I am no engineer but....
I live on the lake so I am biased, but I also realized that this is only being done for political feel good purposes. The bad part is they are giving the residents in Kingwood and the people who flooded nothing but false hope, when in actuality nothing has been done to prevent another flood from happening. That is the really sad part. The lake was designed for water storage to be a constant level reservoir. Nothing will change the height of future floods unless you add many, many, many more flood gates (there are only 4 now). The entire dam would need to be redesigned to accomplish this.
I figure that using flow estimates during Harvey provided by the following NPR article this would only DELAY the time period that flood waters would rise by 30 minutes.
The height of the flood in Kingwood and surrounding areas would not change at all, only the time before structures flooded would be delayed while the lake is filling back up to it's designed capacity of 42.5'.
Lake Houston capacity is 160,000 acre/feet (from wikipedia).
At a 40' level, the lake is now 90% full....so this constant level lake only has the flood retention ability to store another 16,000 acre feet of water (160,000 * .9 = 144,000) before the water begins to flow over the 3,000' long spillway. During Harvey the our favorite meteorologist, Jeff Lidner from the Harris County Flood Control District said that the flow rate of the Lake Houston Dam on the San Jacinto River on Tuesday afternoon, August 29, 2017 was 168 million gallons per minute. That sounds like a lot of water...and it is. The spillway is just over 3,000 feet long and had 8 feet of water going over it during Harvey.
168,000,000 / 325,851 = 515 acre feet/minute. So that means that every minute there was 515 acre feet of water going over the spillway of the Lake Houston Dam every minute. Now divide 16,000 (the additional capacity that had artificially been created by lowering the lake level to 40' which is 90% of its capacity.....
16,000 acre feet / 515 acre feet/minute = 31 minutes of time before you fill the lake back up to 42.5' and water starts going over the spillway again just like it did during Harvey.http://en.wikipedia.org/wiki/Lake_Houstonhttp://www.npr.org/sections/thetwo-...ward-louisiana