Model mode-coupling equations for the resistive drift-wave instability are derived and numerically solved to study the properties of turbulence near a plasma edge. The wavenumber spectrum of the turbulence is found to exhibit an inverse cascade to form an isotropic, two-dimensional Kolmogorov spectrum, ${k}^{\ensuremath{-}3}$, in the large-wave-number regime. The turbulence has a broad frequency spectrum with a large saturation level and produces Bohm-type particle diffusion.