Contributed by Willow McConochie

 

CLAIM: Tides that are above 10.3 feet will flood the marsh.

EVIDENCE: We measured the salinity of water samples with refractometers on May 16th, after a 10.3 tide. Our sample 2A, taken at the upstream culvert, had 25-27 ppt of salt, 2B had 13-15 ppt. Both of the samples from the outlet at the marsh had 0 ppt of salt. We also found out that the sample at end of the culvert, on the left hand side had 7-4 ppt.  May 29th, we recorded in nine different places and all of them had 3-10 ppt of salt, and most had 3 ppt. This was very soon after a 10.6 foot tide. The location with the most ppt, was the marsh side of the dam on the right hand side, we recorded 10 ppt.

Data Table, May 16, 2018

DATE	SAMLE #	LOCATION	PPT	TEMP (ºC)	GROUP
5/16	1A	outlet at marsh	0	26	Willow, Gwen, Maggie/Mya, Lydia, Thomas
5/16	1B	outlet at marsh	0	NA	Addie, Lute, Adrien
5/16	2A	upstream culvert	25 27	NA	Mya, Lydia, Thomas/Addie, Lute, Adrien
5/16	2B	upstream culvert	13 15	12	Willow, Gwen, Maggie/Henry, Zeke, Shaun, James
5/16	3A	left of ocean, end of culvert	4 7	NA	Willow, Gwen, Maggie/Henry, Zeke, Shaun, James

 

 

REASONING: Our 10.3 tide was an estimation; we used the rule of twelfths to estimate it. The whole tide cycle takes twelve hours, and every hour, the tide either rises or recedes 1/12. Here is the calculation: May 16 – high tide was at 12:18 pm, and was a 10.3 foot tide. At 11:15 am, we measured 26 inches of water in the culvert, 1 hour before high tide.

• 1/12 of 10.3 = 1/12 x 10.3/1 = 0.86 feet= 10.25 inches
• 26 + 10.25 = 36.25 inches. 36.25 inches of water will be in the culvert at  high tide.

The difference of elevation from the dam to the culvert is 3.3 feet. and there was only 36.25 inches of water in the culvert. In order for this tide to flood the marsh, there would have to be 40 inches of water in the culvert.

Additionally, if our claim wasn’t true, then all of the samples we took, that were above the dam, would have had 0 ppt of salt. And we are sure that we did the calculations correctly, and we checked the refractometer to make sure that it was reading 0 ppt with distilled water.