We present the results for the nonlinear three-dimensional simulations of the patch structuring with two primary sources of the instabilities, the gradient drift instability (GDI) and velocity-shear-driven or the Kelvin-Helmholtz (KH) instability. These primary instabilities are combined to account for the large variability of the statistical and spectral characteristics of the satellite data by Basu et al. (1988, 1990). The interaction of the velocity-shear-driven instability with the GDI and the effect of these two dominant instabilities on mesoscale structuring have been investigated. We demonstrate that the GDI induces strong anisotropy on the density fluctuation spectra and accelerates the inverse energy cascade. The inclusion of the primary KH instability with strong shear results in production of small-scale turbulence, creates a cascade toward the smaller scales, and appears to be the dominant mechanism for isotropization of the density fluctuation spectra in the noon-midnight and dawn-dusk directions. The transition to small-scale turbulence, which occurred in our simulations of the patch structuring by multiple drives, has been demonstrated with turbulence statistics.