|Posted: Dec 14, 2008Post Subject: How to interpret "Cache Creek - At Rumsey (Calc)"
|CDEC operates a gauge on Cache Creek at Rumsey. Apparently, the site location isn't a very good one, inasmuch as changes to the channel continually seem to change the calibration of the gauge, especially at low flows. Right now (December 2008) the gauge seems well-calibrated, but after the first heavy rain, who knows? In any case, to cover our bases, Dreamflows reports two entries for Cache Creek - At Rumsey, as follows:|
This one - marked Cache Creek - At Rumsey Bridge (Calc) on the reports - is the sum of three different upstream gauges. They are: No. Cache Creek - Rel Indian Valley Dam, Cache Creek - Below Clear Lake, and Bear Creek - Above Cache Creek. The computation includes an estimate for flow travel time. The gauges are relatively far upstream. This computation tends to be accurate when flows are low, i.e. during summer, fall, and in winter/spring during major lulls between storms. On the other hand, it tends to be inaccurate when flows are high, especially during and just after a major storm. This is because the computation fails to take side-streams and seepage into account, and while they're negligible in summer and fall, they can be very significant in winter.
On the other hand, the other Dreamflows flow site - marked Cache Creek - At Rumsey (Gage) - reports the actual flow as it comes off the CDEC gauge and tends to be inaccurate at low flows but accurate at higher flows. See this posting for more details.
As a general rule of thumb, then, use Cache Creek - At Rumsey (Gage) at higher flows, and use Cache Creek - At Rumsey (Calc) the rest of the time.
|Until now, Dreamflows reported two flow sites for Cache Creek at Rumsey, see previous post in this thread.|
USGS took over operation of the physical gauge in 2015, and appears to have done a good job of keeping it calibrated since then. Consequently, the Cache Creek - At Rumsey Bridge (Calc) computed virtual gauge is no longer needed, so has been taken off the Dreamflows reports. To match, Cache Creek - At Rumsey Bridge (Gage) has been renamed to just Cache Creek - At Rumsey Bridge.
Bottom line: Dreamflows now reports only one flow site at Rumsey, and it's a physical gauge called Cache Creek - At Rumsey Bridge.