Non-Point Source Pollution Modeling in the Red River Watershed

Non-Point Source Pollution Modeling in the Red River Basin

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Sixteenth Tennessee Water Resources Symposium

Acknowlegements

This project is funded by the Tennessee Department of Environment & Conservation (TDEC). The Environmental Program Manager for TDEC is Dr. Sherry Wang, Water Pollution Control Division. The Principal Investigator for Austin Peay State University (APSU) is Dr. Gregory S. Ridenour, Geosciences Program. Technical and administrative assistance have been provided by Mr. Mike Wilson, GIS Manager, Mr. Ken Kirk, GIS Analyst, and Ms. Amy Johnson, Technical Clerk, all from the APSU GIS Center. Additional advice has come from Mr. Phil Blondin, GIS Manager, Montgomery County Planning Commission. The APSU student workers are Robb Hodges (lead student and webmaster for this site), Jackie Overholser, Matt Norfleet, and Jeff Pancirov.

Disclaimer

The reproducibility of APSU’s land cover map is currently being conducted by another group of student workers. A confusion (error) matrix will be assembled that compares the current map with sample areas reclassified by the second group. Accuracy of the map will be quantified as percent agreement and the kappa index.

Objectives

First, to model pollutant loading in the Red River Watershed with PLOAD

using standard land cover data retrieved from EPA's BASINS site and pollutant loading coefficients compiled from PLOAD's documentation and Internet sources
using more detailed land cover maps we developed from air photo interpretation and some of the pollutant loading coefficients calculated from TVA's IPSI (Integrated Pollutant Source Identification) model
considering the impact of BMP’s in livestock areas based on Walker's (2005) approach for reducing non-point phosphorous losses to improve water quality by improving potassium management.

Second, to map existing or to create new spatial databases for incorporation into future, more sophisticated pollutant loading models that include

water quality measurements collected by APSU’s Biology Department (under the supervision of Dr. Steve Hamilton) for model calibration and verification
riparian buffer classification (based on TVA's matrix employed in their IPSI-based studies) assessed by aerial photography and compared with field studies by the Red River Watershed Association (RRWA), whose workers included APSU students working on this pollutant loading model
karst topography (sinkhole distribution and volume)

The PLOAD Model

EPA's BASINS (Better Assessment Science Integrating Point and Nonpoint Sources) software integrates a geographic information system (ArcView GIS), national watershed data, and state-of-the-art environmental assessment and modeling tools into one convenient package. The heart of BASINS is its suite of interrelated components essential for performing watershed and water quality analysis, including 1) national databases, 2) assessment tools for evaluating water quality and point source loadings at a variety of scales, 3) utilities for local data import, land use and DEM reclassification, watershed delineation, and management of water quality observation data, 4) watershed and water quality models, and 5) post-processing output tools for interpreting model results.

The model we are using is PLOAD, which estimates nonpoint sources (NPS) of pollution on an annual average basis for any user-specified pollutant. PLOAD was designed to be a generic, analytical tool for end users that it can be used as a screening tool in a wide range of applications including NPDES stormwater permitting, watershed management, or reservoir protection projects. The application's organization and structure facilitates modification and customization. The PLOAD application requires pre-processed GIS and tabular input data for land use, watersheds, site and area data, pollutant loading rates, impervious terrain factors, and, optionally, pollutant reduction BMP data and/or point source facility locations and loads.

The user may calculate the NPS loads using either EPA's Simple Method, endorsed by EPA for screening NPDES stormwater projects and applicable to watersheds with areas less than one square mile, or the the export coefficient approach, which is appropriate for our study area. Loads (L_p) for each pollutant are calculated as

L_P = Σ_U(L_U × A_U)

where L_PU = pollutant loading rate for land use type u, lbs/acre/year
A_U = area of land use type u, lbs/acre

Best management practices (BMPs), which serve to reduce NPS loads, may also be included in the model to recalculate pollutant loads by determining the percent of the watershed area serviced by BMPs in decimal percent (%AS_BMP) as

%AS_BMP = AS_BMP/A_B

where AS_BMP = area serviced by the BMP, acres
A_B = area of watershed, acres,

the pollutant loads (lbs) remaining after removal by each BMP (L_BMP)

L_BMP = (L_P × %AS_BMP) × [1 – %EFF_BMP/100]

where L_P = Raw watershed load, lbs
%EFF = Percent load reduction of BMP

and the total pollutant loads accounting for BMPs (L), a cumulative total of areas which are and are not influenced by BMPs:

L = ( Σ_BMP(L_BMP)) + L_P × (A_B – ( Σ_AS(AS_BMP))

Finally, there are several product alternatives that may be specified to show the NPS pollution results as maps or tabular lists.

Data

Spatial. A rather generalized land cover map accompanies the download of BASINS from the US EPA's website. We have provided additional detail by utilizing aerial photography to differentiate the Agriculture areas into cow pastures, horse pastures, row crops, tobacco, grasslands, pastures classified from low resolution aerials, poultry, and swine. Additionally, these same subcategories of Agriculture were reclassified from areas identified as Forested in the BASINS land cover. Land cover adjacent to streams was also classified using TVA’s Riparian Buffer Classification Matrix, whose categories (adequate, marginal, or inadequate at removing pollutants) are based on vegetation type, width, and percent coverage.

Attribute. The event mean concentration (EMC) table is used to calculate the pollutant loads for urban land use types. The impervious factor table is used to calculate the EMC runoff coefficient. The BMP table contains percentage removal efficiency multipliers for each BMP type that are used to calculate pollutant load reductions.

Image Resolution. Three types of aerial photography were used in this project. In Montgomery County, 6-inch resolution was used for the urban areas. For the remainder of the county, 12-inch resolution was used. The remaining counties in Tennessee, as well as the counties in Kentucky, were digitized using 1 meter resolution aerial photography. All of the aerials used were taken in 2004 and were available in color. The high resolution aerial photography taken in Montgomery County was provided by Homeland Security funding. These images were taken in the month of December to limit the amount of deciduous canopy that may obscure the view of the landscape.

September, 9th 2005

Objectives

The PLOAD Model

Data

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