I live on a lake that is managed primarily as flood control. It has a fixed lake elevation - right at 259.5. As long as river levels down stream are not too high, during periods of high water, they dump water continuously until the lake level gets back to 259.5 - whatever the month of the year. I used to live on a lake built for hydropower and flood control. A lot of the old hydro reservoirs in AR were built back in the mid 20th century. Things were different back then. Not many lake users, facilities were crude at best, no multi gozillion dollar marinas, etc. The water management plan back when these lakes were constructed back in the 40’s and 50’s worked around the “rule curve”. The “rule curve” represented a parabolic graph of water levels based on time of the year. Typically, lakes were expected to be a the low point early winter, after peak generation periods in summer and fall. For example, that might be elevation 535 on lake “X” at mid December. The lake elevation would be at a low point early winter in anticipation of catching winter and spring rains - and reducing downstream releases for flood control. The “rule curve” planned for gradual increases in lake elevation through the winter and spring when most rain occurs in AR. On lake “X”, that might be from elevation 535 in Dec to elevation 548 first of June. Two purposes were served - slowing the release of spring rains downstream, and catching and holding water in preparation for summer hydro releases. As a by product, lake levels were elevated during the summer recreation season. The rule curve parabolic graph would typically be at its highest point first part of summer. Summer rainfall is reduced and regular hydro releases lowered lake elevation for the next six months, until back to a low point elevation of early December. The straight flood control lakes were not designed to have fluctuating water levels. Without excessive rain or drought, they could theoretically remain at the same pool elevation 12 months a year.
The rule curve worked pretty good for for a lot of years. Several of the AR Corps lakes I am familiar with started seeing public and private pressure to modify the water control plans in the 80’s. Marinas were growing in size - once designed to stable rental 16 footers, houseboats were now taking over. Marina facilities do not do well sitting on the lake bottom all winter. Some lakes saw housing developments around the lakeshore. Local towns were becoming a tourist based industry due to lake visitation. Motels and restaurants were supported largely by lake visitors. Campgrounds were upgraded. It didnt matter much what the lake elevation was when a campground amounted to picnic tables and outbouses. Developed camp pads, water, electric, flush bathroom and shower facilities, sewer, and even cable - the campgrounds started catering to more and more “off season campers”, who demanded more consistent water levels throughout the year. On many lakes, the rule curve was greatly modified - or abandoned - in support of the various local demands.
A water control plan used to manage the lake levels in the reservoirs is devised from years of historical hydrography, rainfall and drought information, human occupation, power demands, etc. - both upstream and downstream of the dam. It was always odd to me that the Govt bought flowage easements above the dam, allowing them to flood private land, and restricting development, in those areas - and didnt buy flowage easement downstream in most cases. Over half my property is in a flowage easement - cant build anything in that ground. A lot of development has occurred in historical flood plains downstream of the dams. People were lulled into complacency by years of fairly stable water in the river valleys. I know in the past decade or two, some serious flooding of developed areas has occurred not far downstream. That development causes the corps some pause when a large water release is desired, but to do so would put water on downstream development. I always thought, how great would it have been, if the Govt would have bought all the normally flooding bottom ground, made public ground, and allowed to flood as needed. But, no deal.
And then came the rains. Rain amounts that would have been considered abnormal back in the 1950’s, are now average. And it isnt just rainfall amounts upstream, but downstream, and even areas hundreds of miles away. Rainfall and snow in Minnesota could affect water releases from AR Corps lakes. Downstream water levels often restrict water releases from upstream dams. Many folks will be griping about high water in a local reservoir, completely ignoring that if the Corps released that water, it would flood someone downstream. The graph below shows the difference in average annual AR rainfall of the over the past 120 years. The five year 2015 - 2019 period is by far the wettest period in AR in that 120 years. Far wetter than when most of the AR dams were built and water control plans developed.
It is difficult to accommodate all the changes, challenges, and mother nature - that have occurred over the past 70 years since these dams were built. It isnt as easy as just modifying lake levels at hydropower dam. Generator efficiency varies with lake level. Rainfall in another basin can effect water releases 500 miles away. There are many factors that contribute to the Corps ability to manage their projects - and it is unlikely that a lake project can effect one change and make a big difference - kind of like our turkey flock.
