Greater environmental considerations and the desire to reduce pollution overflows to watercourses are requiring engineers to develop a better understanding of the processes involved in pollution transport through sewer networks. Furthermore, developments in modelling techniques and computer power are allowing urban drainage modellers to increase the complexity of their software and so demand additional data that can be incorporated. Presently, an important aspect is quantifying the retention time and dispersion of pollutants entering an urban drainage system. Manholes provide a means of sewer access for maintenance and inspection. Under storm flow conditions they are liable to surcharge above the level of the pipe soffit. This creates a storage volume that has an impact on the longitudinal dispersion and travel time of soluble pollutants in sewer systems. A laboratory investigation has been completed to quantify these effects for various manhole configurations. These include step heights between the inlet and outlet pipes, benching and extreme high surcharge conditions. In addition, re·analysis of previously acquired data has allowed variations in manhole diameter to be considered. Numerical modelling using computational fluid dynamics, combined with laser light sheet visualisation of the flow structures within manholes, has provided greater insight into the processes causing longitudinal dispersion. The coefficients required for two existing longitudinal dispersion models, the advection dispersion equation and the aggregated dead zone model, have been determined by means of an optimisation process. This has been undertaken with computer software specifically written for the purpose. The technique adopted for optimisation is fully detailed. Final conclusions regarding the longitudinal dispersion due to surcharged manholes are presented.

In this study, stage, streamflow, and precipitation data was collected from small watersheds in the Swanton Pacific Ranch for the first two hydrologic years following the 2020 CZU Lightning Complex. The Little Creek watershed was setup for high-resolution data collection with four separate stage gauge sites (Main Stem, North Fork, South Fork, and Upper North Fork) and four rain gauge sites (Al Smith House, Ridgeline, Upper North Fork, and Landing 23). Stage gauge sites were also established at Queseria, Archibald, and Mill creeks. Preliminary post-fire rating curves were developed for the four sites of Little Creek. The Main Stem (MS) and North Fork (NF) post-fire curves showed some flattening of the slope indicating channel filling, while the South Fork (SF) curve displayed a steepening indicating channel scouring. The Upper North Fork (UNF) rating curve did not indicate any shifts. However, at the time of this study the rating curves were incomplete due to limitations in streamflow measurements. Linear regression models were fit to pre-fire data (hydrologic years 2000-2008) to predict peak flows and storm flow volumes. Antecedent precipitation index (API) and total storm precipitation depth were found to be significant predictors while peak 1-hour rainfall intensity was not. Comparison of post-fire observations to pre-fire model predictions indicated that there were increases in both peak flow and storm flow volumes in Little Creek. However, these findings are not statistically significant due to the limited post-fire observations (n

River export has a strong influence on the productivity of coastal waters. During storm events, rivers deliver disproportionate amounts of nutrients and organic matter to estuaries. Anthropogenic changes to the land use/cover (LULC) and water use also have a strong influence on the export of nutrients and organic matter to estuaries. This study specifically addressed the following questions: 1) How does river water chemistry vary across LULC patterns in the Mission and Aransas river watersheds? 2) How do fluxes of water, nutrients, and organic matter in the rivers vary between base flow and storm flow? 3) How do variations in nutrient/organic matter concentrations and stable isotope ratios of particulate organic matter (POM) in Copano Bay relate to river inputs? Water was collected from the Mission and Aransas rivers and Copano Bay from July, 2007 through November, 2008 and analyzed for concentrations of nitrate, ammonium, soluble reactive phosphorus (SRP), dissolved organic nitrogen, dissolved organic carbon, particulate organic nitrogen, particulate organic carbon (POC), and the stable C and N isotope ratios of the POM. The first half of the study period captured relatively wet conditions and the second half was relatively dry compared to long term climatology. Riverine export was calculated using the USGS LOADEST model. The percentage of annual constituent export during storms in 2007 was much greater than in 2008. Concentration-discharge relationships for inorganic nutrients varied between rivers, but concentrations were much higher in the Aransas River due to waste water contributions. Organic matter concentrations increased with flow in both rivers, but POM concentrations in the Aransas River were two fold higher due to large percentages of cultivated crop land. Values of [delta]¹³C-POC show a shift from autochthonous to allochthonous organic matter during storm events. Following storm events in Copano Bay, increases and quick draw down of nitrate and ammonium concentrations coupled with increases and slow draw down of SRP illustrate nitrogen limitation. Organic matter concentrations remained elevated for ~9 months following storm events. The [delta]¹³C-POC data show that increased concentrations were specifically related to increased autochthonous production. Linkages between LULC and nutrient loading to coastal waters are widely recognized, but patterns of nutrient delivery (i.e. timing, duration, and magnitude of watershed export) are often not considered. This study demonstrates the importance of sampling during storm events and defining system-specific discharge-concentration relationships for accurate watershed export estimation. This study also shows that storm inputs can support increased production for extended periods after events. Consideration of nutrient delivery patterns in addition to more traditional studies of LULC effects would support more effective management of coastal ecosystems in the future. / text