A comparison of current patterns with their corresponding tidal heights showed that the Bay’s currents underwent changes from the beginning to end of a tidal stage (flood or ebb). These changes could be defined by tidal height, with distinctions between neap and spring tides. To describe how the current patterns relate to tidal height, the patterns are referred to by the tidal range in which they occur. Table 4 shows the relative tidal distinctions. The Spring sampling season should not be confused with the spring tidal ranges.

Table 4. Tidal ranges for spring and neap tides.

spring flood tide spring ebb tide

early 0.9 - 1.2 m 2.1+ m

mid 1.2 - 2.1 m 2.1 - 1.2 m

late 2.1+ m 1.2 - -0.9 m

neap tidal range (flood and ebb)

Figures 10 and 11 show the Spring season current meter readings for the Bay transect, S section. The flood tide began with an east-flowing surface layer (Figure 10a). A section of water moved northward along the bottom of the shallower areas, and a west flowing mass moved along the bottom of station 4. As the northward layer dissipated, the eastward layer was confined to the surface by the incoming westward layer (Figure 10b). As the flood tide ended, the westward layer dominated, forcing the eastward water into the shallow region, stations 1 and 2 (Figure 10c).

The ebb tide for the S section began with a prevalent westward moving water mass, with southward flow close to shore (Figure 11a). The westward flow was then limited to the shallow region, as a southward flow dominated (Figure 11b). Towards the end of the ebb tide (Figure 11c), the southward water mass was broken up by the reemergence of an east-flowing water mass, similar to the beginning of the flood tide.

The Spring sampling period early flood currents for the Bay transect, B section were dominated by an eastern flowing water mass (Figure 12a), with patches of north and south moving currents. The late flood (Figure 12b) was still predominantly eastward, with a south-flowing water mass around station 7 and a northward moving water mass in the deep region of station 4. This emerging current system appeared to be creating an eddy.

The early ebb (Figure 12c) was similar to the late flood, with the greatest mixing localized around Whatcom Creek at station 7 (shown by the increased complexity of the profile). The late ebb current patterns (Figure 12d) exhibited more mixing, with a southward flow breaking up the eastward water mass, and westward pockets of water forming. The top 2 meters of Figure 12d showed a counterclockwise spiral at station 7; westward flowing Whatcom Waterway discharge was adjacent to a south-flowing water mass that is mixing with an eastward moving water mass. A similar formation is seen from a depth of 8 to 10 meters at station 4.

The early flood currents for the complete Bay transect (sections S and B) (Figure 13a) showed the study area divided into two trends. West of station 6, the currents moved west and south. East of station 6, the currents moved east and north. During the late ebb (Figure 13b), the eastern flow on the west side of the transect replaced a westward flow. The northward flow shifted east to the center of the transect. At station 7, a large west moving water mass separated two opposite flowing spirals. From east to west, the spiral to the left of station 7 flowed N-E-S-W; to the right the spiral flowed W-S-E-N.

The early ebb for the entire Bay transect (Figure 14a) is dominated by a southward flow, interspersed with east-moving patches. By the end of the ebb tide, the southern flow has been restricted to the surface layer, and a western flow occurred in all depths below 3 meters (Figure 14b). Eastward moving patches at the surface in both Figure 14a and 14b could be due to the wind. These southward and westward moving spring ebb current patterns are markedly different than the eastward moving neap pattern.

The interpolated velocities for the ebb and flood profiles were not very informative. The velocities for a late flood are fairly homogenous, with slightly slower values in the shallower region of S1 and around the Whatcom Waterway at B1 (Figure 15a). The late ebb background velocities are the same, but there was a faster water mass moving through stations B2 and B3, and along the surface of S3 and SB4 (Figure 15b).

The late flood current directions for the winter sampling period showed a southward flowing surface layer over a deeper eastward flowing layer across the Bay transect (Figure 16a). The early ebb tide current directions (Figure 16b) were compiled only a few hours after the flood, but the differences are very noticeable. A southward flow broke up the eastward flow, confining most of the eastward water to the shallower regions. The emergence of the westward flowing water is also visible.

The current velocities for this sampling period (Figure 17) relate the progression of a storm event. For the morning flood tide (Figure 17a), current velocities through most of the study area were low, with some faster moving water in the shallow region. The winds continually increased through the ebb tide (Figure 17b), with a corresponding increase in current velocities moving westward of B7 where the sampling run began. The fastest current velocity, 0.5 m/s, taken at station 3 at the end of the sampling run, was the highest measured velocity of the study.

For the August 8, 1996 flood tide (Figure 18a), the 2 m drogue floated in a clockwise semi-circle, ultimately moving towards shore. The 5 m drogue floated east to west before being reset closer to shore at mid-tide because it (mistakenly) appeared to be leaving the study area. The 5 m drogue then moved northeast, similar to the 2 m drogue. During the ebb tide (Figure 18b), the surface drogue reversed its previous course, floating in a counter-clockwise semi-circle seaward. The 5 m drogue followed a path similar to its flood tide pattern (before it was reset).

On August 13, 1996's flood tide, the 2 m and 5 m drogues were released south of Squalicum Harbor (Figure 19a). The 2 m drogue headed northeast before it stopped moving and was reset further off shore. The reset drogue quickly traveled northward, then moved even more rapidly west, hugging the breakwaters of Squalicum Harbor. The 5 m drogue followed a very similar path to the 2 m drogue’s original course, becoming mired in the same "dead" area that necessitated the latter to be reset.

On August 19, 1996, the 2 m and 5 m drogues were released in the same area for the corresponding ebb tide, shown in Figure 19b. The drogues were released closer to shore, in anticipation of a southward movement. For the most part, this did not occur. Both drogues moved primarily eastward, and a little towards the south. The 2 m drogue underwent long periods with no movement, and was reset twice.

The east side of the Bay transect was sampled on both a neap and spring tidal cycle. On June 19 (Figure 20a), the 2 m and 5 m drogues were released for part of the ebb tide. The surface drogue floated towards the Waterway before turning back, resulting in a in a counter-clockwise spiral. The 5 m drogue generally moved to the northwest. On June 20 (Figure 20b), the drogues were released for the corresponding ebb. The 5 m drogue did not experience any movement; it was set to 2 m and re-released. Both drogues primarily moved in circles, with a slight net movement to the east.

On August 28, 1996, the spring flood tide for this area was sampled, with two drogues set at 2 m and three set at 5 m. Both 2 m drogues (Figure 21a) moved northeastward, towards but not into, the mouth of Whatcom Waterway. The 5 m drogues followed a similar path (Figure 21b), although much slower. None of the 5 m drogues reached the mouth of the waterway.

On September 1, 1996, the corresponding ebb tide was sampled for this area, again with two drogues set at 2 m, and three set at 5 m. One surface drogue rapidly moved southeast (Figure 22a), before having to be reset because of low boat fuel. Re-released in the original location, it moved westward, giving evidence to different current patterns for early and late spring ebb tides. The other 2 m drogue floated in an almost perfect counter-clockwise circle off the end of the dock. Conversely, the 5 m (Figure 22b) drogues zigzagged their way northwest.

The current direction study represents a collection of observations obtained through different methods. The drogues represent tidal composites of nearshore Lagrangian currents, and the current meters represent Eulerian currents for different times of various tidal influences. Drogue movements were considered constant along the shore for the duration of the flood or ebb tide. All the collected current data were overlaid, noting the depth and position of the currents in the tidal cycle. Analysis of the data revealed that current observations through the study area varied both between flood and ebb tides, and between tides with varying tidal heights. The results are shown in figures 23-26. During this study, winds were predominantly from the south, and little data were collected on periods of southerly winds. Hence, the following diagrams are primarily for periods of northerly winds.

Figure 23a shows the influence of the Nooksack on the surface currents for an early flood tide. Eastward flow dominates the study area, with a small westward near shore flow, possibly Coriolis movement of Whatcom Creek runoff. The south-flowing water at the mouth of Whatcom Waterway would probably reverse during a north wind. This pattern would probably hold for the duration of a neap tide, or for periods of high Nooksack runoff. Near the end of a spring flood (Figure 23b), northward tidal currents push back Nooksack runoff causing the formation of an eddy. The tidal currents also hamper water movement around Whatcom Waterway.

The flood patterns at depth are much more complex. The tide first moved directly north, splitting the study area into opposite flow patterns (Figure 24a). As the tide progressed (Figure 24b), the general flood tide pattern of Bellingham Bay was seen; an eastern flow at all stations with water exiting the study area southward on the east side. The late spring flood showed the previous eastward tidal currents interrupted by a northward flow (Figure 25a). The eastward movement was temporarily halted, and a counter-clockwise spiral formed south of the bio-treatment lagoon. Tidal flow up the Whatcom Waterway was enhanced by the tidal height.

The ebb tide, near the surface (Figure 25b), was much simpler. Nooksack runoff flowed eastward into the study area, exiting primarily on the east side and periodically south through the entire area.

The deep ebb tide underwent a change in current directions as the tide progressed, as shown by the change in trajectory of the reset drogue in Figure 26a. The tide began (Figure 26a) in a pattern similar to the shallow ebb, without the Whatcom Creek runoff. As the tide ebbed (Figure 26b), a gyre formed through the entire study area. The reason for the gyre’s formation is unclear. A possibility could be that it is caused by Nooksack runoff attempting to leave the study area, but forced back by denser, more saline waters. During the Spring sampling period, the bottom waters of Bay stations 6 and 7 underwent a change of 6 ppt during the course of the ebb tide. However, during the Summer sampling period, these bottom water only experienced a change of 2 ppt, and that sampling period was the clearest example of the westward flow.

Vertical Profiles of Suspended Sediment and Water Transport

The tidally averaged vertical profiles of residual velocity and sediment concentrations for the Creek and Waterway transects for the Spring and Summer sampling periods are shown in Figure 35. The Creek transect showed weak gravitational circulation for both flood and ebb tides, strongest during the floods. During ebb tides, there was no net up-estuary movement of sediment or water. The Waterway showed negative transport in the bottom layers in the Spring season flood, and at all depths for the Summer flood. The Waterway’s Spring season ebb showed up-estuary movement in upper layers, down-estuary movement in the mid layers, and chaotic mixing in the bottom layers. The net sediment transport through the water column showed greater concentrations in the bottom layers, and slightly greater during floods than ebbs. The largest sediment concentrations were seen in the Waterway Spring ebb, possibly due to the mixing in the bottom layers.

There was over a magnitude of difference in residual water transport between the Whatcom Creek and the Whatcom Waterway (Figure 36). The Creek showed gravitational circulation in the Creek transect during floods, and down-estuary transport at all depths during ebbs. The Waterway exhibited more complex transport patterns. The Spring season flood showed a surface layer of water moving up-estuary over a down-estuary flowing layer, possibly due to wind effects. Even during the ebb tide, the Waterway still experienced up-estuary tidal movement along the bottom. During the Summer sampling period, with 1/10th of the Whatcom Creek discharge as in the Spring sampling period (Table 2), the flood tide encountered little resistance from down-estuary flow. As a result, all water movement was directed up-estuary.

Although sediment concentrations were consistently higher along the bottom depths,

vertical profiles of residual sediment transport (Figure 37) show more transport in the upper depths. The patterns are very similar to the residual water movement, indicating sediment transport is primarily dependent on water transport. The Spring season ebb tide for the Waterway does show some tidal pumping of sediment along the bottom. The low water transport along the bottom for the Summer flood, however, resulted in low sediment transport. The greatest concentrations of suspended sediment occurred in the lower depths of this tide, indicating that residual suspended sediment transport is more of a function of residual water transport than sediment concentrations (Figure 36).

The transport of materials varies over time, and is shown for the Creek transect in Figure 38. During the Spring season ebb tide, there was a slight increase in sediment concentrations as velocity and water transport increased. During the Summer ebb tide, there was a much more noticeable increase in sediment concentrations as the tide ebbed (Figure 38). For the Spring season flood, the sediment concentrations doubled. However, for both sampling periods, the velocity and water transport dropped sharply during the flood tides and the higher concentrations of suspended sediment were not transported across the transect.

Sediment concentrations and water velocity during the Waterway flood tides

(Figure 39) changed little in comparison to water transport. All three flood diagrams show large variability in the direction and quantity of water transport, with extremes occurring at the beginning and end of the sampling runs. In contrast, the ebb tide is more constant in sediment concentrations, velocities, and water transport over the tide’s course

(Figure 39).

The Spearman rank correlation was used to test relationships between total suspended solids (TSS), particulate inorganic matter (PIM), particulate organic matter (POM), turbidity, depth, salinity, and velocity. TSS was generally negatively correlated with depth from bottom (increasing with water depth). PIM and POM were only correlated with depth in half the cases. TSS was positively correlated with salinity in all the transects for all sampling periods except Bay stations 1-4 in the Spring sampling, and Bay stations 4-7 for the Summer sampling periods. TSS and velocity in the Waterway were positively correlated for the Spring and negatively correlated for the Summer sampling periods. TSS and temperature were seldom correlated.

Turbidity was positively correlated with TSS in all the transects during the Summer sampling period, but only in the Waterway for Spring, and not in the Winter samplings. Turbidity and depth from bottom correlated at Bay stations 4-7 for the Spring and Summer periods, correlated positively for Bay transect stations 1-4 for Winter and negative for Summer. Turbidity and depth from bottom were negatively correlated in the Creek transect for Summer, but were not correlated in the Waterway. Turbidity and salinity were not correlated in the Bay transect, and only sporadically in the Creek and Waterway transects. Most of these results show the Bay as a homogeneous system, with correlations dependent on time and location; no parameters were correlated in all the transects or through all the sampling periods.

Comparisons of suspended sediment concentrations show differences in seasonal and temporal variation (Appendix 3.9). PIM and TSS concentrations in the Waterway transect were significantly the highest during the Spring and Winter season samplings, but were the significantly lowest for the Summer season sampling. The Creek transect during Spring and Summer had significantly less POM and TSS than the Waterway in Spring, but was not significantly different than the Waterway in Summer. The average amount of POM decreased from the Spring to Winter season sampling periods, with the Spring Waterway and Spring Bay stations 1-4 significantly different than the Summer and Winter Waterway sampling periods.

These results show the Waterway transect generally having a greater concentration of suspended matter than the other transects, except for the Summer sampling period. This could be due to the mixing of the fresh and saline waters in a shallow area.

The Spring sampling period in the Waterway had a significantly greater turbidity than all the other transects. The Waterway transect and Bay stations 1-4 for both Spring and Summer seasons had higher turbidities than the others, with the Winter sampling period (for Waterway and Bay transects) having the least. These results show again that turbidity and well correlated for this study.