AbstractObservations have long associated ice streams with the presence of meltwater at the bed. More recently, theoretical models have been able to reproduce ice stream behavior as a consequence of the coupled dynamics of ice and subglacial meltwater. In this paper we analyze the properties of ice streams that form in a coupled model of ice flow and subglacial hydrology. We see that there is a natural length scale defining ice stream separation and width. This arises as a result of the balance between effective pressure gradients driving meltwater away from ice streams and the enhanced water production in the streams due to the fast ice flow. We further discuss how the model interacts with topography, and we show that small perturbations to a uniform bed have a strong effect on where ice streams emerge in the model. However, in many cases ice streams then evolve to be closer to the dimensions defined by the natural length scale of the unperturbed system. The nondimensional parameter that defines this length scale is therefore of fundamental importance in the model.