[env-trinity] Accidental turbidity release to the Trinity River Nov. 24, 2010
Krause, Andreas F
AKrause at usbr.gov
Fri Nov 26 14:20:54 PST 2010
Hello Trinity River Enthusiasts:
An accidental release of turbidity (silt that makes the water cloudy) to the Trinity River occurred on November 24. The turbidity originated from construction at Lowden Meadows restoration site, located on the mainstem Trinity River just upstream of Grass Valley Creek at River Mile 104.4. The site was completely separated from the river by a series of containment structures to prevent turbidity caused by construction activities from entering the river. Restoration construction activities are being wrapped up in the area. For several days prior, the site was actively being pumped out to clear the turbidity from the water in preparation for removing the containment structures. Sometime early morning on Nov. 24, the downstream containment structure failed and washed just downstream. This failure prematurely connected the construction area with the Trinity River allowing turbidity to be released. The turbidity released is non-toxic.
The cause of the failure was an unanticipated increase in flow releases from Lewiston Dam. The Bureau of Reclamation maintains a steady release of 300 cubic feet per second (cfs) from Lewiston Dam to the Trinity River throughout the winter. The dam releases are based on provisional real-time readings from the Trinity River at Lewiston stream gage (#11525500) operated by the U.S. Geological Survey. Around midnight, the real time readings from the streamgage dropped from 300 cfs to 150 cfs. Consequently, the Bureau of Reclamation, following standard operating procedures, increased the releases from Lewiston Dam by 150 cfs to maintain the 300 cfs winter base flow. Once it was light in the morning, the Bureau of Reclamation visually inspected the stream gage and found it was reading erroneously. The flow drop from 300 cfs to 150 cfs reported by the gage never occurred. Therefore, the corrective action taken by the Bureau of Reclamation inadvertently increased the flow from 300 cfs to 450 cfs. Once discovered, flow releases were brought back down to the 300 cfs target. The reason for the stream gage malfunction is under investigation but was likely caused by the freezing temperatures experienced that night.
The failure of the containment structure at Lowden Meadows coincided with the unanticipated 450 cfs flow release. This flow increase could not have been reasonably foreseen and was not accounted for in the design of the containment structures. The remains of the containment structure that washed downstream were immediately removed from the river the morning of Nov 24. The Trinity River Restoration Program has notified the regulatory agencies (California Department of Fish and Game, California Water Quality Control Board, U.S. Army Corps of Engineers) about the accidental turbidity release. A very minor amount of turbidity is still washing out of the affected area. The site is expected to completely clear within the next day or so. We apologize for any inconvenience the turbidity releases may have caused.
Please contact me if you have any additional questions or concerns.
Acting Branch Chief - Restoration Implementation Group
Trinity River Restoration Program
email: akrause at usbr.gov
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