May 2016

I’ve archived the May 2016 Water Level Chart (at left). The most notable features of the May chart are the lack of rainfall for the month and the inexorable fall of the lake level despite the gate having been mostly closed on the afternoon of Thursday, May 19th. In fact, after the gate closure, there was almost no noticeable reduction in the rate at which the lake lost water during the month (0.025′ before vs. 0.019′ after). The lake level started out at -47.88″ below the top of the dam and fell an average of only 0.02′ per day (less than 1/4″) ending up at -55.68″ below the top of the dam, for a total loss of -7.8″. The lake fell 28 out of 31 days during the month while remaining unchanged on only 3 days. Not once during the month did the lake level rise. 

I wrote about the gate closure back on May 21st (see: “Clary Lake Dam’s Gate Almost But Not Quite Closed“). I presume the dam operator left the gate partly open to maintain minimum outlet flows as required by the Clary Lake water level order, but clearly the gate was left open too much: in my estimation, net outflows (including evaporation) have exceeded inflows by as much as 5 CFS (Cubic Feet per Second). Any way you look at it, the simple fact that the lake level continues to fall indicates the gate opening is too great: minimum flows are never supposed to exceed inflows. For more information about minimum flows and where they come from see Minimum Flows Explained.

Average rainfall for May is around 3.7″ but we received only 1.79″ of rain for the entire month, considerably less than 1/2 the normal amount. Less precipitation means less runoff obviously; it is likely that if we’d been receiving the normal amount of rain for the month that the lake level would have more or less stabilized once the gate was lowered.