This graph measures water levels downstream from Argo Dam. Water levels are not supposed to fluctuate this much – it's not good for the river.
Update: I checked with USGS to make sure that the gauges were working fine, and got back this result:
We're pretty certain everything is working just fine there. I believe we have a hydrologic technician there today making a streamflow measurement and he'll verify the operation of the equipment at the same time. Tom
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Flow at Barton Dam was through the gates from Aug 31 to Sept 5 coincident with the higher fluctuation. This was also the case Aug 19-20.
The city just sent the first report on run-of-river operation to FERC to fulfill a request by the US Fish and Wildlife Service as part of the operating agreement modifications to address the lack of gauging above and below the Barton Dam (which was required by the original 1984? Exemption for the dam). Data includes hourly flows through the powerhouse and gates.
Quick visual inspection of the data shows that flow fluctuation through the turbine is roughly equivalent to variation at the USGS gauge. Comparison is somewhat difficult because the tabulated data isn’t in electronic form, and the one hour averages from the city don’t match the 15 minute intervals from USGS.
http://elibrary.ferc.gov/IDMWS/common/opennat.asp?fileID=13057301
I’ll be interested to see the next report which should include the period you’ve highlighted. Hopefully the data will be available electronically in the future, even if not in realtime.
Another piece of the Huron flow picture that you may be interested in the is the Allen’s Creek gauge. It’s important to note that peak flows are not reported accurately – flow is calculated as flow velocity (ft/s)* channel width(8 ft) * channel depth(ft), however when depth reaches a certain level velocity is no longer reported. The box culvert where the sensor is located is 8×10 feet and in heavy storms shows depths of up to ~14 feet indicating excess pressure of several feet of water or around 2psi… consistent with blowing manhole covers off and flooding Depot street. The gauge tops out around 350cfs, but flows can exceed 1000cfs according to the 1982 Allen Drain study:
http://a2docs.org/doc/223 (which you posted)