On reefs, interaction between the flow and complex bottom topography results in drag forces on currents, dissipation of wave energy, and generation of turbulence. Here, field observations on a shallow backreef were used to investigate wave and current interactions with the bottom at scales of individual colonies across a coral reef patch. Wave direction was aligned with current direction, and the ratio of wave orbital velocities to current (𝜎𝑤/𝑢̅) was less than 0.5. The time-averaged flow was a network of wakes behind colonies. Wake signatures were also observed for wave orbital velocities associated with longer period (13 - 32 s) waves but were absent for shorter period (3 - 5 s) waves. This pattern was explained by a modified Keulegan-Carpenter number 𝐾𝐶𝑐 = 𝑢̅𝑇/𝐿 representing the ratio of wave period (T) to time scale for advection of water past an obstacle with length scale L by the current (L/𝑢̅). Turbulent dissipation rates were elevated in obstacle wakes. For examples where KCc > 1, time-averaged dissipation varied in proportion to the mean of the cubed total (wave plus current) velocity, consistent with parameterization as work done by a quadratic drag force that varied with incident velocity during the wave cycle. Bulk friction coefficients estimated from volume-integrated dissipation in colony wakes together with topography measurements were similar to previous estimates from the reef-scale momentum budget. These results illustrate that, although uncertainties are large, a quadratic drag law in conjunction with spatial averaging is a reasonable approach for scaling up colony to reef-scale drag and dissipation