Wireless sensor networks suffer from unbalanced energydepletion since sensor nodes sitting around the sink need to carry moretraffic loads and thus would deplete energy faster, leading to what isknown as "energy hole" problem. This phenomenon is due to intrinsicmany-to-one traffic pattern of wireless sensor networks. In this paper,we deploy an analytical model to characterize the "energy hole" problemand describe an iterative process to determine the optimum value of themodel parameters. Then, we propose a balanced energy depletion strategybased on the derived optimal parameters to mitigate the "energy hole"problem. Finally, extensive simulations have been performed to validatethe analysis and the effectiveness of the energy strategy.