USGS Gauge Information

[oasis man]

Question for the board:
Why is it that the USGS water data sites now show the "cfs" charts to be frozen (flatlined at the bottom of the graph), but the gauge height graphs look like they are still recording valid data?? Don't they transmit the data from only one sensor and calculate the cfs from the height??
Thanks,
OM

 

[Mark Griffin]

From the USGS-
Ice-affected streamflow refers to the effects of channel ice on the relation between stream stage (water-surface elevation) and streamflow. Because of physical blockage of the channel and increased flow resistance from ice cover, these effects result in lower streamflows than would be expected from corresponding stages during open-water conditions. In addition, ice effects create uncertainty in real-time streamflow estimates that are needed to help control floods and facilitate navigation.

Because many rivers are frozen during the winter, the discharges computed from the stage-discharge relation are meaningless. Therefore, discharges are not shown on our web site during the ice-affected period because the discharges are not correct and would be misleading.

I guess that means that even with the stage being measured, the channel is being affected by the ice and it's better to report the gage as ice effected, rather than give a cfs flow that is most likely significantly incorrect. The stability of the channel is a key factor in the stage-discharge relation. If the ice (or other factors) changes the channel at all, the cfs could never be correct. Even with the water and air at 34°, shore ice and chunks of ice in the channel would cause problems getting an accurate cfs measurement. I think so anyway. :shrug:

 

[oasis man]

Strteam flows with ice present

Mark,
Thank you for your answer. If I understand you correctly, when the USGS cfs plot is flatlined at the bottome of the graph (due to ice) , I should also ignore the gage height graph, even though it might look sensible. ?
Regards,
OM

 

[Fly Tier]

OM,
If you look further into the USGS gage data, the 15 minute interval or the previous day data, they will tell you when the gage is not funtioning due to ice.
If you have the particular gage number or location you are referring to, I can look up the details and get back to you on its functionality and readings

Mark,
Thank you for your answer. If I understand you correctly, when the USGS cfs plot is flatlined at the bottome of the graph (due to ice) , I should also ignore the gage height graph, even though it might look sensible. ?
Regards,
OM

 

[Big_Spinner]

Hi,

Gauge height is still reading correctly unless the chamber that has the water is frozen.

The other problem is that the chamber may be higher or lower than true reading due to ice in the channel.

This was a problem for NYS when they tried to maintain minimum flows during the winter. They now use a measure of inflow into the reservoirs (by change in res height) to calculate the other natural flows that would effect gage readings. This then gives them a fairly accurate reading of flow at Hale Eddy (for example) and they then release water to maintain 225. This is a whole lot better than the old methods. IT still tends to react a bit slowly in situations like we just encountered.

Example: As the gauges were approaching levels when extra releases would be needed, we encountered a hard freeze. This shut down gauges and stopped some significanbt inflow overnight. I think (but I am not sure) that levels dropped below the minimums for a day or two. West Branch release is now about 125 cfs and East Branch is about 150 to maintain their respective minimums (WB = 225 and EB = 175). Releases a couple of days earlier would have resulted in less anchor ice and channelization.

I have been working on a way to get quicker anticipatory responses to alleviate this problem. Progress is being made.

See ya,

Jim