DRAINMOD APPLICATION ABE 527 Computer Models in Environmental and Natural Resources

Review drainage design… soil water characteristic… hourly rainfall, daily max & min temperature relative yield input data set Note: A DRAINMOD hydrology simulation can be run without specifying a relative yield input data set.

Objectives After this lecture, you should get familiar with DRAINMOD application as for: How to input your own data to DRAINMOD required format; What to consider for calibration purpose; and How to use the model to predict subsurface drain flow, water table depth, and crop yield. for different drain spacings.

Soil:Clermont silt loam soil Slope:<1%; and land- leveled after drain installation Area:6.2 ha Southeast Purdue Agriculture Center Drainage Field (SEPAC) Monitoring : Subsurface drain flow Water quality samples

- Hourly rainfall - Daily maximum and minimum temperatures (measured on site or from nearby stations) Model Inputs

- Hourly rainfall - Daily maximum and minimum temperatures Model Inputs

- Drainage design parameters Model Inputs Drain spacing, L5 m10 m20 m40 m Drain depth, b75 cm Effective radius, r e 1.1 cm Distance from surface to restricting layer, h 120 cm Maximum surface storage, S m 1.0 cm Note: parameter to be calibrated— Surface micro storage S 1

- Soil properties: soil water characteristic, saturated hydraulic conductivity Model Inputs cont. Note: parameters to be calibrated— lateral Ksat; volumetric moisture at 0 cm tension; and the vertical hydraulic conductivity of the restrictive layer

- Crop parameters Model Inputs cont. MonthDayRoot depth (cm) Time distributions of effective rooting depths

Calibration Procedure 1. Choose most uncertain parameters to be calibrated Range of parameter needed to be calibrated Volumetric soil moisture at 0 m tension (cm 3 /cm 3 ) LayerRange Layer 1 (0-25 cm) Layer 2 (25-30 cm) Layer 3 ( cm) Horizontal Ksat (cm/hr) Layer 1 (0-25 cm) Layer 2 (25-30 cm) Layer 3 ( cm) Vertical Ksat of restrictive layer (cm/hr) Surface Micro storage S 1 (cm)0.3-1

Calibration Procedure cont. 2. Choose plot and year to be calibrated Year Drain flow ratio W20/E20W10/E10W5/E West block and east block need to be calibrated separately. --W20 and E20 in were chosen.

Range of parameter needed to be calibrated Volumetric soil moisture at 0 m tension (cm 3 /cm 3 ) LayerRange Layer 1 (0-25 cm) Layer 2 (25-30 cm) Layer 3 ( cm) Horizontal Ksat (cm/hr) Layer 1 (0-25 cm) Layer 2 (25-30 cm) Layer 3 ( cm) Vertical Ksat of restrictive layer (cm/hr) Surface Micro storage (cm)0.3-1

Calibration Objective Functions (1) Nash-Sutcliffe efficiency: (2) Absolute percent error: Aggregated function, combining (1) and (2):

Automatic Calibration Parameter values against model Nash-Sutcliffe efficiencies

Identify Optimum Parameter Set

Representative observed and predicted drain flow graph

Observed and predicted water table graph

Predicted and observed relative yields

SUMMARY  Nash-Sutcliffe efficiency (EF) for daily drain flow ranging from to 0.81;  EF for water table depth from to 0.9;  Statistical tests of EF indicating insignificant difference among the three drain spacings;  Both observed and predicted relative yields indicating yields decreasing with the increase of drain spacing;  Average percent errors ranging from 1.3 to 9.7% for corn yield and from -0.8 to 10.3% for soybean yield.