Mine backfilling with power plant ash is gaining increasing attention from the power and mining industries for its bulk disposal. In the USA and other countries, mine backfilling with ash is considered as a viable option for stability improvement, subsidence control, and mine site rehabilitation. This paper presents the results of rheological studies conducted on fly ash and mixtures of fly ash and bottom ash samples collected from NTPC Talcher, Odisha. The complex hydro-mixture slurry indicated non-Newtonian pseudo-plastic behavior in the mass concentration range of 60-67.5%. A non-Newtonian power law head loss model was used to evaluate the head loss of ash slurry in pipelines having nominal bores in the range of 100-300mm. The results indicated that the addition of bottom ash to fly ash slurry at a given solids concentration has a beneficial effect in reducing the pumping power requirement. A design chart for the fly ash mixture slurry has been formulated indicating the variation in backfilling rate with relative head requirements for a given length of pipeline for a range of pipe sizes and transport velocities. This is expected to provide relevant pipe flow and operational conditions for bulk disposal of fly ash for mine backfilling purpose.