Kennebec estuary. The few data available for the Kennebec estuary support 

 the results of the Ketchum model. The estuary is comprised of only two 

 segments as a result of its shallow, narrow topography and considerable fresh- 

 water inflow (figure 5-12). Consequently, the model predicts a short flushing 

 time with strong nontidal and extremely strong tidal currents. The strong 

 current regimes and constricted topography should result in intense mixing. 



Francis and coworkers (1953) sampled this estuary below Bath during a fall 

 period of low flow and found it to be stratified only slightly. In one area, 

 ("Doubling Bends") they observed great turbulence that was not noted elsewhere 

 and that should cause intense vertical mixing. Because of their observation 

 of slight vertical salinity gradients, they concluded that this mixing was not 

 complete. Stomrael (1953), commenting on the data above, described the 

 Kennebec as having such intense vertical mixing that vertical salinity 

 differences were only a small fraction of the horizontal differences. He 

 attributed the mixing to strong tidal and nontidal currents interacting with 

 the rough bottom. 



Sheepscot estuary . The Sheepscot is one of the most complex of Maine's 

 estuaries. The upper part is somewhat isolated by a rock-ledge reversing 

 falls below Sheepscot Village. Between the falls and Wiscasset the estuary is 

 shallow with extensive mud flats, and below Wiscasset it is narrow and more 

 deeply bounded by rock ledge. From Barters Island southward, the estuary 

 deepens further and has several interconnections: through Goose Rock passage 

 to Wiscasset via Montsweag Bay, via the Sasanoa River to the Kennebec, through 

 Ebenecook Harbor via a complex of small islands to Townsend Gut and Boothbay 

 Harbor, and several back waters, such as Cross River and Back River (see atlas 

 map 1 and figure 5-2 for locations). Each of these contributes in a 

 complicated manner to the circulation, on which data are scarce. The Ketchum 

 model cannot account for much of this complexity but illustrates a number of 

 the major features of. the estuary that have been documented (figure 5-13). 



Stickney (1959) hypothetically divided the estuary into an upper and lower 

 section at Wiscasset. Unpublished data by Larsen refer only to the upper 

 section and Garside and coworkers (1978) provided additional data on the lower 

 section, so that Stickney' s framework is adopted for modeling. 



According to Ketchum' s model, the upper portion of the estuary, because of its 

 shallowness, experiences a rapid tidal exchange and flushes quickly (figure 5- 

 13). The effect of riverflow into this small volume results in rapidly 

 changing salinity. The shallowness of the region can be expected to result in 

 strong tidal mixing and, consequently, small vertical salinity gradients. 

 This is supported by June, 1974, tidal cycle data at the Sheepscot Village 

 bridge (figure 5-14). The salinity range is from to 15 ppt with little 

 surface to bottom variabiity, and the curve is asymmetrical (Stickney 1959). 

 At stations farther up the estuary, the asymmetry becomes more pronounced 

 (because of the influence of the falls; figure 5-15) with salinity increasing 

 rapidly on the flood tide and decreasing slowly on the ebb tide. 



5-24 



