Wivenhoe Dam near Brisbane, Australia is at the center of controversy in its role in the recent flood. The dam, as is commonly the case, is expected to serve two seemingly contradictory functions. On the one hand it is a buffer against drought, meaning that it is desirable to keep it more full in the eventuality of low precipitation. On the other hand, the dam is a buffer against floods, meaning that it is desirable to keep it more empty in the eventuality of heavy precipitation. Since keeping the reservoir full and empty are not simultaneously possible, it then is necessary to balance these objectives. Since future precipitation is uncertain, the dam's management is thus a matter of decision making under uncertainty (where risks are known) and ignorance (where they are not).A reader (thanks DB!) passes on a lengthy article from the Great Plains Examiner out of Bismark-Mandan, North Dakota on the management of upper basin reservoirs on the Missouri River. The article describes a decision context and outcome remarkably similar to what we saw in Australia earlier this year.
The period between March 20 and May 6 has been difficult for the Army Corps of Engineers to explain. During that span, the Corps’ water managers kept river levels low and stockpiled near-record amounts of water behind the three upper basin dams on the Missouri River, despite evidence that the Rocky Mountains were holding a lot more snow than normal.The article includes a remarkable admission from Jody Farhat, the chief water manager for the Missouri River reservoir system:
The reservoirs were so full by early May that they couldn’t contain the late-spring rainfall that pounded Montana and the Dakotas.
Public records studied by the Great Plains Examiner show Fort Peck, Garrison and Oahe dams each were holding more than 99 percent of their total water capacity in late April. Lake Sakakawea, the largest reservoir along the river, had risen 10 feet into the flood-control zone before the Corps of Engineers began ramping up release rates from Garrison Dam to create storage space for the heavy rain and melting snow.
Emergency releases from the reservoirs in June flooded communities along a 1,700-mile stretch of the Missouri River. Almost immediately, people who live in the watershed accused federal water managers of mismanagement, officials with the Corps of Engineers pointed at their operations manuals . . . They said the problem wasn’t how they managed the reservoirs; instead, they blamed a set of conflicting congressional mandates and pressure from political leaders up and down the river system to manage the water for special interests including recreational boaters, environmentalists and the energy industry.
By the end of April, Lake Sakakawea had risen to near-record levels and the Corps of Engineers realized for the first time that the mountains were holding about 40 percent more snow than average. Until then, the Corps was expecting about 10 percent more snow than normal, Farhat said.Wow.
“By May 1, we were going ‘Holy smokes, this is not just a little-above-normal water year. It’s way above normal,’” she said.
Larry Larson asks a question to which I suspect he has an answer:
“What were they doing in the winter months and early spring when this was building?” asked Larry Larson, executive director of the Association of State Floodplain Managers. “Were they preparing for it, or were they playing the odds and then found themselves caught in a box?”