These are growing in the middle part of the pond, at the deepest point. That's been under water apart from a short spell of drought in May, when it was just mud. The other plant is surviving, but not thriving near the pond margin, where it is only under water when the pond is full, which has been a rare occurrence since last winter.
Grace, James B., and Robert G. Wetzel. "Niche differentiation between two rhizomatous plant species: Typha latifolia and Typha angustifolia." Canadian Journal of Botany 60.1 (1982): 46-57.