Monday, January 24, 2011

How small objects move in water

In my article The State's "trump card" is a Joker, continued, I included some photographs of 2 logs floating upstream in Baxter Creek on December 22, 2010. The photographs were taken from 9:30 - 9:35 a.m. The water level during this time rose from 6.44 feet to 6.55 feet, according to preliminary water levels published by the NOAA Richmond 9414863 station. They were travelling in the expected direction for a rising tide, but the speed surprised me: a rate of 1.2 mph maximum (assuming a mere 5 minute lapse time) or 1.0 mph minimum (assuming nearly 6 minutes lapse time). The winds were very mild, ranging from 2.5 mph to a maximum gust of 4.0 mph, and from the NW/WNW, so obviously the logs were not getting any help from the wind.

On December 23, I was again at the site during a rising tide, but I arrived when the tide was still quite low, as I had a number of experiments I wanted to conduct.  One of these experiments was to see how small objects behave in the water just in front of the south breakwater, specifically the section of breakwater that Conner would have to come across to wash ashore.  For this experiment, I used pop bottles partially filled with water.

The first pop bottle was put into the water in front of the breakwater at 7:52 a.m. The preliminary water level was 3.30 feet, Winds at 1.3 mph from the NNW. The last photograph was taken at 7:54, 2 minutes later.








The bottle ended up caught in a crevice under one of the large rocks, as shown in this video.




I didn't see that pop bottle for another 3 hours when I spotted it at 11:09 a.m. floating northward towards the other debris I had put down.  It had finally broken loose from the rocks sometime between 11:02 (PWL 6.23 ft) when it wasn't in a photograph of that spot and 11:09 when it was.  By this time, the water level was 6.30 feet.  The red arrow points to the bottle, and the orange arrow to the rock frequently referred to in the Conner Recovery Site Field Trip - October 6, 2010 series of articles.  That rock measures to be 7.2 inches tall, so that is how deep the water is at this water level.  It took a water level of 6.23 feet to dislodge it from the rocks.


In the second experiment, I used another pop bottle.  This time, the pop bottle was out in the open, and it behaved rather unexpectedly.  I put the bottle in the water at 8:02 a.m., PWL 3.42 feet, Winds from the NW at 2.5 mph.  You can see how calm the waters are.  Over the course of the 8 minutes that I monitored its movement, the winds were as low as 1.6 mph.  In the first picture, you can barely see the white end of the pop bottle behind the very large rock.  The movement is southeast initially, and then mostly south.  This is against an incoming tide with virtually no wind to aid its movement.









On September 5, 2004, George and Valerie Harris and I were at the Conner site and we threw in some water balloons, which moved westward and finally washed into the rocks near the SW corner.  The water level was 4.7 feet when we threw the balloons in and the winds were from the NNW at 10.4 mph.  The water balloons moved contrary to the wind.

On July 5, 2006, I conducted the same kind of experiment with a plastic doll.  The doll was put into the water at the same place as the 2nd pop bottle, with a PWL of 5.77-5.79 feet.  Winds were gusty that day, as you can tell by the wave action.  UC Richmond data gives the wind speed at 10-12 mph, with maximum gusts up to 18 mph.  Point Isabel shows stronger winds preceding the high tide, up to about 17 mph, and stronger gusts also, about 23 mph, with even stronger winds and gusts just after the tide peaked.

This video was taken 8 minutes after the doll was put into the water, the water level was 5.82-5.84 feet, and wind was from the SW.  Warning:  Don't watch the video if seeing a doll in the water will upset you.



This next video of the plastic doll was taken after the tide peaked and the water level dropped from 5.71 to 5.68 feet during the duration of the clip.  Even though this is now an ebb current, going out of the Bay, the doll is not being pulled away from the rocks, but has moved a little bit west.  Wind is still from the SW.  Warning:  Don't watch the video if seeing the doll thrown into the rocks will upset you.



Summary
One pop bottle circled around the rocks and then got caught in a crevice.  It took a 6.23 ft water level to break it loose from the rocks and float it onto the site, where it soon joined the other debris.

One pop bottle floated south, away from the site, going against the incoming tidal current with no assistance from the wind.

Water balloons floated west alongside the breakwater contrary to the wind.

The plastic doll floated eastward fairly consistent with the direction of the wind, unable to wash ashore because of the huge size of the rocks in that section of the breakwater.  When the tide changed to an ebb tide, the doll did not wash out into the Bay but continued to bob up and down along the shoreline moving westward until a very large wave threw her into the rocks.

4 comments:

Bruce Dombrowski said...

Well,
I certainly hope the the trash was cleaned up after the experiment. balloons are a danger to wildlife. and if the police want to charge you with littering, they have all the evidence they need. lol

Burkey said...

The blog looks great.

Marlene Newell said...

Thanks, Burkey. It's part of the new additions to Google's blog experience -- I like the template much, much better than the old one.

Burkey said...

It looks great and is easier on the eyes, the neutral colors are somehow gentler.