Table 1.3. Tidal Ranges in the Galveston Bay System for 1988. 
Time 
Height 
Ranges 
Mean 
Position 
High 
Low 
High 
Low 
Mean 
Tide 
Location 
Nlat. 
W long. 
H.M.’ 
H.M. 1 
(ft) 
(ft) 
diurnal 
(fth 
Level 
(ft)’ 
Galveston Channel 
29*19’ 
94*48’ 
— 
— 
— 
— 
1.4 
0.7 
Texas City 
29*23’ 
94*53’ 
+0033 
+0041 
0.00 
0.00 
1.4 
0.7 
Clear Lake 
29*34’ 
95*04' 
+0605 
+0640 
0.64 
0.64 
0.9 
0.4 
Morgan Point 
29*41’ 
94*59’ 
+1021 
+0519 
0.71 
0.71 
1.0 
0.5 
Trinity Bay 
29*44’ 
94*42' 
+1039 
+0515 
0.71 
0.71 
1.0 
0.5 
East Bay 
29*31’ 
94*29' 
+0316 
+0418 
0.86 
0.86 
1.2 
0.6 
Christmas Bay 
29*05' 
95*10’ 
+0232 
+0231 
0.64 
0.64 
0.9 
0.4 
San Luis Pass 
Gulf of Mexico 
29*05' 
95*07’ 
-0009 
-0009 
0.86 
0.86 
1.2 
0.6 
(Galveston area) 
29*17 
94*47’ 
-0106 
-0106 
1.50 
1.50 
2.1 
1.1 
’H.M. = Hours and minutes to be added to or subtracted from the time of high or low water at 
a reference station. + = tide at subordinate station is later than at the reference station and 
should be added. - = tide is earlier and should be subtracted. 
’Mean diurnal range is the difference in height between mean higher high water and mean 
lower low water. 
’Mean tide level is a plane midway between mean low water and mean high water. 
Source: U.S. Department of Commerce tide tables, 1987. 
feet at Port Lavaca for Hurricane Carla in 1961; 40 feet at sea for Hurricane Carla in 1961; and 30 inches 
near Brownsville for four or five days during Hurricane Beulah in 1967. Saltwater flooding from 
Carla extended as much as 15 miles inland in the Galveston-Houston vicinity. Galveston has been the 
principal landfall site of four hurricanes since 1900; Hurricane Alicia in 1983 was the most recent (12). 
Bay Circulation 
Principal mechanisms that drive the circulation in the Galveston Bay System are prevailing 
winds, tides and freshwater inflow. Prevailing winds and normative speeds are documented above 
(Figure 6); salinity and nutrient gradients may be modeled, given a holistic understanding of the bay 
circulation system. 
Tides 
Tides are an important driving force in all bay systems; in the Galveston Bay System, tides are 
relatively weak (13). Tides cycle every 14 days. There are 14 days of one high and low tide followed 
by 14 days of two high tides and two low tides of different magnitudes. The tidal station inside the 
Galveston Channel records a mean annual tidal range of 1.4 feet, whereas the mean annual tidal range 
for the Gulf of Mexico at Galveston Pier is 2.1 feet (Table 3). The maximum tidal range in the bay for 
a 1988 spring tide is 2.4 feet. The tidal range decreases northward into upper Galveston and Trinity 
Bays, eastward in East Bay, and westward in West Bay as circulation becomes increasingly distant 
from the inlets. However, because of the location and orientation of the Intracoastal Waterway, tides 
appear tohave higher velocities than expected in East and West Bays. 
Approximately 80 percent of the tidal exchange between the Gulf of Mexico and the Galveston 
Bay System occurs through Bolivar Roads (13). Less than 20 percent of the tidal exchange occurs 
14 
