Donald E. Barbe

Water quality modeling for a sinusoidally varying waste discharge concentration

Abstract Biochemical oxygen demand modeling in a river involves derivation and solution of the governing partial differential equation which describes concentration change with time and space brought on by convective, dispersive, and decay processes and the loading function. In this study, a sinusoidal variation in waste discharge concentration is considered. The governing partial differential equation is solved analytically by a transform method and by assuming that the solution varies periodically in time. The concepts of memory length and memory time are used to indicate when the solution becomes quasi-steady (periodic). The analytical solution is compared with two other solutions. The three solutions produce comparable results. However, the analytical solution is much easier to apply. The analytical solution extends the number of boundary conditions which a modeler can apply to describe real engineering problems.

CLIMATIC EFFECT ON WATER QUALITY EVALUATION

An advisory discouraging swimming and other primary contact recreation in Lake Pontchartrain was issued in 1985 by the Louisiana Department of Health and Hospitals (LDHH). The advisory is still in effect today for the south shore area of the lake and names fecal coliform bacteria as the causative pollutant. The suspected source of the contamination in this area is urban stormwater runoff that is collected and pumped to the lake and may be contaminated by sanitary sewer cross-flows. A water quality shoreline study was initiated in the south shore area of the lake in New Orleans by the Department of Civil & Environmental Engineering at the University of New Orleans (UNO). The objective was to determine if the reduced bacteria levels are a result of decreased pollution or if this is a temporary phenomenon caused by a short-term climatic effect. Five monitoring stations were selected for study on the basis of proximity to drainage canals that discharge the stormwater runoff and current or previous use for primary contact recreation. Fecal coliform concentrations was found to be “wet” weather-dependent at all stations except one. There appears to be an active continuous bacteria source near this site since fecal coliform levels there cannot be directly linked to urban runoff. For the remaining areas a general rule of thumb for recreational use of these south shore water is that the user should assume that the water is unsuitable for primary contact recreation, especially in the near vicinity of urban drainage canals, for at least two to three days following a storm event. Precipitation analysis showed a reduction in mean total annual rainfall during the study period amounting to nearly one-third of the typical mean total annual rainfall for the area. Therefore, lower fecal coliform concentrations observed may be due to uncharacteristic drought conditions rather than decreased pollution.

A Statistical Methodology to Discover Precipitation Microclimates in Southeast Louisiana: Implications for Coastal Watersheds*

Abstract This study quantifies the spatial distribution of precipitation patterns on an annual basis for southeast Louisiana. To compile a long-term record of 24-h rainfall, rainfall reports collected by National Weather Service (NWS) cooperative observers were gathered from National Climatic Data Center (NCDC) archives, private collections of observational data held at regional and local libraries, NWS offices, and local utility providers. The reports were placed into a digital database in which each station’s record was subjected to an extensive quality control process. This process produced a database of daily rainfall reports for 59 south Louisiana stations for the period 1836–2002, with extensive documentation for each site outlining the differences between the study’s data and the data available from the NCDC Web page. A statistical methodology was developed to determine if the four NCDC climate divisions for southeast Louisiana accurately depict average monthly rainfall for the area. This method em...

Modeling microbial levels using precipitation data and seasonal analysis

Abstract This paper presents models for estimating fecal coliform concentrations in the Bogue Falaya and Tchefuncte Rivers as a function of basin average precipitation. Fecal coliform data from the Louisiana Department of Health and Hospitals were available for a period of 15 years (1975 through 1991). Precipitation data from the Louisiana Climate Center at Louisiana State University were available for 49 years (1943 through 1991). The climate of the area is characterized by different precipitation/runoff mechanisms for the summer and winter seasons. This seasonal effect has been successfully applied in modeling fecal coliform in the Tchefuncte River as a function of discharge (Barbe and Francis, 1995). Even though a seasonal effect was found for the Tchefuncte River, no seasonal effect was evident for the Bogue Falaya River. A reason for this difference is discussed. Statistical analysis entailed regression analysis to determine the relationship between precipitation and fecal coliform concentration and ...

Fate of Pathogens in Stormwater Plumes

Modern tools for management of recreational waters include field monitoring, laboratory analyses and computer modeling. A case study of a brackish receiving wa…

Urban Rainwater Composition Study

Rainwater samples have been collected in New Orleans from October 1999 to October 2000. The samples were analyzed for water quality parameters: pH, total Kjeld…