Kevin M. Brannan

MODELING BACTERIA FATE AND TRANSPORT IN WATERSHEDS TO SUPPORT TMDLS

Fecal contamination of surface waters is a critical water-quality issue, leading to human illnesses and deaths. Total Maximum Daily Loads (TMDLs), which set pollutant limits, are being developed to address fecal bacteria impairments. Watershed models are widely used to support TMDLs, although their use for simulating in-stream fecal bacteria concentrations is somewhat rudimentary. This article provides an overview of fecal microorganism fate and transport within watersheds, describes current watershed models used to simulate microbial transport, and presents case studies demonstrating model use. Bacterial modeling capabilities and limitations for setting TMDL limits are described for two widely used watershed models (HSPF and SWAT) and for the load-duration method. Both HSPF and SWAT permit the user to discretize a watershed spatially and bacteria loads temporally. However, the options and flexibilities are limited. The models are also limited in their ability to describe bacterial life cycles and in their ability to adequately simulate bacteria concentrations during extreme climatic conditions. The load-duration method for developing TMDLs provides a good representation of overall water quality and needed water quality improvement, but intra-watershed contributions must be determined through supplemental sampling or through subsequent modeling that relates land use and hydrologic response to bacterial concentrations. Identified research needs include improved bacteria source characterization procedures, data to support such procedures, and modeling advances including better representation of bacteria life cycles, inclusion of more appropriate fate and transport processes, improved simulation of catastrophic conditions, and creation of a decision support tool to aid users in selecting an appropriate model or method for TMDL development.

BMP IMPACTS ON SEDIMENT AND NUTRIENT YIELDS FROM AN AGRICULTURAL WATERSHED IN THE COASTAL PLAIN REGION

The goal of the Nomini Creek watershed monitoring study was to quantify the effectiveness of BMPs at the watershed scale and to determine if the improvements in water quality could be sustained over a long–term period. Information on the long–term effectiveness of BMPs is critical since BMPs are being implemented under the state cost–share program to reduce nonpoint source pollution (NPS) to the Chesapeake Bay. The Nomini Creek project started in 1985 and was completed in 1997. A pre– versus post–BMP design was used. A combination of managerial and structural BMPs was implemented. Major BMPs implemented in the Nomini Creek watershed included no–tillage, filter strips, and nutrient management. The data collected at the 1463 ha Nomini Creek watershed consisted of land use, hydrologic, water quality, soils, and geographical information. The BMPs implemented at Nomini Creek reduced average annual loads and flow–weighted concentrations of nitrogen (N) by 26% and 41%, respectively. Average annual total–N loads discharged from the watershed were reduced from 9.57 kg/ha during the pre–BMP period to 7.05 kg/ha for the post–BMP period. Largest reductions were observed for dissolved ammonium–N, soluble organic–N, and particulate–N. In contrast, nitrate–N loads increased after BMP implementation. Increase in nitrate exports was likely due to ammonification and nitrification, and subsequent leaching of particulate–N species that were conserved on the field. In comparison to N, reductions in phosphorus (P) loads and concentrations were not significant. BMP implementation resulted in a mere 4% reduction for total–P with a corresponding 24% reduction in flow–weighted concentration. The average annual total–P loads exported from the watershed were 1.31 and 1.26 kg/ha for the pre– and post–BMP periods, respectively. Reductions in total–P loads were due to decreases in particulate–P. Exports of ortho–P and dissolved organic–P increased after BMP implementation. It is likely that some of this post–BMP increase in dissolved P fractions was associated with dissolution and leaching of particulate–P, and higher rainfall–runoff activity in the watershed during the post–BMP period. In comparison to nutrients, there was no significant change in suspended solids discharged from the watershed. Overall, the findings of this study indicate that the BMPs were effective in reducing the losses of some forms of nutrients, such as ammonium–N and particulate–P, from the Nomini Creek watershed, but additional BMPs are necessary to achieve significant reductions in all forms of N and P.

Comparison of hydrologic calibration of HSPF using automatic and manual methods

The automatic calibration software Parameter Estimation (PEST) was used in the hydrologic calibration of Hydrological Simulation Program-Fortran (HSPF), and the results were compared with a manual calibration assisted by the Expert System for the Calibration of HSPF (HSPEXP). In this study, multiobjective functions based on the HSPEXP model performance criteria were developed for use in PEST, which allowed for the comparison of the calibration results of the two methods. The calibrated results of both methods were compared in terms of HSPEXP model performance criteria, goodness-of-fit measures (R-2, E, and RMSE), and base flow index. The automatic calibration results satisfied most of the HSPEXP model performance criteria and performed better with respect to R2, E, RMSE, and base flow index than manual calibration results. The results of the comparison with the manual calibration suggest that the automatic method using PEST may be a suitable alternative to manual method assisted by HSPEXP for calibration of hydrologic parameters for HSPF. However, further research of the weights used in the objective functions is necessary to provide guidance when applying PEST to surface water modeling.

ANIMALWASTE BMP IMPACTS ON SEDIMENT AND NUTRIENT LOSSES IN RUNOFF FROM THE OWL RUN WATERSHED

The results of the 10-year study conducted in the Owl Run watershed clearly indicate the beneficial impacts of the best management practices (BMPs) on the surface water quality. The main objective of the study was to determine the effectiveness of a system of animal waste BMPs for improving surface water quality. Precipitation, streamflow, total suspended solids, nitrogen (N), and phosphorus (P) water quality parameters were measured at the main outlet and in three subwatersheds. A pre- and post-BMP comparisons of annual water quality parameters were performed. Reductions in all forms of N and most forms of P were observed due to the implementation of BMPs. For the average annual values at the main watershed outlet, BMPs were effective in reducing both loads and concentrations of all forms of N with the largest reductions in soluble organic N (62%) and the smallest reduction for nitrate-N (35%). Furthermore, BMPs were effective in reducing both loads and concentrations of most forms of P with the largest reductions in particulate-P (78%) and the smallest reduction for soluble P (39%). However, BMPs were not effective in reducing orthophosphorus-P. The system of BMPs implemented in the Owl Run watershed was effective in reducing nutrient loadings, especially N loadings. However, when P is the main water quality concern, implementation of P-based nutrient management plans should be considered.

Simulating Fecal Coliform Bacteria Loading from an Urbanizing Watershed

Abstract The fate and transport of fecal coliform bacteria in the urbanizing Polecat Creek watershed, located in Virginia, was simulated using the Hydrological Simulation Program—FORTRAN (HSPF). Both point and nonpoint sources of fecal coliform were included in the simulation. Hydrologic and water quality parameters of HSPF were calibrated and validated using observed data collected from October 1994 to June 2000 at three monitoring stations. The percent errors in total runoff volumes between observed and simulated values ranged from 0.4 to 4.2% for the calibration period, and 0.4 to 6.7% for the validation period. The geometric mean of simulated fecal coliform concentrations at the outlet of the watershed was 10% lower than that of observed values for the calibration period. HSPF moderately under-predicted the geometric mean concentration by 16.4% for one sub-watershed and slightly over-predicted by 7.3% for another. Observed fecal coliform concentrations were compared with the range defined by the minimum and maximum simulated concentrations occurring within a 3-day window centered on the day the water sample was collected. Over 42% of grab sample data collected at the three monitoring sites in the watershed fell within the max–min range of simulated concentrations over the 3-days window for the calibration period. For all monitoring sites, 39.5% of the total samples taken during the validation period fell in the range of simulated concentrations over the 3-day window period. Results presented in this study demonstrate that HSPF reasonably represents the hydrology and water quality of an urbanizing watershed and that it could be utilized as a planning tool for future assessment of land use impacts on fecal coliform on in-stream concentrations.

Comparison of HSPF and SWAT models performance for runoff and sediment yield prediction.

A watershed model can be used to better understand the relationship between land use activities and hydrologic/water quality processes that occur within a watershed. The physically based, distributed parameter model (SWAT) and a conceptual, lumped parameter model (HSPF), were selected and their performance were compared in simulating runoff and sediment yields from the Polecat Creek watershed in Virginia, which is 12,048 ha in size. A monitoring project was conducted in Polecat Creek watershed during the period of October 1994 to June 2000. The observed data (stream flow and sediment yield) from the monitoring project was used in the calibration/validations of the models. The period of September 1996 to June 2000 was used for the calibration and October 1994 to December 1995 was used for the validation of the models. The outputs from the models were compared to the observed data at several sub-watershed outlets and at the watershed outlet of the Polecat Creek watershed. The results indicated that both models were generally able to simulate stream flow and sediment yields well during both the calibration/validation periods. For annual and monthly loads, HSPF simulated hydrologic and sediment yield more accurately than SWAT at all monitoring sites within the watershed. The results of this study indicate that both the SWAT and HSPF watershed models performed sufficiently well in the simulation of stream flow and sediment yield with HSPF performing moderately better than SWAT for simulation time-steps greater than a month.

Stream discharge measurement using a large-scale particle image velocimetry (LSPIV) prototype

New technologies have been developed for open-channel discharge measurement due to concerns about costs, accuracy, and safety of traditional methods. One emerging technology is large-scale particle image velocimetry (LSPIV). LSPIV is capable of measuring surface velocity by analyzing recorded images of particles added to the stream surface. LSPIV has several advantages over conventional measurement techniques: LSPIV is safer, potentially automated, and produces real-time measurements. Therefore, the goal of this study was to evaluate the accuracy and feasibility of using LSPIV to measure instantaneous discharge in low-order streams. The specific objectives were: (1) to determine optimum operating parameters for applying LSPIV under various conditions, (2) to design, develop, and test a prototype under controlled laboratory conditions, and (3) to develop and test the field equipment for a variety of stream flow conditions. The laboratory experiment results indicated that LSPIV accuracy was influenced by camera angle, surface disturbances (Froude number), and flow tracer concentration. Under field conditions, the prototype acquired consistent images and performed image processing using accepted input parameters. The accuracy of LSPIV for use in field applications was evaluated using a permanent weir. Overall, 18 discharge measurements were taken with each measuring device. The LSPIV prototype was accurate, with a mean error of -1.7%, compared to the weir measurements. The root mean square error (RMSE) was similar for LSPIV and current meter discharge measurements with the area-velocity method when compared to the weir. Finally, the LSPIV discharge measurements had an uncertainty of approximately ±14% (at a 95% confidence level). Therefore, LSPIV showed the potential to become competitive with conventional discharge measurement techniques.

“Aménagement en courbes de niveau,” Increasing Rainfall Capture, Storage, and Drainage in Soils of Mali

Food security is a concern in many parts of the tropics, but it is an acute problem in a band of countries bordering the Sahara desert on the south-Sub-Saharan Africa. Crop productivity and production, stability, and resilience to adverse events seem to be diminishing with time. Low productivity is related to both adverse soil conditions and insufficient rainfall amounts and distribution. Portions of the region receive substantial amounts of rainfall, yet much is lost during intense storms. A rainfall capturing technology “Aménagement en courbes de niveau” (ACN), a variant of closely spaced, narrow-base terraces, has been developed in Mali and has proven beneficial in several West African countries. A field where ACN had been installed was instrumented to quantify the effects of ACN on soil/water availability. Capacitance probes were installed to 160 cm so that soil moisture measurements could easily be taken two to three times a week during 2 years—2003 and 2004. Soil moisture profiles indicated that substantially more water was retained in soils where the ACN technology was installed than where it was not present. The ACN technology led to increased soil moisture during the first month of rains. However, the differences in soil moisture were greatest at the end of the rainy season when soil moisture of the subsoil was much greater where the ACN technology had been implemented. Moisture contents were greater in the soil profile 80–160 cm with values ranging 0.18–.21 cm3 cm−3 compared to 0.15 in the No-ACN plots.

TMDL Modeling of Fecal Coliform Bacteria with HSPF

Fecal coliform TMDLs were developed for nine watersheds in Virginia using the HSPF model. The primary HSPF algorithms used to simulate FC loading and fate in the models are described in detail. Parameter values are summarized for all HSPF parameters related to FC simulation, as well as source data used external to the model for developing input loads from the various individual FC sources. Although there are many areas of uncertainty in modeling fecal coliform, a scientific approach was used in the evaluation of sources, the representation of the sources, and the evaluation of parameters used to simulate fecal coliform fate and transport with the HSPF model for nine sub-watersheds. The similarity of source reductions called for in each of the nine TMDLs support recommendations for the regional application of key results from TMDL studies to watersheds with similar sources and for the use of adaptive implementation as presented in a recent National Research Council report to Congress assessing the scientific basis of TMDLs (NRC, 2001).

ASTOCHASTIC MODEL FOR SOLUTE TRANSPORT IN MACROPOROUS SOILS

A stochastic, physically based, finite element model for simulating flow and solute transport in soils with macropores (MICMAC) was developed. The MICMAC model simulates preferential movement of water and solutes using a cylindrical macropore located in the center of a soil column. MICMAC uses Monte Carlo simulation to represent the stochastic processes inherent to the soil-water system. The model simulates a field as a collection of non-interacting soil columns. The random soil properties are assumed to be stationary in the horizontal direction, and ergodic over the field. A routine for the generation of correlated, non-normal random variates was developed for MICMAC’s stochastic component. The model was applied to fields located in Nomini Creek Watershed, Virginia. Extensive field data were collected in fields that use either conventional or no-tillage for the evaluation of the MICMAC model. The field application suggested that the model underestimated the fast leaching of water and solutes from the root zone. However, the computed results were substantially better than the results obtained when no preferential flow component was included in the model.