of 0.58, and 0.83, respectively, demonstrating a satisfactory simulation of water temperature. Heat loads were simulated using the MINUHET and Hybrid models, demonstrating less Percent BIAS of the Hybrid approach in simulation of watershed total heat load than MINUHET alone. Furthermore, a number of practices were implemented to reduce thermal loading within a watershed. These included infiltration practices, methods for decreasing absorption of thermal energy primarily by reducing albedo, and increased vegetation canopies. An index titled Percentage of Time Temperature Exceeded 21°C Threshold (PTTET) for trout habitat was used to represent the effectiveness of thermal mitigation practices. Installing concrete pavement (thermal diffusivity: 15×10-7 m²/s, pavement thickness: 0.20 m, and heat capacity: 4.0×106 J/m³⋅°C) and Acrylic Coated Galvalume (ACG) roofs for all pavement and roofs, respectively, in the watershed reduced heat load by 45%, and the PTTET index declined 4.5%. Installing bioretention with 61 cm of media thickness, and soil-media infiltration rate of 25 mm/hr. for 53 selected parking lots in the watershed, resulted in 11.1% reduction in watershed heat load and 1.4% reduction in PTTET. Planting forest canopies for the entire pervious area of the watershed, sufficient to shade 90% of all lands, resulted in reduction in heat load by 24% and PTTET by 4.6%. / Master of Science / Development within urbanized regions increase impervious surfaces, which further cause significant storm events in watersheds. The increased impervious surfaces result in hotter stormwater particularly during hot summers, which has diverse effects on aquatic health of downstream receiving streams. The main objective of the current study is to evaluate the thermal impact of urbanization on aquatic health habitats in Stroubles Creek Watershed, Blacksburg, Virginia. To aim this goal and achieve the thermal evaluation of the highly urbanized Stroubles Creek Watershed, a U.S. Environmental Protection Agency’s Storm Water Management Model (SWMM) and a Minnesota Urban Heat Export Tool (MINUHET) models from scratch of the Stroubles Creek watershed, using Town of Blacksburg and Virginia Tech Physical Facility information were developed. This necessitated combining information from a wide variety of sources, including geologic maps, geodatabases, hydraulic models, computer-aided design (CAD) files, and scanned as-built information. In addition to the models, a hybrid model was developed that combines SWMM and MINHET outputs. The temperatures and heat loads at the downstream of the watershed were predicted using SWMM, MINUHET, and Hybrid models for two summer periods of 2016 and 2015, and the predicted temperature were compared to the criteria for survival of aquatic health such as trout. Furthermore, a number of thermal mitigation strategies such as bioretentions systems, concrete pavements (which has lighter color compared to asphalt pavements), and increased vegetation canopies were simulated within the MINUHET and SWMM models configurations to reduce simulated temperatures and heat loads at the watershed scale. The simulated temperatures and heat loads represented that concrete pavements results in better performance of thermal mitigation within watersheds than bioretention systems, and increased vegetation canopies.

Stream ecosystems are increasingly at risk for thermal impairment as urbanization intensifies, resulting in more heated runoff from impervious cover that is less likely to be cooled naturally. While several best management practices, including bioretention filters, have been able to reduce thermal pollution, success has been limited. The extent of thermal mitigation required to prevent ecological damage is unknown. A calibrated runoff temperature model of a case study watershed in Blacksburg, VA was developed to determine the cumulative treatment volume of bioretention filters required to reduce thermal impacts caused by runoff from development in the watershed to biologically acceptable levels. A future build out scenario of the study watershed was also analyzed. Results from this study established that runoff thermal pollution cannot be fully reduced to goal thresholds during all storms using bioretention filter retrofits. While retrofitting significantly decreased temperatures and heat exports relative to the controls, increasing treatment volumes did not really enhance mitigation. Alternate thermal mitigation methods which actively remove runoff volume should be considered where more thermal mitigation is required. / Master of Science / Stream temperature is a significant ecological, biological, and chemical property affecting the long-term health of streams. However, as development intensifies, stream ecosystems are increasingly at risk of being damaged by thermal pollution, which causes warmer and less stable temperatures that distress aquatic organisms. While several stormwater management methods that reduce runoff-related pollution, known as best management practices (BMPs), were found to also decrease thermal pollution, their success has been limited. Furthermore, the extent of thermal mitigation required to prevent ecological damage is unclear. This study aimed to determine how much treatment by a popular BMP, the bioretention filter, was necessary across a watershed in Blacksburg, VA to adequately reduce thermal pollution to protect stream health. Mitigation impacts were tested on both existing and predicted future development conditions through model simulations. Results from this study established that thermal pollution from runoff cannot be fully reduced to goal thresholds consistently using bioretention filter retrofits. While retrofitting significantly decreased thermal pollution, increasing treatment volume did not considerably enhance mitigation. Results suggested that bioretention filters are not an effective method, and alternate thermal mitigation practices which actively remove runoff volume should instead be considered where intensive reductions in thermal pollution are necessary.