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NEARSHORE WAVE AND CURRENT MEASUREMENTS IN THE COASTAL BEND
Philippe Tissot, Larry Dell, James Rizzo & Deidre
Williams
Conrad Blucher Institute Texas A&M University-Corpus Christi
American Shore and Beach Protection Association, Texas
Chapter Symposium, March 20, 2015
Outline
• Motivation
• Experimental Geometry
• Experimental Limitations
• General Metocean Conditions during Study Period
• Correlations
• Initial Nowcasts & Operational Model Predictions Comparisons
• Conclusions & Future Work
Study Location
Bob Hall Pier, North Padre Island, Corpus Christi, Texas
Current profilers: Xylem (Sontek) Argonaut SL500 (500khz, 2-D)
378 m
Nearshore (looking) sensor
Offshore (looking) sensor
Map/sattelite imagery from Google
51 m
120 m
Current Profilers Winch Boxes
Across-shore Current Profiler I-Beam
NWLON Wind Sensors
Longshore Current Profiler I-Beam
NWLON Stilling Well
Solar Panels
Instrument Installation
Experimental Geometry
54” (137 cm)
124” (314 cm)
120” (306 cm)
Water Depth: 244” (620 cm)
Offshore Looking Sensor (vertical)
Offshore Looking Sensor Current profile: 10-120 m in 11m cells
Average currents: 21-109m
+Y or North
+X or Offshore
Nearshore Looking Sensor Current profile: 1.50-51.5 m in 5m cells Average currents: 21.5-46.5m
+X or South (-X for North)
+Y or Offshore
measurements for 4/9/2014 3:00-4:00 PM CST pwl = 6.54+/0.0.2m above station datum
~ 30m
I-Beam & winch for offshore looking sensor
Sensor
I-Beam
Pier Pile
Offshore Looking Sensor Deployment Geometry
Pier Pile
NWLON Pile
Offshore Looking Sensor Experimental Geometry
Interference up to 15-20m
Picture from Sontek (http://www.sontek.com/productsdetail.php?ADP-Acoustic-Doppler-Profiler-4)
Potential interference from piling with side
lobes
Offshore Longshore Current
0 1000 2000 3000 4000-10
0
10
20
30
40
50
60
70
Time [30 min increments]
Sig
na
l to
No
ise
Ra
tio
10-21m 21-32m 32-43m 43-54m 54-65m 65-76m 76-87m 87-98m 98-109m 109-120m
0
10
20
30
40
50
60
70
Sig
nal
to N
ois
e R
ati
o
10-21m 21-32m 32-43m 43-54m 54-65m 65-76m 76-87m 87-98m 98-109m 109-120m0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
Sta
nd
ard
Err
or
[m/s
] Standard Error
Signal to Noise Ratio
Signal to Noise Ratio
Offshore Longshore Current
10-21m 21-32m 32-43m 43-54m 54-65m 65-76m
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
|Lo
ng
sh
ore
Cu
rre
nt|
[m
/s]
0 500 1000 1500 2000 2500 3000 3500 4000-1
-0.5
0
0.5
1
Lo
ng
sh
ore
Cu
rren
t [m
/s]
21-32m
32-43m
43-54m
54-65m
Offshore longshore current are consistently measured in the range 21-65m from the offshore looking sensor
Bin 5
0 100 200 300 400 500 600
-5
-4
-3
-2
-1
0
Ele
va
tio
n, m
(N
AV
D8
8)
Distance Across Shore, m
Legend
Jul 2007
Sep 2010
Oct 2011
Sep 2012
Sep 2013
Nearshore Bathymetry
~ 1.6 m
Profile History 245-m south of Bob Hall Pier
0 200 400 600 800 1000 1200-10
-8
-6
-4
-2
0
2
4
6
Ele
va
tio
n,
m (
NA
VD
88
)
Distance Across Shore, m
Distance Across-shore, m
Distance Across-shore, m
5%
10%
15%
WEST EAST
SOUTH
NORTH
0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1414 - 1616 - 18
General Metocean Conditions (6/1/14-3/19/15)
Variable Median Range
Significant Wave Height 0.64m 0.04-1.8m
Typical Wave Period 5.9s 2.0-11.2s
Nearshore Longshore Current [m/s] 0.00m/s [-0.8m/s , 0.9m/s]
Offshore Longshore Current [m/s] -0.01m/s [-1.2m/s , 1.4m/s]
Wave & Longshore Current
• Meteorological conditions from NWLON station • Ocean conditions from project current profilers
Wind
Bob Hall Pier Significant Wave Height Distribution
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.80
50
100
150
200
250
Signficant Wave Height [m]
Freq
uen
cy
Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 Jan-1 Feb-1 Mar-1-15
-10
-5
0
5
10
15
Win
d S
peed
[m
/s]
Alongshore and Cross-shore Wind During Study Period
Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 Jan-1 Feb-1 Mar-1-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
W
ate
r L
evel [m
ab
ove m
sl]
Bob Hall Pier Water Levels and Tidal Predictions
Tidal Predictions
Measured Water Levels
Alongshore wind median: -0.0m/s (+ Northwest) Cross-shore wind median: 3.1m/s (+ Onshore)
Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 Jan-1 Feb-1 Mar-1-1.5
-1
-0.5
0
0.5
1
1.5
Long
shor
e C
urre
nt [m
/s]
'Offshore' Longshore Current
"Nearshore' Longshore Current
Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 Jan-1 Feb-1 Mar-1-1.5
-1
-0.5
0
0.5
1
1.5
Lo
ng
sho
re C
urr
ent
[m/s
]
Alo
ng
sho
re W
ind
/ 10
[m
/s]
Alongshore Wind / 10
Longshore Current
Longshore Currents Comparison of Longshore Current with Alongshore Wind
(offshore looking sensor)
Comparison of Nearshore and Offshore Longshore Current
Correlations
Correlation of longshore currents with along shore wind: • Nearshore longshore current = 0.74 • Offshore longshore current = 0.85
Correlation of longshore currents with significant wave height: • Nearshore longshore current = 0.22 • Offshore longshore current = 0.04
Other Correlations: • Significant wave height and across shore currents
(nearshore = 0.23, offshore = 0.15) • Cross-shore wind & significant wave height = 0.24
Pearson pair correlations computed over matching data pairs for the period June 1, 2014 through March 19, 2015
Longshore Current Correlations (Pearson)
6/19 71/ 8/1 9/1 10/1 11/1 12/1 12/31-1
-0.5
0
0.5
1
1.5
Lo
ng
sh
ore
Cu
rren
t [m
/s]
TABS D Longshore Current
Nearhsore Longshore Currrent
Offshore Longshore Current
• TABS Network (GERG) • Data: 6/19/14-1/2/15 • Correlation = 0.69 • Differences during large
wave events (Dolly) & frontal passages
Use relationship between significant wave height (Hm0) and water level standard deviation (σ) *:
Nearshore Wave Nowcast
*See: Park, Heitsenrether & Sweet (2014) Water Level and Wave Height Estimates at NOAA Tide Stations from Acoustic and Microwave Sensors, J. Atm. Oc. Tech 31, 2294-2308. Also Parke & Gill (1995), Shih & Rodgers (1981).
𝐻 𝑚0 = 𝛼𝜎
0 0.1 0.2 0.30
0.5
1
1.5
2
Water Level Standard Deviation [m]
Sig
nific
ant W
ave H
eig
ht [m
]
y = 6.519*x + 0.1114
data
linear fit
-1 -0.5 0 0.5 10
100
200
300
400
500
600
700
Model - Measurement [m]
# C
ases
Unbiased Stdev = 0.15m
• Historical reconstruction of significant wave height: swh = 6.52 (stdev of water levels) + 0.11
• Applied to hourly data from Bob Hall Pier 3/1/2003-3/1/2014
Nearshore Wave Nowcast
0 0.5 1 1.5 2 2.5 3 3.50
1000
2000
3000
4000
5000
Significant Wave Height
Fre
qu
en
cy
3/1/03 1/1/04 1/1/05 1/1/06 1/1/07 1/1/08 1/1/09 1/1/10 1/1/11 1/1/12 1/1/13 1/1/140
0.5
1
1.5
2
2.5
3
3.5
Sig
nif
ican
t W
ave H
eig
ht
[m] Reconstructed Wave Height History
Emily Rita
Ike
Longshore Current Nowcast
• Train Neural Network to nowcast Longshore current based on
– alongshore wind: RMSE = 0.100 (0.003) m/s
– + offshore longshore current: RMSE = 0.095 (0.002) m/s
– + wave: RMSE = 0.074 (0.003) m/s
– based on std(water level) instead: RMSE = 0.080 (0.002) m/s
0 1000 2000 3000 4000 5000 6000 7000-1
-0.5
0
0.5
1
1.5
Time [30 mins 6/18 - 12/31/2014]
Lo
ng
sh
ore C
urren
t [m
/s]
Measurements
ANN (1 input)
ANN(2 inputs)
-0.4 -0.2 0 0.2 0.40
200
400
600
800
1000
1200
1400
Model - Measurements [m/s]
# C
ases
Unbiased Stdev = 0.07m/s
NGOFS Comparison
Comparison with NOAA’s Northern Gulf of Mexico Operational Forecast System (NGOFS) 6/19/14 – 3/6/2015
Bob Hall Pier
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Observed Current (m/s)
Pre
dic
ted
Cu
rre
nt
(m/s
)
Longshore Current Comparison
y = 0.4*x + 0.0016
All data
Linear Correction Model
Wind Over 20 mph
y=x line
R-Squared = 0.725RMSE = 0.0515
RMSE=0.14m/s (without correction)
Nearshore Across-shore Current (bins)
6/10 7/1 8/1 9/1 9/25-1
0
1
2
Acr
oss-
sho
re C
urr
en
t [m
/s]
Bob Hall Pier Nearshore Across-shore Current for Bin 1 (1.5-6.5 m)
Cross Shore Current
Standard Error
Signal Strength
6/19 7/1 8/1 9/1 9/25-1
0
1
2
Acr
oss
-sh
ore
Cu
rren
t [m
/s]
Bob Hall Pier Nearshore Across-shore Current for Bin 5 (21.5-26.5 m)
Signal Strength
Standard Error
Across-shore Current
6/19 7/1 8/1 9/1 9/25-1
0
1
2
Bob Hall Pier Nearshore Across-shore Current for Bin 10 (46.5-51.5 m)
Time 6/19-9/25 2014
Acro
ss-s
ho
re C
urr
en
t [m
/s]
Across-shore Current
Standard Error
Signal Strength
30min sampling 6min sampling
6/10 7/1 8/1 9/1 9/25-1
0
1
2
3A
cro
ss-s
ho
re C
urr
en
t [m
/s]
Bob Hall Pier Nearshore Across-shore Current
Time 6/19-9/25 2014
46.5-51.5m
21.5-26.5m
1.5-6.5m
Goal: Assessment of conditions favorable to onset of rip currents Measurements: Across-shore current in 10 x 5m bins, 30 minutes measurements (17 min averages) till 9/2 followed by 4 minutes measurements every 6 minutes
9/3: Impact of Tropical Storm Dolly swh: 1.6m twp: 10.2s 6 m/s onshore wind
8/27: High Wind Event swh: 1.2m twp: 8s 6 m/s onshore wind
9/22: Cold Front swh: 1.2m twp: 7s 10 m/s onshore wind
3650 3700 3750 3800 3850 3900
-1
-0.5
0
0.5
1
1.5
Acro
ss-s
ho
re C
urr
en
t [m
/s]
Bob Hall Pier Nearshore Current Profile
1.5-6.5 m
6.5-11.5 m
11.5-16.5 m
16.5-21.5 m
21.5-26.5 m
26.5-31.5 m
31.5-36.5 m
36.5-41.5 m
41.5-46.5 m
46.5-51.5 m
http://lighthouse.tamucc.edu/qc/260 – stations 259 and 260
Web Access to Data
Discussion/ Conclusion
• Two current profilers/wave sensors installed at Bob Hall Pier, Corpus Christi, Texas, recording nearshore conditions
• Observations strongly correlated to alongshore nearshore wind
• Comparison of measurements with NOAA operational models (NGOFS, NWPS)
• Accuracy of nowcast using other observations and/or NOAA model outputs? (extreme events?)
Questions/Suggestions? • Funding from the Texas General Land Office (TGLO) R&D 2014-2015 Funding
Cycle, Award No. 13-437-000-7896, is gratefully acknowledged.
• The CBI field crew and information technology team are gratefully acknowledged for efficiently and creatively resolving problems during the project.
Two Horizontal Acoustic Doppler Current Profilers (HADCP), with acoustic vertical wave and pressure sensors, were installed during the spring 2014 on Bob Hall Pier, Corpus Christi, Texas. The sensors provide near real-time measurements of nearshore conditions including current profiles in X & Y as well as significant wave height and period. The instruments are gathering a rare long-term data set of nearshore conditions along the Texas coast at this location. One of the HADCPs’ mounted at the end of the pier measures offshore to a distance of 120m depending on conditions. The other HADCP is mounted perpendicular and measures current velocities from the pier northward to 50m. This sensor is set up to detect rip currents in the nearshore of a beach frequented by swimmers and surfers. CBI will describe the installation process, the performance of the sensors, and will present on the measured parameters, data, and the correlation with atmospheric forcing. The sensors provide near real-time information to facilitate the prediction of oil movement and the deployment of protection measures in case of oil spill. The measurements will also help to better understand and model sediment transport along the coast and more specifically for the periodic renourishment and maintenance of the nearby popular beaches located along the Texas Coast such as Mustang Island State Park, Padre Bali Park, and North Padre Island. Other applications include providing information appropriate for search and rescue operations, reporting surf conditions, and alerting beach-goers to conditions favorable to the onset of rip currents.
Abstract
Alternate Study Location
Slide
~ 4km
cbi.tamucc.edu/dnr/station – stations 259 and 260
Web Access to Data
6/19 7/1 8/1 9/1 9/25-1
-0.5
0
0.5
1
Time 6/19-9/25 2014
Lo
ng
sh
ore
Cu
rren
t [m
/s]
Bob Hall Pier Nearshore Longshore Current
Nearshore Currents
6/19 7/1 8/1 9/1 9/25-1
-0.5
0
0.5
1
1.5
2
Acr
oss
-sh
ore
Cu
rre
nt [
m/s
]
Bob Hall Pier Nearshore Across-shore Current Profile
Cross Shore Currents - Waves
• Waves could influence sensor readings for the furthest bins of the nearshore looking sensor (1.2m wave illustrated below)
Argonaut SL500 Specifications
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