FEEDBACK CONTROLLED-DRAINAGE SUBROUTINE INCORPORATED IN DRAINMOD-N2 MODEL TO PREDICT NITRATE LOSS IN DRAINAGE WATER MANAGEMENT SYSTEM
Location: Sugarcane Research Unit
Project Number: 6410-13000-010-07
Specific Cooperative Agreement
Start Date: Apr 01, 2010
End Date: Mar 31, 2015
1) Modify the current version of DRAINMOD-N2 by incorporating program code to simulate a feedback controlled-drainage mode of automated operation for drainage water management systems using various feedback signals, such as drain outlet water level, field water table depth, rainfall amounts and/or intensity, etc.
2) Conduct verification runs with the modified model using previous input data sets from the NCSU and ARS investigators, plus one or more Midwestern data sets, to insure the model runs remain stable and that simulated hydrologic functions are not changed by the incorporated program code when conventional subsurface drainage, fixed-weir controlled- drainage, and subirrigation modes are simulated.
3) Conduct preliminary runs with the modified model to simulate Nitrate transport (loss) in the controlled-drainage effluent when using input data sets available from the NCSU and ARS investigators, or other data sets that may be available, for comparison of simulated and field measured Nitrate loss in controlled-drainage.
• The ARS investigator will provide Fortran program code changes made in DRAINMOD ver. 3 (that did not include nutrient transport, only hydrology) during the late 1980’s to simulate automatic feedback-control adjustments of the outlet weir elevation, or desired controlled water level, at the subsurface drainpipe outlet in the controlled-drainage and subirrigation modes for automated water table depth control with respect to normal increases in crop root-zone depth during the growing season, and major changes in water table depth due to rainfall or drought.
• The NSCU investigators will employ a Research Associate to assist in making the required program code changes/inserts in DRAINMOD-N2 and to conduct the verification and specified preliminary runs under direction of NCSU investigators.
Note: The modified model should retain the procedure (routine) currently in DRAINMOD-N2 to change elevation (depth) of the outlet weir a specified distance via a step-wise adjustment on Julian date(s) listed in the input data set.
• The ARS investigator will periodically review simulation results with NCSU investigators and Research Associate to ensure the automated operation is properly simulated with the modified model, and to make suggested changes as/if needed.
• Upon completion of the above steps, a technical paper on the modified model will be prepared by the NCSU and ARS investigators for publication, and the paper should outline the additional steps needed to validate/calibrate the modified model for major geographic regions to account for differences in topography, climate, soils, crops, cultural and fertility practices, and water management system designs.