Watershed Management Assessment Through Modeling:

SALT and CEAP Dr. Claire Baffaut

Water Quality Short Course

Boone County Extension Office

April 12, 2007

Watershed Assessment

• Inventory potential sources of pollution

• Determine pollution pathways

• Link the characteristics of the watershed with the water quality in its streams, lakes, and groundwater.

• Predict water quality when land use or land management change in the watershed.

Water Quality Data

Why don’t we just use measured data?

•Data are limited in frequency and duration.

•Pollutant concentrations are first and foremost dependent on weather.

•Measured concentrations or flow can be the result of several factors.

Example: Atrazine in Goodwater Creek

Possible ReasonsPercent Crop Area in No-Till

and Conservation TillagePercent Area Protected

by Waterways

Estimated average corn planting dates from 1992 to 2004.

0

20

40

60

80

100

120

140

160

180

19921994

19961998

20002002

2004

year

Julia

n da

y fo

r av

erag

e co

rn

plan

ting

Modeling can help find what is responsible for measured flows or

concentrations.

What is a Model?

• A mathematical equation is a model– The USLE equation (for soil loss estimation)

• Computer simulation model for watershed assessment: – A combination of equations that represent the

different processes in the watershed.– These equations link the topography, the soil

characteristics, the management, and the weather to flow and water quality.

Field Level: EPIC Environmental Policy Integrated Climate model

Watershed Level: APEX or SWAT

• Ponds and reservoirs• Streams and waterways• Subsurface and groundwater flow

What can we do with modeling?

Watershed scale

Farm scale

Field scale

Stream and river issues

How dirty is it ?

Where do water and pollutants come from ?

How much water is there ?

What is affecting flow and pollutant concentrations ?

Farm issues

• What is the best way to distribute the manure between different fields to minimize environmental impacts?

• How can we maximize profits while minimizing environmental impacts?

Field problems

• How much soil is lost from the field?

• How long will it take to loose productivity?

• How much phosphorus is leaving the field?

• How much carbon can the soil sequester?

• How much nutrient is lost to percolation?

What if scenarios

What happens if…

– a toxic substance leeks out of an industrial site.

– the number of CAFO’s in an area increases.

– agricultural land becomes residential or industrial.

– better management practices are implemented.

Data requirements

USER INPUT

Topographic data(GIS)

Weather data(National Weather Service)

Soil and Land use data(GIS)

Management data(??)

DATABASES

Weather database

Fertilizer database

Tillage database

Crop database

Management Data

• Census data.– Some data on total fertilizer amounts, or crops

being grown. Usually on a county basis.– Little information on tillage practices, timing

of operations, rotations implemented …

• Panel consensus. – Form of interview where the panel members

have to agree that a practice is representative.

Garbage in Garbage out

MODELMODELGarbage Garbage

In Color, still

MODELMODELGarbage Garbage

Even if animated, it is still

MODELMODELGarbage in

Garbage out

Model Calibration

To be accepted, a model needs to be calibrated

• Calibration: Adjusting the parameters of the model to have good agreement between model predictions and measured data over a period of time.

• Validation: Verifying that the model results and the measured data match over a different period of time.

Examples of answers provided by models

6 Selected AgNPS-SALT ProjectsLong

Branch

Upper and Lower Maries River

Jenkins Basin

Flat Creek

Miami Creek

BMPs Fully Simulated With SWAT

• Erosion control through tillage and terraces

• Erosion control through grade stabilization structures (ponds)

• Woodland protection (livestock exclusion)

• Grassland establishment / improvement

• Pasture management

• Poultry litter export

Predicted Change in Stream Loads after Implementation of the Project

Watershed SedimentTotal

NitrogenTotal

Phosphorus

Miami Creek -8 % -11 % -29 %

Long Branch -2 % -8 % -11 %

Flat Creek -17 % -7 % -14 %

Maries River -22 % -20 % -19 %

Jenkins Basin -11 % -8 % -17 %

Conclusion: Why Model?

• Link watershed characteristics, watershed management, and water quality. That allows to:– Understand the link.– Focus the action where it is most useful.

• Predict the consequences of “what if” scenarios without having to try them.

• BUT because garbage in causes garbage out, there is a need to understand the model and calibration process:– Development of specific databases for Missouri.– Training.