Fable
The fish pond gatekeeper and the sluice gate
The reservoir management office set a water level warning line: once the water level exceeds six meters, open the gate to release water; below four meters, close the gate to store water. For the first two years, it was executed rigidly. Administrator Xiao Zou received the instruction—release when above six meters, without asking why, without checking the weather forecast, without discussion.
One year, continuous heavy rain upstream sent the water level surging from 5.8 meters to 6.2 meters. Xiao Zou immediately opened the gates to release water. After releasing all day, the water level dropped back to 5.5 meters. That same afternoon, the city happened to be holding a dragon boat race, and the downstream channel was churned up so badly by the released water that the race was canceled. The city leaders called to chew him out. Xiao Zou felt wronged: the regulation says open the gates at six meters—what did I do wrong by following the regulation?
After old engineer Duan took over management, he changed a line into a range. Within the range was the safe water level: four meters to six meters. Below four meters, water must be stored; above six meters, water must be released. In this middle "tolerable window," whether to release or store depended on weather, downstream activity, and power generation demand, and the manager could make a judgment.
Xiao Zou asked Lao Duan: then don’t the precise numbers become meaningless? Lao Duan said: No, the precise numbers tell you where the bottom line is. If it exceeds six meters and no water is released, the dam will burst—that is absolutely not to be crossed. But at five and a half meters, you can buffer a little according to downstream conditions, and that buffering capacity is your operating space. Without that space, every time you exceed the limit you have only one set of actions, and either upstream or downstream someone will suffer.
The management office later set a new rule: when the water level is between four and six meters, the administrator may dispatch according to actual conditions, but each dispatch must record the reason and be reviewed at month-end. If the water level exceeds six meters more than twice in a month, it means the previous dispatch was too conservative, and pre-release should start earlier the next month. If it falls below four meters more than three times, it means the previous approach was too aggressive, and the next month should be more conservative.
A year after the new rules took effect, the dragon boat race was no longer flooded out, and the farmland downstream was no longer parched. Little Zou summed it up: in the past, looking at a single line, the feeling of pressure was "never touch it, or you'll have to pay." Now, looking at a range, the feeling of pressure is "how much room is left, how much to use for this dispatch and how much to keep." A single line makes people tense; a range lets them make judgments.
Someone from the neighboring reservoir came to visit and asked Old Duan: isn't your six-meter warning line the same as our six-meter warning line? Old Duan took him to the console: there were two lines on the screen—one was the six-meter red line, and beside it was a five-and-a-half-meter orange line. Old Duan pointed at the orange line and said: above the orange line we start acting; we don't wait until the red line to panic. The space between the orange line and the red line gives us composure.
After the visitor returned, he modified the control panel and added an intermediate range. During internal training he said: a high water level is not what's frightening; what's frightening is having only one option, one point in time, one chance in your operation. Manage the space beyond the red line well, and only then can the red line hold.