[Tweeters] RE Estimating Tides at Grays Harbor
bdriskell at comcast.net
Fri Apr 30 16:44:15 PDT 2021
Marine scientist here, please pardon the lecture. The executive summary is: There are no good ad hoc guesses for estimating the right time to meet the tide.
Firstly, it is not the timing that is important, it is the tidal height. Consider the birds behaviors. Generally, shorebirds work to feed where the food is best and effort is least. Thus, they will feed during low tides and rest when the food is covered. On a rising tide, they get pushed higher and higher up the beach until they reach a zone where food is no longer found (or not worth the effort). Then, it's nap time or time to move on. The reverse is going to happen on the dropping tide. They will show up when food is exposed and continue to follow the dropping tide down and then back up through the exposed cycle.
From my rough observations, I have estimated that the birds at Bottle Beach (across Grays Hbr from Bowerman) are pushed into viewing range at approx +4-+5' incoming tide. Note I have not checked this tidal value at other GH beaches but suspect it represents a rich intertidal feeding zone and thus, may generally apply to most beaches of the region. However, I caution, this +4-+5' was based only on birds at Bottle Beach coming close enough to view; it might not be an absolute for other beaches. At Hayton Reserve (Skagit), I think the birds are pushed off the Sound and show up in the basin at ~+8' tide and then only stay until the basin fills (unknown departure height; perhaps Marv or Gary can confirm).
Now the lecture. Westport is the reference station for all of Gray's Harbor; actual tide data is collected there. Elsewhere in Gray's Hbr, at Aberdeen, for example, the reported tides are modeled based on long-term data from the Aberdeen location. Heights and times at in-between landmark locations, like those published in the non-official tide charts, are interpolated
for the local sites using published corrections for time and elev.
For the shorebirds, as you've observed, the "2 hr before high tide" estimate might work at times but will more often disappoint. Here's why: in Washington, there are two high and two low tides per day--and for complicated reasons, they are not equal. But consider, if your 2-hrs-before-high for the first tide did just happen to deliver the right tide level, how, if they are not equal, could it possibly work for 2-hours-before the second high of a different height to also get the desired height? Automatically, half of the visitors expecting the same "right" height are going to be showing up at the wrong time.
But back to the task, the ONLY way to estimate the correct timing is to consult a tide chart (available online) and see when the tides are crossing at that height.
Diana M.s astute advice in the previous mssg about wind and weather also applies but is harder to adjust for. Generally, onshore winds push more water into the system (higher highs), offshore winds speed it out. High pressure weather modestly decreases heights yielding lower low tides. Low pressure weather may produce higher tides. And it gets even more complicated but I'm stopping here.
And please, build and share your own observations. Do some fact-checking! Check your old photos for your own best-time-at-the-beach on that once memorable day. Then dip into the tide charts for that date & time and see what the tide height was. Oh, the accolades you'll receive (and the disappointments you'll banish) when you can land your birding party on the beach at the right tide for optimal viewing! (Is that Nobel worthy?)
may the (tidal) force be with you...
Date: Thu, 29 Apr 2021 14:02:26 -0700
From: Dianna Moore<osdlm1945 at gmail.com>
To: Elston Hill<elstonh at yahoo.com>
Cc: tweeters<tweeters at u.washington.edu>
Subject: Re: [Tweeters] Tides at Grays Harbor
<CA+P8rU+KXEmt-0gDuNrDw3wfD64Us6DZRm3-8vcG2jLvfGCSFA at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Thanks for sharing this, Elston. I tell everyone who calls about the "best"
time to view to be aware of the time and level of high tide, especially if
it's windy at the refuge (the wind pushes the water higher and it stacks up
at the far/east end of the mud flats), or if going to Bottle Beach...go
even earlier than the recommended two hours early.
Meanwhile, out here on the beach....well, you can tell the migration is in
full swing. Just lovely!!!
On Thu, Apr 29, 2021 at 12:19 PM Elston Hill<elstonh at yahoo.com> wrote:
> My wife and I went to Grays Harbor on Monday. I had the tide charts and
> being a total novice I thought we needed to arrive a little bit before high
> tide. Fortunately, I tend to arrive way to early for most events, so we
> arrived at the NWR more than two hours before high tide. We got there just
> in time for a great shore bird show. Most of the us left almost two hours
> before the high tide on my tide charts as the show was over. On my way out
> I encountered a number of sophisticated birders (people with big scopes)
> coming in. I think they missed the show.
> The same thing happened to us the next day at Bottle Beach. We arrived
> about 2 1/2 hours before the high tide and again arrived just in time for
> the show. The birds were all gone by two hours before high tide. I heard
> someone say that the tides were unusually high. And when we came back to
> Bottle Beach the next morning for a quiet walk, we could see that the tide
> rose more than two feet higher than the point where the water covered the
> mud flats and the shore birds left.
> I do not qualify as a serious birder, but I thought this information might
> be useful if my observations are correct. It appears that the timing for
> viewing shore birds depends not only on high tides but also on how high the
> tide will be.
> Tweeters mailing list
> Tweeters at u.washington.edu
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