We now know that the tide and tidal-inlet velocity are largely in phase – thanks to the WHOI (Raubenheimer & Elgar) AWACS deployment over the weekend. That information will be posted here later. Today we did another test dye release. Recall that previously we did a test dye release at the start of the ebb on medium tide with ENE winds. The dye flowed down the inlet and then out over the southern ebb shoal – never exiting the “channel”. We wanted to to see what would happen at a lower tide (the southern ebb shoal is nearly dry) and with more WSW winds. Check out the photos below. They were shot from the house balcony in chronological order covering about 15-20 minutes. We poured in 1 gallon of Rhodamine WT dye @ 23%.
In the first photo below, dye had just released for ~2 min from our boat (in the picture). It makes a nice small contained patch that is advecting out of the inlet (to the right)
The patch continues to spread out across the deep part of the channel as it is advected out of the inlet
Spreading continues as it is advected below.
This time the dye stays in the limits of the main (“new”) channel not going over the shoals to the south or north. The principal axis of the dye is angled though. Dye closer to the southern shoal is advecting offshore more rapidly. This region is shallow. Mostly 1.5-2 m deep.
The dye then continues to advect offshore in the center of the main channel. However, it has now slowed down a LOT. Note the water depths continue to decrease, between 1-2 m. There is no strong jet of current at this point.
In the end the dye crossed the channel opening (which had a lot of current induced breaking on it – it is shallow!), but did not really advect much farther offshore. The strong WSW (sideshore) wind had set up an alongshore current seaward of the shoals. The dye then slowly advected alongshore to the NE. (+y). This is fairly different from last time but again no dye went far offshore. This suggests that putting a wirewalker out at 12 m depth (>1 km offshore of the shoal), is not a good idea.
BELOW IS FROM THE EMAIL FROM TOM HSU TO THE NRI EMAIL LIST. REPOSTING HERE FOR CONVENIENCE:
We have established a site to disseminate our model results:
If you look at the left frame in this webpage, under “model prediction”, you will see the case runs. Once you click, it will take you to another page where you can read some overview of model results for this specific case and a “download” bottom where you can download velocity and free-surface data at various location in the model domain (30 min interval). Currently, we only posted one case run using old bathymetry. We plan to post new runs next week using new bathy that Jesse provided (Thanks! Jesse).
Please let us know if you have any comment or question. Thanks!
As the WHOI guys were deploying the AWACS, we did a preliminary investigation of dye and drifter releases. We were curious to see where it would go and how far dye could be visually tracked from a boat. The model simulations made it look like dye and drifters would just JET a few kilometers offshore on the main channel.
We went out at about 10:45, just as the tide was starting to ebb. We admired the WHOI folks deploying their AWACS in their wimpy (yet fast) boat. For sure, Whit was the saltiest dog on that vessel!
We released 3 drifters and Guza poured a gallon of 23% Rhodamine off the side of the boat at about x=-800 m and y=-100 m in the RIVET coordinate system (see photo below). For reference see the bathymetery map that Jesse made in an earlier post.
Above is what the dye looked like a few minutes after released from the boat. The dye was advected fairly rapidly near the shoreline and spread longitudinally. Eventually it hit the opening of the inlet. The photo below shows the dye patch as it hits the inlet mouth. This location is about x=0 m and y=-300 m in RIVET coordinates. It is the view in the roughly +y direction from the rental house
Later (photo below), the dye moves both along the beach to the south and offshore, but over the shoal – not in the channel.
This can be more clearly seen a little while later in the photos below.
The photo below shows the view later on (15-20 minutes after the first photo above) more towards the south (in +x and slightly in the -y direction). A blob (fraction) of the dye is clearly moving alongshore down the beach – as other parts of the patch spread out over the entire ebb shoal.
In the end the dye broadly spread out over the entire shoal to the south. The 3 drifters that we released also crossed over the southern ebb shoal and went offshore eventually into 4 m depth where we picked them up. No dye was observed to go out of the newly dredged main channel. This may have been because we released at the start of ebb as the tide was still relatively high. The map below highlights in slightly transparent pink the approximate visual extent of the dye patch about 30-45 minutes after the dye was released.
At extremely low tide, the ebb tidal velocity is still very strong and it is now visually clear that likely very little transport is occuring over the southern ebb shoal. It is in ankle to knee depth water. So perhaps inlet tracer transport and fate depends a lot on the tidal stage. This will be fun.
Notice who carries the heavy frame and who carries the cable…girls kick ass. That’s Regina, Britt, CAR-E, and the wimpy guy in orange is Levi.
AWAC deployed near the mouth of the inlet to get 24 hours of data to check phase lags between sea surface and slack tide (34.529434, -77.343110). However, Britt don’t need no stinkin’ AWACs. She predicted slack at 10:20 this morning…perfect, within 1-2 minutes according to the floats and drifting boat. That was 2 hrs 30 minutes (within a minute or two) after high tide. We’ll see if the model (Britt) is correct when we recover the sensor tomorrow and look at the data this weekend.
Saw Guza, Falk, Mrs. Falk, and boat-driver Bill in the Pink Turtle about to release drifters at 11 am this morning.
A new bathymetry for the new river inlet has been posted on the new river inlet FRF web site. Please go there for all the details. A big thank you to Jesse McNinch and the entire FRF crew. An gridded bathymetric image is shown below. Note that there are two channels; the old one more to the north and the new dredged one slightly south of it.
Jenna, rope queen. You should see her on a quarter horse chasing a steer that needs to be branded. I suggest you not annoy her.
33 ADVs calibrated, 11 profilers calibrated, 5 combo-sensors calibrated tomorrow, 33 pressure gages getting bench tested for offsets, 19 profiler frames assembled (a lot of nuts and bolts, way a lot, and there are twice as many to go to attach the sensors). 30 sets of ground lines and float lines cut and spliced, 2 boats in the water (lesson learned: check that the boat plug is installed…). As Bob Dylan said “twenty years of schooling, and they put you on the day shift.”
We learned about bull sharks and alligators, but the turtle huggers did not show up for a scheduled lesson on saving turtles and plovers, so we are learning where things lie on the priority lists.
All is well, weather is perfect, sand is moving (can see it with your eyes) already, and waves are supposed to get big this weekend, so likely the surveys Jesse and his team busted their butts for over the last two days are not going to work. They will redo it after the storm, possibly with help from the Feddersen-Guza jet ski team.
Totally wonderful to be working with the CCS guys again, but they are getting nervous about racing the newly named “Pink Turtle” for pink slips.
The LARC continues to survey despite a 15-20 mph sea breeze. They are on the other side of the inlet, and have surveyed a lot. Waves on the ebb tide shoal are directionally beserk. Colliding crests with 90 degs (and more) spread. Small crests, but they combine to make 3′ local peaks. 3-5 sec peak period. Steep, savage little bastards that buck small craft around.
I talked to the LARC driver (he came ashore 75 m upcoast from our house). He says they
* cut a shallow new channel all the way out.
* have 3-4 more hrs work tomorrow to complete the survey
Real time New River wave info can be found at the CDIP web page or at http://cdip.ucsd.edu/
Click on “Recent” and scroll down to New River Inlet NC Buoy. This buoy is in 130 m water depth, directly offshore of the New River Inlet. It was just deployed so there are only a few days of data. Detailed information is found at
The afternoon sea breeze makes 3 sec slop/chop. In addition, the
Marsonborough Inlet Buoy is down by Wilmington and it has more history.
One can see the wave height grow, and period drop, during the afternoon of several days this week/month.
Regional wave/weather forecast is at
A POTENT LOW PRESSURE SYSTEM AND COLD FRONT WILL APPROACH FROM THE WEST THIS WEEKEND.
Sat…S winds 15 to 20 kt…increasing to 20 to 25 kt. Seas 3 to 5 ft. A chance of showers and thunderstorms.
Here’s a local surf AND WIND forecast…..
Bill and Kent are driving from San Diego to New River Inlet, hauling boats and gear.
Here’s a typical situation, Kent with the wimpy automatic gas truck pulling a light load trying to hang with the power stroke diesel pulling a much heavier load. He’s a good sport and a great traveling companion.
The youtube movie below shows Log10 dye concentration (no units) at New River Inlet released just up the inlet over t=2-4 hr. This simulation is forced by the M2 tide and has no stratification, no wind, and no waves. Top: time series of tidal elevation at (x,y)=(0,0) m. The red dashed line represents the current time location. Bottom: plan view of Log10 surface dye concentration. Only a subset of the model domain is shown. Land values are white and dashed lines represent bathymetry contours (2, 4, 6, 8, 10, 12 m depth). The colorbar gives log10 concentration: Check the video below:
I also looked at the bottom dye concentration. Although there are subtle differences the movies look pretty much the same. For these purposes this unstratified simulation is pretty well-mixed.
At first release, the dye jets about 2 km offshore of the inlet mouth. There is a significant amount of dye flux back into the inlet. However, this may be a result of no wind, no waves, no alongshore tidal propagation, and no other shelf-scale forcing mechanisms that drive shelf-scale alongshore currents.
If folks are interested in the .mp4 video file (better resolution) it can be downloaded via NRI_dye_surface_delft3d
Please feel free to leave comments and suggestions. -falk