Using AGNPS

Credits:

These materials were adapted from Dean Larry Huggins ASM 521 class.

AGNPS

AGricultural Non-Point Source (AGNPS) is a distributed parameter model developed by USDA, Agricultural Research Service (ARS) scientists and engineers. It predicts soil erosion and nutrient transport/loadings from agricultural watersheds for real or hypothetical storms i.e., it's an event-based model. Its distributed model design is achieved by subdividing a watershed to be simulated into a grid of square elemental areas, assumed to have uniform physical characteristics, and then applying three lumped parameter models to each element:

Erosion modeling is based on the USLE applied on a storm basis; thus, it uses an EI-index, but for single storm events.
Its hydrology is based on the Soil Conservation Service Curve Number technique.
AGNPS uses another ARS developed model named CREAMS to predict nutrient/pesticide and soil particle size generation, transport and interaction.

Outflows from one element become inputs to adjacent ones. Thus, AGNPS integrates lumped model predictions for each element's behavior into a distributed watershed simulation.

Each AGNPS elemental area, typically about 100 m square, requires 22 parameters (coefficients) to describe its antecedent conditions, physical characteristics (e.g. soil type and slope steepness), management practices and rainfall. To predict NPS pollution, the USLE, SCS Curve No. hydrology, and CREAMS relationships are computed for each element as a function of time. Nineteen output parameters are computed, as function of time, for each watershed element.

AGNPS-GRASS developers recommend its use on watersheds up to 20,000 ha. (80 sq.mi.) in size.

To learn how to use AGNPS, proceed to the Beginner's Tutorial. See more about the developers.