Noor B. Hashim

Hydrodynamic Modeling of St. Louis Bay Estuary and Watershed Using EFDC and HSPF

Abstract St. Louis Bay estuary is a vital water body in the Mississippi Gulf Coast Region and greatly affects the water quality in the Mississippi Sound. As the first step of total maximum daily load (TMDL) study, a hydrodynamics model was developed by integrating Hydrological Simulation Program Fortran (HSPF) and Environmental Fluid Dynamics Code (EFDC). In this application the EFDC model was configured to simulate time-varying surface water elevation, velocity, salinity, and water temperature. The HSPF was applied to compute the fresh water discharge from the upstream watersheds. The model reasonably simulated the tidal range and phase. The simulated water temperature and salinity showed good and fairly good agreement with observations. The calculated correlation coefficients between computed and observed velocity were lower compared with those for water level, temperature, and salinity, but the magnitudes of simulated velocity were found to be in the range of observed data. The wind data was found to have strong impacts on velocity simulation by modeling verification tests. Near the study area, there is wind data available only at one station, which has been applied to the entire modeling domain. The lack of high-resolution wind data makes it very difficult to simulate the velocity distribution well. It is anticipated and recommended that the development of this model be continued to synthesize additional field data into the modeling process.

Fecal coliform modeling under two flow scenarios in St. Louis Bay of Mississippi

St. Louis Bay, along with its two major tributaries, Wolf River and Jourdan River, are included in the Mississippi 1998 Section 303(d) List for violation of the designated water use of recreation and shellfish harvesting. Fecal coliform was identified as one of the pollutants that caused the water quality impairment. In order to facilitate the total maximum daily loads (TMDL) development, the fecal coliform dynamics was investigated under 2 flow scenarios with a calibrated and validated modeling framework by integration of Environmental Fluid Dynamic Code (EFDC) and Hydrological Simulation Program Fortran (HSPF). EFDC was used to model the hydrodymics and fecal coliform transportation in the Bay and the tributaries, whereas HSPF was applied to compute the flow and fecal coliform loadings from the watersheds. The total amount of precipitation in the dry year simulation corresponds to a 50-year return period of low flow condition, and a 10-year return period of high flow condition for wet weather simulation. For EFDC modeling, the fecal coliform sources considered were the contributions from the 2 upper watersheds (no tidal influence), the 28 small surrounding watershed, and 12 municipal, industrial, and domestic point sources. When simulating the fecal coliform loadings from the 2 upper watersheds using HSPF, the simulated non-point source loadings of fecal coliform included wildlife, land application of hog and cattle manure, land application of poultry litter, and grazing animals. The EFDC modeling results indicated that the wet weather exerted greater stress on fecal coliform water quality conditions. The number of exceedance of fecal coliform water quality standard in wet year simulation is much higher than that in dry year simulation. The impact of the upper rural watersheds loads on fecal coliform levels in the St. Louis Bay is much less significant than that from the surrounding urban runoff. Fecal coliform TMDL development should be based on high flow conditions since the decision makers are more concerned about worse scenarios. This fecal coliform modeling research would provide useful information of critical condition selection for TMDLs development in similar coastal areas.

Modeling nutrient dynamics under critical flow conditions in three tributaries of St. Louis Bay

The pesticides originally designed to kill target organisms are dangerous for many other wild species. Since they are applied directly to the environment, they can easily reach the water basins and the topsoil. A dataset of 125 aromatic pesticides with well-expressed aquatic toxicity towards trout was subjected to quantitative structure activity relationships (QSAR) analysis aimed to establish the relationship between their molecular structure and biological activity. A literature data for LC50 concentration killing 50% of fish was used. In addition to the standard 2D-QSAR analysis, a comparative molecular field analysis (CoMFA) analysis considering the electrostatic and steric properties of the molecules was also performed. The CoMFA analysis helped the recognition of the steric interactions as playing an important role for aquatic toxicity. In addition, the transport properties and the stability of the compounds studied were also identified as important for their biological activity.Previous research results indicated that dry weather condition has complicated impacts on nitrogen dynamics; monitored and modeling data showed both increased and decreased levels. In order to facilitate the total maximum daily loads (TMDLs) development at three tributaries of St. Louis Bay estuary, the nitrogen dynamics were investigated for two designed critical flow conditions by integrating Hydrological Simulation Program Fortran (HSPF), Environmental Fluid Dynamics Code (EFDC), and Water Quality Analysis Simulation Program (WASP). The total amount of precipitation during the dry year corresponded to a flow condition with return period of 50 years, and 10-year return period for wet year. The dry year contributed more total nitrogen (TN) loads per unit flow volume. At the upstream tributaries, the computed peak reach-averaged TN concentrations were significantly higher for dry weather simulation than wet conditions, whereas at the near-bay tributary, there were no significant differences in the peak TN concentrations. Hence, for the upstream tributaries, the nitrogen TMDL calculation should be based on dry weather condition since the decision-makers are more concerned about the worse scenario.

Assessment of water quality conditions in the St. Louis Bay watershed

The water quality data from 14 sampling stations in the St. Louis Bay watershed were analyzed to evaluate the water quality conditions. The differences in water quality parameters between base and storm flow events were compared to identify the pollutant sources. The results indicated that fecal coliform was the primary cause for water quality impairment of the study area. The overall water quality conditions were good in terms of dissolved oxygen, eutrophication, and total suspended solid (TSS). The dominant sources of bio-chemical oxygen demand (BOD) could be from the failing septic system; the majority of the water samples exceeding Mississippi Department of Environmental Quality (MDEQ) target levels were from base flow events. Different from BOD, the majority of the water samples exceeding the water quality criteria and MDEQ target levels were from the storm events for fecal coliform, chemical oxygen demand, total organic carbon, TKN, NO3, NH3, chlorophyll a, and TSS. Based on cluster analysis, the sampling stations were classified into two major categories: upstream and near-coast stations. The major differences between upstream and near-coast stations are elevation, soil texture, and impacts of human activity. The results from this research would provide useful information for total maximum daily load calculation, development of a computational watershed model, and development of best management practices for the St. Louis Bay watershed and similar study area.

Application and evaluation of two nutrient algorithms of hydrological simulation program fortran in Wolf River watershed

This study performs a comparison of two nutrient algorithms of Hydrological Simulation Program Fortran, PQUAL/IQUAL and AGCHEM. Watershed nutrient models with, PQUAL/IQUAL and AGCHEM, were developed and calibrated separately with observed data in the Wolf River watershed. Compared to AGCHEM modules, the PQUAL/IQUAL algorithm was found to have several disadvantages. Examples are: (i) it is a simple loading estimation algorithm, and cannot represent the soil nutrient processes; and (ii) the interactions of modeled nutrient species in the soil cannot be simulated. The AGCHEM modules are capable of explicitly representing the comprehensive nutrient processes in the soil such as fertilization, atmospheric deposition, manure application, plant uptake process, and the transformation processes. Therefore, AGCHEM modules afford the ability to evaluate the alternative management practice and model the interactions between nutrient species. However, our modeling results indicated that the inclusion of AGCHEM modules do not significantly improve the nutrient modeling performance but rather take much more time in model development. The nutrient algorithms selection for total maximum daily loads development depends on the data availability, required modeling accuracy, and available time for model development.

Impact of urbanization on the sediment yield in tropical watershed using temporal land-use changes and a GIS-based model

Abstract Abundant rainfall areas promote sediment yield at both sub-watershed and watershed scale due to soil erosion and increase siltation of river channel, but it can be curtailed through planned urbanization. The urbanization of Skudai watershed is analysed from historical and future perspective. A GIS-based model (Hydrological Simulation Programme-FORTRAN-HSPF) is used to modelled sediment flow using basin-wide simulation, and the output result is utilized in evaluating sediment yield reduction due to increased urbanization by swapping multiple temporal land-use of decadent time-steps. The analysis indicates that sediment yield reduces with increase urban built-up and decrease forest and agricultural land. An estimated 12 400 tons of sediment will be reduced for every 27% increase in built-up areas under high rainfall condition and 1 490 tons at low rainfall. The sensitivity analysis of land-use classes shows that built-up, forest and barren are more sensitive to sediment yield reduction compared to wetland and agricultural land at both high and low rainfall. The result of the study suggests that increased urbanization reduced sediment yield in proportion to the rainfall condition and can be used as an alternative approach for soil conservation at watershed scale independent of climate condition.