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Xipe Totec

(43,890 posts) Tue Aug 29, 2017, 09:08 AM Aug 2017

MSNBC - The Brazos (de Dios) River - Arms of God - Will crest at 59' above flood stage Wednesday

Just seen on MSNBC news.

It's already in people's houses and it's going to rise another 10' or more.

4 replies

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MSNBC - The Brazos (de Dios) River - Arms of God - Will crest at 59' above flood stage Wednesday (Original Post) Xipe Totec Aug 2017 OP

I think that means at 59 feet, which is above the flood level muriel_volestrangler Aug 2017 #1

Yup. Igel Aug 2017 #2

There's a note at the first Richmond link relating their heights to NAVD muriel_volestrangler Aug 2017 #4

Shit. B2G Aug 2017 #3

muriel_volestrangler

(101,316 posts)

1. I think that means at 59 feet, which is above the flood level

Reply to Xipe Totec (Original post)

Tue Aug 29, 2017, 10:54 AM

Aug 2017

rather than "59 feet above the flood level".

Current situation at Richmond (close to Houston):
https://waterdata.usgs.gov/tx/nwis/uv?cb_00065=on&format=gif_stats&site_no=08114000&period=&begin_date=2017-08-22&end_date=2017-08-29

normal mean level: 12 feet, current level 52 feet, flood stage 48 feet.

or downriver near Rosharon:

http://water.weather.gov/ahps2/hydrograph.php?wfo=HGX&gage=ROST2

Flood stage 43 feet, current level 52.5 feet (was 20 feet at start of Saturday)

Igel

(35,309 posts)

2. Yup.

Reply to muriel_volestrangler (Reply #1)

Tue Aug 29, 2017, 01:56 PM

Aug 2017

Used to think the numbers were in some sense absolute, above average sea level, but not so sure now. The area's low lying, but the 0 point may just be an arbitrary point that the flood plain map drawer said it is.

Still, if you look at flood gauge information (for example at https://www.harriscountyfws.org/GageDetail/Index/1660?span=24 Hours&v=rainfall) and see that stream elevation is 79' (which is current conditions at that gauge) you won't find that it's 79' above the sea bed. I'm near a high point in that watershed and my phone says I'm 100' above sea level, so maybe it is "feet above (average) sea level." I think I remember that the base elevation of a waterway is the level of the body of water it drains into, but that may just be the simplistic hydrology we teach high school students.

muriel_volestrangler

(101,316 posts)

4. There's a note at the first Richmond link relating their heights to NAVD

Reply to Igel (Reply #2)

Tue Aug 29, 2017, 03:35 PM

Aug 2017

"Add 27.02 to gage readings to convert to elevation above NAVD 1988"

The North American Vertical Datum of 1988 (NAVD 88) is the vertical control datum of orthometric height established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988.

NAVD 88 was established in 1991 by the minimum-constraint adjustment of geodetic leveling observations in Canada, the United States, and Mexico. It held fixed the height of the primary tidal bench mark, referenced to the International Great Lakes Datum of 1985 local mean sea level height value, at Rimouski, Quebec, Canada. Additional tidal bench mark elevations were not used due to the demonstrated variations in sea surface topography, i.e., that mean sea level is not the same equipotential surface at all tidal bench marks.

https://en.wikipedia.org/wiki/North_American_Vertical_Datum_of_1988

so there, the water level is now 79 feet above sea level (27+52).

B2G

(9,766 posts)

3. Shit.

Reply to Xipe Totec (Original post)

Tue Aug 29, 2017, 02:18 PM

Aug 2017

My cousin lives just south of the Brazos.

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