| Accurate hydrologic models are needed to aid engineers and researchers design, install and evaluate efficient and cost-effective agricultural water management systems to reduce risks associated with food production, and to reduce soil erosion and water pollution. One model used for the alluvial soils of Louisiana is DRAINMOD. This model does not accurately predict infiltration and runoff for the crusting-prone alluvial soils of Louisiana. The main goal of this study was to modify the current DRAINMOD model to incorporate the effects of rainfall intensity and deep chiseling to improve its estimation of infiltration and surface runoff. The second goal was to use information gained from the modified DRAINMOD model to assess how long farmers and environmentalists benefit from a particular deep chiseling operation and determine optimum deep chiseling frequency for given climatic conditions. A methodology for using a five-minute rainfall time increment subroutine within DRAINMOD was developed. Field experiments yielded an initial vertical saturated hydraulic conductivity of 2.0 cm/hr, a final vertical saturated hydraulic conductivity of 0.50 cm/hr and exponent of 0.03 cm-1 for model calibration. Deep chiseling modifications resulted in the DRAINMOD-STMAX, DRAINMOD-Ks and the combined DRAINMOD-Ks-STMAX models. DRAINMOD-STMAX, DRAINMOD-K s and DRAINMOD-Ks-STMAX model improved surface runoff prediction by 57%, 73%, and 82% respectively in 1995/96 season and by 27%, 45%, and 62% respectively in 1996/7 season. Using DRAINMOD-K s STMAX model, deep chiseling a Commerce silt loam soil increased infiltration by 9.4% and reduced runoff by 19.7% in 1995/96 season and by 5.7% and 19.2% respectively in 1996/97 season. All benefits resulting from deep chiseling were lost after 115 cm of rainfall since deep chiseling. Farmers should deep chisel once every year when annual rainfall is greater than 100 cm and once every two to three years when annual rainfall is less than 100 cm. Sixty percent or more of the maximum deep chiseling benefits had been lost by planting time; therefore, farmers need to deep chisel their fields just before planting. Further work is needed in the field to determine other factors affecting variation of Ks, to validate the DRAINMOD-STMAX, DRAINMOD-Ks and DRAINMOD-Ks-STMAX models, and to incorporate rainfall intensity subroutine. |
