Yesterday (May 6th) was the first day of dye releases. Although we had a couple of glitches things overall went very smooth. In the AM we deployed 15 fluorometers (measure dye concentration) at the SIO and WHOI current meter locations. Combined with the velocity measurements, this allows one to make flux measurements of dye out or into the inlet. The NPS/RSMAS crew set up their mooring and catamarans. The SIO-MPL guys got their REMUS into position. The dye pump was calibrated (see image below) for the exact length of tubing to be used. That is a 30 gallon drum of Rhodamine WT!
Dye release began at 1245 at a rate of 21.6 gallons per hour. As the tides are in a spring phase right now the tidal currents were very strong, and in < 10 minutes dye had gotten to the entrance of the main channel. Below is the view from HQ which looks out over the main channel (to the left) and the SW ebb shoal (to the right). It is pink!
After about 1.5 hours, the entire 30 gallon drum had been released and the dye pump shut off. The tidal inlet experiment, then quickly became an inner-shelf experiment. We had jetskis, REMUS, boats with CTD and towed arrays, and an airplane sampling the dye plume as it advected towards Surf City. Below is an aerial hyperspectral image from Luc Lenain of the dye patch (note this is not a final product just a quick and dirty first cut).
One issue that the airborne observations had was the shadows due to the clouds. But the dye patch can clearly be seen in the image. Also note the boat wake.
The NPS boast and our Sally-Ann were also doing CTD casts. Below are some images from the CTD casts in the dye patch. The first is earlier on and measured 7ppb near the surface and a strong dye, T, and salinity -cline at 4-5 m depth. Near the bottom there is no dye.
Sometimes however, dye was maximum in mid water column. See the image below.
The MPL REMUS was also hard at work out there. Below is an 3D(lat, lon, and Z) of offshore plume dye concentration.
Lots of good stuff on day 1. There is a ton of more data collected by the NPS/RSMAS guys and our ski and all the moored and tripod instruments. Day 2 dye release begins at 1230
Today we have near gale force winds at New River Inlet. But there are model simulations to work up. As readers will recall, the FRF did a recent (Apr 16/17) bathymetry survey after the dredging of the main channel. The upshot is that the main channel is still very shallow and narrow. We have done two test dye releases (see earlier posts). In contrast to model predictions based on bathymetry ~ 1 year old (see earlier posts w/ NEARCOM tide / drifter and Delft3D tide / dye results) where there is a strong tidal jet that strongly advects stuff many km offshore, the dye both time just ooozed over the southern ebb shoal or out the new channel and northern part of the shoal. Clearly there was no strong tidal jet. Also, Britt & Steve also have found that tidal velocities are basically in phase with tidal elevations, ie, progressive, whereas the models were predicting a 1.5 hr lag (half progressive/standing). So both NEARCOM and Delft3D are being re-run with the new bathymetry. Here are some preliminary results from Delft3D run with just tidal forcing and a dye release.
As can be seen the tidal velocities are very strong inside the inlet but decrease rapidly at and offshore of the shoal (not here log10 velocities is colored). Bathymetry contours (4, 6, 8 m depth) are shown as dashed.
More interesting is the dye simulation. Now ~42 hours (previously only 20 hours) of the model has been finished, however this dye simulation is very different from previous simulations on the old bathy. See the youtube video below. It is clear that the dye behaves very differently oozing evenly out over the entire shoal rather than in a jet. The dye does not make it as far offshore. This is qualitatively consistent with our preliminary dye deployments. Note that there is no wind or stratification in this run. All the other model parameters (eddy diffusivities, etc.) were the same as the previous run.
For ease of comparison, take a look at the dye simulation with the old bathymetry but the same conditions (below). Clearly quite different.
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
The schedule for RIVET dye and drifter releases have been tentatively schedule for:
May 1, 2, 3, 4: Drifter Release Experiments
May 5 : Turnaround Instrument Day
May 6,7,8 : Dye Release Experiments with Airborne Dye Observations
May 9th: Turnaround
May 10,11, 12: Dye Release Experiments with Airborne Dye Observations
May 13th : Turnaround
May 14, 15, 16, 17: Drifter Release Experiments
May 18th: Turnaround
May 19, 20, 21: Dye Release Experiments: no airborne dye observations
Some details on the drifter and dye releases:
SIO (Feddersen/Guza) have 30 surfzone capable GPS tracked (and transmitting to shore) drifters which will be released on drifter days. The plan is to release on ebb tide and track the drifters for as long as possible – hopefully into the flood tide. Please see earlier post on numerical simulations of drifters at New River Inlet.
On the dye release days, we will be releasing 20-30 gallons/day of 23% Rhodamine WT dye. This will be tracked at fixed locations (WireWalkers, ADV, and ADCP locations) and via mobile platforms at the surface by jetskis (and plane), and subsurface by Boat and REMUS (Terrill).