Shoaling and Clipping in LMich debunked
Craig
clipping and shoaling "prevent" waves over 3.2 feet in
SW Lake Michigan, and he claims that lower water levels
have caused this.
Now he uses a bathymetry image from NOAA that "proves" this.
(I turned him on to this a number of years ago)
He forgot to check the scale... which is in meters.
So here are a few magnified images and we see that:
1) I stated that at one of the breaks (the first sandbar)
the depth was 17 feet. Then down to 25-29. Off shore it is
75 feet, then down to 250 feet (at the bottom of the Chippewa
Basin).
Clipping may prevent a 15-20 foot wave, but NOT a six foot wave..
by any stretch.
First: the Bathymetry of the South Chippewa Basin. Note the
blue portion... 150 METERS deep. Note the red portions...
25-50 meters deep. Deep enough for 800-1000 foot freighters
to tarry.
http://www.lakesurf.com/michigansmaller.jpg
Here is one break magnified that I say has shoulder to head
high waves from time to time. Again, the RED is 20-50 meters deep.
The arrow points out the location of the break.
Finally, the following navigational chart shows that break's sandbars
and exactly where waves break on bigger days.
http://www.lakesurf.com/Whihala.jpg
The chart is dated 9/30/2002.
Now what is it that prevents a six to eight foot wave?
Whose BIG LIE is being perpetrated?
People who surf here regularly know Gleshna is
the Great Lakes surfing dunce.
And another thing, Gleshna, you care a lot more about your
alt.surfing "credibility" than I do. I surfed today,
the buoys were at 5 ft on a NW. You likely didn't.
Gleshna
>(I turned him on to this a number of years ago)
The fact is that the image was posted by someone else. I obtained this via
Google-Groups. Craig, please, try to get your facts straight.
>I stated that at one of the breaks (the first sandbar)
>the depth was 17 feet. Then down to 25-29. Off shore it is
>75 feet, then down to 250 feet (at the bottom of the Chippewa
>Basin).
Craig, I would suggest that you consider wave length relative to the bottom.
Gleshna
Craig
wavelength
and shoaling prevent Lake Michigan waves from approaching even their
averages.
The graphics and claculations I provide prove otherwise.
The periods are cleaned up by geographical and man-made
features like jetties and piers.
Note that the calculations are the SMB, which is pretty simplistic. I
have also
worked with JONSWAP, which is an add-in function to Mathematica.
Results are pretty similar.
The point is that if we know the MEAN wave is about 7.2 ft, there are
numerous samples far above that, depending upon the probability
distribution. The jetties and piers clean that all up, leaving us
(locals) with fun surf.
Under the posted constrains:
28 knots idealized wind N to S for 19.5 hours
Average Wave period 8.1 seconds
5% chance that wave exceeds 35 feet
Average 7.2 ft
Now this is using a NORMAL probability distribution. Change that and:
waves have a far higher probability of very small size, far higher
frequency
of large waves exceeding ten feet.
And given cleanups and given shoaling....fairly frequent observations
of chest to head high surf in southern Lake Michigan.
Sndbchguy cleared up a lot when he RESPONDED to the following back in
2000:
> First off, I live next to Lake Michigan and have been there > mostly
my whole life, except when I lived in LA and other > places (when i
lived next to the Pacific).I have NEVER seen a > wave bigger than
about 8 feet here. And that was during a 60 > mph wind storm. But that
was onshore. > What about in open water?? I have seen Greg Schmidt's
page. > > I was looking for a method to calculate (very approximately)
> the maximum wave height given fetch, surface wind speed, etc. > This
is pretty easy to do using algebra, by using constants and > then
backing out the wave height parameter, given acceleration > due to
gravity will be 9.81 m/s^2, etc. This method is the > Sverdrup, Munk
and Bretschneider method used for limited fetch. > > The maximum
possible wave height, given the other constants, > would also be at
the point of maximum possible fetch, right? > Given a body of water
that is long and narrow from north to > south, the greatest possible
wave would be the at the greatest > point of fetch from north to south
before the bottom gets "in > the way". > > I thought there might be a
fairly easy method to determine the > maximum wave height, given other
constants. Simplistic, maybe. > But good conversation. > > Also, the
methods documented do not take into account > salinity?? Salt water is
heavier than fresh water, where > salinity = 1.80655 Cl. > Would this
also play a part?? Well, there really isn't a maximum height, per
se...only probabilities of observing a wave of a specific height, or
the heights of various averages of wave height. A bit of background: A
wind blowing over the surface of the water carries energy. Shear
between the moving wind and the nearly quiescent sea water results in
energy being transferred from the wind into the water. The energy
transfered to the water is expressed in the form of waves. This
transfer doesn't occur instantaneously, so the wind must blow for some
time to produce the maximum waves that are possible for that wind
speed. At the same time, the waves are moving more or less along the
mean direction of the wind, so the wind must blow over a distance that
is related to the speed of the waves and the time required to transfer
the energy (this is essentially the "fetch" required to bring the
waves to the maximum size that wind can produce). The size of the
waves no longer increases when the loss of energy matches the rate at
which the wind can transfer energy to the water. The loss mechanisms
include wave breaking (e.g. "white-caps"), and the movement of waves
(and hence energy) away from the area where they are being generated.
The first waves formed are the small capillary waves, whose
characteristics are determined by the surface tension of the water and
gravity (and the wind, of course). By various mechanisms, the energy
input into these waves is transferred into the longer wavelength and
period waves that are governed by the forces of gravity and inertia.
The energy transferred into these 'gravity' waves are, in turn, passed
onto other gravity waves of ever increasing period and wavelength by
various mechanisms (wave breaking is one of them). As a result, there
are waves of a wide range of wavelengths present within (or
immediately outside) of the area of generation. If this area is
sufficient long that the input of energy from the wind matches the
loss of energy due to wave breaking and the propagation of waves (and
energy) out of the area, the collection of waves (of all the
wavelengths present)is said to be a "fully developed sea" (or "FDS").
Among this range of wavelengths (or, equivalently, periodicities),
there will be one wavelength (period) that has the highest average
energy. The energy of these waves is commonly called Em, and is
sometimes expressed in units of square feet. For convenience, in the
subsequent discussion I'll designate the square-root of Em as E12
(which will have the dimensions of feet). With that background, here's
some relationships between average wind speed, V, (in knots) and other
quantities (from: Oceanography and Seamanship, Wm. G. Van Dorn, Dodd,
Mead & Company, NY, ISBN: 0-396-06888-X -- highly recommended as an
intro to oceanography and waves): E12 = 0.0068*V^2 (note: * indicates
multiplication; ^ indicates the power to which V is to be raised, i.e.
here it indicates V-squared) Fm = 3.65*V^(4/3) = minimum fetch (miles)
to reach a fully developed sea tm = 6.43*V^(1/3) = minimum wind
duration (hrs) to establish a FDS Tm = 0.38*V = period (seconds)
associated with the longest wavelengths in the collection of waves Ta
= 0.29*V = average observable wave period (seconds) La = 3.4*(Ta)^2 =
0.28*V^2 = average wavelength of the waves in the FDS So, given the
length of some path along the Great Lakes, you can calculate the
maximum wind speed for which you can achieve a fully developed sea
(FDS): V(knots) = (Fm(miles)/3.65)^(3/4) Then, if you want, you can
also calculate how long the wind must blow at that speed (tm) to
generate the FDS. Once you're satisfied that you can generate a FDS,
calculate the energy, Em, at the maximum in the spectrum of waves.
When you have Em (and hence E12), you are ready to calculate the wave
heights according to various ways of measuring that height. So,
assuming that you are either in, or just downwind, from an area where
there is a fully developed sea, here's the relationship between
various wave height averages and E12 (again, from Van Dorn): Hf =
1.41*E12 = most frequent (most probable) wave height Ha = 1.77*E12 =
average height of all the waves H3 = 2.83*E12 = significant wave
height (= average height of the largest 1/3 of the waves = wave
heights reported by the NDBC buoys, etc.) H10 = 3.60*E12 = average
wave height of the highest 10 percent of the waves. But the maximum
wave height doesn't, of course, stop there (there is graph of wave
height vs probability in Van Dorn). For example, Van Dorn notes that
out of every 2600 waves, there will be a 5% probability of observing a
wave that is 6.6*E12, or about four times the height of the average
wave. Note that the farther you get away from the area with the FDS
the smaller the heights will be associated with each of these averages
(as waves are traveling with different wave speeds, according to their
period, and thus the energy in the collection of them is spread out
over an increasing length of time as you are increasingly distant from
the source of their generation). I hope that this helps. With regard
to the effect of the density of the water: In deep water, the energy
will be split between the wave-associated orbital motion of the water
and the wave height. Since sea water has a density about 3.5% greater
than fresh water, the height of fresh water waves would be expected to
be about 3.5% higher than waves of equivalent energy in the ocean (and
the orbital velocities would increase by the square-root of 1.035 =
1.017, or a 1.7 percent increase). sdbchguy
sdbchguy <sdbchguy...@hotmail.com.invalid> wrote: > ....<ad
nauseum...clipped>... [ad nauseum continued]: Sorry about that...I'd
intended to do the calcs in my previous post--but I couldn't resist
taking a break to hit the surf. So here's the calcs: It appears to me
that the longest straight-line path, i.e. the maximum fetch, in Lake
Michigan is a little over 300 miles (311 mi from Gary, IN to just east
of Manistique, WI). The highest wind speed for which the seas will
become fully developed over that fetch is: V = (Fm/3.65)^(3/4) =
(311/3.65)^0.75 = 28.0 knots (any higher wind speed will not produce
any larger waves) The time that this wind must constantly blow at this
speed to achieve a fully developed sea is: tm = 6.43*V^(1/3) =
6.43*(28.0)^0.33 = 19.5 hours If those conditions are met, then the
seas (just offshore of Gary, assuming a wind from the north) would
have the following characteristics: E12 = sqr-rt (Em) = 0.0068*V^2 =
0.0068*(28.0)^2 = 5.34 feet Hf = most frequent (i.e. most probable)
wave height = 1.41*E12 = 1.41*5.34 = 7.5 ft Ha = average height of all
waves = 1.77*5.34 = 9.5 ft H3 = significant wave height = 2.83*5.34 =
15.1 ft H10 = 10-percentile wave height = 3.60*5.34 = 19.2 ft The
average wave period will be: Ta = 0.29*V = 0.29*28.0 = 8.1 sec ..and
the period of the waves with the maximum energy will be: Tm = 0.38*V =
10.6 sec 2600 waves of 8.1 sec period will arrive offshore of Gary
within a period of slightly less than 6 hours. During that time, there
will be a 5% probability that one wave will have a height of 35 ft (or
more). Under these idealized conditions, the waves aren't all that
small, are they? On the other hand, the shape will be terrible.
sdbchguy
Craig
surf greater than five feet might be to calculate
the number of days at the north end and south end
of winds >15 to 20 mph. The buoy statistics are dubious
at best.
kemz...@kacm.com (Craig) wrote in message news:<948675dc.02111...@posting.google.com>...
TiKiMaTT
drive to the beach.......but i still can't figure out if it's big enough
to surf .........do you offer a surfing for dummies handbook, would be
interested.............
The Supreme Court
>PUT UP OR SHUT UP. SHOW A SOUTHERN LAKE MICHIGAN SURFING
>SHOT IN WHICH THERE IS CLEARLY MORE THAN 3.2 FEET OF STEEP
>WAVE FACE AND A RIDER. CAN THAT REALLY BE THAT TOUGH ?
PA,
It's clear that LM maxes out at 3.2 feet.
Gleshna
>of chest to head high surf in southern Lake Michigan.
Define, frequent please.
Amazingly, lake surfers tend to take only pictures of smaller lakes such as the
ones that are posted here. I wonder why Lake surfers with frequent head high
waves would only take pictures of smaller waves for posting on the internet.
Maybe the waves are too big to surf?
Craig, a picture of you surfing a head high wave on the southend of Lake
Michigan would be a simple way to support all of your claims.
Gleshna
Gleshna
>Gleshna's thesis for the last MANY years has been that
>clipping and shoaling "prevent" waves over 3.2 feet in
>SW Lake Michigan, and he claims that lower water levels
>have caused this.
Yesterday I surfed waves that were maybe shoulder high. I believe that the
increased water level has allowed the larger waves into the surf zone here.
My original post that somehow triggered your obsession of bitching at me,
worried that the lowering of the Lake by several feet would result in less
potential height. Over the past couple of years, I believe this was the case.
However, the shape was at time superior.
Gleshna
rodNDtube
ROFL! Like, dude... a picture of YOU might PROVE that you live in the
Mid-West. Go ahead Craig, post a pic of OldMans and pass it off as a
Lake Michigan "secret spot." Puke!
Rod Rodgers
eMail: rrod...@bcpl.net
Homepage: http://www.rodNDtube.com/
GuidoPalooza: http://www.rodndtube.com/gp/guidopalooza.html
rodNDtube
Does this support your hypothesis that GL surfers are all stubby folks
with extremely long necks and narrow, tall heads. The Almanac indicates
that GL people are generally the same height as those from the superior
land of Frisco (where the heads are rounder and puffy and shiny).