Non point source pollutant modeling
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Non-Point Source Pollutant Modeling. Analysis and Prediction David Munn. Non-Point Source Pollution. Does not come from a single source Results from pollutants being washed out of large areas during storms Difficult to model without use of GIS or current NPSP models. Goals.

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Non-Point Source Pollutant Modeling

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Non point source pollutant modeling

Non-Point Source Pollutant Modeling

Analysis and Prediction

David Munn

Non point source pollution

Non-Point Source Pollution

  • Does not come from a single source

  • Results from pollutants being washed out of large areas during storms

  • Difficult to model without use of GIS or current NPSP models



  • Predicting pollutant runoff loads

  • Defining problem areas within the Watershed

  • Determine what factors effect pollutant loading

  • Determine streams with highest impact

  • Pollutants considered:

    • BOD

    • Suspended Solids

  • Total Phosphorous

  • Total Nitrogen

Study area

Study Area

  • Brazos County

  • Buffered boundary

Process overview

Process Overview

  • Gather data

  • Data preparation

    • Reproject grids and shapefiles

    • Clip themes and set analysis extents

  • Calculate curve numbers

  • Delineate watersheds

  • Calculate pollutant contribution

  • Determine weighted accumulation

  • Analyze data

Data themes


  • DEM

    • TNRIS

  • Soil Classification


  • County Boundaries

    • ESRI, Tiger files

  • Land Use/Land Cover

    • Txdata, Provided by Dr. Olivera

  • Precipitation

    • Txdata, Annual and Monthly

  • LULC Pollutant Contribution Data

    • Cornell University Hydraulics Study



  • Reprojected grids using ArcInfo-Workstation

  • Reprojected geographic shapefiles using CRWR-Vector

  • Data Already in a Projection was reprojected using ArcCatalog

  • Final Projection: State Plane 1927

    • Central Texas, Zone 5376

    • Units = feet

Delineating watersheds


Burned in Streams

Filled Sinks

Determined Flow Direction

Determined Flow Accumulation

Defined Streams

Segmented Streams

Defined Outlets

Delineated Watersheds

Vectorized Grids

Delineating Watersheds

Curve numbers

Curve Numbers

  • Used to determine runoff

  • STATSGO data spatially documents soil types (component makeup)

  • Scripts provided by CVEN 689 Website

    • Soilgrp script – calculates % of hydrologic groups per soil type

    • cn script – creates curve numbers based on soil composition

Run off

Rainfall given per month (January)

Calculate Run-off (mm) using SCS method

Map Calculator combined formulas with rainfall and CN

Created new grid giving run-off depth per cell


Pollutant contributions

Pollutant Contributions

Q (mm)

Cell size (ft2)

Pollutant Concentration (mg/l)

= Mass (mg)

* Map Calculator

Pollutant flow accumulation

Pollutant Flow/Accumulation

  • Weighted flow accumulation

  • Executed in ArcInfo

  • Assigns weights to cells based on a Grid






  • Determine what land-uses and soil types contribute the largest amount of pollutants

  • Determine what rivers suffer the greatest impact

  • Locate areas that contribute large masses of pollutants

Land use relationships zonal summaries

Land Use Relationships (Zonal Summaries)

Soil type relationships zonal summaries

Soil Type Relationships(Zonal Summaries)

Impacted rivers

Impacted Rivers

  • Method

    • Map query

    • Changed to shapefile

  • Results too dependent on general accumulation

  • More statistical work needed

Areas of concern

Areas of Concern

* TP / TN

* BOD / SS



  • Urban areas contributed the largest mass of BOD and suspended solids per unit area

  • Agricultural areas contributed the largest mass of Nitrogen and Phosphorous / area

  • Rivers > 700,000 cell accumulation were impacted

  • Soil types differed in impact between pollutants

    • Nutrients:

      Crocket-Luling-Benchley & Zack-Zulch-Booneville

    • BOD and Suspended Solids


Future applications

Future Applications

  • Determining Pollutant Concentrations

    • Calculate run-off volume using weighted accumulation

    • Sum run-off volumes with base flows

    • Calculate in-stream concentrations

  • Better Statistical Analyis of Impacted Rivers




  • Calculating pollutant contributions

    (map calculator)

  • Floating point analysis



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