Rainfall interception is one mechanism by which tree canopies can reduce surface runoff in urban areas. The objectives of this research were to: 1) quantify rainfall interception by urban tree canopies, and 2) determine the influence of vegetation and microenvironmental factors on rainfall interception rates. In the city of Denton, Texas, 30 mature post oak (Quercus stellata) and blackjack oak (Quercus marilandica) trees were selected for study. Trees were assigned to one of three categories: clusters of trees on greenspace (CG), isolated trees on greenspace (IG), and isolated trees surrounded by pavement (IP). Throughfall (the volume of water that travels through the canopy and reaches the soil surface) collectors were placed beneath these trees and rainfall collectors were placed in nearby open areas. Throughfall and rainfall were collected daily from 19 March to 4 July. Interception was calculated as the difference between throughfall and gross rainfall. Over the study period, there were 27 days with measurable rainfall; daily rainfall ranged from 1-51 mm. Over the sampling period, rainfall interception for individual trees ranged from -10% to 49%, indicating high spatial variability in interception. Percent interception was highest for the CG treatment (22.7 ± 3.8 SE), intermediate for IG (27.4 ± 2.3 SE), and lowest for IP (9.1 ± 4.9 SE). Factors like wind exposure, wind-driven rain and overall tree health may help explain this variability. This research will contribute to our knowledge of hydrological fluxes in urban areas and the role of urban green infrastructure in stormwater runoff mitigation.

The rapid development of once-rural landscapes often produces detrimental effects on surface water quality entering local reservoirs through vulnerable stream channels. This study presents a methodology that incorporates geographic information systems (GIS) and remote sensing techniques for the creation of a stream corridor evaluation mechanism, coined the water quality corridor management (WQCM) model. Specifically, the study focuses on determining the viability of the WQCM model in assessing the stream corridor conditions within a northern Denton County pilot study region. These results will aid in the prediction and evaluation of the quality of stream water entering reservoirs that serve as the primary drinking water source for local municipalities.

Urbanization causes various environmental issues including water pollution, air pollution, and solid waste. Urbanization of watersheds has a profound influence on the quality of stormwater runoff. The quality of stormwater runoff is highly associated with land use. This study analyzed the exceedance frequency of stormwater quality in five watersheds of Denton over eleven years and also analyzed the relationship between stormwater quality and land use/cover of each watershed. The results showed that the most of the water quality parameters that were examined in the Lower Pecan watershed exceeded their threshold most frequently. The higher frequency of exceedance in this watershed can be attributed to the wastewater treatment plant and landfill site. Total suspended solids and turbidity were frequently exceeded in Hickory and Clear Creek watersheds. Conductivity was found to have highest percentage of exceedance in Upper Pecan and Cooper watersheds. Thus, rural watersheds were related with higher exceedance of TSS and turbidity whereas urban watersheds were related with higher exceedance of conductivity.

Rain gardens are low impact developments designed to mitigate a suite of issues associated with urban stormwater runoff. The site for this study was a Denton City rain garden at the Denton Waste Water Treatment Plant. Nitrogen and phosphorus removal was examined in light of two overflow events comprised of partially treated wastewater from an upslope anaerobic digester pond. Nitrate removal efficiency was examined across differing dry spell intervals of 5, 8, and 12 d, displaying a moderate negative correlation (r2 = 0.59). Continued phosphorus removal capacity was assessed, showing phosphorus removal in cases where P was in excess of 0.8 mg/L, reflecting an equilibrium phosphorus concentration. A high expanded shale component in the soil media (25%) was likely a factor in the continued removal of phosphorus. Overall the rain garden proved to be a large source of nitrate (+425%) and total nitrogen (+61%) by mass. The study showed that while the rain garden intercepted a large volume of partially treated wastewater during the overflow events, preventing it from reaching a nearby creek, the mitigation of an acute event has extended to a chronic one as nitrogen is gradually processed and flushed from the system as nitrate.

In order to better understand runoff characteristics from natural gas well sites in north central Texas, the City of Denton, with assistance through an EPA funded 104b3 Water Quality Cooperative Agreement, monitored storm water runoff from local natural gas well sites. Storm water runoff was found to contain high concentrations of total suspended solids (TSS). Observed TSS concentrations resulted in sediment loading rates that are similar to those observed from typical construction activities. Petroleum hydrocarbons, in contrast, were rarely detected in runoff samples. Heavy metals were detected in concentrations similar to those observed in typical urban runoff. However, the concentrations observed at the gas well sites were higher than those measured at nearby reference sites. Storm water runoff data collected from these sites were used to evaluate the effectiveness of the water erosion prediction project (WEPP) model for predicting runoff and sediment from these sites. Runoff and sediment predictions were adequate; however, rainfall simulation experiments were used to further characterize the portion of the site where drilling and extraction operations are performed, referred to as the "pad site." These experiments were used to develop specific pad site erosion parameters for the WEPP model. Finally, version 2 of the revised universal soil loss equation (RUSLE 2.0) was used to evaluate the efficiency of best management practices (BMPs) for natural gas well sites. BMP efficiency ratings, which ranged from 52 to 93%, were also evaluated in the context of site management goals and implementation cost, demonstrating a practical approach for managing soil loss and understanding the importance of selecting appropriate site-specific BMPs.

With the advent of national storm water regulations, municipalities with populations greater than 100,000 are required to obtain National Pollutant Discharge Elimination System Permits (NPDES) for storm water discharges. In addition to the sampling required for the permit process, the City of Fort Worth contracted with the University of North Texas' Institute of Applied Sciences to conduct acute toxicity testing using Pimephales prcmelas and Ceriodaphnia dubia on storm water samples received from the Dallas/Fort Worth Metroplex. A Toxicity Identification Evaluation (TIE) was performed on four samples that exhibited acute toxicity to C. dubia. High levels of metals as well as diazinon were some of the probable toxicants found.