Energy dissipation in the Duplin River

Overview Using data from instruments moored during DUPLEX I, we estimated energy dissipation at each station (Table 2). Dissipation estimates (Table 2) suggest that most of the tidal energy is dissipated near the mouth. Station 1 dissipation is greater by an order of magnitude than at the other stations. Most of the dissipation can be accounted for by the M2 tide, but the increasing energy of the overtides from the mouth to the head can add from 17% (near the mouth) to 63% (Station 5). The maximum dissipation of 0.18 W/ms (Table 2) occurs in the lower Duplin River. This suggests that tidal mixing is significantly greater there than farther upstream. Even so, the dissipation rate is an order of magnitude smaller than values of about 1W/ms for the Satilla River (Seim et al, in prep) and 2-4 W/ms for Coos Bay, Oregon (Blanton, 1969). The small dissipation rate in the Duplin River may be characteristic of relatively short tidal creeks. The correlation nu for a large tidal creek tributary to the Satilla (White Oak Creek) is only 0.08 m/s which is of the same order as the correlations in the Duplin. This suggests that "closed" tidal creeks have conditions closer to a standing wave and thus dissipate less energy than the more "open" coastal plain estuaries where the tidal wave can propagate farther upstream (Blanton et al., 2002). The maxima in energy dissipation found between Stations 1 and 2 of the DUPLEX I experiment is consistent with the temporal distribution of salinity at the various moorings (Fig. 3). The large gradient observed at Station 2 signifies that the mixing to that point preserves the salinity differences between Duplin River and Doboy Sound. At Stations 3 and 5, these differences have been smeared out so that the tidaladvection of the salinity gradient was relatively small.