Oops - fell asleep B4 getting this posted, last night...
Visual evidence (abc13 report, 5 pm(?), 8/30/17, showed Buffalo Bayou (I’m fairly sure), in downtown Houston, greatly down from crest levels, with pretty good current. By greatly down, I mean 10-12 ft. This corresponds fairly well with the data on NWS’ website. Plus the camera angle may have fooled me a bit. :-)
What kind of volume can the Bayou carry past downtown, if the levels downstream have subsided, as evidently* they must have?
*I do not see any gauges down near the Houston Ship Channel.
Update and some clarification, as of 10:30 pm 8/30/17:
ACE’s Lindner says Addicks/Barker levels have crested. (This doesn’t explain Mandatory Evac order last night for SW Barker), but will drain very slowly, as controlled release is “a very tiny fraction” of the water detained.
Addicks outflow was reduced by 500 cfs to check gate integrity. (Shallow reporters do us a disservice, not sure what can be checked dropping outflow from 8000 cfs to 7500 cfs, except maybe pore pressure around the structure, but 500 cfs doeesn’t sound like they’re very worried. Not that any reporters bothered to ask.)
Buffalo Bayou holding steady levels from Addicks to Highway 8, was expected to gain a foot further down, around Piney Point. Water backing up on tributaries feeding the Bayou, primarily north of Bayou and west of Highway 8, Rummel Creek seems to be a focus.
Overflow from north end of Addicks holding steady, low total flow, it appears to have turned south before Rummel Creek, and may never reach Bayou, complex flows, unmapped previously.
“100,000 affected homes” quote amended to apply to all of Harris County. 3000 homes above Addicks, 1000 above Barker, 73,000 total affected from T.S. Allison, ACE expects more from Harvey.
Releases to continue indef, lowering levels in anticipation of future rain events.
My observations...They may not have a solid grasp on total Buffalo Bayou thruput, only levels. In a wide floodplain, additional flow can spread out without changing measured levels. Downstream, in a constricted channel, this would translate to level changes seemingly not connected to upstream events. Difficult to intuit a body of water with a convex upper surface, but river crests and storm surges prove exactly that. These level maxima move downstream, but manifest differently depending on many factors, width, depth, drag, detention, intentional or accidental, etc.
The completed cofferdam for the new gate outlet at Addicks is immediately west of the active gate, (visible on Google maps) but I haven’t found one for Barker. At the time of the Google maps image, I see no sign of penetration or excavation into the embankment itself, looks like they put up the cofferdam and started drying the work area when the shot was taken. Folks expecting the usual pair of cofferdams will be disapointed. In this case, the “diversion tunnel” already exists, in the form of the current gate outlet, and downstream protection where the embankment penetration occurs is either obviated by existing topography, or hadn’t been started when Google image captured.
Finally, big picture observations...detention structures save lives, until capacity is exceeded, or development encroaches. Over time, development will ALWAYS encroach, like percolating water, percolating financial pressure WILL find a way. At that point, flood management has huge “hot potato” political potential, especially in a Fake News environment. I haven’t seen any factionalization over why these homes flood instead those, partly I’m sure because of the U shaped detention geometry, there isn’t a choice. But math and logic rarely impede the MSM...I am very glad I’m not the ACE, manning the gatewheels that open homes to flood, with advance foreknowlege.
Update and some clarification, as of 10:30 pm 8/30/17:
ACE’s Lindner says Addicks/Barker levels have crested. (This doesn’t explain Mandatory Evac order last night for SW Barker), but will drain very slowly, as controlled release is “a very tiny fraction” of the water detained.
Addicks outflow was reduced by 500 cfs to check gate integrity. (Shallow reporters do us a disservice, not sure what can be checked dropping outflow from 8000 cfs to 7500 cfs, except maybe pore pressure around the structure, but 500 cfs doeesn’t sound like they’re very worried. Not that any reporters bothered to ask.)
Buffalo Bayou holding steady levels from Addicks to Highway 8, was expected to gain a foot further down, around Piney Point. Water backing up on tributaries feeding the Bayou, primarily north of Bayou and west of Highway 8, Rummel Creek seems to be a focus.
Overflow from north end of Addicks holding steady, low total flow, it appears to have turned south before Rummel Creek, and may never reach Bayou, complex flows, unmapped previously.
“100,000 affected homes” quote amended to apply to all of Harris County. 3000 homes above Addicks, 1000 above Barker, 73,000 total affected from T.S. Allison, ACE expects more from Harvey.
Releases to continue indef, lowering levels in anticipation of future rain events.
My observations...They may not have a solid grasp on total Buffalo Bayou thruput, only levels. In a wide floodplain, additional flow can spread out without changing measured levels. Downstream, in a constricted channel, this would translate to level changes seemingly not connected to upstream events. Difficult to intuit a body of water with a convex upper surface, but river crests and storm surges prove exactly that. These level maxima move downstream, but manifest differently depending on many factors, width, depth, drag, detention, intentional or accidental, etc.
The completed cofferdam for the new gate outlet at Addicks is immediately west of the active gate, (visible on Google maps) but I haven’t found one for Barker. At the time of the Google maps image, I see no sign of penetration or excavation into the embankment itself, looks like they put up the cofferdam and started drying the work area when the shot was taken. Folks expecting the usual pair of cofferdams will be disapointed. In this case, the “diversion tunnel” already exists, in the form of the current gate outlet, and downstream protection where the embankment penetration occurs is either obviated by existing topography, or hadn’t been started when Google image captured.
Finally, big picture observations...detention structures save lives, until capacity is exceeded, or development encroaches. Over time, development will ALWAYS encroach, like percolating water, percolating financial pressure WILL find a way. At that point, flood management has huge “hot potato” political potential, especially in a Fake News environment. I haven’t seen any factionalization over why these homes flood instead those, partly I’m sure because of the U shaped detention geometry, there isn’t a choice. But math and logic rarely impede the MSM...I am very glad I’m not the ACE, manning the gatewheels that open homes to flood, with advance foreknowlege.