Temporal coherencies are compared for individual pulse arrivals of 100 and 800 Hz centered broadband signals propagating through identical shallow channels during periods of low and high internal wave energy. All 100 Hz modes are clean, distinct in time, and remarkably coherent (t(coh)>1 h). A near continuum of modes is observed for the 800 Hz signal with much shorter coherence times. Higher order modes are less coherent. Internal wave scattering appears to dominate the 100 Hz signals, whereas bottom scattering also randomizes the 800 Hz signal. Observations are consistent with similar measurements for this and other sites for intermediate frequencies.