Deanys River estuary . The Dennys River is the major fresh water inflow to 

 Cobscook Bay but no hydrographic data on it exist. The Ketchum model has been 

 applied to this estuary between the upper boundary at Dennysville and the 

 lower boundary at the constriction between the inner and outer parts of the 

 Bay, across from Cobscook State Park. This estuary is similar to the 

 Narraguagus and Machias and probably is mixed well and flushed well as a 

 reult of the high tidal and nontidal flows (figure 5-23). 



St. Croix River estuary . The Ketchum model has been applied to this 

 estuary (figure 5-24). The upper boundary was set at the Calais Road Bridge 

 and the lower boundary at the point where the estuary widens rapidly in the 

 vicinity of Robbinston on the United States side and St. Andrews on the 

 Canadian side. The model results indicate that only the upper segment, the 

 first few kilometers below Calais, will have salinities below oceanic levels. 

 The low fresh water flow into the rapidly widening estuary results in this 

 section flushing fairly slowly, but the high tidal range and exchange farther 

 down the estuary will result in this portion flushing rapidly. Ketchum and 

 Keen (1953) computed a flushing time of 8 days for the estuary above St. 

 Andrews, compared to 6 days in our application of the model. Both the Dennys 

 and St. Croix Rivers discharge into the Passamaquoddy Bay/Cobscook Bay 

 complex. It is evident from the salinity distribution (figures 5-23 and 5-24) 

 that this area would not be defined as estuarine on the basis of its salinity 

 but it will be discussed briefly below, nevertheless. 



Passamaquoddy and Cobscook Bays . This complex system of bays and 

 interconnecting channels has been the focus of study, at least in part, 

 because of potential oil refinery and marine terminal sitings and tidal power 

 development. The most complete study of the region, summarizing work up to 

 1959, is appendix 1 of the International Passamaquoddy Fisheries Board Report 

 to the International Joint Commission (Bumpus 1959). The reader is referred 

 to this detailed source, which has been used in preparing this brief summary. 



Cobscook Bay has a mean depth of 26 feet (8 m) at low tide. A narrow channel 

 about 66 to 98 feet (20 to 30 m) deep exists in the lower bay. The bay bottom 

 is regular and slopes to the channel, has little relief, and is a submerged 

 valley. Passamaquoddy Bay was probably shaped by glacial and ice sheet 

 action, the latter forming the shallow, gently sloping northern part of the 

 bay and the former the deep steeply sloping region from the northern side of 

 Deer Island to Midjik Bluff. The average low water depth is 79 feet (24 m) . 



Tidal exchange of water establishes extremely strong currents and mixing. 

 Fresh water input from the St. Croix, Magaguadavic , Digdeguash, and the Dennys 

 Rivers is small compared to the tidal exchange and contributes little to the 

 current regime. For example, the intertidal volume of Cobscook Bay is 490 

 million cubic meters while during half tide (6 hrs and 12 min) the Dennys 

 River mean discharge is slightly under 2 million cubic meters. About 20% of 

 the water in Passamaquoddy Bay and 50% of the water in Cobscook Bay exchange 

 on each tide. 



Forrester (1959) presents tidal current data and maps for the Passamaquoddy 

 Bay and mouth of Cobscook Bay region at hourly tide stages. These current 

 patterns are complex and the reader is referred to the source for specific 

 information. 



5-36 



