Multimegaton scale in under-ice and underwater detectors of atmospheric neutrinos with a few GeV energy threshold (PINGU, ORCA) open up new possibilities in the determination of neutrino properties, and in particular the neutrino mass hierarchy. With a dense array of optical modules it will be possible to determine the inelasticity, y, of the charged current nu(mu) events in addition to the neutrino energy E-nu and the muon zenith angle theta(mu). The discovery potential of the detectors will substantially increase with the measurement of y. It will enable (i) a partial separation of the neutrino and antineutrino signals, (ii) a better reconstruction of the neutrino direction, (iii) the reduction of the neutrino parameters degeneracy, (iv) a better control of systematic uncertainties, and (v) a better identification of the nu(mu) events. It will improve the sensitivity to the CP-violation phase. The three-dimensional (E-nu, theta(mu), y), nu(mu) oscillograms with the kinematical as well as the experimental smearing are computed. We present the asymmetry distributions in the E-nu - theta(mu) plane for different intervals of y and study their properties. We show that the inelasticity information reduces the effect of degeneracy of parameters by 30%. With the inelasticity, the total significance of establishing mass hierarchy may increase by (20-50)%, thus effectively increasing the volume of the detector by a factor of 1.5-2.