HYDROLOGICAL SIMULATION PROGRAM-FORTRAN (HSPF)

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Methods

Two small, upland watersheds with previously developed bacterial impairment TMDLs were identified. Both watersheds required that low-flow DD modeling approaches be used to develop the TMDL. Using the previously developed TMDL modeling files as a foundation, low-flow DD modeling approaches were applied to both watersheds to compare their effects on simulated in-stream fecal coliform concentrations. Livestock DD sources of bacteria were incrementally reduced using each treatment (described in the following sections) and the results were compared statistically.

Low-Flow Direct Deposit Modeling Approaches

The user control input (UCI) files for both watersheds were calibrated for hydrology during the TMDL study. The calibrated hydrology parameters remained unchanged as each combination of low-flow DD modeling approaches (“treatments”) was implemented. Fecal coliform loading parameters were based accepted TMDL study protocols (Benham et al., 2004, Benham et al., 2006). Estimates of die-off rates and fecal coliform concentrations present in subsurface flows (interflow or groundwater) were based on values commonly used for bacterial impairment TMDLs in Virginia. Neither watershed was calibrated to observed water quality data to avoid biasing the model toward any particular treatment. The evaluated low-flow modeling approaches address low-flow issues by either modifying the DD bacteria load entering the stream or by modifying the simulated hydrology by retaining water volume within the reach during low-flow conditions. The following sections provide a detailed description of each treatment.

Control

The Control treatment (Appendix A, page 72) was simulated using the UCI files calibrated for hydrology with bacteria loading rates specific to each watershed. The Control simulated DD loads input to the reach without correction for low-flow conditions. This provided the foundation for each treatment tested, each of which modified the ‘Control’ UCI file.

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Flow Stagnation

The flow stagnation (FS) method is based on the reasoning that during periods of low flow, water tends to collect in pools and discharge (stream flow) ceases. The FS method modifies the hydrology by simulating zero discharge and retaining water volume within the reach. The FS method stops the transport of bacteria to downstream reaches during low-flow conditions, thus minimizing the occurrence of unrealistically high simulated instream fecal coliform concentrations. Simulation of fecal coliform loading to the stream continues in the reach, but bacteria are transported downstream only when sufficient water volume exists to produce discharge from the reach. By modifying the hydrology, the FS method affects the simulated in-stream fecal coliform concentration regardless of the bacteria source category (i.e., livestock, wildlife, and human). The FS method was implemented in both the Beaver Creek (Benham et al., 2005b) and Old Womans Creek (Benham et al., 2006b) TMDLs. The FS method is applied through modification of the FTABLEs that define a given stream reach. The FTABLE for each reach is modified by adding an additional line entry (see Table 2.1) that corresponds to the desired flow stagnation depth. In this study 0.0122 m (0.48 in) was used as the flow stagnation depth within each reach. Below this depth, there is no discharge from the reach. Although no discharge is simulated, there is water in the reach and thus the FTABLE contains entries for volume and surface area.

ABSTRACT
ACKNOWLEDGEMENTS 
TABLE OF CONTENTS
LIST OF FIGURES 
LIST OF TABLES
1 LITERATURE REVIEW
1.1 BACTERIA AND INDICATOR ORGANISMS 
1.2 WATER QUALITY STANDARDS 
1.2.1 Virginia Water Quality Standards
1.3 HYDROLOGICAL SIMULATION PROGRAM-FORTRAN (HSPF)
1.3.1 HSPF Hydrology
1.3.2 HSPF Water Quality
1.3.3 Evaluation Summary of HSPF
1.4 MOTIVATION FOR RESEARCH
1.5 GOAL AND OBJECTIVES 
2 METHODS
2.1 LOW-FLOW DIRECT DEPOSIT MODELING APPROACHES 
2.1.1 Control
2.1.2 Flow Stagnation
2.1.3 Direct Deposit Stage Cut-off
2.1.4 Surface Area
2.1.5 Stage Cut-off + Flow Stagnation
2.1.6 Surface Area + Flow Stagnation
2.1.7 Surface Area + Stage Cut-off
2.1.8 Stage Cut-off + Surface Area + Flow Stagnation
2.2 STUDY WATERSHEDS
2.2.1 Old Womans Creek
2.2.2 Long Glade Run
2.3 MODEL INPUT REQUIREMENTS
2.3.1 Hydraulic Function Tables (FTABLEs)
2.3.2 Climate Data
2.3.3 Bacteria Loading Rates
2.4 DIRECT DEPOSIT ALLOCATION LEVELS 
2.5 MONTE CARLO SIMULATIONS 
2.6 MODEL OUTPUT
2.6.1 Response Variables
2.7 STATISTICAL ANALYSIS
2.7.1 Statistical tests
3 RESULTS
3.1 OLD WOMANS CREEK 
3.1.1 Instantaneous Violation Rate.
3.1.2 Geometric Mean Violation Rate
3.1.3 Maximum Fecal Coliform Concentration
3.2 LONG GLADE RUN 
3.2.1 Instantaneous Violation Rate
3.2.2 Geometric Mean Violation Rate
3.2.3 Maximum Fecal Coliform Concentration
4 DISCUSSION 
4.1 OLD WOMANS CREEK 
4.1.1 Flow Stagnation
4.1.2 Direct Deposit Stage Cut-off
4.1.3 Surface Area
4.1.4 Combination treatments
4.2 LONG GLADE RUN 
5 SUMMARY AND CONCLUSIONS.
5.1 SUMMARY 
5.2 CONCLUSIONS 
6 REFERENCES
APPENDIX A USER CONTROL INPUT FILES 

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