by Tom Hsu, Fengyan Shi, and Julie Chen (UDEL): I just like to follow up with Falk’s comments on time series and phase lag between surface elevation and flow velocity magnitude. More information from the model run is attached. In this document, you will find time series at four different locations. Please also notice that in these figures, we show tidal velocity magnitude (not individual components), which is probably more representative. Basically, max ebb occurs 0.5~1 hour before low tide.
As Falk mentioned, the results seems to be sensitive to bottom friction used. We are evaluating the sensitivity and will give you an update soon. We also plan to run realistic tide, which can make a difference in phase. Once we have update, we will post on the blog (and we may provide a link where you can download more specific and detailed data from our own website).
Bathymetry: from Summer 2011
Offshore Conditions: Normally incident waves Hs=1 m. Drag coef Cd=0.01, Tide Level =0.623 m
Time series of tidal elevation and tidal velocity magnitude:
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).
Below is a google earth image of the WHOI (Raubenheimer/Elgar) & SIO (Feddersen/Guza) sensor deployment plan. We coordinated last week to get the best coverage from all of our sensors. Steve Elgar made the nice map below. It will change once we get the new survey after the dredging, but this gives an idea of # of instruments and their distribution. Note, the red symbols are WHOI (Raubenheimer/Elgar).
- Black center = ADCP + pressure
- Red = ADV + P
The other symbols are SIO (Feddersen/Guza)
- White Squares = ADV (vector, denoted SIO-V*)
- Magenta circ = Aquadopps (denoted SIO-A*)
- White Diamonds = WireWalker (CTD+F) + ADCP: the WireWalker are set up in a cross-shore array from the entrance of the dredged channel. One in ~8 m depth and another in ~ 12 m depth. Each WW will measure dye and turbidity with an Ecotripplett (ET)
- Additional: 13 WetLabs EcoTriplett (ET) (not shown in image) to deploy across these locations to meet two goals 1) measure the dilution downstream from the release point 2) measure something like the total flux in and out of the inlet. To this end one plan is to deploy ET near: a) for Downstream Dilution: 04, 0a, 06, 08, 0c; and (b) for Flux: 85, 86, 87, 78, SIO-V7, SIO-V6, SIO-A3, 17
The thick white line is the location of the new (to be dredged) channel. The very thin white lines mark the location of the “current” channel. The medium white contour marks an educated guess of the 4 m depth contour.
There are many other instruments being deployed by various groups (NPS/UMiami, UNH, SIO-Terrill, WHOI-Traykovski/Geyer) among others.
In order to get an idea of the offshore extent of the tidal jet, exchange, and overall dispersion, Matt Spydell has taken the NEARCOM (tide+waves) model output provided by Tom Hsu, Fengyan Shi, and Jia-Lin Chen @ UDEL and released numerical drifters inside the inlet at the start of the ebb tide. These drifters are advected by the currents and also randomly dispaced in a random walk (for details see Spydell et al. JGR 2012 in press) with a diffusivity of 0.1 m^2/s. Arguably this is small for the inlet but ….
The top panel shows the tidal elevation. time=0 is 1.5 hr after high tide. The panels below show the numerical drifters as red dots. At t=1min after release, they are tightly clustered near the release location. The drifters then get ejected out the inlet after 1 hour. They spread and eventually some start to get pulled back to the inlet on a flood tide (t =480 min, 8 hrs after release).
It is interesting to compare this to releasing drifters right at high tide (1.5 hours before the release above). Now, the drifter rush all the way up the inlet before turning around on ebb tide and being ejected roughly 6 hours after release.
Note, in this simulations after 8 hrs, some drifters are more than 3 km from shore!
In order to plan drifter and dye deployments as part of RIVET at new river inlet, we’ve been looking at model simulations from UDEL (Hsu et al. – NEARCOM), U Miami (Reniers et al. – Delft3D) as part of the DRI, and also UNC (Leuttich et al. – ADCIRC) who have graciously given us some model simulation data. We’ll be posting results from each of the simulations here.
First up is NEARCOM (U Del). They ran 3 scenarios. They are:
- M2 Tides + normally incident waves (offshore Hsig = 1 m)
- M2 Tide only (no waves)
- M2 Tide + waves but with drag coefficient 10X larger
The (U,V,eta) over the inlet domain was decomposed into principal components to get major axis and minor axis tidal ellipses. Then the phase lag between the tide level (eta) and the major axis tidal velocity was computed (zero is a progressive wave, 90 deg is a standing wave). Below is shown (left panels) the phase difference and (right panel) std of major axis velocity (multiply by sqrt(2) to get peak amplitude) for the 3 cases above.
Things to note:
- The waves do not seem to have a strong effect on the tidal currents
- Friction makes a big difference
- It is hard to tell how many hrs the velocity lags the tide level in this plots. Soon we will have ADCIRC and Delft3D runs analyzed to compare to. This will make it easier to see.
For the tide+waves NEARCOM (#1 above) run a time series is a little clearer. Below is a eta (blue), U,V (red,green) timeseries over 12 hours of at one location inside the inlet.
Note how the maximum in tide occurs at t=4 hrs, but the velocity does not start to ebb (switch sign, see red) until t=5.75 hrs or so.
The idea of this blog site is to have a place to put all the pre and post experiment ideas and analysis for the entire RIVET teams to share. This should serve as a supplement to the dri-nr mailing list.
WE’ll be posting pre experiment model simulation results soon.
Also: don’t forget the RIVET coordinate system information can be found at: