Possible physical liabilities explored in report

The report details the potential decommissioning liabilities related to hydrology and hydraulics, including “flooding during and after dam removal; changes in the river hydrograph affecting daily peak flows, seasonal flows and river morphology; presence of remnant dam structures within restored river channel; and reservoir drawdown and diversion methods for each reservoir and as a system.”

The report states, “The risks of flooding above current conditions would not be expected to increase substantially over the current condition. The four existing dams were not constructed to provide flood control and therefore the flood risk would not be expected to increase if they were removed.”

The report also states that there is little development along much of the river stretch that would be damaged by any flooding if it were to occur.

Also discussed are the uncertainties surrounding releases from  PacifiCorp-owned Keno Dam, which controls flows between the J.C. Boyle Dam and Iron Gate Dam, the amount of water and sediment that could be released during reservoir draw down and the uncertain future of Keno Dam if the other four dams are taken out of the river system.

“Future ownership of Keno Dam is a high liability with moderate uncertainty given the unknown future ownership and the undefined operational requirements needed to balance fisheries, water quality, and agricultural diversions.”

The report’s authors identify flooding potential in the lower Klamath River as a data gap for the entire river system, calling for an update to existing flood plain maps for the river without dams and identifying new flood risks.

Another data gap discussed is the reservoir draw down and sediment passage sequencing, which the authors state would require a detailed dewatering, dam removal and sediment passage operations plan, “linked to available seasonal water supplies.”

A final data gap for the river system is identified as operation and maintenance of Keno Dam and reservoir, with the report stating that the data gap may be filled by reviewing PacifiCorp’s Operation and Maintenance plan for Keno.

The report also details specific data gaps and solutions for each dam, including scour analysis on the Highway 66 bridge and other minor bridges upstream from J.C. Boyle Dam and performing an analysis of hatchery water supply and availability at Iron Gate Dam.

The next physical liability, of much debate around the county, concerns the sediment behind the three largest dams.

The potential liabilities are listed as “Uncertainty with existing volume and grain size estimates for sediment accumulation in the J.C. Boyle, Copco 1 and Iron Gate Reservoirs; accumulation of organic matter and nutrients in reservoir sediments and the potential water quality impacts if material is released to the river during decommissioning; passing excessive suspended solids could affect the health of aquatic species, clog raw water intakes, and affect irrigator crops and other water users downstream in the short and long terms; reservoir sediment could be contaminated with hazardous or regulated constituents; riverbed aggradation downstream could result from releases of coarse sediment, increasing flood stage for property currently in the floodplain; rapid rates of reservoir draw down could result in sloughing and landslides that affect reservoir restoration, slope stabilization, erosion, and the amount of sediment to be managed” and the regulations under the Clean Water Act that do not allow the natural erosion  that would be caused by the sediment release rates proposed in a 2006 “Dam and Sediment Investigation.” Other draw down and sediment release proposals were not evaluated in the report.

Generally, the data gaps identified in the report call for various studies to make up for the lack of information, specifically, the report states that a previously conducted sediment study did not present a representative sample, so the report’s authors call for “a statistically valid and representative sampling program following Environmental Protection Agency protocols.” The aforementioned study found no dangerous levels of toxins in the sediment behind the dams, but the report claims that the study had not been thorough enough to fully represent the true nature of the sediments.