The equilibrium interaction between the processes of charge formation on the surface of a nanochannel and ionic distribution within the confined electrolyte is studied for situations where electric-double-layer (EDL) are of size comparable to the nanochannel cross-dimension and the mean-field surface electrostatic potential is comparable to or larger than the thermal energy per unit charge of an ion. The effects of channel size, pH, ionic composition and the compact region of the electric double layer are investigated. The results can be used for understanding electrokinetic phenomena involving current conduction and fluid flow in nanochannels, as demonstrated through a comparison of the theoretical results with measured electrical conductance data.