Tidal Surveys in Rustico Bay, Prince
Edward Island, 2009 and 2011
C.S. Crane1, J. W. Thompson1, S. E. Schofield1 and G. Bugden2
1
PEI Department of Environment, Labour and Justice
P.O. Box 2000
Charlottetown, PEI
C1A 7N8
c/o [email protected]
2
Fisheries and Oceans Canada
P.O. Box 1035
Dartmouth, Nova Scotia
B2Y 4T3
c/o [email protected]
February, 2012
Summary
Tidal surveys were carried out in the Rustico Bay area in 2009 and 2011 using Hobo
level loggers to monitor tide heights.
The 2009 results showed that there is a 4%-5% attenuation of tides in the mid Wheatley
River and Hunter/Clyde estuaries compared to Rustico Bay. This was consistent with
earlier studies. MacNeil ( 2009) indicated that the attenuation in Wheatley River was due
to the presence of a sill under the Oyster Bed Bridge and its’ removal was recommended.
The 2011 results indicated that the 4% -5% attenuation of tide in the mid Wheatley River
is still present despite dredging that was carried out at Oyster Bed Bridge in the fall of
2009. A further 5% attenuation at an upper estuary station indicates that that the
attenuation may be due to slight hydraulic control exerted by bottom friction.
The 2011 results also show that there is no difference between the tides recorded in the
mid Wheatley estuary and the Crooked Creek tributary of that estuary. Water levels in
Crooked Creek do change with the tides and do not remain at one level during mid
summer. Local residents’ perception that this is occurring may be related to the
occurrence of nearly diurnal tides that may display long periods of low tide during
daylight hours.
The 2011 study also showed that water levels in Chapel Creek and Horne’s Creek are
93% - 94% of those present in Rustico Bay. This attenuation is not due to bridges or
causeways as neither tributary has these structures. Instead factors such as a narrow
opening at the mouth of each estuary and bottom friction may play a role.
i
Table of Contents
SUMMARY ............................................................................................................I
TABLE OF CONTENTS .......................................................................................II
INTRODUCTION ..................................................................................................1
2009 SURVEY ......................................................................................................1
2009 Tidal Observations .............................................................................................................................. 2
2011 SURVEY ......................................................................................................5
2011 Wheatley River Tidal Observations................................................................................................... 6
2011 Tidal Observations - Other Sites in Rustico Bay .............................................................................. 9
CONCLUSIONS .................................................................................................11
REFERENCES ...................................................................................................11
Figure 1. Logger locations in Rustico Bay, 2009........................................................................................ 2
Figure 2. Measured tide heights in Rustico Bay area, June 30 - July 30 2009. ....................................... 3
Figure 3. Measured tide heights in Rustico Bay during a period of large (spring) tides, July 2009...... 4
Figure 4. Measured tide heights in Rustico Bay during a period of small (neap) tides, July 2009........ 4
Figure 5. Measured tide heights in Rustico Bay, July 17 2009. ................................................................ 5
Figure 6. Logger locations - Rustico Bay, 2011.......................................................................................... 6
Figure 7. Measured tide heights in Rustico Bay, July 6 to August 17, 2011............................................ 7
Figure 8. Measured tide heights in Wheatley River during a period of large (spring) tides, July 2011.8
Figure 9. Measured tide heights in Wheatley River during a period of small (neap) tides, August
2011. ..................................................................................................................................................... 8
Figure 10. Measured tide heights for Chapel Creek, Hornes's Creek and Wheatley River (Site 1) for
a large (spring) tide, July 2011......................................................................................................... 10
Figure 11. Measured tide heights for Chapel Creek, Horne's Creek and Wheatley River (Site 1) for a
small (neap) tide, August 2011. ........................................................................................................ 10
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Introduction
This study on tides in Rustico Bay was conducted by the PEI Department of
Environment, Labour and Justice during the summers of 2009 and 2011.
In 2009 the motivation for the study was to determine the range of tides present in the
Rustico Bay and the Hunter/Clyde and Wheatley River estuaries. This was part of an
effort to develop a method to determine nutrient loading criteria for Island estuaries. It is
also possible to use this data to compare the upstream and downstream tidal ranges
present in Rustico Bay.
The 2009 tidal survey results were presented to Wheatley River Improvement Group
(WRIG) in the fall of 2010. The group indicated at that time that it would like to see the
work repeated with a later summer sample date and the inclusion of additional upstream
areas. Specifically there was a request to determine if tidal ranges in the upper Wheatley
River and Crooked Creek portions of the estuary were different from those present in the
lower estuary and Rustico Bay and if tidal ranges stay at the same level in Crooked Creek
in mid-summer Additional information was also collected for Horne’s Creek and Chapel
Creek in 2011; for comparison to other sites in the bay and for input into a nutrient
criteria model developed using data from the initial 2009 survey.
The results of the 2009 and 2011 surveys are considered separately in the following
pages.
2009 Survey
The 2009 survey was conducted between June 30th and July 30, 2009. Three Hobo U20
Water Level Loggers were programmed to take a pressure reading every 5 minutes and
were deployed, mounted on concrete blocks, at the sites shown in Figure 1. A fourth
logger was deployed just upstream of Rustico Harbour however this logger was
improperly launched and did not collect any data.
An additional logger was deployed in the dry at a nearby site in order to measure
atmospheric pressure. This data was used to compensate for atmospheric pressure and
produce instrument depths (water levels) for each deployed Hobo logger using the
software provided by Hobo. The manufacturer’s specifications for these loggers indicate
that the accuracy for water depth when compensated in this manner is ± 1.0 cm.
The loggers were not surveyed in and comparisons to the Canadian Hydrographic Service
(CHS) tide predictions for Rustico were not made at this time. Previous studies, including
W.F. Baird (1996 and 1998) and MacNeil 2009, have indicated that the range and timing
of the tides in upstream areas generally match those of downstream areas and that the tide
is not significantly restricted by features located downstream of Rustico Bay. As a result
no loggers were placed outside of the bay.
1
Figure 1. Logger locations in Rustico Bay, 2009.
Data was normalized by determining each logger’s mean instrument depth for the entire
deployment and then subtracting this value from all measured depths for that instrument.
All instruments could then be plotted on the same graph. The data was plotted using
Excel 2003.
2009 Tidal Observations
All tidal observations made at the three logger sites are shown in Figure 2. Details of the
period of spring (large) and neap (small) tides are shown in Figures 3 and 4. The results
indicate that a minor storm surge, which resulted in a higher than expected tide, occurred
around July 6th. These figures also illustrate that the range and timing of tides observed
for Rustico Bay are generally the same as those of the Hunter/Clyde and Wheatley Rivers
however there is a slight attenuation of tides at both upstream locations. Although very
similar for most tides, not all upstream high tide levels are as high as those in Rustico
Bay and some low tides are not as low. It is estimated that about 95% to 96% of the
Rustico Bay tidal range is present in the Hunter/Clyde and Wheatley Rivers.
These results are similar to those presented for Wheatley River by both W.F. Baird and
Associates (1998) and MacNeil (2009) who attribute a slight (5 %) reduction in tidal
2
ranges observed in Wheatley River to hydraulic control exerted by the Oyster Bed Bridge
(Figure 1). MacNeil (2009) believed that, although the opening in the Oyster Bed Bridge
is large enough to accommodate the tidal ranges present, there is a small delay in the
movement of tides through the opening. He indicated that when tides on the downstream
side of the bridge begin to change before an entire rising tide can be admitted water levels
do not get quite as high on the upstream side as they do on the downstream side. When
falling tides begin to change before all of the tide can escape through the bridge the
upstream water level does get quite as low as on the downstream side (MacNeil, 2009).
1
0.8
0.6
Tide Height (m)
0.4
0.2
0
-0.2
-0.4
-0.6
30/06/2009
04/07/2009
08/07/2009
12/07/2009
16/07/2009
20/07/2009
24/07/2009
28/07/2009
01/08/2009
Date
Hunter/Clyde
Rustico Bay
Wheatley River
Figure 2. Measured tide heights in Rustico Bay area, June 30 - July 30 2009.
MacNeil (2009) attributed the differences in upstream tide timing and levels to the Oyster
Bed Bridge channel itself and not to shallow areas found both upstream and downstream
of the structure. The removal of debris (remnants of an older bridge structure) in the
bridge channel, which would increase the depth of the bridge gap by 0.5 m, was
recommended as a way to restore the upstream tide to nearly 100% of the downstream
tide (MacNeil, 2009). This work was completed in mid September 2009 (Shelley ColeArbing, PEI Department of Transportation and Intrastructure Renewal, personal
communication).
The 2009 Hunter/Clyde results also show a 4%-5% attenuation in range and are similar
to those of Baird and Associates (1998). Again slight hydraulic control is being exerted
on the tides in the Hunter/Clyde River. This could be caused by the Rusticoville
Bridge or by other factors, however it was beyond the scope of this project to determine
what those might be.
3
1
0.8
0.6
Tide Height (m)
0.4
0.2
0
-0.2
-0.4
-0.6
July 18, 2009
July 19, 2009
July 20, 2009
July 21, 2009
July 22, 2009
July 23, 2009
Date
Hunter/Clyde River
Rustico Bay
Wheatley River
Figure 3. Measured tide heights in Rustico Bay during a period of large (spring) tides, July 2009.
1
0.8
0.6
Tide Height (m)
0.4
0.2
0
-0.2
-0.4
-0.6
July 24, 2009
July 25, 2009
July 26, 2009
July 27, 2009
July 28, 2009
July 29, 2009
July 30, 2009
Date
Hunter/Clyde
Rustico Bay
Wheatley River
Figure 4. Measured tide heights in Rustico Bay during a period of small (neap) tides, July 2009.
4
The 2009 results also provide some insight into the local residents’ observation that the
tides in the Crooked Creek tributary of the Wheatley River stay at the same level or do
not change much during mid summer. When tides are large (spring tides) the tides in
Rustico Bay become nearly diurnal (one high tide and one low tide a day). As a result
there are long periods when the water level at low tide does not change very much. If this
long low tide were to occur during daylight hours it would seem to a casual observer that
the tides are not changing at all. The tidal observations from July 17, 2009 illustrate this
point as the tide level did not change much over the 14 hour period from 6 am to 8 pm
(Figure 5). This cycle was also repeated on July 18th and 19th (Figure 3), although the
timing of the low tide would have been shifted to later in the day as the tide cycle
progressed.
July 17, 2009
1
0.8
0.6
Tide Height (m)
0.4
0.2
0
-0.2
-0.4
-0.6
12:00:00 AM
3:00:00 AM
6:00:00 AM
9:00:00 AM
12:00:00 PM
3:00:00 PM
6:00:00 PM
9:00:00 PM
12:00:00 AM
Date
Hunter/Clyde
Rustico
Wheatley
Figure 5. Measured tide heights in Rustico Bay, July 17 2009.
2011 Survey
The 2011 survey was conducted between July 6th and August 17, 2011. Six Hobo U20
Water Level Loggers were programmed to take a pressure reading every 5 minutes and
were deployed at the sites shown in Figure 6. An additional logger was deployed in the
dry at the Oyster Bed Bridge (Figure 6). This data from this logger was used to
compensate for atmospheric pressure and produce instrument depths (water levels) for
each deployed Hobo logger as previously described.
5
Figure 6. Logger locations - Rustico Bay, 2011.
The loggers were not surveyed in and no comparisons to the Canadian Hydrographic
Service (CHS) tide predictions for Rustico were made.
The loggers were collected on August 17th and downloaded. Data from each logger were
normalized and plotted as previously described.
2011 Wheatley River Tidal Observations
Four level loggers were deployed in the Wheatley River (Figure 6). All results for all
loggers are shown in Figure 7 while details of the period of spring (large) and neap
(small) tides in Wheatley River and Rustico Bay are shown in Figures 8 and 9.
These results show that the range and timing of tides observed in Rustico Bay are
generally the same as the three upstream sites (Wheatley River 1, Wheatley River 2 and
Crooked Creek). There is a slight (4% - 5%) attenuation of tides between the mid estuary
site (Wheatley River 1) and Rustico Bay site despite the dredging effort carried out at the
Oyster Bed Bridge in 2009.
6
1
0.8
0.6
Tide Height (m)
0.4
0.2
0
-0.2
-0.4
-0.6
6-Jul-11
9-Jul-11
12-Jul-11
15-Jul-11
18-Jul-11
21-Jul-11
24-Jul-11
27-Jul-11
30-Jul-11
2-Aug-11
5-Aug-11
8-Aug-11
11-Aug-11 14-Aug-11 17-Aug-11
Date
Chapel Creek
Horne's Creek
Crooked Creek
Figure 7. Measured tide heights in Rustico Bay, July 6 to August 17, 2011.
7
Wheatley 2
Wheatley 1
Oyster Bed
1
0.8
0.6
Tide Height (m)
0.4
0.2
0
-0.2
-0.4
-0.6
July 12, 2011
July 13, 2011
July 14, 2011
July 15, 2011
July 16, 2011
July 17, 2011
Date
Crooked Creek
Wheatley 2
Wheatley 1
Rustico Bay
Figure 8. Measured tide heights in Wheatley River during a period of large (spring) tides, July 2011.
1
0.8
0.6
Tide Height (m)
0.4
0.2
0
-0.2
-0.4
-0.6
August 3, 2011
August 4, 2011
August 5, 2011
August 6, 2011
August 7, 2011
August 8, 2011
Date
Crooked Creek
Wheatley 2
Wheatley 1
Rustico Bay
Figure 9. Measured tide heights in Wheatley River during a period of small (neap) tides, August
2011.
8
The tidal ranges present in Wheatley River (Wheatley River 1) and in Crooked Creek are
virtually identical (Figures 8 and 9). There is no evidence from these results to support a
belief that tide levels in Crooked Creek are different than in other areas of the Wheatley
river estuary or that they do not change during mid summer. The tides in the Crooked
Creek portion of the estuary are behaving the same as in the main part of the estuary and,
except for a slight attenuation of range (approximately 5%) and a lag time of a few
minutes, are very similar to the tides present in Rustico Bay (Figures 8 and 9).
The tide ranges present at the uppermost site (Wheatley River 2) are attenuated by an
additional 5% over that observed between Rustico Bay and Wheatley River 1/Crooked
Creek. This suggests that bottom friction, and not the opening at Oyster Bed Bridge, is
the cause of the tidal restriction in the area. If the opening was the cause there would be a
noticeable change in levels and timing between Rustico Bay and Wheatley River 1 and
little or no change between Wheatley River 1 and Wheatley River 2. Instead the results
show an almost uniform change from Rustico Bay to Wheatley River 1 to Wheatley
River 2 indicating an equal change as you move upstream from one of these uniformly
spaced stations to another. This coupled with the observation that the largest differences
in tidal heights are present when the tides are lowest (Figure 9) indicate that bottom
friction is the cause of the slight hydraulic control present the Rustico Bay/Wheatley
River system.
2011 Tidal Observations - Other Sites in Rustico Bay
Level loggers were also deployed in Chapel Creek and Horne’s Creek between July 6th
and August 17th (Figure 6).
The data collected from these loggers show that the tidal ranges present in Chapel Creek
and Horne’s Creek are very similar to those recorded in the Wheatley River. The tidal
ranges for Chapel Creek, Horne’s Creek and Wheatley River are shown below for both a
large (spring) tide (Figure 10) and a small (neap) tide (Figure 11).The tidal range at these
two sites are approximately 93% and 95% of the range present in Rustico Bay
respectively.
Neither Chapel Creek nor Horne’s Creek have a bridge/causeway and both have
reductions in tidal range greater than that observed in Wheatley River and Crooked
Creek. Both of these small creeks have constrictions at the mouth that may be
contributing to a slight reduction in upstream tidal ranges and bottom friction may also be
playing a role as once again the largest differences between tide heights are present at the
lowest tides (Figure 11).
9
1
0.8
0.6
Tide Height (m)
0.4
0.2
0
-0.2
-0.4
-0.6
July 12, 2011
July 13, 2011
July 14, 2011
July 15, 2011
July 16, 2011
July 17, 2011
Date
Chapel Creek
Horne's Creek
Rustico Bay
Figure 10. Measured tide heights for Chapel Creek, Hornes's Creek and Wheatley River (Site 1) for a
large (spring) tide, July 2011.
1
0.8
0.6
Tide Height (m)
0.4
0.2
0
-0.2
-0.4
-0.6
August 3, 2011
August 4, 2011
August 5, 2011
August 6, 2011
August 7, 2011
August 8, 2011
Date
Chapel Creek
Horne's Creek
Rustico Bay
Figure 11. Measured tide heights for Chapel Creek, Horne's Creek and Wheatley River (Site 1) for a
small (neap) tide, August 2011.
10
Conclusions
•
•
•
•
•
There is a small attenuation in tidal flows upstream of the Oyster Bed Bridge
(4%-5% in mid Wheatley River and 8% - 10 % in upper Wheatley River). This
attenuation is likely not due to a constriction at the bridge itself. The removal of
debris from the bridge gap in 2009 has not increased the tidal range above the
bridge and, as attenuation gets greater upstream, bottom friction is a more likely
cause.
There is a similar (5%) restriction in tidal range present in the Hunter/Clyde
River. This could relate to a constriction at the Rusticoville Bridge however other
factors such as bottom friction could also play a role. It was beyond the scope of
this project to determine the cause of the reduction.
There is no difference between the tides recorded in the Wheatley River estuary
and the Crooked Creek tributary of that estuary. Water levels in Crooked Creek
do change with the tides and do not remain at one level during mid summer.
Local residents’ observation that the tidal ranges in Crooked Creek do not change
during mid-summer could be related to the occurrence of nearly diurnal tides that,
by coincidence alone, display a long period of low tide during daylight hours.
Water levels observed in Chapel Creek and Horne’s Creek are very similar to
those found above the Oyster Bed Bridge but have approximately 93% -95% of
the tidal range present in Rustico Bay. These slight attenuations are not due to
constrictions by bridges/causeways since none are present. Factors such as a
narrow opening at the mouth of each tributary and bottom friction may play a
role.
References
W.F. Baird and Associates. 1996. Numerical Modelling of Rustico Inlet, P.E.I.. For
Canadian Heritage - Parks Canada.
W.F. Baird and Associates. 1998. Computer Modelling of Rustico Bay Hydrodynamics.
For Parks Canada.
MacNeil, M. 2009. Physical Assessment of Tide Propagation at Oyster Bed Bridge –
Tidal Observations, Bathymetry and Analysis. For the PEI Department of Transportation
and Public Works.
11