# Presentation: 306754

## AGNPS Watershed Modeling with GIS Databases

- Las Vegas, NV
- 28 Jul - 1 Aug 2002

- Second Federal Interagency Hydrologic Modeling Conference

## AGNPS Watershed Modeling with GIS Databases

- Michael P. Finn
- E. Lynn Usery
- Douglas J. Scheidt
- Thomas Beard
- Sheila Ruhl
- Morgan Bearden
- U.S. Geological Survey
- Mid-Continent Mapping Center
- Rolla, MO

## Outline

- Introduction
- Study Areas
- GIS Databases for Parameter Extraction
- AGNPS Parameter Generation
- Creating AGNPS Input, Output, and Images
- Results

## Objectives

- Use GIS databases as input to AGNPS Pollution Model
- Demonstrate automatic extraction of input parameters
- Create a tool for generating input, executing the model, and analyzing output

## Introduction

- Agricultural NonPoint Source (AGNPS) Pollution Model – USDA lead agency
- AGNPS operates on a cell basis and is a distributed parameter, event-based model
- AGNPS requires 22 input parameters
- Elevation, land cover, and soil data served as the base of extraction for the input

## Study Areas

- Four Watersheds
- Little River, GA
- Piscola Creek, GA
- Sugar Creek, IN
- EL68D Wasteway, WA
-  Watershed Boundaries
- NAWQA Boundary
- GIS Weasel

## Georgia Watersheds

## Indiana Watershed

## Washington Watershed

## GIS Databases for Parameter Extraction

- USGS 30-m DEMs
- USGS 30-m National Land Characteristics Data
- Augmented with recent Landsat TM data
- Soil databases from USDA soil surveys
- Scanned separates, rectified, vectorized, and tagged
- Resampled the 30-m data to 60, 120, 210, 240, 480, 960, and 1920 meters
- 210-m roughly matches 10 acre grid size

## AGNPS Parameter Generation

- AGNPS Data Generator
- Input parameter generation
- Details on generation of parameters
- Extraction methods

## AGNPS Data Generator

- Created to provide interface between GIS software (Imagine) and AGNPS
- Developed interface for Imagine 8.4, running on WinNT/ 2000

## AGNPS Data Generator

## Input Parameter Generation

- 22 parameters; varying degrees of computational development
- Simple, straightforward, complex

## Input Parameter Generation

## Details on Generation of Parameters

- Cell Number
- Receiving Cell Number
- SCS Curve Number
- Uses both soil and land cover to resolve curve number

## Details on Generation of Parameters  (continued)

- Slope Shape Factor

## Details on Generation of Parameters  (continued)

- Slope Length
- A concern; max value should be 300 ft.
- Parameters 10, 11, 12, 14, 15, 16, and 17
- Uses Spatial Modeler to look up attributes from soils or land cover
- Example: p10 is Overland Manning’s Coefficient
- Parameters 13, 18, 19, 20, and 21
- Hard coded on advice from experts
- Example: p13 is Practice Factor (conservation) coded to 1 (worst case)

## Details on Generation of Parameters  (continued)

- Type of Channel
- Uses TARDEM program
- Creates a Strahler steam order

## Extraction Methods

- Used object-oriented programming and macro languages
- C/ C++ and EML
- Manipulated the raster GIS databases with Imagine
- Extracted parameters for each resolution for both boundaries using AGNPS Data Generator

## Creating AGNPS Input, Output, and Images

- Input Data File Creation
- Format generated parameters into AGNPS input file
- Use a “stacked” image file to create AGNPS data file (“.dat”)  -- ASCII

## Creating AGNPS Input, Output, and Images  (continued)

- Output Image Creation
- AGNPS Creates a nonpoint source (“.nps”) file
- ASCII File like the input; tabular/ numerical form

## Creating AGNPS Input, Output, and Images  (continued)

## Creating AGNPS Input, Output, and Images  (continued)

- Output Image Creation  (continued)
- Combined “.nps” file with Parameter 1 to create multidimensional images
- Users can graphically display AGNPS output
- Process: create image with “n” layers, fill layers with AGNPS output data, set projection and stats for image
- Multi-layered (bands) images per model event

## Creating AGNPS Input, Output, and Images  (continued)

## Creating AGNPS Input, Output, and Images  (continued)

## Creating AGNPS Input, Output, and Images  (continued)

## Creating AGNPS Input, Output, and Images  (continued)

## Results

- Collaboration continues to quantify the impact of spatial resolution on model results
- Demonstrated the use of GIS databases as sources in watershed modeling, particularly with AGNPS
- Demonstrated methods of automatic extraction of AGNPS input parameters from GIS databases
- Showed implications of results for 4 watersheds
- Demonstrated the practicality of AGNPS Data Generator as an AGNPS – GIS interface

## AGNPS Watershed Modeling with GIS Databases

- Las Vegas, NV
- 28 Jul - 1 Aug 2002

- Second Federal Interagency Hydrologic Modeling Conference