The new Minimum Flows Recommendation (see Clary Lake Assessment 3-Apr-13) gives me pause for thought.
First, I’m not quite sure how they came up with this- it appears to be based in large part upon section 6 of Chapter 587, the Standard Allowable Alteration method of determining required water levels in Class GPA (Great Pond Act) waters which however discriminates between a 1′ draw down from April 1st through July 31st and another 1′ draw down (for a total of 2′) between August 1st and March 31st as opposed to a total maximum draw down of 2′.
Second, the document quotes some numbers from the bathymetric survey (the figures 17% of the total lake volume and 14% of the total lake surface area come directly from the data table) but does not arrive at a draw down corresponding to the 25% volume reduction or the 25% area reduction. I’m not complaining, but why? Are they perhaps aware of problems with the modeling of the wetland area?
Third, and I’ve already mentioned this in response to David Hodsdon’s comment on another post, they suggest that the figures they’ve come up with are ONLY intended to protect the main basin of the lake:
Recommended within basin water levels are protective for the maintenance of suitable Water quality, resident fish and Wildlife habitat, and prevention of shoreline erosion. However, it is quite apparent that significant dewatering of valuable Wetland habitat will result in the vicinity of the outlet stream, above the dam.
What’s up with that? One can’t lower the water level in the basin without also lowering the water level in the marsh. How can a 2′ draw down be protective of water quality, resident fish and Wildlife habitat, etc., and yet contribute to “significant dewatering of valuable wetland habitat”?
This sentence is a new addition to the minimum flows recommendation they prepared a year ago.
Fourth and finally, they list minimum outflows which must be met unless inflows are less. How are we supposed to measure inflows? I assume if you’re letting water out and the lake is not falling, then inflows equal outflows. If you’re letting water out and the lake is falling, then outflows are greater than inflows. Finally, if you’re letting water out and the lake is rising, you’re not letting out enough water. This hit-or-miss approach seems amateurish and error prone. Surely there is a better way!
There is: We install a top weir in the dam with stop logs at some level such as 12″ below the top of the dam and walk away and let mother nature take care of it. I wonder what they’ll think of such a plan.
It is also interesting to note that the minimum flow figures are identical to those published a year ago.
Filed under Petition News and Technical Lake Stuff with a hint of Editorial.