2011 Annual Report
1a.Objectives (from AD-416)
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.
1b.Approach (from AD-416)
• 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.
The current version of the hydrological model, DRAINMOD NII, was modified to simulate automatic controlled drainage (ACD) and automatic controlled drainage/ sub-irrigation (ACD-SI) systems. The model simulates the automatic system according to field water table depth (WTD) signals. In this approach, the model checks the predicted water table depth on a daily basis to be within a predefined desired range. The upper boundary of the desired range is the shallowest level of the water table (WT) after which the plant will have yield losses due to excess water stresses, and the lower boundary is the deepest level of WT after which the plant will have yield losses due to deficit stresses. The upper limit was chosen to be 30cm from the soil surface and the lower limit equals three times the maximum root depth during the growing season. DRAINMOD automated the drainage system by increasing the depth of the control structure (weir) when the WT is shallower than the upper limit to drain the excessive water and switching to subirrigation mode when the WT is deeper than the lower limit. The modified model was applied for two U.S. datasets from North Carolina and Illinois to simulate the drainage systems for five drainage managements: Conventional Drainage (CVD), Fixed Controlled Drainage (FCD), Sub-Irrigation (SI), Automatic Controlled Drainage (ACD), and Automatic Controlled Drainage Sub-Irrigation (ACD-SI) systems. We conducted the simulations for 12 drainage intensities (i.e., different combinations of drain depths and drain spacings). The results showed that the model has similar performances for the FCD and ACD systems. The ACD-SI system significantly improved the model predictions compared to the other drainage systems. The ranges of reductions in drainage losses were increased from (25%-41%), (27%-45%) for the FCD and ACD systems to (36%-51%), (47%-62%) for the ACD-SI system for the NC, IL datasets respectively. Also, the ranges of reductions in nitrogen losses in drainage water for the two simulated datasets were increased from (6%-57%), (21%-35%) for the FCD and ACD systems to (21%-69%), (36%-52%) for the ACD-SI system. The ACD-SI system has a great economic impact since it increases the relative crop yield and reduces the amount of water required for subirrigation compared to the traditional sub-irrigation system. The results of this study are very beneficial in design and operation of drainage systems. Monitoring activities were done by e-mail exchanges between the Sugarcane Research Unit's Authorized Departmental Officer's Representative (ADODR) and the Sponsor's Designated Representative.