LEACHM reflecting transportation and transformation processes that are involved in land disposal of sewage effluent
Based on these factors, LEACHM was selected to estimate nitrate nitrogen leaching from land surface to groundwater to make longer-term management decisions at a LTS.
The 4 models are: LEACHM (Hutson and Wagenet 1992), a deterministic, process-based model that simulates water transport using Richards' equation; GLEAMS (Leonard et al.
In LEACHM simulations, degradation rate constants and associated half-life values for each pesticide were taken from the literature data (Wauchope et al.
A consistent trend was that LEACHM under-predicted the soil water contents below 0.
With the exception of LEACHM, all 4 models gave a good description of measured bromide values at 3 depths, except during the first month, when LEACHM and GLEAMS predictions were nearly 8-9 times higher than those observed in the suction cups at 0.
1998), were much more satisfying for both study sites than those obtained with GLEAMS and LEACHM models.
For example, Webb and Lilburne (1999) compared the DRASTIC index with a pesticide leaching index generated using LEACHM model simulations against measured values for metalaxyl and MCPA in the Canterbury Plains of New Zealand's South Island.
Simulations of water, bromide, and pesticide movement were carried out using GLEAMS, LEACHM, HYDRUS-2D, and SPASMO.
LEACHM (LEACHP is the pesticide module of the LEACHM model) is a mechanistically based model of water and solute movement and pesticide chemistry (Hutson and Wagenet 1995).
VARLEACH is a simple model, whereas LEACHM
represents more comprehensive and complex models (Table 1).
The estimates from LEACHM
were also compared with estimates using the GLEAMS model.