NB KVK How is estuary exchange flow modulated by channel depth? Jige (Dove) Guo, Robert Chant Abstract Reference Number: Guided by 3 data sets denoted as 2008, 2002 and 1998 in the map, effects of channel deepening in Newark Bay as a result of systematic dredging on salinity field and exchange flow were discussed. While the Hansen and Rattray theory predicts that exchange flow should increase with H 3 it also suggests that horizontal salinity gradient should decrease with H 3 and thus the exchange flow would remain constant with channel deepening. Results from this study reveal that ds/dx remained nearly constant with deepening due to bathymetric constraints thus allowing the exchange flow to increase with H 3. In general we suggest that exchange flow in short estuaries (defined by their physical length relative to their salt intrusion length) will be more sensitive to channel deepening than long estuaries whose salinity gradient is able to adjust to the deepening. Finally the increase in the exchange flow is accompanied by an increase in tidal asymmetries in vertical velocity shear characterized by increased shear on the ebb tide. KVK Under low river flow (< 30 m 3 /s) condition, exchange flow in KVK increased by more than 2 factors from 1998 to 2008 as the channel deepened by about 5m. Flow profiles at maximum flood and ebb tide indicated that this increase was due to more pronounced flood ebb asymmetry when the channel was deeper. Velocity shear at maximum flood showed no big change with depth while shear at maximum ebb was augmented by more than a factor of 2 after channel deepening. Bottom velocity at maximum ebb significantly reduced after deepening, suggesting that the currents driving sediment out of estuary weakened and the estuary would trap more sediment and contaminants as it became deeper. Discussion CTD data 2002 (moor1) 2002 (moor2) 2008 (deploy1) 2008 (deploy2) H (m) Q (m 3 /s) ds/dx (psu/km) H3H3 ds/dxUEUE Data Ratio 2.71 ADCP data1998 (noaa1) 1998 (noaa2) 2008 (deploy1) 2008 (deploy2 H (m) U E (cm/s) Flood shear (cm/s) Ebb shear (cm/s) psu Bottom salinity at NB site increased by about 2 psu during the spring and stayed almost the same during the neap after channel deepening by about 1.6 meters. Bottom salinity at KVK site increased by about 2 psu during both the spring and the neap after channel depth increased by about 2.7 meters. The combined result show little variation in along channel salinity gradient except during the neap when ds slightly increased due to the increase in KVK and the lack of change in NB. Abstract Under low river flow (< 30 m 3 /s) condition, along channel salinity gradient ds/dx showed no significant change as the channel deepened by about 2.7 meters. Under low river flow (< 30 m 3 /s) condition, exchange flow U E increased by more than 2 factors as the channel deepened by about 5 meters. The ratio of estuary exchange flow at different depths closely follows the Hansen and Rattray scaling as a result of ds/dx not being able to adjust with change in depth in a short estuary and U E being solely modulated by H 3. Funded by the Hudson River Foundation